Treatment for Endogenous Cushing's Syndrome

This is an open label, single arm study with a Screening Phase, a Dose Titration Phase, a 6-month Maintenance Phase, and a 6-month Extended Evaluation Phase designed to assess efficacy, safety, tolerability, and PK of COR-003 in subjects with endogenous CS. Following an initial screening and washout period, as applicable, this study will be conducted in three treatment phases as follows: * Dose Titration Phase: approximately 2 to 21 weeks to achieve an effective and tolerable maximum dose (the Therapeutic Dose). Dose titration will occur in increments of 150 mg with a starting dose of 150 mg twice daily (BID) over a period of approximately 2 to 21 weeks to achieve an effective and tolerable maximum dose (the Therapeutic Dose). * Maintenance Phase: 6 months of treatment at the Therapeutic Dose following the Dose Titration Phase. Once the Therapeutic Dose has been reached and confirmed from the mean of a total of four adequately collected 24 hour urine collections for UFC measurements, subjects will enter into the Maintenance Phase of the study and will be asked to return to the clinic monthly for 6 months for assessment of efficacy and safety. During the Maintenance Phase, doses may not be increased to maintain UFC levels at or below ULN of the assay unless it is confirmed that a dose increase is deemed medically necessary at the discretion of the Investigator after discussion with the Medical Monitor. Prior to the End of Maintenance Phase Visit, four complete 24 hour urine collections will be obtained and subjects may enter the Extended Evaluation Phase. * Extended Evaluation Phase: 6 months of continued treatment after the Maintenance Phase. In the 6-month Extended Evaluation Phase, subjects will return to the clinical site every 90 days (±14 days) for safety and efficacy evaluations. Efficacy will be assessed primarily by measuring mean UFC concentrations at specified times as described in the clinical protocol. Safety will be assessed primarily by physical examinations with vital sign measurements, adverse events, clinical laboratory measures, electrocardiography, and pituitary MRI. An independent Data Safety Monitoring Board (DSMB) will review the safety of the drug throughout the study. Membership of the DSMB is described in a Charter.