Phthalocyanine Labels for Near-Infrared Fluorescence Imaging of Solid Tumors

Diamagnetic metal complexes of phthalocyanines with n-butoxyl groups in all the alpha-benzo positions of the macrocycle skeleton, MPc(OBu)(8), have strong near-infrared absorptions and intense fluorescences that are Stokes shifted by more than 15 nm. Interestingly, the silicon complex 6 is also remarkably photostable and nontoxic. The use of 6 in the fluorescence imaging of BALB/c mice bearing a 4T1-luc2 tumor in the mammary fat pad unambiguously revealed the presence of the tumor when it was only 1 mm in diameter and was not visible with the naked eye. Compound 6 has an intrinsic ability to accumulate in the tumor, adequate spectroscopic properties, and excellent stability to function as a NIR fluorescent label in the early detection of tumors.