title: Rapid upregulation of cytoprotective nitric oxide in breast tumor cells subjected to a photodynamic therapy-like oxidative challenge.
abstract: Many tumor cells produce nitric oxide (NO) as an antiapoptotic/progrowth molecule which also promotes antiogenesis and tumor expansion. This study was designed to examine possible antagonistic effects of endogenous NO on tumor eradication by photodynamic therapy (PDT). Using COH-BR1 breast cancer cells sensitized in mitochondria with 5-aminolevulinic acid (ALA)-generated protoporphyrin IX as a model for ALA-based PDT, we found that caspase-9 activation and apoptotic death following irradiation were strongly enhanced by 1400W, an inhibitor of inducible nitric oxide synthase (iNOS). RT-PCR and Western analyses revealed a substantial upregulation of both iNOS mRNA and protein, beginning ca 4 h after irradiation and persisting for at least 20 h. Accompanying this was a strong 1400W-inhibitable increase in intracellular NO, as detected with the NO probe, DAF-2-DA. Short hairpin RNA-based iNOS knockdown in COH-BR1 cells dramatically reduced NO production under photostress while enhancing caspase-9 activation and apoptosis. These findings suggest that cytoprotective iNOS/NO induction in PDT-treated tumor cells could reduce treatment efficacy, and point to pharmacologic intervention with iNOS inhibitors for counteracting this.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: Reshma
authors.initials: R
authors.lastname: Bhowmick
authors.forename: Albert W
authors.initials: AW
authors.lastname: Girotti
mesh_terms: D001943:Breast Neoplasms / Q000503:physiopathology / Q000532:radiotherapy; D002478:Cells, Cultured; D019610:Cytoprotection; D005260:Female; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010084:Oxidation-Reduction; D010778:Photochemotherapy; D015854:Up-Regulation
chemical_list: D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II