Antitumor activity of the dual PI3K/mTOR inhibitor gedatolisib and the involvement of ABCB1 in gedatolisib resistance in canine tumor cells

Abstract

The phosphatidylinositol 3‑kinase/mammalian target of rapamycin (PI3K/mTOR) signaling pathway is a therapeutic target for various types of human tumors, and dual PI3K/mTOR inhibitors demonstrate antitumor activities in both preclinical and clinical studies. However, resistance mechanisms limit their abilities. As the molecular mechanisms involved in the cellular resistance are not clear in any canine tumors, an understanding of resistance mechanisms would support the potential use of dual PI3K/mTOR inhibitors in canine tumors. The antitumor activity of gedatolisib on cell viability, protein phosphorylation, and cell cycle distribution was assessed using 12 canine tumor cell lines from 6 types of tumors. In addition, the molecular deter‑ minants involved in the cellular sensitivity to gedatolisib were explored by investigating the involvement of serum‑and‑gluco‑ corticoid‑induced kinase 1 (SGK1), PIK3CA, and ATP‑binding cassette, subfamily B, member 1 (ABCB1). The results demon‑ strated that gedatolisib decreased cell viability in all cell lines, with IC50 values <1 µM in 10 of the 12 lines. Gedatolisib inhib‑ ited Akt and mTOR complex 1 substrate phosphorylation and induced G0/G1 cell cycle arrest. However, certain cell lines with higher IC50 values were more resistant to these effects. These cell lines exhibited higher ABCB1 activity and the ABCB1 inhibitor cyclosporin A enhanced the decrease of cell viability caused by gedatolisib. SGK1 overexpression did not confer resistance to gedatolisib. The mutations of E545K and H1047R in PIK3CA were not observed. The present results indicated that gedatolisib decreased cell viability in canine tumor cell lines and ABCB1 played an important role in gedatolisib resistance, supporting the potential use of gedatolisib for canine tumors.