Rapid induction of apoptosis in human keratinocytes with the photosensitizer QLT0074 via a direct mitochondrial action

• Published in: Apoptosis (London) 2003-06, Vol.8 (3), p.269-275
• Main Authors: LI, R, BOUNDS, D. J, GRANVILLE, D, IP, S. H, JIANG, H, MARGARON, P, HUNT, D. W. C
• Format: Article
• Language: English
• Subjects: Ageing, cell death; Antioxidants - pharmacology; Apoptosis; Apoptosis - drug effects; Apoptosis - radiation effects; Biological and medical sciences; Caspases - drug effects; Caspases - radiation effects; Cell Compartmentation - drug effects; Cell Compartmentation - physiology; Cell Line, Transformed; Cell physiology; Cells; Cytochrome; Cytochromes c - drug effects; Cytochromes c - radiation effects; Cytotoxicity; Dose-Response Relationship, Drug; Fluorescence microscopy; Fundamental and applied biological sciences. Psychology; Humans; Keratinocytes - drug effects; Keratinocytes - metabolism; Keratinocytes - radiation effects; Membrane Proteins - drug effects; Membrane Proteins - radiation effects; Mitochondria - drug effects; Mitochondria - metabolism; Mitochondria - radiation effects; Molecular and cellular biology; Oxidizing agents; Photic Stimulation; Photochemotherapy; Photodynamic therapy; Photosensitizing Agents - radiation effects; Photosensitizing Agents - toxicity; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerases; Porphyrins - pharmacology; Porphyrins - radiation effects; Porphyrins - toxicity; Proteins; Proteins - drug effects; Proteins - radiation effects; Pyrrolidine; Pyrrolidines - pharmacology; Reaction Time - drug effects; Reaction Time - radiation effects; Reactive Oxygen Species - metabolism; Thiocarbamates - pharmacology
• ISSN: 1360-8185; 1573-675X
• DOI: 10.1023/A:1023624922787

QLT0074 is a newly introduced, porphyrin-derivative for use in photodynamic therapy (PDT). In the current study, the intracellular distribution of QLT0074 and the mode of cell death induced by photosensitization with this compound in vitro were assessed for transformed human HaCaT keratinocytes. Fluorescence microscopy studies indicated a distribution of the drug to the cytoplasm, nuclear membrane and mitochondria of these cells. In the absence of light, QLT0074 produced no evidence of apoptosis-related biochemical changes or affected cell viability. When combined with blue light exposure, cytotoxicity was exerted in a QLT0074- and light-dose-related manner. Appearance of the mitochondrial protein cytochrome c in the cytosolic fraction and expression of the apoptosis-associated mitochondrial 7A6 antigen were demonstrable following photosensitization at nano-molar levels of QLT0074. Evidence of processing of the apoptosis-effector molecules caspase-3, -6, -7, -8 and -9 as well as cleavage of the caspase-3 substrate poly (ADP-ribose) polymerase (PARP) were demonstrable subsequent to cytochrome c release after PDT. Treatment with the anti-oxidant pyrrolidine dithiocarbamate (PDTC) inhibited cytochrome c release, caspase-3 activation and PARP cleavage associated with PDT thereby supporting the contention that QLT0074 induces apoptosis through the generation of reactive oxygen species upon light activation. QLT0074 is a potent photosensitizer with the capacity to directly initiate apoptosis by acting upon mitochondria.