Study On Immunoregulatory Mechanism And Immunotherapeutic Efficacy Of Polydopamine Based Nanosystem

Immunotherapy has brought innovation and hopes to cancer treatment.However,it still faces great challenges,for example,low response rate and poor therapeutic effect for"cold"tumors lacking cytotoxic T cells infiltration.Photothermal therapy(PTT)-induced immunogenic cell death(ICD)provides the opportunity for the transformation of an immune"cold"tumor into a"hot"tumor.PTT can not only kill tumor cells in a minimally invasive manner,but also releases immunogenic damage-associated molecular patterns(DAMPs),such as tumor-associated antigens,calreticulin,high mobility group protein B1,and adenosine triphosphate(ATP).These DAMPs promote the maturation of antigen-presenting cells,activate effector T cells,and provoke systemic immune responses,producing in situ vaccine effects.However,limited by immunosuppressive mechanisms in the tumor microenvironment(TME),the effect of ICD alone is often insufficient to trigger strong and effective anti-tumor immunity.TME,the battlefield for the immune system to attack solid tumors,greatly affects the anti-tumor effect.This study found that the tumor photothermal ICD process is accompanied by the negative feedback regulation of the adenosine-A2AR metabolic pathway in TME.Tumor cells rapidly metabolize the immune-promoting ATP into the immunosuppressive adenosine that inhibits DC maturation and CD8~+T cell activity and promotes the infiltration and function of myeloid-derived suppressor cells(MDSCs)by binding to its ligation A2AR.This negative feedback regulation severely hinders the antitumor effect.In this regard,an acid-responsive polyethylene glycol-polydopamine nanosystem loaded with adenosine receptor A2AR inhibitor SCH58261(PPDAIn)was designed to improve the effect of photothermal immunotherapy.The hydrophobic inhibitor SCH58261 is highly loaded on the polydopamine nanoparticles(PDA)by hydrogen bonds,π-π,and hydrophobic interactions,which can be released with photothermal response in the tumor.Phenylboronic acid-polyethylene glycol(BPEG)reacts with catechol on the surface of PDA forming an acid-responsive boronate bond.Upon reaching the acidic TME,the PEG shell selectively detaches and exposes the mussel-mimicking adhesive polydopamine,causing the nano-formulated inhibitor to accumulate in tumor tissue.Experimental results show that tumor ICD is successfully induced by the PDA photothermal effect,and the nano-inhibitor blocks the immunosuppressive effects of the A2AR metabolic checkpoint.The anti-tumor immune responses are effectively enhanced by promoting DC maturation,increasing tumor CD8~+T lymphocyte infiltration,and reducing the number and function of tumor MDSCs.Furthermore,this synergistic therapy significantly regresses the primary tumor,inhibits distal tumor growth,and prevents lung metastasis.Studies have reported that tumor hypoxia promotes the hydrolysis of ATP into adenosine in TME.In addition,tumor hypoxia accelerates the formation of tumor immunosuppressive microenvironment through various pathways,including promoting the polarization of M1 to M2 macrophages,inhibiting the antitumor function of cytotoxic T lymphocytes,and increasing infiltration of regulatory T cells(Treg),and inducing the PD-L1 expression in the tumor.Hypoxia is a major obstacle in tumor immunotherapy.The overly abundant hyaluronic acid(HA)in tumors and the rapid growth of tumor cells are mainly responsible for tumor hypoxia.Hyaluronidase(HAase)can specifically decompose HA.Intriguingly,we found that appropriate heating can significantly enhance the activity of bovine testis-derived HAase.Therefore,in this study,we synthesized mesoporous polydopamine nanoparticles(m PDA)capable of efficiently loading HAase with a pore size of 10 nm.By remotely controlling the laser irradiation,the generated photoheat enhances the HAase activity in the nano-delivery system,accelerates the tumor HA degradation,and relieves the tumor’s hypoxic immunosuppressive microenvironment.Experiment results show that the activity of HAase is increased by about 5 times,and the PTT is realized with the photothermal property of m PDAase.In vivo experiments show that the infiltration of immunosuppressive cells(MDSC,M2 macrophages,and Treg)decreased,while the infiltration of immune-activated cells(mature DC,M1 macrophages,and CD8~+T cells)increased.Tumor growth is significantly inhibited.Taken together,the m PDAase nanosystem achieves the following benefits:i)efficient HAase loading and photoacoustic imaging detectable in vivo;ii)remotely boosting HAase activity in vivo to efficiently relieve hypoxia and promote nanoparticle penetration;iii)PTT synergistically improved hypoxia by reducing tumor cell and disrupting HA,and iv)an in situ vaccine effect produced by PTT that maximizes the immune effects of hypoxia relief.In summary,the study has investigated the regulation of tumor immunosuppressive microenvironment and the enhancement of tumor photothermal immunotherapy effects based on the photothermal properties and versatility of polydopamine nanomaterials.The work reported herein innovatively explored the negative feedback regulation of adenosine-A2AR immunity in the TME during the photothermal ICD process and blocked the A2AR metabolic immune checkpoint with nano-inhibitors,which provided a new idea for enhancing the ICD induced anti-tumor immune response and tumor metabolic immunotherapy.In addition,the work also explored the feasibility of using a simple photothermal nanosystem to remotely enhance HAase activity and increase tumor matrix degradation,synergistically with PTT to alleviate tumor hypoxia that greatly contributes to tumor immunosuppressive microenvironment formation.We explored a simple and effective strategy for improving tumor hypoxic immunosuppressive microenvironment and promoting tumor photothermal immunotherapy.This study enriches the application of PDA nanomaterials in tumor immune regulation,deepens the understanding of tumor photothermal immunity,and develops novel methods for regulating tumor immunosuppressive microenvironment.