PI3K inhibitors synergize with FGFR inhibitors to enhance antitumor responses in FGFR2-mutant endometrial cancers

Improved therapeutic approaches are needed for the treatment of recurrent and metastatic endometrial cancer (EC). ECs display hyper-activation of the MAPK and PI3K pathways, the result of somatic aberrations in genes such as FGFR2, KRAS, PTEN, PIK3CA and PIK3R1. FGFR2, as well as the PI3K pathway, have emerged as potential therapeutic targets in EC. Activation of the PI3K pathway is seen in >90% of FGFR2mutant ECs. This study aimed to examine the efficacy of the pan-FGFR inhibitor BGJ398 with pan-PI3K inhibitors (GDC-0941, BKM120) and the p110α-selective inhibitor BYL719. We assessed synergy in three FGFR2mutant EC cell lines (AN3CA, JHUEM2 and MFE296) and the combination of BGJ398 and GDC-0941 or BYL719 showed strong synergy. A significant increase in cell death and decrease in long-term survival was seen when PI3K inhibitors were combined with BGJ398. Importantly, these effects were seen at low concentrations correlating to only partial inhibition of AKT. The combination of BGJ398 and GDC-0941 showed tumor regressions in vivo, whereas each drug alone only showed moderate tumor growth inhibition. BYL719 alone resulted in increased tumor growth of AN3CA xenografts, but in combination with BGJ398 resulted in tumor regression in both AN3CA and JHUEM2-derived xenografts. These data provide evidence that sub-therapeutic doses of PI3K inhibitors enhance the efficacy of anti-FGFR therapies and a combination therapy may represent a superior therapeutic treatment in FGFR2mutant EC patients