The pharmacokinetics of recombinant human relaxin in nonpregnant women after intravenous, intravaginal, and intracervical administration

Relaxin as a treatment for musculoskeletal fibrosis: What we know and future directions

Fibrotic changes in musculoskeletal diseases arise from the abnormal buildup of fibrotic tissue around the joints, leading to limited mobility, compromised joint function, and diminished quality of life. Relaxin (RLX) attenuates fibrosis by accelerating collagen degradation and inhibiting excessive extracellular matrix (ECM) production. Further, RLX disrupts myofibroblast activation by modulating the TGF-β/Smads signaling pathways, which reduces connective tissue fibrosis. However, the mechanisms and effects of RLX in musculoskeletal pathologies are emerging as increasing research focuses on relaxin's impact on skin, ligaments, tendons, cartilage, joint capsules, connective tissues, and muscles. This review delineates the actions of relaxin within the musculoskeletal system and the challenges to its clinical application. Relaxin shows significant potential in both in vivo and in vitro studies for broadly managing musculoskeletal fibrosis; however, challenges such as short biological half-life and sex-specific responses may pose hurdles for clinical use.

Identification of Novel Series of Potent and Selective Relaxin Family Peptide Receptor 1 (RXFP1) Agonists

Relaxin H2 is a clinically relevant peptide agonist for relaxin family peptide receptor 1 (RXFP1), but a combination of this hormone's short plasma half-life and the need for injectable delivery limits its therapeutic potential. We sought to overcome these limitations through the development of a potent small molecule (SM) RXFP1 agonist. Although two large SM HTS campaigns failed in identifying suitable hit series, we uncovered novel chemical space starting from the only known SM RXFP1 agonist series, represented by ML290. Following a design-make-test-analyze strategy based on improving early dose to man ranking, we discovered compound 42 (AZ7976), a highly selective RXFP1 agonist with sub-nanomolar potency. We used AZ7976, its 10 000-fold less potent enantiomer 43 and recombinant relaxin H2 to evaluate in vivo pharmacology and demonstrate that AZ7976-mediated heart rate increase in rats was a result of RXFP1 agonism. As a result, AZ7976 was selected as lead for continued optimization.

Synthesis of A11Cys-B11Cys Disulfide Surrogates of H2 Relaxin through an Intermolecular Native Chemical Ligation-Assisted Diaminodiacid Strategy

We report an intermolecular native chemical ligation-assisted diaminodiacid strategy for the flexible construction of A11Cys-B11Cys disulfide surrogates of H2 relaxin. The practicality of this strategy was evidenced by the synthesis of four new H2 relaxin analogs, among which H2-2a-B28Ile is found to exhibit improved potency, selectivity, and stability compared with native H2 relaxin.

A Lipidated Single-B-Chain Derivative of Relaxin Exhibits Improved In Vitro Serum Stability without Altering Activity

Human relaxin-2 (H2 relaxin) is therapeutically very important due to its strong anti-fibrotic, vasodilatory, and cardioprotective effects. Therefore, relaxin’s receptor, relaxin family peptide receptor 1 (RXFP1), is a potential target for the treatment of fibrosis and related disorders, including heart failure. H2 relaxin has a complex two-chain structure (A and B) and three disulfide bridges. Our laboratory has recently developed B7-33 peptide, a single-chain agonist based on the B-chain of H2 relaxin. However, the peptide B7-33 has a short circulation time in vitro in serum (t1/2 = ~6 min). In this study, we report structure-activity relationship studies on B7-33 utilizing different fatty-acid conjugations at different positions. We have shown that by fatty-acid conjugation with an appropriate spacer length, the in vitro half-life of B7-33 can be increased from 6 min to 60 min. In the future, the lead lipidated molecule will be studied in animal models to measure its PK/PD properties, which will lead to their pre-clinical applications.

Single-Shot Solid-Phase Synthesis of Full-Length H2 Relaxin Disulfide Surrogates

Chemical synthesis of insulin superfamily proteins (ISPs) has recently been widely studied to develop next-generation drugs. Separate synthesis of multiple peptide fragments and tedious chain-to-chain folding are usually encountered in these studies, limiting accessibility to ISP derivatives. Here we report the finding that insulin superfamily proteins (e.g. H2 relaxin, insulin itself, and H3 relaxin) incorporating a pre-made diaminodiacid bridge at A-B chain terminal disulfide can be easily and rapidly synthesized by a single-shot automated solid-phase synthesis and expedient one-step folding. Our new H2 relaxin analogues exhibit almost identical structures and activities when compared to their natural counterparts. This new synthetic strategy will expediate production of new ISP analogues for pharmaceutical studies.

Porcine Relaxin but Not Serelaxin Shows Residual Bioactivity after In Vitro Simulated Intestinal Digestion-Clues for the Development of New Relaxin Peptide Agonists Suitable for Oral Delivery

Despite human recombinant H2 relaxin or serelaxin holding promise as a cardiovascular drug, its actual efficacy in chronic treatment of heart failure patients was hampered by the need to be administered by multiple daily IV injections for a long time, with obvious drawbacks in terms of patients' compliance. This in vitro study aimed at exploring the molecular background for a possible administration of the peptide hormone relaxin by the oral route. Serelaxin and purified porcine relaxin (pRLX) were subjected to simulated intestinal fluid (SIF) enzymatic digestion in vitro to mimic the behavior of gastroprotective formulations. The digestion time course was studied by HPLC, and the relative bio-potency of the intact molecules and their proteolytic fragments was assessed by second messenger (cAMP) response in RXFP1 relaxin receptor-bearing THP-1 human monocytic cells. Both intact proteins (100 ng/mL) induced a significant cAMP rise in THP-1 cells. Conversely, SIF-treated serelaxin showed a brisk (30 s) bioactivity decay, dropping down to the levels of the unstimulated controls at 120 s, whereas SIF-treated pRLX retained significant bioactivity for up to 120 s. After that, it progressively declined to the levels of the unstimulated controls. HPLC analysis indicates that this bioactivity could be ascribed to a minor component of the pRLX sample more resistant to proteolysis. When identified and better characterized, this peptide could be exploited for the development of synthetic relaxin agonists suitable for oral formulations.

Liposomal Entrapment or Chemical Modification of Relaxin2 for Prolongation of Its Stability and Biological Activity

Relaxin (RLX) is a protein that is structurally similar to insulin and has interesting biological activities. As with all proteins, preservation of RLX’s structural integrity/biological functionality is problematic. Herein, we investigated two methods for increasing the duration of relaxin-2’s (RLX2) biological activity: synthesis of a palmitoyl RLX2 conjugate (P-RLX2) with the use of a Palmitoyl-l-Glu-OtBu peptide modifier, and encapsulation into liposomes of P-RLX2, RLX2, and its oxidized form (O-RLX2). For liposomal encapsulation thin-film hydration and DRV methods were applied, and different lipid compositions were tested for optimized protein loading. RLX2 and O-RLX2 were quantified by HPLC. The capability of the peptides/conjugate to stimulate transfected cells to produce cyclic adenosine monophosphate (cAMP) was used as a measure of their biological activity. The stability and bioactivity of free and liposomal RLX2 types were monitored for a 30 d period, in buffer (in some cases) and bovine serum (80%) at 37 °C. The results showed that liposome encapsulation substantially increased the RLX2 integrity in buffer; PEGylated liposomes demonstrated a higher protection. Liposome encapsulation also increased the stability of RLX2 and O-RLX2 in serum. Considering the peptide’s biological activity, cAMP production of RLX2 was higher than that of the oxidized form and the P-RLX2 conjugate (which demonstrated a similar activity to O-RLX2 when measured in buffer, but lower when measured in the presence of serum proteins), while liposome encapsulation resulted in a slight decrease of bioactivity initially, but prolonged the peptide bioactivity during incubation in serum. It was concluded that liposome encapsulation of RLX2 and synthetic modification to P-RLX2 can both prolong RLX2 peptide in vitro stability; however, the applied chemical conjugation results in a significant loss of bioactivity (cAMP production), whereas the effect of liposome entrapment on RLX2 activity was significantly lower.

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 as an anti-fibrotic treatment: Perspectives, challenges and future directions

Fibrosis refers to the scarring and hardening of tissues, which results from a failed immune system-coordinated wound healing response to chronic organ injury and which manifests from the aberrant accumulation of various extracellular matrix components (ECM), primarily collagen. Despite being a hallmark of prolonged tissue damage and related dysfunction, and commonly associated with high morbidity and mortality, there are currently no effective cures for its regression. An emerging therapy that meets several criteria of an effective anti-fibrotic treatment, is the recombinant drug-based form of the human hormone, relaxin (also referred to as serelaxin, which is bioactive in several other species). This review outlines the broad anti-fibrotic and related organ-protective roles of relaxin, mainly from studies conducted in preclinical models of ageing and fibrotic disease, including its ability to ameliorate several aspects of fibrosis progression and maturation, from immune cell infiltration, pro-inflammatory and pro-fibrotic cytokine secretion, oxidative stress, organ hypertrophy, cell apoptosis, myofibroblast differentiation and ECM production, to its ability to facilitate established ECM degradation. Studies that have compared and/or combined these therapeutic effects of relaxin with current standard of care medication have also been discussed, along with the main challenges that have hindered the translation of the anti-fibrotic efficacy of relaxin to the clinic. The review then outlines the future directions as to where scientists and several pharmaceutical companies that have recognized the therapeutic potential of relaxin are working towards, to progress its development as a treatment for human patients suffering from various fibrotic diseases.

Women-specific routes of administration for drugs: A critical overview

The woman's body presents a number of unique anatomical features that can constitute valuable routes for the administration of drugs, either for local or systemic action. These are associated with genitalia (vaginal, endocervical, intrauterine, intrafallopian and intraovarian routes), changes occurring during pregnancy (extra-amniotic, intra-amniotic and intraplacental routes) and the female breast (breast intraductal route). While the vaginal administration of drug products is common, other routes have limited clinical application and are fairly unknown even for scientists involved in drug delivery science. Understanding the possibilities and limitations of women-specific routes is of key importance for the development of new preventative, diagnostic and therapeutic strategies that will ultimately contribute to the advancement of women's health. This article provides an overview on women-specific routes for the administration of drugs, focusing on aspects such as biological features pertaining to drug delivery, relevance in current clinical practice, available drug dosage forms/delivery systems and administration techniques, as well as recent trends in the field.

Anti-apoptotic and Matrix Remodeling Actions of a Small Molecule Agonist of the Human Relaxin Receptor, ML290 in Mice With Unilateral Ureteral Obstruction

Diseases, such as diabetes and hypertension, often lead to chronic kidney failure. The peptide hormone relaxin has been shown to have therapeutic effects in various organs. In the present study, we tested the hypothesis that ML290, a small molecule agonist of the human relaxin receptor (RXFP1), is able to target the kidney to remodel the extracellular matrix and reduce apoptosis induced by unilateral ureteral obstruction (UUO). UUO was performed on the left kidney of humanized RXFP1 mice, where the right kidneys served as contralateral controls. Mice were randomly allocated to receive either vehicle or ML290 (30 mg/kg) via daily intraperitoneal injection, and kidneys were collected for apoptosis, RNA, and protein analyses. UUO significantly increased expression of pro-apoptotic markers in both vehicle- and ML290-treated mice when compared to their contralateral control kidneys. Specifically, Bax expression and Erk1/2 activity were upregulated, accompanied by an increase of TUNEL-positive cells in the UUO kidneys. Additionally, UUO induced marked increase in myofibroblast differentiation and aberrant remodeling on the extracellular matrix. ML290 suppressed these processes by promoting a reduction of pro-apoptotic, fibroblastic, and inflammatory markers in the UUO kidneys. Finally, the potent effects of ML290 to remodel the extracellular matrix were demonstrated by its ability to reduce collagen gene expression in the UUO kidneys. Our data indicate that daily administration of ML290 has renal protective effects in the UUO mouse model, specifically through its anti-apoptotic and extracellular matrix remodeling properties.

Pulmonary myeloid cell uptake of biodegradable nanoparticles conjugated with an anti-fibrotic agent provides a novel strategy for treating chronic allergic airways disease

Asthma (chronic allergic airways disease, AAD) is characterized by airway inflammation (AI), airway remodeling (AWR) and airway hyperresponsiveness (AHR). Current treatments for AAD mainly focus on targeting AI and its contribution AHR, with the use of corticosteroids. However, there are no therapies for the direct treatment of AWR, which can contribute to airway obstruction, AHR and corticosteroid resistance independently of AI. The acute heart failure drug, serelaxin (recombinant human gene-2 relaxin, RLX), has potential anti-remodeling and anti-fibrotic effects but only when continuously infused or injected to overcome its short half-life. To alleviate this limitation, we conjugated serelaxin to biodegradable and noninflammatory nanoparticles (NP-RLX) and evaluated their therapeutic potential on measures of AI, AWR and AHR, when intranasally delivered to a preclinical rodent model of chronic AAD and TGF-β1-stimulated collagen gel contraction from asthma patient-derived myofibroblasts. NP-RLX was preferentially taken-up by CD206⁺-infiltrating and CD68⁺-tissue resident alveolar macrophages. Furthermore, NP-RLX ameliorated the chronic AAD-induced AI, pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), chemokines (CCL2, CCL11) and the pro-fibrotic TGF-β1/IL-1β axis on AWR and resulting AHR, as well as human myofibroblast-induced collagen gel contraction, to a similar extent as unconjugated RLX. Hence, NP-RLX represents a novel strategy for treating the central features of asthma.

Hepatic macrophages act as a central hub for relaxin-mediated alleviation of liver fibrosis

Relaxin is an antifibrotic peptide hormone previously assumed to directly reverse the activation of hepatic stellate cells for liver fibrosis resolution. Using nanoparticle-mediated delivery, here we show that, although relaxin gene therapy reduces liver fibrosis in vivo, in vitro treatment fails to induce quiescence of the activated hepatic stellate cells. We show that hepatic macrophages express the primary relaxin receptor, and that, on relaxin binding, they switch from the profibrogenic to the pro-resolution phenotype. The latter releases exosomes that promote the relaxin-mediated quiescence of activated hepatic stellate cells through miR-30a-5p. Building on these results, we developed lipid nanoparticles that preferentially target activated hepatic stellate cells in the fibrotic liver and encapsulate the relaxin gene and miR-30a-5p mimic. The combinatorial gene therapy achieves synergistic antifibrosis effects in models of mouse liver fibrosis. Collectively, our findings highlight the key role that macrophages play in the relaxin-primed alleviation of liver fibrosis and demonstrate a proof-of-concept approach to devise antifibrotic strategies through the complementary application of nanotechnology and basic science.

The Prognosis of Arthrofibroses: Prevalence, Clinical Shortcomings, and Future Prospects

Fibrosis is the dysregulated biosynthesis of connective tissue that results from persistent infection, high serum cholesterol, surgery, trauma, or prolonged joint immobilization. As a disease that impacts connective tissue, it is prevalent across the body and disrupts normal extracellular and tissue organization. Ultimately, fibrosis impairs the tissue structural, mechanical, or biochemical function. This review describes the clinical landscape of joint fibrosis, that is, arthrofibrosis, including the risk factors and causes, as well as current clinical treatments and their shortcomings. Because treating arthrofibrosis remains an unmet clinical challenge, we present several animal models used for exploration of the physiopathology of arthrofibrosis and summarize their use for testing novel treatments. We then discuss therapeutics for the prevention or treatment of arthrofibrosis that are in preclinical development and in ongoing clinical trials. We conclude with recent findings from molecular biological studies of arthrofibroses that shed insight on future areas of research for improved treatments.

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.

Antifibrotic strategies for medical devices

A broad range of medical devices initiate an immune reaction known as the foreign body response (FBR) upon implantation. Here, collagen deposition at the surface of the implant occurs as a result of the FBR, ultimately leading to fibrous encapsulation and, in many cases, reduced function or failure of the device. Despite significant efforts, the prevention of fibrotic encapsulation has not been realized at this point in time. However, many next-generation medical technologies including cellular therapies, sensors and devices depend on the ability to modulate and control the FBR. For these technologies to become viable, significant advances must be made in understanding the underlying mechanism of this response as well as in the methods modulating this response. In this review, we highlight recent advances in the development of materials and coatings providing a reduced FBR and emphasize key characteristics of high-performing approaches. We also provide a detailed overview of the state-of-the-art in strategies relying on controlled drug release, the surface display of bioactive signals, materials-based approaches, and combinations of these approaches. Finally, we offer perspectives on future directions in this field.

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.

The future of bronchodilation: looking for new classes of bronchodilators

Available bronchodilators can satisfy many of the needs of patients suffering from airway disorders, but they often do not relieve symptoms and their long-term use raises safety concerns. Therefore, there is interest in developing new classes that could help to overcome the limits that characterise the existing classes.At least nine potential new classes of bronchodilators have been identified: 1) selective phosphodiesterase inhibitors; 2) bitter-taste receptor agonists; 3) E-prostanoid receptor 4 agonists; 4) Rho kinase inhibitors; 5) calcilytics; 6) agonists of peroxisome proliferator-activated receptor-γ; 7) agonists of relaxin receptor 1; 8) soluble guanylyl cyclase activators; and 9) pepducins. They are under consideration, but they are mostly in a preclinical phase and, consequently, we still do not know which classes will actually be developed for clinical use and whether it will be proven that a possible clinical benefit outweighs the impact of any adverse effect.It is likely that if developed, these new classes may be a useful addition to, rather than a substitution of, the bronchodilator therapy currently used, in order to achieve further optimisation of bronchodilation.

Coatings Releasing the Relaxin Peptide Analogue B7-33 Reduce Fibrotic Encapsulation

The development of antifibrotic materials and coatings that can resist the foreign body response (FBR) continues to present a major hurdle in the advancement of current and next-generation implantable medical devices, biosensors, and cell therapies. From an implant perspective, the most important issue associated with the FBR is the prolonged inflammatory response leading to a collagenous capsule that ultimately blocks mass transport and communication between the implant and the surrounding tissue. Up to now, most attempts to reduce the capsule thickness have focused on providing surface coatings that reduce protein fouling and cell attachment. Here, we present an approach that is based on the sustained release of a peptide drug interfering with the FBR. In this study, the biodegradable polymer poly(lactic-co-glycolic) acid (PLGA) was used as a coating releasing the relaxin peptide analogue B7-33, which has been demonstrated to reduce organ fibrosis in animal models. While in vitro protein quantification was used to demonstrate controlled release of the antifibrotic peptide B7-33 from PLGA coatings, an in vitro reporter cell assay was used to demonstrate that B7-33 retains activity against the relaxin family peptide receptor 1 (RXFP1). Subcutaneous implantation of PLGA-coated polypropylene samples in mice with and without the peptide demonstrated a marked reduction in capsule thickness (49.2%) over a 6 week period. It is expected that this novel approach will open the door to a range of new and improved implantable medical devices.

Human Relaxin-2 Fusion Protein Treatment Prevents and Reverses Isoproterenol-Induced Hypertrophy and Fibrosis in Mouse Heart

Background

Heart failure is one of the leading causes of death in Western countries, and there is a need for new therapeutic approaches. Relaxin‐2 is a peptide hormone that mediates pleiotropic cardiovascular effects, including antifibrotic, angiogenic, vasodilatory, antiapoptotic, and anti‐inflammatory effects in vitro and in vivo.

Methods and Results

We developed RELAX10, a fusion protein composed of human relaxin‐2 hormone and the Fc of a human antibody, to test the hypothesis that extended exposure of the relaxin‐2 peptide could reduce cardiac hypertrophy and fibrosis. RELAX10 demonstrated the same specificity and similar in vitro activity as the relaxin‐2 peptide. The terminal half‐life of RELAX10 was 7 days in mouse and 3.75 days in rat after subcutaneous administration. We evaluated whether treatment with RELAX10 could prevent and reverse isoproterenol‐induced cardiac hypertrophy and fibrosis in mice. Isoproterenol administration in mice resulted in increased cardiac hypertrophy and fibrosis compared with vehicle. Coadministration with RELAX10 significantly attenuated the cardiac hypertrophy and fibrosis compared with untreated animals. Isoproterenol administration significantly increased transforming growth factor β1 (TGF‐β1)–induced fibrotic signaling, which was attenuated by RELAX10. We found that RELAX10 also significantly increased protein kinase B/endothelial NO synthase signaling and protein S‐nitrosylation. In the reversal study, RELAX10‐treated animals showed significantly reduced cardiac hypertrophy and collagen levels.

Conclusions

These findings support a potential role for RELAX10 in the treatment of heart failure.

Relaxin gene delivery mitigates liver metastasis and synergizes with check point therapy

Activated hepatic stellate cell (aHSC)-mediated liver fibrosis is essential to the development of liver metastasis. Here, we discover intra-hepatic scale-up of relaxin (RLN, an anti-fibrotic peptide) in response to fibrosis along with the upregulation of its primary receptor (RXFP1) on aHSCs. The elevated expression of RLN serves as a natural regulator to deactivate aHSCs and resolve liver fibrosis. Therefore, we hypothesize this endogenous liver fibrosis repair mechanism can be leveraged for liver metastasis treatment via enforced RLN expression. To validate the therapeutic potential, we utilize aminoethyl anisamide-conjugated lipid-calcium-phosphate nanoparticles to deliver plasmid DNA encoding RLN. The nanoparticles preferentially target metastatic tumor cells and aHSCs within the metastatic lesion and convert them as an in situ RLN depot. Expressed RLN reverses the stromal microenvironment, which makes it unfavorable for established liver metastasis to grow. In colorectal, pancreatic, and breast cancer liver metastasis models, we confirm the RLN gene therapy results in significant inhibition of metastatic progression and prolongs survival. In addition, enforced RLN expression reactivates intra-metastasis immune milieu. The combination of the RLN gene therapy with PD-L1 blockade immunotherapy further produces a synergistic anti-metastatic efficacy. Collectively, the targeted RLN gene therapy represents a highly efficient, safe, and versatile anti-metastatic modality, and is promising for clinical translation.

Relaxin gene therapy: A promising new treatment option for various diseases with aberrant fibrosis or irregular angiogenesis

Relaxin (RLX) is an insulin-like polypeptide hormone that was initially introduced for its pregnancy-related function. Subsequent studies revealed that RLX possesses anti-fibrotic functions in tumors and nonreproductive tissues, such as skin, lungs, and others. This aspect of the RLX has been explored for the treatment of various illnesses, such as cardiac fibrosis, liver fibrosis, and solid tumors. With gene therapy coming into age with increasing number of products being approved by regulatory bodies in Europe and United States, we aim to discuss how RLX have been utilized in scope of gene therapy for treatment of various illnesses.

Relaxin and fibrosis: Emerging targets, challenges, and future directions

The peptide hormone relaxin is well-known for its anti-fibrotic actions in several organs, particularly from numerous studies conducted in animals. Acting through its cognate G protein-coupled receptor, relaxin family peptide receptor 1 (RXFP1), serelaxin (recombinant human relaxin) has been shown to consistently inhibit the excessive extracellular matrix production (fibrosis) that results from the aberrant wound-healing response to tissue injury and/or chronic inflammation, and at multiple levels. Furthermore, it can reduce established scarring by promoting the degradation of aberrant extracellular matrix components. Following on from the review that describes the mechanisms and signaling pathways associated with the extracellular matrix remodeling effects of serelaxin (Ng et al., 2019), this review focuses on newly identified tissue targets of serelaxin therapy in fibrosis, and the limitations associated with (se)relaxin research.

Relaxin-2 for heart failure with preserved ejection fraction (HFpEF): Rationale for future clinical trials

Heart Failure with preserved Ejection Fraction (HFpEF), a distinct sub-entity of chronic heart failure characterized by generalized inflammatory non-compliance of the cardio-vascular system, is associated with high mortality and still an unmet medical need. Many novel and promising therapeutic approaches have failed in large studies. This review focuses on basic research, pre-clinical and clinical findings that may account for the potential benefit of relaxin-2 in HFpEF. The peptide combines short-term hemodynamic advantages, such as moderate blood pressure decline and functional endothelin-1 antagonism, with a wealth of protective effects harboring long-term benefits, such as anti-inflammatory, anti-fibrotic, and anti-oxidative actions. These pleiotropic effects are exerted through a complex and intricate signaling cascade involving the relaxin-family peptide receptor-1, the glucocorticoid receptor, the nitric oxide system, and a cell type-dependent variety of down-stream mediators.

Population pharmacokinetics of serelaxin in patients with acute or chronic heart failure, hepatic or renal impairment, or portal hypertension and in healthy subjects

AIMS

Serelaxin is a recombinant human relaxin-2 peptide being developed for the treatment of acute heart failure (AHF). The present analyses aimed to evaluate serelaxin pharmacokinetics following intravenous administration and to identify covariates that may explain pharmacokinetic variability in healthy subjects and patients.

METHODS

Serum concentration-time data for 613 subjects from nine phase I and II studies were analysed using a nonlinear mixed-effects model to estimate population pharmacokinetics and identify significant covariates. A quantile regression analysis was also conducted to assess the relationship between clearance and covariates by including sparse data from a phase III study.

RESULTS

A three-compartment disposition model was established to describe serelaxin pharmacokinetics. Three out of 23 covariates, including baseline body mass index (BMI) and estimated glomerular filtration rate (eGFR) and study A1201, were identified as significant covariates for clearance but with a moderate impact on steady-state concentration, reducing the intersubject variability from 44% in the base model to 41% in the final model with covariates. The steady-state volume of distribution (Vss) was higher in patients with AHF (544 ml kg^-1 ) or chronic heart failure (434 ml kg^-1 ), compared with typical nonheart failure subjects (347 ml kg^-1 ). Quantile regression analysis showed that a 20% increase in BMI or a 20% decrease in eGFR decreased serelaxin clearance by 9.2% or 5.2%, respectively.

CONCLUSIONS

Patients with HF showed higher Vss but similar clearance (and therefore steady-state exposure) vs. non nonheart failure subjects. BMI and eGFR were identified as the main covariates explaining intersubject variability in clearance; however, the impact of these covariates on steady-state concentration was moderate and therefore unlikely to be clinically relevant.

Relaxin as a Therapeutic Target for the Cardiovascular Complications of Diabetes

Cardiovascular complications are the major cause of mortality in patients with diabetes. This is closely associated with both macrovascular and microvascular complications of diabetes, which lead to organ injuries in diabetic patients. Previous studies have consistently demonstrated the beneficial effects of relaxin treatment for protection of the vasculature, with evidence of antioxidant and anti-remodeling actions. Relaxin enhances nitric oxide, prostacyclin and endothelium-derived hyperpolarization (EDH)-type-mediated relaxation in various vascular beds. These effects of relaxin on the systemic vasculature, coupled with its cardiac actions, reduce pulmonary capillary wedge pressure and pulmonary artery pressure. This results in an overall decrease in systemic and pulmonary vascular resistance in heart failure patients. The anti-fibrotic actions of relaxin are well established, a desirable property in the context of diabetes. Further, relaxin ameliorates diabetic wound healing, with accelerated angiogenesis and vasculogenesis. Relaxin-mediated stimulation of vascular endothelial growth factor (VEGF) and stromal cell-derived factor 1-α, as well as regulation of metalloproteinase expression, ameliorates cardiovascular fibrosis in diabetic mice. In the heart, relaxin is a cardioprotective molecule in several experimental animal models, exerting anti-fibrotic, anti-hypertrophy and anti-apoptotic effects in diabetic pathologies. Collectively, these studies provide a foundation to propose the therapeutic potential for relaxin as an adjunctive agent in the prevention or treatment of diabetes-induced cardiovascular complications. This review provides a comprehensive overview of the beneficial effects of relaxin, and identifies its therapeutic possibilities for alleviating diabetes-related cardiovascular injury.

Relaxin-2 connecting peptide (pro-RLX2) levels in second trimester serum samples to predict preeclampsia

OBJECTIVES

Preeclampsia is a serious complication of pregnancy, threatening fetal and maternal health. The aim of our study is to examine the association between preeclampsia and the connecting peptide of the pregnancy hormone relaxin (pro-RLX2) as a potential new biochemical marker.

STUDY DESIGN

This is a nested case/control study derived from the cohort of pregnancies delivering at Women & Infants Hospital. Cases were identified at a clinic or by hospital codes, and individually confirmed by record review. Stored samples were available from 'integrated' Down syndrome screening. Results were expressed as multiples of the median (MoM).

MAIN OUTCOME MEASURES

Preeclampsia was classified as early/severe, late/severe, or mild based on professional guidelines.

RESULTS

Fifty-one cases were each matched with five control pregnancies. Population distribution parameters were derived for cases and controls. As shown previously, discrimination between cases and controls (applying MoM analysis) was possible for PlGF (0.576, p < .05), inhibin A (1.45, p < .05) and endoglin (1.278, p < .05). No association with preeclampsia was found for pro-RLX2. However, pro-RLX2 correlates with Inhibin A and Endoglin.

CONCLUSIONS

Endoglin, Inhibin A and PlGF are highly predictive of preeclampsia. Quantification of pro-RLX2 is not able to predict preeclampsia. Nevertheless, the potential involvement of relaxin 2/pro-RLX2 in the pathophysiology of preeclampsia requires further study.

Quantification of Relaxin-2 Connecting Peptide (Pro-RLX2) in Human Blood Samples

BACKGROUND

The peptide hormone relaxin-2 is implicated in diverse physiological and pathophysiological processes. Several assays are available for quantification of human relaxin-2, but because stability of the mature peptide in serum is limited, measurement of the more stable connecting peptide (pro-RLX2) might be beneficial.

METHODS

Pro-RLX2 was measured in a sandwich immunoluminometric assay using 2 monoclonal antibodies. The concentration of pro-RLX2 was detected in healthy pregnant (n = 100) and healthy male and nonpregnant female (n = 81) subjects and compared with the concentration of mature relaxin-2 in a subset of samples.

RESULTS

The pro-RLX2 immunoassay has an analytical and functional assay sensitivity (FAS) of 1.59 pmol/L and 1.7 pmol/L, respectively. The analyte is stable in EDTA plasma samples for 8 days at room temperature, dilutes in a linear fashion, and recovery was 103%. The assay system is not biased by common interfering substances. Measurement of 80% of plasma samples from healthy males and females is below the FAS {median 1.49 pmol/L [interquartile range (IQR) of 0.925-2.14 pmol/L]}, and no concentration difference between male and nonpregnant female plasma samples was observed. The median plasma concentration in healthy pregnant women is increased up to 562 pmol/L (IQR 341-789 pmol/L). During pregnancy, pro-RLX2 concentrations decrease with increasing gestation. The correlation coefficient with the R&D assay for mature relaxin-2 was 0.96 (P < 0.0001).

CONCLUSION

Pro-RLX2 is stable in plasma of healthy individuals. Although samples of pregnant women are reliably measurable, most samples from healthy nonpregnant women and men are below the detection limit. Determination of pro-RLX2 concentrations might indicate rate of synthesis of relaxin-2 during pregnancy and therapeutic application of recombinant relaxin (Serelaxin).

Serelaxin in clinical development: past, present and future

The availability of highly purified recombinant human relaxin, serelaxin, has allowed clinical trials to be conducted in several indications and the elucidation of its pharmacology in human subjects. These studies have demonstrated that serelaxin has unique haemodynamic properties that are likely to contribute to organ protection and long-term outcome benefits in acute heart failure. Clinical observations support its consideration for therapeutic use in other patient populations, including those with chronic heart failure, coronary artery disease, portal hypertension and acute renal failure.

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.

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.

Recombinant human relaxin versus placebo for cervical ripening: a double-blind randomised trial in pregnant women scheduled for induction of labour

Background

Nonclinical studies indicate that the hormone relaxin is a good candidate for a safe cervical ripening agent that does not cause uterine contractions.

Methods

This Phase II study (conducted November 2, 2005–October 20, 2006) was a randomised, double blind, placebo controlled trial testing 24-h intravenous infusion of serelaxin (recombinant human relaxin) or placebo for cervical ripening in 72 healthy, primiparous women. Eligible subjects had a singleton pregnancy ≥40 weeks, were planned for elective induction, had vertex presentation of the fetus, intact membranes and a Bishop score at screening ≤4. In Part A of the study, safety evaluation of three escalating doses of serelaxin (7.5, 25 or 75 μg/kg/day) or placebo was performed in 22 subjects admitted to the hospital 24 h prior to scheduled induction (n = 7, 4, 4, and 7 subjects, respectively). The highest safe dose from Part A and placebo were then tested in Part B for safety and cervical ripening (n = 25 subjects/arm). Planned randomisation ratio was of 4:2 (serelaxin:placebo) for each dose group in Part A and 1:1 for Part B. For analysis, subjects in Part B were pooled with those receiving the same dose in Part A and all subjects receiving placebo were pooled. The primary efficacy endpoint was change from baseline in Bishop score at 6, 12 and 24 h or end of study drug administration. Maternal safety evaluations included adverse events and vital signs through 4 weeks. Fetal assessments included serial heart rate monitoring and nonstress testing. Neonatal assessments included Apgar scores, NICU admissions, and adverse events through 4 weeks.

Results

Overall, 74 subjects were randomized and 72 were treated. There were no significant differences between the groups receiving the highest safe dose of serelaxin (75 μg/kg/day) and placebo in the primary or secondary efficacy endpoints. Changes from baseline in Bishop score at 24 h were 4.19 ± 1.9 and 3.26 ± 2.26 in the pooled placebo and serelaxin groups, respectively (p = 0.2507). Serelaxin was well tolerated and no anti-serelaxin antibodies were detected in either subjects or neonates.

Conclusion

Serelaxin infusion at the end of pregnancy was well tolerated but did not advance cervical ripening.

Trial registration

Clinicaltrials.gov identifier NCT00259103 (15 November 2005).

Chemically synthesized dicarba H2 relaxin analogues retain strong RXFP1 receptor activity but show an unexpected loss of in vitro serum stability

Peptides and proteins are now acknowledged as viable alternatives to small molecules as potential therapeutic agents. A primary limitation to their more widespread acceptance is their generally short in vivo half-lives due to serum enzyme susceptibility and rapid renal clearance. Numerous chemical approaches to address this concern have been undertaken in recent years. The replacement of disulfide bonds with non-reducible elements has been demonstrated to be one effective means by eliminating the deleterious effect of serum reductases. In particular, substitution with dicarba bonds via ring closure metathesis has been increasingly applied to many bioactive cystine-rich peptides. We used this approach for the replacement of the A-chain intramolecular disulfide bond of human relaxin 2 (H2 relaxin), an insulin-like peptide that has important regulatory roles in cardiovascular and connective tissue homeostasis that has led to successful Phase IIIa clinical trials for the treatment of acute heart failure. Use of efficient solid phase synthesis of the two peptide chains was followed by on-resin ring closure metathesis and formation of the dicarba bond within the A-chain and then by off-resin combination with the B-chain via sequential directed inter-chain disulfide bond formation. After purification and comprehensive chemical characterization, the two isomeric synthetic H2 relaxin analogues were shown to retain near-equipotent RXFP1 receptor binding and activation propensity. Unexpectedly, the in vitro serum stability of the analogues was greatly reduced compared with the native peptide. Circular dichroism spectroscopy studies showed subtle differences in the secondary structures between dicarba analogues and H2 relaxin suggesting that, although the overall fold is retained, it may be destabilized which could account for rapid degradation of dicarba analogues in serum. Caution is therefore recommended when using ring closure metathesis as a general approach to enhance peptide stability.

Synthetic covalently linked dimeric form of H2 relaxin retains native RXFP1 activity and has improved in vitro serum stability

Human (H2) relaxin is a two-chain peptide member of the insulin superfamily and possesses potent pleiotropic roles including regulation of connective tissue remodeling and systemic and renal vasodilation. These effects are mediated through interaction with its cognate G-protein-coupled receptor, RXFP1. H2 relaxin recently passed Phase III clinical trials for the treatment of congestive heart failure. However, its in vivo half-life is short due to its susceptibility to proteolytic degradation and renal clearance. To increase its residence time, a covalent dimer of H2 relaxin was designed and assembled through solid phase synthesis of the two chains, including a judiciously monoalkyne sited B-chain, followed by their combination through regioselective disulfide bond formation. Use of a bisazido PEG7 linker and "click" chemistry afforded a dimeric H2 relaxin with its active site structurally unhindered. The resulting peptide possessed a similar secondary structure to the native monomeric H2 relaxin and bound to and activated RXFP1 equally well. It had fewer propensities to activate RXFP2, the receptor for the related insulin-like peptide 3. In human serum, the dimer had a modestly increased half-life compared to the monomeric H2 relaxin suggesting that additional oligomerization may be a viable strategy for producing longer acting variants of H2 relaxin.

Serelaxin: a novel therapy for acute heart failure with a range of hemodynamic and non-hemodynamic actions

Acute heart failure (AHF) is characterized by high morbidity and mortality and high costs. Although the treatment of AHF has not changed substantially in recent decades, it is becoming clear that treatment strategies for AHF need to address both the immediate hemodynamic abnormalities giving rise to congestion as well as prevent organ damage that can influence long-term prognosis. Serelaxin, the recombinant form of human relaxin-2, a naturally occurring peptide hormone, has been found to significantly improve symptoms and signs of AHF, prevent in-hospital worsening heart failure, as well as significantly improve 180-day cardiovascular and all-cause mortality after a 48-h infusion commenced within 16 h of presentation (RELAX-AHF study). Available data suggest that the clinical benefits may be attributable to a potential combination of multiple actions of serelaxin, including improving systemic, cardiac, and renal hemodynamics, and protecting cells and organs from damage via anti-inflammatory, anti-cell death, anti-fibrotic, anti-hypertrophic, and pro-angiogenic effects. This manuscript describes the short- and long-term effects of serelaxin in AHF patients, analyzing how these effects can be explained by taking into account the range of hemodynamic and non-hemodynamic actions of serelaxin. In addition, this paper also addresses several aspects related to the role of serelaxin in the therapy of AHF that remain to be clarified and warrant further investigation.

Acute treatment with relaxin protects the kidney against ischaemia/reperfusion injury

Although recent preclinical and clinical studies have demonstrated that recombinant human relaxin (rhRLX) may have important therapeutic potential in acute heart failure and chronic kidney diseases, the effects of acute rhRLX administration against renal ischaemia/reperfusion (I/R) injury have never been investigated. Using a rat model of 1-hr bilateral renal artery occlusion followed by 6-hr reperfusion, we investigated the effects of rhRLX (5 μg/Kg i.v.) given both at the beginning and after 3 hrs of reperfusion. Acute rhRLX administration attenuated the functional renal injury (increase in serum urea and creatinine), glomerular dysfunction (decrease in creatinine clearance) and tubular dysfunction (increase in urinary excretion of N-acetyl-β-glucosaminidase) evoked by renal I/R. These beneficial effects were accompanied by a significant reduction in local lipid peroxidation, free radical-induced DNA damage and increase in the expression/activity of the endogenous antioxidant enzymes MnSOD and CuZnSOD superoxide dismutases (SOD). Furthermore, rhRLX administration attenuated the increase in leucocyte activation, as suggested by inhibition of myeloperoxidase activity, intercellular-adhesion-molecule-1 expression, interleukin (IL)-1β, IL-18 and tumour necrosis factor-α production as well as increase in IL-10 production. Interestingly, the reduced oxidative stress status and neutrophil activation here reported were associated with rhRLX-induced activation of endothelial nitric oxide synthase and up-regulation of inducible nitric oxide synthase, possibly secondary to activation of Akt and the extracellular signal-regulated protein kinase (ERK) 1/2, respectively. Thus, we report herein that rhRLX protects the kidney against I/R injury by a mechanism that involves changes in nitric oxide signalling pathway.

Regulation of receptor signaling by relaxin A chain motifs: derivation of pan-specific and LGR7-specific human relaxin analogs

Relaxin peptides are important hormones for the regulation of reproductive tissue remodeling and the renal cardiovascular system during pregnancy. Recent studies demonstrated that two of the seven human relaxin family peptides, relaxin H2 (RLN2) and INSL3, signal exclusively through leucine-rich repeat-containing G protein-coupled receptors, LGR7 and LGR8. Although it was well characterized that an RXXXRXXI motif at the RLN2 B chain confers receptor activation activity, it is not clear what roles RLN2 A chain plays in receptor interaction. Analyses of relaxin family genes on syntenic regions of model tetrapods showed that the A chain of RLN2 orthologs exhibited a greater sequence divergence as compared with the receptor-binding domain-containing B chain, foreshadowing a potential role in receptor interactions; hence, defining receptor selectivity in this fast evolving peptide hormone. To test our hypothesis that select residues in the human RLN2 A chain play key roles in receptor interaction, we studied mutant peptides with residue substitution(s) in the A chain. Here, we showed that alanine substitution at the A16 and A17 positions enhances LGR8-activation activity of RLN2, whereas mutation at the A22-23 region (RLN2A22-23) ablates LGR8, but not LGR7, activation activity. In addition, we demonstrated that the functional characteristics of the RLN2A22-23 mutant are mainly attributed to modifications at the PheA23 position. Taken together, our studies indicated that ThrA16, LysA17, and PheA23 constitute part of the receptor-binding interface of human RLN2, and that modification of these residues has led to the generation of novel human RLN2 analogs that would allow selective activation of human LGR7, but not LGR8, in vivo.

Protective effects of relaxin in ischemia/reperfusion-induced intestinal injury due to splanchnic artery occlusion

1. Splanchnic artery occlusion (SAO) followed by reperfusion causes endothelial injury and inflammation which contribute to the pathophysiology of shock. We investigated the effects of relaxin (RLX), known to afford protection against the deleterious effects of cardiac ischemia/reperfusion, given to rats subjected to splanchnic artery occlusion and reperfusion (SAO/R)-induced splanchnic injury. 2. RLX (30 ng kg(-1), 15 min. before reperfusion) significantly reduced the drop of blood pressure and high mortality rate caused by SAO/R. RLX also reduced histopathological changes, leukocyte infiltration (myeloperoxidase) and expression of endothelial cell adhesion molecules in the ileum. RLX counteracted free radical-mediated tissue injury, as judged by significant decrease in the tissue levels of peroxidation and nitration products (malondialdehyde, nitrotyrosine), DNA damage markers (8-hydroxy-2'-deoxyguanosine, poly-ADP-ribosylated DNA) and consumption of tissue antioxidant enzymes (superoxide dismutase). As a result, RLX led to a reduction of ileal cell apoptosis (caspase 3, terminal deoxynucleotidyltransferase-mediated UTP end labeling). The effects of RLX appear specific, as inactivated RLX substituted for the bioactive hormone had no effects. 3. In conclusion, these results show that RLX exerts a clear-cut protective effect in SAO/R-induced splanchnic injury, likely due to endothelial protection, decreased leukocyte recruitment and hindrance of free radical-mediated tissue injury leading to cell death, lethal complications and high mortality rate. Thus, RLX could be used therapeutically in intestinal ischemia.

The vagina as a route for systemic drug delivery

Exhaustive efforts have been made toward the administration of drugs, via alternative routes, that are poorly absorbed after the oral administration. The vagina as a route of drug delivery has been known since ancient times. In recent years, the vaginal route has been rediscovered as a potential route for systemic delivery of peptides and other therapeutically important macromolecules. However, successful delivery of drugs through the vagina remains a challenge, primarily due to the poor absorption across the vaginal epithelium. The rate and extent of drug absorption after intravaginal administration may vary depending on formulation factors, vaginal physiology, age of the patient and menstrual cycle. Suppositories, creams, gels, tablets and vaginal rings are commonly used vaginal drug delivery systems. The purpose of this communication is to provide the reader with a summary of advances made in the field of vaginal drug delivery. This report, therefore, summarizes various vaginal drug delivery systems with an introduction to vaginal physiology and factors affecting drug absorption from the vaginal route.