Metabolism and disposition of GTS-21, a novel drug for Alzheimer's disease

Xenobiotica. 1999 Jul;29(7):747-62. doi: 10.1080/004982599238362.


1. GTS-21, a novel drug for Alzheimer's disease, is currently under clinical development. In the current study, the metabolism and disposition of GTS-21 have been evaluated in rat and dog after single oral and intravenous administration. 2. Following oral administration of [14C]GTS-21 to rat, radioactivity was primarily excreted in the faeces (67%) via the bile with possible enterohepatic circulation. Urinary excretion of radioactivity in rat and dog was 20 and 19% respectively. 3. GTS-21 was rapidly and extensively absorbed after oral administration and rapidly cleared from plasma. The maximum concentration ratio of GTS-21 to total radioactivity in plasma was low, indicating first-pass or pre-systemic biotransformation. 4. In rat, GTS-21 showed linear pharmacokinetics over doses ranging from 1 to 10 mg/kg with an absolute bioavailability of 23%. In dog, the absolute bioavailability was 27% at an oral dose of 3 mg/kg. 5. GTS-21 was O-demethylated to yield compounds that were then subject to glucuronidation. Three of the metabolites in rat urine were isolated and characterized as 4-OH-GTS-21, 4-OH-GTS-21 glucuronide and 2-OH-GTS-21 glucuronide. The major urinary metabolites were 4-OH-GTS-21 glucuronide and 2-OH-GTS-21 glucuronide. 6. In vitro chemical inhibition of cytochrome P450 in human liver microsomes indicated that CYPIA2 and CYP2E1 were the isoforms primarily responsible for the O-demethylation of GTS-21, with some contribution from CYP3A.

MeSH terms

  • Alzheimer Disease / drug therapy
  • Animals
  • Area Under Curve
  • Benzylidene Compounds / chemistry
  • Benzylidene Compounds / metabolism*
  • Benzylidene Compounds / pharmacokinetics*
  • Bile / chemistry
  • Biological Availability
  • Carbon Radioisotopes / pharmacokinetics
  • Cytochrome P-450 Enzyme System / drug effects
  • Cytochrome P-450 Enzyme System / metabolism
  • Dogs
  • Feces / chemistry
  • Humans
  • Male
  • Microsomes, Liver / drug effects
  • Microsomes, Liver / metabolism
  • Molecular Structure
  • Nicotinic Agonists / chemistry
  • Nicotinic Agonists / metabolism*
  • Nicotinic Agonists / pharmacokinetics*
  • Pyridines / chemistry
  • Pyridines / metabolism*
  • Pyridines / pharmacokinetics*
  • Rats
  • Rats, Sprague-Dawley
  • Urine / chemistry


  • Benzylidene Compounds
  • Carbon Radioisotopes
  • Nicotinic Agonists
  • Pyridines
  • 3-(2,4-dimethoxybenzylidene)anabaseine
  • Cytochrome P-450 Enzyme System