Abstract 1907: Src-Met signaling confers apoptosis resistance to EGFR and PI3K co-targeting independently of AKT and ERK pathway activation in head and neck cancer

Purpose: Molecularly targeted agents will play a major role in the next generation of personalized cancer therapies. However, intrinsic and acquired resistance to targeted agents poses challenges to the success of such treatments. The purpose of the current study was to investigate the intrinsic resistance of head and neck cancer (HNC) cell lines to apoptosis induced by the combination of EGFR inhibitor erlotinib and PI3K inhibitor BKM120. Methods: In a panel of 10 malignant and 1 premalignant HNC cell lines, we evaluated cell growth inhibition (by SRB assay), IC50, combination index, dose reduction index (by CalcuSyn Software), and apoptosis (by Annexin-V staining). Protein expression levels were measured by Western blotting. Small molecule inhibitors and siRNA-mediated knockdown strategies were used to inactivate and shut down the expression of the relevant proteins, respectively. Results: We have reported previously that single targeting of EGFR with erlotinib or PI3K with BKM120 (pan-PI3K inhibitor) suppressed cellular growth without inducing significant apoptosis. Co-targeting EGFR and PI3K demonstrated in vitro synergy in all except the JHU022 cell line and more effectively inhibited HNC xenograft growth in vivo. The combination of erlotinib and BKM120 induced variable apoptosis: some cell lines were very sensitive (MDA686TU, MDA686LN, 93-VU-147T), some moderately (Fadu, SqCCy1, MDA1483, UPCI:SCC090) and others were resistant (UD-SCC2, MSK-LEUK1, JHU022) to apoptosis induction. We found that the resistant cell line JHU022 expressed very high levels of p-Met (Y1234/1235). Inhibition of Met with small molecule inhibitor crizotinib or siRNA rendered this cell line highly sensitive to apoptosis induced by the combination of erlotinib and BKM120. Although inhibition of hepatocyte growth factor (HGF), the only known ligand for Met, with soluble neutralization antibody had no effect on Met phosphorylation, inhibition of Src family kinases (SFK) with dasatinib abolished Met phosphorylation at Y1234/1235. Dasatinib also made this cell line sensitive to apoptosis. Ablation of c-Src with siRNA had similar effects on p-Met (Y1234/1235) and apoptosis. Interestingly, inhibition of Met had no effects on AKT and ERK phosphorylation, two critical downstream pathways of receptor tyrosine kinases including Met. Conclusions: Our results strongly suggest that co-targeting of EGFR and PI3K has synergistic activity, is effective in vivo, and induces apoptosis of some HNC cell lines. Some resistant cell lines express a high level of p-Met as a downstream target of SFK, which confers resistance of these cells to EGFR and PI3K co-targeting. Finally, Met confers apoptosis resistance independently of AKT and ERK pathway activation. Citation Format: Abu S. Anisuzzaman, Abedul Haque, Zhuo G. Chen, Dong M. Shin, A.R.M. Ruhul Amin. Src-Met signaling confers apoptosis resistance to EGFR and PI3K co-targeting independently of AKT and ERK pathway activation in head and neck cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1907.