BACKGROUNDTumor-necrosis factor related to apoptosis inducing ligand protein(TRAIL), like tumor-necrosis factor (TNF) and Fas, is a member of TNF cytokine supper family. Many researches have showed that TNF-α can reverse the resistance to some chemotherapeutic agents in cancer cell lines, and some anticancer drugs can result in up-regulations of death receptor (DR) and further lead to the enhancement of apoptosis induced by TRAIL. In order to clarify if TRAIL can reverse the resistance to cisplatin in cancer cells, the effects of recombinant human tumor-necrosis factor related to apoptosis inducing ligand protein (rhTRAIL) on apoptosis in human lung adenocarcinoma cell lines resistant to cisplatin (DDP) in vitro was explored.

METHODSHuman lung adenocarcinoma cell lines resistant to cisplatin, A549/DDP cells, were cultured in regular condition. At 24 hours after TRAIL and DDP, alone or combined, microculture tetrazolium (MTT) dye was used to evaluate the cytotoxic effects. And besides, to detect the apoptotic effects of rhTRAIL on A549/DDP cells, flow cytometry assay was used to test the apoptosis proportion, diphenylamine assay (DPA) was applied to detect the percent of DNA fragmentation and Caspase-3 chluorometric assay was performed to test the activity of Caspase-3 among these cells.

RESULTSA549/DDP cells were not sensitive to low-dose rhTRAIL alone. The rate of growth inhibition and the apoptotic indexes such as the apoptosis proportion, the percent of DNA fragmentation and the activity of Caspase-3, had all no significant changes with rhTRAIL concentration less than 25μg/L (P > 0.05). But treated with higher-dose rhTRAIL more than 50μg/L, the four values changed obviously: 68.6%, (27.13± 0.66)%, (37.4±2.0)% and 0.117±0.011, respectively (P < 0.05). With combination of different concentration of rhTRAIL and 3mg/L DDP, the cyto-toxic and apoptotic effect was comparatively more apparent. The combination of rhTRAIL and 3mg/L DDP presented synergistic effect on A549/DDP, 12.5μg/L concentration of rhTRAIL together with 3mg/L DDP could kill 30.4% of A549/DDP cells. Furthermore, the rate of cell apoptosis, percent of DNA fragmentation and activity of caspase-3 increased to (19.39±0.54)%,(17.3±4.1)% and 0.138±0.009, which were significantly different from those of rhTRAIL alone (P < 0.01).

CONCLUSIONSHigh-dose rhTRAIL can also induce the cells resistant to cisplatin to apoptosis, but the cytotoxic and apoptotic effects of rhTRAIL alone are weaker than those of combination of rhTRAIL and low-dose cisplatin which can augment the apoptotic effect induced by rhTRAIL. rhTRAIL is expected to be an efficient biologic drug for treatment of lung cancer resistant to chemotherapy.