Preclinical evaluation of PI3K inhibitor BYL719 as a single agent and its synergism in combination with cisplatin or MEK inhibitor in nasopharyngeal carcinoma (NPC).

Nasopharyngeal carcinoma (NPC) is endemic to Southeast Asia and over 40% of NPC tissues harbor PIK3CA amplifications. This study aims to study the preclinical activity of a novel PI3K inhibitor, BYL719, in 6 NPC cell lines: C666-1, CNE-2, HK1, HK1-EBV, HONE-1 and HONE-1-LMP1. Over 70% of growth inhibition was attained when NPC cell lines were exposed to increasing concentrations of BYL719, with IC50 values at the low micro-molar range. Two BYL719-sensitive cell lines that harbor PIK3CA mutations, CNE-2 and HONE-1, were selected for further analysis on the effect of BYL719 on cell cycle progression, apoptosis and PI3K signaling. BYL719 significantly reduced the phosphorylation of Akt, and the Akt-mTOR axis downstream effector S6 in these 2 cell lines, but a feedback activation of MAPK was observed at 72 hours post-treatment. BYL719 induced G0/G1 cell cycle arrest and apoptosis in both cell lines. In 3D cell culture models, the growth of NPC spheroids was significantly inhibited in a dose-depending manner. When BYL719 was combined with a MEK inhibitor (AZD6244) in a 3D cell culture system, strong synergism on NPC cell growth was observed with attenuation of MAPK activation. A synergistic inhibitory effect on growth was observed when BYL719 was combined with higher dose levels of cisplatin. These data suggest that BYL719 has preclinical activity in NPC cell lines especially in those which harbor PIK3CA mutation. Combination with a MEK inhibitor maybe a useful strategy that warrants further investigation.