Inhibition of SUMOylation enhances responses to irreversible electroporation in pancreatic cancer

Abstract

Abstract Objective The revolutionary results of immunotherapy have not yet translated to pancreatic cancer (PC). Irreversible electroporation (IRE) is a non-thermal ablative therapy that can generate tumor-specific immune responses, yet not sufficient to eradicate distant metastatic disease. Post-translational protein modification (PTM) by small ubiquitin-like modifier (SUMO) is involved in carcinogenesis and PD-L1 mediated immunosuppression. TAK-981 is a novel inhibitor of SUMOylation that has demonstrated induction anti-tumor immune responses in preclinical models. Our hypothesis is that TAK-981 will augment the effects of IRE in an immunocompetent orthotopic mouse model of PC. Methods The PC cell line (KPC4580P) was derived from an autochthonous tumor arising in a genetically engineered mouse model (KPC). The tumors were implanted orthotopically into the pancreas via laparotomy. Once tumors reached 5-7 mm in diameter, mice were randomized to one of four treatment groups: IRE alone, TAK-981 alone, IRE + TAK-981, or no treatment. IRE versus sham laparotomy (150 x 90 microsec pulses at 1500 V/cm) was performed once through second laparotomy. TAK-981 (7.5mg/kg) versus vehicle was delivered via subcutaneous injection twice weekly x four doses, starting on the day of IRE. Tumors were harvested on day 14 for flow cytometric analysis. Results Ultrasound was performed on days 8, 14 and 20 after initiation of treatment. Tumor growth in the IRE + TAK-981 group was significantly inhibited compared to sham-treated tumors (Fig. 1, *p=0.0002), and this effect persisted to day 20, even after treatment with TAK-981 was stopped on day 11 (p < 0.01). Flow cytometry revealed a greater than 2-fold increase in CD8+ T-cells (Fig. 2a, *p <0.05) and 4-fold increase in IFN-gamma+ CD8+ T-cells (Fig. 2b, *p=0.01) in tumors treated with the combination relative to sham-treated tumors. Conclusion Our results suggest that the combination of IRE with TAK-981 is associated with better local tumor control and a significant increase of CD8+ T-cells and IFN-gamma+ CD8+ T-cells. We expect that this combination might contribute systemic immune responses that would prevent or even eradicate distant metastasis. Given that immunosuppression mediated by PD-L1 is regulated by ubiquitination and is seen in 50% of PC tumors, targeting PTM with TAK-981 might also render PC responsive to immunotherapy with checkpoint inhibitors.