Tumor and stromal cell targeting with Nintedanib and Alpelisib overcomes intrinsic bladder cancer resistance.

Bladder cancer is a highly prevalent tumor, requiring the urgent development of novel therapies, especially for locally advanced and metastatic disease. Nintedanib is a potent anti-fibrotic angio-kinase inhibitor, which has shown clinical efficacy in combination with chemotherapy in locally advanced muscle invasive BC patients. Nintedanib inhibits Fibroblast Growth Factor receptors (FGFRs), validated targets in patients with BC harboring FGFR3/2 genetic alterations. Here, we aimed at studying its mechanisms of action to understand therapy resistance, identify markers predictive of response, and improve the design of future clinical trials. We have used a panel of genetically well-characterized human BC cells in order to identify the molecular and transcriptomic changes induced upon treatment with Nintedanib, in vitro and in vivo, at the tumor and stroma cell levels. We showed that BC cells display an intrinsic resistance to Nintedanib treatment in vitro, independently of their FGFR3 status. However, Nintedanib has higher antitumor activity on mouse xenografts. We have identified PI3K activation as a resistance mechanism against Nintedanib in BC and evidenced that the combination of Nintedanib with the PI3K inhibitor Alpelisib has synergistic antitumor activity. Treatment with this combination is associated with cell cycle inhibition at the tumoral and stromal levels and potent non-tumor cell autonomous effects on -smooth muscle (SMA)-positive tumor infiltrating cells and tumor vasculature. The combination of Nintedanib with PI3K inhibitors not only reversed BC resistance to Nintedanib but also enhanced its anti-angiogenic effects.