Department of Pharmacology, New York University School of Medicine, New York, New York, United States of America.
PLoS One. 2011;6(10):e25790. doi: 10.1371/journal.pone.0025790. Epub 2011 Oct 17.
Modafinil is a mild psychostimulant with pro-cognitive and antidepressant effects. Unlike many conventional stimulants, modafinil has little appreciable potential for abuse, making it a promising therapeutic agent for cocaine addiction. The chief molecular target of modafinil is the dopamine transporter (DAT); however, the mechanistic details underlying modafinil's unique effects remain unknown. Recent studies suggest that the conformational effects of a given DAT ligand influence the magnitude of the ligand's reinforcing properties. For example, the atypical DAT inhibitors benztropine and GBR12909 do not share cocaine's notorious addictive liability, despite having greater binding affinity. Here, we show that the binding mechanism of modafinil is different than cocaine and similar to other atypical inhibitors. We previously established two mutations (W84L and D313N) that increase the likelihood that the DAT will adopt an outward-facing conformational state--these mutations increase the affinity of cocaine-like inhibitors considerably, but have little or opposite effect on atypical inhibitor binding. Thus, a compound's WT/mutant affinity ratio can indicate whether the compound preferentially interacts with a more outward- or inward-facing conformational state. Modafinil displayed affinity ratios similar to those of benztropine, GBR12909 and bupropion (which lack cocaine-like effects in humans), but far different than those of cocaine, β-CFT or methylphenidate. Whereas treatment with zinc (known to stabilize an outward-facing transporter state) increased the affinity of cocaine and methylphenidate two-fold, it had little or no effect on the binding of modafinil, benztropine, bupropion or GBR12909. Additionally, computational modeling of inhibitor binding indicated that while β-CFT and methylphenidate stabilize an "open-to-out" conformation, binding of either modafinil or bupropion gives rise to a more closed conformation. Our findings highlight a mechanistic difference between modafinil and cocaine-like stimulants and further demonstrate that the conformational effects of a given DAT inhibitor influence its phenomenological effects.
莫达非尼是一种轻度精神刺激剂，具有认知促进和抗抑郁作用。与许多传统兴奋剂不同，莫达非尼滥用潜力很小，因此成为治疗可卡因成瘾的有前途的治疗剂。莫达非尼的主要分子靶标是多巴胺转运蛋白（DAT）；然而，莫达非尼独特作用的机制细节仍不清楚。最近的研究表明，给定的 DAT 配体的构象效应影响配体的强化性质的大小。例如，非典型的 DAT 抑制剂苯环丙胺和 GBR12909 尽管具有更高的结合亲和力，但并不具有可卡因的臭名昭著的成瘾性。在这里，我们表明莫达非尼的结合机制与可卡因不同，与其他非典型抑制剂相似。我们之前建立了两种突变（W84L 和 D313N），增加了 DAT 采用外向构象状态的可能性-这些突变大大增加了可卡因样抑制剂的亲和力，但对非典型抑制剂的结合几乎没有或相反的影响。因此，化合物的 WT/突变体亲和力比可以指示化合物是否优先与更外向或更内向的构象状态相互作用。莫达非尼的亲和力比苯环丙胺、GBR12909 和安非他酮（在人类中缺乏可卡因样作用）更相似，但与可卡因、β-CFT 或哌甲酯的亲和力比相差甚远。虽然锌（已知稳定外向转运体状态）处理将可卡因和哌甲酯的亲和力增加了两倍，但对莫达非尼、苯环丙胺、安非他酮或 GBR12909 的结合几乎没有或没有影响。此外，抑制剂结合的计算建模表明，虽然 β-CFT 和哌甲酯稳定“开放到外”构象，但莫达非尼或安非他酮的结合会导致更封闭的构象。我们的研究结果强调了莫达非尼和可卡因样兴奋剂之间的机制差异，并进一步证明了给定的 DAT 抑制剂的构象效应会影响其现象学效应。
