ENHANCED EXPRESSIONS OF GLUCOSE-6-PHOSPHATE-DEHYDROGENASE AND CYTOSOLIC ALDEHYDE DEHYDROGENASE, AND ELEVATION OF REDUCED GLUTATHIONE LEVEL IN CYCLOPHOSPHAMIDE-RESISTANT HUMAN LEUKEMIA-CELLS

Elevation of activity and mRNA level of a cytosolic aldehyde dehydroge nase-l (ALDH1), which oxidizes aldophosphamide, was previously observe d in a cyclophosphamide-resistant murine leukemia cell line. However, changes in other enzyme(s) which may detoxify the drug or produce anti -alkylating agent(s), have not been examined. The human leukemia cell line, K562, was made 30-fold resistant against 4-hydroperoxyphosphamid e (4HC) by exposing the cells to increasing concentrations of the drug . Resistance against cisplatin was also increased by about 3-fold. Act ivities of glucose-6-phosphate dehydrogenase (G6PD) and ALDH1 were ele vated more than 7-fold in the resistant cells. The mRNA level of the t wo enzymes was also proportionally elevated. The concentration of redu ced glutathione (GSH) was higher in the resistant cells (i.e., 21.1 ve rsus 4.68 nmole per 10(6) cells), while activities of gamma-glutamylcy steine synthetase and glutathione synthetase, and the expressions of o ther human ALDH genes were not increased in the resistant cells. These findings suggest that the acquired resistance against 4HC is a conseq uence of transcriptional activation of two genes, i,e,, one encoding t he G6PD, a major enzyme regenerating anti-alkylating GSH, and the othe r encoding ALDH1, which has a high activity for oxidation of aldophosp hamide derived from 4HC. (C) 1998 Academic Press.