The preclinical pharmacokinetics of Tolinapant—A dual cIAP1/XIAP antagonist with in vivo efficacy

AT-IAP (1-{6-[(4-fluorophenyl)methyl]-3,3-dimethyl-1H,2H,3H-pyrrolo[3,2-b]pyridin-1-yl}-2-[(2R,5R)-5-methyl-2-{[(3R)-3-methylmorpholin-4-yl]methyl}piperazin-1-yl]ethan-1-one) was identified as a novel potent non-alanine small molecule dual inhibitor of cIAP1/XIAP protein. AT-IAP was assessed in preclinical species, demonstrating favorable bioavailability in rodent species and oral efficacy at 30 mg/kg in MDA-MB-231 mouse xenograft models. The major metabolic route of AT-IAP was identified to be CYP3A driven, resulting in low oral exposure in non-human primate (NHP) studies, given the comparatively high expression of equivalent CYP3A. AT-IAP metabolite identification studies determined ring opening of the morpholino or piperazine moiety. An extensive campaign of optimisation resulted in increased polarity by the addition of a hydroxymethyl, which led to the identification of tolinapant (1-(6-[(4-Fluorophenyl)methyl]-5-(hydroxymethyl)-3,3-dimethyl-1 H,2 H,3 H-pyrrolo[3,2- b]pyridin-1-yl)-2-[(2 R,5 R)-5-methyl-2-([(3R)-3-methylmorpholin-4-yl]methyl)piperazin-1-yl]ethan-1-one) with reduced CYP3A metabolism. Tolinapant showed oral bioavailability in rodents and NHP in the range 12-34% at 5 mg/kg. Non-linear pharmacokinetics in NHP were observed at oral doses in the range 5-75 mg/kg. Pharmacodynamic modulation and efficacy were demonstrated in A375 mouse xenograft models at dose ranges between 5 and 20 mg/kg. On-target engagement, as measured by reduction of cIAP 1 protein levels, was confirmed in NHP surrogate tissues and applied to target activity assessments in tolinapant phase1/2 clinical trials.