In vivo detection of ifosfamide by P-31-MRS in rat tumours: Increased uptake and cytotoxicity induced by carbogen breathing in GH3 prolactinomas

The direct detection and monitoring of anti-cancer drugs in vivo by magnetic resonance spectroscopy (MRS) may lead to improved anti-cancer strategies. P-31-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 protactinoma over the first 2 h following a dose at 250 mg kg(-1) i.v. was calculated to be 0.42 mu mol g(-1) wet weight, with a half-life of elimination (t(1/2)) 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 lambda mol g(-1) wet weight, although t(1/2) elimination rates were unchanged. IF was also detected in the liver in vivo, with a t(1/2) of about 1 h. Carbogen breathing did not affect the maximum peak area (C-max) or the t(1/2) 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 atone. 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.