ODP353 Sustained Suppression of IGF1 with AZP-3813, a Bicyclic 16-Amino Acid Peptide Antagonist of the Human Growth Hormone Receptor and a Potential New Treatment for Acromegaly

Medical treatment of acromegaly is based on either suppressing pituitary GH secretion or inhibiting GH action by preventing interaction with its receptor in order to suppress the elevated levels of IGF1. AZP-3813 is a 16-amino acid, bicyclic peptide antagonist of the GH receptor (GHR) with a KD of 1.9nM for the human GHR, and 18.5nM for the rat GHR. The circulating half-life of AZP-3813 in the rat is 11.2 hours. In previous studies, AZP-3813 was demonstrated to suppress IGF1 secretion in juvenile rats in a dose-related manner, and to maintain IGF1 suppression when given over 4 days. To examine the ability of chronic AZP-3813 treatment to maintain suppression of IGF1 levels, we injected normal, 5-week old (∼150g), male Sprague Dawley rats subcutaneously either with vehicle or with AZP-3813 at doses of either 10 or 30mg/kg QD for 19 days (n=7/group). Blood samples were collected immediately prior to either vehicle or AZP-3813 injection on days 1, 2, 3, 7, 10, 15 and 19, and 24h after the last injection (day 20). Samples were assayed for total IGF1 content by radioimmunoassay, and samples collected on days 2, 10 and 19 were also analyzed for AZP-3813 content by LC-MS/MS. At the initiation of treatment, the average body weight of the rats was 150.3 + 3.0g, and over the 20 days of the study animals treated with vehicle gained an average of 158.4 + 4.9g. In contrast, rats treated QD with 10 or 30mg/kg AZP-3813 gained 23.6 + 2.1 and 27.9 + 2.2% less weight than the vehicle-treated controls, respectively. Accumulation of AZP-3813 levels in the blood was observed with repeated daily injections of both 10 and 30mg/kg, increasing from day 2 levels by 107.1 + 12.5 and 125.2 + 36.3%, respectively, by day 19. In the vehicle-treated control rats, IGF1 levels increased from an initial 395.1 +16.3ng/ml to 674.4 + 19.8ng/ml by day 20. Twenty-four hours after the first injections of 10 and 30mg/kg AZP-3813, IGF1 levels were suppressed by 27.6 + 3.4 and 29.2 + 3.3%, respectively, versus vehicle-treated control levels, and, with continued treatment, a similar magnitude of IGF1 suppression was maintained through day 20 despite the progressively increasing levels of IGF1 observed in the vehicle-treated rats. At study termination on day 20, animals treated with 10 and 30mg/kg AZP-3813 were observed to have 4.1 and 4.6% shorter femur length, 1.1 and 3.6% shorter body length, and 7.7 and 13.3% less liver weight, respectively, as compared with vehicle-treated control rats. These results demonstrate that with continued treatment, the potent GHR antagonist activity exhibited by AZP-3813 translates to sustained in vivo suppression of IGF1 levels and associated parameters, and support its development as a potential therapy for acromegaly. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m., Monday, June 13, 2022 1:05 p.m. - 1:10 p.m.