An alternative cyclodextrin based formulation for oral anticancer drug exemestane: In vitro and cell culture studies

Abstract

summary Exemestane (EXE) is an irreversible aromatase inactivator used for the treatment of postmenopausal breast cancer. EXE is orally active but its bioavailability is about 5% due to its low solubility in water. It is known that cyclodextrin (CD) complexation enhances oral bioavailability of poorly soluble drugs. Thus, it was aimed to design and develop cyclodextrin complexes containing EXE and prepare a novel tablet formulation to improve aqueous solubility, dissolution and in vitro permeability. Introduction Estrogen suppression is an important approach to the management of hormone-responsive cancer. Therefore, aromatase inhibition is a well-established therapeutic option in postmenopausal, hormone dependent breast cancer [1]. EXE is an orally active aromatase inactivator, which is absorbed 42% from the gastrointestinal tract and preclinical data indicated that the absolute bioavailability was about 5% due to its low solubility in water and the first pass effect through liver [2,3]. Cyclodextrins (CD) are enzymatic degradation products of starch with a hydrophilic outer surface and an apolar cavity. CDs have the ability to interact with poorly water-soluble drugs and drug candidates resulting in an increase in their apparent water solubility and dissolution rates. It is also reported that CDs show permeability enhancer effects and that they can be considered practically nontoxic upon oral administration [4]. In this study, EXE's inclusion complexes were prepared and characterized using different CD derivatives (methyl-β-cyclodextrin (M-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CD)) and different preparation techniques and consequently a new tablet formulation was developed using the inclusion complex with optimal dissolution and permeation properties. Experimental methods Phase solubility studies: 0, 5,10,15, 20, 25, 30%w/v solutions ofM-β-CD,HP-β-CD andHP-γCD, all in distilled water, were added to 25 mg EXE and magnetically stirred. 7 days after which 1 mL CD drug suspensions from each vials were filtered through 0.45 μm polycarbonate membrane filter fitted in a stainless still filter holder. The experiments were performed with three replications. The filtrates were quantitatively analysed by an HPLCmethod for EXEwhichwas validated previously [5]. The apparent stability constants (K1:1) of the complexes were calculated. Preparation of inclusion complexes: The inclusion complexes of EXE with either methyl-β-cyclodextrin (M-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CD) were prepared by both kneading and coprecipitation methods [6] and the molar ratio of EXE:CDs were 1:1. Physical mixtures were also prepared. Characterization of inclusion complexes: Differential scanning calorimetry (DSC), Fourier transformationinfrared spectroscopy (FTIR), Proton NMR spectrometry (H NMR), Scanning electron microscopy (SEM), and X-Ray diffractometry were used to characterize both the complexes and the physical mixtures. Preparation of tablet formulation: Since phase solubility studies, solid state characterization techniques and dissolution studies indicate that M-β-CD and kneading method show the optimumresults, a tablet formulationwas developed using EXE:M-β-CD kneaded (MBK) inclusion complex. Avicel pH 102, Sodium Starch Glycolate and Magnesium Stearate were used as tablet excipients. No solubility enhancer was added to the formulation. The tablets were prepared by direct compression method. Dissolution study of inclusion complexes and tablets: Dissolution studies for EXE, EXE complexes, EXE: M-β-CD tablets and Aromasin® tablets were carried out with six replications. The dissolution medium was 900 mL of 0.5% sodium lauryl sulphate solution (SLS) and 900 mL of distilled water at 37 °C. The difference factors (f1) and the similarity factors (f2) were calculated for tablet formulations to compare dissolution profiles. Transport/permeability studies with Caco-2 cells: Caco-2 cell culture studies were performed on EXE, EXE:CD inclusion complexes which were prepared by kneading method with both M-β-CD, HP-β-CD and HP-γ-CD. Apparent permeability coefficient (Papp:cm/s) was calculated. Statistical analysis of data was performed by Kruskal Wallis One Way Variance Analysis. Result and discussion Phase solubility studies showed that the solubility of EXE increased linearly as a function of the CD concentration, a feature of AL-type complexes. K1:1 was found to be 3722.25M-1 forM-β-CD, 3728.16M-1 for HP-β-CD and 3729.22 M-1 for HP-γ-CD. EXE's solubility with M-βCDwas found tobe 513 times better than EXE. Corresponding solubility diagrams of EXE with M-β-CD, HP-β-CD and HP-γ-CD are presented respectively in Fig. 1. Abstracts / Journal of Controlled Release 148 (2010) e74–e84 e83