Biological activities of phthalocyanines--XV. Radiolabeling of the differently sulfonated 67Ga-phthalocyanines for photodynamic therapy and tumor imaging.

Phthalocyanines have been advanced as photosensitizers for the photodynamic therapy of cancer and selectively sulfonated derivatives have shown promise as tumor imaging agents. In order to study the effect of the degree of sulfonation on their biodistribution pattern, we prepared a series of sulfophthalocyanines (PcS) labeled with 67Ga. Direct chelation of metal free phthalocyanines with 67Ga gave chelates which demetallated on further purification whereas condensation of 67Ga with phthalic acid precursors, following purification and fractionation on Sep-Pak C18 cartridges, gave stable products. The distribution pattern of the [67Ga]GaPcS among human plasma proteins was strongly affected by the degree of sulfonation of the PcS. The lower sulfonated GaPcS showed significant binding to the various lipoprotein fractions whereas increased sulfonation favored association to albumin. The use of the 67Ga allowed for the validation of spectrophotometric quantification of GaPcS in biological samples and confirmed the in vivo stability of the radiolabeled complex.