PROJECT SUMMARY There is an urgent need to develop effective strategies to combat drug addiction, a major public health burden. Unfortunately, current efforts are hampered by a focus on a very limited range of drug targets. Decades of work have established that the transcription factor DFosB plays a critical role in drug addictive behaviors in rodent models, with validation in humans available as well. In response to chronic cocaine or opioids (e.g., heroin) administration, DFosB mediates aspects of drug seeking, reward, self-administration, and relapse. Due to its unusual stability, DFosB accumulates to very high levels in the brain in regions critical for reward, making it an attractive target for addiction therapies. However, critical mechanistic aspects of DFosB function are not known, making it difficult to pursue DFosB as a therapeutic target. It is not known how DFosB molecules are arranged in vivo, what molecular features control their ability to bind to DNA and turn genes on or off, and whether these features can be targeted strategically with small molecules in order to regulate DFosB function in vivo to combat drug use disorders. We hypothesize that, by modulating ∆FosB with small molecules, we can selectively regulate key strategic DFosB gene targets, and thereby the long-term neural and behavioral adaptations that DFosB triggers in response to chronic drug use. To test our hypotheses, we propose to 1) optimize a series of validated lead compounds into high-affinity chemical probes targeting DFosB in vitro and in vivo; 2) unravel how key molecular features in DFosB regulate its actions; and 3) determine how targeting these features either with our chemical probes or novel genetic tools alters behaviors in animal models of addiction. To this end, we have an outstanding translational research team overseeing a robust and effective experimental platform that draws on our prior combined work. We have already achieved important milestones. First, we have discovered that DFosB partners not only with JunD but also with itself in order to bind DNA, and these two species are structurally and functionally very different. Second, we have uncovered a molecular switch in ∆FosB that controls its binding to DNA and that works differently in heteromeric vs. homomeric ∆FosB complexes. Third, we have developed a large panel of lead compounds that target DFosB and that we can leverage to gain both fundamental mechanistic insight into DFosB function, as well as assess their in vivo effects on addictive behaviors. Together, our work creates a powerful, previously unavailable, and highly actionable platform to test the utility of DFosB as a therapeutic target. The positive impact of this work will be to further de-risk DFosB as a therapeutic target by creating comprehensive, mechanism-based knowledge onto which a drug discovery program will be anchored, focused on a completely novel target to combat addiction. This innovative proposal will provide novel in...