ESPE Abstracts

Background: Once-daily growth hormone (GH) therapy is an effective treatment for children with growth hormone deficiency (GHD), but compliance wanes with ongoing treatment. A once -weekly GH, somatrogon (hGH-CTP), is being developed to reduce the treatment burden of daily dosing for children and caregivers and potentially improve compliance and long-term efficacy. The impact of once-weekly somatrogon on long-term safety, local tolerability and immunogenicity was assessed in patients treated with somatrogon for a period of up to 4 years in an open-label extension (OLE) of the somatrogon Phase 2 study.

Objective: To evaluate the safety, local tolerability and immunogenicity of long-term exposure to somatrogon in GHD children.

Design: A multicenter, open-label, controlled extension of a Phase 2 trial in children with GHD (ClinicalTrials.gov: NCT01592500).

Methods: Forty-eight GH-treatment-naïve prepubertal children with GHD that completed 12-months of treatment in the main Phase 2 study continued in the OLE. All eligible subjects were treated at the 0.66 mg/kg/wk dose after the first year of the extension study.

Results: Data from the 12-month Phase 2 study showed comparable height velocity and insulin-like growth factor-1 (IGF-1) values in weekly somatrogon-treated compared to daily Genotropin-treated subjects. In the OLE portion of the study, there were 214 AEs occurring in 44 subjects (91.7%). One subject was discontinued because of an SAE of exacerbation of thoracic scoliosis. The majority of AEs (68.8%) were mild in nature and were deemed not related to somatrogon. The most frequent AEs were upper respiratory infections (31.3%), rhinitis (18.8%) and bronchitis (10.4%). Twelve AEs (3%) related to somatrogon were of a similar nature and severity as reported for daily r-hGH products. Somatrogon treatment showed that IGF-1 and IGF-binding peptide-3 (IGFBP-3) levels were maintained within the normal range with ongoing somatrogon therapy. Low titers of anti-somatrogon antibodies were detected in 16 subjects but no neutralizing anti-somatrogon antibodies were identified. The growth rate remained within expected range in all subjects. Thirty-eight subjects (79%) are continuing in the fifth year of the OLE.

Conclusion: Somatrogon treatment demonstrated a favorable safety profile and local tolerability after four years of dosing in GHD pediatric subjects. The safety and tolerability from the OLE study were comparable to that observed in the 12-month main Phase 2 study and the reported safety profile of daily r-hGH. Serum IGF-1 SDS values were maintained within the normal range, and a growth rate comparable to that reported for daily hGH was observed.