Antitumor activity of the MEK inhibitor TAK-733 against melanoma cell lines and patient-derived tumor explants

The goal of this study was to investigate the activity of the selective MEK1/2 inhibitor TAK-733 in both melanoma cell lines and patient-derived melanoma xenograft models. In vitro cell proliferation assays using the sulforhodamine B assay were conducted to determine TAK-733 potency and melanoma responsiveness. In vivo murine modeling with eleven patientderived melanoma explants evaluated daily dosing of TAK-733 at 25 or 10 mg/kg. Immunoblotting was performed to evaluate ontarget activity and downstream inhibition by TAK-733 in both in vitro and in vivo studies. TAK-733 demonstrated broad activity in most melanoma cell lines with relative resistance observed at IC 50 > 0.1 mmol/L in vitro. TAK-733 also exhibited activity in 10 out of 11 patient-derived explants with tumor growth inhibition ranging from 0% to 100% ( P < 0.001-0.03). Interestingly, BRAF^V600E and NRAS mutational status did not correlate with responsiveness to TAK-733. Pharmacodynamically, pERK was suppressed in sensitive cell lines and tumor explants, confirming TAK-733-mediated inhibition of MEK1/2, although the demonstration of similar effects in the relatively resistant cell lines and tumor explants suggests that escape pathways are contributing to melanoma survival and proliferation. These data demonstrate that TAK-733 exhibits robust tumor growth inhibition and regression against human melanoma cell lines and patient-derived xenograft models, suggesting that further clinical development in melanoma is of scienti fic interest. Particularly interesting is the activity in BRAF wild-type models, where current approved therapy such as vemurafenib has been reported not to be active.