STUDIES ON PORPHYRIN RELATED-COMPOUNDS AND TUMOR-TISSUE AFFINITIES .1. SYNTHESIS OF A CARRIER FOR TUMOR IMAGING AGENT, BIFUNCTIONAL CHELATING AGENT COUPLED PORPHYRIN (ATN-2)

A carrier for a new tumor imaging agent, a bifunctional chelating agent (BCA)-coupled porphyrin (ATN-2), has been synthesized from protoporphyrin dimethyl ester in 4 steps. At first, the hydrobromination of protoporphyrin dimethyl ester is carried out to obtain a monobromo derivative. The derivative is treated with ethylene glycol. The resulting porphyrin has an ether group at the either 7- or 12-position of the ring. Metallation with GaCl3 of the porphyrin having a ethylene glycol residue affords Ga-metalloporphyrin. Final condensation of the metalloporphyrin with diethylenetriaminepentaacetic acid (DT-PA) gave BCA-coupled porphyrin (ATN-2). The chelation of ATN-2 with (In-Cl3)-In-111 easily afforded [In-111]ATN-2. This agent was used for imaging transplantable pancreatic carcinoma in Syrian golden hamster at 72 h after postinjection. The efficacy of the new agent was compared with that of [Ga-67]citrate. The images with [In-111]ATN-2 were found to be clearer than those with [Ga-67] citrate. Therefore, ATN-2, a carrier for (InCl3)-In-111, seems to be more useful for tumor imaging agents.