Background There is a dearth of approved therapies for patients with stage III melanoma. Recent studies have demonstrated that RhoJ - a small GTPase of the cdc42 family - is known to bind and activate PAK kinases. This interaction accelerates the growth of nascent melanoma tumors, inhibit apoptosis, and stimulate angiogenesis, implicating a role for RhoJ in promoting the growth of early stage tumors. Hypothesis Based on our extensive data, we hypothesize that RhoJ promotes the growth of early stage melanoma tumors and is an ideal therapeutic target for stage III melanomas. To test our hypothesis, we propose a multidisciplinary approach that includes three main aims distributed over a five-year period. Aims We have built a structure-activity relationship that has led to the identification of the potent and efficacious (in vitro and in vivo) ARN22089 lead compound. Based on these results, in Aim1 we will expand and optimize this active chemical scaffold with additional molecules that disrupt RhoJ signaling. Our results show that this novel 2,4-substituted pyrimidine scaffold specifically inhibits RhoJ/PAK interactions, disrupting the downstream RhoJ-PAK signaling in melanoma cell lines. We will generate back-up compounds from this series, while also looking for a new active scaffold with a different core structure, as a follow-up strategy. In Aim2, we will extend our computational and biophysical studies of RhoJ/inhibitor/PAK interaction to aid the rational design of more potent RhoJ inhibitors and improve our understanding of RhoJ structure, function, and inhibition. In Aim 3, we will further optime our compounds in order to tune the ADMET profile and identify the best candidate for preclinical development. Expected Results We expect to further advance the development of a new treatment for stage III melanoma tumors, toward preclinical studies. In doing so, we will advance our knowledge on RhoJ structure, function, and inhibition. Impact On Cancer This project will help develop and validate a new strategy and novel therapeutics to treat stage III melanoma tumors, a major unmet and urgent medical need.