Vemurafenib Cooperates with HPV to Promote Initiation of Cutaneous Tumors

Matthew Holderfield,Dylan Daniel,Lise Boussemart,Frank Mccormick,Majid Ghoddusi,Ludovic Lacroix,Nancy Pryer,Stephan Vagner,Gorana Tomasic,Michel Favre,Lisa Lomovasky,Caroline Robert,Ben Weisburd,Darrin Stuart,Edward Lorenzana

doi:10.1158/0008-5472.can-13-1065-t

Matthew Holderfield, Dylan Daniel + Show 13 more

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https://doi.org/10.1158/0008-5472.can-13-1065-t

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Abstract

Treatment with RAF inhibitors such as vemurafenib causes the development of cutaneous squamous cell carcinomas (cSCC) or keratoacanthomas as a side effect in 18% to 30% of patients. It is known that RAF inhibitors activate the mitogen-activated protein kinase (MAPK) pathway and stimulate growth of RAS-mutated cells, possibly accounting for up to 60% of cSCC or keratoacanthoma lesions with RAS mutations, but other contributing events are obscure. To identify such events, we evaluated tumors from patients treated with vemurafenib for the presence of human papilloma virus (HPV) DNA and identified 13% to be positive. Using a transgenic murine model of HPV-driven cSCC (K14-HPV16 mice), we conducted a functional test to determine whether administration of RAF inhibitors could promote cSCC in HPV-infected tissues. Vemurafenib treatment elevated MAPK markers and increased cSCC incidence from 22% to 70% in this model. Furthermore, 55% of the cSCCs arising in vemurafenib-treated mice exhibited a wild-type Ras genotype, consistent with the frequency observed in human patients. Our results argue that HPV cooperates with vemurafenib to promote tumorigenesis, in either the presence or absence of RAS mutations.

Highlights

50% of melanomas harbor a single activating Valine to Glutamic acid point mutation of the BRAF kinase [1]
Because transcriptional targets of the mitogen—activated protein kinase (MAPK) pathway are often a more sensitive marker for extracellular signal—regulated kinase (ERK) activity [21], Dusp6 mRNA levels were measured by quantitative PCR (qPCR) and were found to be increased 3-fold in skin from vemurafenib-treated mice (Fig. 1B), demonstrating that vemurafenib paradoxically activates the MAPK pathway in genetically wild-type mouse epidermis, but is insufficient for cutaneous squamous cell carcinomas (cSCC) tumorigenesis
Vemurafenib effectively inhibited ERK phosphorylation and proliferation of BRAF-mutated cells, ERK phosphorylation was stimulated and proliferation increased in RAS/RAF wild-type cells, though to markedly higher levels in the KRAS-mutated cell (Fig. 1C)

Summary

Introduction

50% of melanomas harbor a single activating Valine to Glutamic acid point mutation of the BRAF kinase [1]. Constitutive BRAF activation leads to phosphorylation of the downstream effectors MAP–ERK kinase (MEK), extracellular signal—regulated kinase (ERK), which in turn activates transcription factors that promote proliferation of cancer cells. Preclinical data demonstrate that RAF inhibitors paradoxically stimulate ERK phosphorylation in RAS-mutated cancer cells [6,7,8,9] through allosteric and catalytic mechanisms that relieve the auto-inhibition of wild-type RAF kinase [10]

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