Abstract B027: Synergism of SUMOylation Inhibition with Irinotecan for the Treatment of Pancreatic Cancer

Abstract Chemotherapy is currently the standard of care for pancreatic cancer (PDAC) patients but responses are transient with high toxicity; therefore, improved, less toxic therapies are needed. Irinotecan (IRI), a standard agent for PDAC that inhibits Topoisomerase 1 (Top1) to cause DNA damage in cancer cells. We investigate a new strategy of combining IRI with sumoylation inhibition (SUMOi, Subasumstat [SST]). Top1 is heavily SUMOylated enabling the repair of Top1 induced DNA damage. We hypothesize SST will synergize with IRI by augmenting DNA damage-mediated cancer cell death, thus improving efficacy and allowing for de-escalation of IRI dosing. In Vitro Synergy: KPC46 murine PDAC (KPMP) cells and human PDAC organoids were treated with 5-FU, Irinotecan, Oxaliplatin, Gemcitabine, or Cisplatin and SST (1nM- 500nM, 24hrs), viability was assessed with cell titer glo, and synergy plots were generated using Combenefit. Survival Experiments: NSG and F1 hybrid (F1H) mice underwent orthotopic KPC46 cell injection; IP injections with SST (15mg/kg q48h) and/or IRI (F1H:25mg/kg, NSG:12.5mg/kg) qweekly were initiated when tumors reached 3-5mm. Tumor Volume (TV) was assessed with ultrasound. Human Slice Culture: Patient tumor slices were incubated in 200nM SST and/or IRI for 5 days. Flow Cytometry (FC) was conducted for EPCAM and PanCK PDAC cell markers. Western Blot (WB): KPC46 cells were treated with SST and/or IRI (100nM) for 24 hours. Blots were probed for Top1 (chromatin protein fraction), γ-H2AX, and cleaved caspase-3 (whole cell protein).In vitro synergy screening of SST and standard PDAC chemotherapies revealed the greatest synergy between SST and IRI occurring as low as 50nM, based on synergy plots. Synergistic cytotoxicity was replicated in vivo using the KPMP[YC1] orthotopic model in NSG mice. SST+IRI treatment resulted in the greatest survival increase (IRI:16, SST:17, SST+IRI=24 days; p=0.008) and tumor volume (TV) decrease (after 2 weeks of treatment, AvgTV: IRI=358mm3, SST (all mice dead), SST+IRI=132mm3; p=0.001). SST immune priming properties were evaluated by means of an orthotopic model using KPMP cells in immunocompetent F1H mice. SST+IRI treatment resulted in the greatest survival increase (IRI:15d, SST:15d, SST+IRI: 22d[YC2] ; p=0.03]) and TV decrease (after 2 weeks of treatment, AvgTV: IRI=400, SST=350, SST+IRI=150 mm3; p =0.002). In human slices, compared to control, SST+IRI treatment yielded the greatest decrease in PANCK+ and EPCAM+ cells (IRI:24.4%, SST:15.5%, SST+IRI:9.5%). WB of KPMP cells exposed to SST and IRI showed that, compared to control, the greatest increase in the chromatin bound Top1, total cell ϒ- H2AX, and cleaved caspase 3 (Band Intensity: IRI: 0.1, SST:0.15, SST+IRI: 0.52; p=0.009) occurred in the SST+IRI case. SST+IRI exhibits synergistic cytotoxicity on PDAC cells in both murine and human models by enhancing cancer cell apoptosis due to increased Top1 binding and dsDNA breaks. Clinically, addition of SST could serve as an adjunct to FOLFIRINOX and SST+IRI can be an alternative second line treatment to FOLFIRI. Citation Format: Asimina Courelli, Leonie Ren, Herve Tiriac, Yuan Chen, Andrew Lowy. Synergism of SUMOylation Inhibition with Irinotecan for the Treatment of Pancreatic Cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr B027.