CX-F9, a novel RSK2 inhibitor, suppresses cutaneous melanoma cells proliferation and metastasis through regulating autophagy.

Approximately 60% of melanoma have BRAF mutation which leads to the abnormal activation of MAPK signaling pathway. Therefore, targeting these signaling pathways is particularly important for melanoma therapy. Ribosomal S6 Kinase 2 (RSK2) is a downstream target of ERK1/2 in MAPK/ERK pathway and inhibition of RSK2 suppresses the tumorigenesis and metastasis of neoplasm. We investigated whether CX-F9, a novel RSK2 inhibitor predicted by computer, inhibits the malignant phenotype of melanoma cells. In this study, we found knockdown of RSK2 expression in melanoma cells induces autophagy and inhibits its proliferation, migration and invasion. CX-F9 directly binds to RSK2 and inhibits the kinase activity. CX-F9 significantly suppressed cell proliferation, induced autophagy, apoptosis and cycle arrest, as well as inhibited migration and invasion in SK-MEL-5 and SK-MEL-28 cells. Western blotting revealed that CX-F9 declined the activation of p-CREB. Moreover, CX-F9 inhibited tumor formation and metastasis in vivo. Furthermore, CX-F9 suppressed cell proliferation, migration, invasion in BRAF inhibitor resistant melanoma cells. These findings reveal a new RSK2 inhibitor CX-F9 could significantly suppressed malignant phenotype of melanoma in vitro and in vivo, which provide a novel strategy for melanoma treatment in clinic.