Synthesis and evaluation of multivalent nitroimidazole-based near-infrared fluorescent agents for neuroblastoma and colon cancer imaging.

Hypoxia is one of key characteristics of microenvironments of solid tumors, and evaluation of hypoxia status in solid tumors is important to determine cancer stage and appropriate treatment. In the present study, novel, multivalent, near-infrared (NIR) fluorescent imaging agents were developed to measure tumor hypoxia. These agents were synthesized using an amino acid as a backbone to connect mono-, bis-, or tris-2-nitroimidazole as a hypoxia-sensitive moiety to enhance uptake by the tumor and to attach sulfo-Cyanine 5.5 as an NIR fluorophore to visualize tumor accumulation. Studies of physical characteristics demonstrated that the novel NIR imaging agents showed suitable optical properties for in vitro and in vivo imaging and were stable in serum. In vitro cellular uptake studies in SK-N-BE(2) and SW620 cell lines demonstrated that NIR imaging agents bearing 2-nitroimidazole structures showed significantly higher tumor uptake in hypoxic cells than in normoxic cells. Moreover, in vivo optical imaging studies using SK-N-BE(2) and SW620 xenografted mice demonstrated that novel, multivalent, 2-nitroimadazole NIR imaging agents with two or three 2-nitroimidazole moieties showed higher uptake in tumor than the control agents with only one 2-nitroimidazole. These observations suggest that novel, multivalent, NIR agents could serve as potential optical imaging agents for evaluating tumor hypoxia.