The low immunogenicity, insufficient infiltration of T lymphocytes, and dismal response to immune checkpoint blockade therapy pose major difficulties in immunotherapy of pancreatic cancer. Photoimmunotherapy by photodynamic therapy (PDT) can induce an antitumor immune response by triggering immunogenic cell death in the tumor cells. Notwithstanding, PDT‐driven oxygen consumption and microvascular damage can further aggravate hypoxia to exaggerates glycolysis, leading to lactate accumulation and immunosuppressive tumor microenvironment. Herein, a supramolecular prodrug nanoplatform codelivering a photosensitizer and a prodrug of bromodomain‐containing protein 4 inhibitor (BRD4i) JQ1 for combinatory photoimmunotherapy of pancreatic cancer are demonstrated. The nanoparticles are fabricated by host–guest complexation between cyclodextrin‐grafted hyaluronic acid (HA‐CD) and adamantine‐conjugated heterodimers of pyropheophorbide a (PPa) and JQ1, respectively. HA can achieve active tumor targeting by recognizing highly expressed CD44 on the surface of pancreatic tumors. PPa‐mediated PDT can enhance the immunogenicity of the tumor cells and promote intratumoral infiltration of the cytotoxic T lymphocytes. Meanwhile, JQ1 combats PDT‐mediated immune evasion through inhibiting expression of c‐Myc and PD‐L1, which are key regulators of tumor glycolysis and immune evasion. Collectively, this study presents a novel strategy to enhance photoimmunotherapy of the pancreatic cancer by provoking T cells activation and overcoming adaptive immune resistance.

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BACKGROUND Immunotherapy targeting programmed death-1 (PD-1) or programmed death-ligand-1 (PD-L1) has been shown to be effective in a variety of malignancies but has poor efficacy in pancreatic ductal adenocarcinoma (PDAC). Studies have shown that PD-L1 expression in tumors is an important indicator of the efficacy of immunotherapy. Tumor cells usually evade chemotherapy and host immune surveillance by epigenetic changes. Protein arginine methylation is a common posttranslational modification. Protein arginine methyltransferase (PRMT) 1 is deregulated in a wide variety of cancer types, whose biological role in tumor immunity is undefined. AIM To investigate the combined effects and underlying mechanisms of anti-PD-L1 and type I PRMT inhibitor in pancreatic cancer in vivo . METHODS PT1001B is a novel type I PRMT inhibitor with strong activity and good selectivity. A mouse model of subcutaneous Panc02-derived tumors was used to evaluate drug efficacy, toxic and side effects, and tumor growth in vivo . By flow cytometry, we determined the expression of key immune checkpoint proteins, detected the apoptosis in tumor tissues, and analyzed the immune cells. Immunohistochemistry staining for cellular proliferation-associated nuclear protein Ki67, TUNEL assay, and PRMT1/PD-L1 immunofluorescence were used to elucidate the underlying molecular mechanism of the antitumor effect. RESULTS Cultured Panc02 cells did not express PD-L1 in vitro , but tumor cells derived from Panc02 transplanted tumors expressed PD-L1. The therapeutic efficacy of anti-PD-L1 mAb was significantly enhanced by the addition of PT1001B as measured by tumor volume (1054.00 ± 61.37 mm 3 vs 555.80 ± 74.42 mm 3 , P < 0.01) and tumor weight (0.83 ± 0.06 g vs 0.38 ± 0.02 g, P < 0.05). PT1001B improved antitumor immunity by inhibiting PD-L1 expression on tumor cells (32.74% ± 5.89% vs 17.95% ± 1.92%, P < 0.05). The combination therapy upregulated tumor-infiltrating CD8+ T lymphocytes (23.75% ± 3.20% vs 73.34% ± 4.35%, P < 0.01) and decreased PD-1+ leukocytes (35.77% ± 3.30% vs 6.48% ± 1.08%, P < 0.001) in tumor tissue compared to the control. In addition, PT1001B amplified the inhibitory effect of anti-PD-L1 on tumor cell proliferation and enhanced the induction of tumor cell apoptosis. PRMT1 downregulation was correlated with PD-L1 downregulation. CONCLUSION PT1001B enhances antitumor immunity and combining it with anti-PD-L1 checkpoint inhibitors provides a potential strategy to overcome anti-PD-L1 resistance in PDAC.