Biotransformation of topotecan in the isolated perfused rat liver: identification of three novel metabolites.
This study evaluates the metabolism of the anticancer drug topotecan (TPT) in the isolated perfused rat liver of male Wistar-rats. Using a sensitive high-performance liquid chromatography method, in bile TPT, its ring-opened hydroxycarboxylate form and three new metabolites could be quantified. Enzymatic hydrolysis of the metabolites with beta-glucuronidase and mass spectroscopy revealed the existence of glucuronidated TPT as well as unconjugated and glucuronidated bidesmethyl TPT. Biliary secretion of glucuronidated N-bidesmethyl TPT was fast reaching a maximum already after 15 min(30.6 +/- 15.1 pmol/g liver.min), whereas secretion of TPT, topotecan glucuronide and N-bidesmethyl TPT was delayed (maximum at 30 min: 431 +/- 19, 6.4 +/- 2.1 and 12.7 +/- 2.7 pmol/g liver.min, respectively). No release of TPT metabolites into the perfusate was detected. The amount of TPT, TPT glucuronide, N-bidesmethyl TPT and N-bidesmethyl TPT glucuronide excreted into bile during 60 min of perfusion was 2.10 +/- 0.483%, 0.031 +/- 0.006%, 0.058 +/- 0.013% and 0.108 +/- 0.012% of TPT cleared from the perfusate over 60 min, respectively. In conclusion we could identify three novel TPT metabolites, however, their overall metabolism in the rat liver is low.
Institute of Pharmaceutical Chemistry, University of Vienna, Austria.
P
P
Platzer
S
S
Schaden
T
T
Thalhammer
G
G
Hamilton
B
B
Rosenberg
I
I
Silgoner
W
W
Jäger
D000818:Animals; D001646:Bile / Q000737:chemistry / Q000378:metabolism; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D005965:Glucuronates / Q000032:analysis; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D015394:Molecular Structure; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D012680:Sensitivity and Specificity; D013997:Time Factors; D019772:Topotecan / Q000493:pharmacokinetics*
D005965:Glucuronates; D019772:Topotecan