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In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii
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Short Communication
In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii Harald Seifert a,b,∗, Danuta Stefanik a, Melanie Olesky c, Paul G. Higgins a,b a
Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Cologne, Germany German Center for Infection Research (DZIF), partner site Bonn-Cologne, Germany c Tetraphase Pharmaceuticals, Watertown, Massachusetts, USA b
a r t i c l e
i n f o
Article history: Received 19 August 2019 Accepted 20 October 2019 Available online xxx Editor: Prof. A Tsakris Keywords: International clone Oxacillinase Tetracycline Tigecycline Colistin Multidrug resistance
a b s t r a c t The activity of the novel, fully synthetic fluorocycline antibiotic TP-6076 against carbapenem-resistant Acinetobacter baumannii (CRAB) isolates with defined carbapenem resistance mechanisms was compared against reference antimicrobials with known activity against Acinetobacter spp. The susceptibility of 323 non-duplicate CRAB isolates to TP-6076, amikacin, ampicillin/sulbactam (SAM), cefepime, colistin, doxycycline, eravacycline, imipenem, levofloxacin, meropenem, minocycline, rifampicin, sulbactam, tigecycline, tobramycin and trimethoprim/sulfamethoxazole (SXT) was determined by the broth microdilution method. TP-6076 showed greater activity than comparator antimicrobials of the tetracycline class, SAM, levofloxacin, amikacin, tobramycin, SXT and colistin. MIC50 and MIC90 values for TP-6076 were 0.06 mg/L and 0.25 mg/L, respectively. In comparison, doxycycline, eravacycline, minocycline and tigecycline MIC50/90 values were 32/≥64, 0.5/1, 4/8 and 1/2 mg/L, respectively. Compared with other compounds, TP-6076 was the most active antimicrobial against CRAB, including isolates that were resistant to other antiAcinetobacter reference drugs including SAM, colistin, the aminoglycosides amikacin and tobramycin, and levofloxacin. TP-6076 is a promising new agent that may be a useful addition to the limited armamentarium of drugs targeting this problematic pathogen. © 2019 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.
1. Introduction Acinetobacter baumannii is a nosocomial pathogen known for its multidrug resistance and propensity for epidemic spread [1]. In the past decade, carbapenem resistance in A. baumannii has become an increasing concern. Resistance to carbapenems in A. baumannii is mainly mediated through the action of carbapenem-hydrolysing class D β -lactamases (CHDLs) and, less frequently, metallo-β -lactamases (MBLs) [2,3]. Whilst carbapenems are not significantly affected, drug efflux, especially through the resistance–nodulation–cell division (RND) type efflux pumps, plays a major role in resistance to aminoglycosides, fluoroquinolones and tetracyclines, and these efflux pumps have been shown to be overexpressed during antimicrobial therapy [4]. Frequently, colistin is the only remaining therapeutic option, but resistance has developed even to this drug [5]. TP-6076 is a novel, fully synthetic antibiotic of the tetracycline class that inhibits bacterial protein synthesis through bind-
∗ Corresponding author. Present address: Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Goldenfelsstr. 19–21, 50935 Cologne, Germany. Tel.: +49 221 478 32009; fax: +49 221 478 32035. E-mail address: [email protected] (H. Seifert).
ing to the 30S ribosomal subunit [6]. TP-6076 differs from currently approved tetracyclines in the unique C4 diethylamino, C7 trifluoromethyl and C8 unsubstituted pyrrolidinoyl substituents. TP-6076 has demonstrated potent antimicrobial activity against a wide range of Gram-positive, Gram-negative and anaerobic bacteria, including multidrug-resistant (MDR) Enterobacteriaceae and A. baumannii as well as strains with acquired tetracycline efflux determinants [7]. Early phase 1 single ascending and multiple ascending dose studies are completed, and TP-6076 continues to be evaluated in clinical studies [8]. In this study, the activity of TP-6076 was compared with that of reference antimicrobials with known activity against Acinetobacter spp., including aminoglycosides, β -lactams, colistin, fluoroquinolones, tetracyclines and trimethoprim/sulfamethoxazole (SXT), against a collection of well-characterised carbapenemresistant A. baumannii (CRAB) isolates harbouring acquired oxacillinases, MBLs or with an upregulated intrinsic OXA-51like carbapenemase. 2. Materials and methods Antimicrobial susceptibility testing was performed by the broth microdilution method in freshly prepared cation-adjusted
https://doi.org/10.1016/j.ijantimicag.2019.10.010 0924-8579/© 2019 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.
Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010
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Table 1 MIC distribution, MIC50 and MIC90 values, and antimicrobial susceptibility rates of 323 carbapenem-resistant Acinetobacter baumannii isolates. Antimicrobial agent b
TP-6076 Amikacin SAMc Cefepime Colistin Doxycycline Eravacyclineb Imipenem Levofloxacin Meropenem Minocycline Rifampicinb Sulbactamb Tigecyclineb Tobramycin SXTg
No. of isolates at MIC (mg/L) ofa :
MIC (mg/L)
≤0.015
0.03
0.06
0.125
0.25
0.5
1
2
4
8
16
32
64
128
≥256
21
43
138
83
36
2 5
13
12
70 13 161
160 35 60
48 26 11 0 6 0 22 94 3 68 5 12
12 4 2 12 5
4 16 1 11 4 1 7 97 22 82 14 51 1 12 17
15 53 26 2 13
12 96 47 1 66
35 108 75 4 137d
41 40 87 2
174 6 85 12
76 135 40 31 2 87
184 19 97 1 8 123
48 20 116
7 5e 36
1 12
3 41
1 6
28 2
21 16
28 86
6 137d
9
153
1
3 16
11f
1f
10 25
1 11 48
1
2
10
12
7 3 3
27 27 6
3 37
47 38 11
45 2 153 16 29
35 72 171 10 20 5 5
Susceptibility
MIC50
MIC90
Range
%S
%I
%R
0.06 256 32 128 1 32 0.5 32 16 64 4 4 32 1 128 32
0.25 ≥512 128 ≥512 4 ≥64 1 64 32 128 8 32 64 2 ≥256 ≥64
≤0.008–0.5 0.5 to ≥512 4 to ≥512 4 to ≥512 0.25 to ≥512 0.06 to ≥64 0.03–8 8–256 0.125 to ≥128 8–256 ≤0.06–32 1 to ≥512 2 to ≥256 0.125–8 0.125 to ≥256 ≤0.06 to ≥64
– 18.9 6.2 0.9 86.4 31.9 – 0.0 3.7 0.0 64.7 – – – 29.1 19.2
– 3.7 16.4 8.0 – 1.2 – 0.0 10.8 0.0 25.4 – – – 3.7 –
– 77.4 77.4 91.0 13.6 66.9 – 100.0 85.4 100.0 9.9 – – – 67.2 80.8
MIC, minimum inhibitory concentration; MIC50/90 , MICs required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant; SAM, ampicillin/sulbactam; SXT, trimethoprim/sulfamethoxazole. a Susceptible breakpoint values are indicated in boldface. b No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. c For ampicillin/sulbactam, only the ampicillin concentration is given. d ≥64 mg/L. e ≥128 mg/L. f ≤0.06 mg/L. g For trimethoprim/sulfamethoxazole, only the trimethoprim concentration is given.
Müller–Hinton broth following Clinical and Laboratory Standards Institute (CLSI) recommendations [9]. Microtitre trays containing freeze-dried antibacterial agents were provided by Merlin Diagnostica (Bornheim, Germany). A total of 323 non-duplicate CRAB isolates were tested against TP-6076, amikacin, ampicillin/sulbactam (SAM), cefepime, colistin, doxycycline, eravacycline, imipenem, levofloxacin, meropenem, minocycline, rifampicin, sulbactam, tigecycline, tobramycin and SXT. Resistance to carbapenems had been previously determined by Etest (bioMérieux, Nürtingen, Germany). The concentration ranges tested in two-fold dilutions were as follows: TP-6076, 0.008–16 mg/L; amikacin, 0.125–256 mg/L; ampicillin/sulbactam, 0.25/0.125–256/128 mg/L; cefepime, 0.125–256 mg/L; colistin, 0.03–256 mg/L; doxycycline, 0.03–32 mg/L; eravacycline, 0.008– 16 mg/L; imipenem, 0.125–256 mg/L; levofloxacin, 0.03–64 mg/L; meropenem, 0.125–256 mg/L; minocycline, 0.06–128 mg/L; rifampicin, 0.125–256 mg/L; sulbactam, 0.06–128 mg/L; tigecycline, 0.03–64 mg/L; tobramycin, 0.06–128 mg/L; and trimethoprim/sulfamethoxazole, 0.06/1.19–32/608 mg/L. Minimum inhibitory concentrations (MICs) were interpreted following CLSI guidelines, and susceptibility rates were determined using CLSI breakpoints where applicable [10]. Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 were used as quality control strains. Isolates were collected from various body sites in patients from multiple European and Asian countries between 2005 and 2016 and included outbreak-related as well as sporadic isolates. R The isolates had previously been characterised using DiversiLab (bioMérieux) and multilocus sequence typing (MLST) and represented isolates belonging to the eight previously described major international clonal (IC) lineages 1 (n = 28), 2 (n = 233), 3 (n = 1), 4 (n = 9), 5 (n = 1), 6 (n = 2), 7 (n = 16) and 8 (n = 5), whilst 28 isolates did not cluster with any of the international clonal lineages [3]. The carbapenem resistance mechanisms in the isolates were determined as described previously [11] and comprised 256 isolates with blaOXA-23-like , 23 isolates with blaOXA-40-like , 33 isolates with blaOXA-58-like , 1 isolate with blaOXA-23-like and blaOXA-58-like , 3 isolates with blaNDM-1 and 7 isolates with overexpression of intrinsic blaOXA-51 .
3. Results Table 1 shows the MIC distribution, MIC range, MIC50 and MIC90 values (MICs required to inhibit 50% and 90% of the isolates, respectively) and susceptibility rates. All isolates were resistant to imipenem and meropenem and the majority of isolates were also resistant to SAM (77.4%), cefepime (91.0%), the aminoglycosides amikacin (77.4%) and tobramycin (67.2%), SXT (80.8%) and levofloxacin (85.4%), and they also exhibited high sulbactam and rifampicin MICs. The resistance rate to colistin was 13.6%. The MIC50/90 values for TP-6076 were 0.06/0.25 mg/L. No isolates had a TP-6076 MIC of >0.5 mg/L. In comparison, doxycycline, eravacycline, minocycline and tigecycline MIC50/90 values were 32/≥64, 0.5/1, 4/8 and 1/2 mg/L, respectively. There was no correlation found between type of blaOXA gene and the MIC for TP-6076 (Table 2). The MIC50/90 values for TP-6076 were 0.06/0.25 mg/L for isolates with OXA-23-like (n = 256) and were only slightly lower at 0.06/0.125 mg/L both for isolates with OXA-40-like (n = 23) and isolates with OXA-58-like (n = 33) carbapenemases, and MICs ranged from 0.03–0.125 mg/L in isolates overexpressing intrinsic OXA-51-like carbapenemase (n = 7). Of note, there were remarkable differences regarding resistance rates to other antimicrobials depending on the blaOXA type, with isolates harbouring OXA-23-like enzymes showing higher resistance rates to amikacin and SAM and lower resistance rates to colistin, doxycycline, levofloxacin and SXT than isolates with other oxacillinases. However, these differences may in part be coincidental and should not be overemphasised because the strain collection is clearly dominated by IC2 OXA-23-like isolates while the number of isolates representing other resistance mechanisms and strain types is rather low. Since there were only three isolates harbouring NDM, a separate analysis of this subgroup is not justified, but MICs for TP-6076 in these isolates ranged from <0.008–0.03 mg/L. Similarly, no impact was observed of clonal strain type on TP-6076 MICs (Table 3). The MIC50/90 values for TP-6076 were 0.06/0.25 mg/L for IC1 isolates (n = 28), for IC2 isolates (n = 233) and for isolates not clustering with any of the previously described ICs (n = 28). Again, there were considerable differences regarding resistance rates to other antimicrobials depending on clonal
Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010
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Table 2 MIC50 and MIC90 values and MIC range (in mg/L) and susceptibility rates of 312 carbapenem-resistant Acinetobacter baumannii isolates harbouring different blaOXA types. Antimicrobial blaOXA-23-like (n = 256) agent MIC50 MIC90 MIC range a
TP-6076 Amikacin SAMb Cefepime Colistin Doxycycline Eravacyclinea Imipenem Levofloxacin Meropenem Minocycline Rifampicina Sulbactama Tigecyclinea Tobramycin SXTc
0.06 ≥512 64 128 1 0.5 0.25 64 16 128 0.25 4 8 0.5 64 32
0.25 ≥512 128 ≥512 2 ≥64 1 128 64 256 8 ≥512 32 2 ≥256 ≥64
≤0.008–0.5 0.5 to ≥512 8–256 16 to ≥512 0.5–8 0.06 to ≥64 0.03–1 8–128 0.125 to ≥128 16–256 ≤0.06–8 2 to ≥512 2–128 0.125–2 0.125 to ≥256 0.25 to ≥64
blaOXA-40-like (n = 23)
blaOXA-58-like (n = 33)
%S
%I
%R
MIC50
MIC90
MIC range
%S
%I
%R
MIC50
MIC90
MIC range
%S
%I
%R
– 14.9 1.6 4.4 95.7 73.9 – 0.0 8.7 0.0 87.0 – – – 34.8 26.1
– 3.1 12.1 21.7 – 0.0 – 0.0 21.7 0.0 0.0 – – – 0.0 –
– 82.0 86.3 73.9 4.3 26.1 – 100.0 69.6 100.0 13.0 – – – 65.2 73.9
0.06 256 16 256 1 32 0.5 32 16 64 4 4 32 1 ≥256 32
0.125 ≥512 128 ≥512 4 ≥64 1 64 32 128 16 32 64 2 ≥256 ≥64
≤0.008–0.25 0.5 to ≥512 4–256 4 to ≥512 0.5 to ≥512 0.125 to ≥64 0.06–8 8–128 1 to ≥128 16–256 ≤0.06–32 1 to ≥512 4–128 0.125–8 0.125 to ≥256 0.125 to ≥64
– 13.0 21.7 0.0 86.7 20.7 – 0.0 2.3 0.0 58.6 – – – 29.3 19.1
– 13.0 30.4 2.3 – 1.6 – 0.0 9.4 0.0 28.5 – – – 1.6 –
– 74.0 47.9 97.7 13.3 77.7 – 100.0 88.3 100.0 12.9 – – – 69.1 80.9
0.06 16 16 32 1 1 0.5 32 8 8 1 4 8 1 16 ≥64
0.125 256 128 128 4 ≥64 0.5 32 16 16 8 32 64 2 128 ≥64
0.015–0.25 1 to ≥512 4–128 16–256 0.25 to ≥512 0.25 to ≥64 0.125–2 16–64 0.25–32 8–32 0.125–8 2–64 4–64 0.25–4 0.5 to ≥256 1 to ≥64
– 51.5 21.2 0.0 75.8 72.7 – 0.0 3.0 0.0 84.8 – – – 15.2 3.0
– 0.0 45.5 39.4 – 0.0 – 0.0 6.1 0.0 15.2 – – – 21.2 –
– 48.5 33.3 60.6 24.2 27.3 – 100.0 90.9 100.0 0.0 – – – 63.6 97.0
MIC50/90 , minimum inhibitory concentrations required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant; SAM, ampicillin/sulbactam; SXT, trimethoprim/sulfamethoxazole. a No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. b For ampicillin/sulbactam, only the ampicillin concentration is given. c For trimethoprim/sulfamethoxazole, only the trimethoprim concentration is given. Table 3 MIC50 and MIC90 values and MIC range (in mg/L) and susceptibility rates of 289 carbapenem-resistant Acinetobacter baumannii isolates representing international clonal lineages IC1 and IC2 and unclustered isolates. Antimicrobial IC1 (n = 28) agent MIC50 MIC90 MIC range TP-6076a Amikacin SAMb Cefepime Colistin Doxycycline Eravacyclinea Imipenem Levofloxacin Meropenem Minocycline Rifampicina Sulbactama Tigecyclinea Tobramycin SXTc
0.06 128 32 64 1 1 0.5 16 8 32 0.5 2 16 1 0.5 8
0.25 256 128 ≥512 2 4 0.5 64 32 64 1 ≥512 64 1 32 ≥64
≤0.008–0.25 1 to ≥512 4–128 4 to ≥512 0.5–32 0.125 to ≥64 0.06–2 8–64 2–64 8–256 0.125–16 2 to ≥512 2–128 0.125–4 0.125 to ≥256 0.25 to ≥64
IC2 (n = 233)
Unclustered (n = 28)
%S
%I
%R
MIC50 MIC90 MIC range
%S
%I
%R
MIC50 MIC90 MIC range
– 7.1 10.7 7.1 85.7 92.9 – 0.0 7.1 0.0 92.9 – – – 67.9 28.6
– 7.1 32.1 10.7 – 0.0 – 0.0 21.4 0.0 0.0 – – – 3.6 –
– 85.8 57.2 82.2 14.3 7.1 – 100.0 71.5 100.0 7.1 – – – 28.5 71.4
0.06 ≥512 32 128 1 ≥64 0.5 32 16 64 4 4 32 1 ≥256 32
– 15.9 3.0 0.0 85.0 17.2 – 0.0 1.3 0.0 51.9 – – – 28.3 19.3
– 1.7 13.3 6.0 – 0.0 – 0.0 7.3 0.0 35.2 – – – 4.3 –
– 82.4 83.7 94.0 15.0 82.8 – 100.0 91.4 100.0 12.9 – – – 67.4 80.7
0.06 128 16 256 1 2 0.25 32 16 64 1 4 8 0.5 32 16
0.25 ≥512 128 256 8 ≥64 1 64 32 128 16 8 64 2 ≥256 ≥64
0.015–0.5 0.5 to ≥512 8–256 16 to ≥512 0.25 to ≥512 0.125 to ≥64 0.06–8 8–128 1 to ≥128 8–256 ≤0.06–32 1 to ≥512 4–128 0.125–8 0.125 to ≥256 ≤0.06 to ≥64
0.25 ≥512 128 ≥512 8 32 1 128 64 256 4 ≥512 64 2 ≥256 ≥64
≤0.008–0.5 0.5 to ≥512 4 to ≥512 4 to ≥512 0.5–16 0.06–32 0.03–8 8–256 0.125 to ≥128 16–256 ≤0.06–4 2 to ≥512 2 to ≥256 0.125–4 0.125 to ≥256 0.125 to ≥64
%S
%I
%R
– 21.4 25.0 3.6 85.7 82.2 – 0.0 21.4 0.0 100.0 – – – 25.0 25.0
– 14.3 28.6 14.3 – 7.1 – 0.0 14.3 0.0 0.0 – – – 0.0 –
– 78.6 46.4 82.1 14.3 10.7 – 100.0 64.3 100.0 0.0 – – – 75.0 75.0
MIC50/90 , minimum inhibitory concentrations required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant; SAM, ampicillin/sulbactam; SXT, trimethoprim/sulfamethoxazole. a No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. b For ampicillin/sulbactam, only the ampicillin concentration is given. c For trimethoprim/sulfamethoxazole, only the trimethoprim concentration is given.
lineage, with isolates representing IC2 showing higher resistance rates to SAM, doxycycline, levofloxacin and minocycline than isolates representing other clonal lineages. However, these differences should be interpreted with caution. In terms of MIC90 , TP-6076 showed ≥2- to 256-fold higher activity than the tetracycline comparators doxycycline, eravacycline, minocycline and tigecycline for all subgroups of isolates tested. Table 4 shows the MIC distribution, MIC50 and MIC90 values, and susceptibility rates of TP-6076, doxycycline, eravacycline, minocycline and tigecycline for a subset of 89 A. baumannii isolates with elevated tigecycline MICs (≥2 mg/L). In this subset, TP-6076 was 8-fold more active than eravacycline, the second most active tetracycline derivative, and was 16-fold more active than tigecycline with MIC50/90 values of 0.125/0.25 mg/L vs. 1/2 mg/L for eravacycline and 2/4 mg/L for tigecycline. Among the 44 A. baumannii isolates resistant to colistin, TP-6076 MICs ranged from ≤0.008– 0.25 mg/L, and MIC50/90 values were 0.125 mg/L and 0.25 mg/L, respectively.
4. Discussion The World Health Organization (WHO) has listed A. baumannii among the critical-priority bacteria that urgently require discovery, research and development of new antimicrobials [12]. Outbreaks caused by MDR A. baumannii have been increasingly reported around the globe, with isolates representing IC2 accounting for the majority of isolates recovered worldwide [13,14]. In particular, widespread resistance to carbapenems is a matter of great concern that often leaves the clinician with few remaining treatment options [15]. Currently, colistin is frequently the only drug showing measurable activity against CRAB, but its known toxicity and low serum and tissue concentrations limit its therapeutic use. In addition, resistance to colistin is increasingly being reported, in particular from countries where this compound is frequently used to combat infections caused by carbapenem-resistant A. baumannii, Enterobacteriaceae and P. aeruginosa [5]. Over the last decade, only a few new drugs with activity against MDR
Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010
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H. Seifert, D. Stefanik and M. Olesky et al. / International Journal of Antimicrobial Agents xxx (xxxx) xxx Table 4 MIC distribution, MIC50 and MIC90 values, and susceptibility rates of TP-6076, doxycycline, eravacycline, minocycline, and tigecycline of 89 carbapenemresistant Acinetobacter baumannii isolates with elevated tigecycline MICs (≥2 mg/L). Antimicrobial agent b
TP-6076 Doxycycline Eravacyclineb Minocycline Tigecyclineb
No. of isolates at MIC (mg/L) ofa : 0.06
0.125
0.25
0.5
12
41
34
2 20 8
MIC (mg/L)
1
2
4
8
7 57 11
13 11 2 68
0 0 18 20
2 1 36 1
16
13
32
64
7
60c
1
Susceptibility
MIC50
MIC90
Range
%S
%I
%R
0.125 ≥64 1 8 2
0.25 ≥64 2 16 4
0.06–0.5 1 to ≥64 0.5–8 0.5–16 2–8
– 22.5 – 43.8 –
– 2.2 – 40.4 –
– 75.3 – 15.7 –
MIC, minimum inhibitory concentration; MIC50/90 , MICs required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant. a Susceptible breakpoint values are indicated in boldface. b No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. c ≥64 mg/L.
Gram-negative pathogens have been introduced into clinical practice, and those developed, such as ceftolozane/tazobactam, ceftazidime/avibactam, plazomicin and meropenem/vaborbactam, have only poor activity against CRAB isolates. Eravacycline, the first fully-synthetic fluorocycline antibiotic developed, is one of the few new drugs with promising activity against Acinetobacter spp. that has made it to the market [16,17]. Eravacycline is currently indicated for the treatment of complicated intra-abdominal infections only, with cures rates ranging between 93–100% reported in clinical studies, however A. baumannii is only rarely involved in intra-abdominal infections [18]. Tigecycline, an earlier tetracycline derivative antibiotic that possesses good in vitro activity against A. baumannii, is associated with a number of clinical side effects such as nausea, vomiting, diarrhoea, abdominal pain and headache, and both breakthrough bacteraemia and resistance mediated by efflux have compromised it clinical usefulness for the treatment of patients with A. baumannii infections [4,19]. Therefore, there is an urgent need for new drugs that are unaffected by the current β -lactamases and efflux pumps to target MDR A. baumannii [12]. In a previous study of 121 CRAB isolates from 13 Greek hospitals, all but 1 of which were located in Athens, MIC50/90 values for TP-6076 were 0.03/0.06 mg/L and only 7 isolates (5.8%) had TP-6076 MICs of ≥0.125 mg/L [7]. In the current study, the corresponding MIC50/90 values were higher at 0.06/0.25 mg/L and 121 isolates (37.5%) with TP-6076 MICs of ≥0.125 mg/L were observed. In the former study, minocycline MICs were also considerably lower than in the current study, with 88.4% vs. 64.7% of isolates showing MICs ≤ 4 mg/L. Of note, in the Greek study, colistin resistance was considerably higher than in the current study (43.0% vs. 13.6%). These differences may reflect variations in testing methodology but also differences in the epidemiological background. Whilst in the Greek study no information regarding the epidemiological background was provided, it may well be that the majority of isolates, which were mainly collected from hospitals in Athens, were actually clonally related and might represent a limited number of A. baumannii strain types. The observed lower TP6076 MICs could be explained if the isolates primarily harboured acquired OXA-24/40-like and OXA-58-like oxacillinases in which slightly lower MICs compared with isolates possessing OXA-23-like carbapenemases were observed in the current study. Unfortunately, the authors did not investigate the underlying carbapenem resistance mechanisms of the isolates. In the current study, TP-6076 MIC50 and MIC90 values did not differ substantially between isolates representing different international clonal lineages or with different carbapenem resistance mechanisms. Murine thigh and lung infection models challenged with A. baumannii demonstrated potent in vivo efficacy for TP-6076 [20]. Furthermore, multiple doses of TP-6076 ranging from 6–40 mg every 24 h (with or without a loading dose) were generally well tolerated in a phase 1 clinical
study [11]. Currently, TP-6076 is being investigated in a phase 1, open-label, randomised, bronchopulmonary pharmacokinetic and safety study of healthy subjects at an intravenous dose of 30 mg TP-6076 every 24 h for 4 consecutive days to assess the potential utility of this agent in A. baumannii pneumonia (https://clinicaltrials.gov/ct2/show/NCT03691584). In conclusion, TP-6076, currently in phase 1 clinical testing, is a promising new agent with excellent activity against CRAB that may offer a useful addition to the limited armamentarium of drugs targeting this problem pathogen. Funding: This work was supported in part by Tetraphase Pharmaceuticals, Inc. (Watertown, MA, USA). Competing interests: tec, MSD, Roche, Shionogi and Tetraphase, and has received payments for lectures from Gilead and MSD; MO is an employee of Tetraphase Pharmaceuticals; PGH has received research support from the German Research Foundation (DFG) and the German Centre for Infection Research (DZIF). DS declares no competing interests. Ethical approval: Not required.
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[16] Livermore DM, Mushtaq S, Warner M, Woodford N. In vitro activity of eravacycline against carbapenem-resistant Enterobacteriaceae and Acinetobacter baumannii. Antimicrob Agents Chemother 2016;60:3840–4. [17] Seifert H, Stefanik D, Sutcliffe JA, Higgins PG. In-vitro activity of the novel fluorocycline eravacycline against carbapenem non-susceptible Acinetobacter baumannii. Int J Antimicrob Agents 2018;51:62–4. [18] Solomkin JS, Gardovskis J, Lawrence K, Montravers P, Sway A, Evans D, et al. IGNITE4: results of a phase 3, randomized, multicenter, prospective trial of eravacycline vs meropenem in the treatment of complicated intraabdominal infections. Clin Infect Dis 2019;69:921–9. doi:10.1093/cid/ciy1029. [19] Gerson S, Nowak J, Zander E, Ertel J, Wen Y, Krut O, et al. Diversity of mutations in regulatory genes of resistance–nodulation–cell division efflux pumps in association with tigecycline resistance in Acinetobacter baumannii. J Antimicrob Chemother 2018;73:1501–8. [20] Olesky M, Newman J, Zhou J, Fyfe C, Weiss W, Pulse M. In vivo efficacy of TP-6076 in murine thigh and lung infection models challenged with Acinetobacter baumannii. In: Abstracts of the 29th European Congress of Clinical Microbiology and Infections Diseases (ECCMID); 12–16 April 2019, Amsterdam, the Netherlands. Basel, Switzerland. ESCMID; 2019. [abstract P1994].
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Short Communication
In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii Harald Seifert a,b,∗, Danuta Stefanik a, Melanie Olesky c, Paul G. Higgins a,b a
Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Cologne, Germany German Center for Infection Research (DZIF), partner site Bonn-Cologne, Germany c Tetraphase Pharmaceuticals, Watertown, Massachusetts, USA b
a r t i c l e
i n f o
Article history: Received 19 August 2019 Accepted 20 October 2019 Available online xxx Editor: Prof. A Tsakris Keywords: International clone Oxacillinase Tetracycline Tigecycline Colistin Multidrug resistance
a b s t r a c t The activity of the novel, fully synthetic fluorocycline antibiotic TP-6076 against carbapenem-resistant Acinetobacter baumannii (CRAB) isolates with defined carbapenem resistance mechanisms was compared against reference antimicrobials with known activity against Acinetobacter spp. The susceptibility of 323 non-duplicate CRAB isolates to TP-6076, amikacin, ampicillin/sulbactam (SAM), cefepime, colistin, doxycycline, eravacycline, imipenem, levofloxacin, meropenem, minocycline, rifampicin, sulbactam, tigecycline, tobramycin and trimethoprim/sulfamethoxazole (SXT) was determined by the broth microdilution method. TP-6076 showed greater activity than comparator antimicrobials of the tetracycline class, SAM, levofloxacin, amikacin, tobramycin, SXT and colistin. MIC50 and MIC90 values for TP-6076 were 0.06 mg/L and 0.25 mg/L, respectively. In comparison, doxycycline, eravacycline, minocycline and tigecycline MIC50/90 values were 32/≥64, 0.5/1, 4/8 and 1/2 mg/L, respectively. Compared with other compounds, TP-6076 was the most active antimicrobial against CRAB, including isolates that were resistant to other antiAcinetobacter reference drugs including SAM, colistin, the aminoglycosides amikacin and tobramycin, and levofloxacin. TP-6076 is a promising new agent that may be a useful addition to the limited armamentarium of drugs targeting this problematic pathogen. © 2019 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.
1. Introduction Acinetobacter baumannii is a nosocomial pathogen known for its multidrug resistance and propensity for epidemic spread [1]. In the past decade, carbapenem resistance in A. baumannii has become an increasing concern. Resistance to carbapenems in A. baumannii is mainly mediated through the action of carbapenem-hydrolysing class D β -lactamases (CHDLs) and, less frequently, metallo-β -lactamases (MBLs) [2,3]. Whilst carbapenems are not significantly affected, drug efflux, especially through the resistance–nodulation–cell division (RND) type efflux pumps, plays a major role in resistance to aminoglycosides, fluoroquinolones and tetracyclines, and these efflux pumps have been shown to be overexpressed during antimicrobial therapy [4]. Frequently, colistin is the only remaining therapeutic option, but resistance has developed even to this drug [5]. TP-6076 is a novel, fully synthetic antibiotic of the tetracycline class that inhibits bacterial protein synthesis through bind-
∗ Corresponding author. Present address: Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Goldenfelsstr. 19–21, 50935 Cologne, Germany. Tel.: +49 221 478 32009; fax: +49 221 478 32035. E-mail address: [email protected] (H. Seifert).
ing to the 30S ribosomal subunit [6]. TP-6076 differs from currently approved tetracyclines in the unique C4 diethylamino, C7 trifluoromethyl and C8 unsubstituted pyrrolidinoyl substituents. TP-6076 has demonstrated potent antimicrobial activity against a wide range of Gram-positive, Gram-negative and anaerobic bacteria, including multidrug-resistant (MDR) Enterobacteriaceae and A. baumannii as well as strains with acquired tetracycline efflux determinants [7]. Early phase 1 single ascending and multiple ascending dose studies are completed, and TP-6076 continues to be evaluated in clinical studies [8]. In this study, the activity of TP-6076 was compared with that of reference antimicrobials with known activity against Acinetobacter spp., including aminoglycosides, β -lactams, colistin, fluoroquinolones, tetracyclines and trimethoprim/sulfamethoxazole (SXT), against a collection of well-characterised carbapenemresistant A. baumannii (CRAB) isolates harbouring acquired oxacillinases, MBLs or with an upregulated intrinsic OXA-51like carbapenemase. 2. Materials and methods Antimicrobial susceptibility testing was performed by the broth microdilution method in freshly prepared cation-adjusted
https://doi.org/10.1016/j.ijantimicag.2019.10.010 0924-8579/© 2019 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.
Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010
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Table 1 MIC distribution, MIC50 and MIC90 values, and antimicrobial susceptibility rates of 323 carbapenem-resistant Acinetobacter baumannii isolates. Antimicrobial agent b
TP-6076 Amikacin SAMc Cefepime Colistin Doxycycline Eravacyclineb Imipenem Levofloxacin Meropenem Minocycline Rifampicinb Sulbactamb Tigecyclineb Tobramycin SXTg
No. of isolates at MIC (mg/L) ofa :
MIC (mg/L)
≤0.015
0.03
0.06
0.125
0.25
0.5
1
2
4
8
16
32
64
128
≥256
21
43
138
83
36
2 5
13
12
70 13 161
160 35 60
48 26 11 0 6 0 22 94 3 68 5 12
12 4 2 12 5
4 16 1 11 4 1 7 97 22 82 14 51 1 12 17
15 53 26 2 13
12 96 47 1 66
35 108 75 4 137d
41 40 87 2
174 6 85 12
76 135 40 31 2 87
184 19 97 1 8 123
48 20 116
7 5e 36
1 12
3 41
1 6
28 2
21 16
28 86
6 137d
9
153
1
3 16
11f
1f
10 25
1 11 48
1
2
10
12
7 3 3
27 27 6
3 37
47 38 11
45 2 153 16 29
35 72 171 10 20 5 5
Susceptibility
MIC50
MIC90
Range
%S
%I
%R
0.06 256 32 128 1 32 0.5 32 16 64 4 4 32 1 128 32
0.25 ≥512 128 ≥512 4 ≥64 1 64 32 128 8 32 64 2 ≥256 ≥64
≤0.008–0.5 0.5 to ≥512 4 to ≥512 4 to ≥512 0.25 to ≥512 0.06 to ≥64 0.03–8 8–256 0.125 to ≥128 8–256 ≤0.06–32 1 to ≥512 2 to ≥256 0.125–8 0.125 to ≥256 ≤0.06 to ≥64
– 18.9 6.2 0.9 86.4 31.9 – 0.0 3.7 0.0 64.7 – – – 29.1 19.2
– 3.7 16.4 8.0 – 1.2 – 0.0 10.8 0.0 25.4 – – – 3.7 –
– 77.4 77.4 91.0 13.6 66.9 – 100.0 85.4 100.0 9.9 – – – 67.2 80.8
MIC, minimum inhibitory concentration; MIC50/90 , MICs required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant; SAM, ampicillin/sulbactam; SXT, trimethoprim/sulfamethoxazole. a Susceptible breakpoint values are indicated in boldface. b No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. c For ampicillin/sulbactam, only the ampicillin concentration is given. d ≥64 mg/L. e ≥128 mg/L. f ≤0.06 mg/L. g For trimethoprim/sulfamethoxazole, only the trimethoprim concentration is given.
Müller–Hinton broth following Clinical and Laboratory Standards Institute (CLSI) recommendations [9]. Microtitre trays containing freeze-dried antibacterial agents were provided by Merlin Diagnostica (Bornheim, Germany). A total of 323 non-duplicate CRAB isolates were tested against TP-6076, amikacin, ampicillin/sulbactam (SAM), cefepime, colistin, doxycycline, eravacycline, imipenem, levofloxacin, meropenem, minocycline, rifampicin, sulbactam, tigecycline, tobramycin and SXT. Resistance to carbapenems had been previously determined by Etest (bioMérieux, Nürtingen, Germany). The concentration ranges tested in two-fold dilutions were as follows: TP-6076, 0.008–16 mg/L; amikacin, 0.125–256 mg/L; ampicillin/sulbactam, 0.25/0.125–256/128 mg/L; cefepime, 0.125–256 mg/L; colistin, 0.03–256 mg/L; doxycycline, 0.03–32 mg/L; eravacycline, 0.008– 16 mg/L; imipenem, 0.125–256 mg/L; levofloxacin, 0.03–64 mg/L; meropenem, 0.125–256 mg/L; minocycline, 0.06–128 mg/L; rifampicin, 0.125–256 mg/L; sulbactam, 0.06–128 mg/L; tigecycline, 0.03–64 mg/L; tobramycin, 0.06–128 mg/L; and trimethoprim/sulfamethoxazole, 0.06/1.19–32/608 mg/L. Minimum inhibitory concentrations (MICs) were interpreted following CLSI guidelines, and susceptibility rates were determined using CLSI breakpoints where applicable [10]. Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 were used as quality control strains. Isolates were collected from various body sites in patients from multiple European and Asian countries between 2005 and 2016 and included outbreak-related as well as sporadic isolates. R The isolates had previously been characterised using DiversiLab (bioMérieux) and multilocus sequence typing (MLST) and represented isolates belonging to the eight previously described major international clonal (IC) lineages 1 (n = 28), 2 (n = 233), 3 (n = 1), 4 (n = 9), 5 (n = 1), 6 (n = 2), 7 (n = 16) and 8 (n = 5), whilst 28 isolates did not cluster with any of the international clonal lineages [3]. The carbapenem resistance mechanisms in the isolates were determined as described previously [11] and comprised 256 isolates with blaOXA-23-like , 23 isolates with blaOXA-40-like , 33 isolates with blaOXA-58-like , 1 isolate with blaOXA-23-like and blaOXA-58-like , 3 isolates with blaNDM-1 and 7 isolates with overexpression of intrinsic blaOXA-51 .
3. Results Table 1 shows the MIC distribution, MIC range, MIC50 and MIC90 values (MICs required to inhibit 50% and 90% of the isolates, respectively) and susceptibility rates. All isolates were resistant to imipenem and meropenem and the majority of isolates were also resistant to SAM (77.4%), cefepime (91.0%), the aminoglycosides amikacin (77.4%) and tobramycin (67.2%), SXT (80.8%) and levofloxacin (85.4%), and they also exhibited high sulbactam and rifampicin MICs. The resistance rate to colistin was 13.6%. The MIC50/90 values for TP-6076 were 0.06/0.25 mg/L. No isolates had a TP-6076 MIC of >0.5 mg/L. In comparison, doxycycline, eravacycline, minocycline and tigecycline MIC50/90 values were 32/≥64, 0.5/1, 4/8 and 1/2 mg/L, respectively. There was no correlation found between type of blaOXA gene and the MIC for TP-6076 (Table 2). The MIC50/90 values for TP-6076 were 0.06/0.25 mg/L for isolates with OXA-23-like (n = 256) and were only slightly lower at 0.06/0.125 mg/L both for isolates with OXA-40-like (n = 23) and isolates with OXA-58-like (n = 33) carbapenemases, and MICs ranged from 0.03–0.125 mg/L in isolates overexpressing intrinsic OXA-51-like carbapenemase (n = 7). Of note, there were remarkable differences regarding resistance rates to other antimicrobials depending on the blaOXA type, with isolates harbouring OXA-23-like enzymes showing higher resistance rates to amikacin and SAM and lower resistance rates to colistin, doxycycline, levofloxacin and SXT than isolates with other oxacillinases. However, these differences may in part be coincidental and should not be overemphasised because the strain collection is clearly dominated by IC2 OXA-23-like isolates while the number of isolates representing other resistance mechanisms and strain types is rather low. Since there were only three isolates harbouring NDM, a separate analysis of this subgroup is not justified, but MICs for TP-6076 in these isolates ranged from <0.008–0.03 mg/L. Similarly, no impact was observed of clonal strain type on TP-6076 MICs (Table 3). The MIC50/90 values for TP-6076 were 0.06/0.25 mg/L for IC1 isolates (n = 28), for IC2 isolates (n = 233) and for isolates not clustering with any of the previously described ICs (n = 28). Again, there were considerable differences regarding resistance rates to other antimicrobials depending on clonal
Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010
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Table 2 MIC50 and MIC90 values and MIC range (in mg/L) and susceptibility rates of 312 carbapenem-resistant Acinetobacter baumannii isolates harbouring different blaOXA types. Antimicrobial blaOXA-23-like (n = 256) agent MIC50 MIC90 MIC range a
TP-6076 Amikacin SAMb Cefepime Colistin Doxycycline Eravacyclinea Imipenem Levofloxacin Meropenem Minocycline Rifampicina Sulbactama Tigecyclinea Tobramycin SXTc
0.06 ≥512 64 128 1 0.5 0.25 64 16 128 0.25 4 8 0.5 64 32
0.25 ≥512 128 ≥512 2 ≥64 1 128 64 256 8 ≥512 32 2 ≥256 ≥64
≤0.008–0.5 0.5 to ≥512 8–256 16 to ≥512 0.5–8 0.06 to ≥64 0.03–1 8–128 0.125 to ≥128 16–256 ≤0.06–8 2 to ≥512 2–128 0.125–2 0.125 to ≥256 0.25 to ≥64
blaOXA-40-like (n = 23)
blaOXA-58-like (n = 33)
%S
%I
%R
MIC50
MIC90
MIC range
%S
%I
%R
MIC50
MIC90
MIC range
%S
%I
%R
– 14.9 1.6 4.4 95.7 73.9 – 0.0 8.7 0.0 87.0 – – – 34.8 26.1
– 3.1 12.1 21.7 – 0.0 – 0.0 21.7 0.0 0.0 – – – 0.0 –
– 82.0 86.3 73.9 4.3 26.1 – 100.0 69.6 100.0 13.0 – – – 65.2 73.9
0.06 256 16 256 1 32 0.5 32 16 64 4 4 32 1 ≥256 32
0.125 ≥512 128 ≥512 4 ≥64 1 64 32 128 16 32 64 2 ≥256 ≥64
≤0.008–0.25 0.5 to ≥512 4–256 4 to ≥512 0.5 to ≥512 0.125 to ≥64 0.06–8 8–128 1 to ≥128 16–256 ≤0.06–32 1 to ≥512 4–128 0.125–8 0.125 to ≥256 0.125 to ≥64
– 13.0 21.7 0.0 86.7 20.7 – 0.0 2.3 0.0 58.6 – – – 29.3 19.1
– 13.0 30.4 2.3 – 1.6 – 0.0 9.4 0.0 28.5 – – – 1.6 –
– 74.0 47.9 97.7 13.3 77.7 – 100.0 88.3 100.0 12.9 – – – 69.1 80.9
0.06 16 16 32 1 1 0.5 32 8 8 1 4 8 1 16 ≥64
0.125 256 128 128 4 ≥64 0.5 32 16 16 8 32 64 2 128 ≥64
0.015–0.25 1 to ≥512 4–128 16–256 0.25 to ≥512 0.25 to ≥64 0.125–2 16–64 0.25–32 8–32 0.125–8 2–64 4–64 0.25–4 0.5 to ≥256 1 to ≥64
– 51.5 21.2 0.0 75.8 72.7 – 0.0 3.0 0.0 84.8 – – – 15.2 3.0
– 0.0 45.5 39.4 – 0.0 – 0.0 6.1 0.0 15.2 – – – 21.2 –
– 48.5 33.3 60.6 24.2 27.3 – 100.0 90.9 100.0 0.0 – – – 63.6 97.0
MIC50/90 , minimum inhibitory concentrations required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant; SAM, ampicillin/sulbactam; SXT, trimethoprim/sulfamethoxazole. a No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. b For ampicillin/sulbactam, only the ampicillin concentration is given. c For trimethoprim/sulfamethoxazole, only the trimethoprim concentration is given. Table 3 MIC50 and MIC90 values and MIC range (in mg/L) and susceptibility rates of 289 carbapenem-resistant Acinetobacter baumannii isolates representing international clonal lineages IC1 and IC2 and unclustered isolates. Antimicrobial IC1 (n = 28) agent MIC50 MIC90 MIC range TP-6076a Amikacin SAMb Cefepime Colistin Doxycycline Eravacyclinea Imipenem Levofloxacin Meropenem Minocycline Rifampicina Sulbactama Tigecyclinea Tobramycin SXTc
0.06 128 32 64 1 1 0.5 16 8 32 0.5 2 16 1 0.5 8
0.25 256 128 ≥512 2 4 0.5 64 32 64 1 ≥512 64 1 32 ≥64
≤0.008–0.25 1 to ≥512 4–128 4 to ≥512 0.5–32 0.125 to ≥64 0.06–2 8–64 2–64 8–256 0.125–16 2 to ≥512 2–128 0.125–4 0.125 to ≥256 0.25 to ≥64
IC2 (n = 233)
Unclustered (n = 28)
%S
%I
%R
MIC50 MIC90 MIC range
%S
%I
%R
MIC50 MIC90 MIC range
– 7.1 10.7 7.1 85.7 92.9 – 0.0 7.1 0.0 92.9 – – – 67.9 28.6
– 7.1 32.1 10.7 – 0.0 – 0.0 21.4 0.0 0.0 – – – 3.6 –
– 85.8 57.2 82.2 14.3 7.1 – 100.0 71.5 100.0 7.1 – – – 28.5 71.4
0.06 ≥512 32 128 1 ≥64 0.5 32 16 64 4 4 32 1 ≥256 32
– 15.9 3.0 0.0 85.0 17.2 – 0.0 1.3 0.0 51.9 – – – 28.3 19.3
– 1.7 13.3 6.0 – 0.0 – 0.0 7.3 0.0 35.2 – – – 4.3 –
– 82.4 83.7 94.0 15.0 82.8 – 100.0 91.4 100.0 12.9 – – – 67.4 80.7
0.06 128 16 256 1 2 0.25 32 16 64 1 4 8 0.5 32 16
0.25 ≥512 128 256 8 ≥64 1 64 32 128 16 8 64 2 ≥256 ≥64
0.015–0.5 0.5 to ≥512 8–256 16 to ≥512 0.25 to ≥512 0.125 to ≥64 0.06–8 8–128 1 to ≥128 8–256 ≤0.06–32 1 to ≥512 4–128 0.125–8 0.125 to ≥256 ≤0.06 to ≥64
0.25 ≥512 128 ≥512 8 32 1 128 64 256 4 ≥512 64 2 ≥256 ≥64
≤0.008–0.5 0.5 to ≥512 4 to ≥512 4 to ≥512 0.5–16 0.06–32 0.03–8 8–256 0.125 to ≥128 16–256 ≤0.06–4 2 to ≥512 2 to ≥256 0.125–4 0.125 to ≥256 0.125 to ≥64
%S
%I
%R
– 21.4 25.0 3.6 85.7 82.2 – 0.0 21.4 0.0 100.0 – – – 25.0 25.0
– 14.3 28.6 14.3 – 7.1 – 0.0 14.3 0.0 0.0 – – – 0.0 –
– 78.6 46.4 82.1 14.3 10.7 – 100.0 64.3 100.0 0.0 – – – 75.0 75.0
MIC50/90 , minimum inhibitory concentrations required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant; SAM, ampicillin/sulbactam; SXT, trimethoprim/sulfamethoxazole. a No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. b For ampicillin/sulbactam, only the ampicillin concentration is given. c For trimethoprim/sulfamethoxazole, only the trimethoprim concentration is given.
lineage, with isolates representing IC2 showing higher resistance rates to SAM, doxycycline, levofloxacin and minocycline than isolates representing other clonal lineages. However, these differences should be interpreted with caution. In terms of MIC90 , TP-6076 showed ≥2- to 256-fold higher activity than the tetracycline comparators doxycycline, eravacycline, minocycline and tigecycline for all subgroups of isolates tested. Table 4 shows the MIC distribution, MIC50 and MIC90 values, and susceptibility rates of TP-6076, doxycycline, eravacycline, minocycline and tigecycline for a subset of 89 A. baumannii isolates with elevated tigecycline MICs (≥2 mg/L). In this subset, TP-6076 was 8-fold more active than eravacycline, the second most active tetracycline derivative, and was 16-fold more active than tigecycline with MIC50/90 values of 0.125/0.25 mg/L vs. 1/2 mg/L for eravacycline and 2/4 mg/L for tigecycline. Among the 44 A. baumannii isolates resistant to colistin, TP-6076 MICs ranged from ≤0.008– 0.25 mg/L, and MIC50/90 values were 0.125 mg/L and 0.25 mg/L, respectively.
4. Discussion The World Health Organization (WHO) has listed A. baumannii among the critical-priority bacteria that urgently require discovery, research and development of new antimicrobials [12]. Outbreaks caused by MDR A. baumannii have been increasingly reported around the globe, with isolates representing IC2 accounting for the majority of isolates recovered worldwide [13,14]. In particular, widespread resistance to carbapenems is a matter of great concern that often leaves the clinician with few remaining treatment options [15]. Currently, colistin is frequently the only drug showing measurable activity against CRAB, but its known toxicity and low serum and tissue concentrations limit its therapeutic use. In addition, resistance to colistin is increasingly being reported, in particular from countries where this compound is frequently used to combat infections caused by carbapenem-resistant A. baumannii, Enterobacteriaceae and P. aeruginosa [5]. Over the last decade, only a few new drugs with activity against MDR
Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010
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H. Seifert, D. Stefanik and M. Olesky et al. / International Journal of Antimicrobial Agents xxx (xxxx) xxx Table 4 MIC distribution, MIC50 and MIC90 values, and susceptibility rates of TP-6076, doxycycline, eravacycline, minocycline, and tigecycline of 89 carbapenemresistant Acinetobacter baumannii isolates with elevated tigecycline MICs (≥2 mg/L). Antimicrobial agent b
TP-6076 Doxycycline Eravacyclineb Minocycline Tigecyclineb
No. of isolates at MIC (mg/L) ofa : 0.06
0.125
0.25
0.5
12
41
34
2 20 8
MIC (mg/L)
1
2
4
8
7 57 11
13 11 2 68
0 0 18 20
2 1 36 1
16
13
32
64
7
60c
1
Susceptibility
MIC50
MIC90
Range
%S
%I
%R
0.125 ≥64 1 8 2
0.25 ≥64 2 16 4
0.06–0.5 1 to ≥64 0.5–8 0.5–16 2–8
– 22.5 – 43.8 –
– 2.2 – 40.4 –
– 75.3 – 15.7 –
MIC, minimum inhibitory concentration; MIC50/90 , MICs required to inhibit 50% and 90% of the isolates, respectively; S, susceptible; I, intermediate; R, resistant. a Susceptible breakpoint values are indicated in boldface. b No Clinical and Laboratory Standards Institute (CLSI) breakpoint available. c ≥64 mg/L.
Gram-negative pathogens have been introduced into clinical practice, and those developed, such as ceftolozane/tazobactam, ceftazidime/avibactam, plazomicin and meropenem/vaborbactam, have only poor activity against CRAB isolates. Eravacycline, the first fully-synthetic fluorocycline antibiotic developed, is one of the few new drugs with promising activity against Acinetobacter spp. that has made it to the market [16,17]. Eravacycline is currently indicated for the treatment of complicated intra-abdominal infections only, with cures rates ranging between 93–100% reported in clinical studies, however A. baumannii is only rarely involved in intra-abdominal infections [18]. Tigecycline, an earlier tetracycline derivative antibiotic that possesses good in vitro activity against A. baumannii, is associated with a number of clinical side effects such as nausea, vomiting, diarrhoea, abdominal pain and headache, and both breakthrough bacteraemia and resistance mediated by efflux have compromised it clinical usefulness for the treatment of patients with A. baumannii infections [4,19]. Therefore, there is an urgent need for new drugs that are unaffected by the current β -lactamases and efflux pumps to target MDR A. baumannii [12]. In a previous study of 121 CRAB isolates from 13 Greek hospitals, all but 1 of which were located in Athens, MIC50/90 values for TP-6076 were 0.03/0.06 mg/L and only 7 isolates (5.8%) had TP-6076 MICs of ≥0.125 mg/L [7]. In the current study, the corresponding MIC50/90 values were higher at 0.06/0.25 mg/L and 121 isolates (37.5%) with TP-6076 MICs of ≥0.125 mg/L were observed. In the former study, minocycline MICs were also considerably lower than in the current study, with 88.4% vs. 64.7% of isolates showing MICs ≤ 4 mg/L. Of note, in the Greek study, colistin resistance was considerably higher than in the current study (43.0% vs. 13.6%). These differences may reflect variations in testing methodology but also differences in the epidemiological background. Whilst in the Greek study no information regarding the epidemiological background was provided, it may well be that the majority of isolates, which were mainly collected from hospitals in Athens, were actually clonally related and might represent a limited number of A. baumannii strain types. The observed lower TP6076 MICs could be explained if the isolates primarily harboured acquired OXA-24/40-like and OXA-58-like oxacillinases in which slightly lower MICs compared with isolates possessing OXA-23-like carbapenemases were observed in the current study. Unfortunately, the authors did not investigate the underlying carbapenem resistance mechanisms of the isolates. In the current study, TP-6076 MIC50 and MIC90 values did not differ substantially between isolates representing different international clonal lineages or with different carbapenem resistance mechanisms. Murine thigh and lung infection models challenged with A. baumannii demonstrated potent in vivo efficacy for TP-6076 [20]. Furthermore, multiple doses of TP-6076 ranging from 6–40 mg every 24 h (with or without a loading dose) were generally well tolerated in a phase 1 clinical
study [11]. Currently, TP-6076 is being investigated in a phase 1, open-label, randomised, bronchopulmonary pharmacokinetic and safety study of healthy subjects at an intravenous dose of 30 mg TP-6076 every 24 h for 4 consecutive days to assess the potential utility of this agent in A. baumannii pneumonia (https://clinicaltrials.gov/ct2/show/NCT03691584). In conclusion, TP-6076, currently in phase 1 clinical testing, is a promising new agent with excellent activity against CRAB that may offer a useful addition to the limited armamentarium of drugs targeting this problem pathogen. Funding: This work was supported in part by Tetraphase Pharmaceuticals, Inc. (Watertown, MA, USA). Competing interests: tec, MSD, Roche, Shionogi and Tetraphase, and has received payments for lectures from Gilead and MSD; MO is an employee of Tetraphase Pharmaceuticals; PGH has received research support from the German Research Foundation (DFG) and the German Centre for Infection Research (DZIF). DS declares no competing interests. Ethical approval: Not required.
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Please cite this article as: H. Seifert, D. Stefanik and M. Olesky et al., In vitro activity of the novel fluorocycline TP-6076 against carbapenem-resistant Acinetobacter baumannii, International Journal of Antimicrobial Agents, https://doi.org/10.1016/j.ijantimicag.2019. 10.010