Nanoparticle-induced excessive mitophagy combined with immune checkpoint blockade for enhanced cancer immunotherapy

Tumor microenvironment (TME) is the major obstacle in cancer immunotherapy due to its adverse effects on tumor-infiltrating immune cells. Emerging evidences have revealed that mitophagy plays an important role in regulating cell fate and immune microenvironment. Targeted regulation of mitophagy could be a promising strategy for enhanced cancer immunotherapy, which however remains unexploited due to the absence of robust therapeutic platform. We herein developed a mitophagy-induced RNA interfering (RNAi) nanoplatform composed of a hydrophilic polyethylene glycol (PEG) shell and an endosomal pH-responsive hydrophobic core encapsulating the complexes of mitophagy-inducer carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and small interfering RNA (siRNA) for enhanced breast cancer (BCa) immunotherapy. Using the orthotopic and metastatic BCa tumor models, we demonstrate that this nanoplatform could effectively induce excessive mitophagy in BCa cells to suppress their proliferation and silence PD-L1 expression to block its immunosuppressive effect on CD8⁺T cells. More importantly, excessive mitophagy could inhibit CC motif chemokine ligand 2 (CCL2) secretion from BCa cells and thus alleviate the immunosuppressive effect on CD8⁺T cells via impairing the tumor infiltration of tumor-associated macrophages (TAMs), regulatory T cells (Tregs), and myeloid-derived suppressor cells (MDSCs), which could ultimately combine with the PD-L1 silencing to synergistically enhance the antitumor immunity and inhibit BCa tumor growth. STATEMENT OF SIGNIFICANCE: Amplification of mitophagy in tumor cells has been considered as a promising strategy for effective cancer therapy due to its important role in regulating cell fate and TME. We herein developed a mitophagy-induced RNAi nanoplatform, which could effectively induce BCa cell death via amplifying mitophagy and enhance the tumoricidal ability of CD8⁺T cells via silencing PD-L1 expression. More importantly, this nanoplatform-induced excessive mitophagy could inhibit tumor-derived CCL2 secretion and thus remodel the immunosuppressive TME via impairing the tumor infiltration of TAMs, Tregs, and MDSCs, leading to enhanced antitumor immunity and significant inhibition of BCa tumor growth. The nanoplatform developed herein could be used as an effective tool for enhanced cancer immunotherapy.