Article thumbnail

Nitric Oxide Synthase Inhibition Enhances the Antitumor Effect of Radiation in the Treatment of Squamous Carcinoma Xenografts

By Robert J. G. Cardnell and Ross B. Mikkelsen


This study tests whether the nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine (L-NNA), combines favorably with ionizing radiation (IR) in controlling squamous carcinoma tumor growth. Animals bearing FaDu and A431 xenografts were treated with L-NNA in the drinking water. IR exposure was 10 Gy for tumor growth and survival studies and 4 Gy for ex vivo clonogenic assays. Cryosections were examined immunohistochemically for markers of apoptosis and hypoxia. Blood flow was assayed by fluorescent microscopy of tissue cryosections after i.v. injection of fluorospheres. Orally administered L-NNA for 24 hrs reduces tumor blood flow by 80% (p<0.01). Within 24 hrs L-NNA treatment stopped tumor growth for at least 10 days before tumor growth again ensued. The growth arrest was in part due to increased cell killing since a combination of L-NNA and a single 4 Gy IR caused 82% tumor cell killing measured by an ex vivo clonogenic assay compared to 49% by L-NNA or 29% by IR alone. A Kaplan-Meyer analysis of animal survival revealed a distinct survival advantage for the combined treatment. Combining L-NNA and IR was also found to be at least as effective as a single i.p. dose of cisplatin plus IR. In contrast to the in vivo studies, exposure of cells to L-NNA in vitro was without effect on clonogenicity with or without IR. Western and immunochemical analysis of expression of a number of proteins involved in NO signaling indicated that L-NNA treatment enhanced arginase-2 expression and that this may represent vasculature remodeling and escape from NOS inhibition. For tumors such as head and neck squamous carcinomas that show only modest responses to inhibitors of specific angiogenic pathways, targeting NO-dependent pro-survival and angiogenic mechanisms in both tumor and supporting stromal cells may present a potential new strategy for tumor control

Topics: Research Article
Publisher: Public Library of Science
OAI identifier:
Provided by: PubMed Central

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.

Suggested articles


  1. (2007). A Phase II study of SU5416 in patients with advanced or recurrent head and neck cancers.
  2. (2002). Activation of constitutive nitric-oxide synthase activity is an early signaling event induced by ionizing radiation.
  3. Arginine deprivation and argininosuccinate synthetase expression in the treatment of cancer.
  4. (2004). Arginine pathways and the inflammatory response: interregulation of nitric oxide and polyamines: review article.
  5. (2006). Autophagy for cancer therapy through inhibition of pro-apoptotic proteins and mammalian target of rapamycin signaling.
  6. (1999). Blockage of the vascular endothelial growth factor stress response increases the antitumor effects of ionizing radiation.
  7. (2008). Chronic hypoxia decreases synthesis of homologous recombination proteins to offset chemoresistance and radioresistance.
  8. (2001). Chronic hypoxia modulates tumour cell radioresponse through cytokineinducible nitric oxide synthase.
  9. DG Dichloroacetate induces apoptosis and cell-cycle arrest in colorectal cancer cells.
  10. (2005). Early reoxygenation in tumors after irradiation: determining factors and consequences for radiotherapy regimens using daily multiple fractions.
  11. (2007). Effect of nitricoxide synthesis on tumour blood volume and vascular activity: a phase I study.
  12. (2007). Endostatin improves radioresponse and blocks tumor revascularization after radiation therapy for A431 xenografts in mice.
  13. (2009). Endothelial nitric oxide synthase mediates lymphangiogenesis and lymphatic metastasis.
  14. (2002). Enhancement of vascular targeting by inhibitors of nitric oxide synthase.
  15. (2001). Epidermal growth factor receptor as a genetic therapy target for carcinoma cell radiosensitization.
  16. (2005). epidermal growth factor receptor by ionizing radiation and modulation by SHP2.
  17. (1989). Epidermal growth factor receptor gene expression, protein kinase activity, and terminal differentiation of human malignant epidermal cells.
  18. (2003). Evaluation of hypoxia-inducible factor-1alpha (HIF-1alpha) as an intrinsic marker of tumor hypoxia in U87 MG human glioblastoma: in vitro and xenograft studies.
  19. (2004). Greater cell cycle inhibition and cytotoxicity induced by 2-deoxy-D-glucose in tumor cells treated under hypoxic vs aerobic conditions.
  20. (2009). Hypoxia promotes human pulmonary artery smooth muscle cell proliferation through induction of arginase.
  21. (2000). In vivo enhancement of tumor radioresponse by C225 antiepidermal growth factor receptor antibody.
  22. (2002). Increased radiosensitivity with chronic hypoxia in four human tumor cell lines.
  23. (1994). Induction of hypoxia in experimental murine tumors by the nitric oxide synthase inhibitor, NG-nitro-L-arginine.
  24. (1997). Inhibition of nitric oxide synthase induces a selective reduction in tumor blood flow that is reversible with Larginine.
  25. (1996). Inhibition of nitric oxide synthesis by NG-nitro-L-arginine methyl ester (L-NAME): requirement for bioactivation to the free acid, NG-nitro-L-arginine.
  26. (2005). Inhibition of nuclear factor-kappaB and target genes during combined therapy with proteasome inhibitor bortezomib and reirradiation in patients with recurrent head-and-neck squamous cell carcinoma.
  27. (2005). Inhibition of protein-tyrosine phosphatases by mild oxidative stresses is dependent on S-nitrosylation.
  28. (2002). Insulin increases the sensitivity of tumors to irradiation: involvement of an increase in tumor oxygenation mediated by a nitric oxide-dependent decrease of the tumor cells oxygen consumption.
  29. (2001). Ionizing radiation-induced, mitochondria-dependent generation of reactive oxygen/nitrogen.
  30. (2003). Irradiation-induced angiogenesis through the up-regulation of the nitric oxide pathway: implications for tumor radiotherapy.
  31. (2007). MKP-1 switches arginine metabolism from nitric oxide synthase to arginase following endotoxin challenge.
  32. (2002). Modulation of the tumor vasculature functionality by ionizing radiation accounts for tumor radiosensitization and promotes gene delivery.
  33. Nelin LD Hypoxia-induced proliferation of human pulmonary microvascular endothelial cells depends on epidermal growth factor receptor tyrosine kinase activation.
  34. (2009). Nitric oxide synthase inhibition enhances the tumor vascular-damaging effects of combretastatin a-4 3-o-phosphate at clinically relevant doses.
  35. (2003). Nitric oxide-mediated promotion of mammary tumour cell migration requires sequential activation of nitric oxide synthase, guanylate cyclase and mitogen-activated protein kinase.
  36. (2003). Oxi4503, a novel vascular targeting agent: effects on blood flow and antitumor activity in comparison to combretastatin A-4 phosphate.
  37. (2009). Promotion of autophagy as a mechanism for radiation sensitization of breast tumor cells.
  38. (1997). Radioenhancement by cisplatin with accelerated fractionated radiotherapy in a human tumour xenograft.
  39. (2005). Red wine polyphenol-induced, endothelium-dependent NO-mediated relaxation is due to the redox-sensitive PI3-kinase/Akt-dependent phosphorylation of endothelial NO-synthase in the isolated porcine coronary artery.
  40. (2007). Regulation of HIF1alpha stability through S-nitrosylation.
  41. (2007). Role of activated nuclear factor-kappaB in the pathogenesis and therapy of squamous cell carcinoma of the head and neck.
  42. (2008). Systems biologydefined NF-kappaB regulons, interacting signal pathways and networks are implicated in the malignant phenotype of head and neck cancer cell lines differing in p53 status.
  43. (2006). The role of nitric oxide in tumour progression.
  44. (2007). Thrombospondin-1 limits ischemic tissue survival by inhibiting nitric oxidemediated vascular smooth muscle relaxation.
  45. (2004). Tumor microenvironmental physiology and its implications for radiation oncology.
  46. (2008). Tumor recovery by angiogenic switch from sprouting to intussusceptive angiogenesis after treatment with PTK787/ZK222584 or ionizing radiation.
  47. (2008). Tumour maintenance is mediated by eNOS.
  48. (2007). Tyrosine nitration of IkappaBalpha: a novel mechanism for NF-kappaB activation.