The off-label use of racemic ketamine and the FDA approval of (S)-ketamine are promising developments for the treatment of depression. Nevertheless, racemic ketamine and (S)-ketamine are controlled substances with known abuse potential and their use is associated with undesirable side effects. For these reasons, research efforts have focused on identifying alternatives. One candidate is (2R,6R)-hydroxynorketamine ((2R,6R)-HNK), a ketamine metabolite that in preclinical models lacks the dissociative and abuse properties of ketamine while retaining its antidepressant-like behavioral efficacy. (2R,6R)-HNK’s mechanism of action however is unclear. The main goals of this study were to perform an in-depth pharmacological characterization of (2R,6R)-HNK at known ketamine targets, to use target deconvolution approaches to discover novel proteins that bind to (2R,6R)-HNK, and to characterize the biodistribution and behavioral effects of (2R,6R)-HNK across several procedures related to substance use disorder liability. We found that unlike (S)- or (R)-ketamine, (2R,6R)-HNK did not directly bind to any known or proposed ketamine targets. Extensive screening and target deconvolution experiments at thousands of human proteins did not identify any other direct (2R,6R)-HNK-protein interactions. Biodistribution studies using radiolabeled (2R,6R)-HNK revealed non-selective brain regional enrichment, and no specific binding in any organ other than the liver. (2R,6R)-HNK was inactive in conditioned place preference, open-field locomotor activity, and intravenous self-administration procedures. Despite these negative findings, (2R,6R)-HNK produced a reduction in immobility time in the forced swim test and a small but significant increase in metabolic activity across a network of brain regions, and this metabolic signature differed from the brain metabolic profile induced by ketamine enantiomers. In sum, our results indicate that (2R,6R)-HNK does not share pharmacological or behavioral profile similarities with ketamine or its enantiomers. However, it could still be possible that both ketamine and (2R,6R)-HNK exert antidepressant-like efficacy through a common and previously unidentified mechanism. Given its pharmacological profile, we predict that (2R,6R)-HNK will exhibit a favorable safety profile in clinical trials, and we must wait for clinical studies to determine its antidepressant efficacy.

外消旋氯胺酮的标签外使用和 FDA 批准 (S)-氯胺酮是治疗抑郁症的有希望的进展。然而，外消旋氯胺酮和(S)-氯胺酮是具有已知滥用潜力的受控物质，并且它们的使用会产生不良副作用。由于这些原因，研究工作集中在寻找替代方案上。一种候选药物是 (2R,6R)-羟基去甲氯胺酮 ((2R,6R)-HNK)，这是一种氯胺酮代谢物，在临床前模型中缺乏氯胺酮的解离和滥用特性，同时保留其抗抑郁药样行为功效。然而(2R,6R)-HNK 的作用机制尚不清楚。本研究的主要目标是对已知氯胺酮靶点的 (2R,6R)-HNK 进行深入的药理学表征，使用靶点解卷积方法发现与 (2R,6R)-HNK 结合的新型蛋白质，并描述 (2R,6R)-HNK 在与物质使用障碍倾向相关的多个程序中的生物分布和行为影响。我们发现，与 (S)- 或 (R)-氯胺酮不同，(2R,6R)-HNK 不直接与任何已知或提议的氯胺酮靶标结合。对数千种人类蛋白质进行的广泛筛选和目标反卷积实验没有发现任何其他直接的 (2R,6R)-HNK-蛋白质相互作用。使用放射性标记的 (2R,6R)-HNK 进行的生物分布研究揭示了非选择性大脑区域富集，并且在除肝脏以外的任何器官中没有特异性结合。 (2R,6R)-HNK 在条件性位置偏好、开放场运动活动和静脉自我给药程序中不活跃。 尽管有这些负面结果，(2R,6R)-HNK 在强迫游泳测试中减少了不动时间，并且使整个大脑区域网络的代谢活动小幅但显着地增加，并且这种代谢特征与诱导的大脑代谢特征不同。通过氯胺酮对映体。总之，我们的结果表明 (2R,6R)-HNK 与氯胺酮或其对映体在药理学或行为特征上没有相似之处。然而，氯胺酮和 (2R,6R)-HNK 仍然有可能通过一种常见且先前未知的机制发挥抗抑郁样功效。鉴于其药理学特征，我们预测 (2R,6R)-HNK 将在临床试验中表现出良好的安全性，我们必须等待临床研究来确定其抗抑郁功效。