Function-Blocking ERBB3 Antibody Inhibits the Adaptive Response to RAF Inhibitor

Abstract

ERBB3/HER3 expression and signaling is upregulated in mutant BRAF melanoma as an adaptive, pro-survival response to FDA-approved RAF inhibitors. Since compensatory ERBB3 signaling counteracts the effects of RAF inhibitors, co-targeting ERBB3 may increase the efficacy of RAF inhibitors in mutant BRAF models of melanoma. Here we corroborate this concept by showing that the ERBB3 function-blocking monoclonal antibody huHER3-8 can inhibit neuregulin-1 (NRG1) activation of ERBB3 and downstream signaling in RAF-inhibited melanoma cells. Targeting mutant BRAF in combination with huHER3-8 decreased cell proliferation and increased cell death in vitro, and decreased tumor burden in vivo, compared to targeting either mutant BRAF or ERBB3 alone. Further, the likelihood of a durable tumor response in vivo was increased when huHER3-8 was combined with RAF inhibitor PLX4720. Together, these results offer a preclinical proof of concept for the application of ERBB3 neutralizing antibodies to enhance the efficacy of RAF inhibitors in melanoma to delay or prevent tumor re-growth. Insofar as ERBB3 is often upregulated in response to other kinase-targeted therapeutics, findings may have implications for other cancers as well.

Fibroblast-derived Neuregulin 1 Promotes Compensatory ErbB3 Receptor Signaling in Mutant BRAF Melanoma

“…Both antibodies were able to partially reverse the effect of fibroblastderived conditioned medium on ErbB3 pathway activation and mutant BRAF melanoma cell growth properties. These data are consistent with the ability of ErbB3-targeting agents to increase the efficacy and duration of response of RAF inhibitors in vivo (15) and underscore the use of ErbB3-targeting agents to reduce the protective effects of fibroblast-derived NRG1 on RAF-inhibited melanoma cells. Although pertuzumab and seribantumab target ErbB3/ErbB2 signaling by preventing ErbB3/ErbB2 dimerization or the binding of NRG1 to ErbB3, respectively, other agents may be developed to directly sequester NRG1 (45) or to directly target CAFs (46).…”

“…Levels of phospho-ErbB3 were elevated following RAF inhibitor treatment of melanomas cells in culture, melanoma xenografts, and patient samples (10). Furthermore, application of an ErbB3-neutralizing antibody enhanced the efficacy of the RAF inhibitor PLX4720 in vivo (15). ErbB3 is a member of the EGF receptor family of receptor tyrosine kinases.…”

“…The tumor microenvironment plays a key role in these adaptive responses to targeted inhibitors. For example, stromal fibroblasts may be subverted to phenotypically distinct CAFs, which promote supportive conditions for cancer cell growth through the production of soluble growth factors and the extracellular matrix (13)(14)(15)(16), induction of angiogenesis, and recruitment of inflammatory cells (14). The extent to which stromally derived factors are required for resistance to targeted inhibitors remains to be fully understood.…”

Applications of Systems Biology to Identify Mechanisms of Adaptive Response to Targeted Single and Combinatorial Drug Treatment in Cancer

“…Resistance to BRAFV600E inhibition can involve activation of alternative growth pathways that can diminish dependence on the MAPK pathway Held et al, 2013;Kugel et al, 2014;Roller et al, 2012). Generally, BRAF V600E melanomas strongly depend on signaling through the mutated BRAF V600E…”

“…Compensatory signaling has been overcome by using a secondary drug that targets compensatory signaling pathways, such as targeting ERBB3 activity in vemurafenib treated melanomas (Kugel et al, 2014). Pathway reactivation can sometimes be overcome by targeting a downstream target of the primary drug, such as targeting MAP2K1 and BRAF in tandem (Flaherty et al, 2012a).…”