Spontaneously self-assembled micelles from poly(ethylene glycol)-b-poly(epsilon-caprolactone-co-trimethylene carbonate) for drug solubilization.

Di-block copolymers composed of polyethylene glycol (PEG) and a second block of (co)polyesters of epsilon-caprolactone (CL) and/or trimethylene carbonate (TMC) were synthesized and characterized. Tin octoate was used as catalyst and polymerization were completed over a period of 24 h with high conversion (> 95%). Self-assembling properties in water were evaluated. All di-block copolymers behave similarly except when PCL served as the second block. Stable crew-cut micelles of about 20 nm were obtained by direct dissolution of the liquid di-block copolymers in water at room temperature. When PCL was present as the second block, no solubilization occurred. Drug encapsulation of poorly water-soluble drugs belonging to biopharmaceutics classification system (BCS) class II (ketoprofen and furosemide) was evaluated. Experimental solubility for these two drugs shows a significant enhancement such that a maximum value of 23.4 mg/ml was obtained for ketoprofen in a 10% w/v micellar solution as compared to 0.14 mg in water. In the case of furosemide, the solubility increased from 0.04 mg/ml in water to about 3.2 mg/ml in a 10% w/v micellar solution. Enzymatic degradation of diblock copolymers was also studied in the presence of Pseudomonas lipase in a phosphate buffer solution (pH 7.4). Results indicated rapid degradation of copolymers containing relatively higher amounts of CL compared to TMC suggesting the potential in vivo degradation.

Prediction of drug solubility in amphiphilic di-block copolymer micelles: the role of polymer-drug compatibility.

The goal of the current study was to assess the value of predictive computational approaches for estimating drug solubility in hydrated micelles formed from di-block copolymers of polyethylene glycol (PEG) and random copolyesters of epsilon-caprolactone (CL) and trimethylene carbonate (TMC) using drug-polymer compatibility as assessed through the Flory-Huggins interaction parameter (chi). In order to accomplish this, the compatibility of several well-known model drugs (associated with the four biopharmaceutics classification system (BCS) classes) was assessed with both segments of the amphiphilic di-block copolymer PEG-b-P(CL-co-TMC). Compatibilities were estimated based on the Hansen modification of the Hildebrand approach using Molecular Modeling Pro software. Experimental solubilities for model drugs were determined using a shake-flask technique at various polymer concentrations. The solubilities of 8 compounds in 10% w/v micelle solutions were in relatively good agreement with the predicted drug-polymer compatibility. In addition, the approach allows for the selection of a suitable di-block copolymer for optimal solubilization of a specific drug. Furosemide was assessed as a model with results suggesting that it can be best entrapped in a di-block copolyester containing a relatively high CL content. The data suggests that prediction of drug solubilization of block copolymer-based micelles may be facilitated by assessing the compatibility of the drug for the component polymeric domains.

Monoglyceride-based self-assembling copolymers as carriers for poorly water-soluble drugs.

To develop self-assembling polymers forming polymeric micelles and increasing the solubility of poorly soluble drugs, amphiphilic polymers containing a hydrophilic PEG moiety and a hydrophobic moiety derived from monoglycerides and polyethers were designed. The biodegradable copolymers were obtained via a polycondensation reaction of polyethylene glycol (PEG), monooleylglyceride (MOG) and succinic anhydride (SA). Polymers with molecular weight below 10,000 g/mol containing a minimum of 40 mol% PEG and a maximum of 10 mol% MOG self-assembled spontaneously in aqueous media upon gentle mixing. They formed particles with a diameter of 10 nm although some aggregation was evident. The critical micellar concentration varied between 3x10(-4) and 4x10(-3) g/ml, depending on the polymer. The cloud point (> or = 66 degrees C) and flocculation point (> or = 0.89 M) increased with the PEG chain length. At a 1% concentration, the polymers increased the solubility of poorly water-soluble drug candidates up to 500-fold. Drug solubility increased as a function of the polymer concentration. HPMC capsules filled with these polymers disintegrated and released model drugs rapidly. Polymer with long PEG chains had a lower cytotoxicity (MTT test) on Caco-2 cells. All of these data suggest that the object polymers, in particular PEG1000/MOG/SA (45/5/50) might be potential candidates for improving the oral biopharmaceutical performance of poorly soluble drugs.