The bioreductive enzymes typically upregulated in hypoxic tumor cells can be targeted for developing diagnostic and drug delivery applications. In this study, a new fluorescent probe 4−(6−nitro−1,3−dioxo−1H−benzo[de]isoquinolin−2(3H)−yl)benzaldehyde (NIB) based on a nitronaphthalimide skeleton that could respond to nitroreductase (NTR) overexpressed in hypoxic tumors is designed and its application in imaging tumor hypoxia is demonstrated. The docking studies revealed favourable interactions of NIB with the binding pocket of NTR-Escherichia coli. NIB, which is synthesized through a simple and single step imidation of 4−nitro−1,8−naphthalic anhydride displayed excellent reducible capacity under hypoxic conditions as evidenced from cyclic voltammetry investigations. The fluorescence measurements confirmed the formation of identical products (NIB-red) during chemical as well as NTR−aided enzymatic reduction in the presence of NADH. The potential fluorescence imaging of hypoxia based on NTR-mediated reduction of NIB is confirmed using in-vitro cell culture experiments using human breast cancer (MCF−7) cells, which displayed a significant change in the fluorescence colour and intensity at low NIB concentration within a short incubation period in hypoxic conditions.

Graphical abstract

中文翻译：

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用于癌细胞缺氧荧光成像的硝萘酰亚胺探针

通常在缺氧肿瘤细胞中上调的生物还原酶可用于开发诊断和药物输送应用。在这项研究中，一种基于硝基萘酰亚胺骨架的新型荧光探针 4−(6−nitro−1,3−dioxo−1 H −benzo[ de ]isoquinolin−2(3 H )−yl)benzaldehyde (NIB) 可以响应设计了在缺氧肿瘤中过表达的硝基还原酶 (NTR)，并证明了其在肿瘤缺氧成像中的应用。对接研究揭示了 NIB 与 NTR-大肠杆菌结合口袋的有利相互作用. NIB 是通过 4−nitro−1,8−naphthalic anhydride 的简单单步酰亚胺化合成的，在低氧条件下表现出优异的还原能力，循环伏安法研究证明了这一点。荧光测量证实了在化学过程中形成相同的产物（NIB-红色）以及在 NADH 存在下 NTR 辅助的酶促还原。使用人乳腺癌 (MCF-7) 细胞的体外细胞培养实验证实了基于 NTR 介导的 NIB 减少的缺氧潜在荧光成像，其在低 NIB 浓度下显示出荧光颜色和强度的显着变化在缺氧条件下潜伏期短。

图形概要