One-Year Outcomes of the Open-Label Extension of CHIASMA OPTIMAL, a Phase 3 Study of Oral Octreotide Capsules in Acromegaly
Authors: Samson Susan Leanne , Nachtigall Lisa B , Fleseriu Maria , Molitch Mark E , Giustina Andrea , Ludlam William Henry , Patou Gary , Haviv Asi , Biermasz Nienke , Kennedy Laurence , Sever Mojca Jensterle , Manning Patrick John , Elenkova Atanaska , Melmed Shlomo , Strasburger Christian Joseph 
Published: May 2021

Background: Based on the CHIASMA OPTIMAL study, oral octreotide capsules (OOC) were recently approved in the US as a long-term maintenance therapy for patients with acromegaly previously responding to injectable octreotide or lanreotide, somatostatin receptor ligands (SRLs). Results on longer-term efficacy and safety of OOC from the first 48 weeks of the open-label extension (OLE) of this study are presented here. Methods: Eligible patients had the option to enroll in the OLE of CHIASMA OPTIMAL following the double-blind placebo-controlled (DPC) period; 90% of patients who received OOC in the DPC period enrolled. All patients entering the OLE were initiated on a 60 mg/day dose of OOC and titrated up or down based on insulin-like growth factor I (IGF-I) level and/or acromegaly signs or symptoms. End points in the OLE were exploratory and included the proportion of patients who completed week 48 of the OLE, the proportion who completed as responders (defined as average IGF-I ≤1.0 × upper limit of normal [ULN] at weeks 46/48), and changes in IGF-I from baseline of DPC and OLE until week 48 of the OLE; multiple imputation (MI) was used for missing data. Results: Forty patients entered the OLE (n=20 each; OOC and placebo). Median exposure to OOC in the OLE was &gt; 1 year for those who had been on placebo in the DPC and ≤ 21 months for those who had been on OOC. Dosing of OOC at the end of their participation in the OLE was 40 mg, n=3; 60 mg, n=10; and 80 mg, n=27. In those who received OOC during the DPC, 90% (n=18) completed 48 weeks of the OLE. Of responders at the end of the DPC period (n=14), 92.6% maintained response at OLE week 48. In patients from the OOC group who completed the DPC on study drug, average IGF-I using MI was 0.91 and 0.90 × ULN at OLE baseline and week 48, respectively. The mean change in IGF-I from the baseline of the DPC to OLE week 48 was 0.06 × ULN in patients who completed the DPC on OOC (n=19). In those who received placebo during the DPC, 70% (n=14) completed 48 weeks of the OLE. Of responders at the end of the DPC (n=5), 100% maintained response at OLE week 48. In patients from the placebo group who completed the DPC and did not revert to prior injectable therapy (n=9), the average IGF-I values were 1.09 and 0.87 × ULN at OLE baseline and week 48 respectively, using MI. The mean change in IGF-I from the baseline of the DPC to OLE week 48 was 0.08 × ULN in patients who completed the DPC on placebo (n=9). The most common treatment-emergent adverse events (TEAEs) were gastrointestinal; most were mild or moderate. The incidence of TEAEs was similar between patients who were on OOC or placebo during the DPC. The safety profile during the OLE did not show new concerns with increased duration of drug exposure. Conclusion: Long term maintenance of biochemical response to OOC is durable as assessed following ≤ 21 months of treatment. The OOC safety profile in the extension study is consistent with that of injectable SRLs but without injection-related AEs.