Construction Of Nanomedicines For Activation Of The STING Pathwayand Application To Chemoimmunotherapy

Cancer immunotherapies,such as immune checkpoint blockade therapy and chimeric antigen receptor T-cell immunotherapy,have shown great potential in the treatment of advanced or metastatic tumors.However,a number of factors,including antigen-presenting cell inactivation,insufficient tumor-infiltrating lymphocytes（TILs）,and immunosuppressive tumor microenvironment,have combined to result in extremely low response rates to available immunotherapies in most solid tumors.Therefore,activation of antigen-presenting cells,promotion of infiltration of TILs,and formation of an immune-stimulating tumor microenvironment are among the proven methods to maximize the anticancer potential of immunotherapeutic agents.Studies have shown that chemotherapy can selectively activate antigen-presenting cells and promote tumor infiltration of tumor antigen-specific T cells and natural killer cells by inducing immunogenic cell death（ICD）in cancer cells or activating the c GAS-STING pathway-mediated type I interferon（IFN）signaling pathway,which is one of the most effective strategies to selectively stimulate TILs.Based on this,the specific research of this paper is as follows:1.Glutathione（GSH）-responsive nanoparticles of camptothecin（CPT）prodrugactivating the c GAS-STING pathway for chemo-immunotherapy of colorectal cancer.CPT is a potent chemotherapeutic agent for the treatment of various cancers;however,its low bioavailability and systemic toxicity have limited its clinical application.To this end,a stearic acid-modified CPT prodrug（CPT-SS-SA）was firstly synthesized in this paper.CPT-SS-SA not only releases CPT in the presence of GSH,but it can also further self-assemble with m PEG₂₀₀₀-DSPE to form GSH-responsive nanoparticles（S-NP-CPT）due to the increased lipid solubility of CPT-SS-SA.S-NP-CPT reduced the systemic toxicity of CPT,enhanced the tumor targeting ability of CPT,and effectively inhibited tumor growth.In addition,we demonstrated that S-NP-CPT could activate the c GAS-STING signaling pathway and promote dendritic cell（DC）maturation and tumor infiltration of CD8⁺T cells,providing an experimental theoretical basis for enhanced chemo-immunotherapy.2.Reduction sensitive polymers delivering cationic platinum drugs as STING agonistsfor chemo-immunotherapy of lung cancerPhenanthriplatin（Phen Pt）is a cationic monofunctional platinum（II）drug that binds rapidly to DNA and causes severe DNA damage in tumor cells.However,Phen Pt is a cationic agent with a rapid clearance rate in vivo,leading to poor tumor suppression efficacy and side effects in vivo.For this reason,an amphiphilic polymer(（poly（2-HD-co-HPMDA）-m PEG,PHHM）was designed in this paper,characterized by the presence of a pair of anionic carboxyl groups on the main chain of the polymer with many disulfide bonds that can be triggered by glutathione（GSH）overexpressed in tumor cells.PHHM is then used to encapsulate Phen Pt via electrostatic interactions to form PHHM-Phen Pt nanoparticles（Phen Pt NP）,which deliver Phen Pt in large quantities to tumor sites and induce cellular DNA damage,activate the c GAS-STING pathway,and convert“cold tumors”into“hot tumors”.to“hot tumors”.In addition,the combination of Phen Pt NP with a-PD-L1 immune checkpoint inhibitor induced long-term immune responses in both primary and distant tumors,further demonstrating that Phen Pt NP may improve the efficacy of chemotherapy and thus the responsiveness of existing immunotherapy.3.Tetrahedral DNA nanostructure with interferon stimulatory DNA delivers highlypotent toxins activates the c GAS-STING pathway for chemo-immunotherapyInterferon-stimulated DNA（ISD）has been shown to activate the c GAS-STING pathway and induce a strong anti-tumor immune response,but its low bioavailability,poor stability,and poor selectivity for cancer make it difficult to use for clinical treatment.For this reason,a unique DNA tetrahedra(TDN^ISDs)formed by base complementary pairing of specific sequences of ISD strands and 3 single-stranded DNAs was designed in this paper.It is worth pointing out that TDN^ISDs activate the c GAS-STING pathway more efficiently compared to TDNs containing ISD dimers and TDNs without ISD sequences,suggesting that TDN^ISDs can activate the STING pathway through their physical structure and ISD sequences.By adjusting the length of ISD chains,we prepared TDNs with different length ISD sequences(42bp-TDN^ISD,64bp-TDN^ISDand 84bp-TDN^ISD).Through screening,we found that 84bp-TDN^ISDhad the best immune activation effect.To further improve the therapeutic effect,we further introduced the highly toxic and efficient platinum DNA embedding agent 56MESS,and finally obtained the nanodrug of DNA tetrahedra(84bp-TDN^ISD/56MESS).84bp-TDN^ISD/56MESScan be used not only as a highly toxic and efficient chemotherapeutic drug delivery vehicle,but also as an immunostimulant to activate the c GAS-STING signaling pathway to achieve synergistic activation of STING pathway by chemotherapy-immunotherapy to achieve anti-tumor immune response.In conclusion,in this paper,we modulated the chemical structure of chemotherapeutic drugs by chemical modification,synthesized different structural and functional chemotherapeutic drug carriers by polymerization reactions,constructed nanomedicines to improve the targeting,safety and efficacy of chemotherapeutic drugs,and enhanced the effect of chemotherapeutic drugs to activate the c GAS-STING signaling pathway,selectively stimulated the tumor infiltration of TILs and thus improved the immunosuppressive tumor microenvironment,providing a promising strategy for enhancing chemotherapy-immunotherapy.