Design, synthesis and biological evaluation of bis-aryl ureas and amides based on 2-amino-3-purinylpyridine scaffold as DFG-out B-Raf kinase inhibitors.

By combining the scaffolds of UI-125 and Sorafenib, a series of bis-aryl ureas and amides based on 2-amino-3-purinylpyridine moiety were designed and synthesized as novel DFG-out B-Raf(V600E) inhibitors. Among them, 20c-e, 20g and 21h displayed potent antiproliferative activities against melanoma A375 (B-Raf(V600E)) cell lines with IC50 values of 3.190, 2.276, 1.856, 1.632 μM and 1.839 μM, respectively, comparable with the positive control Vemurafenib (IC50 = 3.32 μM). Selected compounds were tested for the ERK inhibition in human melanoma A375 (B-Raf(V600E)) and SK-MEL-2 (B-Raf(WT)) cell lines by Western blot. The results revealed that our compounds inhibited the proliferation of melanoma A375 cells (B-Raf(V600E)) through ERK pathway, without paradoxical activation of ERK in melanoma SK-MEL-2 cells (B-Raf(WT)). Eventually, 20g and 21h were selected to confirm their inhibitory effects on tumor growth in A375 xenograft models in mice. Compound 20g exhibited equivalent antitumor efficacy in vivo (T/C = 44.37%), compared to Sorafenib (T/C = 37.35%), by 23-day repetitive administration of a single dose of 50 mg/kg without significant body weight loss.