Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand cooperates with chemotherapy to inhibit orthotopic lung tumor growth and improve survival

Bifidobacterium longum as a delivery system of TRAIL and endostatin cooperates with chemotherapeutic drugs to inhibit hypoxic tumor growth

In our previous study, we have shown that vector pBV22210 containing a chloramphenicol resistance and a cryptic plasmid pMB1 from Bifidobacterium longum strain could stably replicate and did not significantly affect the biological characteristics of B. longum. In this study, B. longum was transfected by electroporation with pBV22210 encoding the extracellular domain of TRAIL (B. longum-pBV22210-TRAIL) and its carbohydrate fermentation and growth curve were determined, and its location and inhibitory effect on tumor xenografts in mice were also examined. The results further proved that gene transfection did not change the main biochemical characteristics of B. longum. The results also showed that B. longum-pBV22210-TRAIL resulted in selective location in tumors and exhibited a definite antitumor effect on S180 osteosarcoma. In addition, when a low dosage of Adriamycin (5 mg kg(-1)) or B. longum-pBV22210-endostatin was combined, the antitumor effect was significantly enhanced. The successful inhibition of S180 tumor growth suggested a stable vector in B. longum for transporting anticancer genes combined with low-dose chemotherapeutic drugs or other target genes is a promising approach in cancer gene therapy.

Mesenchymal stem cell delivery of TRAIL can eliminate metastatic cancer

Cancer is a leading cause of mortality throughout the world and new treatments are urgently needed. Recent studies suggest that bone marrow-derived mesenchymal stem cells (MSC) home to and incorporate within tumor tissue. We hypothesized that MSCs engineered to produce and deliver tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a transmembrane protein that causes selective apoptosis of tumor cells, would home to and kill cancer cells in a lung metastatic cancer model. Human MSCs were transduced with TRAIL and the IRES-eGFP reporter gene under the control of a tetracycline promoter using a lentiviral vector. Transduced and activated MSCs caused lung (A549), breast (MDAMB231), squamous (H357), and cervical (Hela) cancer cell apoptosis and death in coculture experiments. Subcutaneous xenograft experiments confirmed that directly delivered TRAIL-expressing MSCs were able to significantly reduce tumor growth [0.12 cm(3) (0.04-0.21) versus 0.66 cm(3) (0.21-1.11); P < 0.001]. We then found, using a pulmonary metastasis model, systemically delivered MSCs localized to lung metastases and the controlled local delivery of TRAIL completely cleared the metastatic disease in 38% of mice compared with 0% of controls (P < 0.05). This is the first study to show a significant reduction in metastatic tumor burden with frequent eradication of metastases using inducible TRAIL-expressing MSCs. This has a wide potential therapeutic role, which includes the treatment of both primary tumors and their metastases, possibly as an adjuvant therapy in clearing micrometastatic disease following primary tumor resection.

Apo2L/TRAIL inhibits tumor growth and bone destruction in a murine model of multiple myeloma

PURPOSE

Multiple myeloma is an incurable disease, for which the development of new therapeutic approaches is required. Here, we report on the efficacy of recombinant soluble Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to inhibit tumor progression and bone destruction in a xenogeneic model of human multiple myeloma.

EXPERIMENTAL DESIGN

We established a mouse model of myeloma, in which Apo2L/TRAIL-sensitive RPMI-8226 or KMS-11 cells, tagged with a triple reporter gene construct (NES-HSV-TK/GFP/Luc), were transplanted directly into the tibial marrow cavity of nude mice. Tumor burden was monitored progressively by bioluminescence imaging and the development of myeloma-induced osteolysis was measured using high resolution in vivo micro-computed tomography.

RESULTS

Tumor burden increased progressively in the tibial marrow cavity of mice transplanted with Apo2L/TRAIL-sensitive RPMI-8226 or KMS-11 cells associated with extensive osteolysis directly in the area of cancer cell transplantation. Treatment of mice with recombinant soluble Apo2L/TRAIL reduced myeloma burden in the bone marrow cavity and significantly protected against myeloma-induced osteolysis. The protective effects of Apo2L/TRAIL treatment on bone were mediated by the direct apoptotic actions of Apo2L/TRAIL on myeloma cells within the bone microenvironment.

CONCLUSIONS

This is the first in vivo study that investigates the efficacy of recombinant Apo2L/TRAIL on myeloma burden within the bone microenvironment and associated myeloma-induced bone destruction. Our findings that recombinant soluble Apo2L/TRAIL reduces myeloma burden within the bone microenvironment and protects the bone from myeloma-induced bone destruction argue against an inhibitory role of osteoprotegerin in Apo2L/TRAIL-induced apoptosis in vivo and highlight the need to clinically evaluate Apo2L/TRAIL in patients with multiple myeloma.

Cancer-expanded myeloid-derived suppressor cells induce anergy of NK cells through membrane-bound TGF-beta 1

NK cells, the important effector of innate immunity, play critical roles in the antitumor immunity. Myeloid-derived suppressor cells (MDSC), a population of CD11b(+)Gr-1(+) myeloid cells expanded dramatically during tumor progression, can inhibit T cells and dendritic cells, contributing to tumor immune escape. However, regulation of NK cell innate function by MDSC in tumor-bearing host needs to be investigated. In this study, we found that the function of NK cells from liver and spleen was impaired significantly in all tumor-bearing models, indicating the impairment of hepatic NK cell function by tumor is a universal phenomenon. Then we prepared the orthotopic liver cancer-bearing mice as tumor model to investigate how hepatic NK cells are impaired. We show that down-regulation of NK cell function is inversely correlated with the marked increase of MDSC in liver and spleen. MDSC inhibit cytotoxicity, NKG2D expression, and IFN-gamma production of NK cells both in vitro and in vivo. After incubation with MDSC, NK cells could not be activated to produce IFN-gamma. Furthermore, membrane-bound TGF-beta1 on MDSC is responsible for MDSC-mediated suppression of NK cells. The impaired function of hepatic NK cells in orthotopic liver cancer-bearing mice could be restored by depletion of MDSC, but not regulatory T cells. Therefore, cancer-expanded MDSC can induce anergy of NK cells via membrane-bound TGF-beta1. MDSC, but not regulatory T cells, are main negative regulator of hepatic NK cell function in tumor-bearing host. Our study provides new mechanistic explanations for tumor immune escape.

Cooperation of the agonistic DR5 antibody apomab with chemotherapy to inhibit orthotopic lung tumor growth and improve survival

PURPOSE

Apomab is a fully human monoclonal antibody that induces programmed cell death through the proapoptotic receptor DR5 in various cancer cells but not in normal cells. Several lung cancer cell lines express DR5 and exhibit apoptosis in response to apomab in vitro.

EXPERIMENTAL DESIGN

We investigated the efficacy of apomab and its interaction with chemotherapy in xenograft models based on human NCI-H460 non-small-cell lung carcinoma cells. In an established model of s.c. tumor xenografts, apomab or Taxol plus carboplatin chemotherapy delayed tumor progression, whereas combined treatment caused tumor regression and a substantially longer growth delay. To test apomab activity in a setting that may more closely mimic lung cancer pathology in patients, we developed a lung orthotopic model.

RESULTS

In this model, microcomputed tomography imaging showed that apomab, chemotherapy, or combination treatment significantly inhibited tumor growth compared with vehicle, whereas the combination caused greater inhibition in tumor growth relative to chemotherapy or apomab. Similarly, histologic analysis revealed that apomab, chemotherapy, or the combination significantly reduced tumor size compared with vehicle, whereas the combination induced significantly greater reduction in tumor size than did chemotherapy or apomab. Furthermore, combined treatment improved 105-day survival relative to vehicle (P = 0.0023) as well as to apomab (P = 0.0445) or chemotherapy (P = 0.0415).

CONCLUSION

These results show a positive interaction of apomab with chemotherapy, evidenced by significant inhibition of tumor growth as well as improved survival, thus supporting further investigation of this therapeutic approach in lung cancer patients.

TRAIL receptor signalling and modulation: Are we on the right TRAIL?

Tumour necrosis factor-related apoptosis-inducing ligand or Apo2 ligand (TRAIL/Apo2L) is a member of the tumour necrosis factor (TNF) superfamily of cytokines that induces apoptosis upon binding to its death domain-containing transmembrane receptors, death receptors 4 and 5 (DR4, DR5). Importantly, TRAIL preferentially induces apoptosis in cancer cells while exhibiting little or no toxicity in normal cells. To date, research has focused on the mechanism of apoptosis induced by TRAIL and the processes involved in the development of TRAIL resistance. TRAIL-resistant tumours can be re-sensitized to TRAIL by a combination of TRAIL with chemotherapeutics or irradiation. Studies suggest that in many cancer cells only one of the two death-inducing TRAIL receptors is functional. These findings as well as the aim to avoid decoy receptor-mediated neutralization of TRAIL led to the development of receptor-specific TRAIL variants and agonistic antibodies. These molecules are predicted to be more potent than native TRAIL in vivo and may be suitable for targeted treatment of particular tumours. This review focuses on the current status of TRAIL receptor-targeting for cancer therapy, the apoptotic signalling pathway induced by TRAIL receptors, the prognostic implications of TRAIL receptor expression and modulation of TRAIL sensitivity of tumour cells by combination therapies. The mechanisms of TRAIL resistance and the potential measures that can be taken to overcome them are also addressed. Finally, the status of clinical trials of recombinant TRAIL and DR4-/DR5-specific agonistic antibodies as well as the pre-clinical studies of receptor-selective TRAIL variants is discussed including the obstacles facing the use of these molecules as anti-cancer therapeutics.

Butein sensitizes human leukemia cells to apoptosis induced by tumor necrosis factor-related apoptosis inducing ligand (TRAIL)

Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) therapy is frequently encountered, requiring combined treatments with sensitizing agents. It is, therefore, important to find nontoxic drugs which can be used together with TRAIL. In this study, we investigated natural compounds that can overcome resistance to TRAIL, and found that butein, a polyphenol, exhibits significant synergism with TRAIL. Treatment with TRAIL in combination with subtoxic concentrations of butein sensitizes TRAIL-resistant human leukemia U937 cells to apoptosis. Butein increased caspase-3 activity and expression of death receptor DR5. The apoptotic cell death induced by combined treatment was significantly reduced by z-DEVD-fmk, a caspase-3 inhibitor, suggesting a critical role of caspase-3 in apoptosis. These results indicate that butein sensitizes TRAIL-resistant U937 cells to TRAIL-induced apoptosis in a caspase-3 dependent manner which might be correlated with upregulation of death receptor DR5. Our data suggests that combined treatment with butein and TRAIL may provide a safe and effective strategy for treating cancer.

Synergism of CPT-11 and Apo2L/TRAIL against two differentially sensitive human colon tumor xenografts

OBJECTIVE

The ability to sustain and grow portions of human tumors as xenografts in SCID mice provides a valuable preclinical opportunity to test the response of human tumors to treatments, both individually and in combination. Using this model, our laboratory has previously demonstrated that the growth of several human adenocarcinomas can be inhibited by Apo2L/TRAIL. Apo2L/TRAIL triggers apoptosis in many types of tumor cells, and when combined with various chemotherapeutic agents results in enhanced inhibition of tumor growth in many xenograft models.

METHODS

To gain further insight into the antitumor potential of Apo2L/TRAIL in combination with chemotherapy, we compared the responses of 2 human colon adenocarcinomas, both of which were sensitive to CPT-11 while one was sensitive and the other comparatively resistant to Apo2L/TRAIL.

RESULTS

In both cases, a greater degree of growth inhibition was achieved when these agents were used in combination. Western blot analysis demonstrated that in the Apo2L/TRAIL-sensitive tumor total cellular expression of Apo2L/TRAIL death receptors (DR4 and DR5) as well as protein expression of the pro-apoptotic molecule BAX were higher and the anti-apoptotic molecule Bcl-2 was lower in comparison to the Apo2L/TRAIL-resistant tumor.

CONCLUSION

These results indicate that both Apo2L/TRAIL-sensitive and -resistant colon tumors will respond to a combination of CPT-11 and Apo2L/TRAIL and predict that this will be useful in the treatment of human colon cancers in a clinical setting.

Ligand-based targeting of apoptosis in cancer: the potential of recombinant human apoptosis ligand 2/Tumor necrosis factor-related apoptosis-inducing ligand (rhApo2L/TRAIL)

Cancer is a leading cause of premature human death and commands considerable research attention. Apoptosis (type 1 programmed cell death) is critical in maintaining tissue homeostasis in metazoan organisms, and its dysregulation underpins the initiation and progression of cancer. Conventional chemotherapy and radiotherapy can induce apoptosis as a secondary consequence of inflicting cell damage. However, more direct and selective strategies to manipulate the apoptotic process in cancer cells are emerging as potential therapeutic tools. Genetic and biochemical understanding of the cellular signaling mechanisms that control apoptosis has increased substantially during the last decade. These advances provide a strong scientific framework for developing several types of targeted proapoptotic anticancer therapies. One promising class of agents is the proapoptotic receptor agonists. Of these, recombinant human apoptosis ligand 2/tumor necrosis factor-related apoptosis-inducing ligand (rhApo2L/TRAIL)-an optimized soluble form of an endogenous apoptosis-inducing ligand-is unique in that it activates two related proapoptotic receptors, DR4 and DR5. Preclinical data indicate that rhApo2L/TRAIL can induce apoptosis in a broad range of human cancer cell lines while sparing most normal cell types. In vitro, and in various in vivo tumor xenograft models, rhApo2L/TRAIL exhibits single-agent antitumor activity and/or cooperation with certain conventional and targeted therapies. Preclinical safety studies in nonhuman primates show rhApo2L/TRAIL to be well tolerated. Moreover, early clinical trial data suggest that rhApo2L/TRAIL is generally safe and provide preliminary evidence for potential antitumor activity. Clinical studies are ongoing to assess the safety and efficacy of this novel agent in combination with established anticancer therapies.

To kill a tumor cell: the potential of proapoptotic receptor agonists

Disturbances in mechanisms that direct abnormal cells to undergo apoptosis frequently and critically contribute to tumorigenesis, yielding a logical target for potential therapeutic intervention. There is currently heightened interest in the extrinsic apoptosis pathway, with several proapoptotic receptor agonists (PARAs) in development. The PARAs include the ligand recombinant human Apo2L/TRAIL and agonistic mAbs. Mechanistic and preclinical data with Apo2L/TRAIL indicate exciting opportunities for synergy with conventional therapies and for combining PARAs with other molecularly targeted agents. Novel molecular biomarkers may help identify those patients most likely to benefit from PARA therapy.

ABT-737 induces expression of the death receptor 5 and sensitizes human cancer cells to TRAIL-induced apoptosis

Because Bcl-2 family members inhibit the ability of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to induce apoptosis, we investigated whether ABT-737, a small molecule Bcl-2 inhibitor, enhances TRAIL killing. We demonstrate that a combination of ABT-737 and TRAIL induced significant cell death in multiple cancer types, including renal, prostate, and lung cancers, although each agent individually had little activity in these tumor cells. All of these cell lines expressed the Mcl-1 protein that is known to block the activity of ABT-737 and TRAIL but did not block the synergy between these agents. However, Bax-deficient cell lines, including DU145 and HCT116 cells and those cell lines expressing low levels of TRAIL receptor, were resistant to apoptosis induced by these agents. To understand how ABT-737 functions to markedly increase TRAIL sensitivity, the levels of specific death-inducing signaling complex components were evaluated. Treatment with ABT-737 did not change the levels of c-FLIP, FADD, and caspase-8 but up-regulated the levels of the TRAIL receptor DR5. DR5 up-regulation induced by ABT-737 treatment occurred through a transcriptional mechanism, and mutagenesis studies demonstrated that the NF-kappaB site found in the DR5 promoter was essential for the ability of ABT-737 to increase the levels of this mRNA. Using luciferase reporter plasmids, ABT-737 was shown to stimulate NF-kappaB activity. Together, these results demonstrate that the ability of ABT-737 and TRAIL to induce apoptosis is mediated through activation of both the extrinsic and intrinsic pathways. Combinations of ABT-737 and TRAIL can be exploited therapeutically where antiapoptotic Bcl-2 family members drive tumor cell resistance to current anticancer therapies.

Targeting the extrinsic apoptosis pathway in cancer

Mutational inactivation of the p53 tumor-suppressor gene, which regulates apoptosis mainly via the cell-intrinsic pathway, reduces the sensitivity of many cancers to conventional treatments. Targeting the cell-extrinsic pathway, which triggers p53-independent apoptosis, offers a unique therapeutic strategy to induce apoptosis in cancer cells. This article focuses on two proapoptotic receptor agonists, recombinant human Apo2-ligand/TNF-related apoptosis-inducing ligand (rhApo2L/TRAIL) and Apomab, which activate death receptor (DR) 4 and/or DR5, thus stimulating the cell-extrinsic pathway. These agents are under investigation for the treatment of solid tumor and hematologic malignancies. Preclinical data indicate that both molecules cause significant regression or growth inhibition of malignant tumors without significant toxicity. Initial data on rhApo2L/TRAIL and Apomab from phase 1 safety trials also confirm that these agents are suitable for further clinical investigation.

P53-mediated upregulation of DcR1 impairs oxaliplatin/TRAIL-induced synergistic anti-tumour potential in colon cancer cells

Oxaliplatin has emerged as a major chemotherapeutic drug in the treatment of advanced colorectal cancer, yet like most conventional cancer therapeutics, its efficacy is often compromised due to p53 mutations. Unlike oxaliplatin, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in a p53-independent manner, and chemotherapy is known to overcome tumour resistance to TRAIL-induced cell death in most cancer cells. Using a panel of colon cancer cell lines, we assessed the ability of oxaliplatin to sensitize to TRAIL-induced apoptosis. We demonstrate that while both drugs additively or synergistically induced apoptosis in almost all cell lines tested, p53 wild-type colon cancer cells such as HCT116, LS513 or LS174T remained resistant. Impaired TRAIL-induced cell death resulted from a strong p53 dependent, oxaliplatin-mediated, DcR1 receptor expression increase. According to our finding, downregulation of DcR1 using siRNA, in p53 wild-type colon cancer cells, restored oxaliplatin/TRAIL synergistic apoptotic activity. On the contrary, exogenous DcR1 overexpression in SW480, a p53-mutated cell line, abolished the synergy between the two drugs. Altogether we demonstrate for the first time that p53 negatively regulates oxaliplatin-mediated TRAIL-induced apoptotic activity through DcR1 upregulation. Our findings could have important implications for future therapeutic strategies, and suggest that the association oxaliplatin/TRAIL should be restricted to patients harbouring a non-functional p53 protein.

TRAIL and cancer therapy

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors are promising targets for the selective eradication of tumor cells while sparing normal cells. Currently, both recombinant TRAIL proteins and TRAIL receptor agonistic antibodies are being tested in the clinic, showing encouraging antitumor activities and mild side effects. Unfortunately, resistance to TRAIL therapy is frequently encountered requiring combined treatments with sensitizing agents. Standard chemotherapeutics can enhance TRAIL sensitivity; however, more specific and less toxic agents are needed to exploit the full antitumor potential of TRAIL. Here, a brief overview of the TRAIL signaling pathway is given together with a short description of early results obtained with TRAIL therapy in the clinic. Mechanisms of TRAIL resistance and ways to overcome these by targeted agents that either neutralize apoptotic blockades or suppress prosurvival signals also triggered by TRAIL are highlighted, such as inhibitors of IAPs, Bcl-2 family members, HDACi, and modulators of NF-kappaB, Raf and EGFR signaling.

Resistance to FasL and tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis in Sezary syndrome T-cells associated with impaired death receptor and FLICE-inhibitory protein expression

Because of the low proliferative potential of tumor cells in patients with Sézary syndrome (SzS), their accumulation has been suggested to be due to defective regulation of apoptosis. We analyzed the sensitivity to soluble Fas-ligand (FasL) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), 2 members of the TNF superfamily in peripheral blood leukocytes (PBL) from patients with SzS. Compared with healthy donors, CD4(+) cells from patients with SzS were completely resistant to FasL in 9 of 16 cases. Of these 9 FasL-resistant cases, 4 revealed a loss in Fas (CD95) expression, whereas the remaining 5 exhibited normal or enhanced Fas expression. In the latter 5 cases, the apoptosis inhibitor cFLIP was overexpressed in CD4(+)/CD26(-) tumor cells compared with CD4(+)/CD26(-) cells from Fas-expressing FasL-sensitive patients and healthy donors. Furthermore, resistance to TRAIL and tumor cell-restricted loss of TRAIL-receptor 2 were observed in 16 of 16 SzS PBLs. It is noteworthy that resistance to FasL could be overcome by the use of a hexameric FasL or upon exposure of SzS cells to interferon-alpha (IFN-alpha) or IFN-gamma, the latter by an increase of Fas expression. Our data on primary SzS lymphocytes reveal frequent resistance to apoptosis induced by FasL and TRAIL, which may contribute to their accumulation in patients with SzS and be relevant at a therapeutic level.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its therapeutic potential in breast and gynecologic cancers

OBJECTIVE

The relationship between the apoptotic pathway and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising area of scientific interest for cancer researchers. TRAIL-receptor-activating agents have demonstrated favorable in vitro and in vivo activity for the treatment of several malignancies including breast and gynecologic cancers.

METHODS

This article reviews the available peer-reviewed literature and our own institution's experience with specific TRAIL-receptor-activating agents. Emphasis was placed on the apoptotic/TRAIL mechanism, preclinical evaluation, and phase I studies in various malignancies.

RESULTS

Preclinical and early phase I studies indicate that these novel agents are safe with enhanced target specificity for malignancy. When these targeted agents are combined with conventional chemotherapy drugs or radiation therapy, they appear to increase cell death over single-agent modalities.

CONCLUSIONS

TRAIL-receptor-activating agents represent an exciting new class of targeted therapies that hold promise to improve the treatment of women with breast and gynecologic malignancies.

Lipid rafts and nonrafts mediate tumor necrosis factor related apoptosis-inducing ligand induced apoptotic and nonapoptotic signals in non small cell lung carcinoma cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is capable of inducing apoptosis in non-small cell lung carcinoma (NSCLC). However, many of the human NSCLC cell lines are resistant to TRAIL, and TRAIL treatment of the resistant cells leads to the activation of nuclear factor-kappaB (NF-kappaB) and extracellular signal-regulated kinase 1/2 (ERK1/2). TRAIL can induce apoptosis in TRAIL-sensitive NSCLC cells through the induction of death-inducing signaling complex (DISC) assembly in lipid rafts of plasma membrane. In the DISC, caspase-8 is cleaved and initiates TRAIL-induced apoptosis. In contrast, TRAIL-DISC assembly in the nonraft phase of the plasma membrane leads to the inhibition of caspase-8 cleavage and NF-kappaB and ERK1/2 activation in TRAIL-resistant NSCLC cells. Receptor-interacting protein (RIP) and cellular Fas-associated death domain-like interleukin-1beta-converting enzyme-inhibitory protein (c-FLIP) mediates the DISC assembly in nonrafts and selective knockdown of either RIP or c-FLIP with interfering RNA redistributes the DISC from nonrafts to lipid rafts, thereby switching the DISC signals from NF-kappaB and ERK1/2 activation to caspase-8-initiated apoptosis. Chemotherapeutic agents inhibit c-FLIP expression, thereby enhancing the DISC assembly in lipid rafts for caspase-8-initiated apoptosis. These studies indicate that RIP and c-FLIP-mediated assembly of the DISC in nonrafts is a critical upstream event in TRAIL resistance and thus targeting of either RIP or c-FLIP may lead to the development of novel therapeutic strategies that can overcome TRAIL resistance in human NSCLC.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway signaling

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/Apo1L is a death ligand, a cytokine that activates apoptosis through cell surface death receptors. TRAIL is thought to be important in host tumor surveillance and metastasis suppression, and various therapeutic agonists that activate TRAIL receptors to induce tumor cell apoptosis are in clinical development. This review discusses recent findings about TRAIL pathway signaling and relates the signaling mechanisms to issues that need to be considered as we try to manipulate TRAIL signaling to treat cancer.

The Potential of Death Receptor 4– and 5–Directed Therapies in the Treatment of Lung Cancer

Aberrations of the intracellular apoptotic balance--reducing proapoptotic signaling and increasing antiapoptotic signaling--are common in cancer cells. Increasing apoptosis through the direct manipulation of the apoptotic machinery offers novel anticancer strategies. Of the 2 main interacting proapoptotic pathways, the extrinsic pathway is characterized by ligand dependent stimulation of cell surface death receptor (DRs). Recombinant ligand and agonistic monoclonal antibodies directed against the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors, DR 4 (TRAIL-R1) and/or DR 5 (TRAIL-R2), are now being explored within clinical trials. These agents appear well tolerated with hints of single-agent activity in lymphoma, colorectal cancer, chondrosarcoma, and non-small-cell lung cancer. Numerous molecular factors influencing sensitivity or resistance have been identified in vitro, but the determinants of clinical benefit remain unclear. Preclinically, synergy with cytotoxic chemotherapy and radiation therapy is well documented, with DR4/5 stimulation helping to tip the intracellular processing of multiple stimuli in favor of cell death. Provided that a wide therapeutic margin relative to normal cells can be maintained, maximizing apoptotic responses to standard treatments through DR4/5-directed therapy, with or without additional blockade of antiapoptotic signaling, has considerable potential in the treatment of lung cancer. Trials of DR4/5-directed therapies in combination with standard first-line chemotherapy for non-small-cell lung cancer are under way.

Enhancement of Apo2L/TRAIL-mediated cytotoxicity in esophageal cancer cells by cisplatin

Although expressing adequate levels of functional tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR4/DR5, significant proportion of cancer cells exhibit resistance to the cytotoxic effect of this ligand. Exposure of Apo2L/TRAIL-refractory cancer cells to cytotoxic chemotherapeutic agents enhances their sensitivity to Apo2L/TRAIL cytotoxicity. This study aims to elucidate the molecular mechanism responsible for the cisplatin-mediated enhancement of Apo2L/TRAIL sensitivity in cultured esophageal cancer cells. Exposure of cancer cells to sublethal concentrations of cisplatin resulted in profound potentiation of their susceptibility to Apo2L/TRAIL cytotoxicity as indicated by 2- to >20-fold reduction in Apo2L/TRAIL IC50 values. Significant activation of caspase-8, caspase-9, and caspase-3 was observed only in cells treated with cisplatin/Apo2L/TRAIL combination and not in those exposed to either agent alone. More importantly, activation of these key caspases was significantly abrogated by overexpression of Bcl2 or by the selective caspase-9 inhibitor. This observation strongly suggested that caspase-8 activation in cells treated with the cisplatin/Apo2L/TRAIL combination was secondary to the mitochondria-mediated amplification feedback loop and activation of the executioner caspase-3 was dependent on the recruitment of the intrinsic pathway characteristic of the type II cell. Profound combination-mediated cytotoxicity and induction of apoptosis was completely suppressed either by Bcl2 overexpression or by inhibition of caspase-9 activity, which conclusively pointed to the essential role of the mitochondria-dependent death signaling cascade in this process. Cisplatin sensitizes esophageal cancer cells to Apo2L/TRAIL cytotoxicity by potentiation of the mitochondria-dependent death signaling pathway that leads to amplification of caspase activation, particularly caspase-8, by the feedback loop to efficiently induce apoptosis.

Doxorubicin enhances TRAIL-induced cell death via ceramide-enriched membrane platforms

Previous studies indicated that signalling via CD95 and DR5 is greatly enhanced by the formation of ceramide-enriched membrane platforms. Here, we employed this concept to convert doses of subtherapeutic TRAIL that were unable to release ceramide and kill leukemic B-cells or ex vivo T lymphocytes, into a very effective apoptotic stimulus. Ceramide production was induced by application of sub-toxic doses of doxorubicin that resulted in an activation of the acid sphingomyelinase (ASM), release of ceramide and formation of ceramide-enriched membrane platforms. The latter served DR5 to cluster after application of very low doses of TRAIL in combination with doxorubicin. Genetic deficiency of the ASM abrogated doxorubicin-induced ceramide release, as well as clustering of DR5 and apoptosis induced by the combined treatment of doxorubicin and TRAIL. These data show that local release of ceramide potentiates very low, otherwise inactive doses of TRAIL that may represent a novel therapeutic concept to treat tumors.

Expression of anti-apoptotic factors modulates Apo2L/TRAIL resistance in colon carcinoma cells

Tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) selectively induces apoptosis in transformed cells. Normal cells and certain tumor cells can evade Apo2L/TRAIL induced cell death, but the determinants of Apo2L/TRAIL sensitivity are poorly understood. To better understand the factors that contribute to Apo2L/TRAIL resistance, we characterized two colon carcinoma lines with pronounced differences in Apo2L/TRAIL sensitivity. Colo205 cells are highly sensitive to Apo2L/TRAIL whereas Colo320 cells are unresponsive. Components of the DISC (death inducing signaling complex) could be immunoprecipitated from both cell lines in response to Apo2L/TRAIL. Sensitizing agents including a proteasome inhibitor conferred Apo2L/TRAIL sensitivity in Colo320 cells, indicating that the apoptotic machinery was intact and functional. We specifically suppressed the expression of Bcl-2, FLIP or XIAP in Colo320 cells. Downregulation of either FLIP or XIAP but not Bcl-2 restored sensitivity of Colo320 cells to Apo2L/TRAIL. Moreover, stable knockdown of XIAP expression in Colo320 subcutaneous tumors resulted in suppression of tumor growth and sensitivity to Apo2L/TRAIL in vivo. Our results indicate that only a specific subset of anti-apoptotic proteins can confer resistance to Apo2L/TRAIL in Colo320 cells. Elucidation of the factors that contribute to Apo2L/TRAIL resistance in tumor cells may provide insight into combination therapies with Apo2L/TRAIL in a clinical setting.

MG-132 Sensitizes TRAIL-Resistant Prostate Cancer Cells by Activating c-Fos/c-Jun Heterodimers and Repressing c-FLIP(L)

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent because it induces apoptosis in cancer cells but not in normal cells. Unfortunately, some cancer cells develop resistance to TRAIL-induced apoptosis. Therefore, it is clinically relevant to determine the molecular mechanisms that differentiate between TRAIL-sensitive and TRAIL-resistant tumors. Previously, we have shown that the antiapoptotic molecule cellular-FLICE-inhibitory protein long isoform [c-FLIP(L)] is necessary and sufficient to maintain resistance to TRAIL-induced apoptosis. We have found that c-FLIP(L) is transcriptionally regulated by the activator protein-1 (AP-1) family member protein c-Fos. Here, we report that MG-132, a small-molecule inhibitor of the proteasome, sensitizes TRAIL-resistant prostate cancer cells by inducing c-Fos and repressing c-FLIP(L). c-Fos, which is activated by MG-132, negatively regulates c-FLIP(L) by direct binding to the putative promoter region of the c-FLIP(L) gene. In addition to activating c-Fos, MG-132 activates another AP-1 family member, c-Jun. We show that c-Fos heterodimerizes with c-Jun to repress transcription of c-FLIP(L). Therefore, MG-132 sensitizes TRAIL-resistant prostate cancer cells by activating the AP-1 family members c-Fos and c-Jun, which, in turn, repress the antiapoptotic molecule c-FLIP(L).

TRAIL receptor-targeted therapy

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family of cytokines. Based on its ability to induce apoptosis selectively in a wide variety of cancer cell lines and human tumor xenografts, TRAIL has been in drug development as a potential biological agent for cancer therapy. A variety of chemotherapy agents have been shown to enhance the cytotoxic effects of TRAIL. The potential benefits of TRAIL as an anticancer therapy have been further indicated by its ability to enhance the efficacy of radiotherapy. Preclinical studies have shown the potential use of agonistic monoclonal antibodies that selectively bind TRAIL death receptors for cancer therapy. This review provides an overview of TRAIL receptor-mediated apoptosis of tumor cells, with TRAIL or agonistic monoclonal antibodies only or with chemotherapy drugs. Treatment of tumor xenografts with these ligands, alone or in combination with chemotherapy or radiation, are discussed along with preliminary information about early clinical trials. Additional clinical trials with TRAIL receptor ligands in combination treatment regimens are required to determine their potential for targeted therapy of cancer.

Development of an orthotopic transplantation model in nude mice that simulates the clinical features of human lung cancer

The objective of the present study was to establish an orthotopic tumor transplantation model in nude mice that closely resembles the clinical features of human lung cancer. The human lung adenocarcinoma A549 cell line and the squamous cell carcinoma SQ5 cell line were used. Tumor cells suspended in serum-free medium were injected directly into the main bronchi of anesthetized female Balb/c athymic nude mice (7-9 weeks old) with or without simultaneous administration of 0.01 M ethylenediaminetetracetic acid (EDTA). In some experiments, lung carcinoma cells harvested from tumors transplanted subcutaneously were recultured and used for intratracheal implantation. Tumor nodules that formed in the lung were counted and confirmed by histological examination. Administration of A549 cells with EDTA resulted in a 70% engraftment rate (n = 10). Recultured A549 cells without and with EDTA resulted in 20% (n = 5) and 80% (n = 5) engraftment rates, respectively. Administration of SQ5 cells without or with EDTA formed 50% (n = 4) and 67% (n = 6) engraftment rates, respectively. Recultured SQ5 cells with EDTA further increased the engraftment rate to 100% (n = 6). Multiple tumors formed mainly in the left lung and the upper lobe of the right lung. Simultaneous administration of EDTA resulted in greater numbers of tumor nodules in the lung. Histological findings revealed that A549 tumor nodules were distributed primarily in alveoli. The SQ5 solid tumors invaded bronchioles and occupied the alveoli. This reproducible orthotopic transplantation model produced tumor growth that simulated the clinical features of human lung cancer.

Anti-idiotype antibody induced cellular immunity in mice transgenic for human carcinoembryonic antigen

In the present study, we have analysed the detailed cellular immune mechanisms involved in tumour rejection in carcinoembryonic antigen (CEA) transgenic mice after immunization with dendritic cells (DC) pulsed with an anti-idiotype (Id) antibody, 3H1, which mimics CEA. 3H1-pulsed DC vaccinations resulted in induction of CEA specific cytotoxic T lymphocyte (CTL) responses in vitro and the rejection of CEA-transfected MC-38 murine colon carcinoma cells, C15, in vivo (Saha et al.,Cancer Res 2004; 64: 4995-5003). These CTL mediated major histocompatibility complex (MHC) class I-restricted tumour cell lysis, production of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), and expression of Fas ligand (FasL) and TNF-related apoptosis-inducing ligand (TRAIL) in response to C15 cells. CTL used perforin-, FasL-, and TRAIL-mediated death pathways to lyse C15 cells, although perforin-mediated killing was the predominant lytic mechanism in vitro. The cytokines IFN-gamma and TNF-alpha synergistically enhanced surface expression of Fas, TRAIL receptor, MHC class I and class II on C15 cells that increased the sensitivity of tumour cells to CTL lysis. CTL activity generated in 3H1-pulsed DC immunized mice was directed against an epitope defined by the idio-peptide LCD-2, derived from 3H1. In vivo lymphocyte depletion experiments demonstrated that induction of CTL response and antitumour immunity was dependent on both CD4+ and CD8+ T cells. The analysis of splenocytes of immunized mice that had rejected C15 tumour growth revealed up-regulated surface expression of memory phenotype Ly-6C and CD44 on both CD4+ and CD8+ T cells. The adoptive transfer experiments also suggested the role of both CD4+ and CD8+ T cells in this model system. Furthermore, mice that had rejected C15 tumour growth, developed tumour-specific immunological memory.

Valproic acid, an antiepileptic drug with histone deacetylase inhibitory activity, potentiates the cytotoxic effect of Apo2L/TRAIL on cultured thoracic cancer cells through mitochondria-dependent caspase activation

Inhibitors of histone deacetylases have been shown to enhance the sensitivity of cancer cells to tumor necrosis factor-related apoptosis-inducing ligand TRAIL-mediated cytotoxicity. Valproic acid (VA), a commonly used antiepileptic agent whose pharmacokinetics and toxicity profiles are well described, is a histone deacetylase inhibitor. This project aims to evaluate if VA can potentiate Apo2L/TRAIL-mediated cytotoxicity in cultured thoracic cancer cells and to elucidate the underlying molecular mechanism responsible for this effect. VA sensitized cultured thoracic cancer cells to Apo2L/TRAIL, as indicated by a 4-fold to a >20-fold reduction of Apo2L/TRAIL IC50 values in combination-treated cells. Although VA (0.5-5 mM) or Apo2L/TRAIL (20 ng/ml) induced less than 20% cell death, VA + Apo2L/TRAIL combinations caused 60% to 90% apoptosis of cancer cells. Moreover, substantial activation of caspases 8, 9, and 3, which was observed only in cells treated with the drug combination, was completely suppressed by Bcl2 overexpression or by the caspase 9 inhibitor. Both the caspase 9 inhibitor and Bcl2 completely abrogated the substantial cytotoxicity and apoptosis induced by this combination, thus highlighting the pivotal role of the type II pathway in this process. These findings provide a rationale for the development of VA and Apo2L/TRAIL combination as a novel molecular therapeutic for thoracic cancers.

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.

The Essential Role of the Mitochondria-Dependent Death-Signaling Cascade in Chemotherapy-Induced Potentiation of Apo2L/TRAIL Cytotoxicity in Cultured Thoracic Cancer Cells

PURPOSE

Despite adequately expressing functional receptors for tumor necrosis factor receptor apoptosis-inducing ligand (TRAIL), many cultured tumor cells are refractory to the cytotoxic effect of this ligand. Cytotoxic chemotherapeutic drugs have been shown to synergize with Apo2L/TRAIL to mediate apoptosis in cancer cells. The main goal of this study was to evaluate the effect of either cisplatin or paclitaxel, two common used chemotherapeutic agents for solid tumors, on enhancing Apo2L/TRAIL cytotoxicity in a panel-cultured thoracic cancer cells and to examine the role of the mitochondria-dependent caspase activation cascade in mediating apoptosis of combination-treated cells.

METHODS

Cultured thoracic cancer cells were treated with cisplatin/Apo2L/TRAIL or paclitaxel/Apo2L/TRAIL sequential combinations in vitro. Cell viability and apoptosis were determined by 4,5-dimethylthiazo-2-yl)-2,5-diphenyl tetrazolium bromide and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assays. Stable transfectants expressing high levels of Bcl-2 were created by retroviral gene transfer. Specific proteolytic activity of caspases 3, 6, 8, and 9 were measured by commercially available kits using fluorescent substrates.

RESULTS

All cell lines preferentially expressed high levels of DR4 and/or DR5 and low levels of DcR1/DcR2; all of which were not altered by chemotherapeutic drug treatments. Pretreatment of these cancer cells with sublethal concentrations of either cisplatin or paclitaxel increased their susceptibility to Apo2L/TRAIL by twofold to >20-fold. Profound synergistic induction of apoptosis was observed in combination-treated cells. Viability of primary normal cells was affected by neither Apo2L/TRAIL nor the combinations of chemotherapy and Apo2L/TRAIL. Overexpression of Bcl-2 or inhibition of caspase 9 activity completely abrogated combination-induced cytotoxicity and apoptosis, indicating the essential role of the mitochondria-dependent death signaling cascade in this process. Robust activation of caspase 8 in combination-treated cells was completely suppressed either by Bcl-2 overexpression or by blocking of the activity of the mitochondria-regulated caspase 9, thus identifying the amplification feedback loop as the source of elevated caspase 8 activity. Finally, mitochondria-mediated amplification of caspase 8 activity was indispensable for complete caspase activation and full execution of apoptosis, because suppression of its activity using the selective caspase 6 inhibitor (located downstream of the caspase 3 but upstream of the caspase 8 in the feedback loop) resulted in profound suppression of not only caspase 8 activity but also those of caspases 9 and 3, as well as complete protection of cancer cells from combination-induced cytotoxicity.

CONCLUSION

Cisplatin or paclitaxel synergistically interacts with Apo2L/TRAIL to mediate profound induction of apoptosis. The mitochondria-dependent caspase activation cascade and the amplification feedback loop are essential for the complete execution of the cell death program. Furthermore, our data identify mitochondria as the direct target for the development of more refined strategies to enhance the therapeutic effect of Apo2L/TRAIL as an anticancer agent.

Apo2l/Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand Prevents Breast Cancer–Induced Bone Destruction in a Mouse Model

Breast cancer is the most common carcinoma that metastasizes to bone. To examine the efficacy of recombinant soluble Apo2 ligand (Apo2L)/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) against breast cancer growth in bone, we established a mouse model in which MDA-MB-231 human breast cancer cells were transplanted directly into the marrow cavity of the tibiae of athymic nude mice producing osteolytic lesions in the area of injection. All vehicle-treated control animals developed large lesions that established in the marrow cavity, eroded the cortical bone, and invaded the surrounding soft tissue, as assessed by radiography, micro-computed tomography, and histology. In contrast, animals treated with recombinant soluble Apo2L/TRAIL showed significant conservation of the tibiae, with 85% reduction in osteolysis, 90% reduction in tumor burden, and no detectable soft tissue invasion. Tumor cells explanted from Apo2L/TRAIL-treated animals were significantly more resistant to the effects of Apo2L/TRAIL when compared with the cells explanted from the vehicle-treated control animals, suggesting that prolonged treatment with Apo2/TRAIL in vivo selects for a resistant phenotype. However, such resistance was readily reversed when Apo2L/TRAIL was used in combination with clinically relevant chemotherapeutic drugs, including taxol, etoposide, doxorubicin, cisplatin, or the histone deacetylase inhibitor suberoylanilide hydroxamic acid. These studies show for the first time that Apo2L/TRAIL can prevent breast cancer-induced bone destruction and highlight the potential of this ligand for the treatment of metastatic breast cancer in bone.

Can targeting apoptosis resolve the cancer saga?

A defect in apoptosis is almost always linked to many pathologies, including cancer. Carcinogenesis has been linked to abnormalities in the apoptotic pathway, and many drugs that are targeted at different parts of this pathway are being developed. There have been many promising drugs that target the extrinsic death receptor pathway as well as the intrinsic mitochondrial apoptotic pathway. There have also been developments in targeting initiator and effector caspases, as well as the death domains that are involved in transducing the apoptotic signals. In this review, the authors will briefly explain how apoptosis deregulation can lead to cancer and discuss drugs that promise success in targeting this anomaly. This article shall also explain how co-treatments with chemotherapy can increase survival of cancer patients. There is a problem of acquired resistance in some of these therapies but there may be ways to overcome this.

Chemotherapy and TRAIL-mediated colon cancer cell death: the roles of p53, TRAIL receptors, and c-FLIP

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has recently attracted attention as a potential therapeutic agent in the treatment of cancer. We assessed the roles of p53, TRAIL receptors, and cellular Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitory protein (c-FLIP) in regulating the cytotoxic effects of recombinant TRAIL (rTRAIL) alone and in combination with chemotherapy [5-fluorouracil (5-FU), oxaliplatin, and irinotecan] in a panel of colon cancer cell lines. Using clonogenic survival and flow cytometric analyses, we showed that chemotherapy sensitized p53 wild-type, mutant, and null cell lines to TRAIL-mediated apoptosis. Although chemotherapy treatment did not modulate mRNA or cell surface expression of the TRAIL receptors death receptor 4, death receptor 5, decoy receptor 1, or decoy receptor 2, it was found to down-regulate expression of the caspase-8 inhibitor, c-FLIP. Stable overexpression of the long c-FLIP splice form but not the short form was found to inhibit chemotherapy/rTRAIL-induced apoptosis. Furthermore, siRNA-mediated down-regulation of c-FLIP, particularly the long form, was found to sensitize colon cancer cells to rTRAIL-induced apoptosis. In addition, treatment of a 5-FU-resistant cell line with 5-FU down-regulated c-FLIP expression and sensitized the chemotherapy-resistant cell line to rTRAIL. We conclude that TRAIL-targeted therapies may be used to enhance conventional chemotherapy regimens in colon cancer regardless of tumor p53 status. Furthermore, inhibition of c-FLIP may be a vital accessory strategy for the optimal use of TRAIL-targeted therapies.

Targeted induction of apoptosis in cancer management: the emerging role of tumor necrosis factor-related apoptosis-inducing ligand receptor activating agents

Targeted induction of programmed cell death or apoptosis via the extrinsic apoptotic pathway represents an unexploited therapeutic strategy to destroy cancer cells. The activation of cell surface receptors by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) results in direct stimulation of apoptotic signaling pathways (extrinsic stimulation). Molecules that directly activate these receptors, such as agonistic monoclonal antibodies to the TRAIL receptors and recombinant TRAIL, are being developed as monotherapies and as part of combination therapies with existing chemotherapeutic drugs and other therapeutic modalities. This article examines the TRAIL receptors as potential targets for activating the TRAIL-mediated apoptosis pathway and presents the current status of novel therapeutics that exploit this pathway, particularly focusing on agonistic monoclonal antibodies to the TRAIL receptors. The preclinical activity, the status of ongoing evaluations, and the potential clinical impact of these novel agents are reviewed.

Anti-tumor activity of TRA-8 anti-death receptor 5 (DR5) monoclonal antibody in combination with chemotherapy and radiation therapy in a cervical cancer model

OBJECTIVES

There is substantial evidence that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) causes apoptosis via activation of death receptors 4 and 5 (DR4 and DR5). We sought to determine the therapeutic potential of TRA-8 (anti-DR5 monoclonal antibody) in combination with chemotherapy and radiation therapy in a cervical cancer model.

METHODS

DR5 expression in 7 human cervical cancer cell lines was analyzed by indirect immunofluorescence using murine TRA-8 in combination with flow cytometry. Cell lines were treated with TRA-8 alone or in combination with cisplatin, topotecan, or radiation, and cytotoxicity assays were performed. Mice were inoculated with ME-180 cancer cells and treated with different combinations of therapy. Animals receiving antibody were injected intraperitoneally with 200 microg of TRA-8. Animals received 9 Gy 60Co radiation divided into 3 fractions and 3 intraperitoneal doses of cisplatin (6 mg/kg) 1 h before radiation. A similar experiment was performed using topotecan (2 mg/kg) as the chemotherapeutic agent.

RESULTS

DR5 was expressed to a varying degree on the cervical cancer cell lines. Combination treatment with TRA-8 and chemotherapy or radiation resulted in synergistic cytotoxicity in vitro. In vivo, combination therapy with TRA-8, cisplatin, and radiation produced tumor growth inhibition that was significantly greater than the other groups. Similar results were seen in combination studies with topotecan.

CONCLUSIONS

These data suggest that DR5 is a good target for activation of the apoptotic pathway. Monoclonal antibodies such as TRA-8 may play an important role in the development of an effective treatment strategy for patients with advanced cervical cancer.

Promoting apoptosis as a strategy for cancer drug discovery

Apoptosis is deregulated in many cancers, making it difficult to kill tumours. Drugs that restore the normal apoptotic pathways have the potential for effectively treating cancers that depend on aberrations of the apoptotic pathway to stay alive. Apoptosis targets that are currently being explored for cancer drug discovery include the tumour-necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors, the BCL2 family of anti-apoptotic proteins, inhibitor of apoptosis (IAP) proteins and MDM2.

Adenovirus-mediated IKKβKA expression sensitizes prostate carcinoma cells to TRAIL-induced apoptosis

Despite the fact that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis in cancer cells, TRAIL resistance in cancer cells has challenged the use of TRAIL as a therapeutic agent. First, prostate carcinoma cell lines (DU145, LNCaP and PC3) were screened for sensitivity to adenovirus delivery of TRAIL (Ad5hTRAIL). As amplified Ikappa B kinase (IKK) activity is responsible for the constitutive nuclear factor-kappaB (NF-kappaB) activation leading to uncontrolled cell growth and metastasis, a dual vector approach using both an adenovirus vector (Ad) expressing the dominant-negative mutant of IKKbeta (AdIKKbetaKA) and Ad5hTRAIL was employed to determine if prostate cancer cells were sensitized to TRAIL in the setting of IKK inhibition. Inhibition of the NF-kappaB pathway through IKK blockade sensitized all three prostate cancer cell lines to TRAIL, regardless of NF-kappaB activation or decoy receptor gene expression. Moreover, a novel quantitative real-time RT-PCR assay and conventional flow cytometry analysis indicated that TRAIL-resistant DU145 and LNCaP cells, but not TRAIL-sensitive PC3 cells, expressed substantial amounts of TRAIL Decoy Receptor 4. In conclusion, TRAIL decoy receptor expression appeared to be the chief determinant of TRAIL resistance encountered in prostate carcinoma cell lines.