Abstract
The induction of apoptosis by doxorubicin (DOX) alone or in the presence of efflux blockers, verapamil (VPL) or trifluoperazine (TFP), and of bcl-2 and mdr-1 gene expression was analysed in murine leukaemic P388 and doxorubicin resistant P388/R84 cells. Incubation with DOX (0.1-1 μM) for 24 hours induced apoptosis in sensitive cells but not in the resistant P388/R84 cells. Flow cytometric analysis of apoptosis by terminal dideoxynucleotidyl (TdT) assay showed that 1 μM DOX induced apoptosis in 70% of P388 cells and in less than 5% of P388/R84 cells. When P388/R84 resistant cells were co-incubated with DOX and efflux blockers (10 μM VPL or 15 μM TFP), enhanced cellular DOX accumulation was accompanied by apoptosis. Quantitative analysis of DNA fragmentation by 14C-thymidine incorporation and gel electrophoresis of fragmented DNA confirmed the results from TdT assay and showed enhancement of DOX-induced DNA fragmentation in the presence of efflux blockers (VPL or TFP). DOX + VPL and DOX + TFP combination treatments induced apoptosis in upto 55% and 83% of P388/R84 cells, respectively. mdr-1 mRNA and P-gp expression were not altered during DOX-induced apoptosis. The results suggest that in murine leukemic cells, down-regulation of bcl-2 mRNA expression occurs during DOX-induced apoptosis and it depends on the cellular drug retention determined by mdr-1/P-gp drug efflux.
Original language | English (US) |
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Pages (from-to) | 3369-3376 |
Number of pages | 8 |
Journal | Anticancer research |
Volume | 17 |
Issue number | 5 A |
State | Published - Sep 1997 |
Externally published | Yes |
Keywords
- Apoptosis
- bcl-2 and mdr-1
- Doxorubicin
- Drug resistance
ASJC Scopus subject areas
- Cancer Research
- Oncology