Laboratory of Toxicology & Pharmacology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, United States.
Chem Res Toxicol. 2013 Mar 18;26(3):379-87. doi: 10.1021/tx300480q. Epub 2013 Feb 26.
Originally identified as an innate cytotoxin, nitric oxide ((·)NO) formation in tumors can influence chemotherapy and exacerbate cancer progression. Here, we examined the hypothesis that (·)NO generation contributes to cancer cell drug resistance toward the widely used anticancer drug Etoposide (VP-16). The UV-vis spectrum of VP-16 was not changed by exposure of VP-16 to (·)NO in aqueous buffer. In contrast, reddish-orange compound(s) characteristic of o-quinone- and nitroso-VP-16 were readily generated in a hydrophobic medium (chloroform) in an oxygen-dependent manner. Similar products were also formed when the VP-16 radical, generated from VP-16 and horseradish peroxidase/H2O2, was exposed directly to (·)NO in chloroform in the presence of oxygen. Separation and spectral analysis of VP-16 reaction extracts by electron spin resonance and UV-vis indicated the generation of the phenoxy radical and the o-quinone of VP-16, as well as putative nitroxide, iminoxyl, and other nitrogen oxide intermediates. Nitric oxide products of VP-16 displayed significantly diminished topoisomerase II-dependent cleavage of DNA and cytotoxicity to human HL-60 leukemia cells. LPS-mediated induction of nitric oxide synthase in murine macrophages resulted in VP-16 resistance compared to Raw cells. Furthermore, (·)NO products derived from iNOS rapidly reacted with VP-16 leading to decreased DNA damage and cytotoxicity. Together, these observations suggest that the formation of (·)NO in tumors (associated macrophages) can contribute to VP-16 resistance via the detoxification of VP-16.
最初被鉴定为一种先天细胞毒素，肿瘤中一氧化氮（(·)NO）的形成可以影响化疗并加剧癌症进展。在这里，我们检验了这样一个假设，即(·)NO 的产生有助于癌细胞对广泛使用的抗癌药物依托泊苷（VP-16）产生耐药性。VP-16 的紫外可见光谱在暴露于（·）NO 于水性缓冲液中时没有改变。相比之下，在疏水性介质（氯仿）中，以氧依赖性方式，很容易生成 VP-16 的邻醌和亚硝基-VP-16 的红棕色化合物。当 VP-16 自由基（由 VP-16 和辣根过氧化物酶/H2O2 产生）直接暴露于氯仿中存在氧气的（·）NO 时，也会形成类似的产物。电子自旋共振和紫外可见分析表明 VP-16 反应提取物的分离和光谱分析生成了 VP-16 的苯氧基自由基和邻醌，以及可能的氮氧化物中间体、硝酮、亚硝酮和其他氮氧化物中间体。VP-16 的一氧化氮产物显示出拓扑异构酶 II 依赖性 DNA 切割和对人 HL-60 白血病细胞的细胞毒性显著降低。与 Raw 细胞相比，LPS 介导的鼠巨噬细胞中一氧化氮合酶的诱导导致 VP-16 耐药。此外，iNOS 衍生的(·)NO 产物与 VP-16 迅速反应，导致 DNA 损伤和细胞毒性降低。总之，这些观察结果表明，肿瘤（相关巨噬细胞）中（·）NO 的形成可能通过 VP-16 的解毒作用导致 VP-16 耐药。
