Over half of cutaneous melanoma tumors have BRAFV600E/K mutations.,Acquired resistance to BRAF inhibitors (BRAFi) remains a major hurdle in attaining durable therapeutic responses.,In this study we demonstrate that approximately 50-60% of melanoma cell lines with vemurafenib resistance acquired in vitro show activation of RhoA family GTPases.,In BRAFi-resistant melanoma cell lines and tumors, activation of RhoA is correlated with decreased expression of melanocyte lineage genes.,Using a machine learning approach, we built gene expression-based models to predict drug sensitivity for 265 common anti-cancer compounds.,We then projected these signatures onto the collection of TCGA cutaneous melanoma and found that poorly differentiated tumors were predicted to have increased sensitivity to multiple Rho kinase (ROCK) inhibitors.,Two transcriptional effectors downstream of Rho, MRTF and YAP1, are activated in the RhoHigh BRAFi-resistant cell lines, and resistant cells are more sensitive to inhibition of these transcriptional mechanisms.,Taken together, these results support the concept of targeting Rho-regulated gene transcription pathways as a promising therapeutic approach to restore sensitivity to BRAFi-resistant tumors or as a combination therapy to prevent the onset of drug resistance.
The development of cutaneous melanoma is influenced by genetic factors, including BRAF mutations and environmental factors, such as ultraviolet exposure.,Its progression has been also associated with the involvement of several tumour microenvironmental molecules.,Among these, nuclear factor-κB (NF-κB) has been indicated as a key player of osteopontin (OPN) and matrix metalloproteinase-9 (MMP-9) activation.,However, whether NF-κB plays a role in the development and progression of melanoma in association with the OPN/MMP-9 axis according to the BRAFV600E mutation status has not been investigated in detail to date.,Thus, in the present study, in order to shed light on this matter, 148 patients with melanoma and 53 healthy donors were recruited for the analysis of OPN, MMP-9 and NF-κB.,Significantly higher circulating levels of OPN and MMP-9 were observed in the patients with melanoma when compared to the healthy donors.,Similar data were obtained for NF-κB p65 activity.,The OPN levels did not differ significantly between melanomas with or without BRAFV600E mutation.,However, as regards NF-κB and MMP-9, significant differences were observed between the melanomas with or without BRAFV600E mutation.,To determine whether NF-κB inhibition is associated with a decrease in the levels of OPN and MMP-9, peripheral blood mononuclear cells from 29 patients with melanoma were treated with the NF-κB inhibitor, dehydroxymethylepoxyquinomycin (DHMEQ), with or without OPN.,As expected, the inhibition of NF-κB induced a marked decrease in both the OPN and MMP-9 levels.,Furthermore, the decrease in MMP-9 levels was higher among melanomas harbouring the BRAFV600E mutation.,Overall, our data suggest that the activation of MMP-9 is associated with the BRAFV600E mutation status.,Furthermore, such an activation is mediated by NF-κB, suggesting its role as therapeutic target in patients with melanoma.