Preparation Of Novel Micelles Responsive To Tumor Microenvironment And Their Properties As Drug Carriers

In recent years,polymer micelles that are responsive to the tumor microenvironment have attracted widespread attention as researchers.However,the polymer micelles cannot be effectively stabilized in body fluid and blood circulation stability and cannot be effectively destabilized intumor and other diseased parts,resulting in insufficient release of anticancer drugs and greatly reducing its therapeutic effect.So far,researchers have made tremendous efforts to resolve these limitations.For example,unimolecules micelles exhibit enhanced stability to environmental changes such as pH,temperature,ionic strength,and dilution due to their unique structure.At the same time carbonate bond or acetal bond disulfide bonds will be responsive to and weak acids and reductions in the tumor microenvironment.We can introduce them into the polymer structure then the polymer micelles become an ideal drug carrier.Dendrimer with hyperbranched structure and multivalent surface is regarded as one of the most promising candidates close to the ideal drug delivery systems,but the clinical translation and scale-up production of dendrimer has been hampered significantly by the synthetic difficulties.Therefore there is considerable scope for the development of novel hyperbranched polymer that can not only address the drawbacks of dendrimer but maintain its advantages.The reversible addition–fragmentation chain transfer self-condensing vinyl polymerization(RAFT-SCVP)technique has enabled facile preparation of segmented hyperbranched polymer(SHP)by using chain transfer monomer(CTM)-based double-head agent during the past decade.Meanwhile,the design and development of block-statistical copolymers has been proved in our recent studies to be a simple yet effective way to address the extracellular stability vs intracellular high delivery efficacy dilemma.To integrate the advantages of both hyperbranched and block-statistical structures,we herein reported the fabrication of hyperbranched block-statistical copolymer-based prodrug with pH and reduction dual sensitivities using RAFT-SCVP and post-polymerization click coupling.The external homo oligo(ethylene glycol methyl ether methacrylate)(OEGMA)block provides sufficient extracellularly colloidal stability for the nanocarriers by steric hindrance,and the interior OEGMA units incorporated by the statistical copolymerization promote intracellular drug release by facilitating the permeation of GSH and H~+for the cleavage of the reduction-responsive disulfide bond and pH-liable carbonate link as well as weakening the hydrophobic encapsulation of drug molecules.The delivery efficacy of the target hyperbranched block-statistical copolymer-based prodrug was evaluated in terms of in vitro drug release and cytotoxicity studies,which confirms both acidic pH and reduction-triggered drug release for inhibiting proliferation of HeLa cells.Interestingly,the simultaneous application of both acidic pH and GSH triggers promoted significantly the cleavage and release of CPT compared to the exertion of single trigger.This study thus developed a facile approach towards hyperbranched polymer-based prodrugs with high therapeutic efficacy for anti-cancer drug delivery.The preparation of tumor acidic pH-cleavable polymers generally requires tedious post-polymerization modifications,leading to batch-to-batch variation and scale-up complexity.To develop a facile and universal strategy,we reported in this study design and successful synthesis of a dual functional monomer,a-OEGMA,which integrates the merits of commercially available oligo(ethylene glycol)monomethyl ether methacrylate(OEGMA)monomer,i.e.,hydrophilicity for extracellular stabilization of particulates and a polymerizable methacrylate for adopting controlled living radical polymerization(CLRP),and an acidic pH-cleavable acetal link for efficiently intracellular destabilization of polymeric carries.To demonstrate the potential of this dual functional monomer for drug delivery applications,amphiphilic block copolymers,poly(?-caprolactone)-b-poly(a-OEGMA)(PCL-b-P(a-OEGMA))with pendant acidic pH-cleavable OEG units were further prepared by a combination of ring-opening polymerization(ROP)of?-CL and subsequent atom transfer radical polymerization(ATRP)of a-OEGMA.The pH-responsive micelles self-assembled from PCL-b-P(a-OEGMA)showed sufficient stability in salt medium,but efficient acidic pH-triggered destabilization that was confirmed by the DLS-monitored size changes of micelles at various incubation periods at pH 5.0 as well as ~1H NMR and SEC-MALLS analyses of the degradation products.The pH-sensitivity was confirmed by an in vitro drug release study as well,which reveals significantly promoted drug release at pH 5.0 relative to the release profile at pH 7.4 due to the destabilization of micelle structure.The delivery efficacy evaluated by an in vitro cytotoxicity study in A549 cells further showed greater cytotoxicity of Dox-loaded PCL-b-P(a-OEGMA)micelles than the pH-insensitive analogues of PCL-b-P(OEGMA).This study therefore presents a facile and robust means toward tumor acidic pH-responsive polymers as well as provides a one solution to the tradeoff between extracellular stability and intracellular high therapeutic efficacy of drug delivery systems using a novel monomer of a-OEGMA with dual functionalities.