Effects of localised tumour hyperthermia on pimonidazole (Ro 03-8799) pharmacokinetics in mice.
We have investigated the effects of localised tumour hyperthermia (LTH; 43.5 degrees C x 30 min) on the acute toxicity and pharmacokinetics of the hypoxic cell sensitizer pimonidazole (Ro 03-8799) in mice. There were three treatment groups: unrestrained controls, sham-treated and LTH treated mice. LTH had minimal effects on the acute toxicity (LD50/7d) of pimonidazole with no significant difference between the three treatment groups. Pharmacokinetic studies were carried out at the maximum tolerated dose (MTD; approximately 60% LD50) of 437 micrograms g-1 i.v. in plasma, brain and tumour. Sham tumour treatment consistently increased plasma drug concentrations compared to unrestrained controls but had minimal effects on the elimination t1/2. The AUC0-infinitive was increased by 35% and the plasma clearance decreased by 26%. By contrast, LTH had minimal effects on these parameters compared to sham treatment. Brain pimonidazole concentrations were increased in restrained mice (sham and LTH treatments) compared to unrestrained controls, but average brain/plasma ratios were similar in all three groups at between 400 and 500%. Sham tumour treatment markedly reduced peak tumour pimonidazole concentrations compared to unrestrained controls giving a 29% lower AUC0-180min. Average tumour/plasma ratios were reduced from 236 to 129%. The most important finding was that LTH further reduced pimonidazole tumour concentrations, giving a 31% lower AUC0-180 min compared to sham treated tumours. Tumour/plasma ratios for pimonidazole were reduced by 41%. Plasma exposure to the pimonidazole N-oxide metabolite, Ro 31-0313, was unaltered by LTH. The markedly reduced drug concentrations in heated tumours may be a result of hyperthermia-stimulated bioreductive drug activation.
Walton
M I
MI
MRC Clinical Oncology and Radiotherapeutics Unit, Cambridge, UK.
Bleehen
N M
NM
Workman
P
P
D000818:Animals; D001831:Body Temperature; D006979:Hyperthermia, Induced; D007928:Lethal Dose 50; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D009593:Nitroimidazoles / Q000493:pharmacokinetics* / Q000633:toxicity; D011838:Radiation-Sensitizing Agents / Q000493:pharmacokinetics* / Q000633:toxicity; D012513:Sarcoma, Experimental / Q000628:therapy*
D009593:Nitroimidazoles; D011838:Radiation-Sensitizing Agents; C033815:pimonidazole