Abstract 1087: TGF-β activated EGFr as a bypass mechanism for the acquired resistance of MET inhibitors in hepatocellular carcinoma

Abstract

Abstract Hepatocellular carcinoma (HCC) patients with an active HGF/c-Met signaling pathway have a significantly worse prognosis. Although targeting strategies using MET tyrosine kinase inhibitors (TKI) are in Phase I/II testing for HCC, monotherapy using TKIs in other cancers has not demonstrated durable responses. In non-small cell lung cancer, bypass mechanisms for resistance to EGFr TKIs include MET amplification and activation. We utilized human HCC MET+ cell lines to explore a mechanism of EGFr activation during MET inhibition, and we examined the effect of combination MET and EGFr TKI therapy on suppressing this bypass mechanism in HCC in vivo. Analysis of 149 HCC specimens using transcriptome profiling and immuno-histochemical staining demonstrates a strong negative correlation between EGFr and MET expression. HCC is predominantly either MET positive [44%] or EGFr positive [45%], and co-expression of MET and EGFr is extremely rare in the same tumor. We have previously demonstrated that treatment of xenograft tumors of human HCC MET+ MHCC97-H cells with a MET TKI resulted in stasis of tumor growth in vivo (You … Rountree. Hepatology. 2011). To understand the mechanism of survival in the MHCC97-H cells after inhibition of MET, we developed an MHCC97-H cell line with stable expression of MET shRNA. This MHCC97-H METneg line demonstrated the slower growth kinetics and the inhibition of both PI3K and MAPK signaling comparable to MET TKI treated xenografts. Screening against 850 kinases and phosphatases identified EGFr activation as a mechanism of survival in this MHCC97-H METneg line. Gene expression analysis of this MHCC97-H METneg cell line demonstrated a 6 fold increase in TGF-β, a ligand of EGFr. MHCC97-H xenograft tumor analysis demonstrates a 20 fold increase in TGF-β expression after MET TKI therapy. In vivo treatment of MHCC97-H tumors with combination MET and EGFr TKI therapy resulted in complete regression of all small tumors (15 mm3 at start of TKI) compared to partial regression when MET TKI was used as monotherapy. Treatment of large tumors (200-300 mm3 at start of TKI) with combination TKI therapy resulted in a significant reduction in tumor volume compared to MET TKI monotherapy. EGFr TKI monotherapy had no effect on tumor growth kinetics. Within MET positive HCC models, MET TKI therapy results in a bypass mechanism through up-regulation of TGF-β and activation of EGFr. This bypass mechanism can be partially overcome with combination EGFr and MET TKI therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1087. doi:1538-7445.AM2012-1087