Abstract 3228: Photodynamic priming enhances immunotherapy responses overcoming oncogenic drivers in pancreatic patient derived tumor organoids

Abstract Photodynamic therapy (PDT) is an anti-cancer therapy that utilizes light, a photoresponsive photosensitizer (PS), and oxygen to confer direct cytotoxicity or vascular damage. PDT alters the tumor microenvironment (TME) transiently in a process termed photodynamic priming (PDP), making it more receptive to subsequent therapies. Previous studies reported that PDP exerts immune stimulatory effects via the release of damage associated molecular patterns (DAMPs) as a potent inducer of immunogenic cell death. Pancreatic cancer (PC) is a lethal human malignancy with no curable treatments available thus far. The desmoplastic stroma in PC limits the delivery of therapeutic agents contributing to treatment resistance. More, the stroma promotes an immunosuppressive TME that leads to immune exclusion, which is largely responsible for the immunotherapy failure in PC. Therefore, there is an unmet need to find more effective combination therapies against PC. In this work, we evaluated whether PDP enhances anti-PD1 therapy response by modulating immunogenicity in PC patient-derived organoids (PDOs). Visudyne (PS) and varied light doses of 25-100 J/cm2 were used for PDP treatments. Our data showed light dose dependent cytotoxicity and the expression of DAMPs including HSP60, calreticulin and HMGB1 in PDOs. Gene expression analysis of PDP treated PDOs showed increases in IFNγ, TNFα and CXCL12 while decreases in PDL1, TGFβ1 and FOXP1. Coculture of healthy donor (HD) monocyte-derived dendritic cells (mDCs) for 24 h with PDOs treated with a sublethal dose of PDP (25 J/cm2) showed increased CD40, CD86 and MHC11 activation markers on mDCs. Addition of matched HD naïve T cells 24 h post mDC-PDO coculture led to the excessive activation of CD4+ and CD8+ T cells highlighted by the PD1 expression on T cells from 0 h of initial T cell coculture to 48 h. This led us to treat PDO-mDC-T cell cocultures at 0 h to 48 h of initial T cell coculture with the anti-PD1 monoclonal antibody, Pembrolizumab. The treatment response was measured by live imaging of PDO growth followed by the analysis of changes in PDO diameter/area from day 0 of PDP to day 7 post-PDP. There were significant decreases in PDO growth in cultures treated with PDP followed by Pembrolizumab at different time points compared to untreated PDOs, untreated PDO-mDC-T cell cocultures, PDOs treated with PDP alone, PDO-mDC-T cell cocultures treated with PDP only or PDO-mDC-T cell cocultures treated with anti-PD1 alone. Also, we sorted T cells from the same cocultures at day 7 of PDP for gene expression analysis of T cell activation markers. There was enhanced expression of IFNγ, TNFα, FAS ligand, Granzyme B, IL2 and IL21 in T cells collected from combination therapy treated cocultures compared to others. Lastly, our data show that PDP can enhance anti-PD1 immunotherapy responses providing insights into a combination therapy option to treat PDAC. Citation Format: Pushpamali De Silva, Demi Wekking, Joanna Joeun Choe, Dario Missael Castellanos, Piotr Zelga, Russell Jenkins, Andrew Scott Liss, Tayyaba Hasan. Photodynamic priming enhances immunotherapy responses overcoming oncogenic drivers in pancreatic patient derived tumor organoids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3228.