The PI3K inhibitor BKM120 has potent antitumor activity in melanoma brain metastases in vitro and in vivo.

Abstract

e20050 Background: In melanoma, the RAF-MEK-ERK and PI3K-AKT signaling pathways play a major role in melanoma progression and drug resistance. On the basis of significant improvement in overall survival, the BRAF inhibitor vemurafenib gained FDA approval for the treatment of patients with metastatic BRAFV600E mutated melanoma. However, vemurafenib appears to be less effective in melanoma brain metastases, and brain metastases are the most common cause of death in patients with metastatic melanoma. In our previous study we reported that the AKT survival pathway is hyperactivated in melanoma brain metastases. Methods: The current study aims to investigate the mechanisms of AKT hyperactivation and the antitumor activity of the PI3K inhibitor BKM120 in melanoma brain metastases in vitro and in vivo. Results: To simulate the tumor environment of brain metastases and extracerebral metastases, brain and matched extracerebral metastatic melanoma cells were stimulated by astrocyte- and fibroblast-conditioned medium, respectively. Both brain and extracerebral metastatic melanoma cells stimulated by astrocyte-conditioned medium showed higher AKT activation and invasiveness in a transwell matrigel invasion assay than cells stimulated by fibroblast-conditioned medium. The PI3K inhibitor BKM120 inhibited the phosphorylation of AKT and the growth of >10 newly isolated cell lines derived from melanoma brain metastases achieving growth inhibition rates of up to 80%. These effects did not depend on BRAF, NRAS or KIT mutation status. Furthermore, BKM120 potently induced apoptosis in brain metastatic melanoma cells and significantly inhibited the tumor growth of human brain metastatic melanoma cells in the brain of nude mice as shown by MRI scans. Conclusions: Brain-derived factors induce hyperactivation of the AKT survival pathway and promote invasiveness and drug resistance of melanoma cells in the brain. The PI3K inhibitor BKM120 inhibits activation of the AKT survival pathway and demonstrates potent antitumor activity in melanoma brain metastases in vitro and in vivo.