Nitric oxide-mediated resistance to photodynamic therapy in a human breast tumor xenograft model: Improved outcome with NOS2 inhibitors

Nitric Oxide. 2017 Jan 30:62:52-61. doi: 10.1016/j.niox.2016.12.003. Epub 2016 Dec 19.

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.

Keywords: Breast cancer; Human tumor xenograft model; Nitric oxide; Photodynamic therapy.

MeSH terms

  • Amidines / pharmacology
  • Aminolevulinic Acid / therapeutic use
  • Animals
  • Apoptosis
  • Apoptosis Regulatory Proteins / metabolism
  • Benzoates / pharmacology
  • Benzylamines / pharmacology
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Line, Tumor
  • Cell Survival
  • Down-Regulation
  • Drug Resistance, Neoplasm
  • Female
  • Heterografts
  • Humans
  • Imidazoles / pharmacology
  • Light
  • Mice, SCID
  • Neoplasm Invasiveness
  • Nitric Oxide / metabolism*
  • Nitric Oxide Synthase Type II / antagonists & inhibitors*
  • Nitric Oxide Synthase Type II / metabolism
  • Oxidative Stress
  • Photochemotherapy*
  • Photosensitizing Agents / therapeutic use
  • Protoporphyrins / pharmacology
  • Sulfides / pharmacology
  • Up-Regulation

Substances

  • Amidines
  • Apoptosis Regulatory Proteins
  • Benzoates
  • Benzylamines
  • Imidazoles
  • N-(3-(aminomethyl)benzyl)acetamidine
  • Photosensitizing Agents
  • Protoporphyrins
  • Sulfides
  • GW 274150
  • 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole
  • Nitric Oxide
  • Aminolevulinic Acid
  • protoporphyrin IX
  • NOS2 protein, human
  • Nitric Oxide Synthase Type II