Laboratoire de Chimie Bioorganique et Medicinale, European School of Chemistry, Polymers and Materials, University of Strasbourg and Centre National de la Recherche Scientifique, UMR 7509, 25, rue Becquerel, F-67087 Strasbourg, France.
Curr Pharm Des. 2012;18(24):3539-66.
The role of redox enzymes in establishing a microenvironment for parasite development is well characterized. Mimicking human glucose-6-phosphate dehydrogenase and glutathione reductase (GR) deficiencies by redox-cycling compounds thus represents a challenge to the design of new preclinical antiparasitic drug candidates. Schistosomes and malarial parasites feed on hemoglobin. Heme, the toxic prosthetic group of the protein, is not digested and represents a challenge to the redox metabolism of the parasites. Here, we report on old and new redox-cycling compounds--whose antiparasitic activities are related to their interference with (met)hemoglobin degradation and hematin crystallization. Three key-assays allowed probing and differentiating the mechanisms of drug actions. Inhibition of β-hematin was first compared to the heme binding as a possible mode of action. All tested ligands interact with the hematin π-π dimer with K(D) similar to those measured for the major antiparasitic drugs. No correlation between a high affinity for hematin and the capacity to prevent β-hematin formation was however deduced. Inhibition of β-hematin formation is consequently not the result of a single process but results from redox processes following electron transfers from the drugs to iron(III)-containing targets. The third experiment highlighted that several redox-active compounds (in their reduced forms) are able to efficiently reduce methemoglobin to hemoglobin in a GR/NADPH-coupled assay. A correlation between methemoglobin reduction and inhibition of β-hematin was shown, demonstrating that both processes are closely related. The ability of our redox-cyclers to trigger methemoglobin reduction therefore constitutes a critical step to understand the mechanism of action of our drug candidates.
氧化还原酶在寄生虫发育微环境的建立中的作用已得到充分研究。通过氧化还原循环化合物模拟人类葡萄糖-6-磷酸脱氢酶和谷胱甘肽还原酶（GR）的缺乏，这对设计新的临床前抗寄生虫药物候选物构成了挑战。血吸虫和疟原虫以血红蛋白为食。血红素是蛋白质的毒性辅基，不能被消化，这对寄生虫的氧化还原代谢构成了挑战。在这里，我们报告了一些新的和旧的氧化还原循环化合物，它们的抗寄生虫活性与它们干扰（代谢）血红蛋白降解和血红素结晶的能力有关。三个关键的测定方法允许探测和区分药物作用的机制。首先比较了β-血红素的抑制作用与血红素结合作为可能的作用模式。所有测试的配体都与血红素π-π二聚体相互作用，K(D)与主要抗寄生虫药物的测量值相似。然而，并没有推断出与血红素的高亲和力与防止β-血红素形成的能力之间存在相关性。因此，抑制β-血红素的形成不是一个单一过程的结果，而是由于药物向含铁（III）靶标转移电子而产生的氧化还原过程的结果。第三个实验表明，几种氧化还原活性化合物（在其还原形式下）能够在 GR/NADPH 偶联测定中有效地将高铁血红蛋白还原为血红蛋白。显示出高铁血红蛋白还原和β-血红素抑制之间存在相关性，表明这两个过程密切相关。我们的氧化还原循环剂触发高铁血红蛋白还原的能力因此构成了理解我们的药物候选物作用机制的关键步骤。
