title: Nitric oxide-mediated resistance to photodynamic therapy in a human breast tumor xenograft model: Improved outcome with NOS2 inhibitors.
abstract: Many malignant tumors employ iNOS-derived NO to resist eradication by chemotherapeutic agents or ionizing radiation. In this study, we determined whether human breast carcinoma MDA-MB-231 cells in vitro and in vivo as tumor xenografts would exploit endogenous iNOS/NO to resist the cytotoxic effects of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT). Broad band visible irradiation of ALA-treated cells resulted in a marked after-light upregulation of iNOS protein which persisted for at least 24 h. Apoptotic killing of ALA/light-challenged cells was significantly enhanced by iNOS inhibitors (1400W, GW274150) and a NO trap (cPTIO), implying that stress-induced iNOS/NO was acting cytoprotectively. We found that cells surviving the photostress proliferated and migrated more rapidly than controls in 1400W- and cPTIO-inhibitable fashion, indicating iNOS/NO involvement. Female SCID mice bearing MDA-MB-231 tumors were used for animal model experiments. ALA-PDT with a 633 nm light source caused a significant reduction in post-irradiation tumor growth relative to light-only controls, which was further reduced by administration of 1400W or GW274150, whereas 1400W had little or no effect on controls. Immunoblot analyses of tumor samples revealed a progressive post-PDT upregulation of iNOS, which reached >5-times the control level after six days. Correspondingly, the nitrite/nitrate level in post-PDT tumor samples was substantially higher than that in controls. In addition, a 1400W-inhibitable upregulation of pro-survival/progression effector proteins such as Bcl-xL, Survivin, and S100A4 was observed after in vitro and in vivo ALA-PDT. This is the first known study to demonstrate iNOS/NO-induced resistance to PDT in an in vivo human tumor model.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Fahey
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA. Electronic address: agirotti@mcw.edu.
authors.forename: Albert W
authors.initials: AW
authors.lastname: Girotti
mesh_terms: D000578:Amidines / Q000494:pharmacology; D000622:Aminolevulinic Acid / Q000627:therapeutic use; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001565:Benzoates / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D005260:Female; D064593:Heterografts; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008027:Light; D016513:Mice, SCID; D009361:Neoplasm Invasiveness; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018384:Oxidative Stress; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011524:Protoporphyrins / Q000494:pharmacology; D013440:Sulfides / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D000578:Amidines; D051017:Apoptosis Regulatory Proteins; D001565:Benzoates; D001596:Benzylamines; D007093:Imidazoles; C104820:N-(3-(aminomethyl)benzyl)acetamidine; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D013440:Sulfides; C409004:GW 274150; C079393:1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole; D009569:Nitric Oxide; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; C496319:NOS2 protein, human; D052247:Nitric Oxide Synthase Type II
keywords: Breast cancer; Human tumor xenograft model; Nitric oxide; Photodynamic therapy