Quick Project Snapshot

Developing small peptidomimetics to target RXFP1 for the treatment of acute heart failure

Florey patented H2 relaxin was recently granted a “breakthrough therapy” designation by the FDA for the treatment of acute heart failure. The indications are that H2 relaxin will enter the clinic soon by next couple of years. It is likely that the beneficial effects of H2 relaxin were also related to its anti-fibrotic effects, which we have shown occurs rapidly and independently of the cause of disease. This project aims to improve this current drug and develop the next generation molecule.

In order to maximize its future translational potential, we will address the three following issues:

  1. Large size and complex structure: The size (53 amino acids) and complex structure (two chains, linked by three disulfide bonds; Fig. 1) of H2 relaxin represent a considerable challenge for its synthesis; limiting modifications of the peptide to optimize its efficacy and stability. 
  2. Cross-reactivity with other receptors: H2 relaxin exerts its biological actions through its cognate receptor, Relaxin Family Peptide Receptor 1 (RXFP1; initially discovered as LGR7). However, it also activates RXFP2, the native receptor for the related insulin-like peptide 3, INSL3; opening the possibility of potential side-effects through RXFP2-mediated physiological processes. 
  3. Short half-life in blood: Like insulin, H2 relaxin has a very short half-life. Hence, when injected into patients, H2 relaxin will lose half its activity within 10 minutes because it is degraded by blood enzymes and cleared by the kidney and liver.

Thus, there is an urgent need to develop simpler H2 relaxin analogues that are easier to prepare and modify, have high selectivity for RXFP1 and retain their activity for an extended therapeutic time-frame in patients with acute heart failure.  A considerable effort has been made to reduce “H2 relaxin” into developing a single chain analogue with RXFP1-specific agonist activity. As the B-chain of H2 relaxin seems to possess most, if not all, of the amino acids responsible for RXFP1 binding and activation, it was probable that a B-chain-only analogue would be active at RXFP1. Preliminary single-chain analogues (such as native B-chain, B1-29) were found to be insoluble (Fig. 1B) and inactive over the years, but, very recently, in an exciting finding we have identified an N-terminus-truncated and C-terminus-extended B-chain analogue (B7-33) (Fig. 1A), which was found to be soluble in water (Fig 1B), binds to RXFP1 (data now shown) and acts as an agonist in over-expressing RXFP1 cells, albeit with less potency compared with native H2-relaxin (Fig 1C). However, unlike “H2 relaxin”, “B7-33 is selective at RXFP1 over RXFP2 (data not shown), and demonstrates similar activity to H2 relaxin in cells natively expressing RXFP1 in vitro (in rat renal myofibrobalst cells, Fig. 1D) and in models of diseases in vivo (Isoproterenol ISO-induced heart fibrosis model Fig. 1E; Ovalbumin OVA-induced lung fibrosis model Fig. 1F, G). The “B7-33” peptide provides us with a great starting point for further development as small peptidomimetic agonists of RXFP1. The peptide "B7-33", however, is less potent compared with native H2 relaxin. This proposal focuses on the utility of this lead compound as the basis for its further modification to improve its potency as well as in vivo stability. We will improve the structures, stability and potency of single chain "B7-33" analogue by using rational and structure-based drug design, point mutations with natural, non-natural, isometric amino acids, dicarba stapling, combinatorial library and lipidation.

Dr Akhter Hossain

Insulin Peptides Group

Insulin is one of the most clinically important peptide drugs on the market. It still represents the only treatment for diabetes (particularly for type 1). There are seven other insulin-like peptides (also called the relaxin family of peptides: H1, H2 and H3 relaxins, INSL3, 4, 5 and 6) which have similar structures to insulin (2 chains, 3 disulfide bonds), but have a diverse range of physiological functions. H2 relaxin is the most studied peptide in our laboratory and has recently passed phase III clinical trials for the treatment of acute heart failure. Our interest and experience lies in the design and development of insulin and insulin-like peptide-based drugs.

All Projects by this Lab

Developing peptidomimetics of insulin-like peptide 5, a novel orexigenic gut hormone, to target its GPCR, RXFP4Developing novel chemical methods to produce insulin mimeticsDeveloping small peptidomimetics to target RXFP1 for the treatment of acute heart failureNovel single-chain peptide mimetics, B7-33, for the treatment of fibrosisNovel relaxin-3 mimetics for controlling feeding and motivated behaviourNovel insulin-like peptide 5 mimetics for controlling colon motilityNovel insulin mimetics for managing diabetes


The Neuropeptides Division primarily conducts multi-disciplinary studies on the relaxin family of peptides/hormones and their receptors. The division focuses on determining the role of these peptides and the receptors they target a wide range of physiological and disease states. These studies are coupled with fundamental drug discovery research on both these and other peptides and their G protein-coupled receptors. The aim of this research is to develop new biological knowledge and fundamental understanding about how to best therapeutically target these peptide systems with the long term view to develop drugs which target the peptide receptors to treat vascular, fibrotic, metabolic and psychiatric diseases.

An example of the success of this approach is the completion of a Phase III trial using the hormone relaxin for the treatment of acute heart failure by the Swiss Pharmaceutical Company Novartis. A Phase IIIb trial is ongoing and the relaxin drug, serelaxin, has been approved in Russia to treat patients with acute heart failure. Hence fundamental research on the mechanism of action of a hormone, in the case of relaxin pioneered at the Florey by the former Neuropeptides Division Head, Prof Geoffrey Tregear, can ultimately lead to its use to treat disease in patients.

All Labs that operate in this Division

Insulin Peptides GroupNeuropeptide Receptor GroupPeptide and Protein Chemistry LaboratoryPeptide Neurobiology LaboratoryReceptor Structure and Drug Discovery Laboratory