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Rapid Upregulation of Cytoprotective Nitric Oxide in Breast Tumor Cells Subjected to a Photodynamic Therapy‐like Oxidative Challenge
Author(s) -
Bhowmick Reshma,
Girotti Albert W.
Publication year - 2011
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2010.00877.x
Subject(s) - downregulation and upregulation , photodynamic therapy , nitric oxide , apoptosis , nitric oxide synthase , gene knockdown , cancer research , chemistry , intracellular , sonodynamic therapy , small hairpin rna , cancer cell , microbiology and biotechnology , cancer , biology , medicine , biochemistry , organic chemistry , gene
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.