Photophysics and photochemistry of hematoporphyrin, hematoporphyrin derivative and uroporphyrin I.

Abstract

The putative action mechanism in photodynamic therapy (PDT) involves serum transport of HPD to tumor tissue, localization and retention of the active constituent, generation of singlet molecular oxygen (Δ) by the action of visible light and the attack of t on the cellular targets. Early workers postulated that tumor tissue membranes are key targets in PDT (Dougherty et al., 1978), which is consistent with evidence that photosensitization of red blood cell membranes by protoporphyrin is mediated by Δ (Lamola et al., 1973). Subsequent studies on photosensitization of model membranes by hematoporphyrin (HP) and HPD are consistent with this hypothesis. However, the specific targets have not been identified and the involvement of non- membrane targets has not been ruled out. HPD is a porphyrin mixture leading to a complicated dependence of the photophysical and photochemical properties on the medium. The active constituent has not been adequately characterized, although there is evidence that it is a covalent dimer or oligomer of porphyrin units (Berenbaum et ai., 1982; Dougherty et al., 1984; Swincer et al., 1985). Dougherty et al. (1984) refer to this material as dihematoporphyrin ether (DHE), which will be used for convenience in this paper, although the structure implied by the terminology has not been proven. The present results were obtained with an enriched HPD material prepared by poiyacryiamide gel filtration of HPD referred to as HpD-A (Grossweiner and Goyal, 1983).KeywordsHuman Serum AlbuminSoret BandRose BengalHematoporphyrin DerivativeHuman Serum Albumin MoleculeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.