Abstract 1638: Preclinical evaluation of the PI3K inhibitor BEZ235 in nasopharyngeal carcinoma cell lines

Undifferentiated nasopharyngeal carcinoma (NPC) is endemic to parts of Asia and ubiquitously associated with Epstein-Barr virus (EBV) infection. AKT is frequently activated in NPC and PIK3CA amplification can be found in 40% of NPC tissues. BEZ235 is a dual inhibitor of PI3K and mTOR, which results in inhibition of downstream effectors AKT, S6 ribosomal protein and 4EBP1. The preclinical activity of BEZ235 was evaluated in 6 NPC cell lines (Table 1). Western Blot analysis showed all 6 NPC cell lines showed basal activation of AKT and mTOR. The effect of BEZ235 on cell growth was evaluated by exposing NPC cell lines to increasing concentrations of BEZ235 (0.1nM, 0.5nM, 1nM, 10nM, 100nM, 1µM& 10µM) for up to 72 hrs followed by MTT assay. Over 80% of growth inhibition was achieved in all NPC cell lines except C666-1 (∼70% inhibition), with the respective IC50 concentrations in the nanomolar range (Table 1). Two representative cell lines (HONE1-LMP-1 and CNE-2 cells) were selected for assessing the effect of BEZ235 on AKT-mTOR signaling, apoptosis, cell cycle and synergism with chemotherapy. Treatment of HONE1-LMP-1 and CNE-2 cells with BEZ235 at 5nM and 50nM for 24-48 hours, resulted in cell cycle arrest at G1 phase, apoptosis (indicated by the induction of PARP cleavage), and moderate reduction of cyclin D1 expression. After BEZ235 treatment, the expression level of phosphorylated (p-)AKT, pS6K, p4EBP-1 and p-mTOR were reduced, but the level of p-p44/42 MAPK was increased in both HONE1-LMP-1 and CNE-2 cells. No synergistic effect on growth inhibition was observed when HONE1-LMP-1 and CNE-2 cells were treated with concomitant BEZ235 and chemotherapy (cisplatin, or paclitaxel). Our preliminary result suggests that BEZ235 has promising activity in most NPC cells, while the increase in p-p44/42 MAPK observed in some cell lines suggest the presence of compensatory MAPK activation that have been previously described with mTORC1 inhibitors in other cancer types. Further investigations are warranted.Table 1: IC50 (growth)% growth inhibition by BEZ235% cells at G1 arrest after BEZ235 (5nM) treatment for 24hrsEBV-associated NPC cell linesHK1-LMP14.1nM∼85%-HONE-1-LMP14.9nM∼75%62%C666-19.5nM∼70%-Poorly-differentiated NPC cell linesHONE-16.4nM∼85%-CNE-25.7nM∼90%58%Well-differentiated NPC cell lineHK14.7nM∼90%- Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-2