Manganese Phthalocyanine Nanoparticles-mediated Free Radical Generation Activates Tumor Immunity

As one of the representative anticancer drugs,metal complexes have high toxicity and side effects in chemotherapy,and their application in photodynamic therapy(PDT)is seriously perplexed by low penetration depth.Therefore,noninvasive sonodynamic therapy(SDT),with deeper tissue penetration and fewer side effects,has become an effective substitute.SDT promotes the production of reactive oxygen species(ROS)by activating sound sensitizers,which can further induce immunogenic cell death(ICD)and initiate the systemic immune response.However,the anoxic microenvironment of most solid tumors seriously limits the efficiency of oxygen-dependent SDT.At the same time,the rapid oxygen consumption of SDT will aggravate the excess of endogenous hydrogen peroxide(H2O2),resulting in poor therapeutic effects.Hence,it is necessary to develop a new O2-independent ROS generation pathway for inducing ICD.In addition,the immune checkpoints in tumor cells will negatively regulate the activity of T cells,which makes synergetic therapy with checkpoint blockade an ideal strategy to achieve long-term anti-tumor efficiency.Based on the above,we formed MnClPc@HSA nanoparticles by encapsulating the MnClPc complex with human serum albumin(HSA),realizing the synergistic therapeutic effect of chemodynamic,sonodynamic and ICD-based immune activation.As a nano-acoustic sensitizer,the nanocomposite converts oxygen(O2)to singlet oxygen(1O2)under ultrasonic stimulation.Meanwhile,the transition between high and low valence states of manganese is used to catalyze the final transformation of H2O2 into 1O2 through intermediates ·O2-.Electron spinresonance spectroscopy(ESR)and fluorescence data both showed that the burst of ROS were achieved under normoxic and anoxic conditions.Co-incubation cell experiments proved that it not only caused the degradation of mitochondrial membrane potential,but also induced ICD,which was characterized by the exposure of CRT at cytomembranes and the excretion of HMGB1 and ATP.This promoted the maturation of dendritic cells(DCs)and enhanced the T cell infiltration at tumor sites ultimately.In addition,immunofluorescence in vivo showed that the macrophages in the tumor after treatment were polarized from M2 to M1,which further increased the expression level of related inflammatory factors.Combined with immune checkpoint inhibitors,the proliferation of distal tumors and lungmetastatic tumors were significantly inhibited while primary tumors were eliminated in the bilateral tumor model of 4T1 tumor-bearing mice.In summary,we described the preparation of a new type of anti-tumor nanoplatform,which ignored the restriction of oxygen deficiency on SDT,and improved the production of intracellular ROS in hypoxic solid tumors to 11.3 times of that of sonodynamic alone by taking the advantage of sonodynamic characteristics and hydrogen peroxide response of MnClPc@HSA.Therefore,the manganese phthalocyanine complex nanoparticles have laid a foundation for activating tumor autoimmunity and exhibited far-reaching clinical application potential.