Abstract 6637: Inhibition of FGFR signaling by lenvatinib activates tumor interferon gamma signaling pathway and potentiates antitumor activity of anti-PD-1 antibody

Background: Lenvatinib mesilate (LEN) is an oral multiple receptor tyrosine kinase (RTK) inhibitor that selectively inhibits the kinase activity of VEGFR1-3, in addition to other proangiogenic and oncogenic pathway-related RTKs including FGFR1-4; PDGFRα; KIT; and RET. To improve the efficacy of immune checkpoint inhibitors (ICI), combination treatments of ICI plus anti-angiogenic inhibitors are currently under investigation. Lenvatinib plus pembrolizumab is approved for 2nd line treatment of advanced endometrial carcinoma that is not microsatellite instability-high or mismatch repair deficient in the US, and several Ph3 clinical trials with this combination are ongoing. Immunosuppressive roles of VEGF in tumor microenvironment have been well studied; however, immunomodulatory effects of FGFR signaling and the effect of FGFR inhibition on antitumor activity of anti-PD-1 antibody (PD-1 Ab) are still largely unknown. In this study, we investigated mechanism of action underlying the activity of LEN and PD-1 blockade in syngeneic mouse renal cell carcinoma (RCC) model. We also explored the relationship between FGFR signaling and interferon (IFN) γ signaling pathway in cancer cells, and examined whether LEN has an impact on IFNγ pathway by FGFR inhibition. Methods: We examined antitumor activity of combination treatment of LEN at 10 mg/kg (po, qd) plus PD-1 Ab at 10 mg/kg (ip, twice weekly) and VEGF-selective inhibitor axitinib (Axi) at 10 mg/kg (po, bid) plus PD-1 Ab in the RAG (murine RCC cell) subcutaneous tumor model. Gene expression profile in tumor tissues or cultured cells was analyzed by qRT-PCR or RNA seq. FGFR and IFNγ signaling pathways and their downstream molecules in tumor tissues and cultured cells were analyzed by western blot (WB) and immunofluorescence (IF). Results: In the RAG model, the combination of LEN and PD-1 Ab showed greater tumor response than each single treatment and Axi plus PD-1 Ab combination. In the tumors, WB analysis revealed LEN treatment increased STAT1 phosphorylation and PD-L1 expression and decreased the expression of SOCS1, a suppressor molecule of JAK-STAT signaling. Increased expression of PD-L1 was also observed in the tumors by IF analysis. WB and qRT-PCR analyses elucidated that activation of FGFR signaling pathway inhibited the induction of B2M, PD-L1 and CXCL10 expression in RAG cells and human cancer cell lines. Inhibition of FGFR by LEN treatment reactivated the IFNγ signaling pathway. Conclusion: Dual inhibitio