Avapritinib

Avapritinib (BLU-285) is a potent and highly selective inhibitor of mutant KIT and PDGFRα with IC50 of 0.6, 0.27 and 0.24 nM for KIT del557-558, KIT D816V and PDGFRA D842V, respectively; displays weak inhibition against WT KIT with IC50 of 73 nM, >150-fold more potent on KIT D816V than several important kinase antitargets such as VEGFR2, SRC and FLT3; inhibits other well-characterized disease-driving KIT mutants both in vitro and in vivo in preclinical models, demonstrates marked activity in patients with diseases associated with KIT and PDGFRA (GIST) activation loop mutations.Gastric Cancer Phase 1 Clinical(In Vitro):Avapritinib (BLU-285) has demonstrated biochemical in vitro activity on the KIT exon 17 mutant enzyme, KIT D816V (IC50=0.27 nM). Cellular activity of Avapritinib on KIT D816 mutants is measured by autophosphorylation in the human mast cell leukemia cell line HMC1.2, and the P815 mouse mastocytoma cell line with IC50=4 and 22 nM, respectively. In Kasumi-1 cells, a t(8;21)-positive AML cell line with a KIT exon 17 N822K mutation, Avapritinib potently inhibits KIT N822K mutant autophosphorylation (IC50=40 nM), downstream signaling, as well as cellular proliferation (IC50=75 nM).\n(In Vivo):In vivo Avapritinib (BLU-285) is well tolerated and has demonstrated dose dependent antitumor efficacy. Complete tumor growth inhibition and ≥75% KIT kinase inhibition is observed with 10 mg/kg once daily, oral dosing of Avapritinib in the aggressive KIT exon 17 mutant driven P815 mastocytoma model grown as a solid tumor allograft as well as in a disseminated model of disease. Disease burden, measured by whole body luciferase imaging (photons/second/mm2), increases 86-fold in the vehicle control animals over the 24 day dosing period with widespread disease detectable in both femurs, the pelvis and circulating in peripheral blood. Avapritinib at both doses (10 or 30 mg/kg orally, once daily) results in a marked reduction of disease burden throughout the study. Avapritinib at either 10 or 30 mg/kg results in tumor regression in all animals with disease abrogation indistinguishable from background signal measurements in several animals by the end of study. Avapritinib is also well tolerated in this in vivo model and has no adverse effects on body weight at either dose.