There are two major goals in this proposal. One is to elucidate if Akt-EphA2 signaling axis is a "driver" mechanism underlying malignant progression of human prostate cancer (PCa); the other is to evaluate therapeutic efficacy of EphA2-targeted small molecules against PCa. Approximately 70% of primary PCa exhibit a loss of at least one PTEN allele and loss of both alleles is associated with advanced disease. PTEN loss leads to activation of PI3K/Akt. While Akt is well-known to control cell proliferation and survival, how it may regulate tumor progression is not well understood. We discovered that Akt may promote tumor cell migration and invasion by co-opting EphA2 kinase. EphA2 has been extensively studied in cancer. It is frequently overexpressed in many different types of human cancer, which is often correlated with tumor progression. While these data suggest EphA2 is an oncogene, strong evidence also exists demonstrating tumor suppressor functions of EphA2. Shedding light on this apparent paradox, we reported recently that EphA2 has diametrically opposite roles in regulating PCa cell migration and invasion. In the presence of ligands called ephrin-As, EphA2 inhibited cell migration and invasion. In contrast, in the absence of ligands EphA2 promoted chemotactic migration and invasion instead. Interestingly the ligand-independent stimulation of cell motility was correlated with phosphorylation of EphA2 on a single serine residue (S897) by Akt. S897A mutation abolished this ligand-independent effect. Preliminary studies show that S897 phosphorylation is detected at invasive front of high grade human PCa and mouse PCa induced by PTEN deletion, suggesting pathological relevance of Akt-EphA2 signaling axis in PCa. The data in aggregate led us to hypothesize that the Akt-EphA2 crosstalk contributes to invasion and metastasis of PCa and can be targeted for PCa therapy. Three aims are proposed. Aim will test the hypothesis that Akt-EphA2 signaling axis is a "driver" mechanism in promoting malignant progression of human PCa. In Aim 2, we will determine ephrin-As can repulse disseminating PCa cells. Aim 3 will investigate whether small molecule targeting EphA2 can be used as potential therapeutic agents to suppress PCa metastasis in vivo.