ERBB activation modulates sensitivity to MEK1/2 inhibition in a subset of driver-negative melanoma.

Katherine E Hutchinson,Mark Kris,Pengcheng Lu,Violeta Sanchez,Adam S Johnson,Jeffrey A Sosman,William Pao,Mark C Kelley,Maria Kuba,Xi Chen,Zhongming Zhao,Douglas B Johnson,Qingguo Wang,Michael F Berger

doi:10.18632/oncotarget.4255

Abstract

Melanomas are characterized by activating "driver" mutations in BRAF, NRAS, KIT, GNAQ, and GNA11. Resultant mitogen-activated protein kinase (MAPK) pathway signaling makes some melanomas susceptible to BRAF (BRAF V600 mutations), MEK1/2 (BRAF V600, L597, fusions; NRAS mutations), or other kinase inhibitors (KIT), respectively. Among driver-negative ("pan-negative") patients, an unexplained heterogeneity of response to MEK1/2 inhibitors has been observed. Analysis of 16 pan-negative melanoma cell lines revealed that 8 (50%; termed Class I) are sensitive to the MEK1/2 inhibitor, trametinib, similar to BRAF V600E melanomas. A second set (termed Class II) display reduced trametinib sensitivity, paradoxical activation of MEK1/2 and basal activation of ERBBs 1, 2, and 3 (4 lines, 25%). In 3 of these lines, PI3K/AKT and MAPK pathway signaling is abrogated using the ERBB inhibitor, afatinib, and proliferation is even further reduced upon the addition of trametinib. A potential mechanism of ERBB activation in Class II melanomas is minimal expression of the ERK1/2 phosphatase, DUSP4, as ectopic restoration of DUSP4 attenuated ERBB signaling through potential modulation of the ERBB ligand, amphiregulin (AREG). Consistent with these data, immunohistochemical analysis of patient melanomas revealed a trend towards lower overall DUSP4 expression in pan-negative versus BRAF- and NRAS-mutant tumors. This study is the first to demonstrate that differential ERBB activity in pan-negative melanoma may modulate sensitivity to clinically-available MEK1/2 inhibitors and provides rationale for the use of ERBB inhibitors, potentially in combination with MEK1/2 inhibitors, in subsets of this disease.

Highlights

Malignant melanoma is comprised of molecular subsets characterized by constitutively activating “driver” mutations in the serine-threonine kinase BRAF, the GTPase NRAS (G12, G13, and Q61), the receptor tyrosine kinase kinase inhibitors (KIT) (W557, V559, L576, K642, and D816), and the Gα GTPases www.impactjournals.com/oncotargetGNAQ (Q209) and GNA11 (Q209) [1,2,3,4,5]
To determine potential differences in the sensitivity of pannegative melanomas to MEK1/2 inhibition, we treated an initial collection of six SNaPshot pan-negative melanoma cell lines (Supplementary Table S3) with the clinicallyavailable MEK1/2 inhibitor, trametinib, and calculated the average IC50 for each in comparison to a well-described BRAF V600E-mutant melanoma line, SK-Mel-28
When we investigated mitogen-activated protein kinase (MAPK) pathway signaling in these six cell lines following treatment with trametinib, the lines less sensitive to trametinib displayed paradoxical activation of MEK1/2 (Figure 1B and Supplementary Figure S1)

Summary

Introduction

Malignant melanoma is comprised of molecular subsets characterized by constitutively activating “driver” mutations in the serine-threonine kinase BRAF (codon V600), the GTPase NRAS (G12, G13, and Q61), the receptor tyrosine kinase KIT (W557, V559, L576, K642, and D816), and the Gα GTPases www.impactjournals.com/oncotargetGNAQ (Q209) and GNA11 (Q209) [1,2,3,4,5]. Despite the exciting advances in targeted treatment for melanoma, up to one-third of tumors express none of these driver mutations, called “pan-negative” Because they have no identifiable drug target, treatment options for these patients are extremely limited. In melanomas previously considered pannegative for common driver mutations, we identified non-V600 BRAF mutations at codons L597 and K601 [21] and BRAF fusions [22] Both alterations activate the MAPK pathway and the induced signaling confers sensitivity to MEK1/2 inhibition. As a result of these studies, MEK1/2 inhibitors are being evaluated for use in the BRAF non-V600-mutant and BRAF fusion subsets through an ongoing, multicenter Phase II clinical trial (NCT02296112) Taken together, these data suggest that constitutive activation of the MAPK pathway is a critical factor in the pathogenesis of most melanomas

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Conclusion