Boronated Metalloporphyrins: A novel approach to the diagnosis and treatment of cancer using contrast‐enhanced MR imaging and neutron capture therapy

Porphyrins are a unique class of metal chelating agents that have shown specific affinity for neoplasms. The water‐soluble free‐base derivative, tetrakiscarborane carboxylate ester of 2,4‐(α,β‐dihydroxyethyl) deuteroporphyrin IX (BOPP), an agent designed for neutron capture therapy, has previously demonstrated selective localization and retention in a C6 murine glioma. In the present work, the authors demonstrate that the manganese chelate of BOPP also selectively localizes in a rat 9L gliosarcoma and preferentially enhances the tumor‐normal brain contrast of T1‐weighted images for at least 92 hours. The data indicate a maximal enhancement of contrast between tumor and normal brain at 24 hours after injection, compared with 5 minutes for manganese (III) tetraphenylporphine sulfonate (TPPS₄). The results also indicate that Mn‐BOPP may have a slower uptake in the 9L glioma than Mn‐TPPS₄ but a longer retention in the tumor. Mn‐BOPP is unique in that it represents, to the authors' knowledge, the first example of a single agent that can enhance contrast between tumor and normal tissue and be potentially effective as an agent for boron neutron capture therapy.