Abstract B043: Synergy of Subasumstat and anti-CD40 improves survival by augmenting tumor macrophage infiltration

Abstract Background: Identification of effective immunomodulatory strategies remains a major unmet need in pancreatic ductal adenocarcinoma (PDAC). Agonistic anti-CD40 antibody (aCD40) exhibits direct cytotoxicity on tumor cells and augments antigen presentation. Subasumstat(SUB), a sumoylation inhibitor, augments innate and adaptive immune responses by increasing interferon signaling. We hypothesized that SUB+aCD40 combination would promote an effective antitumor immune response in an aggressive orthotopic model of PDAC. Methods: 2000 KPC 46 cells were implanted in the pancreas of four groups of F1 hybrid (initial survival, CD8+ T-cell depletion, and clodronate liposome depletion) and nude mice, enrolled when tumors had reached 3-5mm. The vehicle (veh) group received 80ul SUB vehicle (q48 hrs) and 100 ug blank IgG (qwk); SUB only group received 15mg/kg q48h; aCD40 only group received 100ug qwk; SUB+aCD40 group received 15mg/kg SUB q48h and 100 ug aCD40 qwk. Single cell RNA sequencing (scRNASeq) was conducted on n=2 tumors from each group. Immunohistochemistry (IHC) was performed on veh and SUB+aCD40 tumors for macrophage infiltration using F4/80. Flow cytometry (FC) was employed for the presence of lymphoid and myeloid markers in veh, SUB+aCD40, and clodronate depleted SUB+aCD40 (SUB+aCD40+clod) groups. Results: Mice receiving SUB+aCD40 had a significantly improved median survival over those receiving monotherapy or vehicle (24.5d vs. SUB:15.5d, aCD40:20d, veh: 19d). scRNASeq revealed increased tumor infiltrating CD8+ T-cell and myeloid populations when comparing veh and monotherapy to SUB+aCD40. F4/80 IHC confirmed increased macrophage infiltration in SUB+aCD40 vs veh (p = 0.01). The survival advantage conferred by SUB+aCD40 was preserved in both CD8+ T-cell depleted mice (p=0.025) and nude mice (p=0.037), while clodronate eliminated the treatment survival advantage (p=0.39). FC showed increased tumor macrophage/monocyte infiltration in SUB+aCD40 vs veh (veh:11.9%, SUB+aCD40:22.5%, p=0.03) and reduction in SUB+aCD40+clod (12.6%, p=0.01). CD8+ T-cell CD69 expression decreased in the SUB+aCD40+clod group (SUB+aCD40:19%, SUB+aCD40+clod:6%, p< 0.01). CD8 T-cell infiltration (SUB+aCD40:4.95%, SUB+aCD40+clod:3.85%, p=0.27) and CD4/CD8 T-cell ratio (veh: 1.26, SUB+aCD40:0.52, SUB+aCD40+clod:0.69, p=0.09) were not affected by clodronate. Conclusion: SUB+aCD40 therapy confers a survival advantage in the KPC46 model of PDAC in a T-cell independent manner by increasing macrophage/monocyte infiltration. SUB+aCD40 promotes CD8+ T-cell infiltration and activation, but they do not contribute to survival advantage, possibly due to exhaustion. Future work will include addition of therapeutics to mitigate/reverse T-cell exhaustion to harness both innate and adaptive immunity in treating PDAC. Citation Format: Asimina Courelli, Kevin Li, James Lee, Herve Tiriac, Yuan Chen, Andrew Lowy. Synergy of Subasumstat and anti-CD40 improves survival by augmenting tumor macrophage infiltration [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B043.