Dept. of Pharmacology, Toxicology, and Pharmacy, University of Veterinary Medicine Hannover, Germany; Center for Systems Neuroscience Hannover, Germany.
Molecular and Integrative Biosciences and Neuroscience Center (HiLIFE), University of Helsinki, Finland.
Neuropharmacology. 2022 Mar 1;205:108910. doi: 10.1016/j.neuropharm.2021.108910. Epub 2021 Dec 6.
The Na-K-2Cl cotransporter NKCC1 and the neuron-specific K-Cl cotransporter KCC2 are considered attractive CNS drug targets because altered neuronal chloride regulation and consequent effects on GABAergic signaling have been implicated in numerous CNS disorders. While KCC2 modulators are not yet clinically available, the loop diuretic bumetanide has been used in clinical studies to treat brain disorders and as a tool for NKCC1 inhibition in preclinical models. Bumetanide is known to have anticonvulsant and neuroprotective effects under some pathophysiological conditions. However, as shown in several species from neonates to adults (mice, rats, dogs, and by extrapolation in humans), at the low clinical doses of bumetanide approved for diuresis, this drug has negligible access into the CNS, reaching levels that are much lower than what is needed to inhibit NKCC1 in cells within the brain parenchyma. Several drug discovery strategies have been used over the last ∼15 years to develop brain-permeant compounds that, ideally, should be selective for NKCC1 to eliminate the diuresis mediated by inhibition of renal NKCC2. The strategies employed to improve the pharmacokinetic and pharmacodynamic properties of NKCC1 blockers include evaluation of other clinically approved loop diuretics; development of lipophilic prodrugs of bumetanide; development of side-chain derivatives of bumetanide; and unbiased high-throughput screening approaches of drug discovery based on large chemical compound libraries. The main outcomes are that (1), non-acidic loop diuretics such as azosemide and torasemide may have advantages as NKCC1 inhibitors vs. bumetanide; (2), bumetanide prodrugs achieve significantly higher brain levels of the parent drug and have lower diuretic activity; (3), the novel bumetanide side-chain derivatives do not exhibit any functionally relevant improvement of CNS accessibility or NKCC1 selectivity vs. bumetanide; (4) novel compounds discovered by high-throughput screening may resolve some of the inherent problems of bumetanide, but as yet this has not been achieved. Thus, further research is needed to optimize the design of brain-permeant NKCC1 inhibitors. Another major challenge is to identify the mechanisms whereby various NKCC1-expressing cellular targets of these drug within (e.g., neurons, oligodendrocytes or astrocytes) and outside the brain parenchyma (e.g., blood-brain barrier, choroid plexus, endocrine and immune system), as well as molecular off-target effects, might contribute to their reported therapeutic and adverse effects.
钠钾 2 氯共转运蛋白 NKCC1 和神经元特异性钾氯共转运蛋白 KCC2 被认为是有吸引力的中枢神经系统药物靶点，因为改变神经元氯离子调节以及随之对 GABA 能信号的影响与许多中枢神经系统疾病有关。虽然 KCC2 调节剂尚未在临床上应用，但噻嗪类利尿剂布美他尼已在临床研究中用于治疗脑部疾病，并作为在临床前模型中抑制 NKCC1 的工具。布美他尼在一些病理生理条件下具有抗惊厥和神经保护作用。然而，正如在几种从新生儿到成年的物种（小鼠、大鼠、狗，并且可以推断在人类中）中所表明的那样，在用于利尿的批准的布美他尼的低临床剂量下，该药物进入中枢神经系统的通道很少，达到的水平远低于抑制脑实质细胞内 NKCC1 所需的水平。在过去约 15 年中，已经使用了几种药物发现策略来开发具有脑渗透性的化合物，这些化合物理想情况下应该对 NKCC1 具有选择性，以消除通过抑制肾脏 NKCC2 介导的利尿作用。用于改善 NKCC1 阻滞剂的药代动力学和药效学特性的策略包括评估其他临床批准的噻嗪类利尿剂；布美他尼的亲脂性前药的开发；布美他尼侧链衍生物的开发；以及基于大型化合物库的无偏高通量药物发现筛选方法。主要结果是：(1)，与布美他尼相比，非酸性噻嗪类利尿剂如阿佐塞米和托拉塞米可能作为 NKCC1 抑制剂具有优势；(2)，布美他尼前药可显著提高母体药物的脑内水平，并降低利尿活性；(3)，新型布美他尼侧链衍生物在 CNS 可及性或 NKCC1 选择性方面与布美他尼相比没有任何功能相关的改善；(4)，通过高通量筛选发现的新型化合物可能解决布美他尼的一些固有问题，但尚未实现。因此，需要进一步研究来优化脑渗透性 NKCC1 抑制剂的设计。另一个主要挑战是确定这些药物在脑内（例如神经元、少突胶质细胞或星形胶质细胞）和脑实质外（例如血脑屏障、脉络丛、内分泌和免疫系统）的各种 NKCC1 表达细胞靶点以及分子脱靶效应的机制，这些机制可能有助于解释其报道的治疗和不良反应。
