OxyFile #421

Effect of stereochemistry on the oxidative metabolism of the 
cyclophosphamide metabolite aldophosphamide.

Habib AD; Boal JH; Hilton J; Nguyen T; Chang YH; Ludeman SM

Department of Chemistry, Catholic University of America, 
Washington, DC, USA.

Biochem Pharmacol, 50: 3, 1995 Jul 31, 429-33


31P NMR and cell perfusion techniques were used to investigate the 
conversion of the individual enantiomers of aldophosphamide (AP) 
to carboxyphosphamide (CBP) as catalyzed by aldehyde dehydrogenase 
in human erythroleukemia K562 cells. R- and S-cyclophosphamides 
(CPs) were treated with ozone and hydrogen peroxide to yield Rp- 
and Sp-cis-4-hydroperoxycyclophosphamides (Rp- and Sp-cis-4-HO2-
CP); reduction of each hydroperoxide gave the corresponding 
enantiomer of AP [along with its tautomer 4-
hydroxycyclophosphamide (4-HO-CP)]. In separate experiments, K562 
cells embedded in agarose gel threads were perfused at pH 7.4, 21 
+/- 1 degrees, with solutions of 1.4 mM Rp- and Sp-4-HO-CP/AP, 
both with and without added mesna (an acrolein scavenger). A 
comparison of the 31P NMR spectral data derived from the 
experiments revealed little statistical difference (+/- 10-20% 
error limits) in the normalized intensities of the CBP peaks 
arising from the individual AP enantiomers [with added mesna, the 
ratio Rp-CBP:Sp-CBP was 1.00:1.24 +/- 0.13 (average deviation); 
without mesna, the same ratio was 1.00:1.35]. Using conventional 
methods for evaluating the in vitro drug toxicities, CP-resistant 
L1210 cells were treated in separate experiments with Rp- and Sp-
cis-4-HO2-CP; there were no significant differences between the 
toxicities exhibited by the stereoisomers.