OR12-2 Inhibition of Basal and ACTH-stimulated Cortisol Secretion in Humans Using an Oral Nonpeptide ACTH Antagonist (CRN04894)

CRN04894 is a potent orally bioavailable MC2R (adrenal cortex specific ACTH receptor) antagonist (Kb=0.34 nM) that is >1000-fold selective for MC2R over other melanocortin receptor subtypes. In rats receiving continuous administration of ACTH via subcutaneously implanted osmotic pumps, oral administration of CRN04894 over 7 days has previously been shown to result in dose-dependent suppression of basal and ACTH stimulated corticosterone levels. This compound is in clinical development for the treatment of diseases of ACTH excess including congenital adrenal hyperplasia (CAH) and Cushing's Disease. We report initial results from a randomized double-blinded, placebo-controlled single ascending dose study evaluating the safety, pharmacokinetics and pharmacodynamics of CRN04894 in 39 healthy volunteers. After an overnight fast, single doses of CRN04894 were administered at approximately 8 am, 2 hours prior to an IV bolus of ACTH 1-24 (cosyntropin). Serial cortisol over 600 minutes and pharmacokinetics over 168 hours post CRN04894 dose were measured. Two different challenge doses of ACTH 1-24 were studied: 250 μg (supra-pharmacological) and 1 μg (comparable to ACTH concentrations encountered in CAH and Cushing's Disease). CRN04894 was rapidly orally absorbed (median tmax 0.5-1.5 hour), and demonstrated a dose dependent increase in systemic exposure, with an apparent terminal elimination t1/2 of approximately 20 hours. Unstimulated (basal) cortisol measured 2 hours after CRN04894 administration fell in a dose-dependent manner, resulting in reduction near the theoretical maximum with the 80 mg dose cohort (-56.1% [SEM 4.0%, n=12] vs +17.4% in placebo [SEM=18.1%, n=9]). Dose-dependent cortisol suppression following a supra-pharmacological ACTH-stimulated (250 μg) was also observed, with a 41% reduction in the area under the curve (AUC60-600min) post-stimulation at the 80 mg dose. Furthermore, a single dose of 80 mg of CRN04894 reduced the cortisol response (AUC15-120 min) to a disease relevant 1 μg ACTH challenge by 48%, maintaining cortisol concentrations within the normal range seen prior to dosing in a basal unstimulated state. Single doses of CRN04894 were well tolerated with no need for glucocorticoid supplementation. All adverse events (AEs) were considered mild or moderate and there were no serious AEs. The data from this single-dose, proof-of-concept study show that MC2R antagonist CRN04894 was well tolerated after oral delivery in healthy volunteers and demonstrated dose-dependent increases in exposure with lowering of basal and ACTH-stimulated cortisol secretion, including in the presence of disease relevant excess ACTH exposure. Multiple ascending dose evaluations are underway in anticipation of studies in patients with diseases of ACTH excess. Presentation: Sunday, June 12, 2022 11:15 a.m. - 11:30 a.m.