Induction of apoptosis by the adenosine derivative IB-MECA in parental or multidrug-resistant HL-60 leukemia cells: possibile relationship to the effects on inhibitor of apoptosis protein levels

Background: The effects of the A3 adenosine receptor(A3AR) agonist lB-MECA were examined in HL-60 leukemiaand in its multidrug-resistant variant HL60R cells.Methods: Cytotoxicity was evaluated by MTS assays andapoptosis by flow cytometry analyses of DNA fragmentation and phosphatidylserine exposure. The mRNAs of A3AR and inhlbitor of apoptosis proteins (lAPs) were determined by RT-PCR.Results: A3AR expression was similar in HL-60 and HL-60R cells. At ≥ 100 μM, IB-MECAexhibited strong cytotoxic and apoptotic effects in HL-60,but not in HL-60R cells. This activity was not modified bythe A3AR antagonis VUF5574, the P-glycoprotein inhibitor verapamil, the adenosine uptake inhibitor NBTI orthe anti Fas antibody Z B4, HL-60R cells showed higherlevels of different IAPs than H L-60 cells. lB-MECA 100 μMdownregulated HlAP1, NAIP and survivin mRNAs in HL-60, but not in HL-60R cells.Conclusions: The antitumor effects of IB-MECA are not mediated by A3AR in HL-60cells, where the proapoptotic mechanism of the compound may involve downregulation of lAPs. The resistance of HL-60R cells to lB-MECA may depend on theirelevated levels of lAPs.