Tumor Chemoimmunotherapy Based On Polypeptide Nanogel Drug Delivery System

In the past few decades,tumor immunotherapy as a new therapeutic strategy has gained rapid development.This therapy aims to activating immune cells to recognize and eliminate tumor cells,so as to inhibit tumor progression and prevent tumor metastasis and recurrence.Some chemotherapeutics can activate the immune system by inducing immunogenic cell death(ICD)of tumor cells,but it is difficult to induce a strong anti-tumor immune response.This is mainly due to the presence of a large number of immunosuppressive cells,cytokines,and enzymes in the tumor microenvironment,which create a suitable environment for the tumor to grow and evade the attack of the immune system.Therefore,using chemoimmunotherapy that combines chemotherapy and immunotherapy is expected to improve the therapeutic effect.Chemotherapeutics induce ICD of tumor cells.The dying tumor cells release tumor associated antigens and danger-associated molecular patterns to activate antigen-presenting cells.In the meantime,immunomodulators reverse the tumor immunosuppressive microenvironment and activate immune cells to efficiently and specifically kill tumor cells.The combination of the two strategies can effectively restore the monitoring function of immune system,control tumor progression for a long time,and prevent tumor metastasis and recurrence.Drug delivery system based on nanotechnology can improve the efficacy of tumor chemoimmunotherapy in many aspects:(1)Improve the water solubility and bioavailability of drugs;(2)Improve the stability of the drug and prolong the circulation time of the drug in the blood;(3)Deliver the drugs to tumor site through passive or active targeting ability of nanocarrier,reduce the "off-target" effect and avoid the nonspecific aggregation in normal organs;(4)Achieve responsive drug release under the stimulation of tumor microenvironment and enhance the effect of synergistic therapy.Moreover,the drug delivery efficiency of nanoparticles in vivo is affected by their physiochemical properties,such as size,shape,surface charge,porosity and elasticity.Therefore,properly designed nanocarreiers can significantly prolong the half-life of drugs in the blood circulation,improve the drug accumulation in the target site and enhance the anti-tumor effect.To this end,this paper mainly carried out the following work:(1)Exploration of the effect of changing the content of cross-linking agent on the in vivo behaviors of nanogels.We synthesized three methoxy poly(ethylene glycol)-poly(L-phenylalanine-co-L-cystine)(mPEG-P(LP-co-LC))nanogels with diverse proportions of cross-linking agent L-cystine,namely mPEG-P(LP10-co-LC5)(NG10-5),mPEG-P(LP10-co-LC10)(NG10-10),and mPEG-P(LP10-co-LC15)(NG10-15)to select the nanocarrier with the highest drug delivery efficiency.The numbers represent degrees of polymerization of each component.Altering the L-cystine proportion changes the number of disulfide bonds in the core,which directly influences the cross-linking density of nanogels.The three nanogels have similar surface charge and reduction-responsive drug release characteristics,but they have different particle sizes and drug endocytosis efficiencies.Among them,NG10-5 has the smallest diameter,highest cell internalization efficiency,and most rapid aggregation toward tumor after i.v.injection.Doxorubicin(DOX)as a model drug was encapsulated into the nanogels.NG10-5/DOX has the longest circulation time in the blood and the highest accumulation in tumor,and also exerts the most potent anti-tumor effect against murine 4T1 breast cancer.(2)Drug-loaded nanogel used in tumor chemoimmunotherapy.Low dose of DOX was used to induce ICD of tumor cells,which released danger signal to promote the antigen uptake,procession,and presentation by antigen-presenting cells.At the same time,1-methyl-tryptophan(1MT)was used to inhibit the activity of indoleamine 2,3-dioxygenase,relieving its inhibitory effect on the effector T cells.In order to improve the water solubility of 1MT and make the most of the synergistic effect,DOX and 1MT were co-encapsulated into NG10-5.NG110-5/(DOX+1MT)released both drugs in the reductive tumor microenvironment.After treatment,the percentages of regulatory T cells and myeloid-derived suppressor cells were significantly reduced and percentage of tumor infiltrating CD8+T cells was increased.This strategy that combines chemotherapy and immunotherapy can effectively inhibit the tumor growth,indicating the potential of clinical tumor treatment.