Cysteine S-conjugates may act as kidney-selective prodrugs: formation of 6-mercaptopurine by the renal metabolism of S-(6-purinyl)-L-cysteine.
The recent reports that cysteine S-conjugates of several halogenated hydrocarbons are metabolized selectively in the kidney by cysteine conjugate beta-lyase (beta-lyase) to generate thiols suggest that renal beta-lyase might be exploited for site selective delivery of sulfhydryl drugs to the kidney. In this study, the in vitro and in vivo metabolism of S-(6-purinyl)-L-cysteine, the potential precursor of the antitumor and immunosuppressant drug, 6-mercaptopurine, was examined. With renal subcellular fractions, 6-mercaptopurine was identified as a metabolite of S-(6-purinyl)-L-cysteine by its electronic absorption spectrum and by high-performance liquid chromatography. The rate of enzymatic 6-mercaptopurine formation was dependent upon incubation time, substrate and protein concentrations. Aminooxyacetic acid, an inhibitor of renal beta-lyase, inhibited the reaction. The total renal beta-lyase activity with S-(6-purinyl)-L-cysteine as substrate was distributed equally between the cytosolic and mitochondrial fractions and constituted nearly 54% of the activity measured with the prototype substrate, S-(2-benzothiazolyl)-L-cysteine. The apparent Vmax value for the mitochondrial beta-lyase-dependent metabolism of S-(6-purinyl)-L-cysteine to yield 6-mercaptopurine was 4-fold greater than the rate measured with cytosol, whereas the rates of metabolism of S-(2-benzothiazolyl)-L-cysteine by the cytosolic and mitochondrial beta-lyase were similar. When rats were given S-(6-purinyl)-L-cysteine (31.2 mg/kg i.p.) and were sacrificed at 30 min after treatments, 6-mercaptopurine, 6-methyl-mercaptopurine and 6-thiouric acid were detected in the kidney, liver or plasma.(ABSTRACT TRUNCATED AT 250 WORDS)
Hwang
I Y
IY
Department of Comparative Biosciences, University of Wisconsin, Madison.
Elfarra
A A
AA
D000818:Animals; D013437:Carbon-Sulfur Lyases; D003545:Cysteine / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008190:Lyases / Q000502:physiology; D008297:Male; D015122:Mercaptopurine / Q000031:analogs & derivatives* / Q000378:metabolism*; D011355:Prodrugs / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D011355:Prodrugs; C061748:S-(6-purinyl)cysteine; D015122:Mercaptopurine; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase; D003545:Cysteine