Objective: Apo2L/tumor necrosis factor–related
apoptosis-inducing ligand (TRAIL) is a potential anticancer drug that promotes
apoptosis specifically in tumor cells. Because not all cancer
cells are susceptible to Apo2L/TRAIL, the aim of our study was
to determine whether non–small cell lung cancer cells
can be sensitized by chemotherapeutic agents for Apo2L/TRAIL−induced
apoptosis. In addition, endogenous expression levels
of the caspase-inhibiting cellular protease
caspase-8 inhibitory protein
(C-FLIP) were measured to investigate partial resistance to
Apo2L/TRAIL.
Methods: Six human lung cancer cell lines (A549,
NCI-H358, Calu1, Calu6, SkMes1, and SkLu1) were incubated with
soluble Apo2L/TRAIL and two different concentrations each of
cisplatin, paclitaxel, doxorubicin, 5−fluorouracil, and camptothecin.
After 24 hours the rate of apoptosis was measured by annexin
V/propidium iodide staining followed by FACScan analysis. Expression
levels
of C-FLIP in cell lines and lung cancer biopsy specimens
were determined by Western blotting.
Results: Treatment of lung
cancer cells with Apo2L/TRAIL alone resulted in apoptotic cell
death in four cell lines (
P < .001). Combining Apo2L/TRAIL
and chemotherapeutic agents enhanced the rate of apoptosis significantly.
Statistical analysis revealed a synergistic effect of Apo2L/TRAIL
in combination with 1.8 mmol/L camptothecin and 100 µmol/L
cisplatin, each in four of the six cell lines (
P < .002).
Western blot analysis showed that sensitization to Apo2L/TRAIL
did not correlate with the expression of cellular protease
caspase-8 inhibitory protein. Furthermore, no increased cellular protease
caspase-8 inhibitory protein levels relative to those in normal
lung tissue could be found in non–small cell lung cancer
specimens from 12 patients.
Conclusion: Apo2L/TRAIL−induced
apoptosis in non–small cell lung cancer cell lines is
significantly enhanced by chemotherapeutic agents. Resistance
and sensitization to Apo2L/TRAIL are not correlated with the
endogenous expression level of cellular protease
caspase-8 inhibitory
protein, implying that in non–small cell lung cancer other
mechanisms are responsible for inhibition of the Apo2L/TRAIL
pathway. Even though the molecular mechanism remains unclear,
the combination of Apo2L/TRAIL with chemotherapy may be a promising
treatment modality for non–small cell lung cancer.