Abstract 2728: Onartuzumab (MetMAb) restores sensitivity to erlotinib in EGFR mutant NSCLC cells expressing HGF

Abstract

Abstract Background: Onartuzumab (MetMAb) is a humanized monovalent monoclonal antibody that blocks binding of HGF to Met. The combination of onartuzumab + erlotinib is currently being evaluated in a Phase III clinical trial for 2nd/3rd line NSCLC (1). EGFR-activating mutations, including deletions of exon 19 and L858R point mutations, are associated with better response to erlotinib. However, EGFR mutant NSCLC tumors with high HGF expression are less responsive to EGFR small molecule inhibitors (2) (3). Since onartuzumab blocks HGF-induced Met activation, the addition of onartuzumab to erlotinib may be more beneficial than erlotinib alone in such patients. To test this hypothesis preclinically, we engineered the human NSCLC cell line PC9 (exon 19 deletion of EGFR and Met positive) to express hHGF endogenously, and evaluated combination effects of onartuzumab + erlotinib in vitro and in vivo. Methods: PC-9 cells were transfected with hHGF expression plasmids, and a stable clone was selected. For in vitro analyses, parental PC-9 cells and PC-9/hHGF cells were treated with various concentrations of erlotinib combined with 30μg/mL of onartuzumab, and cytotoxicity was examined. Additionally, the phosphorylation status of Met, EGFR, ERK and AKT was examined by western blot analysis of whole cell lysates. For in vivo analyses, PC-9/hHGF cells were inoculated subcutaneously into nude mice. After tumors reached approximately 200 mm3 in volume, onartuzumab (30 mg/kg, IP, Q3W) was administered alone or in combination with erlotinib (50 mg/kg, PO, daily) and tumor volume was measured over time. Results: One stable clone with high expression of hHGF was selected by hHGF ELISA and western blotting. This PC-9/hHGF clone was less sensitive to erlotinib compared to the parental PC-9 in vitro. Adding onartuzumab to erlotinib suppressed proliferation of these PC9/hHGF cells. pERK and pAKT levels were significantly reduced when PC-9/hHGF cells were treated with onartuzumab + erlotinib. In PC-9/hHGF xenograft tumors, onartuzumab or erlotinib alone had modest effects on tumor growth. However, combining onartuzumab and erlotinib dramatically suppressed tumor growth. Conclusions: Overexpression of hHGF decreases response of PC9 cells to erlotinib. Onartuzumab + erlotinib was more efficacious than erlotinib alone on PC9/hHGF cells in vitro and in vivo. These data support the hypothesis that addition of onartuzumab to erlotinib may enhance efficacy of erlotinib in EGFR mutant NSCLC tumors.