Gadolinium(III) texaphyrin: A tumor selective radiation sensitizer that is detectable by MRI

Gadolinium(III) texaphyrin (Gd-tex(2+)) is representative of a new class of radiation sensitizers detectable by magnetic resonance imaging (MRI). This porphyrin-like complex has a high electron affinity [E(1/2) (red.) approximate to 0.08 V versus normal hydrogen electrode] and forms a long-lived pi-radical cation upon exposure to hydrated electrons, reducing ketyl radicals, or superoxide ions. Consistent with these chemical findings, Gd-tex(2+) was found to be an efficient radiation sensitizer in studies carried out with HT29 cells in in vitro as well as in vivo single and multifraction irradiation studies with a murine mammary carcinoma model, Selective localization of Gd-tex(2+) in tumors was confirmed by MRI scanning.