Apoptosis resistance in epithelial tumors is mediated by tumor-cell-derived interleukin-4

Clinical and pathological implications of concurrent autoimmune thyroid disorders and papillary thyroid cancer

Cooccurrences of chronic lymphocytic thyroiditis (CLT) and thyroid cancer (DTC) have been repeatedly reported. Both CLT and DTC, mainly papillary thyroid carcinoma (PTC), share some epidemiological and molecular features. In fact, thyroid lymphocytic inflammatory reaction has been observed in association with PTC at variable frequency, although the precise relationship between the two diseases is still debated. It also remains a matter of debate whether the association with a CLT or even an autoimmune disorder could influence the prognosis of PTC. A better understanding about clinical implications of autoimmunity in concurrent thyroid cancer could raise new insights of thyroid cancer immunotherapy. In addition, elucidating the molecular mechanisms involved in autoimmune disease and concurrent cancer allowed us to identify new therapeutic strategies against thyroid cancer. The objective of this article was to review recent literature on the association of these disorders and its potential significance.

Targeting apoptosis pathways in cancer stem cells

There is a significant void in cancer biology with regard to the elucidation of the mechanisms that underlie tumor formation and progression. Recently, the existence of a hierarchy within cancer cell populations has been demonstrated experimentally for several tumor types. The identification of a tumor cell subset that is capable of self-renewal and, concurrently, generation into more differentiated progeny has engendered new perspectives toward selective targeting of tumors. Although the identification of the so-called "cancer stem cells" (CSCs) is a leap in the study of cancer ontogenesis, therapeutic targeting of such cells is plagued by significant difficulties. CSCs are able to evade the control mechanisms that regulate cell survival and proliferation. Apoptosis is one of the most critical and well-studied mechanisms, governing tissue development and homeostasis through a complex network of molecules that mediate death and survival signals. Escape from such a finely tuned death program is a prerequisite for any tumor-initiating cell. Thus, many compounds have been developed to target cancer cells and induce apoptosis directly or indirectly. Several TRAIL receptor agonists are in Phase I or II trials, and IAP inhibitors are undergoing clinical examination to exploit their ability to enhance ionizing radiation- and chemotherapy-induced apoptosis. Further, the EGF-R/Akt pro-survival signaling axis is one of the most frequently explored sources of targets for indirect apoptosis induction, as evidenced by the significant amount of molecules designed to target this pathway and have been approved by the FDA or are under clinical evaluation. Despite the promise of these magic bullets, the absence of reliable clinical models has considerably diminished the therapeutic potential of targeted therapies considerably. A more systematic molecular characterization of the tumor-initiating cell population in many tumors will allow us to refine the stimuli that force CSCs to die, thus accelerating the development of more effective treatment for cancer.

Antibody-based fusion proteins to target death receptors in cancer

Ideally, an immunotoxin should be inactive 'en route', acquire activity only after tumor cell surface binding and have no off-target effects towards normal cells. In this respect, antibody-based fusion proteins that exploit the tumor-selective pro-apoptotic death ligands sFasL and sTRAIL appear promising. Soluble FasL largely lacks receptor-activating potential, whereas sTRAIL is inactive towards normal cells. Fusion proteins in which an anti-tumor antibody fragment (scFv) is fused to sFasL or sTRAIL prove to be essentially inactive when soluble, while gaining potent anti-tumor activity after selective binding to a predefined tumor-associated cell surface antigen. Importantly, off-target binding by scFv:sTRAIL to normal cells showed no signs of toxicity. In this review, we highlight the rationale and perspectives of scFv:TRAIL/scFv:sFasL based fusion proteins for cancer therapy.

Alternative activation of tumor-associated macrophages by IL-4: priming for protumoral functions

Although macrophages were originally recognized as major immune effector cells, it is now appreciated that they also play many important roles in the maintenance of tissue homeostasis, and are involved in a variety of pathological conditions including cancer. Several studies have demonstrated the contributions of tumor-associated macrophages (TAMs) to tumor initiation, progression, and metastasis. However, the detailed mechanisms underlying how TAMs differ molecularly from their normal counterparts and how the conversion to TAMs occurs have only just begun to be understood. TAMs have been proposed to exhibit phenotypes of 'alternatively activated' macrophages, though there has been limited evidence directly linking the phenotypes of TAMs to the alternative activation of macrophages. This review will focus on IL-4, the prototypic cytokine that induces the alternative activation of macrophages, and review current knowledge regarding the contributions of IL-4 to the phenotypes of TAMs and its effects on tumorigenesis.

Survivin is regulated by interleukin-4 in colon cancer stem cells

Colorectal cancer has provided an important model to test the stem cell hypothesis of cancer origin, which implies that cancer arises as a result of genetic aberrations in stem cells leading to deregulation of the proliferation/differentiation balance. We and others have demonstrated that, similarly to other solid tumors, colon carcinogenesis and progression are dictated by highly apoptosis-resistant stem-like cells. Our data have suggested that protection from apoptosis is achieved by autocrine production of interleukin-4 (IL-4) through up-regulation of anti-apoptotic mediators. In this study, we extend our analysis to another apoptosis inhibitor widely expressed in tumors, namely survivin (also known as BIRC-5, baculoviral IAP repeat-containing protein 5). We show that this protein, with important roles in cell death counteraction and mitotic progression control, is regulated by the IL-4 pathway in colon rectal cancer stem cells (CR-CSC). Hence, the presence of IL-4 increases survivin levels in our model while cytokine neutralization has opposing effects. Treatment with cytokine neutralizing agent or with leflunomide, Stat6 inhibitor, have similar consequences on survivin localization, increasing its nuclear pool, an observation known to be correlated with a good prognosis in colon cancer patients. These results demonstrate that IL-4, through activation of the STAT-6 signaling pathway, is involved in survivin expression levels as well as its localization. These findings shed more light on the molecular mechanisms involved in IL-4-mediated chemoresistance.

Tumor associated macrophages protect colon cancer cells from TRAIL-induced apoptosis through IL-1beta-dependent stabilization of Snail in tumor cells

BACKGROUND

We recently reported that colon tumor cells stimulate macrophages to release IL-1beta, which in turn inactivates GSK3beta and enhances Wnt signaling in colon cancer cells, generating a self-amplifying loop that promotes the growth of tumor cells.

PRINCIPAL FINDINGS

Here we describe that macrophages protect HCT116 and Hke-3 colon cancer cells from TRAIL-induced apoptosis. Inactivation of IL-1beta by neutralizing IL-1beta antibody, or silencing of IL-1beta in macrophages inhibited their ability to counter TRAIL-induced apoptosis. Accordingly, IL-1beta was sufficient to inhibit TRAIL-induced apoptosis. TRAIL-induced collapse of the mitochondrial membrane potential (Delta psi) and activation of caspases were prevented by macrophages or by recombinant IL-1beta. Pharmacological inhibition of IL-1beta release from macrophages by vitamin D(3), a potent chemopreventive agent for colorectal cancer, restored the ability of TRAIL to induce apoptosis of tumor cells cultured with macrophages. Macrophages and IL-1beta failed to inhibit TRAIL-induced apoptosis in HCT116 cells expressing dnIkappaB, dnAKT or dnTCF4, confirming that they oppose TRAIL-induced cell death through induction of Wnt signaling in tumor cells. We showed that macrophages and IL-1beta stabilized Snail in tumor cells in an NF-kappaB/Wnt dependent manner and that Snail deficient tumor cells were not protected from TRAIL-induced apoptosis by macrophages or by IL-1beta, demonstrating a crucial role of Snail in the resistance of tumor cells to TRAIL.

SIGNIFICANCE

We have identified a positive feedback loop between tumor cells and macrophages that propagates the growth and promotes the survival of colon cancer cells: tumor cells stimulate macrophages to secrete IL-1beta, which in turn, promotes Wnt signaling and stabilizes Snail in tumor cells, conferring resistance to TRAIL. Vitamin D(3) halts this amplifying loop by interfering with the release of IL-1beta from macrophages. Accordingly, vitamin D(3) sensitizes tumor cells to TRAIL-induced apoptosis, suggesting that the therapeutic efficacy of TRAIL could be augmented by this readily available chemopreventive agent.

Selective expansion of chimeric antigen receptor-targeted T-cells with potent effector function using interleukin-4

Polyclonal T-cells can be directed against cancer using transmembrane fusion molecules known as chimeric antigen receptors (CARs). Although preclinical studies have provided encouragement, pioneering clinical trials using CAR-based immunotherapy have been disappointing. Key obstacles are the need for robust expansion ex vivo followed by sustained survival of infused T-cells in patients. To address this, we have developed a system to achieve selective proliferation of CAR(+) T-cells using IL-4, a cytokine with several pathophysiologic and therapeutic links to cancer. A chimeric cytokine receptor (4alphabeta) was engineered by fusion of the IL-4 receptor alpha (IL-4Ralpha) ectodomain to the beta(c) subunit, used by IL-2 and IL-15. Addition of IL-4 to T-cells that express 4alphabeta resulted in STAT3/STAT5/ERK phosphorylation and exponential proliferation, mimicking the actions of IL-2. Using receptor-selective IL-4 muteins, partnering of 4alphabeta with gamma(c) was implicated in signal delivery. Next, human T-cells were engineered to co-express 4alphabeta with a CAR specific for tumor-associated MUC1. These T-cells exhibited an unprecedented capacity to elicit repeated destruction of MUC1-expressing tumor cultures and expanded through several logs in vitro. Despite prolonged culture in IL-4, T-cells retained specificity for target antigen, type 1 polarity, and cytokine dependence. Similar findings were observed using CARs directed against two additional tumor-associated targets, demonstrating generality of application. Furthermore, this system allows rapid ex vivo expansion and enrichment of engineered T-cells from small blood volumes, under GMP-compliant conditions. Together, these findings provide proof of principle for the development of IL-4-enhanced T-cell immunotherapy of cancer.

Novel SMAC-mimetics synergistically stimulate melanoma cell death in combination with TRAIL and Bortezomib

BACKGROUND

XIAP (X-linked inhibitor of apoptosis protein) is an anti-apoptotic protein exerting its activity by binding and suppressing caspases. As XIAP is overexpressed in several tumours, in which it apparently contributes to chemoresistance, and because its activity in vivo is antagonised by second mitochondria-derived activator of caspase (SMAC)/direct inhibitor of apoptosis-binding protein with low pI, small molecules mimicking SMAC (so called SMAC-mimetics) can potentially overcome tumour resistance by promoting apoptosis.

METHODS

Three homodimeric compounds were synthesised tethering a monomeric SMAC-mimetic with different linkers and their affinity binding for the baculoviral inhibitor repeats domains of XIAP measured by fluorescent polarisation assay. The apoptotic activity of these molecules, alone or in combination with tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and/or Bortezomib, was tested in melanoma cell lines by MTT viability assays and western blot analysis of activated caspases.

RESULTS

We show that in melanoma cell lines, which are typically resistant to chemotherapeutic agents, XIAP knock-down sensitises cells to TRAIL treatment in vitro, also favouring the accumulation of cleaved caspase-8. We also describe a new series of 4-substituted azabicyclo[5.3.0]alkane monomeric and dimeric SMAC-mimetics that target various members of the IAP family and powerfully synergise at submicromolar concentrations with TRAIL in inducing cell death. Finally, we show that the simultaneous administration of newly developed SMAC-mimetics with Bortezomib potently triggers apoptosis in a melanoma cell line resistant to the combined effect of SMAC-mimetics and TRAIL.

CONCLUSION

Hence, the newly developed SMAC-mimetics effectively synergise with TRAIL and Bortezomib in inducing cell death. These findings warrant further preclinical studies in vivo to verify the anticancer effectiveness of the combination of these agents.

Apigenin inhibits cell growth and alters expression of multiple genes in human hepatoma cell line Huh-7

AIM: To investigate the effects of apigenin on cell growth and gene expression in human hepatoma cell line Huh-7.

METHODS: After Huh-7 cells was cultured and treated with different concentrations of apigenin, cell proliferation was measured by colorimetric methyl thiazolyl tetrazolium (MTT) assay; cell clonogenicity was detected by colony-forming assay; and cell cycle distribution and apoptosis were examined by flow cytometry. The impact of apigenin on the tumorigenicity of Huh-7 cells in nude mice was also detected. The differential gene expression between cells treated and untreated with apigenin was detected by cDNA microarray and verified by quantitative real-time reverse transcription-polymerase chain reaction and Western blot.

RESULTS: Compared with untreated cells, cells treated with apigenin exhibited a marked growth inhibition. The half maximal inhibitory concentration (IC₅₀) of apigenin on cell growth was approximately 10.5 mg/L ± 0.3 mg/L. Apigenin treatment could cause a cell cycle block at G2/M phase, decrease the percentage of cells at G₀/G₁ phase, promote apoptosis, and inhibit the tumorigenicity of Huh-7 cells in vivo. Apigenin treatment could also dramatically alter the expression of 1 764 functionally related genes in Huh-7 cells. Of these differentially expressed genes, the majority are involved in nucleic acid binding and transport, enzyme catalytic activity regulation, transcriptional regulation, cytoskeletal structure and/or adhesion, signal transduction, metabolism, apoptosis or the immune response. Of note, apigenin could significantly downregulate the expression of interleukin-4 receptor and ubiquitin-specific protease 18.

CONCLUSION: Apigenin partially inhibits Huh-7 cell growth in vitro and in vivo by blocking cell cycle at G₂/M phase and promoting apoptosis. Apigenin treatment alters the expression of multiple genes in Huh-7 cells.

Epithelial interleukin-4 receptor expression promotes colon tumor growth

Inflammatory mediators are of considerable interest as potential therapeutic targets in various cancers. Here we investigate whether interleukin (IL)-4 receptor alpha (IL4Ralpha), a component of the receptor complex for the T helper 2 cytokines IL4 and IL13, plays a role in colonic tumorigenesis. IL4Ralpha protein expression was seen in tumor cells of 28/48 human colon adenocarcinomas on a tissue microarray. In human and murine colon tumor cell lines analyzed in vitro, all of which expressed IL4Ralpha, treatment with exogenous ligand resulted in dose-dependent increases in proliferation. IL4 decreased apoptosis only in HCT116 cells. An orthotopic allograft model was used to determine in vivo effects of tumor cell-specific IL4Ra ablation. MC38 murine tumor cells with the IL4Ra gene knocked down showed reduced proliferation but no difference in apoptosis compared with controls after implantation in ceca of syngeneic mice. Mice null for IL4Ra and wild-type controls were treated with azoxymethane and dextran sulfate sodium to induce tumor formation. Mice with global deletion of IL4Ra had significantly fewer and smaller tumors. Reduced tumorigenicity correlated with decreased proliferation and increased apoptosis. Systemic blockade of IL4Ralpha-IL4 interactions with a chimeric soluble receptor protein gave similar results in the cecal implant model. Thus, IL4Ralpha, a component of the IL4R and IL13R, contributes to tumor formation in a mouse model of colitis-associated cancer. Proliferation appears to be directly mediated via IL4Ralpha on the epithelial tumor cells. Survival may be an indirect response mediated via other host cells. Our results support therapeutic targeting of IL4Ralpha in colon cancer.

IL-4 induces cathepsin protease activity in tumor-associated macrophages to promote cancer growth and invasion

Innate immune cells can constitute a substantial proportion of the cells within the tumor microenvironment and have been associated with tumor malignancy in patients and animal models of cancer; however, the mechanisms by which they modulate cancer progression are incompletely understood. Here, we show that high levels of cathepsin protease activity are induced in the majority of macrophages in the microenvironment of pancreatic islet cancers, mammary tumors, and lung metastases during malignant progression. We further show that tumor-associated macrophage (TAM)-supplied cathepsins B and S are critical for promoting pancreatic tumor growth, angiogenesis, and invasion in vivo, and markedly enhance the invasiveness of cancer cells in culture. Finally, we demonstrate that interleukin-4 (IL-4) is responsible for inducing cathepsin activity in macrophages in vitro and in vivo. Together, these data establish IL-4 as an important regulator, and cathepsin proteases as critical mediators, of the cancer-promoting functions of TAMs.

CD4(+) T cells regulate pulmonary metastasis of mammary carcinomas by enhancing protumor properties of macrophages

During breast cancer development, increased presence of leukocytes in neoplastic stroma parallels disease progression; however, the functional significance of leukocytes in regulating protumor versus antitumor immunity in the breast remains poorly understood. Utilizing the MMTV-PyMT model of mammary carcinogenesis, we demonstrate that IL-4-expressing CD4(+) T lymphocytes indirectly promote invasion and subsequent metastasis of mammary adenocarcinomas by directly regulating the phenotype and effector function of tumor-associated CD11b(+)Gr1(-)F4/80(+) macrophages that in turn enhance metastasis through activation of epidermal growth factor receptor signaling in malignant mammary epithelial cells. Together, these data indicate that antitumor acquired immune programs can be usurped in protumor microenvironments and instead promote malignancy by engaging cellular components of the innate immune system functionally involved in regulating epithelial cell behavior.

The mRNA expression of SATB1 and SATB2 in human breast cancer

BACKGROUND

SATB1 is a nuclear protein that has been recently reported to be a 'genome organizer' which delineates specific epigenetic modifications at target gene loci, directly up-regulating metastasis-associated genes while down-regulating tumor-suppressor genes. In this study, the level of mRNA expression of SATB1 and SATB2 were assessed in normal and malignant breast tissue in a cohort of women with breast cancer and correlated to conventional clinico-pathological parameters.

MATERIALS AND METHODS

Breast cancer tissues (n = 115) and normal background tissues (n = 31) were collected immediately after excision during surgery. Following RNA extraction, reverse transcription was carried out and transcript levels were determined using real-time quantitative PCR and normalized against beta-actin expression. Transcript levels within the breast cancer specimens were compared to the normal background tissues and analyzed against TNM stage, nodal involvement, tumour grade and clinical outcome over a 10 year follow-up period.

RESULTS

The levels of SATB1 were higher in malignant compared with normal breast tissue (p = 0.0167). SATB1 expression increased with increasing TNM stage (TNM1 vs. TNM2 p = 0.0264), increasing tumour grade (grade1 vs. grade 3 p = 0.017; grade 2 vs. grade 3 p = 0.0437; grade 1 vs. grade 2&3 p = 0.021) and Nottingham Prognostic Index (NPI) (NPI-1 vs. NPI-3 p = 0.0614; NPI-2 vs. NPI-3 p = 0.0495). Transcript levels were associated with oestrogen receptor (ER) positivity (ER(-) vs. ER(+) p = 0.046). SABT1 expression was also significantly correlated with downstream regulated genes IL-4 and MAF-1 (Pearson's correlation coefficient r = 0.21 and r = 0.162) and SATB2 (r = 0.506). After a median follow up of 10 years, there was a trend for higher SATB1 expression to be associated with shorter overall survival (OS). Higher levels of SATB2 were also found in malignant compared to background tissue (p = 0.049). SATB2 expression increased with increasing tumour grade (grade 1 vs. grade 3 p = 0.035). SATB2 was associated with ER positivity (ER(-) vs. ER(+) p = 0.0283) within ductal carcinomas. Higher transcript levels showed a significant association with poorer OS (p = 0.0433).

CONCLUSION

SATB1 mRNA expression is significantly associated with poor prognostic parameters in breast cancer, including increasing tumour grade, TNM stage and NPI. SATB2 mRNA expression is significantly associated with increasing tumour grade and poorer OS. These results are consistent with the notion that SATB1 acts as a 'master genome organizer' in human breast carcinogenesis.

Efficient killing of human colon cancer stem cells by gammadelta T lymphocytes

Colon cancer comprises a small population of cancer stem cells (CSC) that is responsible for tumor maintenance and resistant to cancer therapies, possibly allowing for tumor recapitulation once treatment stops. We previously demonstrated that such chemoresistance is mediated by autocrine production of IL-4 through the up-regulation of antiapoptotic proteins. Several innate and adaptive immune effector cells allow for the recognition and destruction of cancer precursors before they constitute the tumor mass. However, cellular immune-based therapies have not been experimented yet in the population of CSCs. Here, we show that the bisphosphonate zoledronate sensitizes colon CSCs to Vgamma9Vdelta2 T cell cytotoxicity. Proliferation and production of cytokines (TNF-alpha and IFN-gamma) and cytotoxic and apoptotic molecules (TRAIL and granzymes) were also induced after exposure of Vgamma9Vdelta2 T cells to sensitized targets. Vgamma9Vdelta2 T cell cytotoxicity was mediated by the granule exocytosis pathway and was highly dependent on isoprenoid production by of tumor cells. Moreover, CSCs recognition and killing was mainly TCR mediated, whereas NKG2D played a role only when tumor targets expressed several NKG2D ligands. We conclude that intentional activation of Vgamma9Vdelta2 T cells by zoledronate may substantially increase antitumor activities and represent a novel strategy for colon cancer immunotherapy.

Is TRAIL the holy grail of cancer therapy?

Inducing apoptosis has become an important approach in the development of new anti-cancer treatments. Tumour necrosis factor apoptosis inducing ligand (TRAIL) based therapies have emerged as one of the most promising examples of this as they selectively induce apoptosis in tumour cells. However, many primary tumours are inherently resistant to TRAIL-mediated apoptosis and require additional sensitisation. Here we review apoptotic and non-apoptotic TRAIL-signalling, and the therapeutic effects of TRAIL-based treatments both as monotherapy and in combination with sensitising agents.

Induction of apoptosis in tumor cells as a mechanism of tumor growth reduction in allergic mice

Cancer is the leading cause of mortality worldwide. Analysis of epidemiological data has revealed a negative relationship between allergic conditions and cancer incidence. This study addresses the effects of chronic antigen ingestion by sensitized mice (allergy) on Ehrlich tumor growth in mouse footpad. Mice were sensitized (allergic) or not (sham) with ovalbumin and challenged orally with egg white solution. After one week of oral challenge, all mice were inoculated with experimental Ehrlich tumor (EET) cells in the footpad, and tumor growth was evaluated for 21 days. A decrease in tumor growth occurred, as assessed by paw thickness in the allergic group, which was associated with smaller areas of necrosis, reduced infiltration of neutrophils, and reduced levels of IFN-gamma, IL-4, and IL-10. Although, the tumor proliferation rate was similar in both groups, an increase in apoptosis occurred in allergic mice. In conclusion, analysis of the data obtained allows us to suggest that a concomitant allergic condition would reduce tumor progression through increased tumor cell apoptosis, accompanied by reduced areas of necrosis at the tumor site. Indeed, such findings suggested a possible mechanism for the reduced cancer incidence observed in allergic individuals.

Pro-apoptotic and cytostatic activity of naturally occurring cardenolides

PURPOSE

Cardenoliddes are steroid glycosides which are known to exert cardiotonic effects by inhibiting the Na(+)/K(+)-ATPase. Several of these compounds have been shown also to possess anti-tumor potential. The aim of the present work was the characterization of the tumor cell growth inhibition activity of four cardenolides, isolated from Periploca graeca L., and the mechanisms underlying such an effect.

METHODS

The pro-apoptotic and cytostatic effect of the compounds was tested in U937 (monocytic leukemia) and PC3 (prostate adenocarcinoma). Characterization of apoptosis and cell cycle impairment was obtained by cytofluorimetry and WB.

RESULTS

Periplocymarin and periplocin were the most active compounds, periplocymarin being more effective than the reference compound ouabain. The reduction of cell number by these two cardenolides was due in PC3 cells mainly to the activation of caspase-dependent apoptotic pathways, while in U937 cells to the induction of cell cycle impairment without extensive cell death. Interestingly, periplocymarin, at cytostatic but non-cytotoxic doses, was shown to sensitize U937 cells to TRAIL.

CONCLUSIONS

Taken together, our data outline that cardiac glycosides are promising anticancer drugs and contribute to the identification of new natural cardiac glycosides to obtain chemically modified non-cardioactive/low toxic derivatives with enhanced anticancer potency.

From biochemical principles of apoptosis induction by TRAIL to application in tumour therapy

The tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily which has been shown to selectively kill tumour cells, while sparing normal tissue. This attribute makes TRAIL an attractive drug candidate for cancer therapy. Although most primary tumour cells turned out to be primarily TRAIL-resistant, recent studies evidenced that a variety of cancers can be sensitised to TRAIL-induced apoptosis upon pre-treatment with chemotherapeutic agents or irradiation, while normal cells remain TRAIL-resistant. However, biomarkers that reliably predict which patients may benefit from such combinatorial therapies are required. Thus, it is essential to better understand the mechanisms underlying TRAIL resistance versus sensitivity. In this chapter, we introduce the signalling events which take place during TRAIL-induced apoptosis, describe the physiological function of TRAIL and summarise pre-clinical and clinical results obtained so far with TRAIL-receptor agonists.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

Death receptors as targets for anti-cancer therapy

Human tumour cells are characterized by their ability to avoid the normal regulatory mechanisms of cell growth, division and death. The classical chemotherapy aims to kill tumour cells by causing DNA damage-induced apoptosis. However, as many tumour cells possess mutations in intracellular apoptosis-sensing molecules like p53, they are not capable of inducing apoptosis on their own and are therefore resistant to chemotherapy. With the discovery of the death receptors the opportunity arose to directly trigger apoptosis from the outside of tumour cells, thereby circumventing chemotherapeutic resistance. Death receptors belong to the tumour necrosis factor receptor superfamily, with tumour necrosis factor (TNF) receptor-1, CD95 and TNF-related apoptosis-inducing ligand-R1 and -R2 being the most prominent members. This review covers the current knowledge about these four death receptors, summarizes pre-clinical approaches engaging these death receptors in anti-cancer therapy and also gives an overview about their application in clinical trials conducted to date.