Luminescence Properties of Halogenated Gadolinium Porphyrins

David M. Clark, Jack Owens, Dr. Rosalie A. Richards

Gadolinium porphyrins show selective accumulation in tumor cells and are used as contrast agents for magnetic resonance imaging (MRI). In addition, they have found application as agents in the photodynamic therapy (PDT) of cancers. In PDT, light excites the porphyrin at tumor sites which, in turn, transform triplet oxygen into singlet oxygen. The resulting reactive singlet oxygen degrades cell components leading to tumor death. However, reports show that tumor sites tend to possess low oxygen levels. We have synthesized the gadolinium complex of 2,3,7,8,12,13,17,18-octabromo-meso-tetrakis(4-N-methylpyridinyl)porphyrin, GdTMPyPBr₈. This compound is also luminescent; that is, it emits light when excited. This emission is sensitive to the presence of triplet oxygen, making the porphyrin a potential sensor of oxygen in tumor sites. We plan to combine the PDT properties of this compound with its oxygen-sensing capabilities to optimize its PDT properties.