1: Radiat Res. 2007 Oct;168(4):428-32. Thyroid status is a key modulator of tumor oxygenation: implication for radiation therapy. Jordan BF, Christian N, Crokart N, Grégoire V, Feron O, Gallez B. Laboratory of Biomedical Magnetic Resonance, Université Catholique de Louvain, B-1200 Brussels, Belgium. In normal tissues, thyroid hormones play a major role in the metabolic activity and oxygen consumption of cells. Because the rate of oxygen consumption is a key factor in the response of tumors to radiation, we hypothesized that thyroid hormones may affect the metabolic activity of tumor cells and hence modulate the response to cytotoxic treatments. We measured the influence of thyroid status on the tumor microenvironment in experimental tumors. Hypothyroidism and hyperthyroidism were generated in mice by chronic treatment with propyl thiouracil and l-thyroxine. Thyroid status significantly modified tumor pO(2) as measured with EPR oximetry. Mechanistically, this was the result of the profound changes in oxygen consumption rates. Thyroid status was associated with a significant change in tumor radiosensitivity since the regrowth delay was increased in hypothyroid mice compared to euthyroid mice, an effect that was abolished when temporarily clamped tumors were irradiated. This study provides unique insights into the impact of modulating tumor oxygen consumption and could have implications in the management of cancer patients with thyroid disorders. PMID: 17903037 [PubMed - indexed for MEDLINE] Related Links 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. [Cancer Res. 2002] PMID:12068004 Glucocorticoids modulate tumor radiation response through a decrease in tumor oxygen consumption. [Clin Cancer Res. 2007] PMID:17255286 Nitric oxide-mediated increase in tumor blood flow and oxygenation of tumors implanted in muscles stimulated by electric pulses. [Int J Radiat Oncol Biol Phys. 2003] PMID:12605986 Complex relationship between changes in oxygenation status and changes in R*2: the case of insulin and NS-398, two inhibitors of oxygen consumption. [Magn Reson Med. 2006] PMID:16897769 The quantitative contributions of mitochondrial proton leak and ATP turnover reactions to the changed respiration rates of hepatocytes from rats of different thyroid status. [J Biol Chem. 1993] PMID:8392060