Metalloporphyrin magnetic resonance contrast agents. Feasibility of tumor-specific magnetic resonance imaging.

The criteria for tumor-specific MRI contrast agents are considered. The metalloporphyrins have been shown to be potential tumor-specific contrast agents due to their selective retention by cancer cells. The Mn(III) water-soluble porphyrin complexes are preferred on the basis of relaxivity and stability. Protein binding in human plasma enhances the relaxivity of Mn(III)-tetraphenylsulfonato-porphyrin (MnTTPS). In preliminary work this agent was shown to enhance MRI contrast at 0.5 T in subcutaneous human colon carcinomas grown in nude mice. Here we report further evidence of enhanced contrast in the same system, and extend this work to human breast tumors in nude mice using a 2 T animal imager. Questions of metalloporphyrin stability, toxicity and dose-contrast relationship are discussed.