Near-infrared (NIR) fluorescence imaging holds great promise for
tumor imaging due to low tissue autofluorescence and deep tissue penetration. However, most
tumor-targeting
fluorescent probes require combination of targeting agents and fluorescent reporters. In this study, we described a NIR
heptamethine cyanine dye,
IR-780 iodide, with preferential accumulation in multiple
tumor cells without the necessity of chemical conjugation. The
IR-780 iodide was found to retain in
tumors but not normal cells in multiple
tumor xenografts in nude mice and chemically-induced lung
tumors in C57BL/6 mice. The fluorescent signal of
tumors could persist at least 20 days with a significant signal-to-background ratio. As a lipophilic
cation, a predominant accumulation of
IR-780 iodide was shown in the mitochondria of
tumor cells owing to the high magnitude of mitochondrial membrane potential in
tumor cells than normal cells. We further showed that the transportation of
IR-780 iodide into
tumor cells was mediated by the
organic anion transporter peptides (OATPs) because the
dye accumulation was significantly inhibited by
sulfobromophthalein (BSP), a competitive inhibitor of OATPs. Our study shows that
IR-780 iodide that preferentially accumulates in
tumor cells and is natively NIR fluorescent would be useful in
tumor detection.