A proliferative melanoma cell phenotype is responsive to RAF/MEK inhibition independent of BRAF mutation status

Abstract

Oncogenic mutations within the MAPK pathway are frequent in melanoma, and targeting of MAPK signaling has yielded spectacular responses in a significant number of patients that last for several months before relapsing. We investigated the effects of two different inhibitors of MAPK signaling in proliferative and invasive melanoma cell cultures with various mutations in the MAPK pathway. Proliferative melanoma cells were more susceptible to pathway inhibition than invasive phenotype cells, irrespective of BRAF mutation status, while invasive phenotype cell response was dependent on BRAF mutation status. Critically, MAPK pathway inhibition of proliferative phenotype cells resulted in acquisition of invasive phenotype characteristics. These results show that melanoma cell phenotype is an important factor in MAPK pathway inhibition response. This suggests that while current therapeutic strategies target proliferative melanoma cells, future approaches should also account for the invasive phenotype population.

Phenotype Switching: Tumor Cell Plasticity as a Resistance Mechanism and Target for Therapy

“…In vitro-acquired data show the same trendthe invasive phenotype can be linked to both intrinsic and acquired resistance to BRAF or MEK inhibitors (13,15). Even more striking, proliferative melanoma cells can adopt invasive characteristics upon MAPK inhibition (16), indicating that targeted therapy may actually promote phenotype switching, potentially resulting in metastasis. This hypothesis is supported by the discovery that BRAF inhibition can induce invasion and metastasis in vivo when tumors are therapy resistant (17).…”

Hypoxia Contributes to Melanoma Heterogeneity by Triggering HIF1α-Dependent Phenotype Switching

“…In the hypoxic areas, which are indicated by arrowheads in a 0 , we found downregulation of the melanocytic marker MLANA (Figure 1a Figure S2 online). As proliferative phenotype cell cultures strongly express these melanocytic markers, whereas invasive phenotype cell cultures do not express them at all, their expression indicates a dedifferentiation of the melanoma cells and points toward a gain of invasive phenotype characteristics (Hoek et al, 2006(Hoek et al, , 2008aEichhoff et al, 2010Eichhoff et al, , 2011Zipser et al, 2011). These data suggest that by exposure to a hypoxic microenvironment, melanoma cells downregulate melanocytic marker genes.…”

The epigenetic modifier EZH2 controls melanoma growth and metastasis through silencing of distinct tumour suppressors

“…Human melanoma cell cultures were characterized before 43 , XB2 and Melan-a cell lines were previously described 63 , and HEK293T, B16-F1 and B16-F10 cell lines were purchased (ATCC). All cells (including primary RIM cells) were cultured in growth medium, which was RPMI 1640 supplemented with 10% FCS (16140, Life Technologies), 4 mM L-Glutamine (25030, Life Technologies), penicillin-streptomycin (15070, Life Technologies) and Fungizone Antimycotic (15290, Life Technologies) as previously specified 14,43 .…”

“…Human biopsies were isolated and genotyped as described 43 . Usage of naevus and melanoma biopsies as well as melanoma-derived cell cultures was approved by the official ethical authorities of Canton of Zurich, Switzerland.…”

“…6). To address the relevance of these findings for melanoma growth, we first blocked EZH2 activity in human melanoma cell cultures 43 , either by RNA interference-mediated silencing (RNAi) or by chemical inhibition using GSK503. In agreement with our in vivo findings, RNAi effectively reduced EZH2, while GSK503 application did not affect EZH2 levels.…”