Development and Characterization of a Long-Acting Allosteric Growth Hormone Receptor Antagonist for Acromegaly

Acromegaly is a rare disease caused by growth hormone (GH) hypersecretion from a pituitary adenoma. Pegvisomant is the only approved GH receptor antagonist (GHRA) and is administered via daily subcutaneous injections, which limits real-world effectiveness. Here, we report the discovery and characterization of MAR002, a novel, half-life extended monoclonal antibody GHRA. MAR002 was identified by immunizing transgenic mice with the extracellular domain (ECD) of human and cynomolgus monkey GH receptor (GHR) and engineered with Fc modifications to limit effector function and extend serum half-life. MAR002 was benchmarked against pegvisomant in biophysical assays, cellular signaling inhibition studies, and a head-to-head pharmacokinetic/pharmacodynamic (PK/PD) study in cynomolgus monkeys. MAR002 exhibited higher binding affinity to GHR and >100-fold more potent inhibition of GH-induced GHR signaling than pegvisomant (human half-maximal inhibitory concentration [IC50] 1.05 nM vs 122 nM). Epitope binning demonstrated simultaneous binding of MAR002 and GH to GHR, consistent with an allosteric, non-competitive mechanism; notably, MAR002 inhibitory activity was maintained at supraphysiological GH concentrations, whereas pegvisomant activity was competitively reduced. In cynomolgus monkeys, a single 10 mg/kg intravenous (IV) dose of MAR002 sustained ≥50% IGF-1 suppression for 36 days compared with 15 days for an equimolar pegvisomant dose, with comparable maximal lowering (∼80%). These findings support clinical evaluation of MAR002 as a next-generation long-acting GHRA for acromegaly, with potential for reduced dosing frequency and more consistent suppression of the GH-IGF-1 axis.