Renal cellular transport, metabolism, and cytotoxicity of S-(6-purinyl)glutathione, a prodrug of 6-mercaptopurine, and analogues.
The disposition of S-(6-purinyl)glutathione (6-PG) and its metabolites, including the antitumor agent 6-mercaptopurine (6-MP), was characterized in freshly isolated renal cortical cells from male F344 rats to assess the ability of the kidney to convert 6-PG to 6-MP. The intracellular transport and accumulation of 6-PG and 6-MP, the metabolism of 6-PG to 6-MP, and the potential cytotoxicity of 6-MP, 6-thioxanthine (6-ThXan), and 6-thioguanine (6-ThGua) were determined. 6-PG and 6-MP were accumulated by renal cortical cells by time- and concentration-dependent processes, reaching maximal levels of 14.2 and 1.52 nmol/10(6) cells, respectively, with 1 mM concentrations of each compound. Treatment with acivicin, an inhibitor of 6-PG metabolism by gamma-glutamyltransferase, increased accumulation of 6-PG, and treatment with alpha-keto-gamma-methiolbutyrate, a keto acid cosubstrate that stimulates activity of the cysteine conjugate beta-lyase (beta-lyase), which generates 6-MP, decreased accumulation of 6-PG. Incubation of renal cells with 10 mM 6-PG generated 6-MP at a rate of 2.4 nmol/min per 10(6) cells, demonstrating that the beta-lyase pathway forms the desired product from the prodrug within the intact renal cell. Preincubation of cells with acivicin or aminooxyacetic acid, an inhibitor of the beta-lyase, decreased the net formation of 6-MP, demonstrating further the function of the beta-lyase. 6-MP, 6-ThXan, and 6-ThGua exhibited approximately equivalent cytotoxicity (45-55% release of lactate dehydrogenase with 1 mM at 2 hr) in isolated renal cells. Based on the known antitumor potency of these agents, this suggests that cytotoxicity and antitumor activity occur by distinct mechanisms. The high amount of accumulation of 6-PG and its subsequent metabolism to 6-MP, as compared with the relatively low amount of accumulation of 6-MP, in renal cells suggest that 6-PG can function as a prodrug and is a more effective delivery vehicle for 6-MP to renal cells than 6-MP itself. Administration of 6-PG may be an effective means of treating renal tumors or suppressing renal transplant rejection.
Lash
L H
LH
Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI 48201, USA. lhlash@cms.cc.wayne.edu
Shivnani
A
A
Mai
J
J
Chinnaiyan
P
P
Krause
R J
RJ
Elfarra
A A
AA
D000493:Allopurinol / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics*; D001692:Biological Transport; D005978:Glutathione / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000633:toxicity; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D015122:Mercaptopurine / Q000493:pharmacokinetics* / Q000633:toxicity; D011687:Purines / Q000493:pharmacokinetics* / Q000633:toxicity; D051381:Rats; D011916:Rats, Inbred F344; D014969:Xanthine Oxidase / Q000502:physiology
D000970:Antineoplastic Agents; D011687:Purines; C079307:S-(6-purinyl)glutathione; D000493:Allopurinol; D015122:Mercaptopurine; D007770:L-Lactate Dehydrogenase; D014969:Xanthine Oxidase; D005978:Glutathione