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-established their baseline response levels after a single injectable SRL administration (at pre-study dose). Based on this data, patients may potentially be treated with OOC and for those not responding, either not biochemically controlled or who have adverse effects, they may be able to return to injectable SRLs with immediate IGF-I control after one SRL injection.