Targeting c-Met Receptor Overcomes TRAIL-Resistance in Brain Tumors

Tumor necrosis factor related apoptosis-inducing ligand (TRAIL) induced apoptosis specifically in tumor cells. However, with approximately half of all known tumor lines being resistant to TRAIL, the identification of TRAIL sensitizers and their mechanism of action become critical to broadly use TRAIL as a therapeutic agent. In this study, we explored whether c-Met protein contributes to TRAIL sensitivity. We found a direct correlation between the c-Met expression level and TRAIL resistance. We show that the knock down c-Met protein, but not inhibition, sensitized brain tumor cells to TRAIL-mediated apoptosis by interrupting the interaction between c-Met and TRAIL cognate death receptor (DR) 5. This interruption greatly induces the formation of death-inducing signaling complex (DISC) and subsequent downstream apoptosis signaling. Using intracranially implanted brain tumor cells and stem cell (SC) lines engineered with different combinations of fluorescent and bioluminescent proteins, we show that SC expressing a potent and secretable TRAIL (S-TRAIL) have a significant anti-tumor effect in mice bearing c-Met knock down of TRAIL-resistant brain tumors. To our best knowledge, this is the first study that demonstrates c-Met contributes to TRAIL sensitivity of brain tumor cells and has implications for developing effective therapies for brain tumor patients.     

Current advances and expectations in tumor immunology]

Natural killer (NK) cells and Interferon (IFN)-gamma have been implicated in immune surveillance against tumor. We demonstrated the critical role of perforin in NK cell-mediated cytotoxic activity and anti-tumor effect in IFN-gamma inducible IL-12. And, we recently reported that TRAIL is constitutively expressed on a substantial proportion of murine NK cells in the liver, and which is responsible for spontaneous cytotoxicity and the anti-metastatic activity against TRAIL-sensitive tumor cells along with perforin and Fas ligand. Interestingly, the TRAIL expression on liver NK cells appeared to be regulated by endogenously produced IFN-gamma. Consisting with this finding, IL-12 and NKT cell specific ligand, alpha-Galactosylceramide (alpha-GalCer), induced TRAIL-mediated cytotoxcity and anti-tumor effect, and which was mediated by TRAIL expressed on IFN-gamma-activated NK cells. Tumor necrosis factor(TNF)-related apoptosis-inducing ligand (TRAIL) is a type II transmembrane protein belonging to the TNF family, which preferentially induces apoptotic cell death in various tumor cells in vitro. Preclinical studies in mice and nonhuman primates have shown that administration of recombinant soluble forms of TRAIL could suppress the growth of TRAIL-sensitive tumor xenografts with no apparent systemic toxicity. These studies suggested a potential utility of TRAIL as a cancer therapeutic, although TRAIL expression at protein levels and its physiological roles in tumor surveillance has remained unknown. Presented findings provide the first evidence for the physiological function of TRAIL as a tumor suppressor.     

Restricted expression of tumor necrosis factor-related apoptosis-inducing ligand receptor 4 in human peripheral blood lymphocytes

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumor but not normal cells, thus providing therapeutic possibilities for human cancers. However, it is not fully clear how widespread TRAIL receptors are, or how TRAIL signaling is modulated in normal cells. We characterized cell surface expression of TRAIL receptors in normal healthy donor peripheral blood and report that each of the TRAIL receptors are characteristically expressed on restricted cell populations. TRAIL-R1 is distinctively expressed on B-lymphocytes, TRAIL-R2 on monocytes, TRAIL-R3 on neutrophils and most impressively, CD8+ lymphocytes and NKT lymphocytes but not CD4+ lymphocytes express TRAIL-R4.     

Geraniol inhibits prostate cancer growth by targeting cell cycle and apoptosis pathways

Elongation factor-2 kinase (eEF-2 kinase, also known as calmodulin-dependent protein kinase III), is a unique calcium/calmodulin-dependent enzyme that inhibits protein synthesis by phosphorylating and inactivating elongation factor-2 (eEF-2). We previously reported that expression/activity of eEF-2 kinase was up-regulated in several types of malignancies including Gliomas, and was associated with response of tumor cells to certain therapeutic stress. In the current study, we sought to determine whether eEF-2 kinase expression affected sensitivity of glioma cells to treatment with tumor the necrosis factor-related apoptosis-inducing ligand (TRAIL), a targeted therapy able to induce apoptosis in cancer cells but causes no toxicity in most normal cells. We found that inhibition of eEF-2 kinase by RNA interference (RNAi) or by a pharmacological inhibitor (NH125) enhanced TRAIL-induced apoptosis in the human glioma cells, as evidenced by an increase in apoptosis in the tumor cells treated with eEF-2 kinase siRNA or the eEF-2 kinase inhibitor. We further demonstrated that sensitization of tumor cells to TRAIL was accompanied by a down-regulation of the anti-apoptotic protein, Bcl-xL, and that overexpression of Bcl-xL could abrogate the sensitizing effect of inhibiting eEF-2 kinase on TRAIL. The results of this study may help devise a new therapeutic strategy for enhancing the efficacy of TRAIL against malignant glioma by targeting eEF-2 kinase.     

Death induction by recombinant native TRAIL and its prevention by a caspase 9 inhibitor in primary human esophageal epithelial cells

The cytotoxic death ligand TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) is a tumor-specific agent under development as a novel anticancer therapeutic agent. However, some reports have demonstrated toxicity of certain TRAIL preparations toward human hepatocytes and keratinocytes through a caspase-dependent mechanism that involves activation of the extrinsic death pathway and Type II signaling through the mitochondria. We have isolated and purified both His-tagged protein and three versions of native recombinant human TRAIL protein from Escherichia coli. We found that 5 mm dithiothreitol in the purification process enhanced oligomerization of TRAIL and resulted in the formation of hyper-oligomerized TRAILs, including hexamers and nonomers with an extremely high potency in apoptosis induction. Although death-inducing signaling complex formation was much more efficient in cells treated with hyper-oligomerized TRAILs, this did not convert TRAIL-sensitive Type II HCT116 colon tumor cells to a Type I death pattern as judged by their continued sensitivity to a caspase 9 inhibitor. Moreover, TRAIL-resistant Type II Bax-null colon carcinoma cells were not converted to a TRAIL-sensitive Type I state by hyper-oligomerized TRAIL. Primary human esophageal epithelial 2 cells were found to be sensitive to all TRAIL preparations used, including trimer TRAIL. TRAIL-induced death in esophageal epithelial 2 cells was prevented by caspase 9 inhibition for up to 4 h after TRAIL exposure. This result suggests a possible therapeutic application of caspase 9 inhibition as a strategy to reverse TRAIL toxicity. Hyper-oligomerized TRAIL may be considered as an alternative agent for testing in clinical trials.     

Low extracellular pH augments TRAIL-induced apoptotic death through the mitochondria-mediated caspase signal transduction pathway

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL/APO-2L), a member of the tumor necrosis factor (TNF) gene family, is considered as one of the most promising cancer therapeutic agents due to its ability to selectively kill tumor cells. Although microenvironments of solid tumors (hypoxia, nutrient deprivation, and low pH) often affect the effectiveness of chemotherapy, few studies have been reported on the relationship between tumor microenvironments and TRAIL. In this study, we investigated whether low extracellular pH affects TRAIL-induced apoptotic death. When human prostate carcinoma DU145 cells were treated with 200 ng/ml His-tagged TRAIL for 4 h, the survival was approximately 10% at pH 6.3-6.6 and 61.3% at pH 7.4. Similar results were observed in human colorectal carcinoma CX-1 cell line. The TRAIL-mediated activation of caspase, cytochrome c release, and poly (ADP-ribose) polymerase (PARP) cleavage was promoted at low extracellular pH. Immunoprecipitation followed by western blot analysis shows that low extracellular pH enhances the association of truncated Bid with Bax during treatment with TRAIL. Western blot analysis also shows that the low extracellular pH-enhanced TRAIL cytotoxicity does not involve modulation of the levels of TRAIL receptors (DR4, DR5, and DcR2), FLIP, inhibitor of apoptosis (IAP), and Bcl-2. Overexpression of Bcl-2 effectively prevented low extracellular pH-augmented TRAIL cytotoxicity. Taken together, we propose that TRAIL-mediated cytotoxicity is greatly enhanced in low pH environments by promoting caspase activation.     

Retinoic acid-induced apoptosis in leukemia cells is mediated by paracrine action of tumor-selective death ligand TRAIL

The therapeutic and preventive activities of retinoids in cancer are due to their ability to modulate the growth, differentiation, and survival or apoptosis of cancer cells. Here we show that in NB4 acute promyelocytic leukemia cells, retinoids selective for retinoic-acid receptor-alpha induced an autoregulatory circuitry of survival programs followed by expression of the membrane-bound tumor-selective death ligand, TRAIL (tumor necrosis factor-related apoptosis-inducing ligand, also called Apo-2L). In a paracrine mode of action, TRAIL killed NB4 as well as heterologous and retinoic-acid-resistant cells. In the leukemic blasts of freshly diagnosed acute promyelocytic leukemia patients, retinoic-acid-induced expression of TRAIL most likely caused blast apoptosis. Thus, induction of TRAIL-mediated death signaling appears to contribute to the therapeutic value of retinoids.     

Identification and characterization of a novel agonistic anti-DR4 human monoclonal antibody

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its functional receptors, DR4 and DR5, have been established as promising targets for cancer treatment. Therapeutics targeting TRAIL and its receptors are not only effective in killing many types of tumors, but they also synergize with traditional therapies and show efficacy against tumors that are otherwise resistant to conventional treatments. We describe here the identification and characterization of two human monoclonal antibodies, m921 and m922, that are specific for human DR4. Both antibodies competed with TRAIL for binding to DR4, but only m921 recognized cell surface-associated DR4 and inhibited the growth of ST486 cells. This antibody may have potential for further development as a candidate therapeutic and research tool.Key words: DR4, TRAIL, lymphoma, therapeutic antibody     

Enhanced sensitivity of G1 arrested human cancer cells suggests a novel therapeutic strategy using a combination of simvastatin and TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) preferentially induces apoptosis in tumor cells over normal cells. To study the relationship between cell cycle progression and TRAIL-induced apoptosis, SW480 colon cancer and H460 lung cancer cell lines were examined for their sensitivity to TRAIL after arrest in different cell cycle phases. Cells were synchronized in G0/G1, S, and G2/M phase by serum starvation, aphidicolin, or nocodazole treatment, respectively. We found that arrest of cells in G0/G1 phase confers significantly higher susceptibility to TRAIL-induced apoptosis as compared to cells in late G1, S, or G2/M phase. To determine if cell cycle phase could be harnessed for therapeutic gain in the presence of TRAIL, we used the HMG-CoA reductase inhibitor, Simvastatin and lovastatin, to enrich a cancer cell population in G0/G1. Both simvastatin and lovastatin significantly augmented TRAIL-induced apoptosis in tumor cells, but not in normal keratinocytes. The results indicate that TRAIL, in combination with a HMG-CoA reductase inhibitor, may have therapeutic potential in the treatment of human cancer.     

pVAX1 plasmid vector-mediated gene transfer of soluble TRAIL suppresses human hepatocellular carcinoma growth in nude mice

The extracellular domain of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) may function as a soluble cytokine to selectively kill various cancer cells without toxicity to most normal cells. We used a high-biosafety plasmid pVAX1 as a vector and constructed a recombinant plasmid expressing the extracellular domain (95-281 aa) of human TRAIL fused with signal peptides of human IgGgamma, designated as pVAX-sT. Transduction of human BEL7402 liver cancer cells with pVAX-sT led to high levels of sTRAIL protein in the cell culture media and induced apoptosis. The therapeutic potential of pVAX-sT was then evaluated in the BEL7402 transplanted naked mouse model. Subsequent intratumoral administration of naked pVAX-sT resulted in the expression of soluble TRAIL in the sera and the tumor site, as well as effective suppression of tumor growth, with no toxicity to liver. In conclusion, the successful inhibition of liver cancer growth and the absence of detectable toxicity suggest that pVAX-sT could be useful in the gene therapy of liver cancer.     

肿瘤坏死因子相关的凋亡诱导配体及其与肿瘤治疗前景

肿瘤坏因子相关的凋亡诱导配体（ＴＮＦ－related apoptosis inducing ligand,TRALL)属于肿瘤坏死因子家族,可激活肿瘤细胞的凋亡。本文介绍了ＴＲＡＩＬ的结构与功能,凋亡诱导途径及其肿瘤治疗应用前景。     

Enhanced Sensitivity of G1 Arrested Human Cancer Cells Suggests a Novel Therapeutic Strategy Using a Combination of Simvastatin and TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) preferentially induces apoptosis in tumor cells over normal cells. To study the relationship between cell cycle progression and TRAIL-induced apoptosis, SW480 colon cancer and H460 lung cancer cell lines were examined for their sensitivity to TRAIL after arrest in different cell cycle phases. Cells were synchronized in G0/G1, S, and G2/M phase by serum starvation, aphidicolin, or nocodazole treatment, respectively. We found that arrest of cells in G0/G1 phase confers significantly higher susceptibility to TRAIL-induced apoptosis as compared to cells in late G1, S, or G2/M phase. To determine if cell cycle phase could be harnessed for therapeutic gain in the presence of TRAIL, we used the HMG-CoA reductase inhibitor, Simvastatin and lovastatin, to enrich a cancer cell population in G0/G1. Both simvastatin and lovastatin significantly augmented TRAIL-induced apoptosis in tumor cells, but not in normal keratinocytes. The results indicate that TRAIL, in combination with a HMG-CoA reductase inhibitor, may have therapeutic potential in the treatment of human cancer.

Key Words

TRAIL, Synchronization, Simvastatin, Cancer Therapy, Lovastatin, Cell Cycle, Apoptosis     

Hypoxia inducing factor-1α regulates tumor necrosis factor-related apoptosis-inducing ligand sensitivity in tumor cells exposed to hypoxia

Hypoxia is a common environmental stress. Particularly, the center of rapidly-growing solid tumors is easily exposed to hypoxic conditions. Hypoxia is well known to attenuate the therapeutic response to radio and chemotherapies including tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) protein. HIF-1α is a critical mediator of the hypoxic response. However, little is known about the function of hypoxia-inducible factor-1α (HIF-1α) on hypoxic inhibition of TRAIL-mediated apoptosis. In this study, we investigated whether hypoxic inhibition of TRAIL-mediated apoptosis can be regulated by modulating HIF-1α protein. Hypoxia- and DEF-induced HIF-1α activation inhibited the TRAIL-mediated apoptosis in SK-N-SH, HeLa, A549 and SNU-638 cells. And also, HIF-1α inactivating reagents including DOX increased the sensitivity to TRAIL protein in tumor cells exposed to hypoxia. Furthermore, knock-down of HIF-1α using lentiviral RNA interference sensitized tumor cells to TRAIL-mediated cell death under hypoxic condition. Taken together, these results indicate that HIF-1α inactivation increased TRAIL sensitivity in hypoxia-induced TRAIL-resistant tumor cells and also suggest that HIF-1α inhibitors may have benefits in combination therapy with TRAIL against hypoxic tumor cells.     

Downregulation of Bid is associated with PKCepsilon-mediated TRAIL resistance

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent as it selectively kills tumor cells but spares normal cells. Resistance to TRAIL by tumor cells limits its therapeutic use. We have previously shown that protein kinase C-epsilon (PKCepsilon) acts as an antiapoptotic protein in MCF-7 breast cancer cells. In the present study, we have investigated the mechanism(s) by which PKCepsilon contributes to TRAIL resistance. Overexpression of PKCepsilon inhibited caspase-8 and -9 activation, release of mitochondrial cytochrome c and cell death induced by TRAIL, but did not interfere with the recruitment of caspase-8 to the death-inducing signaling complex. Knockdown/inhibition of PKCepsilon resulted in enhanced sensitivity to TRAIL. The level of Bcl-2 was increased and Bid was decreased by PKCepsilon at both the protein and mRNA level but PKCepsilon had no effect on Bax. Knockdown of Bcl-2 by siRNA reversed TRAIL resistance in PKCepsilon-overexpressing cells, whereas depletion of Bid contributed to TRAIL resistance in MCF-7 cells. A decrease in Bid content was also associated with inhibition of TRAIL-induced caspase-8 activation. Furthermore, PKCepsilon depletion or overexpression of DN-PKCepsilon was associated with a decrease in Bcl-2 protein level. Thus, our results suggest that PKCepsilon acts upstream of mitochondria and mediates TRAIL resistance via both Bcl-2 and Bid in MCF-7 cells.     

Cysteine 230 is essential for the structure and activity of the cytotoxic ligand TRAIL

Unlike other tumor necrosis factor family members, the cytotoxic ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/Apo-2L contains an unpaired cysteine residue (Cys(230)) in its receptor-binding domain. Here we show that the biological activity of both soluble recombinant TRAIL and cell-associated, full-length TRAIL is critically dependent on the presence of Cys(230). Mutation of Cys(230) to alanine or serine strongly affected its ability to kill target cells. Binding to its receptors was decreased by at least 200-fold, and the stability of its trimeric structure was reduced. In recombinant TRAIL, Cys(230) was found engaged either in interchain disulfide bridge formation, resulting in poorly active TRAIL, or in the chelation of one zinc atom per TRAIL trimer in the active, pro-apoptotic form of TRAIL.     

基于TRAIL的肿瘤治疗策略进展

肿瘤坏死因子相关凋亡诱导配体(TRAIL)能选择性诱导肿瘤细胞凋亡,且对机体正常组织细胞无毒副作用,被认为是一种非常有潜力的抗癌药物。我们简要介绍TRAIL及其配体诱导细胞凋亡的机制、肿瘤细胞对TRAIL的耐受机制及其克服策略。     

Amiloride potentiates TRAIL-induced tumor cell apoptosis by intracellular acidification-dependent Akt inactivation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor gene family, is considered as one of the most promising cancer therapeutic agents due to its ability to selectively induce tumor cell apoptosis. In this study, we investigated whether the Na(+)/H(+) exchanger inhibitor, amiloride, promotes TRAIL-induced apoptotic death both in sensitive and resistant tumor cells, HeLa and LNCaP cells, respectively, and its underlying molecular mechanism. Amiloride enhanced TRAIL-induced apoptosis and activation of caspase-3 and -8 in both cells. This compound increased TRAIL-induced mitochondrial cytochrome c release and poly(ADP-ribose) polymerase cleavage. Moreover, amiloride-induced intracellular acidification, and inhibited the phosphorylated activation of the serine/threonine kinase Akt, which is known to promote cell survival, in both tumor cells. These data suggest that amiloride sensitizes both tumor cells to TRAIL-induced apoptosis by promoting Akt dephosphorylation and caspase-8 activation via the intracellular acidification and that Na(+)/H(+) exchanger inhibitors may play an important role in the anti-cancer activity of TRAIL, especially, in TRAIL-resistant tumors with highly active and expressed Akt.     

Deficient tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor transport to the cell surface in human colon cancer cells selected for resistance to TRAIL-induced apoptosis

Many tumor cell types are sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Incubation of TRAIL-sensitive cells with TRAIL invariably leads to resistant survivors even when high doses of TRAIL are used. Because the emergence of resistance to apoptosis is a major concern in successful treatment of cancer, and TRAIL survivors may contribute to therapeutic failure, we investigated potential resistance mechanisms. We selected TRAIL-resistant SW480 human colon adenocarcinoma cells by repeatedly treating them with high and/or low doses of TRAIL. The resulting TRAIL-resistant clones were not cross-resistant to Fas or paclitaxel. Expression of modulators of apoptosis was not changed in the resistant cells, including TRAIL receptors, cFLIP, Bax, Bid, or IAP proteins. Surprisingly, we found that DISC formation was deficient in multiple selected TRAIL-resistant clones. DR4 was not recruited to the DISC upon TRAIL treatment, and caspase-8 was not activated at the DISC. Although total cellular DR4 mRNA and protein were virtually identical in TRAIL-sensitive parental and TRAIL-resistant clones, DR4 protein expression on the cell surface was essentially undetectable in the TRAIL-resistant clones. Moreover, exogenous DR4 and KILLER/DR5 were not properly transported to the cell surface in the TRAIL-resistant cells. Interestingly, TRAIL-resistant cells were resensitized to TRAIL by tunicamycin pretreatment, which increased cell surface expression of DR4 and KILLER/DR5. Our data suggest that tumor cells may become resistant to TRAIL through regulation of the death receptor cell surface transport and that resistance to TRAIL may be overcome by the glycosylation inhibitor/endoplasmic reticulum stress-inducing agent tunicamycin.     

C-type lectin-like molecule-1 (CLL1)-targeted TRAIL augments the tumoricidal activity of granulocytes and potentiates therapeutic antibody-dependent cell-mediated cytotoxicity

The therapeutic effect of anti-cancer monoclonal antibodies stems from their capacity to opsonize targeted cancer cells with subsequent phagocytic removal, induction of antibody-dependent cell-mediated cytotoxicity (ADCC) or induction of complement-mediated cytotoxicity (CDC). The major immune effector cells involved in these processes are natural killer (NK) cells and granulocytes. The latter and most prevalent blood cell population contributes to phagocytosis, but is not effective in inducing ADCC. Here, we report that targeted delivery of the tumoricidal protein tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to granulocyte marker C-type lectin-like molecule-1 (CLL1), using fusion protein CLL1:TRAIL, equips granulocytes with high levels of TRAIL. Upon CLL1-selective binding of this fusion protein, granulocytes acquire additional TRAIL-mediated cytotoxic activity that, importantly, potentiates antibody-mediated cytotoxicity of clinically used therapeutic antibodies (e.g., rituximab, cetuximab). Thus, CLL1:TRAIL could be used as an adjuvant to optimize the clinical potential of anticancer antibody therapy by augmenting tumoricidal activity of granulocytes.