Synthetic non-peptide low molecular weight agonists of the relaxin receptor 1

Cardiomyocyte-specific RXFP1 overexpression protects against pressure overload-induced cardiac dysfunction independently of relaxin

Heart failure (HF) prevalence is rising due to reduced early mortality and demographic change. Relaxin (RLN) mediates protective effects in the cardiovascular system through Relaxin-receptor 1 (RXFP1). Cardiac overexpression of RXFP1 with additional RLN supplementation attenuated HF in the pressure-overload transverse aortic constriction (TAC) model. Here, we hypothesized that robust transgenic RXFP1 overexpression in cardiomyocytes (CM) protects from TAC-induced HF even in the absence of RLN. Hence, transgenic mice with a CM-specific overexpression of human RXFP1 (hRXFP1tg) were generated. Receptor functionality was demonstrated by in vivo hemodynamics, where the administration of RLN induced positive inotropy strictly in hRXFP1tg. An increase in phospholamban-phosphorylation at serine 16 was identified as a molecular correlate. hRXFP1tg were protected from TAC without additional RLN administration, presenting not only less decline in systolic left ventricular (LV) function but also abrogated LV dilation and pulmonary congestion compared to WT mice. Molecularly, transgenic hearts exhibited not only a significantly attenuated fetal and fibrotic gene activation but also demonstrated less fibrotic tissue and CM hypertrophy in histological sections. These protective effects were evident in both sexes. Similar cardioprotective effects of hRXFP1tg were detectable in a RLN-knockout model, suggesting an alternative mechanism of receptor activation through intrinsic activity, alternative endogenous ligands or crosstalk with other receptors. In summary, CM-specific RXFP1 overexpression provides protection against TAC even in the absence of endogenous RLN. This suggests RXFP1 overexpression as a potential therapeutic approach for HF, offering baseline protection with optional RLN supplementation for specific activation.

Synthetic short-chain peptide analogues of H1 relaxin lack affinity for the RXFP1 receptor and relaxin-like bioactivity. Clues to a better understanding of relaxin agonist design

The peptide hormone relaxin (RLX), also available as clinical-grade recombinant protein (serelaxin), holds great promise as a cardiovascular and anti-fibrotic agent but is limited by the pharmacokinetic issues common to all peptide drugs. In this study, by a computational modelling chemistry approach, we have synthesized and tested a set of low molecular weight peptides based on the putative receptor-binding domain of the B chain of human H1 RLX isoform, with the objective to obtain RLX analogues with improved pharmacokinetic features. Some of them were stabilized to induce the appropriate 3-D conformation by intra-chain tri-azolic staples, which should theoretically enhance their resistance to digestive enzymes making them suited for oral administration. Despite these favourable premises, none of these H1 peptides, either linear or stapled, revealed a sufficient affinity to the specific RLX receptor RXFP1. Moreover, none of them was endowed with any RLX-like biological effects in RXFP1-expressing THP-1 human monocytic cells and mouse NIH-3T3-derived myofibroblasts in in vitro culture, in terms of significantly relevant cAMP elevation and ERK1/2 phosphorylation, which represent two major signal transduction events downstream RXFP1 activation. This was at variance with authentic serelaxin, which induced a clear-cut, significant activation of both these classical RLX signaling pathways. Albeit negative, the results of this study offer additional information about the structural requirements that new peptide therapeutics shall possess to effectively behave as RXFP1 agonists and RLX analogues.

Relaxin-2 as a Potential Biomarker in Cardiovascular Diseases

The pleiotropic hormone relaxin-2 plays a pivotal role in the physiology and pathology of the cardiovascular system. Relaxin-2 exerts relevant regulatory functions in cardiovascular tissues through the specific receptor relaxin family peptide receptor 1 (RXFP1) in the regulation of cardiac metabolism; the induction of vasodilatation; the reversion of fibrosis and hypertrophy; the reduction of inflammation, oxidative stress, and apoptosis; and the stimulation of angiogenesis, with inotropic and chronotropic effects as well. Recent preclinical and clinical outcomes have encouraged the potential use of relaxin-2 (or its recombinant form, known as serelaxin) as a therapeutic strategy during cardiac injury and/or in patients suffering from different cardiovascular disarrangements, especially heart failure. Furthermore, relaxin-2 has been proposed as a promising biomarker of cardiovascular health and disease. In this review, we emphasize the relevance of the endogenous hormone relaxin-2 as a useful diagnostic biomarker in different backgrounds of cardiovascular pathology, such as heart failure, atrial fibrillation, myocardial infarction, ischemic heart disease, aortic valve disease, hypertension, and atherosclerosis, which could be relevant in daily clinical practice and could contribute to comprehending the specific role of relaxin-2 in cardiovascular diseases.

Cardiac Gene Therapy With Relaxin Receptor 1 Overexpression Protects Against Acute Myocardial Infarction

•

AAV9 vectors can upregulate Rxfp1 mRNA in murine heart after intravenous injection.

•

RXFP1 upregulation sensitizes the left ventricle to relaxin-induced inotropy.

•

RXFP1 overexpression protects heart from ischemia-reperfusion injury.

Relaxin is a pleiotropic hormone shown to confer cardioprotection in several preclinical models of cardiac ischemia-reperfusion injury. In the present study, the effects of up-regulating relaxin family peptide receptor 1 (RXFP1) via adeno-associated virus serotype 9 (AAV9) vectors were investigated in a mouse model of myocardial infarction. AAV9-RXFP1 vectors were generated and injected in adult male CD1 mice. Up-regulation of Rxfp1 was confirmed via quantitative polymerase chain reaction, and overexpressing animals showed increased sensitivity to relaxin-induced ventricular inotropic response. Overexpressing animals also demonstrated reduced infarct size and preserved cardiac function 24 hours after ischemia-reperfusion. Up-regulation of RXFP1 via AAV9 vectors has potential therapeutic utility in preventing adverse remodeling after myocardial infarction.

Human Recombinant Relaxin (Serelaxin) as Anti-fibrotic Agent: Pharmacology, Limitations and Actual Perspectives

Relaxin (recombinant human relaxin-2 hormone; RLX-2; serelaxin) had raised expectations as a new medication for fibrotic diseases. A plethora of in vitro and in vivo studies have offered convincing demonstrations that relaxin promotes remodelling of connective tissue extracellular matrix mediated by inhibition of multiple fibrogenic pathways, especially the downstream signalling of transforming growth factor (TGF)-β1, a major pro-fibrotic cytokine, and the recruitment and activation of myofibroblast, the main fibrosis-generating cells. However, all clinical trials with relaxin in patients with fibrotic diseases gave inconclusive results. In this review, we have summarized the molecular mechanisms of fibrosis, highlighting those which can be effectively targeted by relaxin. Then, we have performed a critical reappraisal of the clinical trials performed to-date with relaxin as anti-fibrotic drug, in order to highlight their key points of strength and weakness and to identify some future opportunities for the therapeutic use of relaxin, or its analogues, in fibrotic diseases and pathologic scarring which, in our opinion, deserve to be investigated.

Design, synthesis and biological evaluation of anticholinesterase peptides: Fragment-based vs. template-based peptide design

The prevalence of Alzheimer's disease (AD) has become a substantial global concern. Approved AChE inhibitors have been used for symptomatic treatment of AD. Binding of amyloid β (Aβ) to the peripheral anionic site of AChE facilitates the formation of Aβ plaques. Blocking this proposed protein-protein interaction by inhibition of the peripheral anionic site of AChE, in addition to increasing the level of ACh, reduces the Aβ aggregation and might qualify to slow down the progression of disease besides the palliative treatment. Targeting protein-protein interactions consider as one of the most challenging issues in the realm of drug design in which peptides have potentials to excel in. In the present study, we applied two virtual fragment-based and template-based approaches to design peptidic inhibitors of the PAS of AChE. Based on the in silico studies, high scored peptides p2 (WTWYGYWVW) and p10 (NHRMLTRRY) obtained from fragment-based and template-based design respectively. Regarding in vitro results, p2 (IC₅₀ = 16 ± 3.2 μM) and p10 (IC₅₀ = 23.6 ± 4.9 μM) showed significant AChE inhibitory effects. The molecular mechanism of inhibition studied by Lineweaver-Burk plots was mixed inhibition for both peptides. The in vitro results conformed to the in silico results and showed that both peptides occupied the CAS and PAS of AChE. The comparison of two peptide-design approaches revealed that the fragment-based design had more chemical diversity and showed priority to the template-based design. According to the obtained results, peptidic inhibitors of AChE designed by the proposed fragment-based approach might be more efficient in comparison to traditional approaches.

Recent Advances and Computational Approaches in Peptide Drug Discovery

BACKGROUND

Drug design and development is a vast field that requires huge investment along with a long duration for providing approval to suitable drug candidates. With the advancement in the field of genomics, the information about druggable targets is being updated at a fast rate which is helpful in finding a cure for various diseases.

METHODS

There are certain biochemicals as well as physiological advantages of using peptide-based therapeutics. Additionally, the limitations of peptide-based drugs can be overcome by modulating the properties of peptide molecules through various biomolecular engineering techniques. Recent advances in computational approaches have been helpful in studying the effect of peptide drugs on the biomolecular targets. Receptor - ligand-based molecular docking studies have made it easy to screen compatible inhibitors against a target.Furthermore, there are simulation tools available to evaluate stability of complexes at the molecular level. Machine learning methods have added a new edge by enabling accurate prediction of therapeutic peptides.

RESULTS

Peptide-based drugs are expected to take over many popular drugs in the near future due to their biosafety, lower off-target binding chances and multifunctional properties.

CONCLUSION

This article summarises the latest developments in the field of peptide-based therapeutics related to their usage, tools, and databases.

Recombinant human H2 relaxin (serelaxin) as a cardiovascular drug: aiming at the right target

Serelaxin (recombinant human relaxin-2 hormone; RLX-2) had raised expectations as a new medication for cardiovascular diseases. Evidence from preclinical studies indicated that serelaxin has chronotropic, inotropic, and anti-arrhythmic actions on the myocardium and cardioprotective effects mediated by vasodilation, angiogenesis, and inhibition of inflammation and fibrosis. However, clinical trials with serelaxin in patients with acute heart failure (AHF) gave inconclusive results. A critical reappraisal of the comprehensive cardiovascular actions of serelaxin clearly delineates acute myocardial infarction (AMI) as a feasible therapeutic target. Serelaxin acts at multiple levels on the pathogenic mechanisms of AMI and previous in vivo studies suggest that its administration at reperfusion affords myocardial salvage. Thus, serelaxin could be an effective adjunctive medical therapy to coronary angioplasty.

Therapeutic effects of a small molecule agonist of the relaxin receptor ML290 in liver fibrosis

Fibrosis is an underlying cause of cirrhosis and hepatic failure resulting in end stage liver disease with limited pharmacological options. The beneficial effects of relaxin peptide treatment were demonstrated in clinically relevant animal models of liver fibrosis. However, the use of relaxin is problematic because of a short half-life. The aim of this study was to test the therapeutic effects of recently identified small molecule agonists of the human relaxin receptor, relaxin family peptide receptor 1 (RXFP1). The lead compound of this series, ML290, was selected based on its effects on the expression of fibrosis-related genes in primary human stellate cells. RNA sequencing analysis of TGF-β1-activated LX-2 cells showed that ML290 treatment primarily affected extracellular matrix remodeling and cytokine signaling, with expression profiles indicating an antifibrotic effect of ML290. ML290 treatment in human liver organoids with LPS-induced fibrotic phenotype resulted in a significant reduction of type I collagen. The pharmacokinetics of ML290 in mice demonstrated its high stability in vivo, as evidenced by the sustained concentrations of compound in the liver. In mice expressing human RXFP1 gene treated with carbon tetrachloride, ML290 significantly reduced collagen content, α-smooth muscle actin expression, and cell proliferation around portal ducts. In conclusion, ML290 demonstrated antifibrotic effects in liver fibrosis.-Kaftanovskaya, E. M., Ng, H. H., Soula, M., Rivas, B., Myhr, C., Ho, B. A., Cervantes, B. A., Shupe, T. D., Devarasetty, M., Hu, X., Xu, X., Patnaik, S., Wilson, K. J., Barnaeva, E., Ferrer, M., Southall, N. T., Marugan, J. J., Bishop, C. E., Agoulnik, I. U., Agoulnik, A. I. Therapeutic effects of a small molecule agonist of the relaxin receptor ML290 in liver fibrosis.

Targeting the relaxin/insulin-like family peptide receptor 1 and 2 with small molecule compounds

The peptide hormone relaxin has beneficial roles in several organs through its action on its cognate G protein-coupled receptor, RXFP1. Relaxin administration is limited to intravenous, subcutaneous, intramuscular, or spinal injection. Another drawback of peptide-based therapy is the short half-life, which requires continuous delivery of the drug to achieve efficient concentration in target organs. The discovery of a non-peptide small molecule agonist of RXFP1, ML290, provides an alternative to the natural ligand. This review summarizes the development of ML290 and its potential future therapeutic applications in various diseases, including liver fibrosis and cardiovascular diseases. We also discuss the development of small molecule agonists targeting the insulin-like 3 receptor, RXFP2, and propose the potential use of these small molecules in the context of bone and muscle remodeling.

Recent developments in relaxin mimetics as therapeutics for cardiovascular diseases

Cardiovascular disease is the most common cause of mortality worldwide, accounting for almost 50% of all deaths globally. Vascular endothelial dysfunction and fibrosis are critical in the pathophysiology of cardiovascular disease. Relaxin, an insulin-like peptide, is known to have beneficial actions in the cardiovascular system through its vasoprotective and anti-fibrotic effects. However, relaxin has several limitations of peptide-based drugs such as poor oral bioavailability, laborious, and expensive to synthesize. This review will focus on recent developments in relaxin mimetics, their pharmacology, associated signalling mechanisms, and their therapeutic potential for the management and treatment of cardiovascular disease.

Targeting the Relaxin Pathway for Liver Disease Treatment

Hepatic fibrosis is a progressive disease with few treatment options outside of transplantation. Relaxin is a member of the insulin/relaxin superfamily of peptide hormones. Originally known for its roles in pregnancy, relaxin promotes reproductive tissue remodelling and regulates vascular changes, including increased arterial compliance and reduced vascular resistance. Outside of pregnancy, relaxin plays a major role in the protection of organs from excess extracellular matrix accumulation, as demonstrated by the relaxin-null mouse, which develops widespread fibrosis with ageing. Relaxin reduces scarring due to excess collagen deposition by inhibiting collagen production while simultaneously promoting its degradation and can reduce established fibrosis in several animal models of extracellular matrix-associated disease, including liver fibrosis. Treatment with relaxin reduces the myofibroblastic phenotype of activated hepatic stellate cells, the major hepatic collagen-producing cell in fibrosis and cirrhosis. Relaxin also has haemodynamic effects, including vasodilation, and can reduce portal hypertension associated with cirrhosis. In this review, a brief overview of hepatic fibrosis and the role of the hepatic stellate cell will be presented, followed by an introduction to relaxin and its actions. The use of relaxin to treat preclinical models of fibrotic diseases, including liver diseases, will also be discussed. Finally, the completed, current, and ongoing clinical trials of relaxin in human disease will be described, followed by the limitations and future directions for the use of relaxin for disease treatment.

Recent progress in the understanding of relaxin family peptides and their receptors

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Human Relaxin Receptor Is Fully Functional in Humanized Mice and Is Activated by Small Molecule Agonist ML290

Relaxin, a small peptide hormone of the insulin/relaxin family, demonstrated antifibrotic, organ protective, vasodilatory, and proangiogenic properties in clinical trials and several animal models of human diseases. Relaxin family peptide receptor 1 (RXFP1) is the relaxin cognate G protein-coupled receptor. We have identified a series of small molecule agonists of human RXFP1. The lead compound ML290 demonstrated preferred absorption, distribution, metabolism, and excretion profiles, is easy to synthesize, and has high stability in vivo. However, ML290 does not activate rodent RXFP1s and therefore cannot be tested in common preclinical animal models. Here we describe the production and analysis of a mouse transgenic model, a knock-out/knock-in of the human RXFP1 (hRXFP1) complementary DNA into the mouse Rxfp1 (mRxfp1) gene. Insertion of the vector into the mRxfp1 locus caused disruption of mRxfp1 and expression of hRXFP1. The transcriptional expression pattern of the hRXFP1 allele was similar to mRxfp1. Female mice homozygous for hRXFP1 showed relaxation of the pubic symphysis at parturition and normal development of mammary nipples and vaginal epithelium, indicating full complementation of mRxfp1 gene ablation. Intravenous injection of relaxin led to an increase in heart rate in humanized and wild-type females but not in Rxfp1-deficient mice, whereas ML290 increased heart rate in humanized but not wild-type animals, suggesting specific target engagement by ML290. Moreover, intraperitoneal injection of ML290 caused a decrease in blood osmolality. Taken together, our data show humanized RXFP1 mice can be used for testing relaxin receptor modulators in various preclinical studies.

Synthetic non-peptide low molecular weight agonists of the relaxin receptor 1

Relaxin is a small heterodimeric peptide hormone of the insulin/relaxin superfamily produced mainly in female and male reproductive organs. It has potent antifibrotic, vasodilatory and angiogenic effects and regulates the normal function of various physiological systems. Preclinical studies and recent clinical trials have shown the promise of recombinant relaxin as a therapeutic agent in the treatment of cardiovascular and fibrotic diseases. However, there are the universal drawbacks of peptide-based pharmacology that apply to relaxin: a short half-life in vivo requires its continuous delivery, and there are high costs of production, storage and treatment, as well as the possibility of immune responses. All these issues can be resolved by the development of low non-peptide MW agonists of the relaxin receptors which are stable, bioavailable, easily synthesized and specific. In this review, we describe the discovery and characterization of the first series of such compounds. The lead compound, ML290, binds to an allosteric site of the relaxin GPCR, RXFP1. ML290 shows high activity and efficacy, measured by cAMP response, in cells expressing endogenous or transfected RXFP1. Relaxin-like effects of ML290 were shown in various functional cellular assays in vitro. ML290 has excellent absorption, distribution, metabolism and excretion properties and in vivo stability. The identified series of low MW agonists does not activate rodent RXFP1 receptors and thus, the production of a RXFP1 humanized mouse model is needed for preclinical studies. The future analysis and clinical perspectives of relaxin receptor agonists are discussed.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.