2793 - Can Hyperthermia Treatment Restore Sensitivity to Anti-PDL1 Therapy in Immunological Cold Tumors? Lessons Learned from Preclinical Murine Models

G. Gong, N. Li, J. He, M. Chen, J. Yu, and R. Wang; Department of Oncology, Affiliated Zhongshan Hospital of Dalian University, Dalian, China

Purpose/Objective(s): Immunological “cold” tumors remains a therapeutical challenge for the barren tumor microenvironment (TME) lacking dendritic cells (DCs) and cytotoxic T lymphocytes (CTLs). While early studies have suggested that thermal therapy may regulate DCs infiltration and maturation, others observed mitotic abnormalities in cells exposed to hyperthermia. In this study, we hypothesized that hyperthermia may cause mitotic catastrophe, activate cGAS-STING-IFNß signaling, attract DCs to TME, and synergize with immunotherapy. Materials/

Methods: Pan02, LLC and 4T1 cells were used to establish orthotopic tumors. Fever-range hyperthermia (FRH) was applied using a microwave physiotherapy device (41°C, 45mins, each other day, 5 times) +/- aPD-L1 therapy (BioXcell, clone.10F.9G2). In vitro works were carried out by heating various human and murine PDAC cells in a 41°C water-bath for one hour and cells were harvested 0, 12, 24, 36, 48 hour later.
Results: In Pan02, 4T1 and LLC orthotopics, FRH was shown to synergize with aPD-L1 therapy to reduce tumor burden in both heated side and abscopal side. Tissue analyses revealed that FRH significantly increased the infiltration (CD11c+) and maturation (CD11c+CD80+ and CD11c+CD86+) of DCs, as well as IFNß expression. The combination therapy increased the infiltration (CD8a+) and activation (CD8a+GrzB+) of CTLs. No association was found with FoxP3+ T-reg cells, F4/80+ macrophages, Gr1+ 75simertinib and CD11b+Ly6G+ MDSCs. This synergistic effect was abolished in the presence of STING antagonist Sn-011 (10mg/kg, i.p.). In vitro studies showed that cGAS-STING axis was activated by FRH. Mitotic catastrophe, including micronucleated and macronucleated cells, chromosome lagging, multi-polar division, etc, was observed 0-48hrs after FRH. We further examined the impact of FRH on human PDAC cells. Only some (MIA-Paca2, HPAF-II) but not other (PANC-1, BxPC3) cells showed STING activation, but all cells displayed mitotic catastrophe. Additional factors, such as regulation by DDR and TP53 genes, should be further investigated.
Conclusion: Our results suggested that FRH may promote mitotic catastrophe, activate cGAS-STING-IFNß axis and yield DC-mediated immunoactivating effect to synergize with aPD-L1 treatment. FRH could be a promising therapeutic companion with immunotherapy. Upregulated temperature such as fever could be an evolutionary protective factor boosting immune system against cancer and infection.