Background and objective: Recently, it has been demonstrated that topoisomerase I(Topo I) inhibitor is a useful alternative for treatment of the patients with chronic myelogenous leukemia(CML) in accelerated or blast crisis. In order to get insight into pharmalogic activity of Topo I inhibitor, this study was designed to investigate the killing and proapoptotic activity of Topo I inhibitor(Topotecan, TPT) using K562 cell line, which carry abnormal chromosome[t(9;22)] of characteristics of CML.
Methods: The cytotoxic effect of TPT on K562 cells was determined using MTT assay; TPT-induced apoptosis in K562 cells was identified by morphological analysis and Annexin V FITC staining; correlation between TPT-mediated killing or apoptosis and caspase-8 activation was investigated using caspase-8 inhibitor IETD-fmk.
Results: After incubation of K562 cells with 0.15 mumol/L TPT for 12, 24, 48, and 72 h, the survival rates, compared with control, progressively reduced to (92 +/- 36)% [P > 0.05 vs (94 +/- 27)%], (68 +/- 21)% [P < 0.05 vs (119 +/- 13)%], (54 +/- 15)% [P < 0.05 vs (132 +/- 31)%], and (21 +/- 10)% [P < 0.01 vs (114 +/- 19)%]. Targeted cells meanwhile demonstrated phosphatidylserine externalization, cell shrinkage, chromatin margination, karyorrehxis and eventually disintegrate into numerous apoptotic bodies. After exposure to TPT in combination with IETD-fmk for 24 h and 48 h, K562 cells were still survival at viability of (95 +/- 29)% and (87 +/- 11)%, the latter was significantly higher than that of to TPT only [P < 0.05 vs (54 +/- 15)%].
Conclusion: Topoisomerase I inhibitor TPT possess killing activity and was induce apoptosis to K562 cells, which could be dependent on activation of caspase-8.