ABSTRACT
l-Methamphetamine has been occasionally referred to as a stimulant similar to d-methamphetamine, probably owing to insufficient comparative studies. Here, we directly compared psychomotor efficacies and pharmacokinetics of methamphetamine enantiomers in mice. Only d-methamphetamine, but not l-methamphetamine, induced stereotypy and sensitization at 1-10 mg/kg. However, plasma pharmacokinetic parameters of 10 mg/kg l-methamphetamine were ≥tenfold those of 1 mg/kg d-methamphetamine. These results clearly indicate that differential psychomotor efficacies of methamphetamine enantiomers are independent of their pharmacokinetic profiles.
Subject(s)
Brain/drug effects , Central Nervous System Stimulants/pharmacology , Methamphetamine/pharmacology , Motor Activity/drug effects , Animals , Brain/metabolism , Central Nervous System Stimulants/blood , Central Nervous System Stimulants/pharmacokinetics , Dose-Response Relationship, Drug , Male , Methamphetamine/blood , Methamphetamine/pharmacokinetics , Mice , Stereoisomerism , Stereotyped Behavior/drug effects , Time FactorsABSTRACT
Antitumor 2'-deoxycytidine (dCyd) analogs such as gemcitabine (dFdC), cytarabine (Ara-C), and 2'-C-cyano-2'-deoxy-1-ß-d-arabinofuranosylcytosine (CNDAC) are activated by dCyd kinase, whereas cytidine deaminase (CDA) inactivates them by conversion to their uracil forms. To elucidate the relationship between the chemosensitivity to antitumor dCyd nucleosides and CDA expression, we established a stable line of human gastric carcinoma TMK-1 cells constitutively overexpressing CDA (TMK-1/CDA) and examined its chemosensitivity to antitumor dCyd analogs in vitro and in vivo. We observed comparable reactivity for dFdC and Ara-C, and the substrate reactivity of CNDAC to recombinant human CDA was more than 10 times less efficient than those of Ara-C and dFdC. Next, we examined the in vitro chemosensitivity of TMK-1/CDA and observed a marked decrease in the sensitivity of TMK-1/CDA to Ara-C, dFdC, and CNDAC compared with mock-transfected cells. In addition, we transplanted TMK-1/CDA cells into a nude mouse xenograft model and examined their in vivo chemosensitivity to CNDAC. The in vivo antitumor effect of CNDAC on TMK-1/CDA cells was substantially reduced compared with that of mice transplanted with mock-transfected cells. These results indicate that CDA could play an important role in regulating susceptibility to antitumor dCyd analogs in vitro and in vivo. In addition, the expression level of CDA was found to affect the antitumor activity of CNDAC, even though the substrate reactivity of CNDAC to CDA is relatively low.
