Abstract 3712: HGF mediated resistance to BRAF inhibition in BRAF V600E mutant melanoma xenograft models
Authors: Cooke Keegan , Huang Guo , Caenepeel Sean , Ma Hong , Plewa Cherylene , Lee Ki Jeong , Coxon Angela , Hughes Paul E. , Beltran Pedro 
Published: May 2015

Abstract
Background: A key obstacle in the treatment of cancer is resistance to targeted therapy. Recent reports suggest that growth factors and their receptors may play a role in mediating this resistance. HGF/MET signaling has been shown to play a role in mediating resistance to BRAF inhibitors in BRAF mutant melanoma. We studied the role of HGF/MET in mediating resistance to BRAF inhibition in BRAF mutant melanoma xenografts, comparing models of systemic and local HGF expression and evaluating the ability of a MET inhibitor to reverse HGF mediated resistance. The underlying mechanisms of this resistance were evaluated by monitoring changes in PI3K and MAPK signaling. Our data suggest that elevated local HGF expression may be required for resistance to BRAF inhibition in vivo and that resistance can be reversed by treatment with a MET inhibitor.
Methods: To model systemic HGF expression, mice bearing G361 melanoma xenografts were treated with recombinant adeno-associated virus containing an expression cassette for human HGF (AAV-HGF) or GFP as control. Mice were treated with C-1 (10 mg/kg, QD, PO), a BRAF inhibitor, or vehicle, and tumor growth was monitored. Local HGF expression was modeled using G361 xenografts engineered to express HGF under the control of an inducible promoter (tet-HGF). Mice bearing G361 tet-HGF xenografts, with or without doxycycline, were treated and monitored as described above. A follow up study was performed in G361 tet-HGF xenografts to measure the ability of AMG 337 (20 mg/kg, BID, PO), a selective MET inhibitor, to attenuate the HGF mediated rescue of BRAF inhibition. To monitor effects on the PI3K and MAPK pathways, pAKT and pERK levels were measured in tumors. Plasma and tumor HGF levels were also measured.
Results: Systemic expression of HGF via AAV-HGF treatment failed to rescue G361 xenografts from the growth inhibitory effects of C1. In contrast, local doxycycline-induced expression of HGF in mice harboring G361 tet-HGF xenografts conveyed significant (p&lt;0.001) rescue of tumor growth, suggesting that local HGF expression may be required to mediate BRAF inhibitor resistance. Elevated pAKT and pERK levels were detected in HGF rescued tumors, suggesting that PI3K and MAPK signaling pathways play a role in conveying HGF mediated resistance. Combined treatment with AMG 337 prevented the HGF mediated rescue of BRAF inhibition, confirming the role of MET signaling in this rescue mechanism. Plasma HGF levels in mice from the systemic HGF expression groups exceeded those in the local groups (3,049 and 195 pg/mL). However, tumor HGF levels were higher in the local expression groups compared to the systemic groups (26,400 and 477 pg/mL).
Conclusion: Here we demonstrate the role for HGF/MET signaling in mediating resistance to BRAF inhibitors in melanoma and suggest that monitoring HGF levels may be of clinical utility for predicting response to BRAF inhibition and in defining the opportunity for combination therapy with MET inhibitors.
Citation Format: Keegan Cooke, Guo Huang, Sean Caenepeel, Hong Ma, Cherylene Plewa, Ki Jeong Lee, Angela Coxon, Paul E. Hughes, Pedro Beltran. HGF mediated resistance to BRAF inhibition in BRAF V600E mutant melanoma xenograft models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3712. doi:10.1158/1538-7445.AM2014-3712