The Study Of Biodegradable Polymer-Platinum Nanomicelles In Drug Resistant Ovarian Cancer

Platinum based antitumor drugs have been the milestone of the ’war against cancer’ since cisplatin, the first platinum drug, was approved by FDA to cure ovarian and testical cancer in1978. And it still be in widespread use today, especially for the patients of ovarian cancer, colorectal cancer, testical cancer and cancer of the head and neck. Actually, the current standard therapy of ovarian cancer is debulking surgery plus platinum based chemotherapy. However, severe dose limiting toxicities, inherent or acquired drug resistance and tumor relapse have severely limited the effectiveness of platinum drugs. To solve the problem, researchers have been focused on the development of new platinum compounds as well as technical strategies to improve the effictiveness of the current platinum therapy. Polymer-drug conjugates formed nanoparticles is one of the most promising approaches. Using macromolecular polymers as carriers to deliver drugs, it can significantly improve the efficacy of the drug and protecting drugs from premature drug release, which can finaly benefit patients. So In this study, we developed biodegradable polymer platforms, and attaching some platinum compounds to them to prepare nanomiclles, using ovarian cancer cells and mice models to evaluate the efficacy and toxicity in vitro and in vivo.The first part of this thesis described the systhesis of two biodegradable amphiphilic copolymers. The first polymer is (MPEG-b-P(LA-co-MCC)), poly(ethylene glycol)-block-poly(L-lactide-co-2-methyl-2-carboxyl-propylene carbonate). It was by ring-opening polymerization (ROP) of2-methyl-2-carboxyl-propylene carbonate (MBC) with MPEG as a macroinitiator. The second polymer is MPEG-b-PCL-b-PLL. To synthesize it, CL was ring-opening polymerized with MPEG5k as a macroinitiator in the presence of Sn(Oct)2, and Cbz-L-lysine-NCA was polymerized to form-PLL block. We also prepared Rhodamine B and Nile blue labeled polymers for fluorescence imaging.In the second part, we synthesized MPEG-b-PCL-b-PLL/Pt(Ⅳ) conjugate via EDC’HCl/NHS method to conjugate reduction sensitive Pt(Ⅳ) drugs to biodegradable polymers MPEG-b-PCL-b-PLL by forming amide linkages between the polymer and cisPt(IV)-COOH, the tetravalent derivative of cisplatin. Then the polymer-platinum(Ⅳ) conjugates were self-assembled into nanomicelles, which is150-160nm in diameter, and the platinum content is13%. It was sensitivity to both acid and reducing agents and more effective than cisplatin to kill ovarian cancer cells SKOV3, at least partly by increasing the cellular uptake and the DNA-Pt adduct forming. We also used Rhodamine B labeled polymers to form fluorescence nanopartilces and have detected that the polymer-drug micelles are mainly located in cell plasma and full of cell plasma.In the third part, we chelated DACH-Pt onto the prepared biodegradable polymer MPEG-b-P(LA-co-MCC)) to prepare polymer platinum(Ⅱ) conjugates P(Pt) in which polymers were as leaving groups of Pt(Ⅱ) drugs, then assembled into nanomicelles. The micelles are30-40nm in size, and platinum content can be10%, it performed better than free oxalipaltin in vitro. The IC50s of the micelles and oxaliplatin were5.2uM vs15.8uM in A2780,15.2uM vs29.7uM in A2780DDP, and the results of intracellular accumulation and DNA-Pt adducts are also better than oxaliplatin, which means the endocytosis has taken place with high efficiency.Combination of a platinum agent and a sensitizer was realized in one polymer platform in the fourth part of this dissertation. We assembled both DACHPt and Ethacrynic Acid (a GST inhibitor) into a hybrid nanomicelles, M(EA/Pt). Similar with the way we obtain P(Pt), we acquired P(EA) by conjugating EA with MPEG-b-P(LA-co-MCC-OH) via simple DCC/NHS chemistry. The composite nanomicelles M(EA/Pt) can be internalized into cancer cells via endocytosis which conquers the obstacle of reduced cellular uptake by resistant cancer cells. The acidic and reducing environment within cancer cells could make the rapid release of DACHPt and EA possible, which assures the antineoplastic activety of the nanodrug. After release from the polymer carrier, the EA and the platinum play their roles:the DACHPt bind to the bases of the DNA to induce cell killing; the EA acts as platinum sensitizer by inhibiting the activity of GST enzymes which reduces both the GSH levels and the reaction of GSH with DACHPt, resulting in decreased detoxification of DACHPt drugs and thus allow more active platinum species to form DNA-Pt adducts. The M(EA/Pt) was proved to be more efficient with lower systemic toxicity in vitro and in vivo.