The direct detection and monitoring of anti-cancer drugs in vivo by magnetic resonance spectroscopy (MRS) may lead to improved anti-cancer strategies. 31P-MRS has been used to detect and quantify ifosfamide (IF) in vivo in GH3 prolactinomas and N-methyl-N-nitrosourea (MNU)-induced mammary tumours in rats. The average concentration of IF in the GH3 prolactinoma over the first 2 h following a dose of 250 mg kg-1 i.v. was calculated to be 0.42 micromol g-1 wet weight, with a half-life of elimination (t1/2) of 2-4 h. Carbogen (95% oxygen/5% carbon dioxide) breathing increased the amount of IF taken up by the GH3 prolactinoma by 50% (P<0.01) to 0.68 micromol g-1 wet weight, although t1/2 elimination rates were unchanged. IF was also detected in the liver in vivo, with a t1/2 of about 1 h. Carbogen breathing did not affect the maximum peak area (Cmax) or the t1/2 in the liver. Most importantly, the carbogen-induced increase in IF uptake by the tumour caused significant growth delay at all time points in the GH3 tumour growth between day 5 and day 12 (P< 0.01) compared with IF alone. These findings show that carbogen breathing has potential for increasing the efficacy of anti-cancer drugs. Isolated GH3 cells were sensitive to the parent drug (IF) in vitro (IC50 = 1.3 +/- 0.2 mM) suggesting that the GH3 cells may be either expressing P450 enzymes or are sensitive to the parent drug per se
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