Size-Switchable Polymeric Nanocarriers For Hypoxic-Tumor Therapy

Hypoxia is a common feature of solid tumors,not only closely related to tumor recurrence,metastasis and tolerance,but also induces tumor cells inthe same lesion to show heterogeneity,which is one of the mainbarriers to tumor treatment.Therefore,the development of smart nanomedicine for the tumor hypoxic microenvironment can significantly improve the treatment of solid tumors.In this thesis,we developed three size switchable nano-delivery systems based on the characteristics of the tumor hypoxic microenvironment to deliver different therapeutic agents to the deep tissues of the tumor,thereby significantly improving the therapeutic effect of hypoxic tumors.(1)The normoxic and hypoxic microenvironments insolid tumors cause cancer cells to show different sensitivities to various treatments.Therefore,it is essential to develop different therapeutic modalities based on tumor microenvironment.In this study,we designed size-switchable nanoparticles(denoted as SNP_ICG/Ce6)with self?destruction and tumor penetration characteristics for site-specific phototherapy of cancer.This was achieved by photodynamic therapy(PDT)inthe perivascular normoxic microenvironment due to high local oxygen concentrations and photothermal therapy(PTT)inthe hypoxic microenvironment that are not inproximity to blood vessels due to a lack of effective approaches for heat transfer.After intravenous injection,SNP_ICG/Ce6 was accumulated at the perivascular sites of the tumor.The singlet oxygen produced by Ce6 can ablate the tumor cells inthe normoxic microenvironment and simultaneously cleave the thioketal linker,allowing the release of small PAMAM-ICGs with improved tumor penetration for PTT inthe hypoxic microenvironment.This tailored site-specific phototherapy innormoxic and hypoxic microenvironments provides an effective strategy for cancer therapy.(2)Tumor cells inthe normoxic and hypoxic microenvironment of solid tumors have different sensitivities to different chemotherapeutic drugs.To this end,we designed a size-switchable nano-delivery system(iCPAMAM_PR/N3 and NP@DOX_DBCO)with tumor penetration characteristics mediated by tumor acidity and bioorthogonal chemistry to deliver doxorubicin(DOX)to tumors near the blood vessel and deliver hypoxia-activated prodrug PR104A to the hypoxic area away from the blood vessel.After intravenous injection,iCPAMAM_PR/N3 and NP@DOX_DBCO were accumulated intumor tissues through EPR effect and form large-size aggregates through bio-orthogonal click chemistry under the acidic environment of tumor to enhance the drug accumulation and retention intumor sites.Since the maleic acid amide inthe cross-linking agent CDM-TEG-CDM will be slowly cleaved inthe acidic environment of the tumor,the aggregates of iCPAMAM_PR/N3 and NP@DOX_DBCO can be regarded as a drug warehouse,DOX and PAMAM-PR104A continuously release inthe acidic environment of the tumor.DOX was restricted to the extravasation area of the tumor blood vessel due to limited penetration,then efficient chemotherapy on surface tumor cells.The smaller size of PAMAM-PR104A can penetrate into hypoxic areas and efficient chemotherapy on hypoxic tumor cells.This size-switchable nano-delivery system constructed based on tumor acidity and bio-orthogonal click reaction not only paves the way for site-specific chemotherapy innormoxic and hypoxic microenvironments,but also provides a universal drug delivery strategy that enhances tumor accumulation and penetration.(3)Hypoxia,a common feature of most solid tumors,causes severe tumor resistance to chemotherapy.Herein,tumor-acidity and bioorthogonal chemistry mediated size-switchable clustered nanosystem(defined as iCPDN_DBCO plus iCPDN_N3)is designed to overcome hypoxic resistance and enhance chemoimmunotherapy.The nanosystem with initial size of?100 nm,which is favorable for long blood circulation and accumulate effectively around the tumor tissue through the EPR effect.Under the acidic microenvironment,the DBCO group of iCPDN_DBCOcan be quickly exposed which will further react with the N₃ group of iCPDN_N3 through highly efficient bioorthogonal click reaction to form large-sized aggregates(?1200 nm)and demonstrated great tumor retention.Subsequently,the aggregates slowly dissociated to be ultrasmall PDN(?10 nm)has better tumor penetration ability can deliver doxorubicin(DOX)and nitric oxide(NO)to hypoxic tumor tissue.It reverses hypoxia resistance and enhances the chemotherapy effect of DOX inhypoxic tumor cells by down-regulate HIF-1?levels through NO,and boost the anti-tumor immune response induced by DOX through reprogram tumor immune microenvironment.This tumor-acidity and bioorthogonal chemistry mediated size-switchable clustered nanosystem not only paves a way incombining NO and DOX to break hypoxia-induced chemoresistance and enhance antitumor immune responses,but also provides a general drug delivery strategy for enhanced tumor accumulation and penetration.In conclusion,we have designed three smart nanodrug delivery systems with size-switchable for the pathological characteristics of tumor hypoxic microenvironment,which can not only increase the accumulation,retention and penetration of therapeutic agents intumor tissues,but also hierarchically deliver different types of therapeutic agents to different areas of the tumors.This reasonable combination therapy strategy based on tumor cell heterogeneity significantly enhances the therapeutic effect of hypoxic tumors and provides new ideas for smart nanomedicine designed based on tumor pathological characteristics.