LAUSR

Abstract Background: Growth hormone deficiency (GHD) requires long-term daily injections with GH replacement therapy and is associated with considerable treatment burden. Somapacitan is a long-acting GH derivative being developed for once-weekly dosing in adults and children with GHD. A well-established protraction method, successfully used to extend the half-life of insulin and glucagon-like peptide (GLP)-1, has been applied in developing somapacitan: an albumin-binding moiety (1.3 kDa) is attached to a single amino acid substitution in the GH molecule (22 kDa). Objective: To evaluate the efficacy, safety, and tolerability of three once-weekly somapacitan doses, compared with Norditropin®, a daily GH. Methods: This multicenter, open-label, randomized, controlled phase 2 study (ClinicalTrials.gov: NCT02616562) was double-blind with regard to dose levels of somapacitan, and height assessors were blinded to treatment. GH-treatment-naïve prepubertal children with GHD were randomized to somapacitan (N=45) or Norditropin® (N=14). Patients received 0.04 (n=16), 0.08 (n=15) or 0.16 mg/kg/wk (n=14) subcutaneous (sc) somapacitan once weekly, or sc Norditropin® 0.034 mg/kg/day (0.24 mg/kg/wk; n=14). Patients completed 6 months of treatment as follows: somapacitan 0.04 (n=14), 0.08 (n=15) and 0.16 (n=14) mg/kg/wk, and Norditropin® 0.034 mg/kg/day (n=13). Results: At 6 months, mean (SD) annualized height velocity (HV, cm/year) for the three somapacitan doses was 8.0 (2.0), 10.9 (1.9) and 12.9 (3.5), respectively. HV for the 0.08 and 0.16 mg/kg/wk doses did not differ significantly from HV with Norditropin® (11.4 [3.3]). Insulin-like growth factor (IGF)-I increased dose-dependently: change from baseline in IGF-I standard deviation score (SDS) was 1.08, 2.15 and 3.21 for the somapacitan groups, respectively, when measured at peak of the IGF-I profile over the dosing interval, and 2.03 for Norditropin®. Modeling yielded IGF-I SDS average over the dosing interval for the somapacitan 0.16 mg/kg/wk group that was similar to observed values for Norditropin®. Adverse events were mild-to-moderate and most were evaluated as unrelated to treatment by the investigator. One patient had persistent anti-hGH antibodies of low titer and three patients had a single positive measurement of anti-somapacitan antibodies of low titer. All antibody positive samples were negative for in vitro neutralizing antibodies. There were no clinically relevant changes from baseline to Week 26 in any treatment group in mean HbA1c, fasting glucose or insulin. Tolerability was consistent with known properties of GH. Conclusion: In children with GHD, the efficacy, safety and tolerability of once-weekly somapacitan was similar to that of daily Norditropin®. Results from this phase 2 trial provide support for the initiation of a phase 3 trial of somapacitan in children with GHD.