Targeting the hedgehog transcription factors GLI1 and GLI2 restores sensitivity to vemurafenib-resistant human melanoma cells

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Faiao-Flores, F. ; Alves-Fernandes, D. K. ; Pennacchi, P. C. ; Sandri, S. ; Vicente, A. L. S. A. ; Scapulatempo-Neto, C. ; Vazquez, V. L. ; Reis, R. M. ; Chauhan, J. ; Goding, C. R. ; Smalley, K. S. ; Maria-Engler, S. S.

• Document type: Journal article
• Source: Oncogene; v. 36, n. 13, p. 1849-1861, MAR 30 2017.
• Web of Science Citations: 27

Abstract

BRAF inhibitor (BRAFi) therapy for melanoma patients harboring the V600E mutation is initially highly effective, but almost all patients relapse within a few months. Understanding the molecular mechanisms underpinning BRAFi-based therapy is therefore an important issue. Here we identified a previously unsuspected mechanism of BRAFi resistance driven by elevated Hedgehog (Hh) pathway activation that is observed in a cohort of melanoma patients after vemurafenib treatment. Specifically, we demonstrate that melanoma cell lines, with acquired in vitro-induced vemurafenib resistance, show increased levels of glioma-associated oncogene homolog 1 and 2 (GLI1/GLI2) compared with naive cells. We also observed these findings in clinical melanoma specimens. Moreover, the increased expression of the transcription factors GLI1/GLI2 was independent of canonical Hh signaling and was instead correlated with the noncanonical Hh pathway, involving TGF beta/SMAD (transforming growth factor-beta/Sma- and Mad-related family) signaling. Knockdown of GLI1 and GLI2 restored sensitivity to vemurafenib-resistant cells, an effect associated with both growth arrest and senescence. Treatment of vemurafenib-resistant cells with the GLI1/GLI2 inhibitor Gant61 led to decreased invasion of the melanoma cells in a three-dimensional skin reconstruct model and was associated with a decrease in metalloproteinase (MMP2/MMP9) expression and microphthalmia transcription factor upregulation. Gant61 monotherapy did not alter the drug sensitivity of naive cells, but could reverse the resistance of melanoma cells chronically treated with vemurafenib. We further noted that alternating dosing schedules of Gant61 and vemurafenib prevented the onset of BRAFi resistance, suggesting that this could be a potential therapeutic strategy for the prevention of therapeutic escape. Our results suggest that targeting the Hh pathway in BRAFi-resistant melanoma may represent a viable therapeutic strategy to restore vemurafenib sensitivity, reducing or even inhibiting the acquired chemoresistance in melanoma patients. (AU)

• FAPESP's process: 12/04194-1 - The biologic and clinical characterization of the RAS-MAPK and PI3K-AKT pathways in cutaneous and mucosal melanomas among Brazilians and comparison with patients of the United States of America
• Grantee: Vinicius de Lima Vazquez
• Support Opportunities: Regular Research Grants
• FAPESP's process: 15/10821-7 - Hsp90 inhibition effects in therapeutic escape pathways in BRAF-mutant melanoma
• Grantee: Fernanda Faião Flores
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 13/05172-4 - Impact of epithelial-mesenchymal transition proteins in vemurafenib chemoresistant melanoma
• Grantee: Fernanda Faião Flores
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 14/24400-0 - In vitro models for pre clinical studies of melanoma Chemoresistant
• Grantee: Silvya Stuchi Maria-Engler
• Support Opportunities: Regular Research Grants