Targeting Myosin to Treat Polycystic Kidney Disease

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PROJECT SUMMARY The goal of this proposal is to advance a new therapeutic approach targeting myosin for polycystic kidney disease (PKD). PKD is a major life-threatening Mendelian disorder that affects 12,000,000 individuals, representing a market opportunity of ~$1 billion. In PKD, tiny tubules in the kidneys, liver, and other organs gradually expand into fluid-filled cysts, leading to organ failure. PKD is commonly inherited as a loss-of-function mutation in PKD1 or PKD2, encoding polycystin-1 (PC1) or polycystin-2 (PC2), respectively. General treatment involves managing complications of chronic kidney disease, controlling blood pressure, and preparing for renal replacement therapy. Tolvaptan, a vasopressin receptor antagonist, is approved for use in rapidly progressing cases, but its modest efficacy and occasionally severe side effects make it unsuitable for many PKD patients. How cysts form mechanistically remains incompletely understood, which has hampered drug development. Thus a compelling need and market exists for new treatments and targets to slow or reverse PKD. To better model human PKD and develop therapeutic strategies, we have invented PKD1-/- and PKD2-/- human kidney organoids, which undergo PKD-specific cyst formation from tubules, reconstituting the disease phenotype in a petri dish. Organoid studies reveal that PKD cyst formation is highly sensitive to the microenvironment, and that blebbistatin, a myosin II inhibitor, greatly increases cystogenesis. Non-muscle myosin II (NMII), a known target of blebbistatin that confers strength and shape to cells, is strongly expressed in tubular epithelia and redistributed in organoid cysts. Conversely, in preliminary studies, we have discovered a myosin II activator that reduces PKD cystogenesis, suggesting a novel therapeutic strategy. This compound has a well-established safety and bioavailability profile in large animal studies. Based on our preliminary data and the literature, we hypothesize that it directly activates NMII heavy chains to strengthen and stiffen the cytoskeleton of kidney tubules, thus limiting their tendency to deform into cysts. The major goal of this proposal is to demonstrate this mechanism of action as proof of concept for targeted drug development. This will be achieved in independent aims using purified NMII in vitro and in phenotypic human and animal models. Aim #1: Demonstrate that our hit compound activates NMII in assays suitable for drug optimization. Aim #2. Elucidate the targetable function of NMII during PKD cyst formation in organoids and in vivo. Completion of these two aims will connect the dots between our therapeutic hit compound, NMII, and PKD cyst formation from the single molecule to organoid scale, elucidating a novel mechanism of action for treating cystic disease. This will demonstrate proof of concept, further validate the therapeutic hit, and lay the groundwork for deeper drug development efforts in Phase II (lead optimization and pre-clinical testing).