Combination of antibodies directed against different ErbB3 surface epitopes prevents the establishment of resistance to BRAF/MEK inhibitors in melanoma.

Luigi Fattore,Paolo Antonio Ascierto,Alessia Noto,Debora Malpicci,Giuseppe Roscilli,Gennaro Ciliberto,Rita Mancini,Maria Rosaria Torrisi,Claudia De Vitis,Emanuele Marra,Antoni Ribas,Arianna Di Napoli,Luigi Aurisicchio,Francesca Belleudi,Pierpaolo Coluccia,Rosa Camerlingo,Maria Elena Pisanu

doi:10.18632/oncotarget.4485

Abstract

Patients with metastatic melanoma bearing V600 mutations in BRAF oncogene clinically benefit from the treatment with BRAF inhibitors alone or in combination with MEK inhibitors. However, a limitation to such treatment is the occurrence of resistance. Tackling the adaptive changes helping cells survive from drug treatment may offer new therapeutic opportunities. Very recently the ErbB3 receptor has been shown to act as a central node promoting survival of BRAF mutated melanoma. In this paper we first demonstrate that ErbB3/AKT hyperphosphorylation occurs in BRAF mutated melanoma cell lines following exposure to BRAF and/or MEK inhibitors. This strongly correlates with increased transcriptional activation of its ligand neuregulin. Anti-ErbB3 antibodies impair the establishment of de novo cell resistance to BRAF inhibition in vitro. In order to more potently ablate ErbB3 activity we used a combination of two anti-ErbB3 antibodies directed against distinct epitopes of its extracellular domain. These two antibodies in combo with BRAF/MEK inhibitors potently inhibit in vitro cell growth and tumor regrowth after drug withdrawal in an in vivo xenograft model. Importantly, residual tumor masses from mice treated by the antibodies and BRAF/ERK inhibitors combo are characterized almost exclusively by large necrotic areas with limited residual areas of tumor growth. Taken together, our findings support the concept that triple therapy directed against BRAF/MEK/ErbB3 may be able to provide durable control of BRAF mutated metastatic melanoma.

Highlights

Malignant melanoma is the most aggressive form of skin cancer
ErbB3 receptor is rapidly phosphorylated in a broad panel of BRAF-mutated melanoma cell lines upon exposure to a BRAF or to a MEK inhibitor
In contrast to this finding we observed in three cell lines with different BRAF V600 mutations, namely MST-L, LOX-IMVI and WM266, that cell exposure to either vemurafenib as BRAF inhibitor or trametinib as MEK inhibitor, does not lead to increase ErbB3 protein expression but instead causes increased spontaneous phosphorylation of ErbB3 [27]

Summary

Introduction

Malignant melanoma is the most aggressive form of skin cancer. Its incidence has dramatically increased wordwide over the past decades, becoming a major medical problem [1]. BRAF mutations usually affect the Valine 600 codon changing this aminoacid into glutamic acid (V600E) in the majority of cases, and, less frequently, into other aminoacids (V600D, V600R) [6] These mutations cause the constitutive activation of the BRAF kinase, which aberrantly induces MAPK/ERK kinases [6]. The mechanisms at the basis of acquired resistance have been at the center of intensive investigations These have led to discover in the majority of cases a plethora of mutations which cause reactivation of the RAS/RAF/MAPK pathway, including NRAS or KRAS mutations, mutant BRAF amplifications, alternative BRAF splicing, MAP2K1 activating mutations and CDKN2A losses [13,14,15,16]

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Conclusion