Addiction to cocaine and other illicit drugs is estimated to cost our society $181 billion which equates to $603 per U.S. citizen. The cost of addiction can be dramatically lowered through the use of treatments;unfortunately, many drugs of abuse, including cocaine, lack a single approved pharmacotherapy. Addiction to psychomotor stimulants, such as cocaine, is marked by a transition in drug consumption from a casual, recreational style of use to a more compulsive, excessive pattern that arises as a result of drug-induced changes in brain functioning. In order to develop effective treatments, it will likely be necessary to identify and target altered brain functioning underlying addiction. Towards this end, drug-induced changes in glutamate release from cystine-glutamate antiporters have been linked to pathological alterations in neural transmission and normalizing cystine-glutamate exchange blocks compulsive drug-seeking in preclinical models. Further, small-scale clinical studies using acetylcysteine to target cystine-glutamate exchange have shown modest efficacy including reduced drug craving and cocaine use. The efficacy of N-acetyl cysteine is limited due to extensive metabolism in the liver and poor passive transport into the brain. As a result, the present proposal seeks to develop novel chemical entities that are more potent and effective in targeting cystine-glutamate exchange in the brain. Aim 1 will involve the design of 32-40 compounds. Aim 2 will utilize in vitro and in vivo screening techniques to determine which compounds are most effective and potent in targeting cystine-glutamate exchange. Specifically, we will use pure glial cortical cultures to determine the capacity of brain cells to utilize the novel ligands to target cystine-glutamate exchange. Next, we will screen the most promising compounds in vivo by assessing the capacity of these ligands to bypass hepatic metabolism, enter into the brain, and target cystine-glutamate antiporters. Aim 3 will determine the potency and efficacy of these novel compounds in blocking cocaineprimed, stress-primed, and cocaine-paired cue primed reinstatement of cocaine-seeking in preclinical models of compulsive drug seeking. Collectively, these experiments have the potential to identify cystine-glutamate antiporters as a novel target in the treatment of addiction and to generate a series of compounds that may ultimately be effective in treating cocaine addiction.