The Design,Synthesis And Properties Study Of Stimuli-Responsive Amphiphilic Small Molecular Prodrugs

Cancer is one of the biggest diseases to severely threaten the human health and life.Currently,chemotherapy is the primary strategy to cure cancer due to its high medical efficiency.However,there still remain several key limitations in the clinical application including nonspecific biodistribution and low bioavailability of drugs and high side-effect to normal tissue.Drug delivery systems based on nanotechnology(nanomedicine)can serve as one effective nanotherapy to enhance blood circulation time,improve the watersolubility of drugs,increase the biocompatibility of carrier and enhance the medical efficiency,and have attracted growing attention from scientists.As one important role in the family of drug delivery systesms,small molecular drug delivery systems have attracted more and more interest due to their unique properties from precise chemical structure and high sensitivity,which can effectively avoid the excessive or deficient therapy,showing a great potentiality for enhancing drug efficacy and reducing side effects in precision medicine.In addition,amphiphilic small molecular drug delivery system with properties of carrier-free drug delivery and high drug loading can achieve a drug selfdelivery model and is one of the most research hotspots.In this paper,we have designed and synthesized several novel stimuli-responsive amphiphilic small molecular prodrugs and tried to enhance the therapeutic effect of drugs.The more details of these amphiphilic small molecular prodrugs are shown as following:(1)In this study,a reduction-responsive disulfide bond was used to link a hydrophilic targeted drug folic acid(FA)with a hydrophobic anticancer drug camptothecin(CPT),resulting in an amphiphilic small molecular prodrug(FA-CPT)with a precise structure and an accurate drug loading of 36.8 wt%.Additionaly,FA-CPT prodrug with amphiphilic structure can self-assemble into nanoaggregates with an average diameter of 46.4 nm in an aqueous solution.The glutathione(GSH)-triggered release of CPT can reach a maximum rate of 82% under reductive tumor microenviroment(10 mM GSH)in 60 hours,while the release rate is 12% under a physiological environment.More interestingly,the resulting prodrug can also work as a “switchable” fluorescence probe,which exhibits strong fluorescence in medium with high GSH concentration,but a weak fluorescence in the physiological environments.Furthermore,the FA-CPT prodrug shows a superior specificity and higher cytotoxicity for KB tumor cells with FA receptor-positive than those of FA receptor-negative such as A549 tumor cells.(2)To achieve the drug self-delivery model,we further designed and synthesized a new amphiphilic small molecule prodrug,which is composed of a hydrophilic anticancer drug of gemcitabine(GT)and a hydrophobic anticancer of CPT.To achieve the amphiphilic structure,two drugs of GT and CPT were linked by a reduction-responsive disulfide bond,producing an amphiphilic drug-drug conjugate and was abbreviated as GT-CPT.The obtained amphiphilic drug-drug conjugate could self-assemble into nanoaggregates in the aqueous solution and the micellar size of GT-CPT was about 40.9 nm.More importantly,the GT-CPT nanoaggregates showed a strong micellar stability and excellent blood compatibility in vivo,which is very beneficial to improve the drug bioavailability during the treatment process.Additionally,the GT-CPT drug-drug conjugate with precise drug loading(up to ?75 wt%)demonstrated that GT-CPT can be served as a carrier-free model for efficient drug self-delivery,leading to a high therapeutic efficiency.Furthermore,the reduction-responsive disulfide bond in GT-CPT prodrug can be responding to the tumor microenvironment and release drug from GT-CPT nanoaggregates in a controlled way.To be specific,the release rate of CPT drug can reach a maximum of 85% under a 2 mM GSH in 60 h,while only 14% of drug can be released from GT-CPT nanoaggregates under 0 or 2 ?M GSH.More importantly,the disassembly of GT-CPT nanoaggregates caused by the breakage of disulfide bond also work as a “switchable” fluorescence probe in reductive environment.Furthermore,the in vitro results indicated that GT-CPT nanoaggregates not only showed enhanced cytotoxicity individually but also exhibited a prominent synergistic effect on HeLa and MCF-7 cancer cells.(3)To improve the target specificity of amphiphilic small molecular drug delivery system with high therapeutic effect of drugs.In this work,we reported a new design to develop one kind of self-deliverable prodrug amphiphiles,which were composed of a hydrophilic methotrexate(MTX)drug and two hydrophobic anticancer agents of CPT and doxorubicin(DOX),these small molecular drugs were combined with a stimuliresponsive chemical bond(e.g.,GSH-responsive disulfide bond and pH-responsive hydrozone bond),resulting in two amphiphilic drug-drug conjugates(MTX-CPT and MTX-DOX).More importantly,the MTX drug can also be served as a targeted agent to achieve the targeted drug delivery.Due to the amphiphilic structure,two drug-drug conjugates of MTX-CPT and MTX-DOX could self-assemble into nanosized prodrug nanoaggregates in aqueous media.More importantly,two nanoaggregates showed a strong micellar stability in water media with or without fatal bovine serun(FBS)solution.Furthermore,these prodrug nanoaggregates could be sensitive to the tumor microenvironment(e.g.,high GSH concentration and low pH value),and control the drug release process.Meanwhile,the disaggregation of prodrug nanoaggregates could recover the suppressed fluorescence intensity of CPT or DOX drugs,leading to a fluorescencemedicated tumor diagnostics.In addition,MTX molecules in the prodrug nanoaggregates could make nanoaggregates uptake into tumor cells with higher expression of folatereceptors such as KB tumor cells,suggesting an FA receptor-medicated endocytosis process and resulting in a selective and high ability to kill cells.The in vivo experiments of blood compatibility indicated that MTX-CPT and MTX-DOX nanoaggregates showed a good blood compatibility,which is useful to the in vivo performance.Next,we also evaluated the in vivo antitumor effect of MTX-CPT and MTX-DOX nanoaggregates using a xenograft tumor in nude mice,the results demonstrated that MTX-CPT and MTXDOX nanoaggregates showed an outstanding antitumor effect in vivo,and also proved that the synergistic therapeutic effect by co-administrating dual prodrug nanoaggregates on various tumor cells in vitro and a xenograft tumor model in vivo.The haematoxylin and eosin(H&E)assay also indicated that MTX-CPT and MTX-DOX nanoaggregates showed neligible histopathological abnormities or lesions,leading to an excellent biocompatibility.