Reversibly Self-Crosslinkable And Biodegradable Micelles For Tumor Targeted Chemotherapy

Polymeric micellar drugs generally have lower side effects,prolonged circulation time,higher maximum tolerated dose and enhanced tumor therapeutic efficacy as compared to small molecular anticancer drugs,for instance,doxorubicin?DOX?,paclitaxel?PTX?and docetaxel?DTX?.Up to now,several polymeric micellar drugs have been applied to different phases of clinical trials including DOX loaded micelles?e.g.NK911?and DTX loaded micelles?e.g.BIND-014?etc..Genexol-PM,PTX loaded PEG-PLA micelles,has been approved in South Korea for the treatment of breast,lung and ovarian cancers since 2007.However,the therapeutic efficacy of these conventional polymeric micelles is compromised due to their poor in vivo stability,premature drug release,low tumor accumulation,lacking of tumor specificity,inefficient cellular uptake as well as inadequate intracellular drug release.Therefore,further overcoming these disadvantages and enhancing the antitumor efficacy of micellar nanomedicines are desperately needed.Chapter 1 of the thesis introduces the basics and applications of polymeric micelles,presents the cutting-edge research and the bottlenecks on the developments as well as the proposal of the present thesis work.In chapter 2,based on our proprietary monomer dithiolane functionalized trimethylene carbonate?DTC?,we designed tumor active targeting,reduction-sensitive relversibly self-crosslinked and biodegradable micellar nanomedicines?c RGD-RCCMs?for targeted therapy of glioblastoma.The micelles self-assembled from a mixture of amphiphilic diblock copolymer poly?ethylene glycol?-b-poly?e-caprolactone-co-dithiolane trimethylene carbonate??PEG-P?CL-DTC??and cRGD-coupled copolymer cRGD-PEG-P?CL-DTC?.The micelles were subject to self-crosslinking,yielding cRGD-RCCMs with small size?40-50 nm?,narrow size distribution?0.1?,excellent biocompatibility and high DOX loading efficiency.The DOX loaded micelles?DOX-cRGD-RCCMs?showed excellent stability under physiological conditions due to the crosslinking,but rapidly decrosslinked and released drugs under reductive conditions.MTT assay results showed that cRGD-RCCMs had apparent targeting ability to ?_v?₃ overexpressed U87 MG cells.In particular,DOX-cRGD30-RCCMs exhibited the best targeting effect with an IC50 of 1.89 ?g/m L,which was 5.7-and 2.5-times lower than those of DOX-RCCMs and commercial pegylated liposomal DOX?DOX-LPs?,respectively.Moreover,flow cytometry and confocal laser scanning microscopy?CLSM?studies revealed that via ?_v?₃ receptor-mediated endocytosis DOX-cRGD-RCCMs effectively entered into U87 MG cells and quickly released DOX inside the cells.Furthermore,in vivo studies displayed that cRGD-RCCMs had a prolonged circulation time with t1/2 of 4.7 h,which is 3.9-and 11.7-fold as those of PEG-PCL micelles and free DOX,respectively.The biodistribution studies in U87 MG tumor-bearing nude mice revealed a high tumor DOX accumulation?7.7 %ID/g?,ca.3.3 times higher than those in DOX-RCCMs and DOX-LPs.Remarkably,the tumor inhibition of DOX-cRGD-RCCMs increased with cRGD content from 0 to 30%.In particular,DOX-cRGD30-RCCMs strongly suppressed the growth of U87 MG tumor without side-effects and prolonged survival time to 66 days,in contrast to serious adverse effects and short life span of DOX-LPs.Lung cancer is the leading cause of cancer-related deaths worldwide and 80% are non-small cell lung cancer?NSCLC?,which is not curable by surgical treatment and is prone to recurrence.Therefore,it is of paramount importance to develop highly efficient lung cancer targeted micellar nanomedicines.In chapter 3,we designed and synthesized copolymers based on DTC and trimethylene carbonate?TMC?,and lung cancer targeting peptide?CC9?coupled copolymer?CC9-PEG-P?TMC-DTC??.We prepared the lung cancer active-targeting,DTX loaded,reversibly self-crosslinked micelle nanomedicines?DTX-CC9-RCMs?for efficient lung cancer targeted delivery of DTX.DTX-CC9-RCMs are small?48 nm?,stable and reduction sensitive.At CC9 content of 10% DTX-CC9-RCMs displayed the highest cytotoxicity against H460 cells with IC50 of 0.22 ?g/mL,6 and 1.5 times lower than that of DTX-RCMs and free DTX,respectively,mainly due to the effective cell entry by H460 cells via ?_v?_<sub>6 receptor-mediated endocytosis followed by quick DTX release.In vivo biodistribution study in U87 MG tumor bearing mice indicated that for the same nanomedicines DTX accumulation in the tumor site was 2.7 and 4.2 times higher than those of DTX-RCMs and free DTX,respectively.Further in vivo performance of DTX-CC9-RCMs is currently under investigation.In summary,the micellar nanomedicines designed in this thesis are biodegradable,small-sized,easy to prepared,and they are reversibly self-crosslinked affording long circulating,actively tumor-targeting,and quickly drug downloading inside tumor cells,leading to highly enhanced antitumor efficacy.Therefore,the micellar nanomedicines can serve as safe,efficient and multifunctional platform for tumor-targeting therapy,and thus very promising in winning the battle against cancers.