Avutometinib

Avutometinib (Ro 5126766) is a first-in-class dual MEK/RAF inhibitor that allosterically inhibits BRAF^V600E, CRAF, MEK, and BRAF (IC₅₀: 8.2, 56, 160 nM, and 190 nM, respectively). IC50 & Target:IC50: 8.2 nM (BRAF [V600E]), 56 nM (CRAF), 160 nM (MEK),190 nM (BRAF)^[1] In Vitro:Avutometinib (Ro 5126766) is an allosteric inhibitor that binds directly to MEK and prevents its phosphorylation by RAF through the formation of a stable RAF-MEK complex. Ro 5126766 inhibits both the phosphorylation of MEK by RAF and the activation of ERK by MEK. In cell-free MEK and RAF kinase assays, Avutometinib effectively inhibits activation of ERK2 by MEK1 with an IC₅₀ of 160 nM (SD=±0.043) and inhibits the phosphorylation of MEK1 protein by BRAF (IC₅₀=190 nM, SD=±0.003), BRAF^V600E (IC₅₀=8.2 nM, SD=±0.0015), and CRAF (IC₅₀=56 nM, SD=±0.016). Avutometinib effectively inhibits both MEK and ERK phosphorylation in a panel of human tumor cell lines including KRAS/HRAS and BRAF mutant cell lines and KRAS/HRAS and BRAF wild-type cells^[1]. In order to investigate whether the mevalonate pathway affects the sensitivity to MEK inhibitors, human breast cancer MDA-MB-231 cells harboring KRAS and BRAF mutations are treated Avutometinib, with or without statins, which inhibits HMG-CoA reductase, the rate-limiting enzyme in the mevalonate pathway. The combined treatment of Avutometinib with XU 62-320 demonstrates more significant reduction in cell growth in a dose-dependent manner than the single treatment of Avutometinib. The marked combined effects of Avutometinib at 40 nM and XU 62-320 at 0.3 μM is also confirmed on the suppression of the colony formation of the cells^[2]. In Vivo:In KRAS-mutant xenograft models, Avutometinib (Ro 5126766) inhibits growth and causes tumor regressions more effectively than another allosteric MEK inhibitor, PD0325901. Preclinical data from a series of human tumor mouse xenograft models indicates an ED₅₀ for Ro 5126766 of 0.03 to 0.23 mg/kg and an ED₉₀ of 0.15 to 1.56 mg/kg. These effective doses are associated with target trough concentrations of 17 to 133 ng/L and 87 to 901 ng/mL, respectively. ^[1]. In this experiment, Avutometinib or PD0325901 is administrated at their maximum tolerated dose (MTD) in the HCT116 model (1.5 and 25 mg/kg, respectively). These doses inhibit pERK and ERK signaling output at similar degrees in the tumors from the drug-treated mice at 4 hours from the first drug administration. Moreover, in HCT116 models, the ED₅₀ for Avutometinib and PD0325901 are 0.056 and 0.80 mg/kg, respectively. Therefore, the doses used for this experiment are 26.8- and 31.3-fold higher doses than the 50% effective doses, respectively. Daily oral administration of either drug causes significant tumor regression of each these tumors. However, whereas inhibition of tumor growth is maintained for the entire 28-day treatment period in Avutometinib-treated mice, tumor models receiving PD0325901 become refractory after 10 days of treatment^[3].