Cardiac glycosides initiate Apo2L/TRAIL-induced apoptosis in non-small cell lung cancer cells by up-regulation of death receptors 4 and 5.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (Apo2L/TRAIL) belongs to the TNF family known to transduce their death signals via cell membrane receptors. Because it has been shown that Apo2L/TRAIL induces apoptosis in tumor cells without or little toxicity to normal cells, this cytokine became of special interest for cancer research. Unfortunately, cancer cells are often resistant to Apo2L/TRAIL-induced apoptosis; however, this can be at least partially negotiated by parallel treatment with other substances, such as chemotherapeutic agents. Here, we report that cardiac glycosides, which have been used for the treatment of cardiac failure for many years, sensitize lung cancer cells but not normal human peripheral blood mononuclear cells to Apo2L/TRAIL-induced apoptosis. Sensitization to Apo2L/TRAIL mediated by cardiac glycosides was accompanied by up-regulation of death receptors 4 (DR4) and 5 (DR5) on both RNA and protein levels. The use of small interfering RNA revealed that up-regulation of death receptors is essential for the demonstrated augmentation of apoptosis. Blocking of up-regulation of DR4 and DR5 alone significantly reduced cell death after combined treatment with cardiac glycosides and Apo2L/TRAIL. Combined silencing of DR4 and DR5 abrogated the ability of cardiac glycosides and Apo2L/TRAIL to induce apoptosis in an additive manner. To our knowledge, this is the first demonstration that glycosides up-regulate DR4 and DR5, thereby reverting the resistance of lung cancer cells to Apo2/TRAIL-induced apoptosis. Our data suggest that the combination of Apo2L/TRAIL and cardiac glycosides may be a new interesting anticancer treatment strategy.

PG490-mediated sensitization of lung cancer cells to Apo2L/TRAIL-induced apoptosis requires activation of ERK2.

Tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) belongs to the family of programmed cell death-inducing cytokines. Apo2L/TRAIL induces apoptosis in a wide variety of tumor cells. Tumor cells that are resistant to Apo2L/TRAIL-induced apoptosis can be sensitized by chemotherapeutic drugs and other agents via an unknown mechanism. Here we report that PG490 (triptolide), a diterpene triepoxide extracted from the Chinese herb Tripterygium wilfordii and used in traditional Chinese medicine, sensitizes lung cancer but not normal human bronchial epithelial cells to Apo2L/TRAIL-induced apoptosis. Sensitization was accompanied by caspase-3 and caspase-8 activation, whereas no cleavage of caspase-9 was observed. Determination of cell surface receptors by flow cytometry demonstrated no difference in Apo2L/TRAIL-R1 and -R2 expression, the two receptors with functional death domains, between resistant and sensitized cells. In cells treated with the combination of Apo2L/TRAIL and PG490, we observed activation of ERK2, a member of the mitogen-activated protein kinase family. Furthermore, sensitization could be blocked by the ERK inhibitor U0126 but not the p38 inhibitor SB203580, suggesting that activation of ERK2 is required for this effect. In addition, sensitization of lung cancer cells was also seen in ex vivo culture of lung cancer tissue from four patients who underwent surgery. Immunohistochemical staining showed a clear reduction in proliferation cell nuclear antigen (PCNA) in tissue treated with Apo2L/TRAIL and PG490. In conclusion, apoptosis induced by the combination of Apo2L/TRAIL and PG490 warrants further evaluation as a potential new strategy for the treatment of lung cancer.

Cell death induced by down-regulation of heat shock protein 70 in lung cancer cell lines is p53-independent and does not require DNA cleavage.

OBJECTIVE: The inducible form of heat shock protein 70 is known to be overexpressed in tumors and seems to be necessary for the survival of tumor cells via an unknown mechanism. We therefore evaluated whether selective depletion of heat shock protein 70 induces cell death in lung cancer cells. METHODS: An adenovirus expressing antisense heat shock protein 70 and an adenovirus with beta-galactosidase were used for transduction of the lung cancer cell lines A549, NCI-H358, LXF-289, LOU-NH91, normal human bronchial epithelial cells, and normal lung fibroblasts IMR90. Cell death was determined by morphology, propidium iodide uptake, and trypan blue staining; DNA cleavage was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Expression of heat shock protein 70, heat shock cognate 70, and phosphorylated p53 was determined by Western blot analysis. RESULTS: Transduction of lung cancer cells with adenovirus expressing antisense heat shock protein 70 but not with adenovirus with beta-galactosidase resulted in extensive cell death after 96 hours (A549: 53.2 +/- 9.44% versus 12.9 +/- 6.6%; NCI-H358: 48.4 +/- 7.2% versus 25.2 +/- 1.4%; LXF-289: 58.8 +/- 6.5% versus 24.7 +/- 5.4%; LOU-NH91: 82.5 +/- 1.8% versus 38.5 +/- 2.6%). In contrast, adenovirus expressing antisense heat shock protein 70 showed much less cytotoxicity in normal human bronchial epithelial cells (16.0 +/- 0.5% versus 17.1 +/- 7.3%) and in normal lung fibroblasts IMR90 (17.2 +/- 3.6% versus 8.2 +/- 1.6%). After treatment with adenovirus expressing antisense heat shock protein 70, transactivation of p53 in A549 but not in NCI-H358, a cell line deleted for p53 has been observed. Furthermore, 22.0 +/- 3.0% of A549 cells treated for adenovirus expressing antisense heat shock protein 70 stained positive with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling versus 10.2 +/- 4.0% treated with control virus. This effect but not cell death itself was blocked by treatment with 10 micromol/L zVAD-fmk, a broad caspase inhibitor. CONCLUSIONS: Selective down-regulation of heat shock protein 70 induces cell death in lung cancer but not in normal lung cells. The demonstrated effect is p53-independent and does not require DNA cleavage. The data suggest that gene transfer of antisense heat shock protein 70 might be useful in developing new strategies for the treatment of lung cancer.