A helical peptide antagonist of the human growth hormone receptor

The binding of human growth hormone (hGH) to the human growth hormone receptor (hGHR) is a key endocrinological process that controls critical aspects of cell growth, proliferation, and differentiation. Mechanistically, this sequential, asymmetric binding event involves the interaction between a single hGH molecule and distinct sites (sites 1 and 2) on the extracellular domain of a preformed hGHR homodimer. Our group recently identified S1H, a rationally designed peptide sequence mimetic of the hGH site 1-binding helix (residues 36-51) that disrupts the hGH-hGHR interaction and inhibits hGH-mediated phosphorylation of signal transducer and activator of transcription 5 (STAT5) in hGHR-positive cell lines. Structure-activity relationship studies revealed a positive correlation between helical propensity and inhibitory potency of the S1H peptide, prompting the design of structurally "stabilized" S1H variants (SS1H) with improved biological activity. In this study, we employed a chemical strategy, termed hydrocarbon stapling, to generate a series of SS1H peptides that proved to be more helical, proteolytically stable, and biologically active compared to linear (unstructured) S1H. Notably, one SS1H derivative (SS1HB) inhibited hGH-induced STAT5 phosphorylation in hGHR-positive human bladder cancer cells more effectively than pegvisomant, the only hGHR antagonist currently approved by the FDA. Collectively, our results demonstrate that hydrocarbon stapling improves the antagonistic effects of S1H peptides and elevates their potential as chemical probes to study the molecular mechanisms of hGH signaling. It is also anticipated that SS1H peptides will serve as potent lead compounds for developing next-generation therapeutics designed to treat endocrine disorders that manifest along the hGH-hGHR signaling axis.