Karpf, David

Abstract Context Hypoparathyroidism is characterized by insufficient levels of parathyroid hormone (PTH). TransCon PTH is an investigational long-acting prodrug of PTH(1-34) for the treatment of hypoparathyroidism. Objective This work aimed to investigate the safety, tolerability, and efficacy of daily TransCon PTH in adults with hypoparathyroidism. Methods This phase 2, randomized, double-blind, placebo-controlled 4-week trial with open-label extension enrolled 59 individuals with hypoparathyroidism. Interventions included TransCon PTH 15, 18, or 21 µg PTH(1-34)/day or placebo for 4 weeks, followed by a 22-week extension during which TransCon PTH dose was titrated (6-60 µg PTH[1-34]/day). Results By Week 26, 91% of participants treated with TransCon PTH achieved independence from standard of care (SoC, defined as active vitamin D = 0 μg/day and calcium [Ca] ≤ 500 mg/day). Mean 24-hour urine Ca (uCa) decreased from a baseline mean of 415 mg/24h to 178 mg/24h by Week 26 (n = 44) while normal serum Ca (sCa) was maintained and serum phosphate and serum calcium-phosphate product fell within the normal range. By Week 26, mean scores on the generic 36-Item Short Form Health Survey domains increased from below normal at baseline to within the normal range. The Hypoparathyroidism Patient Experience Scale symptom and impact scores improved through 26 weeks. TransCon PTH was well tolerated with no treatment-related serious or severe adverse events. Conclusion TransCon PTH enabled independence from oral active vitamin D and reduced Ca supplements (≤ 500 mg/day) for most participants, achieving normal sCa, serum phosphate, uCa, serum calcium-phosphate product, and demonstrating improved health-related quality of life. These results support TransCon PTH as a potential hormone replacement therapy for adults with hypoparathyroidism.

Abstract Background: Hypoparathyroidism (HP) is caused by a deficiency in parathyroid hormone (PTH), which leads to hypocalcemia and hyperphosphatemia. Standard of care (SoC), i.e. large doses of calcium (Ca) and active vitamin D, worsens hypercalciuria and increases the serum Ca (sCa) x serum phosphate (sP) product. Studies have shown that continuous subcutaneous infusion of PTH(1-34) normalizes sCa, sP, serum magnesium, urine Ca (uCa) and bone turnover better than SoC or once- or twice-daily injections of PTH in HP patients. TransCon PTH, an investigational long-acting prodrug of PTH (1-34) transiently bound to an inert carrier via a linker, is under development as a potential once-daily replacement therapy for HP. Under physiological conditions, linker auto-cleavage occurs, releasing active PTH at a controlled rate with ~60 hour half-life. Phase 1 trial results demonstrated that once-daily TransCon PTH provided a flat, infusion like profile within the normal range of PTH 24 hours per day, increasing sCa while controlling uCa and decreasing sP, with no evidence of bone anabolic activity. Phase 2 Design: PaTH Forward is a global phase 2 trial evaluating the safety, tolerability, and efficacy of TransCon PTH in adult subjects with HP. Patients with HP treated with SoC were randomized at sites worldwide to daily TransCon PTH 15, 18 or 21 µg PTH(1-34) or daily blinded placebo via pen-injector for 4 weeks. The primary composite endpoint requires 1) normal albumin-adjusted sCa, and 2) normal Fractional Excretion of Ca (or ≥50% decrease from baseline), and 3) not taking active D, and 4) taking ≤1000 mg/d of Ca. After four weeks, all subjects enter an open-label extension period with the opportunity to receive TransCon PTH individually optimized to doses of 6 to 30 µg daily to evaluate long-term safety and efficacy. Other endpoints include the impact of treatment on patient experience, CaxP product, bone turnover markers, and bone mass by DXA and TBS to confirm the lack of anabolic effect. Preliminary Results: Approximately 55 subjects are expected to be randomized and dosed. Preliminary diary data on the initial 8 subjects completing 4 weeks of follow-up in the extension trial shows that all have discontinued SoC. Additional information will be presented at ENDO 2020. The Phase 2 trial is designed to inform the starting dose for a global pivotal phase 3 trial and evaluate TransCon PTH as a “true” PTH replacement therapy.