Glutathione S-transferase P1-1 expression modulates sensitivity of human kidney 293 cells to photodynamic therapy with hypericin.
Photodynamic therapy (PDT) relies on light-dependent, tissue-targeted, oxidative stress in tumors that have accumulated a photosensitizing drug. Glutathione S-transferases (GSTs) are often up-regulated in tumors and they modulate oxidative stress by several isoform-dependent mechanisms. GSTs, therefore, are potential confounding factors in PDT. Therefore, we examined this possibility in human kidney 293 cells transfected with a plasmid encoding either green fluorescent protein alone (pIRES-GFP) or both GFP and GSTP1-1 (pIRES-GFP-GSTP). Cells were cultured and treated with light alone, the sensitizer hypericin (HYP) alone, or light and HYP. Cells harboring pIRES-GFP-GSTP exhibited a modest 2-fold increase in GSTP1-1 expression over control cells. On the basis of flow cytometry and microscopy, the light-dependent toxicity of HYP was reduced in cells over-expressing GSTP1-1. Paradoxically, the decreased toxicity in the cells with GSTP1-1 over-expression occurred concomitantly with a modest approximately 2-fold increase in cellular uptake of the drug. Immunoprecipitation of HYP and Western analysis indicated that GSTP1-1 is a major intracellular-binding site for HYP. These results are the first to demonstrate GST expression as a confounding variable of photodynamic therapy. Further, a high-affinity GST inhibitor reversed the GSTP1-1-dependent resistance, suggesting the possible utility of pharmacological strategies to optimize PDT.
Department of Medicinal Chemistry, University of Washington, Box 357610, Seattle, WA 98195, USA.
Michael J
MJ
Dabrowski
Dean
D
Maeda
John
J
Zebala
Weiya Doug
WD
Lu
Sumit
S
Mahajan
Terrance J
TJ
Kavanagh
William M
WM
Atkins
D000873:Anthracenes; D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D002460:Cell Line; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology* / Q000528:radiation effects; D008027:Light; D010569:Perylene / Q000008:administration & dosage / Q000031:analogs & derivatives*; D010778:Photochemotherapy / Q000379:methods*; D016896:Treatment Outcome
D000873:Anthracenes; D010569:Perylene; C004965:hypericin; D005982:Glutathione Transferase