P1.04-37 Dioscin Elicits Anti-Tumor Immunity by Inhibiting Macrophages M2 Polarization via JNK and STAT3 Pathways in Lung Cancer

Abstract

Background: Several reports from different groups suggest that novel KRAS inhibitors are not effective ex vivo, but the mechanism(s) responsible for this are unknown. We performed complex experiments that highlight the huge discrepancy between the marked in vivo and the minimal in vitro effects of KRAS inhibitors. Furthermore, we identified and validated the mechanism of the in vivo-restricted actions of KRAS inhibitors in immunocompetent mice, which can be translated to successful new treatments for patients with KRAS-mutant cancers. Method: We treated tumor cells with defined KRAS mutation status with KRAS inhibitors deltarasin, cysmethynil, and AA12 and used different in vitro assays as readout. Additionally, KRAS silencing and overexpression were done using shRNA and KRAS G12C vectors and included in the experimental setup. In parallel C57BL/6 wildtype mice or deficient in interleukin (IL)-1b (Il1b-/-) or chemokine receptors (Ccr2-/-, Cxcr1-/-, Cxcr2+/-) received s.c. KRAS-mutant or wild-type tumor cells followed by saline or deltarasin treatments. Microarrays were done using a large set of Kras-mutant and Kras-wildtype cell lines. Result: We identified that KRAS inhibitors exerted comparable effects against cancer cells in vitro irrespective of KRAS status. However, mice only with KRAS-mutant tumors responded selectively to deltarasin treatment. Similar in vivo-restricted effects were evident after genetic manipulation of KRAS. Microarrays identified a 42-gene signature specific to Kras-mutant cancer cells and responsive to Kras manipulation, which contained Kras, Ccl2, Il1r1, Ccl7, and Cxcl1. Deltarasin was effective in halting KRAS-mutant flank tumors in Wt, Cxcr1-/-, and Cxcr2+/-, but not in Ccr2-/-and Il1b-/-mice. qPCR results revealed a strong regulation of Il1r1/IL1R1 mRNA expression depending of Kras/ KRAS mutation status and drug treatment. Thereby, KRAS inhibition can be effective in vivo via blockade of the positive feedback loop of KRAS-CCL2-IL1ß. Conclusion: Inflammatory signaling loops are synthetic lethality targets for KRAS mutant tumors and only druggable by KRAS inhibitors in vivo. Hence in vitro drug screens may be suboptimal settings for anti-KRAS drug discovery.