Markers of immune activation and immunotherapy responsiveness are increased in 3D Pancreatic cancer organoids when primed with photodynamic- and chemo-therapy.

Pancreatic ductal adenocarcinoma (PDAC) remains highly resistant to chemotherapy and immunotherapy due to a dense tumor stroma and an immunosuppressive tumor microenvironment. In this study, we explored whether the photodynamic priming (PDP) effect, a fallout of Photodynamic therapy (PDT), an approved treatment, could improve the treatment responses in 3D mouse-derived organoids. The organoids reproduced key features of pancreatic tumors and showed strong resistance to chemotherapy (nanoliposomal irinotecan, nal-IRI) and immune checkpoint inhibitor (anti-PD-1) when used alone. PDP overcame this resistance by enhancing the uptake and activation of nal-IRI, thereby increasing tumor cell death. PDP also triggered immunogenic cell death, marked by the release of danger signals that promote immune activation. When organoids were co-cultured with autologous peripheral blood mononuclear cells (PBMCs), PDP enhanced immune-mediated tumor killing. Notably, combining PDP with low doses of chemotherapy and PD-1 blockade resulted in complete tumor eradication. These effects were associated with increased immune activation and improved responsiveness to immunotherapy. Together, these findings show that PDP remodels the pancreatic tumor microenvironment, enhances chemotherapy efficacy, and sensitizes tumors to immune checkpoint inhibitors. This strategy uses clinically approved agents and offers a promising, translatable approach to overcoming treatment resistance in pancreatic cancer.