[Mechanisms of sensitization by 8-chloro-adenosine of human tumor cells to TRAIL-induced apoptosis].

OBJECTIVE: To study the effect of 8-chloro-adenosine (8-Cl-Ado) on the sensitivity of human hepatoma and breast cancer cell lines to TRAIL-induced apoptosis in vitro and its mechanisms.

METHODS: Recombinant soluble TRAIL (rsTRAIL) or 8-Cl-Ado was used to treat hepatoma cell line BEL-7402 and breast cancer cell line MCF-7 in vitro. MTT assay was used to evaluate cell viability. The effect of cotreatment with rsTRAIL and 8-Cl-Ado was analyzed. NF-kappaB activity reporter plasmid was designed to measure the activity of transcription factor NF-kappaB. After transient transfection with the reporter plasmid, which contains NF-kappaB-responsive elements, into the cell lines, cells were treated with rsTRAIL and/or 8-Cl-Ado, then the activity of the reporter gene luciferase was determined. Different kinds of caspase inhibitors were used to measure the effect of caspases in the rsTRAIL and/or 8-Cl-Ado induced apoptosis.

RESULTS: 8-Cl-Ado could greatly enhance sensitivity of BEL-7402 and MCF-7 cells to reTRAIL. Treatment with 8-Cl-Ado and rsTRAIL inactivated transcription factor NF-kappaB and induced apoptosis in BEL-7402, but not in MCF-7. Caspase family inhibitor could not prevent apoptosis induced by 8-Cl-Ado and rsTRAIL in BEL-7402 cells, however, it could block apoptosis in MCF-7 cells, indicating that two different apoptosis pathways in MCF-7 and BEL-7402 might exist, one was caspase dependent and the other caspase independent. Moreover, all of the inhibitors of caspse-3, -8 and -9 could not block apoptosis induced by the co-treatment.

CONCLUSION: 8-chloro-adenosine can enhance the sensitivity of human hepatoma cell line BEL-7402 and breast cancer cell line MCF-7 to rsTRAIL, even though MCF-7 is TRAIL-resistant. 8-Cl-Ado combined with rsTRAIL can trigger different signal pathways in MCF-7 and BEL-7402, which are caspase dependent and independent, respectively.