title: Subcellular localization of Photofrin and aminolevulinic acid and photodynamic cross-resistance in vitro in radiation-induced fibrosarcoma cells sensitive or resistant to photofrin-mediated photodynamic therapy.
abstract: The subcellular and, specifically, mitochondrial localization of the photodynamic sensitizers Photofrin and aminolevulinic acid (ALA)-induced protoporphyrin-IX (PpIX) has been investigated in vitro in radiation-induced fibrosarcoma (RIF) tumor cells. Comparisons were made of parental RIF-1 cells and cells (RIF-8A) in which resistance to Photofrin-mediated photodynamic therapy (PDT) had been induced. The effect on the uptake kinetics of Photofrin of coincubation with one of the mitochondria-specific probes 10N-Nonyl acridine orange (NAO) or rhodamine-123 (Rh-123) and vice versa was examined. The subcellular colocalization of Photofrin and PpIX with Rh-123 was determined by double-label confocal fluorescence microscopy. Clonogenic cell survival after ALA-mediated PDT was determined in RIF-1 and RIF-8A cells to investigate cross-resistance with Photofrin-mediated PDT. At long (18 h) Photofrin incubation times, stronger colocalization of Photofrin and Rh-123 was seen in RIF-1 than in RIF-8A cells. Differences between RIF-1 and RIF-8A in the competitive mitochondrial binding of NAO or Rh-123 with Photofrin suggest that the inner mitochondrial membrane is a significant Photofrin binding site. The differences in this binding may account for the PDT resistance in RIF-8A cells. With ALA, the peak accumulations of PpIX occurred at 5 h for both cells, and followed a diffuse cytoplasmic distribution compared to mitochondrial localization at 1 h ALA incubation. There was rapid efflux of PpIX from both RIF-1 and RIF-8A. As with Photofrin, ALA-induced PpIX exhibited weaker mitochondrial localization in RIF-8A than in RIF-1 cells. Clonogenic survival demonstrated cross-resistance to incubation in PpIX but not to ALA-induced PpIX, implying differences in mitochondrial localization and/or binding, depending on the source of the PpIX within the cells.
authors.affiliation: Ontario Cancer Institute/Princess Margaret Hospital, Toronto, Canada. wilson@oci.utoronto.ca
authors.forename: B C
authors.initials: BC
authors.lastname: Wilson
authors.forename: M
authors.initials: M
authors.lastname: Olivo
authors.forename: G
authors.initials: G
authors.lastname: Singh
mesh_terms: D000622:Aminolevulinic Acid / Q000493:pharmacokinetics*; D000818:Animals; D017323:Dihematoporphyrin Ether / Q000493:pharmacokinetics*; D005354:Fibrosarcoma / Q000628:therapy*; D017324:Hematoporphyrin Derivative / Q000493:pharmacokinetics*; D010778:Photochemotherapy; D013347:Subcellular Fractions / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D017324:Hematoporphyrin Derivative; D000622:Aminolevulinic Acid; D017323:Dihematoporphyrin Ether