PDGFRα up-regulation mediated by sonic hedgehog pathway activation leads to BRAF inhibitor resistance in melanoma cells with BRAF mutation.

Francesco Sabbatino,Ling Yu,Zachary A Cooper,Giosue’ Scognamiglio,Soldano Ferrone,Xinhui Wang,Dennie T Frederick,Jennifer A Wargo,Stefano Pepe,John M Kirkwood,Keith T Flaherty,Yangyang Wang,David Pepin,Cristina R Ferrone

doi:10.18632/oncotarget.1878

Abstract

Control of BRAF(V600E) metastatic melanoma by BRAF inhibitor (BRAF-I) is limited by intrinsic and acquired resistance. Growth factor receptor up-regulation is among the mechanisms underlying BRAF-I resistance of melanoma cells. Here we demonstrate for the first time that PDGFRα up-regulation causes BRAF-I resistance. PDGFRα inhibition by PDGFRα-specific short hairpin (sh)RNA and by PDGFRα inhibitors restores and increases melanoma cells' sensitivity to BRAF-I in vitro and in vivo. This effect reflects the inhibition of ERK and AKT activation which is associated with BRAF-I resistance of melanoma cells. PDGFRα up-regulation is mediated by Sonic Hedgehog Homolog (Shh) pathway activation which is induced by BRAF-I treatment. Similarly to PDGFRα inhibition, Shh inhibition by LDE225 restores and increases melanoma cells' sensitivity to BRAF-I. These effects are mediated by PDGFRα down-regulation and by ERK and AKT inhibition. The clinical relevance of these data is indicated by the association of PDGFRα up-regulation in melanoma matched biopsies of BRAF-I +/- MEK inhibitor treated patients with shorter time to disease progression and less tumor regression. These findings suggest that monitoring patients for early PDGFRα up-regulation will facilitate the identification of those who may benefit from the treatment with BRAF-I in combination with clinically approved PDGFRα or Shh inhibitors.

Highlights

Over 50% of metastatic melanomas harbor the BRAF(V600E) point mutation (T1799A)[1, 2]
Since acquired BRAF inhibitor (BRAF-I) resistance can be mediated by reactivation of the MAPK pathway or by activation of alternative pathways like PI3K/AKT, we evaluated signaling through these pathways in both parental and resistant cell lines (Figure 1A)
The present study demonstrates that human melanoma cells express PDGFRα both in vitro and in vivo

Summary

Introduction

Over 50% of metastatic melanomas harbor the BRAF(V600E) point mutation (T1799A)[1, 2]. Mutant BRAF(V600E) represents a constitutively active protein serine kinase that leads to the sustained activation of the BRAF→MEK1/2→ERK1/2 MAP kinase pathway[3, 4]. This pathway plays a critical role in the regulation of gene expression as well as cell proliferation and survival, which are all involved in the initiation and progression of melanoma[5, 6]. Clinical trials have demonstrated that the BRAF inhibitor (BRAF-I), PLX4032 (vemurafenib), and other inhibitors in its class (GSK2118436 or dabrafenib) can induce tumor regression in more than 50% of the patients with metastatic melanoma harboring the BRAF(V600E) mutation and improve both progressionfree and overall survival [7, 8]. Complete responses to vemurafenib are only observed in 5% of patients, as a consequence of intrinsic BRAF-I resistance[7, 9]

Methods

Results

Conclusion