An Open-label Phase 2 Study of Eneboparatide, a Novel PTH Receptor 1 Agonist, in Hypoparathyroidism.

CONTEXT: Hypoparathyroidism is a rare disorder characterized by a deficiency in PTH resulting in hypocalcemia, hyperphosphatemia, and hypercalciuria. Eneboparatide is an investigational peptide agonist of the PTH1 receptor for the treatment of chronic hypoparathyroidism (HP). OBJECTIVE: To evaluate the efficacy, safety, and tolerability of eneboparatide in HP patients. DESIGN: Open-label, phase 2 study. PARTICIPANTS: Twenty-eight patients (21 women, 7 men), mean age (range): 58 years (28-72), with HP were enrolled into 2 consecutive cohorts (C1, n = 12 and C2, n = 16). INTERVENTION: Following an optimization period, daily subcutaneous injections of eneboparatide were administered for 3 months at a 20 µg/day (C1) or 10 µg/day (C2) starting dose. Conventional therapy was progressively removed, and eneboparatide could be titrated up to 60 µg (C1) or 80 µg (C2). MAIN OUTCOMES: Proportion of patients achieving independence from conventional therapy, albumin-adjusted serum calcium (ADsCa), 24-h urine calcium (uCa), serum bone turnover markers (serum carboxy-terminal telopeptide of type I collagen and procollagen 1 intact N-terminal propeptide), bone mineral density (BMD), and adverse events (AEs). RESULTS: After 3 months, ≥ 88% of patients achieved independence from conventional therapy while mean ADsCa was maintained within target range (7.8-9 mg/dL). Eneboparatide induced a rapid and sustained reduction of mean 24-hour uCa, even among patients with hypercalciuria. Bone turnover markers slightly increased, and BMD remained unchanged, consistent with progressive resumption of physiologic bone turnover. Eneboparatide was well tolerated with no serious AEs. CONCLUSION: Eneboparatide allowed independence from conventional therapy and maintenance of serum calcium within a target range while normalizing uCa excretion and producing a balanced resumption of bone turnover.