[Synergistic killing effect of the conditionally replicating adenoviruses carrying programmed cell death 5 gene and etoposide on K562 cells].

The expression levels of programmed cell death 5 (PDCD5) are down-regulated in many malignancies. SG611-pdcd5, a recombinant conditionally replicative adenovirus carrying pdcd5 gene expression cassette, can evidently kill the leukemic cells and protect selectively the normal cells. The purpose of this study was to investigate the synergistic killing effect of SG611-pdcd5 and low-dose etoposide (VP-16) on K562 cells. K562 cells were treated with different concentrations of VP-16 or different multiplicities of infection (MOI) of SG611-pdcd5. After 48 hours of incubation the cell viability was determined by using MTT assay. The results showed that the cell viability of SG611-pdcd5 (MOI = 40) plus VP-16 (0.5 µg/ml) group significantly decreased as compared with single SG611-pdcd5 (MOI = 40) treatment group or single VP-16(0.5 µg/ml) treatment group (42.00 ± 5.75% vs 59.45 ± 4.12%; 42.00 ± 5.75% vs 82.91 ± 3.41%, respectively, both p < 0.05). The synergistic killing effect of SG611-pdcd5 plus VP-16 was higher than that of PDCD5 protein plus VP-16 or that of non-replicating adenovirus carrying pdcd5 (Ad-pdcd5) plus VP-16 (both p < 0.05). The cell viability of VP-16 (4.0 µg/ml) plus SG611-pdcd5 (MOI = 40) group, VP-16 (4.0 µg/ml) plus proPDCD5 (40 µg/ml) group and VP-16 (4.0 µg/ml) plus Ad-pdcd5 (MOI = 80) group was 37.09 ± 1.89%, 52.36 ± 1.64% and 73.64 ± 4.33%, respectively. It is concluded that SG611-pdcd5 can promote K562 cell death induced by low-dose VP-16. The combination of SG611-pdcd5 and VP-16 can enhance the killing effect on leukemic cells.