Polymeric Drug Delivery Carriers Improve Tumor Immunotherapy Through The Regulation Of Tumor Microenvironment

Although breakthroughs have been made in tumor immunotherapy,the clinical response rate to most tumors is still low,which mainly because tumor tissues have a strong immunosuppressive microenvironment.Effectively regulating the tumor microenvironment and reversing immunosuppression are effective strategies to improve the effect of tumor immunotherapy.Among them,achieving tumor-associated macrophages(TAMs)repolarization and inducing tumor cell immunogenic cell death(ICD)are two important choices.Drug carrier technology is an important means to reverse the tumor immunosuppressive microenvironment,but the existing carrier materials often face the problems of low drug loading and insufficient tumor site enrichment.In response to these problems,this thesis had developed two types of delivery carrier systems,dendrimer derivatives and injectable hydrogels,which improved the tumor immune microenvironment and enhanced tumor immunotherapy by respectively increasing the loading of the TAMs-repolarizing-drug R848 and the local combined delivery of R848 and the ICD-inducing-drug mitoxantrone(MIT).The specific research contents of this paper are as follows:(1)To solve the problems of low solubility of R848 and low drug loading of common carriers,a PAMAM dendrimer derivative(G4-DEEA)was developed,which could efficiently load R848 to achieve TAMs repolarization and improve tumor immunotherapy.The results of the study showed that the resulting formulation(G4-DEEA@R848)had a drug loading of up to 35.9 wt%,which could effectively repolarize M2 macrophages to M1 phenotype in vitro and induce the maturation and activation of dendritic cells(DCs).In the 4T1 orthotopic breast cancer model,G4-DEEA@R848 showed a stronger tumor inhibitory effect than free drugs with an inhibition rate of 59.6%.The mechanistic studies suggested that G4-DEEA@R848 could improve the tumor microenvironment by repolarizing TAMs into tumor-killing M1 type in vivo,reduced the proportion of bone marrow-derived suppressor cells(MDSCs),and increased the infiltration of cytotoxic T cells.This study provided a simple and effective strategy to improve the delivery efficiency of R848 and enhanced the effect of tumor immunotherapy.(2)Aiming at the problem of insufficient drug enrichment in tumor sites for systemic administration,an injectable temperature-sensitive PLGA-PEG-PLGA hydrogel was developed for co-loading R848 cyclodextrin inclusion compound(N-CD@R848)and MIT.Repolarizing TAMs and simultaneously inducing ICD effects could jointly regulate the tumor immune microenvironment and improve tumor immunotherapy.On the one hand,calreticulin was exposed on the surface of tumor cells,the release of adenosine triphosphate(ATP)and high mobility histone 1(HMGB1)was increased after MIT inducing ICD.Which induced antigenpresenting cells(APCs)to phagocytose tumor antigens and presented it to T cells.On the other hand,N-CD@R848 could effectively induce the conversion of M2 macrophages into tumorkilling M1 type and the activation of APCs.The studies in vivo have shown that MIT/R848@Gel could significantly inhibit the growth and metastasis of 4T1 orthotopic breast cancer,and produced a durable anti-tumor immune memory.In addition,it was found that MIT/R848@Gel local treatment could inhibit the growth of distal tumors by studying in bilateral 4T1 tumor model,indicating that MIT/R848@Gel treatment triggered a systemic antitumor immune response.The mechanistic studies by flow cytometry suggested that MIT/R848@Gel treatment could effectively repolarize TAMs and increase the proportion of cytotoxic T cells in vivo,thereby remodeled the tumor microenvironment and achieved a powerful tumor immune response.