Rigosertib Reverses Hypertrophic Cardiomyopathy in Noonan Syndrome

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BACKGROUND: RASopathies constitute a group of rare genetic disorders caused by mutations in genes along the canonical RAS/mitogen-activated protein kinase (MAPK) signaling pathway, affecting cell growth and differentiation. These syndromes, which include Noonan syndrome (NS), are characterized by developmental delays, distinctive facial dysmorphia, and cardiac defects, notably hypertrophic cardiomyopathy (HCM). Despite their prevalence and impact, therapeutic options for RASopathies remain limited. Rigosertib, a novel dual RAS/MAPK and phosphatidylinositol 3-kinase (PI3K)/AKT pathway inhibitor, is currently in clinical trials for treatment of melanoma and recessive dystrophic epidermolysis bullosa. Here, we identify rigosertib as a candidate therapy for RAF1-associated HCM. METHODS: We performed a drug screen of clinically relevant compounds in transgenic Drosophila models of RASopathies to identify candidate therapeutics. Cardiac-targeted Drosophila models expressing RASopathy-associated transgenes were used to evaluate the effects of rigosertib on cardiac hypertrophy and compare its efficacy with the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib. Therapeutic efficacy was further assessed in a mammalian model using Raf1 L613V/+ knock-in mice treated with rigosertib for 6 weeks. Cardiac structure and function were evaluated by echocardiography, histology, and molecular analyses, including assessment of cardiomyocyte size, fetal gene expression, and extracellular signal-regulated kinase/AKT signaling. Additional NS-associated phenotypes, including skeletal growth and craniofacial abnormalities, were also evaluated. RESULTS: Rigosertib was effective across a panel of transgenic Drosophila RASopathy models, suggesting activity against multiple disease variants. In cardiac-targeted fly models, rigosertib reduced cardiac hypertrophy and outperformed trametinib. In Raf1 L613V/+ mice, 6 weeks of treatment significantly improved left ventricular chamber dimension, posterior wall thickness, heart mass, and cardiomyocyte size, resulting in reversal of cardiac hypertrophy. Rigosertib also normalized fetal gene expression and inhibited extracellular signal-regulated kinase and AKT signaling in primary cardiomyocytes. In addition to reversing cardiac pathology, rigosertib significantly improved other NS-associated features, including increased bone growth and correction of craniofacial abnormalities. CONCLUSIONS: Together, our findings suggest that rigosertib normalizes and reverses RASopathy-associated HCM and other NS-associated syndromic features, supporting its development as a promising treatment for RAF1-associated HCM and, potentially, other RASopathy-dependent pathologies. This study not only highlights the therapeutic potential of rigosertib but also demonstrates the utility of an integrated approach using Drosophila and mammalian models to elucidate drug effects across complex biological systems.