Dasatinib Stimulates Its Own Mechanism of Resistance by Activating a CRTC3/MITF/Bcl-2 Pathway in Melanoma with Mutant or Amplified c-Kit.

ABSTRACT

Amplification or activating mutations of c-Kit are a frequent oncogenic alteration, which occurs commonly in acral and mucosal melanoma. Among c-Kit inhibitors, dasatinib is the most active due to its ability to bind both active and inactive conformations of the receptor. However, its use as a single agent in melanoma showed limited clinical benefit. We first found that sensitivity to dasatinib is restricted to melanoma cell lines harboring c-Kit alteration but, unexpectedly, we observed lower effect at higher concentrations that can readily be found in patient blood. We then investigated relevant pathway alterations and found complete inhibition of MAPK and PI3K/AKT pathways but an increase in MITF and its downstream target Bcl-2 through CRTC3 pathway, which turn on the CREB regulated transcription of MITF. More importantly, dasatinib upregulates MITF and Bcl-2 through SIK2 inhibition revealed by CRTC3 reduced phosphorylation, CREB transcription activation of MITF, MITF transcription activation of Bcl-2 as well as pigmentation. Furthermore, overexpression of MITF renders melanoma cells resistant to all dasatinib concentrations. Selective Bcl-2 inhibition by ABT-199 or Bcl-2 knockout restores the sensitivity of melanoma cells to dasatinib, validating the involvement of MITF and Bcl-2 axis in the resistance of melanoma to dasatinib. In conclusion, we showed for the first time that dasatinib in melanoma stimulates its proper mechanism of resistance, independently of MAPK and PI3K/AKT pathways reactivation commonly associated to secondary c-Kit mutations, but through CRTC3/MITF/Bcl-2 pathway activation at clinically relevant doses which may explain the weak clinical benefit of dasatinib in patients with melanoma. IMPLICATIONS Dasatinib stimulates its proper mechanism of resistance through CRTC3/MITF/Bcl-2 pathway, which may explain its modest clinical efficiency in patients with melanoma.