PH-sensitive Biodegradable Polymersomes For Intracellular Delivery Of Water-Soluble Anticancer Drugs

Hydrophilic therapeutics including proteins need to be delivered right inside cancer cells to induce potent anticancer activity. However, their direct use encountered several barriers, including, rapid elimination following i.v. injection, poor bioavailability, and/or low cell permeability, resulting in side-effects or low drug efficacy. Nanocarriers like polymersomes are very promising to solve these problems. The low loading efficiency of hydrophilic drugs and slow intracellular release, nevertheless, limit their use in cancer therapy. In this thesis, we have designed and synthesized endosomal p H-sensitive biodegradable polymersomes for highly efficient loading and intracellular release of hydrophilic drugs for cancer therapy.In chapter 2, endosomal p H-sensitive chimaeric polymersomes loaded with doxorubicin hydrochloride(DOX?HCl) were designed and showed potent anticancer activity in RAW264.7, MCF-7 cells as well as in drug resistant MCF-7/DOXR cells. We have synthesized carboxylate functionalized triblock copolymer poly(ethylene glycol)-b-poly(2,4,6-trimethoxybenzylidene-pentaerythritol carbonate)-b- poly(succinic acid modified carbonate)(PEG-PTMBPEC-PSAC). Polymersomes prepared there from(CPs) using solvent exchange method were of 145.2-158.3 nm with narrow size distribution(PDI 0.10-0.18). PEG-PTMBPEC-PSAC polymersomes loaded with DOX?HCl(DOX?HCl-CP) displayed small sizes, high drug loading efficiency(96.8%), and p H-sensitivity in terms of drug release(compared to control polymersomes). CLSM observations revealed that DOX?HCl-CP efficiently delivered drug into MCF-7 and MCF-7/DOXR cells following 6 h incubation. MTT assay results demonstrated that these polymersomal drugs have half-maximal inhibitory concentration(IC50) of 0.51 and 0.87 μg/m L similar to free DOX?HCl against RAW 264.7 and MCF-7 cells but 5 times lower than free DOX?HCl against MCF-7/DOXR cells. Co-loading of verapamil with DOX?HCl into these polymersomal drugs significantly enhanced the cytotoxicity(IC50 of 1.96 μg/m L, 29 times lower than that of DOX?HCl), reversing multidrug resistance of MCF-7/DOXR cells by inhibiting function of p-gp on the cell membrane.Subsequently in chapter 3, we explored PEG-PTMBPEC-PSAC polymersomes equipped with PSMA targeting ligand(Acupa) in protein delivery to treat prostate cancer cells. Acupa-PEG-PTMBPEC-PSAC and PEG-PTMBPEC-PSAC at predetermined ratio co-assembled into chimaeric polymersomes(Acupa-CPs) with tunable Acupa surface density and size of ca. 160 nm(PDI 0.11-0.20). The system displayed high protein loading efficiency(67-96%) and acidic p H-triggered protein release. CLSM and MTT studies demonstrated that cytochrome C loaded Acupa10-CPs(CC-Acupa10-CPs) could specifically target and efficiently release proteins into LNCa P cells(PSMA positive) leading to pronounced antitumor activity, in great contrast to CC-CPs or free CC. Most remarkably, granzyme B(Gr B) loaded Acupa10-CPs effectively caused distinct apoptosis of LNCa P cells with a markedly low IC50 of 1.6 n M, accompanied by characteristic cell apoptosis. Further studies indicated that Gr B-Acupa10-CPs targeted mitochondria and enhanced the permeability of mitochondria membrane causing cytosolic release of mitochondrial effector proteins, which activates mitochondria-mediated cell degradation. In addition, CPs and Acupa-CPs had plasma half circulation times of 3 h and 3.3 h in mice, respectively. Therefore, p H-responsive biodegradable chimaeric polymersomes may serve as a new multifunctional platform for efficiently delivering hydrophilic anticancer drugs to cancer cells.