[VIRTUAL] Effect of E7090, an FGFR1-3 selective inhibitor, on resistance to a CDK4/6 inhibitor and endocrine therapy in ER(+)/HER2(-) breast cancer preclinical models (AACR 2021)
E7090, an orally available FGFR1-3 selective inhibitor, is currently under evaluation in a Phase 2 study in patients with unresectable advanced or metastatic cholangiocarcinoma with FGFR2 gene fusion (NCT04238715), and a Phase 1 study as a monotherapy or in combination with fulvestrant (FUL) or exemestane for ER(+)/HER2(-) BC patients (NCT04572295). In this study, we present the roles of FGF/FGFR signaling in resistance to a CDK4/6 inhibitor and/or ET, and activities of E7090 on drug resistance in preclinical ER(+)/HER2(-) BC cell lines and PDx models. Antitumor activities of E7090 (25 or 50mg/kg, Q1Dx14 or x21, p.o.) were evaluated using five ER(+)/HER2(-) BC PDx models, OD-BRE-0438, -0450, -0188, -0704, and IM-BRE-556 with or without prior treatment of FUL (5 mg/mouse, Q7Dx2, s.c.)+palbociclib (PAL, 100mg/kg, Q1Dx14, p.o.)... In ER(+)/HER2(-) BC PDx models, FGFs/FGFRs expression in tumors were induced by treatment of FUL and/or PAL, and antitumor activity of E7090 was enhanced with prior FUL+PAL. In vitro study using cultured ER(+)/HER2(-) BC cell lines indicated that sensitivity against FUL or FUL+PAL was decreased by FGFR activation. Furthermore, a combination antitumor activity of E7090 and FUL was observed in the OD-BRE-0438 model.