Abstract 5499: Preclinical evaluation of PI3K inhibitor BYL719 as a single agent and its synergism in combination with cisplatin or MEK inhibitor in nasopharyngeal carcinoma (NPC) using 3D cell culture system
Authors: Cheong Hio Teng , Wong Chi Hang , Hui Connie Wun Chun , Chan Anthony Tak Cheung , Ma Brigette Buig Yue 
Published: May 2015

Abstract
BYL719 is a novel specific inhibitor against the alpha-isoform of Class I PI3K that imposes impacts on AKT-mTOR signaling axis, thereby mediating relevant pathways such as MAPK, STAT3 and EGFR. The study aims to investigate the effects of BYL719 on nasopharyngeal carcinoma (NPC) which has a high prevalence in Southeast Asia, and its synergism on combination with cisplatin or MEK inhibitor. Six NPC cell lines including C666-1, CNE-2, HK1, HK1-EBV, HONE-1, HONE-1-LMP were selected for this preclinical study. All cell lines had a basal expression in both phosphorylated and total forms of Akt, mTOR and p70S6K which are the downstream pathways of PI3K. MTT assay was used to evaluate the cytotoxicity of BYL719 on NPC, cells were incubated in BYL719 with escalating concentration (10nM, 50nM, 0.1µM, 0.5µM, 1µM, 5µM and 10µM) for 48 or 72 hours in culture medium. The maximum growth inhibition was attained in 72 hours of BYL719 incubation, the IC50s of all cell lines with 72-hour BYL719 treatment were in micromolar range (C666-1=1.85µM, CNE-2=0.90µM, HONE-1=0.56µM, HONE-1-LMP=0.95µM, HK-1-EBV=1.50µM and HK-1=1.53µM). Two sensitive cell lines CNE-2 and HONE-1 were selected for further analysis on apoptosis, cell cycle and BYL719's synergistic effect by 3D cell culture system. After 72 hours of treatment, BYL719 up-regulated mTOR, EGFR, p-EGFR (Y1086), p-STAT3 (Y705) and p-p44/22 MAPK (T202/Y204) in CNE-2 but not in HONE-1, however, it down-regulates mTOR in HONE-1. This suggested that BYL719 is more effective to HONE-1 in inhibiting mTOR downstream pathways and accordingly anti-proliferation. HONE-1 was then used to examine the synergistic effect of BYL719 combined with cisplatin or MEK inhibitor (AZD6244). Drug treatment commenced 72 hours after cell plating and growth inhibition was determined by MTT assay on day 9. As supported by cell viability assay and western blot, strong synergistic effect was expressed when BYL719 was combined with AZD6244. In comparison with using BYL719 alone, there was a 2-fold increase in growth inhibition observed in combination of BYL719 and AZD6244. The combination indices (CI) of 0.6µM BYL719 plus 0.325µM AZD6244 and 0.6µM BYL719 plus 0.65µM AZD6244 are 0.17 and 0.13 respectively, indicating strong synergism in these drug combinations. On the other hand, there was also mild synergistic effect observed when BYL719 was combined with cisplatin, with CI of 0.585 for 0.6µM BYL719 plus 1.2µg/ml cisplatin. The growth inhibition for BYL719 combined with cisplatin was comparable to the effect of high dose cisplatin (1.2µg/ml) administration. BYL719 is effective in NPC growth inhibition, its synergistic effect with MEK inhibitor does provide a great advantage in NPC treatment and is worthwhile for further studies.
Acknowledgement: This work is supported by Novartis
* Denotes co-authorship.
Citation Format: Hio Teng Cheong, Chi Hang Wong, Connie Wun Chun Hui, Anthony Tak Cheung Chan, Brigette Buig Yue Ma. Preclinical evaluation of PI3K inhibitor BYL719 as a single agent and its synergism in combination with cisplatin or MEK inhibitor in nasopharyngeal carcinoma (NPC) using 3D cell culture system. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5499. doi:10.1158/1538-7445.AM2014-5499