Abstract 706: A natural inhibitor of c-Met that sensitizes head and neck cancer cells resistant to EGFR and PI3K co-targeting

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 Cancer Genome Atlas data suggest that both EGFR and PI3K pathways are reasonable targets in head and neck cancers (HNC). However, single agent treatment with EGFR inhibitor erlotinib or pan-PI3K inhibitor BKM120 fails to induce apoptosis of most HNC cell lines. We have previously reported that EGFR and PI3K co-targeting has synergistic antitumor effects both in vitro and in vivo and induces variable apoptosis. The purpose of the current study was to investigate the mechanism of intrinsic resistance to apoptosis induced by the combination of EGFR inhibitor erlotinib and PI3K inhibitor BKM120 and to sensitize the resistant cells with natural extracts. Methods: In a panel of 10 malignant and 1 premalignant HNC cell lines, we evaluated apoptosis by Annexin-V staining. Protein expression levels were measured by Western blotting. Small molecule chemical inhibitors and siRNA-mediated knockdown strategies were used to inactivate and shut down the expression of the relevant proteins, respectively. Results: The combination of erlotinib and BKM120 induced variable apoptosis. Some cell lines were very sensitive (Tu686, 686LN, 93-VU-147T), some were moderately sensitive (Fadu, SqCCy1, 1483, UMSSC90), and others were resistant (UD-SCC2, MSK-LEUK1, JHU022) to apoptosis induction. JHU022 and 1483 cell lines expressed very high levels of phosphorylated c-Met. Targeting c-Met with the small molecule inhibitor crizotinib or siRNA rendered these cell lines highly sensitive to erlotinib and BKM120 induced apoptosis. Moreover, inhibition of Src family kinases (SFK) with the small molecule inhibitor dasatinib or with c-Src-specific siRNA inhibited phosphorylated c-Met. In addition, inhibition of SFK in these cell lines conferred sensitivity to erlotinib and BKM120 induced apoptosis. We also screened several natural extracts isolated from microorganisms. We found that ACM, one of these extracts, strongly induced apoptosis of the resistant cell lines. Moreover, the extract inhibited constitutively active p-Met in the resistant cell line. Conclusions: Our results strongly suggest that some of the resistant cell lines expressed high levels of phosphorylated c-Met downstream of SFK. This confers resistance of these cells to the combination of erlotinib and BKM120 as inhibition of this pathway sensitizes the cells. Moreover, the bacterial extract ACM is a natural inhibitor of c-Met which sensitizes these resistant cell lines. It may be an excellent direction for further drug development. Citation Format: Asm Anisuzzaman, Abedul Haque, Brian Butler, ARM R. AMIN. A natural inhibitor of c-Met that sensitizes head and neck cancer cells resistant to EGFR and PI3K co-targeting [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 706.