Abstract Body (Do not enter title and authors here): Background
Human Relaxin-2 (RLN2) signals via G-protein coupled receptor (GPCR) relaxin family peptide receptor 1 (RXFP1), and exerts vasodilatory, anti-inflammatory, and anti-fibrotic effects in the vasculature and myocardium. Therapeutic use of native RLN2 is limited by its short half-life and need for parenteral administration. Small molecule allosteric RXFP1 agonists may be orally bioavailable and have favorable pharmacokinetic profiles for chronic disease. Several novel RXFP1 agonists based on the ML290 scaffold exhibit biased GPCR signaling compared to native RLN2 with respect to cAMP, cGMP and β-arrestin1 recruitment, with potentially distinct biological effects. While this pathway shows promise for treating heart failure, is unclear if RLN2/RXFP1 agonism would be beneficial in pulmonary hypertension (PH) and right ventricular (RV) failure.
Hypothesis
We hypothesized biased RXFP1 agonism via ML290 or derivatives is advantageous in treating experimental PH and RV failure.
Methods/Results
RXFP1 was highly expressed in hypertrophic media of human PAH versus control lungs, and cultured pulmonary arterial smooth muscle cells (PASMC) and neonatal rat ventricular cardiomyocytes. BRET GPCR assays in HEK293 cells expressing hRXFP1 revealed RLN2, small molecule RXFP1 agonist ML290, ML290 derivative TRND8394, and AZD5462 recruited cAMP signaling similarly, but ML290 and TRND8394 exhibited markedly diminished cGMP and β-arrestin1 recruitment, consistent with biased agonism previously observed in ML290. RLN2 and ML290 inhibited TGFβ-SMAD2/3 signaling and TGFβ1-induced PASMC phenotypic plasticity, inhibiting expression of αSMA, Calponin, Caldesmon, Fibronectin and type 1 Collagen. Serum and PDGF-BB-induced migration of PASMC were inhibited by RLN2, ML290 and derivatives. Humanized RXFP1 knock-in (hRXFP1-KI) mice subjected to SU5416 and hypoxia (FiO2=0.1) for three weeks and treated with ML290, TRND8394, AZD5462 (10 mg/kg/d p.o.), or ACTRIIA-Fc (a.k.a., sotatercept, 2.2 mg/kg/twice weekly i.p.) had comparable improvements in right ventricular systolic pressure (RVSP) vs. disease controls, while treatment with biased compounds ML290 and TRND8394, and ACTRIIA-Fc elicited potent decreases in RV hypertrophy (RV/LV+S).
Conclusion
Small molecule RXFP1 agonists with biased GPCR signaling may elicit more potent effects in experimental PH upon right ventricular hypertrophy than non-biased RXFP1 agonists and represent a promising therapeutic strategy for cardiopulmonary disease.