Solid dispersion of quercetin in cellulose derivative matrices influences both solubility and stability

Abstract

Amorphous solid dispersions (ASD) of quercetin (Que) in cellulose derivative matrices, carboxymethylcellulose acetate butyrate (CMCAB), hydroxypropylmethylcellulose acetate succinate (HPMCAS), and cellulose acetate adipate propionate (CAAdP) were prepared with the goal of identifying an ASD that effectively increased Que aqueous solution concentration. Crystalline quercetin and Que/poly(vinylpyrrolidinone) (PVP) ASD were evaluated for comparison. Powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC) were used to examine the crystallinity of ASDs, physical mixtures (PM) and quercetin. ASDs were amorphous up to 50 wt% Que. Que stability against crystallization and solution concentrations from these ASDs were significantly higher than those observed for physical mixtures and crystalline Que. PVP stabilizes against both Que degradation and recrystallization; in contrast, these carboxylated cellulose derivatives inhibit recrystallization but release Que slowly. PVP ASDs afforded fast and complete drug release, while ASDs using these three cellulose derivatives provide slow, incomplete, pH-triggered drug release.

Introduction

Polyhydroxyaromatic flavonoids effectively protect body tissues against oxidative stress (Andersen and Markham, 2006, Rice-Evans and Packer, 2003). Quercetin (Que, Fig. 1) is an important dietary flavonoid, abundant in foods including onions and apples (Jan et al., 2010, Kelly, 2011). Recent work has shown that Que is much more than just a protective antioxidant; for example, it has been shown to enhance apoptosis of malignant cells, by itself (Chien et al., 2009) and in combination (Siegelin, Reuss, Habel, Rami, & von Deimling, 2009) with other molecules. Que has also been observed to exert anti-inflammatory, antibacterial, antiviral, and muscle-relaxation effects (Bischoff, 2008). Que can arrest cell cycles in both G1 and G2-M phases by inhibiting expression of p53 protein, affect xenobiotic metabolism, and also play a key role in signal transduction (Jan et al., 2010, Kuo, 2002, Lamson and Brignall, 2000). Recent reports indicate that Que may act both as antioxidant to improve normal cell survival and as pro-oxidant to induce apoptosis in cancerous cells (Gibellini et al., 2010, Lamson and Brignall, 2000, Murakami et al., 2008). The potential of Que as a cytotoxic anticancer agent has recently been augmented by the discovery, reviewed by Chen and co-workers, that Que may cause reversal of multidrug resistance (Chen, Zhou, & Ji, 2010). A great deal of effort has been devoted to the study of quercetin as a chemo-preventive and chemotherapeutic agent (Jan et al., 2010).

Study and exploitation of these beneficial properties for therapeutic applications have been impeded by the fact that Que has poor aqueous solubility and low bioavailability. Que water solubility at room temperature and pH 3 was only ca. 400 ng/mL (Zheng, Haworth, Zuo, Chow, & Chow, 2005). It has been reported that dietary blood concentrations are in the 10⁻⁹ to 10⁻⁷ M range (Biasutto, Marotta, Garbisa, Zoratti, & Paradisi, 2010), while therapeutic antioxidant concentrations are in the range of 10⁻⁶ to 10⁻⁵ M (Vargas & Burd, 2010). Thus, realization of the therapeutic promise of quercetin requires enhancement of its solubility and oral bioavailability. The importance of quercetin as a potential therapeutic platform is illustrated by the efforts made to chemically modify Que to enhance solubility and bioavailability while retaining activity (Biasutto, Marotta, De Marchi, Zoratti, & Paradisi, 2006) Others have taken the drug delivery approach to enhance solubility and bioavailability of Que itself. Formation of Que/cyclodextrin inclusion complexes is a promising approach for increasing Que bioavailability (Zheng & Chow, 2009). Ribeiro et al. studied the effective solubilization of quercetin and rutin by micellar formulation with ethylene oxide triblock copolymers, with solubilization exceeding that achieved with β-cyclodextrin (Ribeiro et al., 2009).

Amorphous solid dispersion (ASD) of quercetin is an interesting approach because of its effectiveness, simplicity, and benign nature. ASD is a very attractive way to improve drug solubility and bioavailability for oral delivery, which has been reviewed several times in the past decade (Leuner and Dressman, 2000, Qian et al., 2010, Singh et al., 2010, Timpe, 2010, Tiwari, 2009). Poor drug water solubility is often heavily influenced by high drug crystallinity, because the crystal lattice energy must be overcome for the drug to dissolve. Molecular dispersion of drug in a polymer provides amorphous drug, that when released may form a supersaturated solution. Selection or design of polymer structure is crucial to success (Ilevbare, Liu, Edgar, & Taylor, 2012), since the polymer must stabilize the metastable amorphous drug against crystallization in the solid dosage form, must dissolve in water to an extent adequate to stabilize the drug in supersaturated solution after release and prior to permeation through the enterocytes, and must release the drug at an adequate rate. Water-soluble polymers like PVP are most often employed in ASD studies, but there is increasing interest in polymers that swell in aqueous media like carboxylated polysaccharide derivatives. Polysaccharides generally have low toxicity, high glass transition temperatures (T_g) that promote formulation stability, and may be modified with ester and ether groups to enhance compatibility with drug and to introduce pH-responsiveness. Carboxyl-containing cellulose derivatives are particularly useful since the carboxyl provides specific interactions with drug functionality in addition to pH-triggered release; for example, hydroxypropylmethylcellulose acetate succinate (HPMCAS) (Friesen et al., 2008), cellulose acetate phthalate (CAPhth) (DiNunzio, Miller, Yang, McGinity, & Williams, 2008), and carboxymethylcellulose acetate butyrate (CMCAB) (Posey-Dowty et al., 2007, Shelton et al., 2009) have been used in ASDs to improve the water solubility and bioavailability of hydrophobic drugs. All three have promising properties, yet CAPhth has limited miscibility with drugs, CMCAB is prone to crosslinking, and HPMCAS is an excellent polymer for amorphous solid dispersion, and a component of multiple New Drug Applications before the Food and Drug Administration, yet is a very complex and potentially variable polysaccharide derivative.

There have been some reports of solubility enhancement of Que by solid dispersion. Polymer matrices used in these studies include poly(ethylene glycol) (PEG) (Li, Zhang, Deng, & Liang, 2004), PVP (Costa et al., 2011, Li et al., 2010, Zhu et al., 2007), and polysaccharide derivatives (Lauro et al., 2005, Lauro et al., 2002, Sansone et al., 2010). There have been only a few reports of Que solid dispersions using cellulose derivatives. Lauro et al. prepared quercetin and rutin gastroresistant microparticles by spray-drying using several polymers including cellulose acetate trimellitate (CAT) and CAPhth as matrix polymers (Lauro et al., 2005, Lauro et al., 2002). Recently Sansone et al. also reported that the microparticles of quercetin and CAPhth prepared by spray drying may enhance Que stability and dissolution rate (Sansone et al., 2010). Que dispersions in CMCAB and HPMCAS matrices have not been reported.

Herein we report studies of the effect on Que stability and solubility enhancement of preparing Que solid dispersions, comparing three cellulose derivatives (HPMCAS, CMCAB and CAAdP). The dispersions were characterized by FT-IR, DSC, XRPD and ¹H NMR. Solubility and stability enhancement were studied using UV–vis spectrometry. Results were compared with those of crystalline Que, physical polymer/Que mixtures, and Que/PVP solid dispersions.