Targeting death-inducing receptors in cancer therapy

"Combination-oriented molecular-targeting prevention" of cancer: a model involving the combination of TRAIL and a DR5 inducer

Malignant tumors carry a high risk of death, and the prevention of malignant tumors is a crucial issue in preventive medicine. To this end, many chemopreventive agents have been tested, but the effects of single agents have been found to be insufficient to justify clinical trials. We have therefore hypothesized that combinations of different chemopreventive agents may synergistically enhance the preventive effect of chemopreventive agents used singly. To provide the treating physician with some guideline by which to choose the most effective agents to be combined, we propose a strategy which we have termed the "combination-oriented molecular-targeting prevention" of cancer. As the molecular target of our model, we focused on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which specifically causes apoptosis in malignant tumor cells. Many of these agents were found to up-regulate the expression of death receptor 5, a TRAIL receptor. They were also found to synergistically induce apoptosis in malignant tumor cells when combined with TRAIL. Here, we strongly advocate that the strategy of "combination-oriented molecular-targeting prevention" of cancer will be a practical approach for chemoprevention against human malignant tumors.

Glycolysis inhibition sensitizes tumor cells to death receptors-induced apoptosis by AMP kinase activation leading to Mcl-1 block in translation

Most cancer cells exhibit increased glycolysis for generation of their energy supply. This specificity could be used to preferentially kill these cells. In this study, we identified the signaling pathway initiated by glycolysis inhibition that results in sensitization to death receptor (DR)-induced apoptosis. We showed, in several human cancer cell lines (such as Jurkat, HeLa, U937), that glucose removal or the use of nonmetabolizable form of glucose (2-deoxyglucose) dramatically enhances apoptosis induced by Fas or by tumor necrosis factor-related apoptosis-inducing ligand. This sensitization is controlled through the adenosine monophosphate (AMP)-activated protein kinase (AMPK), which is the central energy-sensing system of the cell. We established the fact that AMPK is activated upon glycolysis block resulting in mammalian target of rapamycin (mTOR) inhibition leading to Mcl-1 decrease, but no other Bcl-2 anti-apoptotic members. Interestingly, we determined that, upon glycolysis inhibition, the AMPK-mTOR pathway controlled Mcl-1 levels neither through transcriptional nor through posttranslational mechanism but rather by controlling its translation. Therefore, our results show a novel mechanism for the sensitization to DR-induced apoptosis linking glucose metabolism to Mcl-1 downexpression. In addition, this study provides a rationale for the combined use of DR ligands with AMPK activators or mTOR inhibitors in the treatment of human cancers.

Tumour-targeted delivery of TRAIL using Salmonella typhimurium enhances breast cancer survival in mice

Background:

An effective cancer therapeutic must selectively target tumours with minimal systemic toxicity. Expression of a cytotoxic protein using Salmonella typhimurium would enable spatial and temporal control of delivery because these bacteria preferentially target tumours over normal tissue.

Methods:

We engineered non-pathogenic S. typhimurium to secrete murine TNF-related apoptosis-inducing ligand (TRAIL) under the control of the prokaryotic radiation-inducible RecA promoter. The response of the RecA promoter to radiation was measured using fluorometry and immunoblotting. TRAIL toxicity was determined using flow cytometry and by measuring caspase-3 activation. A syngeneic murine tumour model was used to determine bacterial accumulation and the response to expressed TRAIL.

Results:

After irradiation, engineered S. typhimurium secreted TRAIL, which caused caspase-3-mediated apoptosis and death in 4T1 mammary carcinoma cells in culture. Systemic injection of Salmonella and induction of TRAIL expression using 2 Gy γ-irradiation caused a significant delay in mammary tumour growth and reduced the risk of death by 76% when compared with irradiated controls. Repeated dosing with TRAIL-bearing Salmonella in conjunction with radiation improved the 30-day survival from 0 to 100%.

Conclusion:

These results show the pre-clinical utility of S. typhimurium as a TRAIL expression vector that effectively reduces tumour growth and extends host survival.

Induction of death receptor ligand-mediated apoptosis in epithelial ovarian carcinoma: The search for sensitizing agents

OBJECTIVE

To assess the abilities of cisplatin, paclitaxel, and flexible heteroarotinoid (Flex-Het) compound (SHetA2) to sensitize ovarian cancer cells to induction of the extrinsic apoptosis pathway by death receptor ligands, tumor necrosis factor alpha (TNFalpha), and TNF-related apoptosis-inducing ligand (TRAIL).

STUDY DESIGN

The effects of various combinations of TNFalpha, TRAIL, cisplatin, paclitaxel, and SHetA2 on viability and apoptosis in two established ovarian cancer cell lines, A2780 and SK-OV-3, and normal human primary endometrial cultures were measured with a cytotoxicity assay, flow cytometric analysis of annexin-V, and propidium iodide staining and Western blot analysis of caspase 8 and 3 activation.

RESULTS

Ovarian cancer and normal cells were resistant to TNFalpha and TRAIL. Cisplatin and paclitaxel did not increase sensitivity to these agents in either cell type. In contrast, combination of SHetA2 with TNFalpha or TRAIL induced a synergistic induction of apoptosis in cancer cells that involved activation of the extrinsic pathway caspase 8 and executioner caspase 3. The TRAIL combination was more potent than the TNFalpha combination. SHetA2 did not harm the viability of normal cells as a single agent or in combination with the death receptor ligands.

CONCLUSIONS

SHetA2, but not cisplatin or paclitaxel, can overcome resistance of ovarian cancer cells to TNFalpha and TRAIL without increasing sensitivity of normal cells to these death receptor ligands.

Novel susceptibility loci for second primary tumors/recurrence in head and neck cancer patients: large-scale evaluation of genetic variants

This study was aimed to identify novel susceptibility variants for second primary tumor (SPT) or recurrence in curatively treated early-stage head and neck squamous cell carcinoma (HNSCC) patients. We constructed a custom chip containing a comprehensive panel of 9,645 chromosomal and mitochondrial single nucleotide polymorphisms (SNP) representing 998 cancer-related genes selected by a systematic prioritization schema. Using this chip, we genotyped 150 early-stage HNSCC patients with and 300 matched patients without SPT/recurrence from a prospectively conducted randomized trial and assessed the association of these SNPs with risk of SPT/recurrence. Individually, six chromosomal SNPs and seven mitochondrial SNPs were significantly associated with risk of SPT/recurrence after adjustment for multiple comparisons. A strong gene-dosage effect was observed when these SNPs were combined, as evidenced by a progressively increasing SPT/recurrence risk as the number of unfavorable genotypes increased (P for trend < 1.00 x 10(-20)). Several polygenic analyses suggest an important role of interconnected functional network and gene-gene interaction in modulating SPT/recurrence. Furthermore, incorporation of these genetic markers into a multivariate model improved significantly the discriminatory ability over the models containing only clinical and epidemiologic variables. This is the first large-scale systematic evaluation of germ-line genetic variants for their roles in HNSCC SPT/recurrence. The study identified several promising susceptibility loci and showed the cumulative effect of multiple risk loci in HNSCC SPT/recurrence. Furthermore, this study underscores the importance of incorporating germ-line genetic variation data with clinical and risk factor data in constructing prediction models for clinical outcomes.

The immunopathology of human biliary cell epithelium

Bile ducts lined with biliary epithelial cells, or cholangiocytes, are the main components of the biliary system in liver. Cholangiocytes participate in the production and transport of bile substances, as well as participate in immune responses. Cholangiocytes protect against pathogens by expressing toll-like receptors and anti-microbial peptides; act as antigen-presenting cells by expressing human leukocyte antigen molecules and costimulatory molecules; recruit leukocytes to the target site by expressing adhesion molecules, cytokines, and chemokines; and induce apoptosis of leukocytes to limit the immune responses. Several cholangiopathies result from dysfunctions of the biliary system. They can broadly be divided into autoimmune, genetic, infectious, drug, and ischemic-injury-induced categories. The pathogenesis of many of these cholangiopathies is unclear and treatment is limited. Further understanding of the complexity of the biliary system is critical for medical advancements in this field.

Autophagy in tumour suppression and promotion

Autophagy, a well-described cellular mechanism for lysosomal degradation of cytoplasmic content, has emerged as a tumour suppression pathway. Recent evidence indicates that the tumour suppressor function of autophagy is mediated by scavenging of damaged oxidative organelles, thereby preventing accumulation of toxic oxygen radicals that would cause genome instability. Paradoxically, however, in some cases autophagy can also promote the survival of cancer cells once tumours have developed. This is attributed to the ability of autophagy to promote cell survival under conditions of poor nutrient supply, as often faced by solid tumours and metastasising cancer cells. In addition, autophagy is frequently upregulated in tumours as a response to therapy and may protect tumours against therapy-induced apoptosis. In this review we discuss the mechanisms that link autophagy to tumour suppression and promotion and provide examples of the dual functions of autophagy in cancer.

Trimeric coiled-coil domain of human pulmonary surfactant protein D enhances zinc-binding ability and biologic activity of soluble TRAIL

Unlike other TNF ligand family members, the homotrimeric tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) contains a buried zinc atom coordinated by three Cys230 residues from each subunit. The bound zinc ion is essential for maintaining the structure stability and bioactivity of TRAIL. To improve characteristics of TRAIL by modification to enhance its zinc-binding ability, we constructed a new variant of TRAIL in which the extracellular region of the ligand was N-terminally fused with a trimeric coiled-coil domain derived from human pulmonary surfactant-associated protein D (ST), and compared its characteristics with that of native TRAIL. Circular dichroism (CD) studies and metal assays showed that two versions of TRAIL folded as predicted into secondary and tertiary structures, and contained stoichiometric Zn(2+) through optimizing bacterial expression and purification. The addition of the human trimeric coiled-coil domain, however, significantly increased the antitumor activity of soluble TRAIL in vitro and in vivo. The accelerated thermal stability studies demonstrated that human serum album (HSA) promoted the aggregation and degradation of native TRAIL, but not ST, and the addition of ZnSO(4) to the solution of native TRAIL with HSA partially inhibited its aggregation, suggesting ST is more difficult to lose its bound zinc ion than native TRAIL. The issue was further confirmed by dialysis assess. This is the first example of modified TRAIL with enhanced zinc-binding ability.

Phenylarsine oxide interferes with the death inducing signaling complex and inhibits tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induced apoptosis

The mechanism by which tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces death is the subject of intense scrutiny due to its preferential targeting of transformed cells for deletion. Based on recent findings that the TRAIL-dependent death inducing signaling complex (DISC) forms and signals at the plasma membrane without being internalized, we investigated the possibility that agents that prevent endocytosis may stabilize the surface bound DISC and thereby enhance TRAIL-dependent signaling. We utilized phenylarsine oxide (PAO), a trivalent arsenical that has been reported to inhibit endocytosis and to induce mitochondrial permeability transition. Therefore PAO could, by two separate and independent activities, enhance TRAIL-induced killing. Paradoxically, we found that rather than synergizing with TRAIL, PAO was an effective inhibitor of TRAIL-induced killing. Recruitment of FADD and caspase-8 to the TRAIL-dependent DISC was diminished in a concentration-dependent manner in cells exposed to PAO. The effects of PAO could not be reversed by washing cells under non-reducing conditions, suggesting covalent linkage of PAO with its cellular target(s); however, 2,3-dimercaptoethanol effectively overcame the inhibitory action of PAO and restored sensitivity to TRAIL-induced apoptosis. PAO inhibited formation of the TRAIL-dependent DISC and therefore prevented all subsequent apoptotic events.

Tricks tumors use to escape from immune control

Tumor escape from the host immune system has been a major problem in immunotherapy of human malignancies. Human tumors are known to develop escape strategies, which might differ among tumors of the same histology. This suggests that host-tumor interactions create the tumor microenvironment that is unique for every tumor. Recent advances in cancer immunology allow for a better understanding of the mechanisms tumors use to execute immune escape and of the relationship the tumor establishes with immune cells. It is now feasible to obtain an "immune signature" of the tumor, that is to define the genetic, molecular and functional profiles of immune cells in the tumor microenvironment. This knowledge might be critically important for the personalized selection of available therapies and thus for clinical outcome.

TAK1 kinase determines TRAIL sensitivity by modulating reactive oxygen species and cIAP

TNF-related apoptosis-inducing ligand (TRAIL) is a potent inducer of cell death in several cancer cells, but many cells are resistant to TRAIL. The mechanism that determines sensitivity to TRAIL-killing is still elusive. Here we report that deletion of TAK1 kinase greatly increased activation of caspase-3 and induced cell death following TRAIL stimulation in keratinocytes and fibroblasts as well as cancer cells. Although TAK1 kinase is involved in NF-κB pathway, ablation of NF-κB did not alter sensitivity to TRAIL. We found that TRAIL could induce accumulation of reactive oxygen species (ROS) when TAK1 was deleted. Furthermore, we found that TAK1 deletion induces TRAIL-dependent downregulation of cIAP, which enhances activation of caspase-3. These results demonstrate that TAK1 deletion facilitates TRAIL-induced cell death by activating caspase through ROS and downregulation of cIAP. Thus, inhibition of TAK1 can be an effective approach to increase TRAIL sensitivity.

Sensitization of human breast cancer cells to natural killer cell-mediated cytotoxicity by proteasome inhibition

The proteasome inhibitor, bortezomib, has direct anti-tumour effects and has been demonstrated to sensitize tumour cells to tumour necrosis factor-related apoptosis-inducing ligand-mediated apoptosis. Natural killer (NK) cells are effective mediators of anti-tumour responses, both through cytotoxic granule killing and apoptosis-inducing pathways. We therefore investigated if bortezomib sensitized human breast cancer cells to killing by the human NK cell line, NK-92. Bortezomib was unable to sensitize MDA-231 breast cancer cells to NK cell-mediated killing in short-term in vitro assays. However, bortezomib did cause these cells to up-regulate apoptosis-related mRNA as well as death receptors on the cell surface. In a long-term in vitro tumour outgrowth assay that allows NK cells to use their full repertoire of killing pathways, bortezomib sensitized three breast cancer cell lines to NK cell-mediated killing, which led to greater anti-tumour effects than either treatment alone. We then used a xenogeneic mouse model in which CB-17 SCID mice were injected with human breast cancer cells. This model displayed the effectiveness of NK-92 cells, but the addition of bortezomib did not increase the survival further or reduce the number of lung metastases in tumour-bearing mice. However, while bortezomib was highly cytotoxic to NK-92 cells in vitro, bortezomib treatment in vivo did not decrease NK-92 function, suggesting that through alternative dosing or timing of bortezomib, greater efficacy may occur from combined therapy. These data demonstrate that combined treatment of human breast cancer with bortezomib and NK cells has the potential to generate superior anti-tumour responses than either therapy alone.

Phorbol ester–induced PKCϵ down-modulation sensitizes AML cells to TRAIL-induced apoptosis and cell differentiation

Despite the relevant therapeutic progresses made in these last 2 decades, the prognosis of acute myeloid leukemia (AML) remains poor. Phorbol esters are used at very low concentrations as differentiating agents in the therapy of myeloid leukemias. Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), in turn, is a death ligand that spares normal cells and is therefore currently under clinical trials for cancer therapy. Emerging evidence, however, suggests that TRAIL is also involved in nonapoptotic functions, like cell differentiation. PKCϵ is differentially modulated along normal hematopoiesis, and its levels modulate the response of hematopoietic precursors to TRAIL. Here, we investigated the effects of the combination of phorbol esters (phorbol ester 4-β-phorbol-12,13-dibutyrate [PDBu]) and TRAIL in the survival/differentiation of AML cells. We demonstrate here that PDBu sensitizes primary AML cells to both the apoptogenic and the differentiative effects of TRAIL via PKCϵ down-modulation, without affecting TRAIL receptor surface expression. We believe that the use of TRAIL in combination with phorbol esters (or possibly more specific PKCϵ down-modulators) might represent a significative improvement of our therapeutic arsenal against AML.

Bortezomib overcomes tumor necrosis factor-related apoptosis-inducing ligand resistance in hepatocellular carcinoma cells in part through the inhibition of the phosphatidylinositol 3-kinase/Akt pathway

Hepatocellular carcinoma (HCC) is one of the most common and aggressive human malignancies. Recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-tumor agent. However, many HCC cells show resistance to TRAIL-induced apoptosis. In this study, we showed that bortezomib, a proteasome inhibitor, overcame TRAIL resistance in HCC cells, including Huh-7, Hep3B, and Sk-Hep1. The combination of bortezomib and TRAIL restored the sensitivity of HCC cells to TRAIL-induced apoptosis. Comparing the molecular change in HCC cells treated with these agents, we found that down-regulation of phospho-Akt (P-Akt) played a key role in mediating TRAIL sensitization of bortezomib. The first evidence was that bortezomib down-regulated P-Akt in a dose- and time-dependent manner in TRAIL-treated HCC cells. Second, LY294002, a PI3K inhibitor, also sensitized resistant HCC cells to TRAIL-induced apoptosis. Third, knocking down Akt1 by small interference RNA also enhanced TRAIL-induced apoptosis in Huh-7 cells. Finally, ectopic expression of mutant Akt (constitutive active) in HCC cells abolished TRAIL sensitization effect of bortezomib. Moreover, okadaic acid, a protein phosphatase 2A (PP2A) inhibitor, reversed down-regulation of P-Akt in bortezomib-treated cells, and PP2A knockdown by small interference RNA also reduced apoptosis induced by the combination of TRAIL and bortezomib, indicating that PP2A may be important in mediating the effect of bortezomib on TRAIL sensitization. Together, bortezomib overcame TRAIL resistance at clinically achievable concentrations in hepatocellular carcinoma cells, and this effect is mediated at least partly via inhibition of the PI3K/Akt pathway.

TRAIL resistance of breast cancer cells is associated with constitutive endocytosis of death receptors 4 and 5

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its agnostic antibodies, which are being evaluated clinically as anticancer therapies, selectively kill cancer cells through the death receptors DR4 and DR5. However, their therapeutic potential is limited by occurring resistance in tumor cells. Here, we compared the apoptotic response of a panel of six human breast cancer cell lines with recombinant human TRAIL and antibodies to DR4 or DR5. Despite their total mRNA and protein expression, TRAIL death receptors, with a higher frequency in DR4, are absent on cell surface in some cell lines. Loss of cell surface expression of DR4 or DR5 accounts for resistance to their corresponding antibody and, importantly, correlates with a decreased sensitivity to TRAIL. TRAIL resistance occurs when both receptors are absent on cell surface regardless of alterations in Bcl-2 family proteins or caspases. Furthermore, inhibition of endocytosis by pharmacologic inhibitors or disruption of clathrin-dependent endocytosis signaling components (adaptor protein 2 and clathrin) restores cell surface expression of the death receptors and sensitize TRAIL-resistant cells to TRAIL-induced apoptosis. DR4 endocytosis appears to be mediated by its cytoplasmic domain EAQC(337)LL. The results show that TRAIL death receptors undergo constitutive endocytosis in some breast cancer cells. Loss of cell surface expression of DR4 and DR5 could be evaluated as a biomarker for TRAIL resistance in breast tumors. Moreover, the clathrin-mediated endocytosis pathway could be a potential target for therapeutics to overcome tumor resistance to TRAIL receptor-targeted therapies.

Selection and Characterization of a Novel Agonistic Human Recombinant Anti-Trail-R2 Minibody with Antileukemic Activity

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising natural anticancer therapeutic agent because through its “death receptors”, TRAIL-R1 and TRAIL-R2, it induces apoptosis in many transformed tumor cells, but not in the majority of normal cells. Hence, agonistic compounds directed against TRAIL death receptors have the potential of being excellent cancer therapeutic agents, with minimal cytotoxicity in normal tissues. Here, we report the selection and characterization of a new single-chain fragment variable (scFv) to TRAIL-R2 receptor isolated from a human phage-display library, produced as minibody (MB), and characterized for the in vitro anti-leukemic tumoricidal activity. The anti-TRAIL-R2 MB2.23 efficiently and specifically bound to membrane-associated TRAIL-R2 on different leukemic cell lines and could act as a direct agonist in vitro, initiating apoptotic signaling as well as complement-dependent cytotoxicity and antibody-dependent cell cytotoxicity, providing a rationale for further investigations of MB2.23 in anticancer therapy.

Interleukin-8 signaling attenuates TRAIL- and chemotherapy-induced apoptosis through transcriptional regulation of c-FLIP in prostate cancer cells

Chemotherapy-induced interleukin-8 (IL-8) signaling reduces the sensitivity of prostate cancer cells to undergo apoptosis. In this study, we investigated how endogenous and drug-induced IL-8 signaling altered the extrinsic apoptosis pathway by determining the sensitivity of LNCaP and PC3 cells to administration of the death receptor agonist tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). TRAIL induced concentration-dependent decreases in LNCaP and PC3 cell viability, coincident with increased levels of apoptosis and the potentiation of IL-8 secretion. Administration of recombinant human IL-8 was shown to increase the mRNA transcript levels and expression of c-FLIP(L) and c-FLIP(S), two isoforms of the endogenous caspase-8 inhibitor. Pretreatment with the CXCR2 antagonist AZ10397767 significantly attenuated IL-8-induced c-FLIP mRNA up-regulation whereas inhibition of androgen receptor- and/or nuclear factor-kappaB-mediated transcription attenuated IL-8-induced c-FLIP expression in LNCaP and PC3 cells, respectively. Inhibition of c-FLIP expression was shown to induce spontaneous apoptosis in both cell lines and to sensitize these prostate cancer cells to treatment with TRAIL, oxaliplatin, and docetaxel. Coadministration of AZ10397767 also increased the sensitivity of PC3 cells to the apoptosis-inducing effects of recombinant TRAIL, most likely due to the ability of this antagonist to block TRAIL- and IL-8-induced up-regulation of c-FLIP in these cells. We conclude that endogenous and TRAIL-induced IL-8 signaling can modulate the extrinsic apoptosis pathway in prostate cancer cells through direct transcriptional regulation of c-FLIP. Therefore, targeted inhibition of IL-8 signaling or c-FLIP expression in prostate cancer may be an attractive therapeutic strategy to sensitize this stage of disease to chemotherapy.

Studies on search for bioactive natural products targeting TRAIL signaling leading to tumor cell apoptosis

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis in many transformed cells but not in normal cells and, hence, has been expected as a new anticancer strategy. During our studies on search for bioactive natural products from various natural resources such as plants and microorganisms, we recently identified several natural products which exhibited activities related to TRAIL signaling. Dimeric sesquiterpenoids isolated from Zingiberaceous plant, Curcuma parviflora, showed enhancement activity of gene expression of TRAIL-receptor and TRAIL-receptor protein level. Several new isoflavone natural products, named brandisianins, were isolated from Leguminosaeous plant, Millettia brandisiana, by our screening study targeting TRAIL-receptor expression enhancement activity. A dihydroflavonol (BB1) that was extracted from Compositaeous plant, Blumea balsamifera, and fuligocandin B, a new anthranilylproline-indole alkaloid isolated from myxomycete were found to exhibit reversal effect of TRAIL resistance activity.

Antibodies targeted to TRAIL receptor-2 and ErbB-2 synergize in vivo and induce an antitumor immune response

Despite the development of human epidermal growth factor receptor-2 (ErbB-2/HER2)-targeted therapies, there remains an unmet medical need for breast cancer patients with ErbB-2 overexpression. We investigated the therapeutic activity of an agonist mAb to mouse tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor-2 (DR5) against ErbB2-driven breast cancer. Established tumors in BALB/c transgenic mice expressing a constitutively active ErbB-2/neuT were treated with anti-DR5 mAb and/or anti-ErbB-2 mAb and monitored for tumor progression. Treatment with anti-DR5 or anti-ErbB2 mAb as single agents significantly delayed tumor growth, although all tumors eventually progressed. Remarkably, treatment with a combination of anti-DR5 and anti-ErbB-2 mAbs induced complete response in a majority of mice. In vivo blockade of CD11b(+) cells, but not natural killer cell depletion, significantly abrogated the early antitumor response. Notably, depletion of CD8(+) T cells provoked primary and secondary tumor relapse, revealing the induction of antitumor immunity by the combination treatment. Combined therapy with anti-DR5 and anti-ErbB-2 mAbs further significantly suppressed the growth of advanced spontaneous tumors in ErbB-2/neuT transgenic mice, even when treatment was delayed until tumors were palpable. We thus demonstrated that the combination of anti-DR5 and anti-ErbB2 mAbs might be an effective form of treatment for ErbB-2-overexpressing breast cancer.

The natural product honokiol preferentially inhibits cellular FLICE-inhibitory protein and augments death receptor-induced apoptosis

Targeting death receptor-mediated apoptosis has emerged as an effective strategy for cancer therapy. However, certain types of cancer cells are intrinsically resistant to death receptor-mediated apoptosis. In an effort to identify agents that can sensitize cancer cells to death receptor-induced apoptosis, we have identified honokiol, a natural product with anticancer activity, as shown in various preclinical studies, as an effective sensitizer of death receptor-mediated apoptosis. Honokiol alone moderately inhibited the growth of human lung cancer cells; however, when combined with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), greater effects on decreasing cell survival and inducing apoptosis than TRAIL alone were observed, indicating that honokiol cooperates with TRAIL to enhance apoptosis. This was also true to Fas-induced apoptosis when combined with Fas ligand or an agonistic anti-Fas antibody. Among several apoptosis-associated proteins tested, cellular FLICE-inhibitory protein (c-FLIP) was the only one that was rapidly down-regulated by honokiol in all of the tested cell lines. The down-regulation of c-FLIP by honokiol could be prevented by the proteasome inhibitor MG132. Moreover, honokiol increased c-FLIP ubiquitination. These results indicate that honokiol down-regulates c-FLIP by facilitating its degradation through a ubiquitin/proteasome-mediated mechanism. Enforced expression of ectopic c-FLIP abolished the ability of honokiol to enhance TRAIL-induced apoptosis. Several honokiol derivatives, which exhibited more potent effects on down-regulation of c-FLIP than honokiol, showed better efficacy than honokiol in inhibiting the growth and enhancing TRAIL-induced apoptosis as well. Collectively, we conclude that c-FLIP down-regulation is a key event for honokiol to modulate the death receptor-induced apoptosis.

Andrographolide sensitizes cancer cells to TRAIL-induced apoptosis via p53-mediated death receptor 4 up-regulation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an important member of the tumor necrosis factor subfamily with great potential in cancer therapy. Andrographolide (Andro), a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, is known to possess potent anti-inflammatory and anticancer activities. Here, we showed that pretreatment with Andro significantly enhances TRAIL-induced apoptosis in various human cancer cell lines, including those TRAIL-resistant cells. Such sensitization is achieved through transcriptional up-regulation of death receptor 4 (DR4), a death receptor of TRAIL. In search of the molecular mechanisms responsible for DR4 up-regulation, we found that the tumor suppressor p53 plays an essential role in DR4 transcriptional activation. Andro is capable of activating p53 via increased p53 phosphorylation and protein stabilization, a process mediated by enhanced reactive oxygen species production and subsequent c-Jun NH(2)-terminal kinase activation. Pretreatment with an antioxidant (N-acetylcysteine) or a c-Jun NH(2)-terminal kinase inhibitor (SP600125) effectively prevented Andro-induced p53 activation and DR4 up-regulation and eventually blocked the Andro-induced sensitization on TRAIL-induced apoptosis. Taken together, these results present a novel anticancer effect of Andro and support its potential application in cancer therapy to overcome TRAIL resistance.

Tumor necrosis factor-related apoptosis-inducing ligand promotes migration of human bone marrow multipotent stromal cells

Adult multipotent stromal cells (MSCs), also known as mesenchymal stem cells, represent an important source of cells for the repair of a number of damaged tissues. Both bone marrow (BM)-derived and amniotic MSCs expressed detectable surface levels of two (tumor necrosis factor-related apoptosis-inducing ligand receptor 2 [TRAIL-R2] and TRAIL-R4) of four transmembrane TRAIL receptors. Although the best-characterized activity of TRAIL-R2 is the transduction of apoptotic signals, neither recombinant TRAIL (rTRAIL) nor infection with an adenovirus-expressing TRAIL induced cytotoxic effects on MSCs. Moreover, whereas rTRAIL did not affect proliferation or differentiation of MSCs along the osteogenic and adipogenic lineages, it significantly promoted the migration of human MSCs in range of concentrations comparable to that of soluble TRAIL in human plasma (100 pg/ml). Since rTRAIL induced the rapid phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in MSC cultures and pretreatment with pharmacological inhibitors of the ERK1/2 pathway efficiently counteracted the rTRAIL-induced human MSC migration, these data indicate that ERK1/2 is involved in mediating the ability of rTRAIL to stimulate MSC migration. Taking into consideration that the soluble factors able to induce MSC migration have not been extensively characterized, our current data indicate that the TRAIL/TRAIL-R system might play an important role in the biology of MSCs. Disclosure of potential conflicts of interest is found at the end of this article.

Recombinant antibodies for cancer therapy

BACKGROUND

Recombinant antibodies have evolved into successful therapeutics with 10 approved for cancer and more in the pipeline. Four of the top ten cancer therapy drugs are recombinant antibodies.

OBJECTIVES

To survey the current state-of-the-art highlighting the reasons for this success and looking ahead to the next generation of antibody therapy.

METHODS

An analysis was carried out to identify preclinical and clinical examples and the underlying concepts and mechanisms that have shown how to design better therapies.

RESULTS/CONCLUSIONS

Greater understanding of the molecular basis of cancer has led to improved antibodies and a greater selection of targets. Fine tuning of successful antibodies through modification of glycosylation, affinity, size and other parameters are paying dividends. Fc-engineering is likely to be predominant in the near future but conjugates, fragments and fusion proteins will continue to be developed and find their place in the arsenal of antibody therapeutics.

Combination of isoliquiritigenin and tumor necrosis factor-related apoptosis-inducing ligand induces apoptosis in colon cancer HT29 cells

OBJECTIVES

Isoliquiritigenin is a chalcone derivative with potential in cancer chemoprevention. Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent, some cancer cells are resistant to TRAIL treatment. Current studies have tried to overcome TRAIL-resistant cancer cells. Here, we show for the first time that isoliquiritigenin overcomes TRAIL resistance in colon cancer HT29 cells.

METHODS

HT29 cells were treated with isoliquiritigenin and/or TRAIL, and apoptosis induction was detected by flow cytometry and fluorescence microscopy. Protein expression relating to the TRAIL pathway was analyzed by Western blotting.

RESULTS

A single treatment with isoliquiritigenin scarcely induced apoptosis in HT29 cells. Combined treatment with suboptimal concentrations of isoliquiritigenin and TRAIL markedly induced apoptosis, however. The effect was blocked by a pan-caspase inhibitor and a caspase-3, 8, 9, or 10 inhibitor, suggesting that the combination facilitates caspase-dependent apoptosis. Furthermore, the apoptosis induced by isoliquiritigenin and TRAIL was blocked by a dominant negative form of the TRAIL receptor. This result indicates that the combined effect is caused by specific interaction between TRAIL and its receptors. Isoliquiritigenin increased the amount of DR5 protein among TRAIL receptors. Isoliquiritigenin did not significantly increase levels of the Bcl-2 family proteins Bcl-2, Bcl-xL, and BAX.

CONCLUSIONS

Our results suggest that isoliquiritigenin has the potential to overcome resistance to TRAIL in cancer cells and its chemopreventive effects may depend on TRAIL function.

Death receptor 5 mediated-apoptosis contributes to cholestatic liver disease

Chronic cholestasis often results in premature death from liver failure with fibrosis; however, the molecular mechanisms contributing to biliary cirrhosis are not demonstrated. In this article, we show that the death signal mediated by TNF-related apoptosis-inducing ligand (TRAIL) receptor 2/death receptor 5 (DR5) may be a key regulator of cholestatic liver injury. Agonistic anti-DR5 monoclonal antibody treatment triggered cholangiocyte apoptosis, and subsequently induced cholangitis and cholestatic liver injury in a mouse strain-specific manner. TRAIL- or DR5-deficient mice were relatively resistant to common bile duct ligation-induced cholestasis, and common bile duct ligation augmented DR5 expression on cholangiocytes, sensitizing mice to DR5-mediated cholangitis. Notably, anti-DR5 monoclonal antibody-induced cholangitis exhibited the typical histological appearance, reminiscent of human primary sclerosing cholangitis. Human cholangiocytes constitutively expressed DR5, and TRAIL expression and apoptosis were significantly elevated in cholangiocytes of human primary sclerosing cholangitis and primary biliary cirrhosis patients. Thus, TRAIL/DR5-mediated apoptosis may substantially contribute to chronic cholestatic disease, particularly primary sclerosing cholangitis.

Combination of treatment with death receptor 5-specific antibody with therapeutic HPV DNA vaccination generates enhanced therapeutic anti-tumor effects

There is currently a vital need for the development of novel therapeutic strategies for the control of advanced stage cancers. Antigen-specific immunotherapy and the employment of antibodies against the death receptor 5 (DR5) have emerged as two potentially promising strategies for cancer treatment. In the current study, we hypothesize that the combination of treatment with the anti-DR5 monoclonal antibody, MD5-1 with a DNA vaccine encoding calreticulin (CRT) linked to human papillomavirus type 16 (HPV-16) E7 antigen (CRT/E7(detox)) administered via gene gun would lead to further enhancement of E7-specific immune responses as well as anti-tumor effects. Our results indicated that mice bearing the E7-expressing tumor, TC-1 treated with MD5-1 monoclonal antibody followed by CRT/E7(detox) DNA vaccination generated the most potent therapeutic anti-tumor effects as well as highest levels of E7-specific CD8+ T cells among all the groups tested. In addition, treatment with MD5-1 monoclonal antibody was capable of rendering the TC-1 tumor cells more susceptible to lysis by E7-specific cytotoxic T lymphocytes. Our findings serve as an important foundation for future clinical translation.

Role and prognostic significance of tumor necrosis factor-related apoptosis-inducing ligand death receptor DR5 in nonsmall-cell lung cancer and precursor lesions

BACKGROUND

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor, DR5, mediates proapoptotic signals and is implicated in the pathogenesis of many neoplasms including nonsmall-cell lung cancer (NSCLC).

METHODS

In this study, immunohistochemical expression of DR5 was examined in 146 cases of stage I and II NSCLC as well as neoplastic precursor lesions and regional lymph node metastases using tissue microarrays.

RESULTS

High DR5 expression was observed in 67.1% of primary NSCLC, 55.6% of bronchial squamous carcinoma in situ, 40% of squamous metaplasia, as well as 76.5% of lymph node metastases. In all of these lesions, DR5 expression was significantly higher than in normal bronchial epithelium. Increased expression of DR5 correlated with poorly differentiated tumors and was inversely correlated with bronchioloalveolar carcinomas. There was no correlation with other clinicopathologic variables. A significant association was found between high DR5 expression and reduced overall survival in univariate analysis. Among smokers, high DR5 and tumor stage were independent predictors of reduced disease-free survival in multivariate analysis, however, DR5 was not an independent prognostic marker among the entire cohort of NSCLC.

CONCLUSIONS

These findings suggest that DR5 plays a role in the development of early-stage NSCLC and the high levels of DR5 expression suggest that these tumors may be susceptible to novel anticancer agents targeting the DR5 receptor and may improve patient survival, particularly for patients who are smokers.

Expression of tumor necrosis factor receptor 6 in the tissue microarrays of gastric carcinoma

AIM: To investigate the expression of tumor necrosis factor receptor 6 (TR6) protein in gastric carcinoma (GC) and its clinical significance.

METHODS: Tissue microarray was constructed using 79 cases of GC tissues, 45 dysplasia (Dys) tissues, 37 intestinal metaplasia (IM) and 42 chronic superficial gastritis (CSG) tissues. Immunohistochemistry was employed to detect the expression of TR6 protein. Statistical analysis was performed to figure out the correlation between TR6 expression and the clinicopathological features of GC.

RESULTS: The positive rate of TR6 protein in GC tissues was significantly higher than that in Dys (χ² = 2.288, P = 0.022), IM (χ² = 2.639, P = 0.008) and CSG tissues (χ² = 3.593, P = 0.000). The expression of TR6 protein in the well-differentiated GC tissues was significantly lower than that in the poorly-differentiated ones (χ² = 2.183, P = 0.029). Moreover, the positive rate of TR6 protein was markedly lower in the groups of TNM stage Ⅰ, Ⅱ or without lymph node metastasis than that in the groups of stage Ⅲ, Ⅳ (χ² = 2.194, P = 0.028) or with lymph node metastasis (χ² = 5.021, P = 0.000). The expression of TR6 was not associated with the age, sex of patients, or the tumor invasive depth.

CONCLUSION: Over-expression of TR6 may play an important role in the pathogenesis, development and metastases of GC. TR6 gene may serve as an important molecular biological indicator in diagnosing and predicating the biological behavior of GC.

Interleukin-21: basic biology and implications for cancer and autoimmunity

Interleukin-21 (IL-21), a potent immunomodulatory four-alpha-helical-bundle type I cytokine, is produced by NKT and CD4(+) T cells and has pleiotropic effects on both innate and adaptive immune responses. These actions include positive effects such as enhanced proliferation of lymphoid cells, increased cytotoxicity of CD8(+) T cells and natural killer (NK) cells, and differentiation of B cells into plasma cells. Conversely, IL-21 also has direct inhibitory effects on the antigen-presenting function of dendritic cells and can be proapoptotic for B cells and NK cells. IL-21 is also produced by Th17 cells and is a critical regulator of Th17 development. The regulatory activity of IL-21 is modulated by the differentiation state of its target cells as well as by other cytokines or costimulatory molecules. IL-21 has potent antitumor activity but is also associated with the development of autoimmune disease. IL-21 transcription is dependent on a calcium signal and NFAT sites, and IL-21 requires Stat3 for its signaling. The key to harnessing the power of IL-21 will depend on better understanding its range of biological actions, its mechanism of action, and the molecular basis of regulation of expression of IL-21 and its receptor.

Tumor-necrosis-factor-related apoptosis-inducing ligand and the regulation of hematopoiesis

PURPOSE OF REVIEW

This review will focus on the emerging role of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/TRAIL-receptors in the pathophysiology of hematopoiesis and on the potential therapeutic applications of either recombinant TRAIL or anti-TRAIL-R1/-R2 agonistic antibodies for the treatment of hematological malignancies.

RECENT FINDINGS

While CD34 stem/progenitor cells do not express TRAIL-receptors and are protected from TRAIL-induced apoptosis, accumulating evidence points to a role for elevated expression/release of TRAIL at the bone marrow level in the pathophysiology of aplastic anemia, Fanconi anemia, and myelodysplastic syndromes. In-vitro data show promising synergistic effects of recombinant TRAIL in association with proteasome or histone deacetylase inhibitors, natural compounds or small molecules in the therapy of myeloid and lymphoid malignancies. Moreover, although both recombinant TRAIL and anti-TRAIL-R1/-R2 antibodies are well tolerated in vivo, anti-TRAIL-R1/-R2 agonistic antibodies show the potential advantage of avoiding the neutralizing activity of the soluble receptor osteoprotegerin.

SUMMARY

While a chronic pathological elevation of TRAIL at the bone marrow level might contribute to the impairment of normal hematopoiesis, the use of recombinant TRAIL and anti-TRAIL-R1/-R2 agonistic antibodies appears particularly promising for the treatment of hematological malignancies in particular, of multiple myeloma, especially if used in association with innovative therapeutic compounds.

Suppression of cFLIP is sufficient to sensitize human melanoma cells to TRAIL- and CD95L-mediated apoptosis

Death ligands such as tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and certain forms of CD95L are attractive therapeutic options for metastatic melanoma. Since knowledge about the regulation of death receptor sensitivity in melanoma is sparse, we have analysed these signaling pathways in detail. The loss of CD95 or TRAIL-R1, but not of TRAIL-R2, surface expression correlated with apoptosis sensitivity in a panel of melanoma cell lines. In contrast, the expression of proteins of the apical apoptosis signaling cascade (FADD, initiator caspases-8 and cFLIP) did not predict apoptosis sensitivity. Since both TRAIL-R1 and -R2 transmit apoptotic signals, we asked whether cFLIP, highly expressed in several of the cell lines tested, is sufficient to maintain resistance to TRAIL-R2-mediated apoptosis. Downregulation of cFLIP in TRAIL-R2-positive, TRAIL-resistant IGR cells dramatically increased TRAIL sensitivity. Conversely ectopic expression of cFLIP in TRAIL-sensitive, TRAIL-R2-expressing RPM-EP melanoma cells inhibited TRAIL- and CD95L-mediated cell death. Thus, modulation of cFLIP is sufficient to sensitize TRAIL-R2-expressing cells for TRAIL. Taken together, albeit expressing all proteins necessary for death receptor-mediated apoptosis, TRAIL-R1 negative melanoma cells cannot undergo TRAIL- or CD95L-induced apoptosis due to expression of cFLIP. Hence, cFLIP represents an attractive therapeutic target for melanoma treatment, especially in combination with TRAIL receptor agonists.

Emerging drugs for biliary cancer

Biliary cancer comprise carcinoma of the gallbladder as well as the intrahepatic, hilar and extrahepatic bile ducts. Furthermore, many different etiologies and risk factors are contributing to the inhomogeneity of this disease. It is often diagnosed at an advanced stage when potentially curative resection is not feasible. Due to the lack of randomised Phase III studies, there is no standard regimen for chemotherapy in biliary cancer. Recent investigations into the underlying molecular mechanisms involved in biliary carcinogenesis and tumour growth have contributed greatly to our understanding of biliary cancer. Through a better understanding of these mechanisms, improved and more specific diagnostic, therapeutic and preventive strategies may be developed. Although fluoropyrimidines and gemcitabine remain the backbone of routine chemotherapy in advanced disease, new agents such as epidermal growth factor receptor blockers and angiogenesis inhibitors may hold promise for improving the outcome for patients with biliary cancer.

CK2 controls TRAIL and Fas sensitivity by regulating FLIP levels in endometrial carcinoma cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has emerged as a promising antineoplastic agent because of its ability to selectively kill tumoral cells. However, some cancer cells are resistant to TRAIL-induced apoptosis. We have previously demonstrated that in endometrial carcinoma cells such resistance is caused by elevated FLICE-inhibitory protein (FLIP) levels. The present study focuses on the mechanisms by which FLIP could be modulated to sensitize endometrial carcinoma cells to TRAIL-induced apoptosis. We find that inhibition of casein kinase (CK2) sensitizes endometrial carcinoma cells to TRAIL- and Fas-induced apoptosis. CK2 inhibition correlates with a reduction of FLIP protein, suggesting that CK2 regulates resistance to TRAIL and Fas by controlling FLIP levels. FLIP downregulation correlates with a reduction of mRNA and is prevented by addition of the MG-132, suggesting that CK2 inhibition results in a proteasome-mediated degradation of FLIP. Consistently, forced expression of FLIP restores resistance to TRAIL and Fas. Moreover, knockdown of either FADD or caspase-8 abrogates apoptosis triggered by inhibition of CK2, indicating that CK2 sensitization requires formation of functional DISC. Finally, because of the possible role of both TRAIL and CK2 in cancer therapy, we demonstrate that CK2 inhibition sensitizes primary endometrial carcinoma explants to TRAIL apoptosis. In conclusion, we demonstrate that CK2 regulates endometrial carcinoma cell sensitivity to TRAIL and Fas by regulating FLIP levels.

Targeting immunosupportive cancer therapies: accentuate the positive, eliminate the negative

In this Commentary we aim to provide an overview of some specific examples of cancer therapeutics, including targeted approaches using monoclonal antibodies and kinase inhibitors, as well as highlight novel approaches for enhancing immunological responses against tumors. We point out that a fundamental property of the cancer cell, genomic instability, confounds the targeted therapies that aim to induce cell death directly while simultaneously enhancing the potential for immunological attack by creating a large number of neoantigens. We argue for combinatorial strategies with agents that target tumor cells to release these antigens together with innovative therapies that enhance immunological responses by interfering with inhibitory checkpoints.

Clearing the TRAIL for Cancer Therapy

The death receptor ligand TRAIL has shown remarkable promise as an anticancer agent. However, TRAIL signaling also activates NF-kappaB, which induces the antiapoptotic regulators Mcl-1 and cIAP2, thus compromising its efficacy. In this issue of Cancer Cell, El-Deiry and colleagues explore pathways that disrupt TRAIL-induced survival signaling and show that the Myc oncoprotein and the Raf kinase inhibitor Sorafenib sensitize otherwise TRAIL-resistant colon cancer cells by effectively reducing NF-kappaB-mediated transcription of Mcl-1. These findings suggest that combining TRAIL with agents that disrupt NF-kappaB regulation or binding or those that directly destabilize or disable Mcl-1 will have therapeutic benefit.