Apoptotic cell death induced by a mouse-human anti-APO-1 chimeric antibody leads to tumor regression

Prospects for the application of antibodies in medicine

Prospects for the Application of Antibodies in Medicine.

Overcoming apoptosis deficiency of melanoma-hope for new therapeutic approaches

The increased incidence of malignant melanoma in the last decades, its high mortality and pronounced therapy resistance pose an enormous challenge. Important therapeutic targets for melanoma are the induction of apoptosis and suppression of survival pathways. Preclinical studies have demonstrated the efficacy of pro-apoptotic Bcl-2 proteins and of death receptor ligands to trigger apoptosis in melanoma cells. In the clinical setting, BH3 domain mimics and death receptor agonists are therefore considered as promising, specific novel treatments to add to the conventional pro-apoptotic strategies such as chemo- or radiotherapy. However, constitutively activated survival pathways, in particular the mitogen-activated protein kinases, protein kinase B/Akt and nuclear factor (NF)-kappaB, all may work in concert to prevent effective therapy. Thus, selective biologicals developed with the aim to inhibit pro-survival signaling are currently tested in melanoma. For highly therapy-resistant tumors such as melanoma, development of novel drug combinations will be essential, and combinations of survival inhibitors and pro-apoptotic mediators appear most promising. The challenge of the near future will be to make a rational choice of the multiple possible combinations and protocols. This review gives a critical overview of proteins involved in melanoma chemoresistance, which are targets for current drug development leading to the best choice for future trials.

TRAIL sensitizes for ionizing irradiation-induced apoptosis through an entirely Bax-dependent mitochondrial cell death pathway

The death ligand TRAIL has been suggested as a suitable biological agent for the selective induction of cell death in cancer cells. Moreover, TRAIL synergizes with DNA-damaging therapies such as chemotherapeutic drugs or ionizing irradiation (IR). Here, we show that synergy of TRAIL and IR, that is, crosssensitization between TRAIL and IR for induction of apoptosis, entirely depends on Bax proficiency in human DU145 and HCT116 carcinoma cells. DU145 prostate carcinoma cells that have lost Bax protein expression due to mutation fail to activate caspase-3 and -9 when exposed to TRAIL and IR. In contrast, TRAIL sensitized for IR-induced apoptosis and vice versa upon reconstitution of Bax expression. Notably, both DU145 and HCT116 still express significant levels of the multidomain proapoptotic Bcl-2 homolog Bak. This indicates that Bak is not sufficient to mediate crosssensitization and synergism between IR and TRAIL. These data clearly establish distinct roles for Bax and Bak in linking the TRAIL death receptor pathway to the mitochondrial apoptosis signaling cascade upon DNA damage by IR.

Multidomain Bcl-2 homolog Bax but not Bak mediates synergistic induction of apoptosis by TRAIL and 5-FU through the mitochondrial apoptosis pathway

The death ligand TRAIL synergizes with DNA-damaging therapies such as chemotherapeutic drugs or ionizing irradiation. Here, we show that the synergism of TRAIL and 5-fluorouracil (5-FU) and cross-sensitization between TRAIL and 5-FU for induction of apoptosis, entirely depend on Bax proficiency in human DU145 and HCT116 carcinoma cells. DU145 prostate carcinoma cells that have lost Bax protein expression due to mutation fail to release cytochrome c and to activate caspase-3 and -9 when exposed to TRAIL and 5-FU. In contrast, TRAIL sensitized for 5-FU-induced apoptosis and vice versa upon reconstitution of Bax expression. Isobolographic analyses of ED50 doses for 5-FU at increasing TRAIL concentrations showed a clear synergism of TRAIL and 5-FU in Bax-expressing cells. In contrast, the effect was merely additive in DU145 cells lacking Bax. Notably, both DU145 and HCT116 Bax-deficient cells still express Bak. This indicates that Bak is not sufficient to mediate cross-sensitization and synergism between 5-FU and TRAIL. Stable overexpression of Bak in DU145 sensitized for epirubicin-induced apoptosis but failed to confer synergy between TRAIL and 5-FU. Moreover, we show by the use of EGFP-tagged Bax and Bak that TRAIL and 5-FU synergistically trigger oligomerization and clustering of Bax but not Bak. These data clearly establish distinct roles for Bax and Bak in linking the TRAIL death receptor pathway to the mitochondrial apoptosis signaling cascade and delineate a higher degree of specificity in signaling for cell death by multidomain Bcl-2 homologs.

Caspase-3 inhibits the growth of breast cancer cells independent of protease activity

In this study, the MCF-7 breast cancer cells that lack caspase-3 were transfected with a wild type (WT) or mutant caspase-3 cDNA. Expression of the WT, but not of the mutant, caspase-3 was associated with increased caspase activity and susceptibility to staurosporine (STS)-induced apoptosis. Both derivatives displayed inhibition of cell growth compared with vector control cells. Growth inhibition was associated with increased expression of the cyclin dependent kinase (CDK) inhibitor p27Kip1 in the WT, but not in the mutant caspase-3 expressing cells. Cyclin D1 expression level was not affected by caspase-3 expression. Phosphorylation of the Akt protein was decreased in both WT and mutant caspase transfected cells, although Akt expression level remained unchanged. These results suggest that caspase-3 might have biological functions independent of its protease activity and that its loss might contribute to tumor development by increasing the growth potential of cancer cells.

CD95/Fas signaling in human melanoma cells: conditional expression of CD95L/FasL overcomes the intrinsic apoptosis resistance of malignant melanoma and inhibits growth and progression of human melanoma xenotransplants

The significance of CD95/Fas ligand expression by melanoma cells has remained a controversial matter in recent years. On the other hand, CD95 activation may represent a powerful tool for eliminating tumor cells. Here, we demonstrate expression of CD95 in 15/17 human melanoma cell lines analysed, but complete lack of CD95 ligand (CD95L). Overexpression of CD95 in a tetracycline-inducible expression system enhanced melanoma cell sensitivity to CD95 ligation but was unable to trigger apoptosis by itself. In clear contrast, all melanoma cells tested responded with increased apoptosis to conditional expression of CD95L (2-10-fold), both after transient and after stable transfection. Activation of caspase-8, Bid cleavage, cytochrome c release and caspase-3 activation followed after CD95L induction indicating a functional CD95-signaling cascade. CD95L was also able to enhance the proapoptotic effect of chemotherapeutics applied in parallel. Nude mouse experiments revealed that tumorigenicity was lost when melanoma xenografts were triggered to express CD95L. In addition, further progression of pre-existing melanomas was inhibited and even regression was seen after induction of CD95L expression. Due to these data, transfection of CD95L proofs as a highly efficient tool against melanoma cells in vitro and in vivo, and targeted expression of CD95L may thus represent a suitable strategy for melanoma therapy.

Characterization of p53-mediated up-regulation of CD95 gene expression upon genotoxic treatment in human breast tumor cells

Death receptor CD95 gene expression is frequently low in human breast tumors and is up-regulated by genotoxic treatments in a p53-dependent manner. We have evaluated the relative contribution of promoter and intronic p53 consensus sites to the regulation of the human CD95 gene in breast tumor cells following doxorubicin treatment. Deletion constructs of the promoter region and site-directed mutagenesis of p53 consensus sites in a fragment spanning 1448 bp of the 5'-promoter demonstrate that these sites are not involved in the observed up-regulation of the CD95 gene upon doxorubicin treatment. In contrast, a p53 consensus site located within the first intron of CD95 gene is absolutely required for the inducible expression of CD95 upon genotoxic treatment in breast tumor cells. Analysis of the transcriptional activity of the two most common p53 mutants found in human breast tumors that are associated with resistance to doxorubicin reveals that these mutations completely eliminate the ability of p53 protein to transactivate CD95 gene expression. On the other hand, Bcl-2 overexpression albeit preventing doxorubicin-induced apoptosis, has no effect on p53-mediated CD95 up-regulation in breast tumor cells. Altogether, these results indicate the lack of involvement of p53 consensus sites of the CD95 promoter region and the pivotal role of intronic p53-responsive element in the regulation of human CD95 gene expression in breast tumor cells. Our results also suggest that in breast cancer patients with certain mutations in the p53 gene, expression of death receptor CD95 in response to genotoxic treatments could be severely compromised.

The kiss of death: promises and failures of death receptors and ligands in cancer therapy

Death receptors and their ligands exert important regulatory functions in the maintenance of tissue homeostasis and the physiological regulation of programmed cell death. Currently, six different death receptors are known including tumor necrosis factor (TNF) receptor-1, CD95 (Fas/APO-1), TNF receptor-related apoptosis-mediating protein (TRAMP), TNF-related apoptosis-inducing ligand (TRAIL) receptor-1 and -2, and death receptor-6 (DR6). The signaling pathways by which these receptors induce apoptosis are similar and rely on oligomerization of the receptor by death ligand binding, recruitment of an adapter protein through homophilic interaction of cytoplasmic domains, and subsequent activation of an inducer caspase which initiates execution of the cell death programme. The ability of these receptors and their ligands to kill malignant cells was discovered early and helped to coin the term 'tumor necrosis factor' for the first identified death ligand. This review summarizes the current and rapidly expanding knowledge about the signaling pathways triggered by death receptor/ligand systems, their potency in experimental cancer therapy, and their therapeutic limitations, especially regarding their toxicity for non-malignant cells.

Altered mechanisms of apoptosis in colon cancer: Fas resistance and counterattack in the tumor-immune conflict

Fas (CD95/APO-1) is a cell surface "death receptor" that mediates apoptosis upon engagement by its ligand, FasL. Fas-mediated apoptosis of lymphocytes normally serves immunoregulatory roles, including tolerance acquisition, immune response termination, and maintenance of immune privilege in certain organs. Colon tumors can exploit this lymphocyte death program by expressing FasL. This may enable colon tumors to mount a "Fas counterattack" against antitumor lymphocytes, impairing antitumor immune responses. FasL-expressing colon tumor-derived cell lines can trigger Fas-mediated apoptosis of cocultured T cells in vitro. FasL expressed in esophageal cancer has been significantly associated with apoptosis and depletion of tumor-infiltrating lymphocytes (TIL) in vivo. FasL may also facilitate metastatic colonization of Fas-sensitive organs such as the liver, by inducing apoptosis of target organ cells. Normal colonic epithelial cells express Fas and are relatively sensitive to Fas-mediated apoptosis. By contrast, colon tumor-derived cell lines are usually resistant to induction of Fas-mediated apoptosis, and colon cancer cells frequently coexpress Fas and FasL. The mechanisms allowing resistance to Fas-mediated apoptosis are complex, and defects have been identified at several levels of Fas signal transduction. The "Bcl-2 rheostat" may be pitched against apoptosis in colon cancer, inasmuch as overexpression of Bcl-2, downregulation of Bak, and mutation of Bax are common defects in colon tumors. Caspase-1 is also downregulated in colon cancer. The high frequency of p53 mutations in late-stage cancers may also inhibit Fas signaling. Fundamental defects in apoptosis signaling may contribute to both immuno- and chemoresistance in colon cancer and allow expression of FasL to counterattack antitumor lymphocytes.

fas-mediated lysis of chronic lymphocytic leukaemia cells: role of type I versus type II cytokines and autologous fasL-expressing T cells

Given the known role of the fas cytolytic pathway in B-cell regulation, we evaluated whether fas-fasL interactions might induce chronic lymphocytic leukaemia (CLL) cell death. De novo CLL cells expressed a low level of surface fas, and were not lysed by fasL-bearing cells. CLL cells cultured in media containing the type I cytokines interleukin (IL)-12 or interferon (IFN)-alpha had increased fas expression, and were readily lysed by fasL-bearing cells. In contrast, the type II cytokine IL-4 did not increase CLL cell fas, and abrogated type I cytokine-induced fas up-regulation. With prolonged culture, IL-4 exposed CLL cells expressed an intermediate level of fas; however, such CLL cells were resistant to fas-mediated lysis. These results indicate that IL-4 inhibits fas-mediated killing of CLL cells at the level of both fas receptor expression and post-receptor events. Additionally, we have defined in vitro culture conditions which generate fasL-bearing T cells from CLL patients; such T cells efficiently mediated fas-based lysis of autologous fas-positive CLL cells. We therefore conclude that type I and type II cytokines differentially regulate the fas pathway in CLL cells, and that a combination of type I cytokines and fasL-expressing T cells may represent a new approach to the immunotherapy of CLL.

The alteration of Fas receptor and ligand system in hepatocellular carcinomas: how do hepatoma cells escape from the host immune surveillance in vivo?

Escape from the immune surveillance may play an important role in tumor outgrowth and metastasis. Alteration of the Fas receptor (Fas)/ligand (FasL) system including soluble forms is regarded as one of the mechanisms preventing the immune system from rejecting the tumor cells. However, less attention has been paid to the role of Fas/FasL interaction in vivo. Therefore, we investigated the expression of Fas and FasL by immunohistochemistry and reverse-transcription polymerase chain reaction (RT-PCR) and measured the serum levels of soluble Fas (sFas) and FasL (sFasL) in 44 patients with hepatocellular carcinoma (HCC). In the noncancerous liver tissues, Fas expression was up-regulated in most cases, and FasL expression was detected in 6 cases. In Fas-positive HCC cases (n = 15), the intrahepatic metastatic foci was less (P =.037), apoptosis of tumor cells was more (P =.004), the disease-free survival rate was higher (P =.004), and p53-positive cases were less (P =.003), compared with Fas-negative cases. The sFas and sFasL levels in HCC patients were significantly higher and lower than those in controls, respectively. RT-PCR and immunohistochemistry revealed generation of sFas in the hepatocytes and tumor-infiltrating mononuclear cells rather than in hepatoma cells. Accordingly, hepatoma cells may eliminate Fas expression on themselves and let the hepatocytes and infiltrating mononuclear cells generate sFas to escape from the immune system and to produce metastasis. FasL might contribute to malignant transformation in some circumstances, because hepatocytes in the pericancerous pseudolobules expressed FasL.

Immunotherapy of B-Cell Lymphoma With CD3x19 Bispecific Antibodies: Costimulation via CD28 Prevents “Veto” Apoptosis of Antibody-Targeted Cytotoxic T Cells

Bispecific antibodies (CD3x19) against the CD3ɛ-chain of the T-cell–receptor/CD3 complex and the CD19 antigen on B cells can target polyclonal, nontumor-specific T cells to B lymphoma cells. This induces T-cell activation, and generation of cytotoxic T cells (CTLs). These polyclonal CTLs, targeted by the CD3x19 bispecific antibodies, can lyse CD19+ B-lymphoma cells. In a xenotransplant model in severe combined immunodeficiency deficient (SCID) mice, we and others observed that CD28 triggering is required for efficient elimination of B-lymphoma cells and cure from the tumor in addition to CD3x19 administration. We also showed that the activation and targeting of CTLs to the target cell by signal one alone, ie, the CD3x19 mab, induces T-cell death by apoptosis. In blocking experiments we showed that this “veto” apoptosis is mediated by the CD95/Fas ligand. Addition of anti-CD28 (signal 2) renders the T cells resistant for veto apoptosis both in vitro and in vivo. We therefore conclude that the role of costimulation in immunotherapy with bispecific antibodies or other T-cell–based immune strategies is not only to facilitate T-cell activation but also to prevent T-cell deletion by apoptosis.

Immunotherapy of B-Cell Lymphoma With CD3x19 Bispecific Antibodies: Costimulation via CD28 Prevents “Veto” Apoptosis of Antibody-Targeted Cytotoxic T Cells

Bispecific antibodies (CD3x19) against the CD3ɛ-chain of the T-cell–receptor/CD3 complex and the CD19 antigen on B cells can target polyclonal, nontumor-specific T cells to B lymphoma cells. This induces T-cell activation, and generation of cytotoxic T cells (CTLs). These polyclonal CTLs, targeted by the CD3x19 bispecific antibodies, can lyse CD19+ B-lymphoma cells. In a xenotransplant model in severe combined immunodeficiency deficient (SCID) mice, we and others observed that CD28 triggering is required for efficient elimination of B-lymphoma cells and cure from the tumor in addition to CD3x19 administration. We also showed that the activation and targeting of CTLs to the target cell by signal one alone, ie, the CD3x19 mab, induces T-cell death by apoptosis. In blocking experiments we showed that this “veto” apoptosis is mediated by the CD95/Fas ligand. Addition of anti-CD28 (signal 2) renders the T cells resistant for veto apoptosis both in vitro and in vivo. We therefore conclude that the role of costimulation in immunotherapy with bispecific antibodies or other T-cell–based immune strategies is not only to facilitate T-cell activation but also to prevent T-cell deletion by apoptosis.

Sensitivity to Fas-mediated apoptosis is null or weak in B-cell non-Hodgkin's lymphomas and is moderately increased by CD40 ligation

The Fas receptor (APO-1/CD95) is capable of inducing apoptosis of lymphoid cells and is expressed in some non-Hodgkin's lymphomas (NHLs). Fas expression is up-regulated at the surface of normal B cells upon triggering of the CD40 receptor. In this report, we investigated the sensitivity of NHLs to Fas-mediated apoptosis induced by anti-Fas monoclonal antibodies (MAbs) and its possible modulation by CD40 ligation in 18 NHL biopsy samples of various histological subtypes. Flow cytometric analysis showed that the fraction of Fas-expressing lymphoma cells was highly variable from sample to sample (from 1% to 93%, mean value 46%). The frequency of apoptotic cells was not significantly increased upon treatment with an anti-Fas MAb compared with control MAb in the 18 NHL cases analysed. The sensitivity of lymphoma cells to Fas-mediated apoptosis was correlated neither with the histological subtypes nor with the level of Fas expression. Activation of neoplastic B cells by CD40 ligation resulted in significant increases in Fas expression and Fas-induced apoptosis among the five B-NHL cases tested. The overall increase in apoptotic rates was moderate and remained lower in tumour samples than in control CD40-activated normal tonsil B cells. Altogether, our results indicate that the sensitivity to Fas-induced apoptosis is null or weak in NHL cells, irrespective of their histological subtype, and that it can be increased to a moderate and variable degree by CD40 ligation on neoplastic B cells. This may be an impediment to the development of Fas-based therapies for NHLs.

Up-regulation of Fas (CD95) in human p53wild-type cancer cells treated with ionizing radiation

Fas is a cell-surface protein which belongs to the tumor-necrosis-factor-receptor family. Signals through Fas are able to induce apoptosis in sensitive cells, and thus modalities for regulating the level of Fas expression on tumor cells are needed. We have studied cellular responses to gamma irradiation. The level of p53 tumor-suppressor protein was found to be elevated 3 hr after irradiation of p53wild-type MCF-7 breast-carcinoma cells. Interestingly, accumulation of p53 was followed by up-regulation of surface Fas levels between 4 and 8 hr after irradiation. The level of Fas up-regulation was dependent on dose and, whereas elevation in the level of p53 was transient, enhancement of Fas expression was stable. Fas up-regulation occurred coincidentally with induction of G1 cell-cycle arrest, a post-irradiation phenomenon known to be dependent on wild-type-p53 activity. We studied 9 other tumor lines, 2 with wild-type p53, 5 with mutant p53, and 2 expressing no p53. All lines expressing wild-type p53 were found to arrest in G1 and to up-regulate Fas after irradiation. In contrast, all 7 p53null and p53mutant lines failed not only to arrest their cell cycles in G1 phase, but also to up-regulate Fas levels in response to treatment. These findings demonstrate a direct correlation between wild-type-p53 activity and Fas up-regulation after treatment with ionizing radiation, strongly suggesting that post-irradiation Fas up-regulation is dependent on wild-type-p53 activity. Since low doses of radiation were sufficient to modulate Fas expression, up-regulation of the Fas death receptor may have clinical implications following radiotherapy.

Sensitivity of Epstein-Barr virus-induced B cell tumor to apoptosis mediated by anti-CD95/Apo-1/fas antibody

Epstein-Barr virus (EBV) can induce uncontrolled B lymphocyte proliferation leading to fatal lymphoma in immunocompromised patients. The sensitivity to apoptosis of B lymphoid cell lines (LCL) derived from EBV-induced lymphoproliferative disorders was investigated. In vitro and in vivo, these B LCL strongly express CD95/Apo-1/fas antigen and undergo apoptosis upon stimulation with anti-Apo-1 monoclonal antibody. When inoculated into severe-combined immunodeficient (scid) mice, human B cells lines developed into rapidly growing tumors. Administration of an agonistic anti-Apo-1 antibody significantly delayed tumor progression. Relapses were frequent, but were not caused by selection of resistant B cells, since B cells from relapsing tumors underwent apoptosis on re-exposure. Induction of apoptosis by an anti-C95/Apo-1/fas-specific antibody could be applied for therapy of EBV-induced B cell tumors and contribute to our understanding of the mechanisms of T cell-mediated elimination of EBV lymphomas in immunodeficient patients.