The human gene-2 relaxin peptide (H2 relaxin) has strong anti-fibrotic [1], vasodilatory [2,3], and cardioprotective effects [4] as a result, H2 relaxin is undergoing/has undergone clinical and preclinical development by several pharmaceutical companies (Relaxera, Novartis, and AstraZeneca to name a few), for its anti-fibrotic and cardioprotective capacities mediated by the activation of its cognate G protein-coupled receptor, RXFP1 [1]. While it possesses enormous promise as a drug, H2 relaxin has a short in vivo half-life (minutes) and as a two (A and B)-chain three disulfide bond peptide is difficult and expensive to produce and modify. H2 relaxin’s strong activation of cAMP signaling may also induce side effects including tumor growth, in long-term use [5]. Excessive cAMP activation in the ischemic heart could also potentially increase heart rate and myocardial workload, further exacerbating contractile demand on myocytes.
In 2016, we reported a potent single-B-chain analogue of H2 relaxin, B7-33 [5]. B7-33 consists of residues 7- 29 of the B chain of H2 relaxin, with the addition of a KRSL sequence from positions 30-33 of the B1-33 isoform of H2 relaxin, which dramatically improves solubility over B1-29 [5]. B7-33, being a single-chain peptide, is far easier and cheaper to produce than the parent peptide, making it an excellent scaffold for modification with the aim of improving its pharmacological properties as an anti-fibrotic therapeutic. Here we detail our attempts towards further minimisation of B7-33, and attempts to improve scaffold activity. We will also report our attempts to improve its stability both in vitro and in vivo.