Components of hematoporphyrin derivatives and their tumor-localizing capacity.

Hematoporphyrin derivative (HPD), a complex mixture of porphyrins derived from hematoporphyrin, has been used for localization and photoradiation therapy of tumors. In this report, we describe characterization of HPD and of its component porphyrins by reverse-phase thin-layer chromatography. Uptake of major HPD components by leukemia L1210 cells in vitro and by the Sarcoma 180 tumor in vivo were also examined. These data suggest that the apparent photosensitization of intact cells mediated by hematoporphyrin was associated with the uptake of more hydrophobic porphyrins present as impurities. In the Sarcoma 180 tumor, the fluorescent porphyrin persisting for two days in vivo after HPD administration was found to migrate with hematoporphyrin in a reverse-phase thin-layer chromatography system. Our results suggest that hematoporphyrin may be unable to cross the cell membrane readily in either direction and that long-persisting fluorescence resulting from exposure of tumor tissues to HPD results from transformation of a membrane-permeable HPD component to hematoporphyrin.