Selenoperoxidase-mediated cytoprotection against merocyanine 540-sensitized photoperoxidation and photokilling of leukemia cells

• Published in: Cancer research (Chicago, Ill.) Vol. 52; no. 19; pp. 5282 - 5290
• Main Authors: FUBAO LIN, GEIGER, P. G, GIROTTI, A. W
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01-10-1992
• Subjects: Animals; Azoles - pharmacology; Biological and medical sciences; Catalase - pharmacology; Cell Death - drug effects; Cell Death - physiology; Cell Death - radiation effects; Glutathione - deficiency; Glutathione Peroxidase - antagonists & inhibitors; Glutathione Peroxidase - pharmacology; Humans; Leukemia L1210 - drug therapy; Leukemia L1210 - enzymology; Leukemia L1210 - metabolism; Leukemia, Experimental - drug therapy; Leukemia, Experimental - enzymology; Leukemia, Experimental - metabolism; Lipid Peroxidation - drug effects; Medical sciences; Mice; Organoselenium Compounds - pharmacology; Photochemotherapy; Photoradiation therapy and photosensitizing agent; Pyrimidinones - pharmacology; Pyrimidinones - toxicity; Radiation Tolerance - drug effects; Radiation-Sensitizing Agents - pharmacology; Selenium - deficiency; Treatment with physical agents; Treatment. General aspects; Tumors; Glutathione peroxidase; Human; Enzyme; Cytotoxicity; Lipids; Malignant hemopathy; L1210-Leukemia; In vitro; Phototherapy; Prevention; Resistance; Treatment; Inhibition; Selenium; Mechanism of action; Photosensitizer; Tumor cell; Peroxidation
• ISSN: 0008-5472; 1538-7445

Photodynamic therapy with the lipophilic sensitizing dye merocyanine 540 (MC540) is a promising new approach for extracorporeal purging of neoplastic cells from autologous remission bone marrow grafts. Resistance-conferring cellular defenses against the cytotoxic effects of MC540/photodynamic therapy have not been well characterized. This study focuses on the cytoprotective effects of the glutathione-dependent selenoperoxidases GPX and PHGPX, which can detoxify a wide variety of hydroperoxides, including lipid-derived species (LOOHs). Murine leukemia L1210 cells were grown in 1% serum media without [L.Se(-)] and with [L.Se(+)] selenium supplementation. L.Se(-) cells expressed 10- to 20-fold lower GPX and PHGPX activities than L.Se(+) controls and were markedly more sensitive to MC540-mediated photoperoxidation (LOOH formation) and clonally assessed photokilling. Susceptibility of L.Se(-) cells to photoperoxidation and photokilling could be fully reversed to L.Se(+) levels by replenishing Se, and partially reversed by treating with Ebselen, a selenoperoxidase mimetic. Altered lipid composition, greater uptake of MC540, and defective catabolism of H2O2 were all ruled out as possible factors in the elevated photosensitivity of L.Se(-) cells. Human leukemia K562 cells (capable of expressing PHGPX but not GPX) exhibited 5- to 10-fold lower PHGPX activity under Se-deficient relative to Se-sufficient conditions. Although MC540 uptake (nmol/mg lipid) by K562 and L1210 cells was essentially the same, the former were more resistant to photoinactivation. However, like murine counterparts, Se-deficient cells were more susceptible to photoperoxidation and photokilling than Se-sufficient controls. These results clearly demonstrate that GPX and/or PHGPX in L1210 cells and PHGPX in K562 cells play an important cytoprotective role during photooxidative stress. Whether membrane damage due to lipid photoperoxidation is causally related to cell death is not certain; however, the parallel effects of Se deficiency on LOOH formation and cell killing are at least consistent with this possibility.