Relaxin receptor agonist

B7-33 is a single-chain fragment of relaxin-2, the pregnancy hormone that softens connective tissue and dilates blood vessels. Full relaxin is a two-chain, three-disulfide protein that is expensive and awkward to make; serelaxin, the recombinant version, failed its phase 3 heart failure trial. B7-33 is an attempt to keep the anti-fibrotic and vasoprotective activity in a much simpler molecule, and the striking finding is that it is a functionally selective agonist at RXFP1 - it drives the anti-fibrotic pERK pathway without the cAMP signalling that relaxin also produces. In animals it replicates serelaxin's vasoprotective functions and reduced left ventricular fibrosis faster than perindopril in a cardiomyopathy model. No human study exists.