Combination of pan-RAF and MEK inhibitors in NRAS mutant melanoma

Abstract

BackgroundApproximately 20% of melanomas contain a mutation in NRAS. However no direct inhibitor of NRAS is available. One of the main signaling pathways downstream of NRAS is the MAPK pathway. In this study we investigated the possibility of blocking oncogenic signaling of NRAS by inhibiting two signaling points in the MAPK pathway.MethodsFourteen NRAS mutated human melanoma cell lines were treated with a pan-RAF inhibitor (PRi, Amgen Compd A), a MEK inhibitor (MEKi, trametinib) or their combination and the effects on proliferation, cell cycle progression, apoptosis, transcription profile and signaling of the cells were investigated.ResultsThe majority of the cell lines showed a significant growth inhibition, with high levels of synergism of the PRi and MEKi combination. Sensitive cell lines showed induction of apoptosis by the combination treatment and there was a correlation between p-MEK levels and synergistic effect of the combination treatment. Proliferation of sensitive cell lines was blocked by the inhibition of the MAPK pathway, which also blocked expression of cyclin D1. However, in resistant cell lines, proliferation was blocked by combined inhibition of the MAPK pathway and cyclin D3, which is not regulated by the MAPK pathway. Resistant cell lines also showed higher levels of p-GSK3β and less perturbation of the apoptotic profile upon the treatment in comparison with the sensitive cell lines.ConclusionsThe combination of PRi + MEKi can be an effective regimen for blocking proliferation of NRAS mutant melanomas when there is higher activity of the MAPK pathway and dependence of proliferation and survival on this pathway.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0293-5) contains supplementary material, which is available to authorized users.

Overcoming resistance to BRAF inhibitors

“…While in the post-sorafenib era the main goal had been to gain specificity towards mutated BRAF lately some effort has been put towards the development of small molecules directed to both BRAF and CRAF and capable to interfere with isoform hetero-and homo-dimerization thus preventing paradoxical activation of CRAF by BRAF inhibitors (72,(105)(106)(107)(108)(109)(110). While this approach has provided promising results in pre-clinical models, their efficacy and the risk of adverse events will have to be tested in early phase trials (NCT02607813, www.clinicaltrials.gov).…”

Targeting RAS -mutant Cancers: Is ERK the Key?

“…Also, in KRAS -mutant tumor cells, unbiased shRNA screening showed that genetic ablation of CRAF enhanced MEK inhibitor response [44,70,45] . And the combination of a pan-RAF inhibitor (PRi, Amgen Compd A) with trametinib showed a synergistic effect on the growth inhibition of NRAS -mutant melanoma cells [71] .…”

Searching for the Chokehold of NRAS Mutant Melanoma

“…In preclinical studies, targeting of MEK and ERK in combination potently suppresses levels of phospho-ERK and induces apoptosis in NRAS mutant cells (Morris et al, 2013; Rebecca et al, 2014). Another approach for vertical pathway inhibition uses combined pan-RAF and MEK inhibition (Atefi et al, 2015). Similarly, single compound, dual RAF/MEK inhibitors are currently investigated for their potential therapeutic activity in RAS mutated malignancies, including melanoma (Wada et al, 2014).…”