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The chemotherapeutic potential of chalcones against leishmaniases: a review
Accepted Manuscript Title: The chemotherapeutic potential of chalcones against leishmaniases: a review Author: Nasir Tajuddeen, Murtala Bindawa Isah, Mukhtar Adeiza Suleiman, Fanie R. van Heerden, Mohammed Auwal Ibrahim PII: DOI: Reference:
S0924-8579(17)30220-0 http://dx.doi.org/doi: 10.1016/j.ijantimicag.2017.06.010 ANTAGE 5160
To appear in:
International Journal of Antimicrobial Agents
Received date: Accepted date:
23-3-2017 17-6-2017
Please cite this article as: Nasir Tajuddeen, Murtala Bindawa Isah, Mukhtar Adeiza Suleiman, Fanie R. van Heerden, Mohammed Auwal Ibrahim, The chemotherapeutic potential of chalcones against leishmaniases: a review, International Journal of Antimicrobial Agents (2017), http://dx.doi.org/doi: 10.1016/j.ijantimicag.2017.06.010. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
THE CHEMOTHERAPEUTIC POTENTIAL OF CHALCONES AGAINST LEISHMANIASES: A REVIEW
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Nasir Tajuddeena, Murtala Bindawa Isahb, Mukhtar Adeiza Suleimanc, Fanie R. van Heerdend and Mohammed Auwal Ibrahimc* a
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria Department of Biochemistry, Umaru Musa Yar’adua University, Katsina, Nigeria c Department of Biochemistry, Ahmadu Bello University, Zaria, Nigeria d School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
b
17 18 19 20 21 22 23 24 25 26 27 28
*Correspondence to: Mohammed Auwal Ibrahim PhD, Department of Biochemistry, Ahmadu Bello University, Zaria, Nigeria. Telephone: +2347031104932; E mail: [email protected] or [email protected]
29 30
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31
Graphical Abstract
32 33
Highlights
34
35
Antileishmanial activity of 278 synthetic and 34 chalcones of plant origin was reviewed
36
The mechanism of antileishmanial activity of chalcone was discussed
37
The structure activity relationship of chalcones against leishmania parasites was
38
analysed
39
Nanoparticles encapsulation of chalcones as delivery agents was examined
40
Conclusion was drawn highlighting the deficiencies in this line of research
41
Abstract
42
Leishmaniases are endemic diseases in tropical and sub-tropical regions of the world and
43
considered to be among the six most important neglected tropical diseases by the World
44
Health Organization (WHO). The current therapeutic arsenal against the disease suffers from
45
series of chemotherapeutic setbacks. However, since the early 1990s, naturally occurring
46
chalcones with promising antileishmanial effects have been reported and several other
47
synthetic chalcones and chalcone-hybrid molecules were confirmed to possess potent activity
48
against various Leishmania species. Herewith, a comprehensive review covering the
49
antileishmanial activity of 34 naturally occuring chalcones, 224 synthetic/semisynthetic
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50
chalcones and 54 chalcone hybrid molecules, is presented. Several chalcones in the
51
synthetic/semisynthetic category had IC50 values < 5µM with very good selectivity against
52
parasites and the structure activity relationships as well as the proposed mechanism of action
53
were discussed. We identified knowledge-gaps with the hope of providing future direction for
54
the discovery of novel antileishmanial drugs from chalcones.
55
Keywords: Chalcone-hybrids, Antileishmanial, Medicinal plants, Leishmaniases
56 57 58 59
1. Introduction
60
Leishmaniases are a group of diseases caused by about 20 different species of Leishmania
61
parasites [1]. These species possess distinct morphological features during development at
62
different life cycle stages. The infective flagellated promastigote forms colonize the gut of
63
sandfly vectors while the intracellular amastigote forms are found in infected mammalian
64
macrophages. In the mammalian hosts, amastigotes are responsible for the different clinical
65
manifestations that classify the infection from single cutaneous lesions caused by Leishmania
66
major to the fatal visceral form called Kala Azar caused by L. donovani [2]. The
67
promastigotes are transmitted in Africa, Asia, and Europe through bite from the female
68
sandfly of Phlebotomus species and in the Americas by Lutzomyia species [3]. About 0.9-1.3
69
million new cases of the disease occur annually in mainly poverty prone tropical and sub-
70
tropical regions it is endemic. The cutaneous lesions accounts for 0.7-1.3 million cases while
71
0.2-0.4 million cases are due to the visceral form. An estimated 399 and 556 million people
72
are at risk of cutaneous and visceral leishmaniases respectively, in high-burden countries [4,
73
5].
74
The therapeutic arsenal against Leishmania is rather ‘old’ and limited [6]. The primary
75
drugs for the treatment of visceral leishmaniasis are the pentavalent antimonials mostly
76
developed over 50 years ago and amphotericin B, while pentamidine, paromomycin, and
77
miltefosine are secondary chemotherapeutic agents [7]. Extended courses of parenteral
78
administration of the drugs often result in patients abandoning treatment half way and this led
79
to increased cases of resistance [8, 9]. Although some of the drugs are still effective, they are
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80
expensive and have a long half-life. Furthermore, side effects including liver, heart and
81
nephro-toxicities, pancreatitis, hypotension, cardiac problems and teratogenicity have been
82
reported with extended use of these drugs [10]. Even though several vaccine candidates have
83
been screened against the disease, none is yet effective [11]. Therefore, there is an urgent
84
need to discover/develop new, safe, inexpensive and effective drugs for the disease.
85
Chalcones (benzylideneacetophenones or 1,3-diaryl-2-propen-1-ones, Fig. 1) are
86
prominent secondary plant metabolites and biogenetic precursors of flavonoids and
87
isoflavonoids. Chemically, they consist of two aryl rings, joined together by an enone linker.
88
The presence of the reactive keto-ethylenic group is an important feature of this class of
89
compounds [12].
90 91
The biological/pharmacological properties of chalcones include, anti-inflammatory [13],
92
antimicrobial [14], antiviral [15], trypanocidal [16], antioxidant and anticancer [17]. Some
93
reviews have highlighted the potential of this group as therapeutic leads against the
94
aforementioned diseases [18-20]. Similarly, several chalcones (natural and synthetic) have
95
been investigated for antileishmanial activity with promising outcomes. In spite of that, a
96
thorough search of the published literature indicates that a comprehensive review on
97
antileishmanial chalcones is not currently available. The subject is covered in some mini
98
reviews [7, 18, 21], but these only briefly mentioned the topic as part of a broader discussion
99
on the anti-infective properties of chalcones and therefore left out several relevant studies and
100
data. This article reviewed all chalcones that were reported to possess antileishmanial activity
101
from 1990 to 2016.
102
The discussion in this article has been organised under the sub-headings of natural,
103
synthetic/semisynthetic chalcones, chalcone-hybrid molecules, in vitro and in vivo activity of
104
chalcones, structural requirements for activity and finally, mechanism of action.
105
2. In vitro antileishmanial activity of chalcones
106
A total of 312 compounds bearing the core chalcone skeleton (Fig. 1) were reported with
107
antileishmanial activity. Out of these, 34 were plants-derived, mainly from plants in the
108
Fabaceae and Piperaceae. The remaining 278 were synthetic/semisynthetic and 54 out of
109
these were chalcone-hybrids. The compounds showed varying degrees of leishmanicidal
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110
activity and we considered those with IC50 values ≤ 10, 10-20 and ≥ 20 µg/mL to have strong,
111
moderate and weak activities, respectively, as adopted by Isah et al. [22].
112
2.1
Antileishmanial activity of natural chalcones
113
Historically, natural compounds have been a good source of safe and effective drugs for
114
humans. Antileishmanial activity-guided fractionations of plant extracts have resulted in the
115
isolation of several antileishmanial chalcones. The first line of validating potency is in vitro
116
investigation of the growth-inhibitory or leishmanicidal activities (Table S1).
117
The first report on antileishmanial chalcones was the bioassay-guided fractionation of
118
Glycyrrhiza glabra (Fabaceae) alcohol root extract, which led to the isolation of licochalcone
119
A (1) (Fig. 2) [23]. The compound strongly inhibited the in vitro growth of L. major and L.
120
donovani promastigotes (IC50 = 2.4 µg/mL for both species). Further time-kill study of 1 on
121
the in vitro growth of L. major showed an inhibitory activity proportional to the incubation
122
period. Using the amastigote form of L. major as a model, 1 also strongly inhibited the in
123
vitro growth of the parasites by more than 95% at a concentration of 1 µg/mL [23]. This
124
study by Chen et al. [23] forms the basis for most of the subsequent studies on
125
antileishmanial chalcones. For instance, the leishmanicidal action of more oxygenated
126
chalcones was subsequently demonstrated by Zhai et al. [24], and the compounds showed
127
similar activity to 1.
128 129
In a different study, activity-guided fractionation of the dichloromethane extract of Piper
130
aduncum
131
methoxychalcone (DMC, 2) (Fig. 3). The compound strongly inhibited L. amazonensis
132
promastigotes, but the effect on amastigotes was low. No apparent toxic effects were
133
observed on macrophages at proportionately high amounts indicating selective toxicity of 2 to
134
the parasites. Electron microscopic studies showed that DMC altered the cell ultrastructure of
135
the parasites, causing damage to amastigote mitochondria at 50 µg/mL and promastigote
136
mitochondria at 40 µg/mL without showing any alteration to macrophages and other
137
mammalian cells even at 100 µg/mL [25]. A separate investigation of P. aduncum ethanol
138
leaf extract led to the isolation of adunchalcone (3) (Fig. 3) with weak activity against
139
promastigotes of L. (V.) braziliensis and L. (V.) chagasi, but moderate activity against L. (L.)
inflorescence
(Piperaceae)
led
to
the
isolation
of
2',6'-dihydroxy-4'-
Page 5 of 28
140
amazonensis and L. (L.) shawi. Its inhibitory effect on L. (L.) amazonensis amastigotes was
141
also weak while selectivity to peritoneal murine macrophages was low [26].
142 143
Antileishmanial activity-guided fractionation of ethanol aerial parts extract of Piper
144
elongatum resulted in the isolation of two dihydrochalcones, 2',6'-dihydroxy-4'-
145
methoxydihydrochalcone (4) and 2',6',4-trihydroxy-4'-methoxydihydrochalcone (5) (Fig. 4).
146
Compound 5 strongly inhibited the in vitro growth of L. tropica and L. infantum
147
promastigotes (IC50 = 3.82 and 6.35 µg/mL, respectively). On the other hand, compound 4
148
had a weak inhibitory effect on the in vitro growth of L. braziliensis and L. tropica
149
promastigotes (IC50 = 27.04 and 21.29 µg/mL, respectively) and a moderate inhibitory effect
150
against L. infantum promastigotes (IC50 = 15.30 µg/mL). However, both compounds were
151
toxic to macrophages [27]. Two dihydrochalcones containing a prenylated benzoic acid
152
moiety (6 and 7), together with three others (4, 5 and 8) (Fig. 4), were isolated from a 90%
153
alcohol leaf extract of Piper dennissi, the compounds had moderate to weak inhibitory effects
154
on L. amazonensis amastigotes (IC50 range from 17.65-49.9 µg/mL) [28]. Two more
155
chalcones, 9 and 10 (Fig. 4) that strongly inhibited the in vitro growth of amastigotes of L.
156
amazonenis (IC50 = 0.25 and 2.23 µg/mL, respectively), were isolated from the ethanol leaf
157
extract of Piper hispidum by bioassay-guided fractionation. However, both compounds were
158
mildly toxic to macrophages [29].
159 160
Chalcones 11 and 12 (Fig. 5) were isolated alongside other phenolic compounds from
161
Psorothamnus polydenius whole plant methanol extract. Both compounds strongly inhibited
162
L. donovani amastigotes but with some toxicity to Vero cells. Furthermore, treatment of L.
163
mexicana pre-infected macrophages with chalcones 11 and 12 reduced the number of infected
164
macrophages by 96% [30]. Comparatively less toxic isoliquiritigenin (13) (Fig. 5), a
165
ubiquitous plant chalcone isolated from Psorothamnus arborescens, displayed activity
166
against L. donovani amastigotes (IC50 = 5.30 µg/mL) [31].
167
Similarly, chalcone 14 (Fig. 5) from Lonchocarpus xuul (Fabaceae) strongly inhibited the
168
growth of L. braziliensis promastigotes (IC50 = 10 µg/mL), but inhibited L. amazonensis and
169
L. donovani promastigotes weakly (IC50 = 26.7 and 40 µg/mL respectively) [32].
170
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171
Three additional chalcones, 15-17 (Fig. 6), with weak L. amazonensis inhibitory activity
172
were isolated from the ethyl-acetate fraction of Calea uniflora ethanol extract (Asteraceae)
173
[33]. A series of plant-derived chalcones; 9, 13 and 18-34 (Fig. 6), were assayed for in vitro
174
antileishmanial activity against promastigotes of L. donovani, L. infantum, L. enrietti, L.
175
major and L. donovani amastigotes. All compounds except 24 and 27 displayed strong
176
promastigote and amastigote growth inhibitions and high toxicity to murine macrophages
177
[34].
178 179 180
The aforementioned in vitro studies suggest that chalcones such as 1, 3, 5, 9, 10, 11, 13
181
and 14 have potent selective inhibitory activity against a range of Leishmania species,
182
although some of them such as 18-34 also appear to be toxic to normal cells. Furthermore, the
183
chalcones seem to possess better in vitro antileishmanial activity than the dihydrochalcones.
184
2.2
Antileishmanial activity of synthetic/semi-synthetic chalcones
185
The promising reports on the activity of natural chalcones led to the synthesis and in vitro
186
antileishmanial assaying of several novel chalcones. The ease of chalcone synthesis by the
187
Claisen-Schmidt reaction certainly contributed to the large number of investigated synthetic
188
chalcones. In these synthetic compounds, several substitutions and modifications to Trans-
189
chalcone (36) (Fig. 7) were reported with varying effect on selective antileishmanial activity.
190
Thus, oxygenated, alkoxylated, halogenated, prenylated, sulphonamide and dihydro-
191
derivatives of chalcones, chalcones incorporating heteroatom(s) in one or more ring,
192
analogues with a five membered heterocyclic ring and chalcones with a benzopyran moiety
193
have been studied. This has helped in identifying some structural features for improved
194
antileishmanial activity (Section 4). A summary of the results for these compounds and their
195
structures are presented respectively in Table S2 and Fig. S1.
196
Notable among the synthetic compounds, 2',4'-dihydroxychalcone (35) (Fig. 7) showed
197
strong selective inhibition of L. amazonensis promastigotes (IC50 = 0.4 µM, SI = 1041.7) and
198
is a promising candidate for further development. The compound was 16 times more potent
199
and 200 times more selective for the parasite than the standard drug pentamidine [35]. Others
200
that have equally shown strong selective in vitro inhibition of leishmania parasites include
201
compounds; 89, 96 [36], 106 [37], 156, 160 [38], 167-170 [39], 189-192, 200 [40], 206, 210
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202
[41] and 215 [42]. The in vivo studies of these chalcones should be the next step in validating
203
their therapeutic potential against leishmaniasis.
204 205 206
2.3
207
An emerging strategy in drug discovery is the fusion of two or more distinct pharmacophores
208
into a single chemical entity called a hybrid molecule which usually has a dual mode of
209
action or a different biological target [43]. Thus, hybrid molecules are often more active than
210
individual drugs. A few studies have been conducted on antileishmanial chalcone-hybrid
211
molecules (Fig. S2) and these are summarised in Table S3.
Antileishmanial activity of chalcone-hybrids
212
Interestingly, triclosan-, paullone- and dihydropyrimidinone-chalcone hybrids (Fig. 8) had
213
better selective antileishmanial activity compared to individual subunits, suggesting
214
synergism between the subunits [44-46]. Similarly, quinolone- and caffeine-chalcone hybrids
215
have demonstrated potent antileishmanial activities [16, 47].
216 217
3. In vivo antileishmanial activity of chalcones
218
A number of chalcones have shown potent activity in animal models (Table S4) which
219
points to their therapeutic relevance considering that xenobiotic metabolism may convert
220
highly active (in vitro) chalcones to inactive metabolites.
221
Intraperitoneal administration of licochalcone A (1) at doses of 2.5 and 5.0 mg/kg body
222
weight (bw) completely prevented lesion development in L. major-infected mice (parasite
223
load in footpad of mice reduced by 80 and 75%, respectively). This was corroborated by the
224
50% inhibition of lesion size in L. major-infected mice at intralesional doses of 1 and 2.5
225
mg/kg bw [48]. In hamster model, 20 mg/kg bw daily intraperitoneal dose of licochalcone A
226
reduced the number of L. donovani parasites in liver and spleen by 98% and 96%
227
respectively. Furthermore, oral administration of (1) to hamsters at doses of 5, 50 and 150
228
mg/kg bw for six days reduced parasite loads in the liver and spleen by 65% and 70%
229
respectively. Oral administration of 1000 mg/kg bw of (1) produced no sign of toxicity in rats
230
for two weeks. Also, no toxicity was recorded after intraperitoneal administration of 100 and
Page 8 of 28
231
150 mg/kg bw to rats and hamsters, respectively [48]. These interesting findings clearly
232
demonstrate the safety of (1) in animal model irrespective of the route of administration.
233
Intraperitoneal treatment of L. (V.) braziliensis-infected hamster footpads with 168
234
showed 83% lesion healing 16 weeks post-infection, similar to the effect observed for
235
amphotericin B. Also, parasite load in tissues of infected animals was significantly lower
236
after treatment with 167 (topical) and 168 (topical and intraperitoneal) compared to untreated
237
animals after 42 days of treatment and the result was similar to amphotericin B. The presence
238
of fibroblasts and collagen fibres in the dermis of animals intraperitoneally treated with 168
239
was observed 3 weeks after the end of treatment, featuring reconstitution of damaged tissues.
240
Moreover, 167 and 168 were non-toxic to uninfected hamsters after 30 days of intraperitoneal
241
administration of 1 and 10 mg/kg bw [46]. Preliminary studies have also indicated that the
242
substituents on the compounds could have an effect on the in vivo activity. For instance, daily
243
intraperitoneal dose (50 mg/kg bw) of compound 190 with alkylated amine substituents
244
produced 48% inhibition after 5 days of treatment while 200 with a geranyl substituent
245
exhibited 83% suppression of parasites at 50 mg/kg/day for 10 days treatment and 76 ± 11%
246
at 100 mg/kg/day for 5 days treatment [40].
247
These few in vivo studies so far conducted show that chalcones are both active and safe in
248
different animal models.
249
4. Biodegradable nanoparticles encapsulation of chalcones and antileishmanial activity
250
Biodegradable nanoparticles have recently gained prominence as target specific delivery
251
agents for drugs, genes and vaccines. They offer considerable advantages including
252
biocompatibility, greater stability in biological fluids, easy preparation, superior
253
encapsulation and easy release profile. A few studies to investigate the effect of nanoparticles
254
encapsulation on antileishmanial activity of chalcones have been conducted with interesting
255
outcomes. The in vitro inhibitory activity of DMC against L. amazonensis was enhanced with
256
encapsulation in polylactic-acid (PLA) nanoparticles. A regimen of DMC-PLA (5 µg of PLA
257
and 1 µg/mL of DMC) inhibited intracellular parasite growth by 53% compared to 23%
258
inhibition observed with free DMC [49]. Similarly, subcutaneous treatment of L.
259
amazonensis infected mice with 200 µg of 2 encapsulated in 1 mg of PLA led to a 90%
260
reduction in parasite load, which was similar to effect of glucantime [49]. Interestingly, doses
261
of DMC (2) as high as 1 mg did not alter the course of lesion development in L. amazonensis
Page 9 of 28
262
infected mice. However, a five times smaller dose of DMC in PLA (200 µg) produced a 60%
263
reduction in lesion size compared to untreated control. A fusion of PLA nanosphere-
264
containing vacuoles with the parasitophorous vacuoles of infected macrophages was
265
consistently observed, indicating that the nanoparticles actually reach the parasite before
266
degradation, improved intracellular bioavailability of DMC and might serve as drug carriers
267
within the cells [49].
268
Nanoparticles fusion also improved the parasite inhibitory activity of Trans-chalcone (36)
269
when administered as an implant with PLA and poly(D,L-lactide-co-glycolide (PGLA) to L.
270
amazonensis-infected mice. Subcutaneous administration of a single dose of 36 (4 mg/kg bw)
271
produced a 21% decrease in lesion size similar to pentamidine treated mice. On the other
272
hand, administration of a similar dose of PLA/36 and PGLA/36 as an ear implant produced
273
11 and 31% decrease in lesion size in L. amazonensis-infected mice [50] which demonstrates
274
that PGLA might be a better vehicle for drug delivery. Soybean lecithin and polysorbate-20
275
nanoemulsions have also shown potential as chalcone drug delivery systems against the
276
amastigote forms [51]. Controlled-release polymers such as PGLA and PLA represent a new
277
strategy for local delivery of chemotherapeutic agents with a potential to maximise
278
antileishmanial effects as demonstrated in the aforementioned studies
279
5. Structural requirements for antileishmanial activity of chalcones and structure-
280
activity relationships
281
In order to investigate structural requirements for activity of chalcones against Leishmania
282
species, Hermoso and co-workers synthesized some di- and triacetylated derivatives of 4 and
283
5, some C6-C3-C6 systems with different substituents, a series of alkyl-substituted propanones
284
and some benzocyclopentanones. Only compounds with a C6-C3-C6 system displayed
285
antileishmanial activity against promastigotes indicating that the two aryl rings are a key
286
requirement for antileishmanial activity of chalcones [27]. This conclusion is further
287
supported by Nielsen et al. [52], who investigated the role of the propenone chain by
288
preparing some α,β-double bond-modified chalcones (including α- and β-alkylated chalcones,
289
dihydrochalcones and acetylenic analogues) and no drastic changes in activity were observed
290
in the leishmanicidal activity. It was thus concluded that the alkylating property of the α,β-
291
unsaturated ketone is of minor importance for antileishmanial activity of chalcones.
292
Published data suggests that the real pharmacophore of the chalcones are the two aryl rings,
293
the α,β-unsaturated ketone mainly functions as a spacer [52]. Further 3D QSAR analyses of a
Page 10 of 28
294
series of substituted chalcones yielded high quality models (antileishmanial model, R2 = 0.73,
295
Q2 = 0.63; lymphocyte-suppressing model, R2 = 0.90, Q2 = 0.80) which indicated that steric
296
interactions between the target and chalcones are the major determinant of potency whilst
297
electronic factors only play a minor role (against parasite and lymphocyte cells). Specifically,
298
ring B and its substitution pattern are mainly responsible for activity while ring A is generally
299
considered to be less important for antileishmanial activity. Bulky substituents at position 2'
300
and 3' are predicted to increase activity while bulky substituents at position 4' are predicted to
301
reduce activity. On the other hand, antilymphocyte activity is influenced by substitution on
302
both rings A and B. Bulky groups at C-2' (ring B) and C-5 and/or -6 of ring A will increase
303
antilymphocyte activity, whereas bulky substitution at 4', 2, 3 and 4 will reduce toxicity.
304
These observations enable the separation of antileishamnial and antilymphocyte actions of
305
chalcones and facilitate the design of highly selective antileishmanial chalcones [53]. Several
306
conventional SAR studies have also documented the importance of steric influence and ring
307
B substitutions to the leishmanicidal activity of chalcones [27, 34, 37, 38]. In addition, some
308
SAR studies also described some level of steric contribution from ring A to antileishmanial
309
activity [37, 38, 54]. For example, in the specific case of 2, with an unsubstituted A-ring,
310
almost any form of substitution (electron-donating or -accepting) at position 4 of ring A led
311
to a decrease in activity [54]. It is also noteworthy that theoretical analyses of chlorine atom
312
substitutions at different positions of ring A point to an intricate relationship between steric
313
bulk and electronic properties of the chlorine atom. Electronegative elements like chlorine are
314
also lipophilic and this may encourage permeability through parasite cell membrane. The
315
influence of ring A on antileishmanial activity is particularly pronounced when the ring is not
316
restricted to substituted benzene rings. For example, good activities were reported with a 1-
317
naphthalenyl, 2-pyridinyl and 4-quinolinyl ring A. The point of attachment of these moieties
318
to the α,β-unsaturated ketone is also important as revealed by the poor activities of the 3-
319
quinolinyl and 2-naphthalenyl compared to the 4-quinolinyl and 1-naphthalenyl derivatives
320
[37].
321
For chromenochalcones, A-ring substitution and the α,β-unsaturated ketone seemed to be
322
quite important for antileishmanial activity [55] because 52 with a hydroxy group at position
323
4 showed the best activity. The size of the substituent at position 4 also appears to play a
324
crucial role. For instance, 53, which has a structure similar to 52 but is methoxylated at C-4
325
was less active against amastigotes. It is possible that a bulkier group at this position reduced
326
activity, but the reduction in activity might also be attributable to the loss of the hydrogen
Page 11 of 28
327
bond donor [55]. In a comprehensive assessment of the effect of substitution pattern,
328
synthetic chromenochalcones with different substitutions on both rings A and B were
329
analysed. The presence of electron-withdrawing and electron-donating groups on ring B and
330
an aromatic heterocyclic ring A improved activity and greater selectivity compared to the
331
unsubstituted parent compounds [40, 41]. Chromenodihydrochalcones are generally less
332
active than chromenochalcones suggesting a role for the α,β-unsaturation in the
333
antileishmanial activity of this class of compounds [55]. Furthermore, removal of the olefinic
334
bond in the benzopyran moiety of chromenochalcones maintained the leishmanicidal activity
335
but reduced toxicity to Vero cells [41].
336
Molecular-modelling coupled with synthetic studies was performed to investigate the
337
influence of steric and electronic effects on antileishmanial activity [38]. It was observed that
338
the insertion of two bulky ortho substituents on the aromatic ring B imposes a structural
339
rigidity and reduces conformational freedom of the phenyl ring, which improved the activity.
340
Importantly, derivatives with significant activity have larger torsion dihedral angles, which
341
were influenced by the bulky groups at ortho position. This demonstrates the steric
342
importance of the carbonyl group and the phenyl ring B moiety to the antileishmanial
343
activity. The electronic potential map of the active chalcones indicated that HOMO density
344
on phenyl ring B, close to the carbonyl, improved antileishmanial activity, whereas HOMO
345
density on ring A far from the carbonyl reduced the activity. This is similar to the findings of
346
Andrighetti-Frohner et al. [36] who reported that molecular volume, weight and dipole
347
moment of chalcones, HOMO density concentrated in centre of the chalcone moiety
348
(specifically the carbonyl group and unsaturated linker between ring A and B) and
349
conformational structure of the compounds are important structural and electronic features
350
for activity of chalcones [36]. The carbonyl group not only contributes from a steric
351
perspective but also from an electronic perspective to the observed antileishmanial activity of
352
chalcone series [38].
353
The antileishmanial activity of chalcones is also affected by prenylation at different
354
positions. For example, chromeno-chalcones (52 and 53) had better activity than chalcone 20
355
from which they were derived, suggesting that prenylation at position 4' improves
356
leishmanicidal activity [40, 55]. Likewise, prenylation at positions 2 and 3 of ring A greatly
357
improved activity and selectivity of chalcones [42]. It is also noteworthy that addition of
358
alkyl amino substituent on rings A or B decreased the activity [40]. The improved activity
Page 12 of 28
359
observed in prenylated chalcones might be a result of increased lipophilicity, facilitating the
360
passage of molecules through cell membrane barriers of macrophages and parasites and
361
resulting in enhanced drug delivery. Kayser and Kiderlen [34] had observed that ability to
362
inhibit the growth of parasite depends on the ratio of a limited number of lipophilic to
363
hydrophilic substituents on aromatic rings and several studies have shown that the nature of
364
substitution on both rings A and B is vital for antileishmanial activity of chalcones.
365
Studies that involved two series of regioisomeric chromene-based chalcones indicated
366
that the series with aryl ring (as opposed to heterocyclic pyran of benzopyran moiety) joined
367
to the β-carbon of α,β-unsaturated carbonyl chain displayed excellent activity against
368
promastigotes. The 3- and 4-chloro substituted forms of the most active series were found to
369
be the most potent. Chloro-substituent in the series with aryl ring directly joined to the
370
carbonyl carbon did not improve activity of the compounds (129-138, Fig. S1) [56].
371
Therefore, for chalcones with a benzopyran ring, the best arrangement for increased activity
372
is when the pyran ring of benzopyran moiety is directly connected to the carbonyl carbon.
373
6. Mechanism of antileishmanial action of chalcones
374
Some insight into possible mechanism of the antileishmanial activity of chalcones has
375
been obtained from electron microscopic studies on possible ultrastructural changes of L.
376
major incubated with licochalcone A (1). Destructive changes to the mitochondria with no
377
apparent changes to other organelles of parasites were observed [23]. Similar destruction of
378
parasite mitochondria was observed with other chalcones [24, 57, 58]. A follow-up study
379
showed that licochalcone A altered the ultrastructure of L. major promastigote and
380
amastigote in a concentration-dependent manner without any alteration to human monocyte-
381
derived macrophages [59]. Licochalcone A also greatly inhibited oxygen consumption and
382
activity of parasite mitochondrial dehydrogenases. These findings suggest that licochalcone
383
A modulates the ultrastructure and function of Leishmania parasite mitochondria [59]. This is
384
further supported by the observation that licochalcone A selectively inhibited the activity of
385
fumarate reductase (FRD) in permeated mitochondria of L. major promastigotes over
386
succinate dehydrogenase (SDH). The inhibitory effect of licochalcone A on crude parasite
387
mitochondria was selective to FRD in addition to the inhibition of SDH, NADH
388
dehydrogenase (NDH), succinate-cytochrome c reductase and NADH-cytochrome c
389
reductase. It was also reported that licochalcone A inhibited the activity of SDH and NDH in
390
PBMC and J774 cells in a concentration- and time-dependent manner. Other oxygenated
Page 13 of 28
391
chalcones have also shown potent inhibitory effects on the FRD [60]. These findings suggest
392
that FRD might be specifically targeted by chalcones.
393
DMC (2) also destroys parasite mitochondria but apparently through different mechanism.
394
A relatively high dose (100 µM) of DMC failed to interfere with the parasite FRD. Rather, 2
395
seemed to act by altering sterol biosynthesis and sterol composition of parasite in a manner
396
different from other known sterol inhibitors. The sterol composition of L. amazonensis
397
promastigotes treated with 2 revealed the accumulation of early sterol precursors which may
398
result in altered membrane fluidity and structure as previously observed by electron
399
microscopy in parasites treated with 2 as well as a reduction in the levels of C-14
400
demethylated and C-24 alkylated sterols, leading to a reduction in exogenous cholesterol
401
uptake [58].
402
Chalcones 167-169 caused several ultrastructural changes in L. (V.) braziliensis including
403
intense atypical vacuolization with cytoplasmic disorganization, formation of binucleated
404
parasites, different levels of mitochondrial changes including a reduction in electron density
405
of the mitochondrial matrix and cristae and mitochondrial swelling. Nucleosome-sized DNA
406
fragments were also identified in promastigotes after treatment with the chalcones indicating
407
DNA fragmentation. Morphological changes of the parasite such as cell shrinkage and
408
cytoplasmic condensation were similarly observed after treatment with these chalcones,
409
which could indicate cell death by apoptosis in multicellular and unicellular organisms [57].
410
Apart from the mechanisms of action by direct effect of chalcones on parasite, modulation
411
of host immune response may also be involved. Some chalcones were reported to
412
significantly stimulate nitric oxide (NO) synthesis and simultaneously reduce the index of
413
infection in macrophages. This suggests that chalcones kill intracellular parasites by a NO-
414
dependent mechanism [39] and induction of NO synthase is essential to the intracellular
415
killing of Leishmania in macrophages [61]. In humans, low production of NO is associated
416
with increased infectivity of the parasite, and NO resistance is associated with non-response
417
to treatment with antimonial therapy[62, 63]. Thus, based on these findings, chalcones seem
418
to mediate leishmanicidal activity via two broad mechanisms; direct action on parasite
419
mitochondria and modulation of host immune system by stimulating NO production in
420
infected macrophages.
Page 14 of 28
421
Ligand or structure-based in-silico drug design and identification of protein targets using
422
molecular-docking studies have recently gained widespread use [64]. Molecular-docking
423
studies on 24 Leishmania enzymes has identified dihydroorotate dehydrogenase, nucleoside
424
hydrolase, oligopeptidase B, methionyl-tRNA synthetase, UDP-glucose pyrophosphorylase,
425
trypanothione reductase and glycerol-3-phosphate dehydrogenase as potential enzyme targets
426
for chalcones. In these studies, the chalcones demonstrated docking preference to most of
427
these protein targets with strong binding energies [35, 65].
428
7. Conclusion
429
A total of 312 chalcones were covered in this review and among them, 35, 79, 81 and 87
430
have shown exceptional promise as potential leishmanicidal candidates with high selectivity
431
to the parasite cells. Conversely, other chalcones such as 36, 131 and 132 have potent
432
antileishmanial activity but their toxicity profiles have not been investigated to warrant a
433
definite statement on their future prospects. The observed toxic effects of 18-34 (except 24)
434
on both the parasite and normal cells further support the need to ascertain the toxicity effects
435
of antileishmanial chalcones. Thus, modifications of chalcones 18-34 that will reduce toxicity
436
to normal cells without compromising the leishmanicidal potency may be worthwhile
437
investigating.
438
This review has also highlighted that a smaller number of natural chalcones have been
439
studied in comparison to synthetic chalcones. This is not surprising because isolating these
440
plant metabolites is often tedious coupled with the low yield after isolation. Additionally,
441
even amongst the studied natural chalcones, only a few had potent parasite killing ability
442
compared to the synthetic chalcones. However, it is clear that a detailed observation of the
443
natural chalcones and their structure-activity relationships can lead to the design of far more
444
potent synthetic/semi-synthetic chalcones. Despite this observation, the synthetic
445
modifications of chalcones were not greatly extended to hybrid molecules even though some
446
of the few studied hybrids, such as 270, 282, 283 and 293, had great potential for further
447
antileishmanial studies.
448
An important deficiency highlighted by this review is the acute shortage of in vivo studies
449
on antileishmanial chalcones. This is of importance taking into cognizance the large number
450
of highly selective and potent chalcones identified via in vitro assays. Still, among the few in
451
vivo studies, some promising results were recorded such as licochalcone A and the increase in
452
the activity of DMC after encapsulation in PLA. Additionally, there may be a need to expand
Page 15 of 28
453
the in vivo studies to address the effects of chalcones on some Leishmania-associated
454
pathological changes considering the crucial role of those alterations during the disease
455
pathogenesis. Finally, studies on the mechanisms of antileishmanial actions are limited to the
456
parasite mitochondrial enzyme systems which practically cannot be the only target. Hence,
457
more holistic in vivo studies are required as the next line of action towards the development
458
of chalcones as chemotherapeutic agents against leishmaniasis.
459 460
Acknowledgements
461
The author MBI was awarded a Ph.D. study fellowship by the TETFund desk office of
462
Umaru Musa Yar’adua University Katsina, Nigeria. FRVH thank the University of KwaZulu-
463
Natal and the National Research Foundation (NRF) (Grant No: 98345, 2016) of South Africa
464
for financial support.
465 466
Declarations
467
Funding: National Research Foundation (NRF) (Grant No: 98345, 2016) of South Africa
468
Competing Interests: No
469
Ethical Approval: Not required
470
Page 16 of 28
471
References
472
[1] Giarolla J, Rando DG, Pasqualoto KF, Zaim MH, Ferreira EI. Molecular modeling as a
473
promising tool to study dendrimer prodrugs delivery. J Mol Struc-THEOCHEM
474
2010;939:133-8.
475
[2] Vendrametto MC, Dos Santos AO, Nakamura CV, Dias Filho BP, Cortez DAG, Ueda-
476
Nakamura T. Evaluation of antileishmanial activity of eupomatenoid-5, a compound isolated
477
from leaves of Piper regnellii var. pallescens. Parasitol Int 2010;59:154-8.
478
[3] Desjeux P. Leishmaniasis: current situation and new perspectives. Comp Immunol
479
Microbiol Infect Dis 2004;27:305-18.
480
[4] Hailu A, Dagne DA, Boelaert M. Leishmaniasis. In: Gyapong J, Boatin B, editors.
481
Neglected Tropical Diseases - Sub-Saharan Africa: Springer International Publishing; 2016.
482
p. 87-112.
483
[5] Organization WH. Leishmaniasis in high-burden countries: an epidemiological update
484
based on data reported in 2014. Weekly epidemiological record. 2016.
485
[6] Almeida OLS, Santos JB. Advances in the treatment of cutaneous leishmaniasis in the
486
new world in the last ten years: a systematic literature review. An Bras Dermatol
487
2011;86:497-506.
488
[7] Sangshetti JN, Khan FAK, Kulkarni AA, Arote R, Patil RH. Antileishmanial drug
489
discovery: Comprehensive review of the last 10 years. Rsc Advances 2015;5:32376-415.
490
[8] Monteiro LM, Löbenberg R, Ferreira EI, Cotrim PC, Kanashiro E, Rocha M, et al.
491
Targeting Leishmania amazonensis amastigotes through macrophage internalisation of a
492
hydroxymethylnitrofurazone nanostructured polymeric system. Int J Antimicrob Agents
493
2017; https://doi.org/10.1016/j.ijantimicag.2017.01.033
494
Page 17 of 28
495
[9] Freitas-Junior LH, Chatelain E, Kim HA, Siqueira-Neto JL. Visceral leishmaniasis
496
treatment: what do we have, what do we need and how to deliver it? Int J Parasitol Drugs
497
Drug Resist 2012;2:11-9.
498
[10] Rybniker J, Goede V, Mertens J, Ortmann M, Kulas W, Kochanek M, et al. Treatment of
499
visceral leishmaniasis with intravenous pentamidine and oral fluconazole in an HIV-positive
500
patient with chronic renal failure—a case report and brief review of the literature. Int J Infect
501
Dis 2010;14:e522-e5.
502
[11] Kumar R, Engwerda C. Vaccines to prevent leishmaniasis. Clin Exp Immunol
503
2014;3:e13.
504
[12] Sakagami H, Masuda Y, Tomomura M, Yokose S, Uesawa Y, Ikezoe N, et al.
505
Quantitative
506
2017;37:1091-8.
507
[13] Luo X-L, Liu S-Y, Wang L-J, Zhang Q-Y, Xu P, Pan L-L, et al. A tetramethoxychalcone
508
from Chloranthus henryi suppresses lipopolysaccharide-induced inflammatory responses in
509
BV2 microglia. Eur J Clin Pharmacol 2016;774:135-43.
510
[14] Simard Fo, Gauthier C, Chiasson Er, Lavoie S, Mshvildadze V, Legault J, et al.
511
Antibacterial Balsacones J–M, Hydroxycinnamoylated Dihydrochalcones from Populus
512
balsamifera Buds. J Nat Prod 2015;78:1147-53.
513
[15] Mohammed MM, Hamdy A-HA, El-Fiky NM, Mettwally WS, El-Beih AA, Kobayashi
514
N. Anti-influenza A virus activity of a new dihydrochalcone diglycoside isolated from the
515
Egyptian seagrass Thalassodendron ciliatum (Forsk.) den Hartog. Nat prod res 2014;28:377-
516
82.
517
[16] Insuasty B, Ramírez J, Becerra D, Echeverry C, Quiroga J, Abonia R, et al. An efficient
518
synthesis of new caffeine-based chalcones, pyrazolines and pyrazolo [3, 4-b][1, 4] diazepines
Structure–Cytotoxicity
Relationship
of
Chalcones.
Anticancer
Res
Page 18 of 28
519
as potential antimalarial, antitrypanosomal and antileishmanial agents. Eur J Med Chem
520
2015;93:401-13.
521
[17] Chen X, Liu Z, Meng R, Shi C, Guo N. Antioxidative and anticancer properties of
522
Licochalcone A from licorice. J Ethnopharmacol 2017;198:331-7.
523
[18] Nowakowska Z. A review of anti-infective and anti-inflammatory chalcones. Eur J Med
524
Chem 2007;42:125-37.
525
[19] Elias D, Beazely M, Kandepu N. Bioactivities of chalcones. Curr Med Chem
526
1999;6:1125.
527
[20] K Sahu N, S Balbhadra S, Choudhary J, V Kohli D. Exploring pharmacological
528
significance of chalcone scaffold: a review. Current medicinal chemistry. 2012;19:209-25.
529
[21] Singh P, Anand A, Kumar V. Recent developments in biological activities of chalcones:
530
A mini review. Eur J Med Chem 2014;85:758-77.
531
[22] Isah MB, Ibrahim MA, Mohammed A, Aliyu AB, Masola B, Coetzer TH. A systematic
532
review of pentacyclic triterpenes and their derivatives as chemotherapeutic agents against
533
tropical parasitic diseases. Parasitology 2016;143:1219-31.
534
[23] Chen M, Christensen SB, Blom J, Lemmich E, Nadelmann L, Fich K, et al.
535
Licochalcone A, a novel antiparasitic agent with potent activity against human pathogenic
536
protozoan species of Leishmania. Antimicrob Agents Chemother 1993;37:2550-6.
537
[24] Zhai L, Chen M, Blom J, Theander TG, Christensen SB, Kharazmi A. The
538
antileishmanial activity of novel o ygenated chalcones and their mechanism of action. J
539
Antimicrob Chemo 1999;43:793-803.
540
[25] Torres-Santos EC, Moreira DL, Kaplan MAC, Meirelles MN, Rossi-Bergmann B.
541
Selective effect of 2′, 6′-dihydroxy-4′-methoxychalcone isolated from Piper aduncum on
542
Leishmania amazonensis. Antimicrob Agents Chemother 1999;43:1234-41.
Page 19 of 28
543
[26] Dal Picolo CR, Bezerra MP, Gomes KS, Passero LFD, Laurenti MD, Martins EGA, et
544
al. Antileishmanial activity evaluation of adunchalcone, a new prenylated dihydrochalcone
545
from Piper aduncum L. Fitoterapia 2014;97:28-33.
546
[27] Hermoso A, Jiménez IA, Mamani ZA, Bazzocchi IL, Piñero JE, Ravelo AG, et al.
547
Antileishmanial activities of dihydrochalcones from Piper elongatum and synthetic related
548
compounds. Structural requirements for activity. Bioorg Med Chem 2003;11:3975-80.
549
[28] Cabanillas BJ, Le Lamer A-C, Castillo D, Arevalo J, Estevez Y, Rojas R, et al.
550
Dihydrochalcones and benzoic acid derivatives from Piper dennisii. Planta Med 2012;78:914-
551
8.
552
[29] Ruiz C, Haddad M, Alban J, Bourdy G, Reategui R, Castillo D, et al. Activity-guided
553
isolation of antileishmanial compounds from Piper hispidum. Phytochem Lett 2011;4:363-6.
554
[30] Salem MM, Werbovetz KA. Antiprotozoal Compounds from Psorothamnus p olydenius.
555
J Nat Prod 2005;68:108-11.
556
[31] Salem MM, Werbovetz KA. Isoflavonoids and Other Compounds from Psorothamnus a
557
rborescens with Antiprotozoal Activities. J. Nat. Prod 2006;69:43-9.
558
[32] Borges-Argaez R, Balnbury L, Flowers A, Giménez-Turba A, Ruiz G, Waterman PG, et
559
al. Cytotoxic and antiprotozoal activity of flavonoids from Lonchocarpus spp. Phytomedicine
560
2007;14:530-3.
561
[33] Lima TC, Souza RJ, Santos AD, Moraes MH, Biondo NE, Barison A, et al. Evaluation
562
of leishmanicidal and trypanocidal activities of phenolic compounds from Calea uniflora
563
Less. Nat prod res 2016;30:551-7.
564
[34] Kayser O, Kiderlen AF. In vitro leishmanicidal activity of naturally occurring chalcones.
565
Phytother Res 2001;15:148-52.
566
[35] Passalacqua TG, Torres FA, Nogueira CT, de Almeida L, Del Cistia ML, dos Santos
567
MB, et al. The 2′, 4′-dihydroxychalcone could be explored to develop new inhibitors against
Page 20 of 28
568
the glycerol-3-phosphate dehydrogenase from Leishmania species. Bioorg Med Chem Lett
569
2015;25:3564-8.
570
[36] Andrighetti-Fröhner CR, de Oliveira KN, Gaspar-Silva D, Pacheco LK, Joussef AC,
571
Steindel M, et al. Synthesis, biological evaluation and SAR of sulfonamide 4-
572
methoxychalcone derivatives with potential antileishmanial activity. Eur J Med Chem
573
2009;44:755-63.
574
[37] Liu M, Wilairat P, Croft SL, Tan AL-C, Go M-L. Structure–activity relationships of
575
antileishmanial and antimalarial chalcones. Bioorg Med Chem 2003;11:2729-38.
576
[38] Bello ML, Chiaradia LD, Dias LRS, Pacheco LK, Stumpf TR, Mascarello A, et al.
577
Trimethoxy-chalcone derivatives inhibit growth of Leishmania braziliensis: synthesis,
578
biological evaluation, molecular modeling and structure–activity relationship (SAR). Bioorg
579
Med Chem 2011;19:5046-52.
580
[39] de Mello TF, Bitencourt HR, Pedroso RB, Aristides SM, Lonardoni MV, Silveira TG.
581
Leishmanicidal activity of synthetic chalcones in Leishmania (Viannia) braziliensis. Exp
582
Parasitol 2014;136:27-34.
583
[40] Gupta S, Shivahare R, Korthikunta V, Singh R, Gupta S, Tadigoppula N. Synthesis and
584
biological evaluation of chalcones as potential antileishmanial agents. Eur J Med Chem
585
2014;81:359-66.
586
[41] Shivahare R, Korthikunta V, Chandasana H, Suthar MK, Agnihotri P, Vishwakarma P,
587
et al. Synthesis, structure–activity relationships, and biological studies of chromenochalcones
588
as potential antileishmanial agents. J Med Chem 2014;57:3342-57.
589
[42] Passalacqua TG, Dutra LA, de Almeida L, Velásquez AMA, Torres FAE, Yamasaki PR,
590
et al. Synthesis and evaluation of novel prenylated chalcone derivatives as anti-leishmanial
591
and anti-trypanosomal compounds. Bioorg Med Chem Lett 2015;25:3342-5.
Page 21 of 28
592
[43] Mishra S, Singh P. Hybrid molecules: The privileged scaffolds for various
593
pharmaceuticals. Eur J Med Chem 2016;124:500-36.
594
[44] Otero E, Vergara S, Robledo SM, Cardona W, Carda M, Vélez ID, et al. Synthesis,
595
leishmanicidal and cytotoxic activity of triclosan-chalcone, triclosan-chromone and triclosan-
596
coumarin hybrids. Molecules 2014;19:13251-66.
597
[45] Reichwald C, Shimony O, Dunkel U, Sacerdoti-Sierra N, Jaffe CL, Kunick C. 2-(3-Aryl-
598
3-oxopropen-1-yl)-9-tert-butyl-paullones: a new antileishmanial chemotype. J Med Chem
599
2008;51:659-65.
600
[46] Rashid U, Sultana R, Shaheen N, Hassan SF, Yaqoob F, Ahmad MJ, et al. Structure
601
based medicinal chemistry-driven strategy to design substituted dihydropyrimidines as
602
potential antileishmanial agents. Eur J Med Chem 2016;115:230-44.
603
[47] Roussaki M, Hall B, Lima SC, da Silva AC, Wilkinson S, Detsi A. Synthesis and anti-
604
parasitic activity of a novel quinolinone–chalcone series. Bioorg Med Chem Lett
605
2013;23:6436-41.
606
[48] Chen M, Christensen S, Theander TG, Kharazmi A. Antileishmanial activity of
607
licochalcone A in mice infected with Leishmania major and in hamsters infected with
608
Leishmania donovani. Antimicrob Agents Chemother 1994;38:1339-44.
609
[49] Torres-Santos EC, Rodrigues JM, Moreira DL, Kaplan MAC, Rossi-Bergmann B.
610
Improvement of in vitro and in vivo antileishmanial activities of 2′, 6′-dihydroxy-4′-
611
methoxychalcone by entrapment in poly (d, l-lactide) nanoparticles. Antimicrob Agents
612
Chemother 1999;43:1776-8.
613
[50] Piñero J, Temporal RM, Silva-Gonçalves AJ, Jiménez I, Bazzocchi IL, Oliva A, et al.
614
New administration model of trans-chalcone biodegradable polymers for the treatment of
615
experimental leishmaniasis. Acta trop 2006;98:59-65.
Page 22 of 28
616
[51] de Mattos CB, Argenta DF, de Lima Melchiades G, Cordeiro MNS, Tonini ML, Moraes
617
MH, et al. Nanoemulsions containing a synthetic chalcone as an alternative for treating
618
cutaneous leshmaniasis: optimization using a full factorial design. Int J nanomedicine
619
2015;10:5529.
620
[52] Nielsen SF, Kharazmi A, Christensen SB. Modifications of the α, β-double bond in
621
chalcones only marginally affect the antiprotozoal activities. Bioorg Med Chem 1998;6:937-
622
45.
623
[53] Nielsen SF, Christensen SB, Cruciani G, Kharazmi A, Liljefors T. Antileishmanial
624
chalcones: Statistical design, synthesis, and three-dimensional quantitative structure− activity
625
relationship analysis. J Med Chem 1998;41:4819-32.
626
[54] Boeck P, Falcao CAB, Leal PC, Yunes RA, Cechinel Filho V, Torres-Santos EC, et al.
627
Synthesis of chalcone analogues with increased antileishmanial activity. Bioorg Med Chem
628
2006;14:1538-45.
629
[55] Narender T, Gupta S. A convenient and biogenetic type synthesis of few naturally
630
occurring chromeno dihydrochalcones and their in vitro antileishmanial activity. Bioorg Med
631
Chem Lett 2004;14:3913-6.
632
[56] Foroumadi A, Emami S, Sorkhi M, Nakhjiri M, Nazarian Z, Heydari S, et al.
633
Chromene‐Based Synthetic Chalcones as Potent Antileishmanial Agents: Synthesis and
634
Biological Activity. Chem Biol Drug Des 2010;75:590-6.
635
[57] de Mello TF, Cardoso BM, Bitencourt HR, Donatti L, Aristides SM, Lonardoni MV, et
636
al. Ultrastructural and morphological changes in Leishmania (Viannia) braziliensis treated
637
with synthetic chalcones. Exp Parasitol 2016;160:23-30.
638
[58] Torres-Santos EC, Sampaio-Santos MI, Buckner FS, Yokoyama K, Gelb M, Urbina JA,
639
et al. Altered sterol profile induced in Leishmania amazonensis by a natural
640
dihydro ymetho ylated chalcone. J Antimicrob Chemo 2009;63:469-72.
Page 23 of 28
641
[59] Zhai L, Blom J, Chen M, Christensen SB, Kharazmi A. The antileishmanial agent
642
licochalcone A interferes with the function of parasite mitochondria. Antimicrob Agents
643
Chemother 1995;39:2742-8.
644
[60] Chen M, Zhai L, Christensen SB, Theander TG, Kharazmi A. Inhibition of Fumarate
645
Reductase inLeishmania major and L. donovani by Chalcones. Antimicrob Agents
646
Chemother 2001;45:2023-9.
647
[61] Liew FY, Li Y, Moss D, Parkinson C, Rogers MV, Moncada S. Resistance to
648
Leishmania major infection correlates with the induction of nitric oxide synthase in murine
649
macrophages. Eur J Immunol 1991;21:3009-14.
650
[62] Campos MB, Gomes CMDC, de Souza AAA, Lainson R, Corbett CEP, Silveira FT. In
651
vitro infectivity of species of Leishmania (Viannia) responsible for American cutaneous
652
leishmaniasis. Parasitol Res 2008;103:771.
653
[63] Souza AS, Giudice A, Pereira JM, Guimarães LH, de Jesus AR, de Moura TR, et al.
654
Resistance of Leishmania (Viannia) braziliensis to nitric oxide: correlation with antimony
655
therapy and TNF-α production. BMC Infect Dis 2010;10:209.
656
[64] Meng X-Y, Zhang H-X, Mezei M, Cui M. Molecular docking: a powerful approach for
657
structure-based drug discovery. Curr Comput Aided Drug Des 2011;7:146-57.
658
[65] Ogungbe IV, Erwin WR, Setzer WN. Antileishmanial phytochemical phenolics:
659
molecular docking to potential protein targets. J Mol Graph Model 2014;48:105-17.
660 661
Page 24 of 28
662 663
Fig. 1. Representative skeleton of a chalcone showing the ring annotations and numbering
664
665 666
Fig. 2. Structure of licochalcone A.
667
668 669
Fig. 3. Structures of 2',6'-dihydroxy-4'-methoxychalcone (DMC) (2) and adunchalcone (3).
670 671
Page 25 of 28
672 673
Fig. 4. Structures of natural chalcones from Piper species
674
675 676
Fig. 5. Structures of chalcones from Psorothamnus and Lonchocarpus species
677 678
Page 26 of 28
679 680
Fig. 6. Structures of plant-derived chalcones 15-34
681 HO
OH
O
O (36)
682
(35)
683
Fig. 7. Structures of 2',4'-dihydroxychalcone (35) and Trans-chalcone (36).
684 685
Page 27 of 28
R
R O O
n
O R
Triclosan-chalcon
O O
H N
R
O
HN
N
H N R
O
O
HN
O R
686
Paullone-chalcone
687
Fig. 8. Structures of some chalcone-hybrids
Dihydropyrimidinone-chalcone
Page 28 of 28
S0924-8579(17)30220-0 http://dx.doi.org/doi: 10.1016/j.ijantimicag.2017.06.010 ANTAGE 5160
To appear in:
International Journal of Antimicrobial Agents
Received date: Accepted date:
23-3-2017 17-6-2017
Please cite this article as: Nasir Tajuddeen, Murtala Bindawa Isah, Mukhtar Adeiza Suleiman, Fanie R. van Heerden, Mohammed Auwal Ibrahim, The chemotherapeutic potential of chalcones against leishmaniases: a review, International Journal of Antimicrobial Agents (2017), http://dx.doi.org/doi: 10.1016/j.ijantimicag.2017.06.010. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
THE CHEMOTHERAPEUTIC POTENTIAL OF CHALCONES AGAINST LEISHMANIASES: A REVIEW
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Nasir Tajuddeena, Murtala Bindawa Isahb, Mukhtar Adeiza Suleimanc, Fanie R. van Heerdend and Mohammed Auwal Ibrahimc* a
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria Department of Biochemistry, Umaru Musa Yar’adua University, Katsina, Nigeria c Department of Biochemistry, Ahmadu Bello University, Zaria, Nigeria d School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
b
17 18 19 20 21 22 23 24 25 26 27 28
*Correspondence to: Mohammed Auwal Ibrahim PhD, Department of Biochemistry, Ahmadu Bello University, Zaria, Nigeria. Telephone: +2347031104932; E mail: [email protected] or [email protected]
29 30
Page 1 of 28
31
Graphical Abstract
32 33
Highlights
34
35
Antileishmanial activity of 278 synthetic and 34 chalcones of plant origin was reviewed
36
The mechanism of antileishmanial activity of chalcone was discussed
37
The structure activity relationship of chalcones against leishmania parasites was
38
analysed
39
Nanoparticles encapsulation of chalcones as delivery agents was examined
40
Conclusion was drawn highlighting the deficiencies in this line of research
41
Abstract
42
Leishmaniases are endemic diseases in tropical and sub-tropical regions of the world and
43
considered to be among the six most important neglected tropical diseases by the World
44
Health Organization (WHO). The current therapeutic arsenal against the disease suffers from
45
series of chemotherapeutic setbacks. However, since the early 1990s, naturally occurring
46
chalcones with promising antileishmanial effects have been reported and several other
47
synthetic chalcones and chalcone-hybrid molecules were confirmed to possess potent activity
48
against various Leishmania species. Herewith, a comprehensive review covering the
49
antileishmanial activity of 34 naturally occuring chalcones, 224 synthetic/semisynthetic
Page 2 of 28
50
chalcones and 54 chalcone hybrid molecules, is presented. Several chalcones in the
51
synthetic/semisynthetic category had IC50 values < 5µM with very good selectivity against
52
parasites and the structure activity relationships as well as the proposed mechanism of action
53
were discussed. We identified knowledge-gaps with the hope of providing future direction for
54
the discovery of novel antileishmanial drugs from chalcones.
55
Keywords: Chalcone-hybrids, Antileishmanial, Medicinal plants, Leishmaniases
56 57 58 59
1. Introduction
60
Leishmaniases are a group of diseases caused by about 20 different species of Leishmania
61
parasites [1]. These species possess distinct morphological features during development at
62
different life cycle stages. The infective flagellated promastigote forms colonize the gut of
63
sandfly vectors while the intracellular amastigote forms are found in infected mammalian
64
macrophages. In the mammalian hosts, amastigotes are responsible for the different clinical
65
manifestations that classify the infection from single cutaneous lesions caused by Leishmania
66
major to the fatal visceral form called Kala Azar caused by L. donovani [2]. The
67
promastigotes are transmitted in Africa, Asia, and Europe through bite from the female
68
sandfly of Phlebotomus species and in the Americas by Lutzomyia species [3]. About 0.9-1.3
69
million new cases of the disease occur annually in mainly poverty prone tropical and sub-
70
tropical regions it is endemic. The cutaneous lesions accounts for 0.7-1.3 million cases while
71
0.2-0.4 million cases are due to the visceral form. An estimated 399 and 556 million people
72
are at risk of cutaneous and visceral leishmaniases respectively, in high-burden countries [4,
73
5].
74
The therapeutic arsenal against Leishmania is rather ‘old’ and limited [6]. The primary
75
drugs for the treatment of visceral leishmaniasis are the pentavalent antimonials mostly
76
developed over 50 years ago and amphotericin B, while pentamidine, paromomycin, and
77
miltefosine are secondary chemotherapeutic agents [7]. Extended courses of parenteral
78
administration of the drugs often result in patients abandoning treatment half way and this led
79
to increased cases of resistance [8, 9]. Although some of the drugs are still effective, they are
Page 3 of 28
80
expensive and have a long half-life. Furthermore, side effects including liver, heart and
81
nephro-toxicities, pancreatitis, hypotension, cardiac problems and teratogenicity have been
82
reported with extended use of these drugs [10]. Even though several vaccine candidates have
83
been screened against the disease, none is yet effective [11]. Therefore, there is an urgent
84
need to discover/develop new, safe, inexpensive and effective drugs for the disease.
85
Chalcones (benzylideneacetophenones or 1,3-diaryl-2-propen-1-ones, Fig. 1) are
86
prominent secondary plant metabolites and biogenetic precursors of flavonoids and
87
isoflavonoids. Chemically, they consist of two aryl rings, joined together by an enone linker.
88
The presence of the reactive keto-ethylenic group is an important feature of this class of
89
compounds [12].
90 91
The biological/pharmacological properties of chalcones include, anti-inflammatory [13],
92
antimicrobial [14], antiviral [15], trypanocidal [16], antioxidant and anticancer [17]. Some
93
reviews have highlighted the potential of this group as therapeutic leads against the
94
aforementioned diseases [18-20]. Similarly, several chalcones (natural and synthetic) have
95
been investigated for antileishmanial activity with promising outcomes. In spite of that, a
96
thorough search of the published literature indicates that a comprehensive review on
97
antileishmanial chalcones is not currently available. The subject is covered in some mini
98
reviews [7, 18, 21], but these only briefly mentioned the topic as part of a broader discussion
99
on the anti-infective properties of chalcones and therefore left out several relevant studies and
100
data. This article reviewed all chalcones that were reported to possess antileishmanial activity
101
from 1990 to 2016.
102
The discussion in this article has been organised under the sub-headings of natural,
103
synthetic/semisynthetic chalcones, chalcone-hybrid molecules, in vitro and in vivo activity of
104
chalcones, structural requirements for activity and finally, mechanism of action.
105
2. In vitro antileishmanial activity of chalcones
106
A total of 312 compounds bearing the core chalcone skeleton (Fig. 1) were reported with
107
antileishmanial activity. Out of these, 34 were plants-derived, mainly from plants in the
108
Fabaceae and Piperaceae. The remaining 278 were synthetic/semisynthetic and 54 out of
109
these were chalcone-hybrids. The compounds showed varying degrees of leishmanicidal
Page 4 of 28
110
activity and we considered those with IC50 values ≤ 10, 10-20 and ≥ 20 µg/mL to have strong,
111
moderate and weak activities, respectively, as adopted by Isah et al. [22].
112
2.1
Antileishmanial activity of natural chalcones
113
Historically, natural compounds have been a good source of safe and effective drugs for
114
humans. Antileishmanial activity-guided fractionations of plant extracts have resulted in the
115
isolation of several antileishmanial chalcones. The first line of validating potency is in vitro
116
investigation of the growth-inhibitory or leishmanicidal activities (Table S1).
117
The first report on antileishmanial chalcones was the bioassay-guided fractionation of
118
Glycyrrhiza glabra (Fabaceae) alcohol root extract, which led to the isolation of licochalcone
119
A (1) (Fig. 2) [23]. The compound strongly inhibited the in vitro growth of L. major and L.
120
donovani promastigotes (IC50 = 2.4 µg/mL for both species). Further time-kill study of 1 on
121
the in vitro growth of L. major showed an inhibitory activity proportional to the incubation
122
period. Using the amastigote form of L. major as a model, 1 also strongly inhibited the in
123
vitro growth of the parasites by more than 95% at a concentration of 1 µg/mL [23]. This
124
study by Chen et al. [23] forms the basis for most of the subsequent studies on
125
antileishmanial chalcones. For instance, the leishmanicidal action of more oxygenated
126
chalcones was subsequently demonstrated by Zhai et al. [24], and the compounds showed
127
similar activity to 1.
128 129
In a different study, activity-guided fractionation of the dichloromethane extract of Piper
130
aduncum
131
methoxychalcone (DMC, 2) (Fig. 3). The compound strongly inhibited L. amazonensis
132
promastigotes, but the effect on amastigotes was low. No apparent toxic effects were
133
observed on macrophages at proportionately high amounts indicating selective toxicity of 2 to
134
the parasites. Electron microscopic studies showed that DMC altered the cell ultrastructure of
135
the parasites, causing damage to amastigote mitochondria at 50 µg/mL and promastigote
136
mitochondria at 40 µg/mL without showing any alteration to macrophages and other
137
mammalian cells even at 100 µg/mL [25]. A separate investigation of P. aduncum ethanol
138
leaf extract led to the isolation of adunchalcone (3) (Fig. 3) with weak activity against
139
promastigotes of L. (V.) braziliensis and L. (V.) chagasi, but moderate activity against L. (L.)
inflorescence
(Piperaceae)
led
to
the
isolation
of
2',6'-dihydroxy-4'-
Page 5 of 28
140
amazonensis and L. (L.) shawi. Its inhibitory effect on L. (L.) amazonensis amastigotes was
141
also weak while selectivity to peritoneal murine macrophages was low [26].
142 143
Antileishmanial activity-guided fractionation of ethanol aerial parts extract of Piper
144
elongatum resulted in the isolation of two dihydrochalcones, 2',6'-dihydroxy-4'-
145
methoxydihydrochalcone (4) and 2',6',4-trihydroxy-4'-methoxydihydrochalcone (5) (Fig. 4).
146
Compound 5 strongly inhibited the in vitro growth of L. tropica and L. infantum
147
promastigotes (IC50 = 3.82 and 6.35 µg/mL, respectively). On the other hand, compound 4
148
had a weak inhibitory effect on the in vitro growth of L. braziliensis and L. tropica
149
promastigotes (IC50 = 27.04 and 21.29 µg/mL, respectively) and a moderate inhibitory effect
150
against L. infantum promastigotes (IC50 = 15.30 µg/mL). However, both compounds were
151
toxic to macrophages [27]. Two dihydrochalcones containing a prenylated benzoic acid
152
moiety (6 and 7), together with three others (4, 5 and 8) (Fig. 4), were isolated from a 90%
153
alcohol leaf extract of Piper dennissi, the compounds had moderate to weak inhibitory effects
154
on L. amazonensis amastigotes (IC50 range from 17.65-49.9 µg/mL) [28]. Two more
155
chalcones, 9 and 10 (Fig. 4) that strongly inhibited the in vitro growth of amastigotes of L.
156
amazonenis (IC50 = 0.25 and 2.23 µg/mL, respectively), were isolated from the ethanol leaf
157
extract of Piper hispidum by bioassay-guided fractionation. However, both compounds were
158
mildly toxic to macrophages [29].
159 160
Chalcones 11 and 12 (Fig. 5) were isolated alongside other phenolic compounds from
161
Psorothamnus polydenius whole plant methanol extract. Both compounds strongly inhibited
162
L. donovani amastigotes but with some toxicity to Vero cells. Furthermore, treatment of L.
163
mexicana pre-infected macrophages with chalcones 11 and 12 reduced the number of infected
164
macrophages by 96% [30]. Comparatively less toxic isoliquiritigenin (13) (Fig. 5), a
165
ubiquitous plant chalcone isolated from Psorothamnus arborescens, displayed activity
166
against L. donovani amastigotes (IC50 = 5.30 µg/mL) [31].
167
Similarly, chalcone 14 (Fig. 5) from Lonchocarpus xuul (Fabaceae) strongly inhibited the
168
growth of L. braziliensis promastigotes (IC50 = 10 µg/mL), but inhibited L. amazonensis and
169
L. donovani promastigotes weakly (IC50 = 26.7 and 40 µg/mL respectively) [32].
170
Page 6 of 28
171
Three additional chalcones, 15-17 (Fig. 6), with weak L. amazonensis inhibitory activity
172
were isolated from the ethyl-acetate fraction of Calea uniflora ethanol extract (Asteraceae)
173
[33]. A series of plant-derived chalcones; 9, 13 and 18-34 (Fig. 6), were assayed for in vitro
174
antileishmanial activity against promastigotes of L. donovani, L. infantum, L. enrietti, L.
175
major and L. donovani amastigotes. All compounds except 24 and 27 displayed strong
176
promastigote and amastigote growth inhibitions and high toxicity to murine macrophages
177
[34].
178 179 180
The aforementioned in vitro studies suggest that chalcones such as 1, 3, 5, 9, 10, 11, 13
181
and 14 have potent selective inhibitory activity against a range of Leishmania species,
182
although some of them such as 18-34 also appear to be toxic to normal cells. Furthermore, the
183
chalcones seem to possess better in vitro antileishmanial activity than the dihydrochalcones.
184
2.2
Antileishmanial activity of synthetic/semi-synthetic chalcones
185
The promising reports on the activity of natural chalcones led to the synthesis and in vitro
186
antileishmanial assaying of several novel chalcones. The ease of chalcone synthesis by the
187
Claisen-Schmidt reaction certainly contributed to the large number of investigated synthetic
188
chalcones. In these synthetic compounds, several substitutions and modifications to Trans-
189
chalcone (36) (Fig. 7) were reported with varying effect on selective antileishmanial activity.
190
Thus, oxygenated, alkoxylated, halogenated, prenylated, sulphonamide and dihydro-
191
derivatives of chalcones, chalcones incorporating heteroatom(s) in one or more ring,
192
analogues with a five membered heterocyclic ring and chalcones with a benzopyran moiety
193
have been studied. This has helped in identifying some structural features for improved
194
antileishmanial activity (Section 4). A summary of the results for these compounds and their
195
structures are presented respectively in Table S2 and Fig. S1.
196
Notable among the synthetic compounds, 2',4'-dihydroxychalcone (35) (Fig. 7) showed
197
strong selective inhibition of L. amazonensis promastigotes (IC50 = 0.4 µM, SI = 1041.7) and
198
is a promising candidate for further development. The compound was 16 times more potent
199
and 200 times more selective for the parasite than the standard drug pentamidine [35]. Others
200
that have equally shown strong selective in vitro inhibition of leishmania parasites include
201
compounds; 89, 96 [36], 106 [37], 156, 160 [38], 167-170 [39], 189-192, 200 [40], 206, 210
Page 7 of 28
202
[41] and 215 [42]. The in vivo studies of these chalcones should be the next step in validating
203
their therapeutic potential against leishmaniasis.
204 205 206
2.3
207
An emerging strategy in drug discovery is the fusion of two or more distinct pharmacophores
208
into a single chemical entity called a hybrid molecule which usually has a dual mode of
209
action or a different biological target [43]. Thus, hybrid molecules are often more active than
210
individual drugs. A few studies have been conducted on antileishmanial chalcone-hybrid
211
molecules (Fig. S2) and these are summarised in Table S3.
Antileishmanial activity of chalcone-hybrids
212
Interestingly, triclosan-, paullone- and dihydropyrimidinone-chalcone hybrids (Fig. 8) had
213
better selective antileishmanial activity compared to individual subunits, suggesting
214
synergism between the subunits [44-46]. Similarly, quinolone- and caffeine-chalcone hybrids
215
have demonstrated potent antileishmanial activities [16, 47].
216 217
3. In vivo antileishmanial activity of chalcones
218
A number of chalcones have shown potent activity in animal models (Table S4) which
219
points to their therapeutic relevance considering that xenobiotic metabolism may convert
220
highly active (in vitro) chalcones to inactive metabolites.
221
Intraperitoneal administration of licochalcone A (1) at doses of 2.5 and 5.0 mg/kg body
222
weight (bw) completely prevented lesion development in L. major-infected mice (parasite
223
load in footpad of mice reduced by 80 and 75%, respectively). This was corroborated by the
224
50% inhibition of lesion size in L. major-infected mice at intralesional doses of 1 and 2.5
225
mg/kg bw [48]. In hamster model, 20 mg/kg bw daily intraperitoneal dose of licochalcone A
226
reduced the number of L. donovani parasites in liver and spleen by 98% and 96%
227
respectively. Furthermore, oral administration of (1) to hamsters at doses of 5, 50 and 150
228
mg/kg bw for six days reduced parasite loads in the liver and spleen by 65% and 70%
229
respectively. Oral administration of 1000 mg/kg bw of (1) produced no sign of toxicity in rats
230
for two weeks. Also, no toxicity was recorded after intraperitoneal administration of 100 and
Page 8 of 28
231
150 mg/kg bw to rats and hamsters, respectively [48]. These interesting findings clearly
232
demonstrate the safety of (1) in animal model irrespective of the route of administration.
233
Intraperitoneal treatment of L. (V.) braziliensis-infected hamster footpads with 168
234
showed 83% lesion healing 16 weeks post-infection, similar to the effect observed for
235
amphotericin B. Also, parasite load in tissues of infected animals was significantly lower
236
after treatment with 167 (topical) and 168 (topical and intraperitoneal) compared to untreated
237
animals after 42 days of treatment and the result was similar to amphotericin B. The presence
238
of fibroblasts and collagen fibres in the dermis of animals intraperitoneally treated with 168
239
was observed 3 weeks after the end of treatment, featuring reconstitution of damaged tissues.
240
Moreover, 167 and 168 were non-toxic to uninfected hamsters after 30 days of intraperitoneal
241
administration of 1 and 10 mg/kg bw [46]. Preliminary studies have also indicated that the
242
substituents on the compounds could have an effect on the in vivo activity. For instance, daily
243
intraperitoneal dose (50 mg/kg bw) of compound 190 with alkylated amine substituents
244
produced 48% inhibition after 5 days of treatment while 200 with a geranyl substituent
245
exhibited 83% suppression of parasites at 50 mg/kg/day for 10 days treatment and 76 ± 11%
246
at 100 mg/kg/day for 5 days treatment [40].
247
These few in vivo studies so far conducted show that chalcones are both active and safe in
248
different animal models.
249
4. Biodegradable nanoparticles encapsulation of chalcones and antileishmanial activity
250
Biodegradable nanoparticles have recently gained prominence as target specific delivery
251
agents for drugs, genes and vaccines. They offer considerable advantages including
252
biocompatibility, greater stability in biological fluids, easy preparation, superior
253
encapsulation and easy release profile. A few studies to investigate the effect of nanoparticles
254
encapsulation on antileishmanial activity of chalcones have been conducted with interesting
255
outcomes. The in vitro inhibitory activity of DMC against L. amazonensis was enhanced with
256
encapsulation in polylactic-acid (PLA) nanoparticles. A regimen of DMC-PLA (5 µg of PLA
257
and 1 µg/mL of DMC) inhibited intracellular parasite growth by 53% compared to 23%
258
inhibition observed with free DMC [49]. Similarly, subcutaneous treatment of L.
259
amazonensis infected mice with 200 µg of 2 encapsulated in 1 mg of PLA led to a 90%
260
reduction in parasite load, which was similar to effect of glucantime [49]. Interestingly, doses
261
of DMC (2) as high as 1 mg did not alter the course of lesion development in L. amazonensis
Page 9 of 28
262
infected mice. However, a five times smaller dose of DMC in PLA (200 µg) produced a 60%
263
reduction in lesion size compared to untreated control. A fusion of PLA nanosphere-
264
containing vacuoles with the parasitophorous vacuoles of infected macrophages was
265
consistently observed, indicating that the nanoparticles actually reach the parasite before
266
degradation, improved intracellular bioavailability of DMC and might serve as drug carriers
267
within the cells [49].
268
Nanoparticles fusion also improved the parasite inhibitory activity of Trans-chalcone (36)
269
when administered as an implant with PLA and poly(D,L-lactide-co-glycolide (PGLA) to L.
270
amazonensis-infected mice. Subcutaneous administration of a single dose of 36 (4 mg/kg bw)
271
produced a 21% decrease in lesion size similar to pentamidine treated mice. On the other
272
hand, administration of a similar dose of PLA/36 and PGLA/36 as an ear implant produced
273
11 and 31% decrease in lesion size in L. amazonensis-infected mice [50] which demonstrates
274
that PGLA might be a better vehicle for drug delivery. Soybean lecithin and polysorbate-20
275
nanoemulsions have also shown potential as chalcone drug delivery systems against the
276
amastigote forms [51]. Controlled-release polymers such as PGLA and PLA represent a new
277
strategy for local delivery of chemotherapeutic agents with a potential to maximise
278
antileishmanial effects as demonstrated in the aforementioned studies
279
5. Structural requirements for antileishmanial activity of chalcones and structure-
280
activity relationships
281
In order to investigate structural requirements for activity of chalcones against Leishmania
282
species, Hermoso and co-workers synthesized some di- and triacetylated derivatives of 4 and
283
5, some C6-C3-C6 systems with different substituents, a series of alkyl-substituted propanones
284
and some benzocyclopentanones. Only compounds with a C6-C3-C6 system displayed
285
antileishmanial activity against promastigotes indicating that the two aryl rings are a key
286
requirement for antileishmanial activity of chalcones [27]. This conclusion is further
287
supported by Nielsen et al. [52], who investigated the role of the propenone chain by
288
preparing some α,β-double bond-modified chalcones (including α- and β-alkylated chalcones,
289
dihydrochalcones and acetylenic analogues) and no drastic changes in activity were observed
290
in the leishmanicidal activity. It was thus concluded that the alkylating property of the α,β-
291
unsaturated ketone is of minor importance for antileishmanial activity of chalcones.
292
Published data suggests that the real pharmacophore of the chalcones are the two aryl rings,
293
the α,β-unsaturated ketone mainly functions as a spacer [52]. Further 3D QSAR analyses of a
Page 10 of 28
294
series of substituted chalcones yielded high quality models (antileishmanial model, R2 = 0.73,
295
Q2 = 0.63; lymphocyte-suppressing model, R2 = 0.90, Q2 = 0.80) which indicated that steric
296
interactions between the target and chalcones are the major determinant of potency whilst
297
electronic factors only play a minor role (against parasite and lymphocyte cells). Specifically,
298
ring B and its substitution pattern are mainly responsible for activity while ring A is generally
299
considered to be less important for antileishmanial activity. Bulky substituents at position 2'
300
and 3' are predicted to increase activity while bulky substituents at position 4' are predicted to
301
reduce activity. On the other hand, antilymphocyte activity is influenced by substitution on
302
both rings A and B. Bulky groups at C-2' (ring B) and C-5 and/or -6 of ring A will increase
303
antilymphocyte activity, whereas bulky substitution at 4', 2, 3 and 4 will reduce toxicity.
304
These observations enable the separation of antileishamnial and antilymphocyte actions of
305
chalcones and facilitate the design of highly selective antileishmanial chalcones [53]. Several
306
conventional SAR studies have also documented the importance of steric influence and ring
307
B substitutions to the leishmanicidal activity of chalcones [27, 34, 37, 38]. In addition, some
308
SAR studies also described some level of steric contribution from ring A to antileishmanial
309
activity [37, 38, 54]. For example, in the specific case of 2, with an unsubstituted A-ring,
310
almost any form of substitution (electron-donating or -accepting) at position 4 of ring A led
311
to a decrease in activity [54]. It is also noteworthy that theoretical analyses of chlorine atom
312
substitutions at different positions of ring A point to an intricate relationship between steric
313
bulk and electronic properties of the chlorine atom. Electronegative elements like chlorine are
314
also lipophilic and this may encourage permeability through parasite cell membrane. The
315
influence of ring A on antileishmanial activity is particularly pronounced when the ring is not
316
restricted to substituted benzene rings. For example, good activities were reported with a 1-
317
naphthalenyl, 2-pyridinyl and 4-quinolinyl ring A. The point of attachment of these moieties
318
to the α,β-unsaturated ketone is also important as revealed by the poor activities of the 3-
319
quinolinyl and 2-naphthalenyl compared to the 4-quinolinyl and 1-naphthalenyl derivatives
320
[37].
321
For chromenochalcones, A-ring substitution and the α,β-unsaturated ketone seemed to be
322
quite important for antileishmanial activity [55] because 52 with a hydroxy group at position
323
4 showed the best activity. The size of the substituent at position 4 also appears to play a
324
crucial role. For instance, 53, which has a structure similar to 52 but is methoxylated at C-4
325
was less active against amastigotes. It is possible that a bulkier group at this position reduced
326
activity, but the reduction in activity might also be attributable to the loss of the hydrogen
Page 11 of 28
327
bond donor [55]. In a comprehensive assessment of the effect of substitution pattern,
328
synthetic chromenochalcones with different substitutions on both rings A and B were
329
analysed. The presence of electron-withdrawing and electron-donating groups on ring B and
330
an aromatic heterocyclic ring A improved activity and greater selectivity compared to the
331
unsubstituted parent compounds [40, 41]. Chromenodihydrochalcones are generally less
332
active than chromenochalcones suggesting a role for the α,β-unsaturation in the
333
antileishmanial activity of this class of compounds [55]. Furthermore, removal of the olefinic
334
bond in the benzopyran moiety of chromenochalcones maintained the leishmanicidal activity
335
but reduced toxicity to Vero cells [41].
336
Molecular-modelling coupled with synthetic studies was performed to investigate the
337
influence of steric and electronic effects on antileishmanial activity [38]. It was observed that
338
the insertion of two bulky ortho substituents on the aromatic ring B imposes a structural
339
rigidity and reduces conformational freedom of the phenyl ring, which improved the activity.
340
Importantly, derivatives with significant activity have larger torsion dihedral angles, which
341
were influenced by the bulky groups at ortho position. This demonstrates the steric
342
importance of the carbonyl group and the phenyl ring B moiety to the antileishmanial
343
activity. The electronic potential map of the active chalcones indicated that HOMO density
344
on phenyl ring B, close to the carbonyl, improved antileishmanial activity, whereas HOMO
345
density on ring A far from the carbonyl reduced the activity. This is similar to the findings of
346
Andrighetti-Frohner et al. [36] who reported that molecular volume, weight and dipole
347
moment of chalcones, HOMO density concentrated in centre of the chalcone moiety
348
(specifically the carbonyl group and unsaturated linker between ring A and B) and
349
conformational structure of the compounds are important structural and electronic features
350
for activity of chalcones [36]. The carbonyl group not only contributes from a steric
351
perspective but also from an electronic perspective to the observed antileishmanial activity of
352
chalcone series [38].
353
The antileishmanial activity of chalcones is also affected by prenylation at different
354
positions. For example, chromeno-chalcones (52 and 53) had better activity than chalcone 20
355
from which they were derived, suggesting that prenylation at position 4' improves
356
leishmanicidal activity [40, 55]. Likewise, prenylation at positions 2 and 3 of ring A greatly
357
improved activity and selectivity of chalcones [42]. It is also noteworthy that addition of
358
alkyl amino substituent on rings A or B decreased the activity [40]. The improved activity
Page 12 of 28
359
observed in prenylated chalcones might be a result of increased lipophilicity, facilitating the
360
passage of molecules through cell membrane barriers of macrophages and parasites and
361
resulting in enhanced drug delivery. Kayser and Kiderlen [34] had observed that ability to
362
inhibit the growth of parasite depends on the ratio of a limited number of lipophilic to
363
hydrophilic substituents on aromatic rings and several studies have shown that the nature of
364
substitution on both rings A and B is vital for antileishmanial activity of chalcones.
365
Studies that involved two series of regioisomeric chromene-based chalcones indicated
366
that the series with aryl ring (as opposed to heterocyclic pyran of benzopyran moiety) joined
367
to the β-carbon of α,β-unsaturated carbonyl chain displayed excellent activity against
368
promastigotes. The 3- and 4-chloro substituted forms of the most active series were found to
369
be the most potent. Chloro-substituent in the series with aryl ring directly joined to the
370
carbonyl carbon did not improve activity of the compounds (129-138, Fig. S1) [56].
371
Therefore, for chalcones with a benzopyran ring, the best arrangement for increased activity
372
is when the pyran ring of benzopyran moiety is directly connected to the carbonyl carbon.
373
6. Mechanism of antileishmanial action of chalcones
374
Some insight into possible mechanism of the antileishmanial activity of chalcones has
375
been obtained from electron microscopic studies on possible ultrastructural changes of L.
376
major incubated with licochalcone A (1). Destructive changes to the mitochondria with no
377
apparent changes to other organelles of parasites were observed [23]. Similar destruction of
378
parasite mitochondria was observed with other chalcones [24, 57, 58]. A follow-up study
379
showed that licochalcone A altered the ultrastructure of L. major promastigote and
380
amastigote in a concentration-dependent manner without any alteration to human monocyte-
381
derived macrophages [59]. Licochalcone A also greatly inhibited oxygen consumption and
382
activity of parasite mitochondrial dehydrogenases. These findings suggest that licochalcone
383
A modulates the ultrastructure and function of Leishmania parasite mitochondria [59]. This is
384
further supported by the observation that licochalcone A selectively inhibited the activity of
385
fumarate reductase (FRD) in permeated mitochondria of L. major promastigotes over
386
succinate dehydrogenase (SDH). The inhibitory effect of licochalcone A on crude parasite
387
mitochondria was selective to FRD in addition to the inhibition of SDH, NADH
388
dehydrogenase (NDH), succinate-cytochrome c reductase and NADH-cytochrome c
389
reductase. It was also reported that licochalcone A inhibited the activity of SDH and NDH in
390
PBMC and J774 cells in a concentration- and time-dependent manner. Other oxygenated
Page 13 of 28
391
chalcones have also shown potent inhibitory effects on the FRD [60]. These findings suggest
392
that FRD might be specifically targeted by chalcones.
393
DMC (2) also destroys parasite mitochondria but apparently through different mechanism.
394
A relatively high dose (100 µM) of DMC failed to interfere with the parasite FRD. Rather, 2
395
seemed to act by altering sterol biosynthesis and sterol composition of parasite in a manner
396
different from other known sterol inhibitors. The sterol composition of L. amazonensis
397
promastigotes treated with 2 revealed the accumulation of early sterol precursors which may
398
result in altered membrane fluidity and structure as previously observed by electron
399
microscopy in parasites treated with 2 as well as a reduction in the levels of C-14
400
demethylated and C-24 alkylated sterols, leading to a reduction in exogenous cholesterol
401
uptake [58].
402
Chalcones 167-169 caused several ultrastructural changes in L. (V.) braziliensis including
403
intense atypical vacuolization with cytoplasmic disorganization, formation of binucleated
404
parasites, different levels of mitochondrial changes including a reduction in electron density
405
of the mitochondrial matrix and cristae and mitochondrial swelling. Nucleosome-sized DNA
406
fragments were also identified in promastigotes after treatment with the chalcones indicating
407
DNA fragmentation. Morphological changes of the parasite such as cell shrinkage and
408
cytoplasmic condensation were similarly observed after treatment with these chalcones,
409
which could indicate cell death by apoptosis in multicellular and unicellular organisms [57].
410
Apart from the mechanisms of action by direct effect of chalcones on parasite, modulation
411
of host immune response may also be involved. Some chalcones were reported to
412
significantly stimulate nitric oxide (NO) synthesis and simultaneously reduce the index of
413
infection in macrophages. This suggests that chalcones kill intracellular parasites by a NO-
414
dependent mechanism [39] and induction of NO synthase is essential to the intracellular
415
killing of Leishmania in macrophages [61]. In humans, low production of NO is associated
416
with increased infectivity of the parasite, and NO resistance is associated with non-response
417
to treatment with antimonial therapy[62, 63]. Thus, based on these findings, chalcones seem
418
to mediate leishmanicidal activity via two broad mechanisms; direct action on parasite
419
mitochondria and modulation of host immune system by stimulating NO production in
420
infected macrophages.
Page 14 of 28
421
Ligand or structure-based in-silico drug design and identification of protein targets using
422
molecular-docking studies have recently gained widespread use [64]. Molecular-docking
423
studies on 24 Leishmania enzymes has identified dihydroorotate dehydrogenase, nucleoside
424
hydrolase, oligopeptidase B, methionyl-tRNA synthetase, UDP-glucose pyrophosphorylase,
425
trypanothione reductase and glycerol-3-phosphate dehydrogenase as potential enzyme targets
426
for chalcones. In these studies, the chalcones demonstrated docking preference to most of
427
these protein targets with strong binding energies [35, 65].
428
7. Conclusion
429
A total of 312 chalcones were covered in this review and among them, 35, 79, 81 and 87
430
have shown exceptional promise as potential leishmanicidal candidates with high selectivity
431
to the parasite cells. Conversely, other chalcones such as 36, 131 and 132 have potent
432
antileishmanial activity but their toxicity profiles have not been investigated to warrant a
433
definite statement on their future prospects. The observed toxic effects of 18-34 (except 24)
434
on both the parasite and normal cells further support the need to ascertain the toxicity effects
435
of antileishmanial chalcones. Thus, modifications of chalcones 18-34 that will reduce toxicity
436
to normal cells without compromising the leishmanicidal potency may be worthwhile
437
investigating.
438
This review has also highlighted that a smaller number of natural chalcones have been
439
studied in comparison to synthetic chalcones. This is not surprising because isolating these
440
plant metabolites is often tedious coupled with the low yield after isolation. Additionally,
441
even amongst the studied natural chalcones, only a few had potent parasite killing ability
442
compared to the synthetic chalcones. However, it is clear that a detailed observation of the
443
natural chalcones and their structure-activity relationships can lead to the design of far more
444
potent synthetic/semi-synthetic chalcones. Despite this observation, the synthetic
445
modifications of chalcones were not greatly extended to hybrid molecules even though some
446
of the few studied hybrids, such as 270, 282, 283 and 293, had great potential for further
447
antileishmanial studies.
448
An important deficiency highlighted by this review is the acute shortage of in vivo studies
449
on antileishmanial chalcones. This is of importance taking into cognizance the large number
450
of highly selective and potent chalcones identified via in vitro assays. Still, among the few in
451
vivo studies, some promising results were recorded such as licochalcone A and the increase in
452
the activity of DMC after encapsulation in PLA. Additionally, there may be a need to expand
Page 15 of 28
453
the in vivo studies to address the effects of chalcones on some Leishmania-associated
454
pathological changes considering the crucial role of those alterations during the disease
455
pathogenesis. Finally, studies on the mechanisms of antileishmanial actions are limited to the
456
parasite mitochondrial enzyme systems which practically cannot be the only target. Hence,
457
more holistic in vivo studies are required as the next line of action towards the development
458
of chalcones as chemotherapeutic agents against leishmaniasis.
459 460
Acknowledgements
461
The author MBI was awarded a Ph.D. study fellowship by the TETFund desk office of
462
Umaru Musa Yar’adua University Katsina, Nigeria. FRVH thank the University of KwaZulu-
463
Natal and the National Research Foundation (NRF) (Grant No: 98345, 2016) of South Africa
464
for financial support.
465 466
Declarations
467
Funding: National Research Foundation (NRF) (Grant No: 98345, 2016) of South Africa
468
Competing Interests: No
469
Ethical Approval: Not required
470
Page 16 of 28
471
References
472
[1] Giarolla J, Rando DG, Pasqualoto KF, Zaim MH, Ferreira EI. Molecular modeling as a
473
promising tool to study dendrimer prodrugs delivery. J Mol Struc-THEOCHEM
474
2010;939:133-8.
475
[2] Vendrametto MC, Dos Santos AO, Nakamura CV, Dias Filho BP, Cortez DAG, Ueda-
476
Nakamura T. Evaluation of antileishmanial activity of eupomatenoid-5, a compound isolated
477
from leaves of Piper regnellii var. pallescens. Parasitol Int 2010;59:154-8.
478
[3] Desjeux P. Leishmaniasis: current situation and new perspectives. Comp Immunol
479
Microbiol Infect Dis 2004;27:305-18.
480
[4] Hailu A, Dagne DA, Boelaert M. Leishmaniasis. In: Gyapong J, Boatin B, editors.
481
Neglected Tropical Diseases - Sub-Saharan Africa: Springer International Publishing; 2016.
482
p. 87-112.
483
[5] Organization WH. Leishmaniasis in high-burden countries: an epidemiological update
484
based on data reported in 2014. Weekly epidemiological record. 2016.
485
[6] Almeida OLS, Santos JB. Advances in the treatment of cutaneous leishmaniasis in the
486
new world in the last ten years: a systematic literature review. An Bras Dermatol
487
2011;86:497-506.
488
[7] Sangshetti JN, Khan FAK, Kulkarni AA, Arote R, Patil RH. Antileishmanial drug
489
discovery: Comprehensive review of the last 10 years. Rsc Advances 2015;5:32376-415.
490
[8] Monteiro LM, Löbenberg R, Ferreira EI, Cotrim PC, Kanashiro E, Rocha M, et al.
491
Targeting Leishmania amazonensis amastigotes through macrophage internalisation of a
492
hydroxymethylnitrofurazone nanostructured polymeric system. Int J Antimicrob Agents
493
2017; https://doi.org/10.1016/j.ijantimicag.2017.01.033
494
Page 17 of 28
495
[9] Freitas-Junior LH, Chatelain E, Kim HA, Siqueira-Neto JL. Visceral leishmaniasis
496
treatment: what do we have, what do we need and how to deliver it? Int J Parasitol Drugs
497
Drug Resist 2012;2:11-9.
498
[10] Rybniker J, Goede V, Mertens J, Ortmann M, Kulas W, Kochanek M, et al. Treatment of
499
visceral leishmaniasis with intravenous pentamidine and oral fluconazole in an HIV-positive
500
patient with chronic renal failure—a case report and brief review of the literature. Int J Infect
501
Dis 2010;14:e522-e5.
502
[11] Kumar R, Engwerda C. Vaccines to prevent leishmaniasis. Clin Exp Immunol
503
2014;3:e13.
504
[12] Sakagami H, Masuda Y, Tomomura M, Yokose S, Uesawa Y, Ikezoe N, et al.
505
Quantitative
506
2017;37:1091-8.
507
[13] Luo X-L, Liu S-Y, Wang L-J, Zhang Q-Y, Xu P, Pan L-L, et al. A tetramethoxychalcone
508
from Chloranthus henryi suppresses lipopolysaccharide-induced inflammatory responses in
509
BV2 microglia. Eur J Clin Pharmacol 2016;774:135-43.
510
[14] Simard Fo, Gauthier C, Chiasson Er, Lavoie S, Mshvildadze V, Legault J, et al.
511
Antibacterial Balsacones J–M, Hydroxycinnamoylated Dihydrochalcones from Populus
512
balsamifera Buds. J Nat Prod 2015;78:1147-53.
513
[15] Mohammed MM, Hamdy A-HA, El-Fiky NM, Mettwally WS, El-Beih AA, Kobayashi
514
N. Anti-influenza A virus activity of a new dihydrochalcone diglycoside isolated from the
515
Egyptian seagrass Thalassodendron ciliatum (Forsk.) den Hartog. Nat prod res 2014;28:377-
516
82.
517
[16] Insuasty B, Ramírez J, Becerra D, Echeverry C, Quiroga J, Abonia R, et al. An efficient
518
synthesis of new caffeine-based chalcones, pyrazolines and pyrazolo [3, 4-b][1, 4] diazepines
Structure–Cytotoxicity
Relationship
of
Chalcones.
Anticancer
Res
Page 18 of 28
519
as potential antimalarial, antitrypanosomal and antileishmanial agents. Eur J Med Chem
520
2015;93:401-13.
521
[17] Chen X, Liu Z, Meng R, Shi C, Guo N. Antioxidative and anticancer properties of
522
Licochalcone A from licorice. J Ethnopharmacol 2017;198:331-7.
523
[18] Nowakowska Z. A review of anti-infective and anti-inflammatory chalcones. Eur J Med
524
Chem 2007;42:125-37.
525
[19] Elias D, Beazely M, Kandepu N. Bioactivities of chalcones. Curr Med Chem
526
1999;6:1125.
527
[20] K Sahu N, S Balbhadra S, Choudhary J, V Kohli D. Exploring pharmacological
528
significance of chalcone scaffold: a review. Current medicinal chemistry. 2012;19:209-25.
529
[21] Singh P, Anand A, Kumar V. Recent developments in biological activities of chalcones:
530
A mini review. Eur J Med Chem 2014;85:758-77.
531
[22] Isah MB, Ibrahim MA, Mohammed A, Aliyu AB, Masola B, Coetzer TH. A systematic
532
review of pentacyclic triterpenes and their derivatives as chemotherapeutic agents against
533
tropical parasitic diseases. Parasitology 2016;143:1219-31.
534
[23] Chen M, Christensen SB, Blom J, Lemmich E, Nadelmann L, Fich K, et al.
535
Licochalcone A, a novel antiparasitic agent with potent activity against human pathogenic
536
protozoan species of Leishmania. Antimicrob Agents Chemother 1993;37:2550-6.
537
[24] Zhai L, Chen M, Blom J, Theander TG, Christensen SB, Kharazmi A. The
538
antileishmanial activity of novel o ygenated chalcones and their mechanism of action. J
539
Antimicrob Chemo 1999;43:793-803.
540
[25] Torres-Santos EC, Moreira DL, Kaplan MAC, Meirelles MN, Rossi-Bergmann B.
541
Selective effect of 2′, 6′-dihydroxy-4′-methoxychalcone isolated from Piper aduncum on
542
Leishmania amazonensis. Antimicrob Agents Chemother 1999;43:1234-41.
Page 19 of 28
543
[26] Dal Picolo CR, Bezerra MP, Gomes KS, Passero LFD, Laurenti MD, Martins EGA, et
544
al. Antileishmanial activity evaluation of adunchalcone, a new prenylated dihydrochalcone
545
from Piper aduncum L. Fitoterapia 2014;97:28-33.
546
[27] Hermoso A, Jiménez IA, Mamani ZA, Bazzocchi IL, Piñero JE, Ravelo AG, et al.
547
Antileishmanial activities of dihydrochalcones from Piper elongatum and synthetic related
548
compounds. Structural requirements for activity. Bioorg Med Chem 2003;11:3975-80.
549
[28] Cabanillas BJ, Le Lamer A-C, Castillo D, Arevalo J, Estevez Y, Rojas R, et al.
550
Dihydrochalcones and benzoic acid derivatives from Piper dennisii. Planta Med 2012;78:914-
551
8.
552
[29] Ruiz C, Haddad M, Alban J, Bourdy G, Reategui R, Castillo D, et al. Activity-guided
553
isolation of antileishmanial compounds from Piper hispidum. Phytochem Lett 2011;4:363-6.
554
[30] Salem MM, Werbovetz KA. Antiprotozoal Compounds from Psorothamnus p olydenius.
555
J Nat Prod 2005;68:108-11.
556
[31] Salem MM, Werbovetz KA. Isoflavonoids and Other Compounds from Psorothamnus a
557
rborescens with Antiprotozoal Activities. J. Nat. Prod 2006;69:43-9.
558
[32] Borges-Argaez R, Balnbury L, Flowers A, Giménez-Turba A, Ruiz G, Waterman PG, et
559
al. Cytotoxic and antiprotozoal activity of flavonoids from Lonchocarpus spp. Phytomedicine
560
2007;14:530-3.
561
[33] Lima TC, Souza RJ, Santos AD, Moraes MH, Biondo NE, Barison A, et al. Evaluation
562
of leishmanicidal and trypanocidal activities of phenolic compounds from Calea uniflora
563
Less. Nat prod res 2016;30:551-7.
564
[34] Kayser O, Kiderlen AF. In vitro leishmanicidal activity of naturally occurring chalcones.
565
Phytother Res 2001;15:148-52.
566
[35] Passalacqua TG, Torres FA, Nogueira CT, de Almeida L, Del Cistia ML, dos Santos
567
MB, et al. The 2′, 4′-dihydroxychalcone could be explored to develop new inhibitors against
Page 20 of 28
568
the glycerol-3-phosphate dehydrogenase from Leishmania species. Bioorg Med Chem Lett
569
2015;25:3564-8.
570
[36] Andrighetti-Fröhner CR, de Oliveira KN, Gaspar-Silva D, Pacheco LK, Joussef AC,
571
Steindel M, et al. Synthesis, biological evaluation and SAR of sulfonamide 4-
572
methoxychalcone derivatives with potential antileishmanial activity. Eur J Med Chem
573
2009;44:755-63.
574
[37] Liu M, Wilairat P, Croft SL, Tan AL-C, Go M-L. Structure–activity relationships of
575
antileishmanial and antimalarial chalcones. Bioorg Med Chem 2003;11:2729-38.
576
[38] Bello ML, Chiaradia LD, Dias LRS, Pacheco LK, Stumpf TR, Mascarello A, et al.
577
Trimethoxy-chalcone derivatives inhibit growth of Leishmania braziliensis: synthesis,
578
biological evaluation, molecular modeling and structure–activity relationship (SAR). Bioorg
579
Med Chem 2011;19:5046-52.
580
[39] de Mello TF, Bitencourt HR, Pedroso RB, Aristides SM, Lonardoni MV, Silveira TG.
581
Leishmanicidal activity of synthetic chalcones in Leishmania (Viannia) braziliensis. Exp
582
Parasitol 2014;136:27-34.
583
[40] Gupta S, Shivahare R, Korthikunta V, Singh R, Gupta S, Tadigoppula N. Synthesis and
584
biological evaluation of chalcones as potential antileishmanial agents. Eur J Med Chem
585
2014;81:359-66.
586
[41] Shivahare R, Korthikunta V, Chandasana H, Suthar MK, Agnihotri P, Vishwakarma P,
587
et al. Synthesis, structure–activity relationships, and biological studies of chromenochalcones
588
as potential antileishmanial agents. J Med Chem 2014;57:3342-57.
589
[42] Passalacqua TG, Dutra LA, de Almeida L, Velásquez AMA, Torres FAE, Yamasaki PR,
590
et al. Synthesis and evaluation of novel prenylated chalcone derivatives as anti-leishmanial
591
and anti-trypanosomal compounds. Bioorg Med Chem Lett 2015;25:3342-5.
Page 21 of 28
592
[43] Mishra S, Singh P. Hybrid molecules: The privileged scaffolds for various
593
pharmaceuticals. Eur J Med Chem 2016;124:500-36.
594
[44] Otero E, Vergara S, Robledo SM, Cardona W, Carda M, Vélez ID, et al. Synthesis,
595
leishmanicidal and cytotoxic activity of triclosan-chalcone, triclosan-chromone and triclosan-
596
coumarin hybrids. Molecules 2014;19:13251-66.
597
[45] Reichwald C, Shimony O, Dunkel U, Sacerdoti-Sierra N, Jaffe CL, Kunick C. 2-(3-Aryl-
598
3-oxopropen-1-yl)-9-tert-butyl-paullones: a new antileishmanial chemotype. J Med Chem
599
2008;51:659-65.
600
[46] Rashid U, Sultana R, Shaheen N, Hassan SF, Yaqoob F, Ahmad MJ, et al. Structure
601
based medicinal chemistry-driven strategy to design substituted dihydropyrimidines as
602
potential antileishmanial agents. Eur J Med Chem 2016;115:230-44.
603
[47] Roussaki M, Hall B, Lima SC, da Silva AC, Wilkinson S, Detsi A. Synthesis and anti-
604
parasitic activity of a novel quinolinone–chalcone series. Bioorg Med Chem Lett
605
2013;23:6436-41.
606
[48] Chen M, Christensen S, Theander TG, Kharazmi A. Antileishmanial activity of
607
licochalcone A in mice infected with Leishmania major and in hamsters infected with
608
Leishmania donovani. Antimicrob Agents Chemother 1994;38:1339-44.
609
[49] Torres-Santos EC, Rodrigues JM, Moreira DL, Kaplan MAC, Rossi-Bergmann B.
610
Improvement of in vitro and in vivo antileishmanial activities of 2′, 6′-dihydroxy-4′-
611
methoxychalcone by entrapment in poly (d, l-lactide) nanoparticles. Antimicrob Agents
612
Chemother 1999;43:1776-8.
613
[50] Piñero J, Temporal RM, Silva-Gonçalves AJ, Jiménez I, Bazzocchi IL, Oliva A, et al.
614
New administration model of trans-chalcone biodegradable polymers for the treatment of
615
experimental leishmaniasis. Acta trop 2006;98:59-65.
Page 22 of 28
616
[51] de Mattos CB, Argenta DF, de Lima Melchiades G, Cordeiro MNS, Tonini ML, Moraes
617
MH, et al. Nanoemulsions containing a synthetic chalcone as an alternative for treating
618
cutaneous leshmaniasis: optimization using a full factorial design. Int J nanomedicine
619
2015;10:5529.
620
[52] Nielsen SF, Kharazmi A, Christensen SB. Modifications of the α, β-double bond in
621
chalcones only marginally affect the antiprotozoal activities. Bioorg Med Chem 1998;6:937-
622
45.
623
[53] Nielsen SF, Christensen SB, Cruciani G, Kharazmi A, Liljefors T. Antileishmanial
624
chalcones: Statistical design, synthesis, and three-dimensional quantitative structure− activity
625
relationship analysis. J Med Chem 1998;41:4819-32.
626
[54] Boeck P, Falcao CAB, Leal PC, Yunes RA, Cechinel Filho V, Torres-Santos EC, et al.
627
Synthesis of chalcone analogues with increased antileishmanial activity. Bioorg Med Chem
628
2006;14:1538-45.
629
[55] Narender T, Gupta S. A convenient and biogenetic type synthesis of few naturally
630
occurring chromeno dihydrochalcones and their in vitro antileishmanial activity. Bioorg Med
631
Chem Lett 2004;14:3913-6.
632
[56] Foroumadi A, Emami S, Sorkhi M, Nakhjiri M, Nazarian Z, Heydari S, et al.
633
Chromene‐Based Synthetic Chalcones as Potent Antileishmanial Agents: Synthesis and
634
Biological Activity. Chem Biol Drug Des 2010;75:590-6.
635
[57] de Mello TF, Cardoso BM, Bitencourt HR, Donatti L, Aristides SM, Lonardoni MV, et
636
al. Ultrastructural and morphological changes in Leishmania (Viannia) braziliensis treated
637
with synthetic chalcones. Exp Parasitol 2016;160:23-30.
638
[58] Torres-Santos EC, Sampaio-Santos MI, Buckner FS, Yokoyama K, Gelb M, Urbina JA,
639
et al. Altered sterol profile induced in Leishmania amazonensis by a natural
640
dihydro ymetho ylated chalcone. J Antimicrob Chemo 2009;63:469-72.
Page 23 of 28
641
[59] Zhai L, Blom J, Chen M, Christensen SB, Kharazmi A. The antileishmanial agent
642
licochalcone A interferes with the function of parasite mitochondria. Antimicrob Agents
643
Chemother 1995;39:2742-8.
644
[60] Chen M, Zhai L, Christensen SB, Theander TG, Kharazmi A. Inhibition of Fumarate
645
Reductase inLeishmania major and L. donovani by Chalcones. Antimicrob Agents
646
Chemother 2001;45:2023-9.
647
[61] Liew FY, Li Y, Moss D, Parkinson C, Rogers MV, Moncada S. Resistance to
648
Leishmania major infection correlates with the induction of nitric oxide synthase in murine
649
macrophages. Eur J Immunol 1991;21:3009-14.
650
[62] Campos MB, Gomes CMDC, de Souza AAA, Lainson R, Corbett CEP, Silveira FT. In
651
vitro infectivity of species of Leishmania (Viannia) responsible for American cutaneous
652
leishmaniasis. Parasitol Res 2008;103:771.
653
[63] Souza AS, Giudice A, Pereira JM, Guimarães LH, de Jesus AR, de Moura TR, et al.
654
Resistance of Leishmania (Viannia) braziliensis to nitric oxide: correlation with antimony
655
therapy and TNF-α production. BMC Infect Dis 2010;10:209.
656
[64] Meng X-Y, Zhang H-X, Mezei M, Cui M. Molecular docking: a powerful approach for
657
structure-based drug discovery. Curr Comput Aided Drug Des 2011;7:146-57.
658
[65] Ogungbe IV, Erwin WR, Setzer WN. Antileishmanial phytochemical phenolics:
659
molecular docking to potential protein targets. J Mol Graph Model 2014;48:105-17.
660 661
Page 24 of 28
662 663
Fig. 1. Representative skeleton of a chalcone showing the ring annotations and numbering
664
665 666
Fig. 2. Structure of licochalcone A.
667
668 669
Fig. 3. Structures of 2',6'-dihydroxy-4'-methoxychalcone (DMC) (2) and adunchalcone (3).
670 671
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672 673
Fig. 4. Structures of natural chalcones from Piper species
674
675 676
Fig. 5. Structures of chalcones from Psorothamnus and Lonchocarpus species
677 678
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679 680
Fig. 6. Structures of plant-derived chalcones 15-34
681 HO
OH
O
O (36)
682
(35)
683
Fig. 7. Structures of 2',4'-dihydroxychalcone (35) and Trans-chalcone (36).
684 685
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R
R O O
n
O R
Triclosan-chalcon
O O
H N
R
O
HN
N
H N R
O
O
HN
O R
686
Paullone-chalcone
687
Fig. 8. Structures of some chalcone-hybrids
Dihydropyrimidinone-chalcone
Page 28 of 28