Synthesis of a 4-nitroimidazole indocyanine dye-conjugate and imaging of tumor hypoxia in BALB/c tumor-bearing female mice

Extending our previous work with 2-nitroimidazole-indocyanine dye-conjugate 4, we prepared the 4-nitroimidazole-piperazine-indocyanine derivative (6). We also prepared imidazole derivative 5 as a control. We compared the in vivo hypoxia targeting performance of both 5 and 6 with the previously tested 4, and 6 showed a higher fluorescent intensity after 15 min post-injection, about 1.5-fold higher than 4 and 2.5-fold higher than 5. Cells treated with 6 under hypoxic conditions showed a higher fluorescence yield when compared to the cells kept under normoxic conditions. All findings were supported with fluorescence images of histological sections of tumor samples using a Li-COR scanner and an immunohistochemistry technique for tumor hypoxia.