In vivo observation of intracellular oximetry in perfluorocarbon-labeled glioma cells and chemotherapeutic response in the CNS using fluorine-19 MRI.

Preclinical development of therapeutic agents against cancer could greatly benefit from noninvasive markers of tumor killing. Potentially, the intracellular partial pressure of oxygen (pO(2) ) can be used as an early marker of antitumor efficacy. Here, the feasibility of measuring intracellular pO(2) of central nervous system glioma cells in vivo using (19) F magnetic resonance techniques is examined. Rat 9L glioma cells were labeled with perfluoro-15-crown-5-ether ex vivo and then implanted into the rat striatum. (19) F MRI was used to visualize tumor location in vivo. The mean (19) F T(1) of the implanted cells was measured using localized, single-voxel spectroscopy. The intracellular pO(2) in tumor cells was determined from an in vitro calibration curve. The basal pO(2) of 9L cells (day 3) was determined to be 45.3 ± 5 mmHg (n = 6). Rats were then treated with a 1 × LD10 dose of bischloroethylnitrosourea intravenously and changes in intracellular pO(2) were monitored. The pO(2) increased significantly (P = 0.042, paired T-test) to 141.8 ± 3 mmHg within 18 h after bischloroethylnitrosourea treatment (day 4) and remained elevated (165 ± 24 mmHg) for at least 72 h (day 6). Intracellular localization of the perfluoro-15-crown-5-ether emulsion in 9L cells before and after bischloroethylnitrosourea treatment was confirmed by histological examination and fluorescence microscopy. Overall, noninvasive (19) F magnetic resonance techniques may provide a valuable preclinical tool for monitoring therapeutic response against central nervous system or other deep-seated tumors.