Increased rate of glutathione synthesis from cystine in drug-resistant MCF-7 cells.
The rate of glutathione synthesis was determined in drug-sensitive and -resistant MCF-7 cells by monitoring the rate of label uptake from [3,3'-13C(2)]-cystine using NMR spectroscopy and mass spectrometry. Compared with the wild-type human mammary adenocarcinoma cell line (MCF-7wt), the isotope incorporation rate was increased 1.6-, 2.4-, and 5.3-fold in the etoposide-resistant MCF-7 cell line (MCF-7vp), doxorubicin-resistant MCF-7 cell line (MCF-7adr), and 4-hydroperoxycyclophosphamide-resistant MCF-7 cell line (MCF-7hc), respectively. The increase in glutathione metabolism in the MCF-7hc line correlated with steady-state levels as determined by biochemical assay. In contrast, both the MCF-7vp and MCF-7adr lines showed increased metabolic synthesis of glutathione but displayed lower steady-state levels compared with the MCF-7wt line. The increased synthetic rates of all resistant lines reflected, in part, contributions from the increased activities of both gamma-glutamyltranspeptidase and gamma-glutamylcysteine synthetase. These results emphasize the importance of monitoring glutathione metabolic rates, rather than steady-state levels of enzymes or substrates, for assessing drug resistance.
Gamcsik
Michael P
MP
Department of Medicine, Duke Comprehensive Cancer Center, Duke University Medical Center, P.O. Box 3843, MSRB 301, Research Drive, Durham, NC 27710, USA. gamcs001@mc.duke.edu
Dubay
George R
GR
Cox
Brandon R
BR
D001943:Breast Neoplasms; D003553:Cystine / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism; D005978:Glutathione / Q000096:biosynthesis* / Q000378:metabolism; D006801:Humans; D014407:Tumor Cells, Cultured; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D003553:Cystine; D005723:gamma-Glutamyltransferase; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione