| Paclitaxel (PTX) is a natural anti-cancer active ingredient which extracted from the stem and bark of yew Taxus species. Clinical studies have shown the significant role of paclitaxel in the treatment of a variety of solid tumors, including lung cancer, breast cancer, advanced ovarian cancer, brain and neck tumors and acute leukemia. Paclitaxel inhibits decomposition of microtubules through the stabilization of tubulin. The cell division is blocked in G2and M phase that promote tumor cell death, thereby inhibiting tumor growth. The solubility of paclitaxel in water is less than0.4μg/mL. Currently in the clinical practice, Cremophor EL and ethanol (1:1, v/v) are used as solvent to increase the solubility of paclitaxel and improve its stability. Cremophor EL releases histamine in vivo degradation that ccould further trigger fatal allergic reactions. Patients have to be pretreatment with antihistamines and glucocorticoids to prevent the occurrence of allergic reactions. In addition, Cremophor EL may change the in vivo process of drug. It presents nonlinear dynamical characteristic and affects the therapeutic effect of drugs. Therefore, it limits the clinical application of paclitaxel injection to a certain extent.At present, many domestic and foreign researchers are committed to the study of new formulations of paclitaxel, including paclitaxel emulsions, liposomes, micelles, nanoparticles and cyclodextrin inclusion complex. Among them, polymeric micelles has low critical micelle concentration and good thermodynamic stability. Taking use of different nature of the polymer hydrophobic block, drugs could wrapped through a variety of methods such as chemical, physical and electrostatic interaction. So it has gotten more attention in the field of application of drug carrier.In order to increase the solubility of the paclitaxel, paclitaxel copolymer micelles (PM-PTX) were prepared utilizing the methoxy polyethylene glycol-poly lactic acid (mPEG-PLA). It could improve the treatment effect of brain cancer and reduce adverse reactions owing to avoiding the use of undesirable solvents. Therefore, PM-PTX had potential clinical application with high effect and low toxicity.In the Chapter I, mPEG-PLA amphiphilic block copolymer was synthesized from D, L-lactide and methoxy polyethylene glycol by using ring-opening polymerization synthesis. The copolymers were identified through infrared spectroscopy,1HNMR analysis and gel permeation chromatography analysis. The melting temperature was41.4℃by differential scanning calorimetry analysis. The critical micelle concentration (CMC) of copolymer micelles is0.043g/L determined by fluorescent probe method. Particle size, encapsulation efficiency, drug loading were as the indexes on the basis of the primary single factor test. Prescription and preparation process of PM-of PTX was optimized by applying the central composite design-response surface method. The optimal prescription:mPEG-PLA was300mg, PTX was81.6mg and hydration volume was13.0mL. Under optimal prescription prepared the PM-PTX which particle size was21.32±0.75nm, Zeta potential was1.179±0.242mV. Entrapment efficiency (EE) and drug loading capacity (DLC) for paclitaxel were99.56±0.46%and21.28±0.10%respectively.0.5%Tween80aqueous solution as release medium, PM-PTX cumulative released77%in10h and up to95%in24h.In Chapter Ⅱ, glioma nude mice model was established through injection of U87cells into the striatum. Then the distribution of DiR micelles in normal and tumor-bearing nude mice were investigated by using of in vivo imaging technology. The results showed a strong fluorescence in the right side of the brain partial in tumor-bearing mice which consistent with the kinds of tumor site right striatum. It showed that the DiR-loaded micelle could accumulate in the brain tumor through the passive targeting effect. Pharmacodynamics was evaluated through survival time of glioma implanted nude mice. The results indicated that the median survival time of mice treated with PM-PTX (29d) was longer than Taxol group (26d) and significantly longer than saline group (23d). The pair-wise comparison of P values were less than0.05which indicated the results between a significant difference. The above results further confirmed that PM-PTX improved glioma uptake and therapeutic effects of PTX.In Chapter Ⅲ, the in vivo acute toxicity of PM-PTX was investigated. Pre-testing to determine the absolutely lethal dose (LD100) of Taxol to ICR mice was45mg/kg, the maximum tolerated dose (LDo) was15mg/kg; LD100of PM-PTX was600mg/kg, and LDo was200mg/kg. Through statistical analysis of Bliss method, the median lethal dose (LD50) of Taxol to ICR mice was27.2mg/kg while PM-PTX was367.9mg/kg (12.5times higher than Taxol). It indicated that the acute toxicity of PM-PTX was significantly lower than Taxol.In summary, PM-PTX we prepared could not only increase the solubility of PTX, but also accumulate drug in tumor tissues through passive targeting effect and release PTX slowly. The result was to improve the therapeutic of PTX on the brain tumor, at the same time reduce side effects significantly. |
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