Amphiphilic Polymer-based Maytansinoid Prodrug:Synthesis,Characterization And Anticancer Studies

In this paper,we delineate a novel nanoparticulate platform that combines rational drug conjugation with subsequent nanoparticle(NP)assembly to systemically deliver a highly cytotoxic maytansine derivative DM1,while remarkably reducing the severe side effects.As comparisons,polyethylene glycol(PEG)-polylactic acids(PLA)-assembled NPs physically encapsulating DM1 were included in experiments.In the first chapter,we briefly summarized the research status of maytansine-based chemotherapeutics,and discussed the recent advances in the development of tumor-targeted nanomedicines.In chapter 2,we designed and synthesized the polymeric prodrug of maytansine.The thiolated DM1 agent was covalently coupled to amphiphilic block co-polymer PEG-b-PLA to generate two prodrug constructs(i.e.,PEG2K-PLA2K-DM1 and PEG2K-PLA4K-DM1)via maleimide-thiol reaction.The products were separated by silica gel column chromatography and characterized by 1H NMR and HPLC.Subsequently,the drug-loaded NPs were prepared using a single-step nanoprecipitation method.The results showed that the grafting ratios of DM1 into copolymers were determined to be higher than 90%and the reaction produced good reproducibility.The particle sizes of NPs were in the range of 20-30 nm.In chapter 3,the in vitro studies of NPs were performed.The in vitro cytotoxicity was determined by MTT assay in several cancer cell lines.Dual AO/EB fluorescent staining was used to evaluate cell apoptosis.Finally,hemolysis assay was carried out to evaluate the blood compatibility of DM1-formulated nanomedicines.In Chapter 4,the maximum tolerated doses of NPs were evaluated using ICR mice,and the in vivo antitumor study was carried on nude mice bearing human triple-negative breast cancer MDA-MB-468 and colorectal cancer LoVo cell xenografts.In vivo evaluations indicated that PEG-PLA-DM1 conjugate-assembled NPs display substantially reduced drug toxicity and superior therapeutic efficacy compared to the free drug forms and NPs that physically encapsulate DM1.In summary,the rational conjugation of assembling copolymers to toxic drugs DM1 enables the alleviation of cancer drug toxicity and effective delivery of anticancer drugs through sustained release,which might represent a promising scaffold for further clinical translation of maytansinoids.