SAT-LB16 Maintenance of Favorable Treatment Effect of Once-Weekly TransCon hGH for Children With Growth Hormone Deficiency: Interim Analysis From the Enlighten Long-Term Extension Trial

Background Once-weekly TransCon hGH is an investigational long-acting prodrug for growth hormone deficiency (GHD) that consists of 3 components: unmodified growth hormone (hGH; somatropin), an inert carrier that protects it, and a linker that temporarily binds the two. In the randomized phase 3 heiGHt Trial evaluating treatment-naïve children with GHD, TransCon hGH demonstrated superior annualized height velocity and ∆ height standard deviation score (SDS) compared to Genotropin and had a similar safety and tolerability profile. Methods Results are reported from an interim analysis of subjects from heiGHt who continued in the ongoing enliGHten long-term extension trial for 26 weeks. In the 52-week heiGHt Trial, treatment-naïve, prepubertal subjects with GHD were randomized 2:1 to receive once-weekly TransCon hGH 0.24 mg hGH/kg/week or an equivalent weekly dose of daily Genotropin. Subjects completing heiGHt could enroll in enliGHten, where all subjects received TransCon hGH. Two groups were analyzed: Group A (TransCon hGH in both heiGHt and enliGHten) and Group B (Genotropin in heiGHt, followed by TransCon hGH in enliGHten). Safety and growth outcomes were evaluated approximately every 13 weeks in heiGHt and enliGHten. IGF-1 was sampled on postdose Day 5 (±1 day) in enliGHten. A by-visit ANCOVA model was used to analyze numeric efficacy endpoints.ResultsAll but one subject who completed heiGHt continued into enliGHten (A: N=103, B: N=55). Baseline characteristics at the start of heiGHt were balanced between groups. The statistically significant treatment difference in ∆ height SDS (Group A vs B) at the end of heiGHt (Week 52, N=159; 1.10 vs 0.96, P=0.0149) was sustained through Week 78 (N=154; 1.39 vs 1.24, P=0.0436), demonstrating persistence of catch-up growth for both groups and maintenance of superior treatment effect for subjects treated with TransCon hGH in the first year of therapy. At Week 78, least-squares mean (SE) IGF-1 SDS on postdose Day 5 (N=153) was 0.52 (0.15) for Group A and 0.59 (0.19) for Group B. Adverse events (AEs) were comparable between groups during heiGHt. During enliGHten, 48.7% (76/156) and 1.9% (3/156) of subjects experienced AEs and serious AEs, respectively; the AE profile was consistent with what was previously observed in heiGHt. A low titer of anti-hGH binding antibodies were detected in 10/156 (6.4%) subjects during treatment with TransCon hGH in heiGHt and enliGHten; no neutralizing antibodies were detected. Lab parameters (HbA1c, cortisol, free thyroxine) were stable and generally remained within the normal range throughout the trials. Mean (SD) BMI SDS was 0.0 (0.8) for Group A and 0.1 (0.9) for Group B at Week 78.Conclusions Children treated with TransCon hGH showed continued improvement of height SDS beyond the first year. Treatment with TransCon hGH through 78 weeks demonstrated an AE and immunogenicity profile comparable to that of a daily hGH therapy.