Improvement of dissolution characteristics of 4-t-butyl-2′-car☐ymethoxy-4′-(3-methyl-2-butenyloxy)chalcone by β-cyclodextrin complexation

iOROPllAM

ELSEVIER

European Journal of PharmaceuticalSciences 3 (1995) 323-328

JOURNAL

OF

PHARMACEUTICAL SCIENCES

Improvement of dissolution characteristics of 4-t-butyl-2'carboxymethoxy-4'-(3-methyl-2-butenyloxy)chalcone by fi-cyclodextrin complexation Shusei Ito a, Yumiko Toriumi a, Miki D e m a c h i a, Takeshi Adachi a, Yuji Ito a, H i d e h u m i Hayashi =, Fumitoshi H i r a y a m a b, K a n e t o U e k a m a u'* ~Research Center, Taisho Pharmaceutical Co., Ltd.. 1-403 Yoshino-cho, Ohmiya-shi, Saitama 330, Japan bFaculty of Pharmaceutical Sciences, Kumamoto University, 5-10e-honmachi, Kumamoto 862, Japan

Received 15 November 1994; accepted27 April 1995 Abstract

The inclusion complexation of 4-t-butyl-2'-carboxymethoxy-4'-(3-methyl-2-butenyloxy)chalcone (SU-740), a newly developed antiulcer agent, with fl-cyclodextrin (fl-CyD) in water and in solid state was investigated for the purpose of improving the low aqueous solubility and oral bioavailability. SU-740 formed 1:1 and 1:2 (guest:host) inclusion complexes in water and in the solid state and the 1:1 stability constant was much higher than the 1:2 stability constant. The dissolution rate of SU-740 was significantly improved by the complexation with /3-CyD, suggesting the enhanced bioavailability. Keywords: 4-t-Butyt-2'-carboxymethoxy-4'-(3-methyl-2-butenytoxy)chal con; /3-Cyclodextrin; Inclusion complexation; Stoichiometry; Dissolution

1. I n t r o d u c t i o n

Cyclodextrins (CyDs) are successfully used to improve various physico- and bio-pharmaceutical properties of drugs. For example, low aqueous solubility and bioavailability and instability of drugs are improved by the inclusion complexation with CyDs ( D u c h ~ n e , 1987; U e k a m a and Otagiri, 1987; Szejtli, 1988). In the practical application of CyDs as drug carrier, the fund a m e n t a l parameters, such as the stoichiometry and stability constant, for the inclusion complexation should be in detail investigated. 4-t-Butyl2'-carboxymethoxy-4'-(3-methyl-2-butenyloxy)chalcone (SU-740, Fig. 1) is a newly d e v e l o p e d chalcone derivative with a p o t e n t antiulcer activi-

ty. H o w e v e r , the aqueous solubility of SU-740 is low (about 2.6 x 10 -6 M in w a t e r at 25°C), thus limiting the dosage form design of the drug. In this study, therefore, the inclusion c o m p l e x a t i o n of SU-740 with fl-CyD in w a t e r and in the solid state was investigated, anticipating an enhancement of solubility and oral bioavailability of the poorly water-soluble drug. F u r t h e r m o r e , our attention was paid on the s t o i c h i o m e t r y - d e p e n dent spectral change of SU-740-/3-CyD complex.

=o

OCH2COOH Corresponding author. Tel. (+81-96) 371-4160; Fax (+81-96) 371 4160. *

0928-0987/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved S S D I 0928-0987(95)00021-6

Fig. 1. Chemical structure of SU-740.

324

S. lto et al. / European Journal of Pharmaceutical Sciences 3 (1995) 323-328

2. Experimental procedures Materials. SU-740 (molecular weight 422.52) was synthesized by Taisho Pharmaceutical Co., Ltd. (Tokyo, Japan)./3-CyD was purchased from Nihon Shokuhin Kako Co., Ltd. (Tokyo, Japan). All other materials and solvents were of analytical reagent grade. Solubility studies. Solubility measurements were carried out according to the method of Higuchi and Connors (1965). SU-740 (10 mg) was added to phosphate buffer (5 ml, pH 6.5, /z =0.2) containing various concentrations of/3-CyD and was shaken for 5 days at 25°C. Concentration of SU-740 in solution was measured by high performance liquid chromatography (HPLC) under the following conditions: a Hitachi chromatograph composed of L-6000 and L-4000 modules; a column, TSK-gel ODS 80T M (4.0 mm by 150 mm, Tohso, Tokyo, Japan); a mobile phase, acetonitrile:methanol:0.02 M KH2PO 4 ( p H = 3) = 7:4:4 (v/v); flow rate, 1.0 ml/min; temperature, 50°C; detection, 330 nm. The complex, which precipitated as micro-crystalline powder, was filtered and dried under a reduced pressure at room temperature for 2 days. This complex was employed for powder X-ray diffraction analysis, differential scanning calorimetry and dissolution studies. The apparent stability constant (K') was calculated from the initial linear portion of the phase solubility diagram according to the following equation based on the assumption that a 1:1 complex is initially formed (Higuchi and Connors, 1965): K' = slope/{intercept • (1 - slope)} (1) Powder X-ray diffractometry and differential scanning calorimetry (DSC). Powder X-ray diffraction patterns were measured by an X-ray diffractometer (Rigaku Denki RAD-3C, Tokyo, Japan) under the following conditions: target CuKa (1.542 .&) monochromated by graphite, voltage 40 kV, current 30 mA. DSC (Perkin-Elmer DSC7, USA) was carried out at a scanning rate of 10°C/min and the sample weight was 2-3 mg. Continuous variation method. The 2.0 x 10 -5 M SU-740 solution (pH 6.5 phosphate buffer, /z =

0.2) was mixed with the 2.0 × 10 -5 M /3-CyD solution at various ratios and shaken for a short time (about 1 min). The ultraviolet (UV) and circular dichroism (CD) spectra were measured by a Hitachi U-3500 UV spectrometer (Tokyo, Japan) and a Jasco J-720 polarimeter (Tokyo, Japan), respectively, at 25°C. The first-derivative of UV spectra was obtained according to the method of Savitzky and Golay (1964), in which the cubic polynomial convolution of 7-points with a wavelength interval of 0.2 nm was employed. The difference values of the first-derivative intensities from zero-point (AD) were measured at 328 nm according to the zero-crossing method (Kitamura and Imayoshi, 1992), and the CD intensities were measured at 305 nm.

Mole ratio method. Various amounts of/3-CyD were added to SU-740 solutions (2.0 x 10 -5 M, pH 6.5 phosphate buffer, /x = 0.2) and the sample solutions were shaken for a short time. The UV and CD spectra were measured under the same conditions of the continuous variation method. The 1:1 and 1:2 (guest:host) stability c o n s t a n t s (KI: l and Kl:2) of SU-740 complexes with /3-CyD were calculated by analyzing the biphasic CD and UV changes according to Eqs. 2 and 3, respectively (Higuchi and Connors, 1965): ADob5 =

[StI(AD,:~K~:,[L ] + ADt:2K,:,Kt:2[L] 2} 1+

+ K,:,&::[z,] 2

(a) [Stl{CD,:IKx:,[L l + CD,:zK,:IK,:a[LI 2} CDoo s =

1 + gl:l[L ] + K , : I K I : 2 [ L ] 2

(3) where ADo~s and CDob s are the observed difference intensities of the first-derivative spectra from zero-point and the observed CD intensities, respectively, in the presence of /3-CyD; ADt:I and ADt: 2 are the difference intensities of the first-derivative spectra between 0 point of the 1:1 and 1:2 complexes at a concentration of 1 M, respectively, and CD~: 1 and C D I : 2 a r e the CD intensities of the 1:1 and 1:2 complexes at a concentration of 1 M, respectively; [St] is a total concentration of SU-740 and [L] is a concentration of uncomplexed /3-CyD. The iteration

S. Ito et al. / European Journal of Pharmaceutical Sciences 3 (1995) 323-328

method (Higuchi and Connors, 1965; Uekama et al., 1988) was applied to Eqs. 2 and 3 to estimate the [L]. As a first approximation, [L] was set to [L,], a total concentration of SU-790. The MULTI program (Yamaoka et al., 1981) was used for a nonlinear least-squares calculation.

Dissolution studies. The dissolution test was performed according to the paddle method in Japanese Pharmacopoeia XII. Sample powder (<100 mesh) of SU-740 and the complex (15 mg as SU-740) was weighed and put into the dissolution medium (900 ml, pH 6.5 phosphate buffer) maintained at 37°C, and the dissolution medium was stirred at 100 rpm. The concentration of SU-740 was measured spectrophotometrically at 330 nm.

3. Results and discussion

3.1. Phase solubility diagram Fig. 2 shows the phase solubility diagram of SU-740-/3-CyD system in pH 6.5 phosphate buffer at 25°C. The system showed a typical Bs-type phase solubility diagram (Higuchi and Connors, 1965), where the solubility of SU-740 was significantly increased by the addition of /3-CyD. The stoichiometry of the complex was determined to be 1:2 (guest:host) by analyzing the length of the plateau region of the phase solubility diagram and the chemical analysis of the

2,5O

~

2.0.

h.-

~

1.5,

~

1.0, 0.5 0.0

o.o

o'.s

¢.o

2'0

Concn. of J]-CyD ( XlO 2 M)

Fig. 2. Phase solubility diagram of SU-740-/3-CyD system in pH 6.5 phosphate buffer at 25°C.

325

solid complex precipitated beyond the plateau region (/3-CyD 1.3 x 10 -2 M ) . The solubility of SU-740 at higher fl-CyD concentration can be taken as the intrinsic solubility of the 1:2 complex. This solubility should be equal to the difference of concentration of SU-740 between the y-intercept and the plateau region, when only one species of the complex is formed. However, it is apparent from Fig. 2 that the concentration of SU-740 at higher fl-CyD concentration was in disagreement with that between the y-intercept and the plateau region. These results suggest that the 1:1 complex is formed at lower /3-CyD concentration, whereas the 1:2 complex is predominantly formed at higher /3-CyD concentration. Therefore, the apparent 1:1 stability constant (K') was calculated from the initial linear portion of the phase solubility diagram using the y-intercept and the slope of the straight-line (Higuchi and Connors, 1965), and was 2.25 x 104 M -~. The powder X-ray diffraction pattern of the complex which precipitated as micro-crystalline powder was different from that of either SU-740 or/3-CyD and the endothermic peak at 138°C of SU-740 due to the melting was disappeared by the complexation with /3-CyD. These results suggest that the precipitates at higher 13-CyD concentration should be the 1:2 complex of SU740 with /3-CyD.

3.2. Stoichiometry and stability constant Fig. 3(A) shows the UV absorption spectra of SU-740 in the absence and presence of /3-CyD. The UV intensity at 328 nm of SU-740 increased at lower/3-CyD concentration, whereas tended to decrease at higher fl-CyD concentration, which was more definitive in the first-derivative spectra of Fig. 3(B). Fig. 4 shows the CD spectra of SU-740 in the presence of /3-CyD, where the optical activity of SU-740 was induced at about 234 nm (negative), 248 nm (positive), 305 nm (positive) and 340 nm (negative). Since SU-740 is optically inactive and/3-CyD has no CD band at wavelength longer than 220 nm under these experimental conditions, the observed optical activities were attributable to the induced Cotton effect of SU-740 by the binding to /3-CyD. The

326

S. lto et al. / European Journal of Pharmaceutical Sciences 3 (1995) 323-328

0.8,~

concentration 0.6. 0

0 ¢n

.t3

0.4,

0.2,

0.0 200

36o 4~o Wavelength(nm)

s6o

2

0.4,

fl-CyD

CD intensity at 305 nm increased at lower

(A)

._>

0.0,

whereas

tended

to

decrease

at

higher/3-CyD concentration, in a similar manner as the U V change. Fig. 5 shows the changes in intensity at 328 nm of the UV-first derivative and that in the CD intensity at 305 nm of SU-740, as a function of fl-CyD concentration. It is of interest to note that both intensities increased steeply at lower /3-CyD concentration, whereas decreased gradually with further increase in concentration of the host. These results suggest that SU-740 forms inclusion complexes with a different stoichiometry depending on concentration of the host. Fig. 6 shows the continuous variation plots (Job, 1928) of changes in the intensities of UV-first derivative at 328 nm and of CD at 305 nm. Both systems gave a peak at a 1:2 molar ratio, indicating a 1:2 (guest:host) stoichiometry. 7 (A) O

6 5

-0.4, t-

ta

> L.

4 3

3~o

-0.8 200

4;0

s~o

).

2

ffl e-

0

Wavelength(nm)

Fig. 3. Absorbance (A) and UV-first derivative spectra (B) of SU-740 (2.0 × 10 -5 M) in the absence and presence of /3-CyD in pH 6.5 phosphate buffer ( ~ = 0.2) at 25°C: 1, SU-740 alone; 2, with /3-CyD (2.0 × 10 -5 M); 3, with flCyD (1.0 × 10 -2 M).

--

0.0

C o n c n . 13-CyD ( X 10 2 M )

12 , 2

~

1.0, "10

"o

E a ¢D

a O

0.8,

~

0.4

0~ r.

m

°6t

0.2

•

i

i

!

250

30O

350

Wavelength

(nrn)

Fig. 4. CD spectra of SU-740 (2.0 x 10 -s M) in the presence of/3-CyD in pH 6.5 phosphate buffer (/~ = 0.2) at 25°C: 1, with/3-CyD (2.0 x 10 -5 M); 2, with fl-CyD (1.0 x 10 -a M); 3, with /3-CyD (1.5 x 10 -2 M).

oo

|

i

=

|

04

08

12

16

Conch.

~-CyD

( X 10 2 M )

Fig. 5. Mole ratio plots for SU-740-fl-CyD system using UV-first derivative spectra (A) and CD spectra (B) in pH 6.5 phosphate buffer (/.L = 0.2) at 25°C. Solid curves show the theoretical ones.

S. lto et al. / European Journal of Pharmaceutical Sciences .3 (1995) 3 2 3 - 3 2 8

e~

327

the second site of the guest, as observed for other inclusion complexes.

10-

© 15

X >

8

0~

"o

X

10 13

"5

tO

r..

E -

05 2'

0~

SU-740 #-CyD

3.3. Dissolution behavior

E

> "E

0 10

;30

5 5

10 0

Fig. 6. Continuous variation plots for SU-740-CI-CyD system using UV-first derivative spectra ( 0 ) and CD spectra (O) in pH 6.5 phosphate buffer (IX = 0.2) at 25°C.

Therefore, the 13-CyD concentration dependence of the U V and CD intensities (Fig. 5) was quantitatively analyzed according to the scheme of the consecutive 1:1 and 1:2 complex formation, i.e., the biphasic profiles were analyzed by the iteration method described in the Experimental Section. Table 1 shows the 1:1 and 1:2 stability constants obtained by the spectral methods, together with the apparent 1:1 stability constant obtained by the solubility method. The theoretical curves (solid line in Fig. 5) of the UV and CD intensities were in good agreement with the experimental values. The stability constants obtained from the U V and CD spectra coincided with each other within an experimental error, whereas that obtained from the solubility method was slightly larger, probably because of influence of the 1:2 complex formation. The first binding site of SU-740 binds /3-CyD much stronger than Table 1 Stability constants of SU-740-/3-CyD complexes in pH 6.5 phosphate buffer at 25°C Method

Kl:l

K1:2

Phase solubility diagram Mole ratio method (UV spectra) Mole ratio method (CD spectra)

2.3 × 1 0 4 M - ] 1.7 x 104 M - t 1.4 x 104 M - ~

-

470 M-1 390 M -

The phase solubility diagram of SU-740-/3-CyD system indicates that in the aqueous solution, the solid 1:2 complex of SU-740 with j3-CyD precipitated at the descending portion. These precipitates were collected and the dissolution test was performed. Fig. 7 shows the dissolution profiles of SU-740 and the complex in pH 6.5 phosphate buffer at 37°C. The dissolution rate of the complex was much faster than that of SU-740, which may be due to the increased solubility by the complexation. This result suggests potential of improvement of oral bioavailability of SU-740. In conclusion, a 1:2 (guest:host) solid complex of SU-740 with ¢J-CyD was prepared on the basis of the solubility diagram and spectroscopic studies. The dissolution rate of SU-740 were significantly improved by the complexation with /3-CyD. These data will provide a rational basis of design and formulation for a fast-dissolving form of SU-740.

100,

:~--~I:--'::I:--::]t:~:::Q:

,

~

:0:

..EZ

-.~

80,

3o 60-

O3

40-

20 •

..r.~

0'(

::O::~"'~ 0

10

20

30

40

50

60

Time (rain)

Fig. 7. Dissolution profiles of SU-740 and SU-740-/3-CyD complex in pH 6.5 phosphate buffer at 37°C: ©, SU-740; O, complex.

328

S. Ito et al. / European Journal o f Pharmaceutical Sciences 3 (1995) 323-328

References Duch~ne, D. (editor) Cyclodextrins and Their Industrial Uses. Edition de Sant6, Paris, 1987. Higuchi, T. and Connors, K.A. (1965) Phase-solubility techniques. Adv. Anal. Chem. Instr. 4, 117-212. Job, P. (1928) Formation and stability of inorganic complexes in solution. Ann. Chem. 9, 113-203. Kitamura, K. and Imayoshi, N. (1992) Second-derivative spectrophotometric determination of the binding constant between chlorpromazine and /3-cyclodextrin in aqueous solution. Anal. Sci. 8, 497-501. Savitzky, A and Golay, M.J.E. (1964) Smoothing and differentiation of data and simplified least squares procedures. Anal. Chem. 36, 1627-1639.

Szejtli, J. Cyclodextrin Technology. Kluwer, Dordrecht, The Netherlands, 1988. Uekama, K., Horiuchi, Y., Kikuchi, M. and Hirayama, F. (1988) Enhanced dissolution and oral bioavailability of a-tocopheryl esters by dimethyl-/3-cyclodextrin complexation. J. Incl. Phenom. 6, 167-174. Uekama, K. and Otagiri, M. (1987) Cyclodextrins in drug carrier systems. CRC Critical Reviews in Therapeutic Drug Carrier Systems 3, 1-40. ¥amaoka, K., Tanigawara, Y., Nakagawa, T. and Uno, T. (1981) A pharmacokinetic analysis program (MULTI) for microcomputer. J. Pharmacobio-Dyn. 4, 879-885.