TRAIL-induced survival and proliferation of SCLC cells is mediated by ERK and dependent on TRAIL-R2/DR5 expression in the absence of caspase-8.

Small cell lung cancer (SCLC) is characterized by an aggressive phenotype and acquired resistance to a broad spectrum of anticancer agents. TNF-related apoptosis-inducing ligand (TRAIL) has been considered as a promising candidate for safe and selective induction of tumor cell apoptosis without toxicity to normal tissues. Here we report that TRAIL failed to induce apoptosis in SCLC cells and instead resulted in an up to 40% increase in proliferation. TRAIL-induced SCLC cell proliferation was mediated by extracellular signal-regulated kinase 1 and 2, and dependent on the expression of surface TRAIL-receptor 2 (TRAIL-R2) and lack of caspase-8, which is frequent in SCLC. Treatment of SCLC cells with interferon-gamma (IFN-gamma) restored caspase-8 expression and facilitated TRAIL-induced apoptosis. The overall loss of cell proliferation/viability upon treatment with the IFN-gamma-TRAIL combination was 70% compared to TRAIL-only treated cells and more than 30% compared to untreated cells. Similar results were obtained by transfection of cells with a caspase-8 gene construct. Altogether, our data suggest that TRAIL-R2 expression in the absence of caspase-8 is a negative determinant for the outcome of TRAIL-based cancer therapy, and provides the rationale for using IFN-gamma or other strategies able to restore caspase-8 expression to convert TRAIL from a pro-survival into a death ligand.

Human agonistic TRAIL receptor antibodies Mapatumumab and Lexatumumab induce apoptosis in malignant mesothelioma and act synergistically with cisplatin.

BACKGROUND: The incidence of malignant pleural mesothelioma (MPM) is associated with exposure to asbestos, and projections suggest that the yearly number of deaths in Western Europe due to MPM will increase until 2020. Despite progress in chemo- and in multimodality therapy, MPM remains a disease with a poor prognosis. Inducing apoptosis by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or agonistic monoclonal antibodies which target TRAIL-receptor 1 (TRAIL-R1) or TRAIL-R2 has been thought to be a promising cancer therapy. RESULTS: We have compared the sensitivity of 13 MPM cell lines or primary cultures to TRAIL and two fully human agonistic monoclonal antibodies directed to TRAIL-R1 (Mapatumumab) and TRAIL-R2 (Lexatumumab) and examined sensitization of the MPM cell lines to cisplatin-induced by the TRAIL-receptor antibodies. We found that sensitivity of MPM cells to TRAIL, Mapatumumab and Lexatumumab varies largely and is independent of TRAIL-receptor expression. TRAIL-R2 contributes more than TRAIL-R1 to death-receptor mediated apoptosis in MPM cells that express both receptors. The combination of cisplatin with Mapatumumab or Lexatumumab synergistically inhibited the cell growth and enhanced apoptotic death. Furthermore, pre-treatment with cisplatin followed by Mapatumumab or Lexatumumab resulted in significant higher cytotoxic effects as compared to the reverse sequence. Combination-induced cell growth inhibition was significantly abrogated by pre-treatment of the cells with the antioxidant N-acetylcysteine. CONCLUSION: Our results suggest that the sequential administration of cisplatin followed by Mapatumumab or Lexatumumab deserves investigation in the treatment of patients with MPM.

p53-induced apoptosis occurs in the absence of p14(ARF) in malignant pleural mesothelioma.

Malignant pleural mesotheliomas (MPMs) are usually wild type for the p53 gene but contain homozygous deletions in the INK4A locus that encodes p14(ARF), an inhibitor of p53-MDM2 interaction. Previous findings suggest that lack of p14(ARF) expression and the presence of SV40 large T antigen (L-Tag) result in p53 inactivation in MPM. We did not detect SV40 L-Tag mRNA in either MPM cell lines or primary cultures, and treatment of p14(ARF)-deficient cells with cisplatin (CDDP) increased both total and phosphorylated p53 and enhanced p53 DNA-binding activity. On incubation with CDDP, levels of positively regulated p53 transcriptional targets p21(WAF), PIG3, MDM2, Bax, and PUMA increased in p14(ARF)-deficient cells, whereas negatively regulated survivin decreased. Significantly, p53-induced apoptosis was activated by CDDP in p14(ARF)-deficient cells, and treatment with p53-specific siRNA rendered them more CDDP-resistant. p53 was also activated by: 1) inhibition of MDM2 (using nutlin-3); 2) transient overexpression of p14(ARF); and 3) targeting of survivin using antisense oligonucleotides. However, it is noteworthy that only survivin downregulation sensitized cells to CDDP-induced apoptosis. These results suggest that p53 is functional in the absence of p14(ARF) in MPM and that targeting of the downstream apoptosis inhibitor survivin can sensitize to CDDP-induced apoptosis.

Cisplatin activates Akt in small cell lung cancer cells and attenuates apoptosis by survivin upregulation.

The inhibitor of apoptosis protein (IAP) survivin is overexpressed in many tumors but is absent in most normal adult tissues. We report high levels of survivin expression in small cell lung cancer (SCLC), and describe the role of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in survivin upregulation. Moreover, the cytoprotective function of survivin in response to the anti-cancer agent cisplatin (CDDP) was investigated. Negative modulation of PI3K/Akt using pharmacological inhibitors or dominant negative Akt (DN-Akt) decreased Akt kinase activity and resulted in decreased survivin expression and phosphorylation on Thr34, whereas transfection of constitutively active Akt (CA-Akt) increased survivin expression and phosphorylation. Interestingly, we found that treatment of SCLC cells with CDDP further increased survivin expression in a cell cycle independent manner by activation of Akt. CA-Akt or lentiviral survivin also inhibited apoptosis induced by CDDP, whereas DN-Akt or survivin-specific RNA interference sensitized cells to CDDP. We identified survivin as an anti-apoptotic protein in SCLC cells that is regulated by Akt, and demonstrate that treatment with the DNA damaging agent CDDP activates the PI3K/Akt/survivin pathway that in part protects cells from drug-induced apoptosis.

Expression and subcellular localization of Ewing sarcoma (EWS) protein is affected by the methylation process.

Ewing sarcoma (EWS) protein contains an N-terminal transcriptional activation domain (EAD) and a C-terminal RNA-binding domain (RBD). Recently, we had shown that EWS protein is not only localized in the nucleus and cytosol, but also on the surface of T cells and that its RBD is extensively asymmetrically dimethylated on arginine residues. Here we show that stimulation of T cells with phytohemagglutinin (PHA) caused a time-dependent 10-fold increase in expression of methylated EWS protein on the cell surface and a sixfold increase in the nuclei of peripheral blood mononuclear cells (PBMC). Mitogenic stimulation of malignant T cell lines, however, did not increase their inherently high expression of EWS protein. This expression seemed to correlate with methionine adenosyltransferase activity and S-adenosyl-L-methionine (AdoMet) utilization in PBMC and tumor cells and thus indicates dependence on the methylation process. Inhibition of methylation in normal and malignant cells with the methylation inhibitor adenosine dialdehyde (AdOx) resulted in a three to fivefold decreased expression of EWS protein not only in the nucleus but also on the cell surface. The inhibitory effect of AdOx was compensated and negligible in PBMC, but not in tumor cells if they were treated simultaneously with mitogenic PHA concentrations. The present findings indicate that expression of EWS protein in the various subcellular compartments is affected by the methylation process, in particular by the availability of intracellular AdoMet.