MON-LB55 Biochemical Control of Most Patients Reverting to Injectable Long-Acting Somatostatin Receptor Ligands Is Achieved After One Dose: Results From the Phase 3, Randomized, Double Blind, Placebo-Controlled Optimal Study

Background: Injectable somatostatin receptor ligands (SRLs) are currently the most widely used medical therapy for acromegaly worldwide. Oral octreotide capsules (OOC) have been formulated as a potential therapy for this disorder and the safety and efficacy were evaluated in the CHIASMA OPTIMAL pivotal study (Samson et al. ENDO 2020). As reported, mean IGF-I levels of the OOC treatment group were maintained within normal range at the end of treatment in all patients. However, some patients may not respond to OOC treatment (25% of OOC group and 68% of placebo groups required rescue, P=0.003). This analysis describes the degree and rapidity with which patients achieve biochemical control (IGF-I ≤1.0 x ULN) when reverted to their prior injectable SRL treatment. Methods: Patients with confirmed acromegaly and receiving a stable dose of injectable SRL (≥3 months) were randomized to OOC (40mg/day; N=28) or placebo (N=28) for 36 weeks. Patients were dose titrated to 60 or 80mg of OOC (or placebo) through week 24 at investigator discretion based on increased IGF-I levels and/or worsening acromegaly signs/symptoms. Patients could be rescued via reversion to prior injectable SRL therapy if they met the predefined withdrawal criteria (i.e., IGF-I ≥1.3 x upper limit of normal [ULN] for 2 consecutive visits on the highest dose, and exacerbation of clinical signs/symptoms) or discontinued treatment early for any other reason. In the study, 7 patients in the OOC group and 19 in the placebo group required rescue. The change in IGF-I from Baseline was compared to the end of the Double-blind Placebo Controlled period. Results: In patients rescued up to week 32 and in whom there were at least 4 weeks of follow up, baseline IGF-I levels (mean of Screening Visit 2 and Baseline) were 0.80 and 0.87 x ULN in the OOC and placebo groups, respectively. In patients receiving rescue therapy, the end of study IGF-I levels (mean of week 34 and 36) were 0.80 and 0.89 x ULN in the OOC and placebo groups, respectively, virtually unchanged. The median time to return to normal baseline IGF-I values following loss of response was 4.0 weeks after discontinuing OOC and 4.0 weeks after discontinuing placebo treatment. Therefore, most patients who required rescue following a short trial of therapy with OOC returned to their baseline values following a single SRL injection. Conclusion: Most treatment failures in the CHIASMA OPTIMAL trial (on either OOC or placebo) rescued with injectable SRL re-es