SAT-408 Bioactivity of Long Acting PTH Fusion Molecules Tested in a Novel Non-Surgical Animal Model of Hypoparathyroidism

Abstract

Introduction: There is an unmet need for the development of long-acting PTH molecules to treat patients with hypoparathyroidism. We have established a novel non-surgical rodent model of hypoparathyroidism using oral Cinacalcet-HCl to test long acting analogues of PTH. Here we have tested the pharmacodynamics properties of two long acting PTH fusion molecules. Methods: PTH fusion molecules tested: Fusion-1 is PTH (1–34) linked to GHBP (residues 1–238), and Fusion-2 is a Hybrid PTH-PTHrP (1) linked to GHBP (residues 1–238). For in vivo studies, normal male wistar rats were gavaged with 30 mg/kg Cinacalcet-HCl, immediately followed by a subcutaneous dose of PTH Fusion at 20 nmol/kg. Control animals received PTH (1–34) and vehicle only. Serum samples were taken and analysed for ionised calcium (iCa). Results: Oral administration of Cinacalcet-HCl caused a reduction in iCa that was significantly different from vehicle controls at 2 to 24hrs post dose (ANOVA P < 0.0001). PTH 1–34 maintained iCa levels for 2 hours after administration above that of Cinacalcet-HCl (AUC±SD (mmol/L).hr from baseline, 0.076 ±0.047 and 0.168±0.0874, t-test P=0.0289) but then levels fell and recovered as for Cinacalcet-HCl alone. Subcutaneous doses of both fusions were able to abrogate the effects of Cinacalcet-HCl from 4hrs post dose onwards giving a prolonged response, with iCa levels quicker to return to baseline levels at 48hrs compared to Cinacalcet-HCl. The AUC±SD (mmol/L).hr from baseline for iCa over 72 hours was 3.93±1.4 for Fusion-1, 5.0±2.7 for Fusion-2 & 10±2.8 for Cinacaclet-HCl and were significantly reduced for both fusions compared to Cinacalcet-HCl alone (t-test P = 0.0028 & P = 0.019, respectively) and not significantly different from vehicle only. Conclusions: Cinacalcet-HCl behaved as expected in terms of iCa lowering (2). PTH maintained iCa but only for 2 hours. Both PTH fusion molecules showed a delayed and prolonged response and reduced the impact of Cinacalcet-HCl induced low iCa levels from 4hrs to 24hrs. These data provide proof of concept for long acting biological activity of these novel PTH fusion proteins. References: 1. Shimizu M, Joyashiki E, Noda H, Watanabe T, Okazaki M, Nagayasu M, et al. Pharmacodynamic Actions of a Long-Acting PTH Analog (LA-PTH) in Thyroparathyroidectomized (TPTX) Rats and Normal Monkeys. J Bone Miner Res. 2016;31(7):1405–12. 2. Nemeth EF, Heaton WH, Miller M, Fox J, Balandrin MF, Van Wagenen BC, et al. Pharmacodynamics of the type II calcimimetic compound cinacalcet HCl. The Journal of pharmacology and experimental therapeutics. 2004;308(2):627–35.