Tumor hypoxia plays a vital role in therapeutic resistance. Consequently, measurements of
tumor pO(2) could be used to optimize the outcome of
oxygen-dependent
therapies, such as, chemoradiation. However, the potential optimizations are restricted by the lack of methods to repeatedly and quantitatively assess
tumor pO(2) during
therapies, particularly in
gliomas. We describe the procedures for repeated measurements of orthotopic
glioma pO(2) by multi-site electron paramagnetic resonance (EPR) oximetry. This oximetry approach provides simultaneous measurements of pO(2) at more than one site in the
glioma and contralateral cerebral tissue. The pO(2) of intracerebral 9L, C6, F98 and U251
tumors, as well as contralateral brain, were measured repeatedly for five consecutive days. The 9L
glioma was well oxygenated with pO(2) of 27-36 mm Hg, while C6, F98 and U251
glioma were hypoxic with pO(2) of 7-12mm Hg. The potential of multi-site EPR oximetry to assess temporal changes in tissue pO(2) was investigated in rats breathing 100% O(2). A significant increase in F98
tumor and contralateral brain pO(2) was observed on day 1 and day 2, however,
glioma oxygenation declined on subsequent days. In conclusion, EPR oximetry provides the capability to repeatedly assess temporal changes in orthotopic
glioma pO(2). This information could be used to test and optimize the methods being developed to modulate tumor hypoxia. Furthermore, EPR oximetry could be potentially used to enhance the outcome of chemoradiation by scheduling treatments at times of increase in
glioma pO(2).