of Carbogen-Breathing

The purpose of this study was to noninvasively monitor tumor oxygenation and redox status during hyperoxygenation treat-ment, such as carbogen-breathing, in a murine tumor model using in vivo electron paramagnetic resonance (EPR) spectros-copy and imaging techniques. The study was performed using implanted lithium phthalocyanine (LiPc) microcrystals as the oximetry probe and 3-carbamoylproxyl (3-CP) as the redox probe in RIF-1 tumors implanted in the upper hind leg of C3H mice. Repetitive measurements of pO2 from the same tumors as a function of tumor growth (8–24 mm in size) showed that the tumors were hypoxic and that the tumor pO2 values were de-creasing with tumor growth. Carbogen-breathing mostly showed an increase in the tumor oxygenation, although there were considerable variations in the magnitude of change among the tumors. The pharmacokinetic studies with 3-CP showed a significant decrease in the overall tumor reduction status in the carbogen-breathing mice. Spatially resolved (im-aging) pharmacokinetic data over the tumor volume were ob-tained to visualize the distribution of the redox status within the tumor. The redox images of the tumor in the air-breathing mice showed significant heterogeneity in the magnitude and spatial distribution of reducing equivalents. On carbogen-breathing the tissue reduction status decreased considerably, with a concomitant decrease in the heterogeneity of distribution of the redox status. The results suggest that 1) carbogen-breathing considerably enhances tissue oxygenation and sig-nificantly decreases the redox status in RIF-1 tumor, and 2) changes in the magnitude and distribution of the redox status within the tumor volume during carbogen-breathing are cor-related with the increased tissue oxygenation. Magn Reso