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In this study, we show that triazoloacridinone derivative C-1305, a potent antitumor compound, in human lymphoblastic (MOLT4) and promyelocytic (HL60) leukemia cells induces G2/M arrest followed by apoptosis. In both type of cells, C-1305 at biological relevant concentrations corresponding to EC90 value, induced a significant increase in the fraction of G2/M cells. The cell cycle perturbations were accompanied by the appearance of sub-G1 fraction, which can be considered as the apoptotic cells population. In both human leukemia cells apoptosis was additionally proved by appearance of DNA fragmentation, activation of caspase-3, PARP cleavage, externalization of phosphatydilserine as well as decrease of the mitochondrial transmembrane potential ΔΨm and ATP depletion. Treatment of lymphoblastic MOLT4 cells with the C-1305 at EC90 concentration, caused massive death by apoptosis. Compared to MOLT4 cells, the capacity of HL60 cells to execute apoptosis after C-1305 treatment at equitoxic dose was significantly weaker, but very effective at high concentration (4× EC90). These differences could originate from different sensitivity of both cell types to cytotoxic action of C-1305 (EC50 value for MOLT4 cells was 8 times lower than for HL60 cells and the EC90 value was 14 times lower, respectively). Collectively, these results show that C-1305 is a novel and potent compound which induces G2/M arrest and subsequent apoptosis of human leukemia cells. This strong ability to induce apoptosis of tumor cells support the view that C-1305 could be consider as a new potent and promising antitumor agent.