Department of Biochemistry, University of Madras, Guindy Campus, Chennai, India.
Department of Biotechnology, Orchid Pharma Limited, Chennai, India.
PLoS One. 2018 Sep 6;13(9):e0202903. doi: 10.1371/journal.pone.0202903. eCollection 2018.
Preliminary cytotoxic analysis of sulphur containing isosteric analogues of calothrixin B identified the useful anti-tumour activity of thia/isothiacalothrixin B which necessitated it's biological evaluation in colon and lung cancer cell lines. The isothia analogues induced cytotoxicity of HCT116 in a time-dependent manner and inhibited the clonogenic survival of HCT116 and NCI-H460 cells in a dose-dependent manner comparable to the standard anti-cancer drug camptothecin. Herein employing flow cytometry, we demonstrate that isothiacalothrixin B analogues inhibited proliferation of colon cancer cells by the arrest of cells in S and G2/M phases over a period of 48 hours at a concentration of 5 μM. Our results also suggest that the cytotoxicity of thia analogues of calothrixin B is partially mediated by induction of cellular DNA strand breaks. The UV-Vis spectroscopic studies with CT-DNA revealed groove binding for calothrixin B and its thia analogues wherein subsequent in silico molecular modelling studies indicated preferential binding to the AT-rich regions of minor groove of DNA. Furthermore, thiacalothrixin B caused transcriptional activation of p21waf1/cip1 promoter and upregulation of its protein levels independent of p53. The induction of DNA damage response pathway leads to apoptosis in isothiacalothrixin B but not in thiacalothrixin B treated cells. The isothia analogues SCAB 4 induced DNA strand breaks and cell cycle arrest even after treatment for a short period (i.e., 4 hours) and the cell cycle effects were irreversible. For the first time, this study provides detailed cellular effects on the potential use of isothiacalothrixin B analogues as cytotoxic agents.
初步的含硫同系物细胞毒性分析表明，Calothrixin B 的硫代/异硫代同系物具有有用的抗肿瘤活性，这使得它有必要在结肠癌和肺癌细胞系中进行生物评估。异硫代类似物以时间依赖性方式诱导 HCT116 的细胞毒性，并以与标准抗癌药物喜树碱相当的剂量依赖性方式抑制 HCT116 和 NCI-H460 细胞的集落存活。在此，我们通过流式细胞术证明，异硫代 Calothrixin B 类似物通过在 5 μM 浓度下在 48 小时的时间内将细胞阻滞在 S 和 G2/M 期来抑制结肠癌细胞的增殖。我们的结果还表明，Calothrixin B 的硫代类似物的细胞毒性部分是通过诱导细胞 DNA 链断裂介导的。与 CT-DNA 的紫外可见光谱研究表明，Calothrixin B 及其硫代类似物与 DNA 的小沟结合，随后的计算机分子建模研究表明，它们优先结合 DNA 小沟的富含 AT 区域。此外，硫代 Calothrixin B 导致 p21waf1/cip1 启动子的转录激活及其蛋白水平的上调，而与 p53 无关。诱导 DNA 损伤反应途径导致异硫代 Calothrixin B 诱导细胞凋亡，但硫代 Calothrixin B 处理的细胞不会。异硫代类似物 SCAB 4 甚至在短时间（即 4 小时）治疗后也能诱导 DNA 链断裂和细胞周期停滞，并且细胞周期效应是不可逆的。这项研究首次提供了有关异硫代 Calothrixin B 类似物作为细胞毒性剂的潜在用途的详细细胞效应。
