Previous work has shown that the sterically shielded near-infrared (NIR) fluorescent
heptamethine cyanine dye, s775z, with a reactive carboxyl group produces fluorescent bioconjugates with an unsurpassed combination of high photostability and fluorescence brightness. This present contribution reports two new reactive homologues of s775z with either a
maleimide group for reaction with a
thiol or a strained
alkyne group for reaction with an
azide. Three
cancer-targeting NIR
fluorescent probes were synthesized, each with an appended
cRGDfK peptide to provide selective affinity for
integrin receptors that are overexpressed on the surface of many
cancer cells including the A549
lung adenocarcinoma cells used in this study. A set of
cancer cell microscopy and mouse
tumor imaging experiments showed that all three probes were very effective at targeting
cancer cells and
tumors; however, the change in the linker structure produced a statistically significant difference in some aspects of the mouse biodistribution. The mouse studies included a mock
surgical procedure that excised the subcutaneous
tumors. A paired-agent fluorescence imaging experiment co-injected a binary mixture of targeted probe with 850 nm emission, an untargeted probe with 710 nm emission and determined the targeted probe's binding potential in the
tumor tissue. A comparison of pixelated maps of binding potential for each excised
tumor indicated a
tumor-to-
tumor variation of
integrin expression levels, and a heterogeneous spatial distribution of
integrin receptors within each
tumor.