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Gadolinium-porphyrins: new potential magnetic resonance imaging contrast agents for melanoma detection

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BACKGROUND: Two new porphyrin-based magnetic resonance imaging (MRl) contrast agents , Gd-hematoporphyrin (Gd-H) and Gd-tetra-carboranylmethoxyphenyl-porphyrin (Gd-TCP) were synthesized and tested in nude mice with human melanoma (MM-138) xenografts as new melanoma contrast agents. METHODS: Subcutaneous xenografts of human melanoma cells (MM-138) were studied in 30 (five groups of six) nude mice. The effect of different contrast agents (Gd-TCP, Gd-H, GdCI3 and Gd-DTPA) on proton relaxation times was measured in tumors and other organs. T) values, signal enhancement and the Gd concentration for different contrast agent solutions were also investigated. RESULTS: The porphyrin agents showed higher relaxivity compared to the clincal agent, Gd-DTPA. A significant 16% and 21% modification in T1 relaxation time of the water in human melanoma tumors grafted in the nude mice was revealed 24 hours after injection ofGd-TCP and Gd-H, respectively. The percentage of injected Gd localized to the tumor measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) was approximately 21% for GdTCP and 28% for Gd-H which were higher than that of Gd-DTPA (10%). CONCLUSIONS: The high concentration of Gd in the tumor is indicative of a selective retention of the compounds and indicates that Gd-TCP and Gd-H are promising MR imaging contrast agents for melanoma detection. Gd-porphyrins have considerable promise for further diagnostic applications in magnetic resonance imaging.

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