Studies On The DTX-loaded Liposomes

Docetaxel is a semisynthetic compound from 10-deacetylbaccatin-III, which is extracted from the needles of the European yew tree, Taxus baccata. It belongs to the taxane class of anticancer agents and has similar mechanisms of action with its analog paclitaxel, i.e. interaction with microtubules. Widespread clinical experience from 1995 indicated that docetaxel has a profound impact in the treatment of a variaty of cancers such as ovarian cancer, breast cancer, non-small-cell lung cancer, and carcinoma of prostate, etc. Docetaxel, which is insoluble in water, is formulated with Tween 80 as solubilizer for clinical use. Its haemolyticus toxicities associated with the surfactant are mainly acute hypersensitivity reactions, which are managed by premedication with corticosteroids and antihistamines. Nonseclectivity of drug distribution following injection results in dose-limiting adverse reactions including neutropenia and fluid retention.To overcome the aboved problems related to Tween 80 and drug, many formulation strategies have been studied. Among drug carrier systems, liposomes are nontoxic for their composition and unique structure similar to cells. Meanwhile, anticancer-drug encapsulation by liposomes can improve the water solubility, modulate the distribution, and decrease drug resistance. In the present study, DTX was taken as the model drug to be wrapped up into liposomes. The main methods and results were as follows:Firstly, HPLC method was applied to determine the content of the DTX. Retrodialysis method were used to separate the free drug and liposomes and determine the entrapment efficiency of DTX-loaded liposomes by HPLC method.Then, DTX-loaded liposomes were prepared using thin-film dispersion method. Single factor screening method was used to evaluate the effects of the weight ratio of drug to lipids, weight ratio of soya lecithin to cholesterol, volume ratio of absolute alcohol to phosphate buffer and bath temperature on the entrapment efficiency of DTX-loaded liposomes. Based on the results, the effects of the weight ratio of drug to lipids, weight ratio of soya lecithin to cholesterol and volume ratio of absolute alcohol to phosphate buffer on the entrapment efficiency were studied by orthogonal test method. The results of orthogonal test indicated the optimized parameters, i.e. the weight ratio of drug to lipids, weight ratio of soya lecithin to cholesterol and volume ratio of absolute alcohol to phosphate buffer was 10:1,1:5,3:1, respectively. The size of DTX-loaded liposomes obtained was 405.7nm with the polydispersity index of 1.000, which indicated the liposomes needed high-pressure homogenization to reduce the particle size. The entrpment efficiency of DTX-loaded liposomes obtained was 92.56%.Finally,200nm DTX-loaded liposomes were obtained by high-pressure homogenization for 10 times under 800bar. The zeta potential was-15.10±2.11mV and the shape was spheroid. The entrapment efficiency and drug loading was 90.76±1.42% and 15.31±1.24%, respectively. To improve the stability of DTX-loaded liposomes, lyophilized powder was prepared using mannitol as protectant for lyophilization. The lyophilized liposomes had good redispersibility and homogeneity with the mean diameter of 230.5nm and zeta potentia of-17.10±3.21mV. The entrapment efficiency and drug loading was 88.45±1.63% and 14.81±1.53%, respectively. The in vitro release of DTX from liposomes was investigated using the dialysis bag diffusion technique. Duopafei(?) injection was taken as a reference and release media was phosphate buffered saline (pH7.4) containing 0.5% Tween 80. DTX-loaded liposomes presented sustained release property and the release curve was fitted with Weibull equation:lnln(1/(1-Q/100))= 0.81251nt-2.3025, r=0.9948. In case of Duopafei(?) injection, the release profile could be described by the first order kinetics equation:ln(100-Q)=-0.198t+4.462, r=0.9990.Conclusions:DTX-loaded liposomes were successfully prepared using the film dispersion-homogenization technique. The particles were uniform with higher entrapment efficiency and drug loading, which proved the formulation and the preparation method were feasible. Encapsulation of DTX into liposomes could resolve the problems related with its poor solubility and was beneficial to utilize EPR effect to penetrate through the leaky pathological vasculature into the tumor interstitium. Lyophilized liposomes were much stable which favours transport and long-term storage. The liposomes showed sustained release property in vitro release that could increase the retention time in blood after injection, therefore enhancing the therapeutic response.