Photosensitized Lysis of Liposomes by Hematoporphyrin Derivative

The spectral properties and efficiency for photosensitizing the lysis of phosphatidylcholine liposomes have been measured for the components of hematoporphyrin derivative (Hpd) after alkaline hydrolysis and fractionation by polyacrylamidc gel chromatography. Two major and two minor Hpd fractions have been identified whose spectral properties correlate with the anoxic sensitizing efficiency and the oxygen enhancement ratio (OER). The fastest moving fraction, which is the putative biologically active component, comprised one‐third of the starting material and had OER = 2.7. Liposome lysis by this fraction was inhibited in the presence of human serum albumin at concentration ratios comparable to those employed for photoradiation therapy. The present results show that Hpd can act as an oxic and anoxic photosensitizer of a model biomembrane and suggest that separation from serum proteins is required for in vivo photosensitization.