Acta Pharmacologica Sinica (2009) 30: 1529–1536; doi: 10.1038/aps.2009.147; published online 12 October  2009

Aim:To investigate the synergistic effects of SG235-TRAIL, a novel oncolytic adenovirus expressing tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and homoharringtonine (HHT) in human leukemia cell lines.

Methods: The combined effect of SG235-TRAIL and HHT was assessed using a crystal violet assay and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, followed by combination index analysis.  Cell apoptosis was measured using flow cytometry combined with fluorescein-isothiocyanate-Annexin V staining.  The activation of caspase pathway and the expression of Bcl-2 family proteins, TRAIL, and E 1A were examined using Western blotting. 

Results: HHT synergized the cytotoxicity of SG235-TRAIL against leukemia cell lines Kasumi-1, KG-1, HL-60, and U937, concomitantly with increased apoptosis and enhanced activity of caspase-3 and -9.  The combination therapy resulted in significantly lower levels of Bcl-2, Mcl-1, and Bid compared to treatment of cells with either HHT or SG235-TRAIL alone, suggesting that HHT sensitizes leukemia cells to SG235-TRAIL virus through alteration of anti-apoptotic signaling elements.  Importantly, HHT combined with SG235-TRAIL did not show significant cytotoxicity to normal human mononuclear cells and mesenchymal stem cells.

Conclusion: Combining oncolytic adenovirus SG235-TRAIL and HHT synergistically enhances cytotoxicity in leukemia cells in vitro, suggesting that the combination therapy could represent a rational approach for the treatment of leukemia.

Keywords: homoharringtonine; oncolytic adenovirus; TRAIL; synergy; apoptosis; Kasumi-1 cells; KG-1 cells; HL-60 cells