Tumor-targeted fluorescent probes for the detection of hNQO1 in cancer cells

Fluorescent probes for single analyte detection might produce "false-positive" signals because the levels of the biomarkers could be up-regulated by some external factors such as drug stimulation, hypoxia, radiation, etc. Tumor-targeted probes capable of simultaneously recognizing two biomarkers could avoid "false-positive" signals and improve the diagnostic accuracy. In this work, three tumor-targeted fluorescent probes have been developed for the detection of hNQO1 in cancer cells, with D-biotin/β-D-galactose/indomethacin (IMC) as the tumor-identifying unit. NNP-Bio and NNP-Gal displayed fast responses (3 min) toward hNQO1 with high sensitivity (∼150-fold fluorescence enhancement) in aqueous solution. The introduction of indomethacin significantly quenched the fluorescence of NNP-Ind, possibly due to the photoinduced electron transfer (PET) from IMC to naphthalimide in the folded state, and the probe emitted strong fluorescence only when both hNQO1 and human serum albumin (HSA) were present. Confocal imaging results showed that all the probes could selectively bioimage cancer cells with overexpression of both hNQO1 and the targeted receptor. Moreover, NNP-Ind could differentiate cancer cells from hNQO1-negative inflammatory cells.