Thiosemicarbazones (TSCs) are a class of biologically active compounds with promising anticancer activity. Their typical mechanism, especially of the clinically far developed representative Triapine, is chelation of iron (Fe), with the Fe-containing enzyme ribonucleotide reductase as primary intracellular target. However, for the subclass of terminally disubstituted, nanomolar-active derivatives like Dp44mT and Me2NNMe2, recent findings suggest that the chelation, stability, and reduction properties of the copper(II) (Cu) complexes are essential for their modes of action. Consequently, it is important to elucidate whether blood serum Cu(II) is a potential metal source for these TSCs. To gain more insights, the interaction of Triapine, Dp44mT or Me2NNMe2 with purified human serum albumin (HSA) as the main pool of labile Cu(II) was investigated by UV-vis and electron paramagnetic resonance measurements. Subsequently, a size-exclusion chromatography inductively coupled plasma mass spectrometry method for the differentiation of Cu species in serum was developed, especially separating the non-labile Cu enzyme ceruloplasmin from HSA. The results indicate that the TSCs specifically chelate copper from the N-terminal Cu-binding site of HSA. Furthermore, the Cu(II)-TSC complexes were shown to form ternary HSA conjugates, most likely via histidine. Noteworthy, Fe-chelation from transferrin was not overserved, even not for Triapine. In summary, the labile Cu pool of HSA is a potential source for Cu-TSC complex formation and, consequently, distinctly influences the anticancer activity and pharmacological behavior of TSCs.

中文翻译：

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人血清白蛋白作为抗癌缩氨基硫脲的铜源。

缩氨基硫脲（TSC）是一类具有良好抗癌活性的生物活性化合物。它们的典型机制，特别是临床上已发展成熟的代表性三甲平，是螯合铁（Fe），其中含铁的核糖核苷酸还原酶作为主要的细胞内靶标。然而，对于末端双取代的纳摩尔活性衍生物（例如 Dp44mT 和 Me2NNMe2）的子类，最近的研究结果表明，铜 (II) (Cu) 配合物的螯合、稳定性和还原特性对其作用模式至关重要。因此，阐明血清 Cu(II) 是否是这些 TSC 的潜在金属来源非常重要。为了获得更多见解，通过 UV-vis 和电子顺磁共振测量研究了 Triapine、Dp44mT 或 Me2NNMe2 与作为不稳定 Cu(II) 主要池的纯化人血清白蛋白 (HSA) 的相互作用。随后，开发了一种尺寸排阻色谱电感耦合等离子体质谱法，用于区分血清中的铜形态，特别是从 HSA 中分离不稳定的铜酶铜蓝蛋白。结果表明，TSC 特异性地螯合 HSA N 端铜结合位点的铜。此外，Cu(II)-TSC 复合物被证明可形成三元 HSA 缀合物，很可能是通过组氨酸形成的。值得注意的是，转铁蛋白的铁螯合作用并没有过度，即使对于三甲平也是如此。总之，HSA 的不稳定铜库是 Cu-TSC 复合物形成的潜在来源，因此明显影响 TSC 的抗癌活性和药理行为。