Current antidepressants act principally by blocking monoamine reuptake by high-affinity transporters in the brain. However, these antidepressants show important shortcomings such as slow action onset and limited efficacy in nearly a third of patients with major depression disorder. Here, we report the development of a prodrug targeting organic cation transporters (OCT), atypical monoamine transporters recently implicated in the regulation of mood. Using molecular modeling, we designed a selective OCT2 blocker, which was modified to increase brain penetration. In a rodent model of chronic depression induced by corticosterone exposure, daily administration of this compound, H2-cyanome, induced positive effects on several behaviors mimicking symptoms of depression, including anhedonia, anxiety, social withdrawal, and memory impairment. Importantly, in this validated model, H2-cyanome compared favorably with the classical antidepressant fluoxetine, with a faster action on anhedonia and better anxiolytic effects. Integrated Z-scoring across these depression-like variables revealed a lower depression score for mice treated with H2-cyanome than for mice treated with fluoxetine for 3 weeks. Repeated H2-cyanome administration increased VTA dopaminergic neuron firing, which may underlie its rapid action on anhedonia. H2-cyanome also modulated in a similar way than fluoxetine several intracellular signaling pathways previously involved in antidepressant response. Our findings provide proof-of-concept of long-term antidepressant efficacy of an OCT blocker, and a mechanistic framework for the development of new classes of antidepressants and therapeutic alternatives for resistant depression and other psychiatric disturbances such as anxiety.

Cre/loxP recombination is a widely used approach to study gene function in vivo, using mice models expressing the Cre recombinase under the control of specific promoters or through viral delivery of Cre‐expressing constructs. A profuse literature on transgenic mouse lines points out the deleterious effects of Cre expression in various cell types and tissues, presumably by acting on illegitimate loxP‐like sites present in the genome. However, most studies reporting the consequences of Cre‐lox gene invalidation often omit adequate controls to exclude the potential toxic effects of Cre, compromising the interpretation of data. In this study, we report the anatomical, neurochemical, and behavioral consequences in mice of adeno‐associated virus (AAV)‐mediated Cre expression in the dopaminergic nuclei substantia nigra, at commonly used viral titers (3 × 109 genome copies/0.3 μL or 2 × 109 genome copies/0.6 μL). We found that injecting AAV‐eGFP‐Cre into the SN engendered drastic and reproducible modifications of behavior, with increased basal locomotor activity as well as impaired locomotor response to cocaine compared to AAV‐eGFP‐injected controls. Cre expression in the SN induced a massive decrease in neuronal populations of both pars compacta and pars reticulata and dopamine depletion in the nigrostriatal pathway. This anatomical injury was associated with typical features of programmed cell death, including an increase in DNA break markers, evidence of apoptosis, and disrupted macroautophagy. These observations underscore the need for careful control of Cre toxicity in the brain and the reassessment of previous studies. In addition, our findings suggest that Cre‐mediated ablation may constitute an efficient tool to explore the function of specific cell populations and areas in the brain, and the impact of neurodegeneration in these populations.