5‐Fluorouracil (5FU) is a widely employed antineoplastic agent that acts as antimetabolite. However, 5FU activity is strongly reduced against a subset of cancer cells called cancer stem cells (CSCs), which are believed to be responsible for chemoresistance and tumour recurrence. It was found that epigallocatechin‐3‐gallate (EGCG), the most abundant catechin present in green tea extract, suppresses CSCs grown in various cancers. This chemosensitizing effect of EGCG was investigated in 5FU‐resistant (5FUR) CRC cells, showing that EGCG enhances 5FU‐induced cytotoxicity. However, the real mechanism of an improved 5FU chemosensitivity in the presence of EGCG was not evaluated. Considering the capability of catechins to form bimolecular noncovalent complexes, in the present study, the interaction of catechins and 5FU was studied by different mass spectrometric approaches. The ESI(+) and ESI(−) spectra of [5FU‐catechin] mixtures were studied, showing the formation of protonated and deprotonated bimolecular complexes, whose nature was confirmed by MS/MS experiments (product and precursor ion scans). To exclude the possible origin of these species as ESI artefacts, a further series of experiments were performed by high‐resolution liquid chromatography–mass spectrometry. By this approach, bimolecular complexes have been detected at retention times different from those of free 5FU and catechins, proving their presence in the original solution. Analogous studies were performed on 5FU‐green tea extract mixtures, showing that 5FU leads to complexes not only with EGCG but also with other catechins. These molecular species, differently to free 5FU drug alone, would in principle possess a new biological activity and could be an explanation of the described activity cited above.

中文翻译：

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质谱在 5-氟尿嘧啶和儿茶素分子复合物研究中的应用

5-氟尿嘧啶 (5FU) 是一种广泛使用的抗肿瘤剂，可作为抗代谢物。然而，5FU 对称为癌症干细胞 (CSC) 的癌细胞亚群的活性显着降低，据信这些细胞是导致化学抗性和肿瘤复发的原因。发现表没食子儿茶素-3-没食子酸酯 (EGCG) 是绿茶提取物中含量最丰富的儿茶素，可抑制在各种癌症中生长的 CSC。在 5FU 抗性 (5FUR) CRC 细胞中研究了 EGCG 的这种化学增敏作用，表明 EGCG 增强了 5FU 诱导的细胞毒性。然而，没有评估在 EGCG 存在下改善 5FU 化学敏感性的真正机制。考虑到儿茶素形成双分子非共价复合物的能力，在本研究中，通过不同的质谱方法研究了儿茶素和 5FU 的相互作用。研究了 [5FU-儿茶素] 混合物的 ESI(+) 和 ESI(-) 光谱，显示质子化和去质子化双分子复合物的形成，其性质已通过 MS/MS 实验（产物和前体离子扫描）证实。为了排除这些物种作为 ESI 人工制品的可能来源，通过高分辨率液相色谱 - 质谱法进行了进一步的一系列实验。通过这种方法，双分子复合物的检测保留时间与游离 5FU 和儿茶素的保留时间不同，证明它们存在于原始溶液中。对 5FU 绿茶提取物混合物进行的类似研究表明，5FU 不仅与 EGCG 形成复合物，而且与其他儿茶素形成复合物。这些分子种类，