OR10-05 Phase 3 FliGHt Trial: Experience of Switching from Daily Growth Hormone Therapy to Once-Weekly TransCon HGH in Children with Growth Hormone Deficiency

Background: The Phase 3 fliGHt Trial evaluated children with growth hormone deficiency (GHD) of a broad range of baseline demographics and treatment durations who switched from daily growth hormone (hGH; somatropin) therapy to once-weekly TransCon hGH. TransCon hGH is an investigational long-acting prodrug consisting of 3 components: hGH, an inert carrier that protects it, and a linker that temporarily binds the two. When injected into the body, at physiologic pH and temperature, unmodified hGH is gradually released in a predictable manner. Methods: All subjects initiated open-label once-weekly TransCon hGH 0.24 mg hGH/kg/week irrespective of prior daily hGH dose. Subjects 3 to 17 years old must have been treated with daily hGH for 13 to 130 weeks; subjects 6 months to 3 years old may have been treatment-naïve or treated with daily hGH for ≤130 weeks. The primary objective was to assess safety and tolerability over this 26-week trial. Efficacy measures included annualized height velocity (AHV), height standard deviation score (SDS), and insulin-like growth factor 1 (IGF-1) SDS. Results: Of the 146 enrolled subjects, 98.6% completed the trial. Mean age at baseline was 10.6 years (range: 1, 17). The majority (97.9%) were treatment-experienced with a prior daily hGH mean dose of 0.29 mg/kg/week (range: 0.13, 0.49); 3 subjects were treatment-naïve and <3 years old. Just over half the subjects (56.8%) experienced a treatment-emergent adverse event (TEAE), with only 4.1% of subjects experiencing a TEAE considered related to study drug. No TEAE led to discontinuation of study drug. The type and frequency of TEAEs reported were similar to the published adverse event profile of daily hGH therapies. Mean hemoglobin A1c remained 5.2% at baseline and Week 26. No neutralizing antibodies were detected; low-titer anti-hGH binding antibodies were detected in 2.8% of subjects. Growth outcomes were as expected for this treatment-experienced heterogenous population, with a least-squares mean (LSM) AHV of 8.7 cm/year (95% CI: 8.2, 9.2) at Week 26 and LSM height SDS change from baseline to Week 26 of +0.25 (95% CI: 0.21, 0.29). In the age-defined subgroups, mean observed AHV at Week 26 ranged from 8.2 to 16.2 cm/year and mean observed height SDS change from baseline to Week 26 ranged from +0.23 to +0.96. Of note, the linear relationship between average IGF-1 SDS and TransCon hGH doses demonstrated in previous treatment-naïve trials was preserved in this population of treatment-experienced children who had dose titrations. Conclusions: TransCon hGH treatment outcomes, including AHV and height SDS, were as expected across a diversity of ages, disease characteristics, and treatment experiences, reflective of a real-world setting. Dose titrations of TransCon hGH demonstrated a predictable IGF-1 response. Switching to TransCon hGH resulted in a similar adverse event profile to daily hGH therapy.