Combination of Bremachlorin PDT and immune checkpoint inhibitor anti-PD-1 shows response in murine immunological T-cell high and T-cell low PDAC models.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most challenging types of cancer with little or no response to immune checkpoint inhibitors (ICIs). Photodynamic therapy (PDT) has been shown to ablate tumors and induce an immune response. In our study, we investigated the effect of photodynamic therapy (PDT), using the photosensitizer Bremachlorin, in its ability to reduce tumor burden and to sensitize immunologically T-cell high and T-cell low murine PDAC tumors to the ICI that blocks programmed cell death-1 (PD-1) immune checkpoint. In addition, we monitored the effect on survival and investigated if there was a response in PDT-treated and non PDT-treated distant tumors. Our results showed that Bremachlorin PDT induces direct tumor killing which increased survival in both 'hot' T-cell high and 'cold' T-cell low PDAC tumors and that it can make the T-cell high tumors more sensitive to ICI blocking PD-1. We found that T-cell high tumor bearing mice had an overall greater response to therapy than T-cell low tumor bearing mice. One mouse with T-cell high tumors exhibited complete tumor regression in both the treated and non-treated distant tumor 90 days after treatment. These results indicate that combining immune checkpoint inhibitors (ICIs) with Bremachlorin PDT could be a promising therapeutic intervention for enhancing PDAC's response to therapy.