DNA repair-based classification of melanoma cell lines reveals an effect of mutations in BRAF and NRAS driver genes on DNA repair capacity

Melanoma, the most serious form of skin cancer, frequently involves the dysregulation of key signaling pathways. Treatment strategies presently target the MAPK/ERK pathway, which is overactive in melanomas due in part to BRAF and NRAS mutations, and involve inhibitors against mutated BRAF (vemurafenib or dabrafenib) or MEK kinases (cobimetinib or trametinib), or a combination of the two. Using an established biochip technology, we assessed base excision repair (BER) and nucleotide excision repair (NER) activities in a collection of BRAF mutated (A-375, Colo 829, HT-144, Malme-3M, SK-mel5, SK-mel24 and SK-mel28) and NRAS mutated (M18, MZ2 and SK-mel2) melanoma cell lines, as well as wild-type controls (A7, CHL-1). We evaluated both basal activities (i.e., without treatment) and repair capacities after treatment with vemurafenib or cobimetinib alone, or in combination. Our results indicate that globally the DNA repair capacity of the cell lines was determined by the mutation status of the BRAF and NRAS genes, indicating that the MAPK pathway participates in the regulation of both BER and NER. Treatment of BRAF mutated melanoma cells with vemurafenib alone or the vemurafenib/cobimetinib combination, but not cobimetinib alone, led to reduced DNA repair capacity in about 60% of the BRAF mutated samples, indicating that signaling pathway inhibition can alter DNA repair activity. Upregulation of some DNA repair activities was also observed in several of the treated samples, suggesting activation of compensatory signaling pathways upon treatment. The data collectively indicate that mutations in the BRAF and NRAS genes exert distinct regulatory effects on the excision/synthesis steps of the BER and NER pathways and that targeted pharmacological inactivation of the signaling mechanism can translate into specific consequences in DNA repair capacity. The heterogeneity of the responses reported herein could help define subtypes of melanoma that are associated with resistance to targeted therapies.