Abstract 3790: Preclinical profile of LGX818: A potent and selective RAF kinase inhibitor

Selective RAF inhibitors have significant activity in patients with metastatic melanoma whose tumors express BRAF V600E . However, not all patients respond equally well to treatment and the duration of response is often limited to less than 6 months. LGX818 was developed with the hypothesis that a more potent inhibitor with excellent pharmacological properties would maximize the degree and duration of patient response. LGX818 is a highly potent RAF inhibitor with selective anti-proliferative and apoptotic activity in cells expressing BRAF V600E . In the A375 (BRAF V600E ) human melanoma cell line LGX818 suppresses phospho-ERK (EC 50 = 3 nM) leading to potent inhibition of proliferation (EC 50 = 4 nM). No significant activity was observed against a panel of 100 kinases (IC 50 > 900 nM) and LGX818 did not inhibit proliferation of > 400 cell lines expressing wild-type BRAF. Contributing to the high potency of LGX818 is the extremely slow off-rate from BRAF V600E which is not observed with other RAF inhibitors. In biochemical assays the dissociation half-life was >24 hours which translated into sustained target inhibition in cells following drug wash-out. Single dose PK/PD studies in human melanoma xenograft models (BRAF V600E ) indicated that LGX818 treatment at oral doses as low as 6 mg/kg resulted in strong (75%) and sustained (>24 hours) decrease in phospho-MEK, even following clearance of drug from circulation. Decreases in phospho-ERK were consistent with phospho-MEK but markers of downstream transcriptional output (DUSP6 and SPRY4) appeared to provide a more sensitive measure of pathway activation. LGX818 induced tumor regression in multiple BRAF mutant human tumor xenograft models grown in immune compromised mice and rats at doses as low as 1 mg/kg. Consistent with the in vitro data, LGX818 was inactive against BRAF wild-type tumors at doses up to 300 mg/kg bid, with good tolerability and linear increase in exposure. Efficacy was also achieved in a more disease-relevant spontaneous metastatic melanoma and a model of melanoma brain metastasis. LGX818 is a potent and selective RAF kinase inhibitor with unique biochemical properties that contribute to an excellent pharmacological profile. A Phase I clinical trial in patients with BRAF mutant tumors is ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3790. doi:1538-7445.AM2012-3790