Bifunctional cascaded single-atom nanozymes for enhanced photodynamic immunotherapy through dual-depressing PD-L1 and regulating hypoxia

As a promising anti-tumor modality, photodynamic immunotherapy (PDIT) has been applied for the treatment of many solid tumors. However, tumor hypoxic condition and immunosuppressive microenvironment severely limit the treatment outcome of PDIT. Here, we have designed a hairpin tetrahedral DNA nanostructure (H-TDN)-modified bifunctional cascaded Pt single-atom nanozyme (PCFP@H-TDN) with encapsulation of the photosensitizer. The PCFP@H-TDN have dual enzyme-like activities, which can catalyze cascade reactions to generate sufficient O₂, reversing the tumor hypoxia and thereby significantly enhancing the anti-tumor effect of PDIT. Meanwhile, H-TDN can not only block the programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) recognition pathway but also target the delivery of PD-L1 antisense oligonucleotides to reduce overall PD-L1 protein expression on the surface of tumor cells, achieving the combination of PD-1/PD-L1 pathway blockade and PD-L1 protein expression silencing. The dual-depressing PD-L1 significantly improves immune checkpoint blockade efficacy. In vivo studies have shown that the constructed PCFP@H-TDN synergistically improved the therapeutic effect of tumors in a multimodal manner through enhancing tumor immunogenicity and upregulating immune cell infiltration at the tumor site. This study provides an efficient nanomedicine to enhance PDIT by depressing PD-L1 and regulating hypoxia.