GLUTATHIONE, CELL-PROLIFERATION, AND 1,3-BIS-(2-CHLOROETHYL)-1-NITROSOUREA IN K562 LEUKEMIA

We have pursued our findings of glutathione reductase (GSSG-R) deficie ncy and disturbed glutathione in cancer patients treated with 1,3-bis- (2-chloroethyl)-1-nitrosourea (BCNU), by investigating how thiol metab olism, cell proliferation, and the nitrosourea interact in human K562 leukemia. Fasting cells arrested in G greatly increased their reduced glutathione (GSH) in response to growth factors. The rise in thiol beg an after several hours, peaked before DNA synthesis, and resulted from increased production. BCNU inactivated GSSG-R rapidly, and later reta rded, doubled, and greatly prolonged GSH formation before stopping DNA synthesis. Pretreatment unlike post treatment with buthionine-S-R-sul foximine (BSO) diminished BCNU's ability to block GSSG-R. Enzyme inhib ition decreased with falling cellular GSH. In the leukemia system as i n vivo, sequential BCNU-induced thiol alterations heralded delayed ant iproliferative effects. Drug timing markedly affected both thiol and D NA syntheses. By destroying GSSG-R and delaying the upregulation of th iol synthesis while escalating GSH utilization and requirements, the n itrosourea created a striking and previously unrecognized window of vu lnerability for GSH-dependent processes. During this period, altered G SH metabolism could contribute indirectly to BCNU's pleiotropic effect s by interfering with DNA alkylation repair, glucose decarboxylation, deoxyribose formation, and possibly by influencing other aspects of pr oliferation. Acquired GSSG-R deficiency was also an early and sensitiv e marker for prodrug breakdown and activation.