T. Efferth et al., 5-azacytidine modulates the response of sensitive and multidrug-resistant K562 leukemic cells to cytostatic drugs, BL CELL M D, 27(3), 2001, pp. 637-648
In an endeavor to improve responsiveness of tumor cells to drug combination
treatments, we analyzed the effect of 5-azacytidine (5AC) as a model compo
und for a new class of drugs, DNA-demethylating agents. We used parental K5
62/WT chronic myelogenous leukemia cells and a multidrug-resistant subline
thereof, K562/ADM. Multidrug-resistant cells were more resistant to daunoru
bicin, but more sensitive to cisplatin than parental K562 cells as measured
by growth inhibition and apoptosis assays. Resistance to daunorubicin can
be explained by amplification of the MDR1 drug transporter gene. Cisplatin
induced more DNA damage in specific genes and in the entire genome of K562/
ADM cells compared to K562/WT cells using PCR stop assays and atomic absorp
tion spectroscopy. Pretreatment with 5AC modulated the response of K562/ADM
cells toward MDR-type drugs (daunorubicin, vincristine, etoposide) and red
uced function and expression of MDR1 as analyzed by flow cytometry and RT-P
CR. Analysis of CpG island methylation in the promotor region of the MDR1 g
ene by bisulfite sequencing and a methylation-sensitive HpaII-digestion/PCR
approach revealed that methylation of the MDR1 promotor of K562/ADM cells
was greater than in K562/WT cells. 5AC treatment completely abolished MDR1
promotor methylation. The unexpected observation that DNA demethylation by
5AC rather decreases than increases MDR1 expression in K5612/ADM cells poin
ts to still unexplored sequences in the MDR1 promotor whose transcriptional
activity may be affected by the methylation status. 5AC pretreatment also
modulated K562/WT and K562/ADM cells to non-MDR-type drugs such as cisplati
n and increased cisplatin-induced DNA damage. (C) 2001 Academic Press.