Synthesis and Application of New Gadolinium-Porphyrins as Potential MR Imaging Contrast Agents for Cancer Detection in Nude Mice

Two new potential magnetic resonance imaging contrast agents, Gd-hematoporphyrin (Gd-H) and Gd-tetra-carboranylmethoxyphenyl-porphyrin (Gd-TCP), were synthesized and applied to nude mice with human melanoma (MM-138) xenografts. These agents showed a high relaxivity because of their greater potential to coordinate water molecules. The reduction of T1 relaxation times of 16 and 21% was observed in human melanoma tumors grafted in the nude mice 24 h after injection of Gd-TCP andGd-H, respectively. The percent of injected Gd, that localized to the tumor and measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), was approximately 21% for Gd- TCP and 28% for Gd-H. A higher concentration of Gd was achieved compared with control indicating selective delivery of Gd-porphyrins to the melanoma xenografts. The data indicate that Gd-TCP can be used as a dual probe for diagnosis in MR imaging and for therapy in boron neutron capture therapy (BNCT).