Photodynamic Action of Protoporphyrin on Resealed Erythrocyte Membranes: Mechanisms of Release of Trapped Markers

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Abstract
When administered to tumor-bearing animals, certain porphyrin photosensitizers, most notably “hematoporphyrin derivative (HPD), tend to become localized in the tumor area. This tissue is then susceptible to selective destruction when the sensitizer is photoactivated by visible light (Dougherty et al., 1975). The mechanisms of porphyrin targeting and cytotoxicity are poorly understood and are currently the subjects of intensive investigation. Recent studies on neoplastic cells in culture have suggested that loss of viability may be closely linked with structural and functional derangements in the plasma membrane (Kessel, 1977; Kohn and Kessel, 1979). However, the exact molecular factors involved have not been elucidated. We have been investigating porphyrin-sensitized photodamage in the human red blood cell (RBC) membrane as a simple model for understanding porphyrin phototoxicity in general. Some of this work may provide new insights into the tumoricidal aspects of this phenomenon.