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Probing the Structure and Stability of the Tumor-localizing Derivative of Hematoporphyrin by Reductive Cleavage with LiAlH₄¹

Departments of Medicine and Pharmacology, Wayne State University School of Medicine [D. K., P. T.], Detroit, Michigan 48201, and Departments of Biochemistry [B. M.] and Chemistry [C. K. C.], Michigan State University, East Lansing, Michigan 48823

A procedure involving the use of the reducing agent lithium aluminum hydride (LiAlH₄) has been designed to explore the nature of the oligomer linkages in the tumor-localizing component of hematoporphyrin derivative (HPD). High-performance liquid chromatography and fast-atom bombardment mass spectrometry were used to determine the reduction products. The results are consistent with a structure wherein ester linkages join hematoporphyrin molecules. The presence of minor amounts of ether-linked porphyrins was confirmed, and their origin was determined through the application of the chemical reduction process to HPD. An increased proportion of ether-linked porphyrins was detected during storage of HPD at room temperature or above. The commercial product Photofrin II, presumably an HPD preparation enriched in the dimcr/oligomer fraction, was found to contain approximately 50% ether link-ages. This product therefore differs from the corresponding fraction of freshly prepared HPD.

¹ Supported in part by grant CA 23378 from the National Cancer Institute, NIH, Department of Health and Human Services.

² To whom requests for reprints should be addressed at the Department of Medicine, Harper-Grace Hospitals, Detroit MI 48201.

Received 5/ 1/87. Accepted 6/ 4/87.