Cell-targeted therapies (smart drugs), which selectively control cancer cell progression with limited toxicity to normal cells, have been developed to effectively treat some cancers. However, many cancers such as metastatic prostate cancer have yet to be treated with current smart drug technology. Here, we describe the thorough preclinical characterization of an RNA aptamer (A9g) that functions as a smart drug for prostate cancer by inhibiting the enzymatic activity of prostate specific membrane antigen (PSMA). Treatment of prostate cancer cells with A9g results in reduced cell migration/invasion in culture and metastatic disease in vivo. Importantly, A9g is safe in vivo and is not immunogenic in human cells. Pharmacokinetic and biodistribution studies in mice confirm target specificity and absence of non-specific on/off-target effects. In conclusion, these studies provide new and important insights into the role of PSMA in driving carcinogenesis and demonstrate critical endpoints for the translation of a novel RNA smart drug for advanced stage prostate cancer.Molecular Therapy (2014); doi:10.1038/mt.2014.117.