PROJECT SUMMARY There are few effective treatment options for smoking cessation. The identification and validation of reliable biomarkers for tobacco use disorder has the potential to greatly facilitate treatment development and improve clinical outcomes. Attentional bias, a behavioral correlate and potential biomarker of addiction, is consistently observed in nicotine users and is related to the risk of subsequent relapse following smoking cessation. Our group has developed and tested a novel virtual reality (VR) nicotine cue exposure paradigm with promising preliminary results, including obtaining large nicotine-related attentional bias effect sizes. Thus, the goal of the proposed project is to validate the attentional bias neurophysiological marker derived from the VR Nicotine Cue Exposure paradigm (VR-AB) as a biomarker of tobacco use disorder and investigate its potential as a predictive marker and candidate surrogate endpoint for use in the development of novel pharmacologic interventions for smoking cessation. To achieve the goals of this project, 200 daily tobacco cigarette users will be assessed on the VR Nicotine Cue Exposure paradigm then pseudo-randomized (matched on age and sex) to receive varenicline or placebo (n per group=100). Following eight days of titration, participants will be assessed again on the VR Nicotine Cue Exposure paradigm at target dose of varenicline (1 mg twice daily). They will then be followed via mobile assessments for eight days on the target dose to assess short-term nicotine use behaviors. Varenicline will be used as a pharmacological challenge to validate the VR-AB marker given this medication’s proven ability to attenuate nicotine craving/cue salience and reinforcement. In accordance with NIDA’s Notice of Special Interest on Biomarker and Biotypes of Drug Addiction (NOT-DA- 20-012) and the FDA’s Biomarkers, EndpointS, and other Tools (BEST) resources, the broad aims of the proposed project are to: (1) validate the reliability of the VR attentional bias (VR-AB) marker and estimate the VR-AB effect size as moderated by varenicline, (2) evaluate VR-AB as a predictive biomarker for response to varenicline, and (3) evaluate VR-AB as a candidate surrogate endpoint by assessing the predictive validity of the VR-AB biomarker on short-term nicotine use behaviors as moderated by varenicline.