SUN-448 Overnight Metyrapone Therapy in Patients with Mild Autonomous Cortisol Secretion (MACS): An Open-Label Phase 2 Clinical Trial

Abstract Disclosure: S.R. Chacko: None. C. Powell: None. B. Ndovu: None. E.Y. Ferreira: None. R. Rosenberg: None. J. Saini: None. S. Nevin: None. K. Yu: None. V. Fell: None. J.J. Larson: None. E. Atkinson: None. I. Bancos: Funding for investigator-initiated research from Esteve. Context: Mild autonomous cortisol secretion (MACS), found in about 50% of patients with adrenal incidentalomas, is associated with increased cardiovascular morbidity. While adrenalectomy improves outcomes in unilateral MACS, safe and effective medical therapy is needed for bilateral MACS. Objectives: To evaluate the tolerability and safety of overnight metyrapone in adults with MACS. Methods: Study design: Open-Label, Phase 2, Clinical Trial (NCT06106295) Participants: Patients >18-years-old with MACS and benign adrenal imaging phenotype were prospectively enrolled between December 2023 and January 2025. MACS was diagnosed based on 1 mg post-dexamethasone suppression test serum cortisol >1.8 mcg/dL. Eligibility required at least one MACS-associated comorbidity (obesity, dysglycemia, dyslipidemia, hypertension, osteopenia or osteoporosis). Intervention: Metyrapone was administered at an initial dose of 250 mg each evening with up titration in 250 mg increments every 2-4 weeks based on tolerance, to a maximum of 1000 mg. Outcomes: The primary endpoint was assessment of treatment-related adverse events (AE), categorized by CTCAE grade. Adrenal insufficiency (AI) was considered an AE, assessed on biochemistry and AddiQoL survey. Sample size: 30 patients projected Results: Twenty-six patients with MACS [median age 66 years (IQR 61-68), 69% women] were enrolled. At the time of analysis, median metyrapone dose was 1000 mg (IQR 750-1000). At median follow-up of 3 months (IQR 2-6), 22 patients (85%) developed at least one AE. None were serious, aside from one patient with an acute kidney injury (AKI), unlikely related to metyrapone. All other AEs were CTCAE Grade 1-2, including dizziness 12%, nausea 6% and fatigue 5%. Of all 90 AEs, 12 (13%) occurred at a dose of 250 mg, 10 (11%) at 500 mg, 20 (22%) at 750 mg and 48 (53%) at 1000 mg. One (1%) was definitely related to metyrapone (hypokalemia), 16 (18%) probably related, 20 (22%) possibly related, 35 (39%) unlikely to be related, and 18 (20%) unrelated to metyrapone. Dose was reduced in 5 patients (19%) due to an AE. Two discontinued metyrapone, one because of AKI, while the other withdrew from the study. Morning serum cortisol was not significantly changed between baseline [11.5 (IQR 9.2-14.8)], 3 months [12.0 (IQR 11.0-15.0)], and 6 months [9.7 (IQR 7.9-12.5)] (normal: 4.8-20 mcg/dL). No patient developed AI (morning serum cortisol <10 mcg/dL and ACTH >60 pg/ml), but plasma ACTH significantly increased from baseline to 3 months [8.0 (IQR 5.4-20.8) vs. 18.0 (IQR 14.0-28.0), P=0.021] (normal: 10-60 pg/ml). Between 3 and 6 months, no significant change occurred in ACTH. AddiQol survey scores did not change significantly between baseline, 3 and 6 months. Conclusion: Metyrapone therapy in patients with MACS demonstrated a favorable safety profile with no occurrence of AI. Further investigation into efficacy and MACS-associated outcomes is warranted. Presentation: Sunday, July 13, 2025