ANTIOXIDANTS SELENOMETHIONINE AND D-PANTETHINE DIFFERENTIALLY AFFECT DOXORUBICIN’S ACTION ON GLUTATHIONE SYSTEM IN HUMAN LEUKEMIA CELLS VARYING IN THEIR RESISTANCE TO CHEMOTHERAPY IN VITRO

Abstract

Rapid development of multiple drug resistance and occurrence of negative side effects in cancer patients arising at the treatment belong to the main problems in cancer chemotherapy. Recently, it was shown that specific antioxidants (selenomethionine – SeMet and D-pantethine – D-Pt) possessed nephro-, myelo- and hepatoprotective activity at doxorubicin’s (Dx) action in tumor-bearing mice. Besides, these antioxidants inhibited a cytotoxic action of Dx toward chemotherapy-sensitive tumor cells, and enhanced the cytotoxic effect of this drug toward selected drug-resistant tumor cell lines (e.g. HL-60/vinc, HL-60/adr), while in other such lines (e.g. HCT-116/Bax(−/−), HCT-116/p53), it was not effective.
The aim of present study was to investigate the molecular mechanisms of the revealed difference in the action of SeMet and D-Pt toward cytotoxic effects of Dx in tumor cells varying in drug resistance. Human leukemia cells of HL-60/wt line and its drug-resistant sublines HL-60/adr (overexpression of MRP-1) and HL-60/vinc (overexpression of P-gp) were used in this study.
Treatment of cells with Dx led to the versatile action of this drug on the level of glutathione in each of the studied cell line and sublines. HL-60/wt cells were characterized by 8-fold lower GSH level under Dx treatment compared to control, while in HL-60/vinc and HL-60/adr cells GSH level was increased 2.2- and 8.2-fold (compared to untreated cells), correspondingly. The use of doxorubicin also led to significant rearrangement of GSSG/GSH ratio in these cell lines, leading to 2-fold elevation of GSSG level HL-60/vinc cells, and 2.5-fold decrease of this index in HL-60/adr cells.
We have shown that a combined effect of SeMet or D-Pt on the background of the cytotoxic action of doxorubicin on HL-60/vinc cells is accompanied by a 2-fold decrease in both oxidized and reduced glutathione levels. Such an effect of these antioxidants can serve as an explanation of their sensitizing effect on the cells of the HL-60/vinc subline under Dx’s action which we observed earlier. It should be noted that treatment with Dx led to a 2.5-fold increase in the activity of glutathione-S-transferase in the leukemia cells of HL-60/vinc subline. The antioxidants effectively reduced this indicator. SeMet and D-Pt differentialy affected the activity of glutathione-S-transferase in HL-60/adr cells.
In conclusion, our data demonstrate an important role of the antioxidants on the functional state of the glutathione system in tumor cells that differ in their drug resistance. The obtained results suggest an important role of glutathione-S-transferase in modulation of cancer drug resistance that is caused by P-glycoprotein overexpression, but not by the overexpression of MRP-1 protein. Selenomethionine and D-pantethine effectively inhibit this enzyme, thus, sensitizing P-gp overexpressing cells towards the action of doxorubicin. This event is accompanied by further decrease in GSH and GSSG levels in these cells, thus sensitizing them to Dx action. Further studies of the molecular mechanisms underlying this phenomenon are in progress.