Cyclosporin a Potentiates the Cytotoxic Effects of Methyl Methanesulphonate in HL-60 and K562 Cells

Methyl methanesulfonate induces necroptosis in human lung adenoma A549 cells through the PIG-3-reactive oxygen species pathway

Methyl methanesulfonate (MMS) is an alkylating agent that can induce cell death through apoptosis and necroptosis. The molecular mechanisms underlying MMS-induced apoptosis have been studied extensively; however, little is known about the mechanism for MMS-induced necroptosis. Therefore, we first established MMS-induced necroptosis model using human lung carcinoma A549 cells. It was found that, within a 24-h period, although MMS at concentrations of 50, 100, 200, 400, and 800 μM can induce DNA damage, only at higher concentrations (400 and 800 μM) MMS treatment lead to necroptosis in A549 cells, as it could be inhibited by the specific necroptotic inhibitor necrostatin-1, but not the specific apoptotic inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-fmk). MMS-induced necroptosis was further confirmed by the induction of the necroptosis biomarkers including the depletion of cellular NADH and ATP and leakage of LDH. This necroptotic cell death was also concurrent with the increased expression of p53, p53-induced gene 3 (PIG-3), high mobility group box-1 protein (HMGB1), and receptor interaction protein kinase (RIP) but not the apoptosis-associated caspase-3 and caspase-9 proteins. Elevated reactive oxygen species (ROS) level was also involved in this process as the specific ROS inhibitor (4-amino-2,4-pyrrolidine-dicarboxylic acid (APDC)) can inhibit the necroptotic cell death. Interestingly, knockdown of PIG-3 expression by small interfering RNA (siRNA) treatment can inhibit the generation of ROS. Taken together, these results suggest that MMS can induce necroptosis in A549 cells, probably through the PIG-3-ROS pathway.

Partial glutathione reductase deficiency as a cause of diverse clinical manifestations in a family with unstable hemoglobin (Hemoglobin Haná, β63(E7) His-Asn)

Hemoglobin Haná [β63(E7) His-Asn] is an unstable hemoglobin variant that was described in a Czech proband and her sister with Heinz body hemolytic anemia. The mother bearing the same mutation was asymptomatic; nevertheless, all three carriers had the same proportion of the mutant globin chains. Assessment of several erythrocyte antioxidant parameters revealed that both symptomatic children, unlike their asymptomatic mother, had significantly decreased glutathione reductase (GR) activity. Their GR activities were restorable in vitro by flavin adenine dinucleotide. The riboflavin supplementation improved their glutathione metabolism and ameliorated their hemolysis. Pre- and post-treatment assessment of the B(2) vitamers indicated suboptimal pre-treatment vitamin B(2) status in both children. This study provides evidence that partial GR deficiency may alter the clinical manifestation of an unstable hemoglobinopathy.

Induction of apoptosis by A3 adenosine receptor agonist N-(3-iodobenzyl)-adenosine-5'-N-methylcarboxamide in human leukaemia cells: a possible involvement of intracellular mechanism

AIM

The sensitivity of cancer cells which exhibit multi-drug resistance phenotype to A3 adenosine receptor (A3AR) agonist N(6)-(3-iodobenzyl)-adenosine-5'-N-methylcarboxamide (IB-MECA) was studied.

METHODS

To establish direct relationship between P-glycoprotein (P-gp, ABCB1 and MDR1) expression and IB-MECA induced cell death, a straightforward method for precise estimation of intracellular level of this A3AR agonist was developed.

RESULTS

We subjected three human leukaemia cell lines HL-60, K562 and K562/HHT to treatment with micromolar concentrations of IB-MECA. Although all cell lines used expressed A3AR, there was a large difference in their sensitivity to IB-MECA. While HL-60 and K562 cells were almost equally sensitive, the K562/HHT cells, which exhibit a multi-drug resistance phenotype because of overexpression of P-gp, were significantly more resistant. We found that the intracellular level of IB-MECA in K562/HHT cells was approx. 10 times lower than those in HL-60 or K562 cells. Inhibitors of P-gp, including cyclosporine A (CsA) and verapamil (Vpa), increased the intracellular level of IB-MECA and reversed the resistance of K562/HHT cells to this drug. Accordingly, shRNA-mediated down-regulation of P-gp significantly increased the intracellular level of IB-MECA in K562/HHT cells which simultaneously exhibited reduced resistance to this A3AR agonist. In addition, an in vitro enzyme-based assay provided evidence that IB-MECA might serve as a substrate for P-gp.

CONCLUSION

Our results suggest that P-gp overexpression prevents cells from IB-MECA induced apoptosis despite the A3AR expression. Pro-apoptotic effect of IB-MECA seemed to strongly depend on its intracellular accumulation rather than on its interaction with A3AR.

Cyclosporin A sensitises Bcr-Abl positive cells to imatinib mesylate independently of P-glycoprotein expression

The effect of cyclosporin A (CsA) on imatinib treated Bcr-Abl positive K562 cells was studied. Similarly to other authors we found that imatinib induced apoptosis and erythroid differentiation in K562 cells. While its low concentrations induced predominantly erythroid differentiation, higher concentrations induced apoptosis. We found that CsA significantly potentiated cytotoxic effects of imatinib. A detailed analysis revealed that CsA shifted the balance between differentiation and apoptosis in favour of apoptosis. Our findings indicated that the observed effect of CsA was mediated neither through inhibition of ERK1/2 (extracellular signal-regulated kinases 1/2), nor through inhibition of p38 MAPK. We further observed that CsA might sensitise cells to apoptosis due to a changed cellular redox status as combined treatment of cells with imatinib and CsA resulted in a dramatic decrease of the ratio between reduced (GSH) and oxidised (GSSG) glutathione GSH/GSSG and in a significant suppression of thioredoxin reductase enzymatic activity. Our results indicated that K562 cells did not express detectable level of P-glycoprotein (P-gp). In addition, CsA did not affect significantly the intracellular level of imatinib. Therefore we excluded the possibility that CsA increased sensitivity of cells to imatinib by the inhibition of P-gp-mediated drug efflux or by another mechanism involving modulation of intracellular drug concentration.