Rad51 is a key protein in DNA repair by homologous recombination and an important target for development of drugs in cancer therapy. 4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) has been used in clinic during the past 30 years as an inhibitor of anion transporters and channels. Recently DIDS has been demonstrated to affect Rad51-mediated homologous pairing and strand exchange, key processes in homologous recombination. Consequently, DIDS has been considered as a potential revertant of radio- and chemo-resistance of cancer cells, the major causes of therapy failure. Here, we have investigated the behavior of DIDS towards serum albumins. The effects of environmental factors, primarily, solvent polarity, on DIDS stability were evaluated, and the mechanisms of interaction of DIDS with human or bovine serum albumin were analyzed using isothermal calorimetry, circular dichroism and fluorescence spectroscopies. DIDS interaction with both serum albumins have been demonstrated, and the interaction characteristics have been determined. By comparing these characteristics for several DIDS derivatives, we have identified the DIDS moiety essential for the interaction. Furthermore, site competition data indicate that human albumin has two DIDS-binding sites: a high-affinity site in the IIIA subdomain and a low-affinity one in the IB subdomain. Molecular docking has revealed the key molecular moieties of DIDS responsible for its interactions in each site and shown that the IB site can bind two ligands. These findings show that binding of DIDS to serum albumin may change the balance between the free and bound DIDS forms, thereby affecting its bioavailability and efficacy against Rad51.

中文翻译：

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Rad51抑制剂DIDS与人和牛血清白蛋白的相互作用：光谱学和等温量热法。

Rad51是通过同源重组修复DNA的关键蛋白，也是癌症治疗药物开发的重要目标。在过去的30年中，4'-diisothiocyanostilbene-2,2'-disulfonic acid（DIDS）已在临床上用作阴离子转运蛋白和通道的抑制剂。最近，已证明DIDS影响Rad51介导的同源配对和链交换，这是同源重组的关键过程。因此，DIDS被认为是癌细胞放射和化学耐药性的潜在逆转剂，这是治疗失败的主要原因。在这里，我们调查了DIDS对血清白蛋白的行为。评估了环境因素（主要是溶剂极性）对DIDS稳定性的影响，并用等温量热法，圆二色性和荧光光谱法分析了DIDS与人或牛血清白蛋白的相互作用机理。已经证明了DIDS与两种血清白蛋白的相互作用，并且已经确定了相互作用特性。通过比较几种DIDS衍生物的这些特征，我们确定了相互作用必不可少的DIDS部分。此外，位点竞争数据表明人白蛋白具有两个DIDS结合位点：IIIA子域中的高亲和力位点和IB子域中的低亲和力位点。分子对接揭示了DIDS在每个位点相互作用的关键分子部分，并表明IB位点可以结合两个配体。