Developing p21-activated kinase 1 (PAK1) activators to treat hypertrophic cardiomyopathy (HCM)

Abstract Despite significant progress in comprehending the genetic and metabolic underpinnings of cardiomyocyte dysfunction, there is still a pressing need for targeted treatments to address hypertrophy and progressive remodelling (e.g., fibrosis), seen in HCM1 . PAK1, a regulator of ion channels and myofilaments in cardiomyocytes, has shown promise in curbing pathological hypertrophy2 . Our hypothesis centres on the potential therapeutic benefits of pharmacologically activating PAK1 in managing hypertrophy and adverse remodelling in HCM. First, we conducted virtual screening and kinase assays to identify potent small molecule PAK1 activators, which significantly increased PAK1 activity by 3 to 5-fold, with an EC50 range between 0.5 and 2.5 μΜ. We then evaluated these compounds on cellular hypertrophy in an in vitro model using neonatal rat cardiomyocytes exposed to isoprenaline (ISO). Among those, JB2020A not only prevented ISO-induced hypertrophy, but also reversed pre-existing cellular hypertrophy induced by ISO 24 hours earlier. Subsequently, we assessed the therapeutic potential of JB2020A in a well-characterised HCM mouse model (i.e., Actc1E99K) 3 , known for its rapid disease progression. We initiated a six-week oral treatment regime at 4 weeks of age, dosing at 10 mg/kg per day. Echocardiography and fibrosis evaluation confirmed that JB2020A led to a significant reduction in cardiac hypertrophy and fibrosis with preserved contractile function. Western blotting analysis revealed increased PAK1 phosphorylation and activation in JB2020A-treated E99K hearts, along with a reduction in pro-apoptotic CHOP expression and an upregulation of protective endoplasmic reticulum (ER) response (e.g., ATF4 and Xbp1), indicating an amelioration of ER stress in HCM. These findings underscore the therapeutic potential of small molecule PAK1 activators as a novel approach for addressing hypertrophy and progressive remodelling in HCM.