Osteosarcoma is the most common primary bone cancer in children and adolescents. A key feature of osteosarcoma is their inherent high growth rates and the increased vasculature to enable rapid growth. Recent data implicate Ca2+/CaM-dependent protein kinase II (CaMKII), a major mediator of Ca2+ signaling, in both the unregulated proliferation of osteosarcoma and in the angiogenesis that supports its growth. Hyperactivity of CaMKII is associated with cell proliferation and resistance to apoptosis, while inhibition of CaMKII suppresses growth of osteosarcoma in animals. We aim to focus medicinal chemistry and preclinical development to generate improved CaMKII inhibitors that incorporate an allosteric site interaction. Our strategy is to start with a potent lead ATP site inhibitor of the kinase and extend it to interact with the helical inhibitory domain of the kinase. Biochemical analysis of inhibitors will measure their interaction with the inactive and active conformations. Medicinal chemistry will be used to develop inhibitors that span the catalytic site with preferential binding to the inactive conformation that is characteristic of allosteric interactions. While our current lead compounds can be used to test efficacy in osteosarcoma, the allosteric inhibitors will be more broadly useful because of greater selectivity. The best inhibitor will be tested for efficacy for its cellular action followed by efficacy on human osteosarcoma xenografted in mice. This will provide a clear path for a Phase II proposal to further improve its potency and other drug-like properties up to IND filing. CaMKII inhibitors may present a new paradigm in osteosarcoma-targeted agents that effectively treat the tumor by the dual mechanism of slowing its rapid growth and blocking its access to nutrients. PUBLIC HEALTH RELEVANCE: Osteosarcoma is the most common primary bone cancer in children and adolescents. A key feature of osteosarcomas is their inherent high growth rates and the increased vasculature to enable rapid growth. Recent data implicate Ca2+/CaM-dependent protein kinase II (CaMKII), a major mediator of Ca2+ signaling, in both the unregulated proliferation of osteosarcoma and in the increased blood vessel formation that upports its growth. We aim to modify an existing potent small molecule inhibitor of CaMKII to increase its selectivity, test it biochemically to ensure it has the desired mechanism of action, then test it on xenografted human osteosarcoma.