Paclitaxel Block Copolymer Micelles

Paclitaxel (Taxol^?), a diterpenoid derived from the bark of the pacific yew tree Taxusbrevifalia, is an anticancer agent with a unique mechanism of action. Its clinical activity has beenwell established for several neoplastic diseases. However, owing to its poor aqueous solubility,paclitaxel is often administrated in a vehicle containing both Cremophor EL (polyethoxylatedcastor oil) and ethanol, which has been demonstrated to cause a number of side effects. In orderto improve water solubility of paclitaxel and avoid being adsorbed by protein and phagocytosingby cells of the reticuloendothelial system, in the dissertation, the following work have been done:Methoxy poly (ethylene glycol)-b-poly (L-lactic acid) diblock copolymer was synthesizedby a ring-opening polymerization of L-lactide using mPEG as a maroinitiator. It was convertedto carboxyl-terminated mPEG-PLA by reacting with succinic anhydride; the latter was reactedwith paclitaxel in the presence of dicyclohexylcarbodiimid? and dimethylaminopyridine.Structures of the polymers synthesized were confirmed by ¹H NMR, and their molecular weightswere determined by gel permeation chromatography. UV spectroscopy was used to determinethe linked paclitaxel, and the released paclitaxel was measured by HPLC.Self-emulsification/solvent evaporation method was used to prepare micells. ¹H NMR andelectron microscopy (SEM) indicate the micelles had a core-shell structure, in which paclitaxelwas enveloped in the core, and the PEG shell made the micelles loaded with paclitaxel lyotropicin water. The sizes of the self-assembly micelles of the amphiphilic block copolymers and theeffects were studied by dynamic light scattering (DLS). The micelle sizes were largelyinfluenced by the hydrophobic chain (PLA) content in the copolymer and the copolymerconcentration in the organic phase. The critical association concentrations (CAC) wereresearched by pyrene monomer fluorescence probe technology, and it decreased with LA/EOdiminish. The stability of the copolymer micelle dispersion was examined by measuring thecritical flocculation concentration, which gradually decreased with increasing the content of thehydrophobic chain in the copolymer. Redispersion experiment results indicated the properties ofthe drug-loaded micelles could be maintained by lyophilization. Any initial burst release was notobserved in the release pattern of all the samples. The drug releasing rate and the accumulatedreleasing amount decreased upon increasing the molecular weight of the hydrophobic chain inthe copolymer and reducing the pH of medium facilitated drug's release. To evaluate the degradation of micells, The changes of molecular weight, molecular weight distribution(polydispersity), loss weight, composition of the polymer were determined byGPC, ¹H NMRtechniques. The results show that in pH7．4 PBS solution at 37℃, in the beginning, paclitaxelhydrolyze from diblock copolymer conjugates rapidly and diffuse from the inner shell, and themore mPEG contend, the faster micells degradation.Hemolytic, local intracutaneous reactivity, toxicology and antitumor activities in vitro wereinvestigated. The results showed that it had no hemolytic, The antitumor activity of paclitaxelconjugate against the woman Hela cancer cells and MCF cancer cells were evaluated using MTTmethod, the similar IC₇₀ with Taxol^? reveal that it had the same antitumor activity with Taxol^?.The toxicology assessments on ECV cells suggested it has lower toxicology compared withTaxol^?·The studies on the stabilities of micells implied that it has good stabilities. During 10 days'storage at sealed condition, it has no significant change in loaded drugs; drug release behaviorand diameter of micells, but it sensitive to humidity, so it suggest micells should be storaged atsealed condition.