[1806] MEK Inhibition Induces Differential Mechanisms of Resistance in Thyroid and Melanoma BRAFV600E Cell Lines

Emma R Dorris, Mohsen Alhashemi, Roisin Dunne, Paul Smyth, John J O'Leary, Orla Sheils. Trinity College Dublin, Dublin, Ireland

Background: Oncogenic mutations in BRAF are common in melanoma and thyroid carcinoma and drive constitutive activation of the MAPK (RAS/RAF/MEK/ERK) pathway. Molecularly targeted therapies of this pathway improves survival compared to chemotherapy; however, responses tend to be short-lived as resistance invariably occurs. In this study the molecular pathology of resistance to therapeutic MEK inhibition in BRAFV600E melanoma and thyroid cells was investigated.
Design: Cell line models of melanoma and thyroid carcinoma, +/- BRAFV600E activating mutation, were treated with the MEK inhibitor PD0325901 and resistant cells were harvested. Resistant and treatment naive samples were assayed for relative gene and protein expression of key members of the MAPK pathway and stemness-markers. Global microRNA expression profiling of naive and resistant cells was performed via next generation sequencing.
Results: Members of the MIR302/373/374/520 family of embryonic stem cell specific cell cycle regulating (ESCC) microRNAs were identified as differentially expressed between resistant BRAFV600E melanoma and thyroid cell lines. Upregulated expression of gene and protein stemness markers, upregulated expression of MAPK pathway genes and downregulation of the ESCC MIR302 cluster in BRAFV600E melanoma indicated an increased stem-like phenotype in resistant BRAFV600E melanoma. Conversely, downregulated expression of gene and protein stemness markers, downregulated expression of MAPK pathway genes, upregulation of the ESCC MIR520 cluster, reeexpression of cell surface receptors, and induced differentiation-associated morphology in resistant BRAFV600E indicate a differentiated phenotype associated with MEK inhibitor resistance in BRAFV600E thyroid cells.
Conclusions: The differential patterns of resistance observed between BRAFV600E melanoma and thyroid cell lines may reflect tissue type or de novo differentiation, but could have significant impact on the response of primary and metastatic cells to MEK inhibitor treatment. This study provides a basis for the investigation of the cellular differentiation/self-renewal access and its role in resistance to MEK inhibition.
Category: Special Category - Pan-genomic/Pan-proteomic approaches to Cancer

Tuesday, March 5, 2013 9:30 AM

Poster Session III # 236, Tuesday Morning


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