The purpose of this study is to evaluate the dose-related safety, tolerability, pharmacokinetics (PK) and pharmacological effects (PD) of CORT125134 and its active metabolite CORT125201 after single and multiple ascending oral doses of CORT125134 in healthy participants.

This is a 3-part, single-center study of single and multiple ascending doses of CORT125134 in healthy participants.

Part I is a single dose study. Initially, participants will be enrolled sequentially into 1 of up to 6 cohorts, each containing 10 participants, in a double-blind, randomized, placebo-controlled assessment of single-ascending doses (SAD) of CORT125134. Within each cohort, 8 participants will be randomly assigned to receive a single dose of CORT125134, and 2 participants will be randomly assigned to receive a single dose of matching placebo. Thereafter, Cohort 7 will be a food-effect cohort, in which all 8 participants will receive a single dose of CORT125134 after a high-fat breakfast (open label). Cohorts 8 and 9 will be pharmacological effect cohorts, in each of which 10 participants will receive a challenge agent (prednisone, 25 mg) alone on Day -19; with an active comparator (mifepristone, 600 mg) on Day -12, and with CORT125134 on Day 1 in an open-label single sequence crossover design. Pharmacological effects will be explored by measuring effects on peripheral blood eosinophil, lymphocyte and neutrophil counts, serum osteocalcin, assay of messenger ribonucleic acid (mRNA) expression of FK506 Binding Protein 5 (FKBP5) and Glucocorticoid-induced Leucine Zipper (GILZ) in whole blood (proof of pharmacological effect Cohort 8) and by measuring effects on oral glucose tolerance (proof of concept Cohort 9).

Part 2 and 3 will be double-blind, randomized, placebo-controlled assessments of multiple oral ascending doses (MAD) of CORT125134. Participants will be enrolled sequentially into 1 of up to 4 cohorts (Cohorts 10-13), each containing 12 participants. Within each cohort, 9 participants will be randomly assigned to receive CORT125134 and 3 participants to receive matching placebo daily for 14 days (Days 1-14). The effects of CORT125134 on response to prednisone challenge will be additionally explored in Cohorts 12 and 13 in a single sequence crossover, with prednisone being given alone on Day -5 and in combination with CORT125134 or placebo on Day 14.

Throughout the study, routine safety tests and assessments of PK (CORT125134 and CORT125201) will be performed, and changes in serum cortisol and plasma adrenocorticotrophic hormone (ACTH) measured.

Inclusion Criteria:

• Provide written informed consent
• Weight <= 102 kilogram (kg); body mass index (BMI) 18-30 kg/meter squared
• Morning serum cortisol in reference range
• Willing and able to communicate, participate in the whole study and to abide by study restrictions including use of contraception

Exclusion Criteria:

• Participation in any clinical research study, received treatment with any investigational drug or device, or donated blood within the previous 3 months
• Has a history of alcoholism, substance abuse, or drug abuse within 1 year; positive screen for alcohol or drugs of abuse
• Current smokers, smoked and/or used tobacco and/or nicotine-containing products within 6 months, or positive screen for carbon monoxide
• Females of childbearing potential, pregnant or breastfeeding, and/or with a positive pregnancy test
• Has a condition that could be aggravated by glucocorticoid blockade or activation
• Has clinically relevant abnormal findings on vital signs, physical examination, laboratory screening tests, or 12-lead electrocardiogram (ECG)
• Has history of clinically significant cardiovascular, renal, hepatic, endocrine, metabolic, chronic respiratory, gastrointestinal or neurological disease
• Has used systemic glucocorticoids within 12 months