Project Abstract Methamphetamine is a highly addictive central nervous system (CNS) psychostimulant that causes long-term damage to regions of the brain that regulate cognitive and psychiatric functions and promote drug-seeking behavior and consequently, makes recovery from methamphetamine extremely difficult. The current standard of care for stimulant use disorder (amphetamine-type, methamphetamine) is behavioral therapies but, unfortunately, the majority of patients relapse to methamphetamine use within one year after treatment. There are currently no FDA-approved therapeutics for methamphetamine addiction. Emerging evidence demonstrates how immune factors can influence addictive behaviors and contribute to substance use disorders. We have a collection of MHC class II constructs that bind to and downregulate the expression of CD74—the primary receptor for macrophage migration inhibitory factor (MIF), a key inflammatory indicator in stimulant use disorder, as well as other diseases. These constructs have therapeutic impact on drug-seeking behavior, and can also impact cognitive function, and inflammation-associated with exposure to methamphetamine, suggesting a therapeutic profile better than previously developed targets. The primary objective of this proposal is to evaluate our current generation molecule, DRhQ, in preclinical animal models of stimulant use disorder. Within the drug development process, DRhQ is moving from the lead optimization stage into the preclinical development stage. DRhQ, in its final monomeric formulation, will be evaluated in this proposal demonstrating the feasibility of the molecule to be used in clinical testing. Two animal models will be utilized to confirm cross-species efficacy. In rats, the impact of DRhQ on cue-induced reinstatement following an extended access model will be evaluated. In mice, we will use an established colony of Cd74 knockout and C57BL/6J control mice to evaluate the effects of DRhQ on methamphetamine intake and preference (2-bottle choice test). We hypothesize that the effects of DRhQ treatment in C57BL/6 mice will be similar to the effect of the Cd74 knockout on methamphetamine use, confirming the mechanism of action for DRhQ. Key brain regions and plasma will be evaluated to identify changes in protein expression following methamphetamine exposure and DRhQ immunotherapy. Collectively, this research will help identify a biomarker for assessing DRhQ treatment response in patients with stimulant use disorder or recovering from methamphetamine use. We expect that following the completion of this one-year project, we will have definitive evidence that provides a strong rationale to advance the drug into clinical testing as a treatment for stimulant use disorder.