Endogenous accumulation of IFN-gamma in IFN-gamma-R(-/-) mice increases resistance to B16F10-Nex2 murine melanoma: a model for direct IFN-gamma anti-tumor cytotoxicity in vitro and in vivo

Bradykinin promotes murine melanoma cell migration and invasion through endogenous production of superoxide and nitric oxide

Spatial confinement and temporal regulation of signaling by nitric oxide (NO) and reactive oxygen species (ROS) occurs in cancer cells. Signaling mediated by NO and ROS was investigated in two sub clones of the murine melanoma B16F10-Nex2 cell line, Nex10C and Nex8H treated or not with bradykinin (BK). The sub clone Nex10C, similar to primary site cells, has a low capacity for colonizing the lungs, whereas the sub clone Nex8H, similar to metastatic cells, corresponds to a highly invasive melanoma. BK-treated Nex10C cells exhibited a transient increase in NO and an inhibition in basal O₂^- levels. Inhibition of endogenous NO production by l-NAME resulted in detectable levels of O₂^-. l-NAME promoted Rac1 activation and enhanced Rac1-PI3K association. l-NAME in the absence of BK resulted in Nex10C cell migration and invasion, suggesting that NO is a negative regulator of O₂^- mediated cell migration and cell invasion. BK-treated Nex8H cells sustained endogenous NO production through the activation of NOS3. NO activated Rac1 and promoted Rac1-PI3K association. NO stimulated cell migration and cell invasion through a signaling axis involving Ras, Rac1 and PI3K. In conclusion, a role for O₂^- and NO as positive regulators of Rac1-PI3K signaling associated with cell migration and cell invasion is proposed respectively for Nex10C and Nex8H murine melanoma cells.

Immunomodulatory Protective Effects of Rb9 Cyclic-Peptide in a Metastatic Melanoma Setting and the Involvement of Dendritic Cells

The cyclic VHCDR3-derived peptide (Rb9) from RebMab200 antibody, directed to a NaPi2B phosphate-transport protein, displayed anti-metastatic melanoma activity at 50–300 μg intraperitoneally injected in syngeneic mice. Immune deficient mice failed to respond to the peptide protective effect. Rb9 induced increased CD8+ T and low Foxp3+ T cell infiltration in lung metastases and high IFN-γ and low TGF-β in lymphoid organs. The peptide co-localized with F-actin and a nuclear site in dendritic cells and specifically bound to MIF and CD74 in a dot-blot setting. Murine bone-marrow dendritic cells preincubated with Rb9 for 6 h were treated with MIF for short time periods. The modulated responses showed stimulation of CD74 and inhibition of pPI3K, pERK, and pNF-κB as compared to MIF alone. Rb9 in a melanoma-conditioned medium, stimulated the M1 type conversion in bone marrow-macrophages. Functional aspects of Rb9 in vivo were studied in therapeutic and prophylactic protocols using a melanoma metastatic model. In both protocols Rb9 exhibited a marked anti-melanoma protection. Human dendritic cells were also investigated showing increased expression of surface markers in response to Rb9 incubation. Rb9 either stimulated or slightly inhibited moDCs submitted to inhibitory (TGF-β and IL-10) or activating (LPS) conditions, respectively. Lymphocyte proliferation was obtained with moDCs stimulated by Rb9 and tumor cell lysate. In moDCs from cancer patients Rb9 exerted immunomodulatory activities depending on their functional status. The peptide may inhibit over-stimulated cells, stimulate poorly activated and suppressed cells, or cause instead, little phenotypic and functional alterations. Recently, the interaction MIF-CD74 has been associated to PD-L1 expression and IFN-γ, suggesting a target for melanoma treatment. The effects described for Rb9 and the protection against metastatic melanoma may suggest the possibility of a peptide reagent that could be relevant when associated to modern immunotherapeutic procedures.

TLR4-mediated immunomodulatory properties of the bacterial metalloprotease arazyme in preclinical tumor models

Despite the recent approval of new agents for metastatic melanoma, its treatment remains challenging. Moreover, few available immunotherapies induce a strong cellular immune response, and selection of the correct immunoadjuvant is crucial for overcoming this obstacle. Here, we studied the immunomodulatory properties of arazyme, a bacterial metalloprotease, which was previously shown to control metastasis in a murine melanoma B16F10-Nex2 model. The antitumor activity of arazyme was independent of its proteolytic activity, since heat-inactivated protease showed comparable properties to the active enzyme; however, the effect was dependent on an intact immune system, as antitumor properties were lost in immunodeficient mice. The protective response was IFNγ-dependent, and CD8(+) T lymphocytes were the main effector antitumor population, although B and CD4(+) T lymphocytes were also induced. Macrophages and dendritic cells were involved in the induction of the antitumor response, as arazyme activation of these cells increased both the expression of surface activation markers and proinflammatory cytokine secretion through TLR4-MyD88-TRIF-dependent, but also MAPK-dependent pathways. Arazyme was also effective in the murine breast adenocarcinoma 4T1 model, reducing primary and metastatic tumor development, and prolonging survival. To our knowledge, this is the first report of a bacterial metalloprotease interaction with TLR4 and subsequent receptor activation that promotes a proinflammatory and tumor protective response. Our results show that arazyme has immunomodulatory properties, and could be a promising novel alternative for metastatic melanoma treatment.

The complex and central role of interferon-γ in graft-versus-host disease and graft-versus-tumor activity

Allogeneic hematopoietic cell transplantation (allo-HCT) is increasingly being performed to treat patients with hematologic malignancies. However, separating the beneficial graft-versus-tumor (GVT) or graft-versus-leukemia effects from graft-versus-host disease (GVHD) has been difficult and remains a significant challenge toward improving therapeutic efficacy and reducing toxicity of allo-HCT. GVHD is induced by donor T cells that also mediate potent anti-tumor responses. However, despite the largely shared effector mechanisms, extensive animal studies have demonstrated the potential of dissociating the GVT effect from GVHD. Also in many clinical cases, long-term remission was achieved following allo-HCT, without significant GVHD. A better mechanistic understanding of the immunopathophysiology of GVHD and GVT effects may potentially help to improve allo-HCT as well as maximize the benefit of GVT effects while minimizing GVHD. In this article, we review the role of IFN-γ in regulation of alloresponses following allo-HCT, with a focus on the mechanisms of how this cytokine may separate GVHD from GVT effects.

Gene Therapy against Murine Melanoma B16F10-Nex2 Using IL-13Ralpha2-Fc Chimera and Interleukin 12 in Association with a Cyclopalladated Drug

Interleukin 13 (IL-13) is immunoregulatory in many diseases, including cancer. The protective or suppressive role of CD1-restricted natural killer T cells (NKT cells) in tumor immunosurveillance and immunity is well documented. Interleukin 12 (IL-12) can activate type I NKT cells to produce interferon-gamma (IFN-gamma), whereas type II NKT cells may produce IL-13. The high-affinity chain of IL-13Ralpha2 may act as negative inhibitor, suppressing the action of IL-13 and helping to maintain tumor immunosurveillance. We constructed an mIL-13Ralpha2-Fc chimera in a eukaryotic expression vector and confirmed the identity of the recombinant protein by immunoblot analysis and binding to IL-13 in chemiluminescent ELISA. Such DNA vaccine was tested against syngeneic B16F10-Nex2 murine melanoma. In vivo experiments showed a protective effect mediated by high production of IFN-gamma and down-regulation of anti-inflammatory interleukins mainly by NKT 1.1(+) T cells. Biochemoterapy in vivo with plasmid encoding mIL-13Ralpha2-Fc in association with plasmid encoding IL-12 and the 7A cyclopalladated drug led to a significant reduction in the tumor evolution with 30% tumor-free mice. We conclude that IL-12 gene therapy, followed by continuous administration of IL-13Ralpha2-Fc gene along with 7A-drug has antitumor activity involving the high production of proinflammatory cytokines and low immune suppression, specifically by NK1.1(+)T cells producing IL-13 and IL-10.

NFAT1 transcription factor is central in the regulation of tissue microenvironment for tumor metastasis

Members of the nuclear factor of activated T cell (NFAT) family of transcription factors were originally described in T lymphocytes but later shown to be expressed in several immune and non-immune cell types. NFAT proteins can modulate cellular transformation intrinsically, and NFAT-deficient (NFAT1-/-) mice are indeed more susceptible to transformation than wild-type counterparts. However, the contribution of an NFAT1-/- microenvironment to tumor progression has not been studied. We have addressed this question by inoculating NFAT1-/- mice with B16F10 melanoma cells intravenously, an established model of tumor homing and growth. Surprisingly, NFAT1-/- animals sustained less tumor growth in the lungs after melanoma inoculation than wild-type counterparts. Even though melanoma cells equally colonize NFAT1-/- and wild-type lungs, tumors do not progress in the absence of NFAT1 expression. A massive mononuclear perivascular infiltrate and reduced expression of TGF-β in the absence of NFAT1 suggested a role for tumor-infiltrating immune cells and the cytokine milieu. However, these processes are independent of an IL-4-induced regulatory tumor microenvironment, since lack of this cytokine does not alter the phenotype in NFAT1-/- animals. Bone marrow chimera experiments meant to differentiate the contributions of stromal and infiltrating cells to tumor progression demonstrated that NFAT1-induced susceptibility to pulmonary tumor growth depends on NFAT1-expressing parenchyma rather than on bone marrow-derived cells. These results suggest an important role for NFAT1 in radio-resistant tumor-associated parenchyma, which is independent of the anti-tumor immune response and Th1 versus Th2 cytokine milieu established by the cancer cells, but able to promote site-specific tumor growth.

Identification of iGb3 and iGb4 in melanoma B16F10-Nex2 cells and the iNKT cell-mediated antitumor effect of dendritic cells primed with iGb3

Background

CD1d-restricted iNKT cells are protective against murine melanoma B16F10-Nex2 growing subcutaneously in syngeneic C57Bl/6 mice as inferred from the fast tumor development in CD1d-KO in comparison with wild type animals. CD1d glycoproteins are related to the class I MHC molecules, and are involved in the presentation, particularly by dentritic cells (DC), of lipid antigens to iNKT cells. In the present work we attempted to identify the endogenous lipid mediator expressed in melanoma cells inducing such immunesurveillance response and study the possibility of protecting animals challenged with tumor cells with lipid-primed DC.

Results

Crude cytosolic and membrane fractions from in vivo growing melanoma contained iNKT-stimulating substances. Lipids were then extracted from these cells and one of the fractions (i.e. F3A) was shown to prime bone marrow-derived dendritic cells (BMDC) to stimulate iNKT murine hybridoma (DN32D3) cells to produce IL-2. The active fraction was analyzed by electrospray ionization-mass spectrometry (ESI-LIT-MS) and both iGb3 and iGb4 were identified along with GM3. When iGb3 was incubated with BMDC and tested with DN32D3 cells, IL-2 was equally produced indicating iNKT cell activation. GM3 consistently inhibited this response. To assess the antitumor response-induced by iGb3, a cytotoxicity assay in vitro was used with [³H]-thymidine labeled B16F10-Nex2 cells. At target/effector (iGb3-activated iNKT) cell ratio of 100^-1-100^-4 tumor cell lysis was shown. The antitumor activity in vivo was tested in mice challenged i.v. with B16F10-Nex2 cells and treated with iGb3- or α-galactosylceramide-primed DCs. A 4-fold lower tumor load in the lungs was observed with either treatment.

Conclusion

Our results show the expression of globo and isoglobohexosylceramides in murine melanoma B16F10-Nex2. The expression of iGb3 and its precursor, iGb4, on tumor cells may prime an effective iNKT cell-dependent antitumor response, modulated negatively by GM3 which is also produced in these cells. iGb3-primed BMDC exerted a significant iNKT cell-mediated anti-tumor activity in mice challenged with melanoma cells.

T-bet plays a key role in NK-mediated control of melanoma metastatic disease

Antitumor responses depend on type 1 immunity, which is severely impaired in mice deficient for the T-box expressed in T cells (T-bet) transcription factor. Both T-bet-deficient (T-bet(-/-)) NK and CTL show defective function, which can be overcome by strong stimuli due to the expression of eomesodermin, another member of the T-box family. The effective response from T-bet(-/-) mice to viral infection and tumor initiation corroborates with these findings. However, T-bet(-/-) animals fail to control cancer metastasis and are, therefore, highly susceptible to tumor spread. The mechanism of T-bet-dependent resistance to metastatic disease is not known. In this study, we show that T-bet plays a role in inhibiting cancer metastasis by regulating the longevity and function of NK cells. Our data demonstrate that the absence of a proper innate immune response driven by NK cells in T-bet(-/-) mice precludes the initiation of a potent adaptive response to tumors. Adoptive transfer of wild-type activated NK cells protects T-bet(-/-) animals after melanoma challenge showing that reconstitution of the NK compartment in these mice is sufficient to mediate a significant reduction in tumor burden. Transfer of T-bet(-/-) A-NK cells fails to do so, due to their reduced in vivo survival, inefficient lysis of cancer cells, and poor IFN-gamma production. Taken together, these results show for the first time an irreplaceable role for T-bet in the NK-mediated cross-talk between innate and adaptive immune responses to metastatic disease.

Antitumor effects in vitro and in vivo and mechanisms of protection against melanoma B16F10-Nex2 cells by fastuosain, a cysteine proteinase from Bromelia fastuosa

In the present work, the antitumor effect of fastuosain, a cysteine proteinase from Bromelia fastuosa, was investigated. In the intravenous model of lung colonization in C57Bl/6 mice, fastuosain and bromelain injected intraperitoneally were protective, and very few nodules of B16F10-Nex2 melanoma cells were detected. Tumor cells treated with fastuosain showed reduced expression of CD44 and decreased invasion through Matrigel, lost their cytoplasmic extensions and substrate adherence, and became round and detached, forming strongly bound cell clusters in suspension. Peritoneal cells recruited and activated by fastuosain treatment (mainly monocytic cells and lymphocytes) migrated to the lung, where pulmonary melanoma metastases grew. Adoptive transference of peritoneal cells recruited by fastuosain had no protective effect against lung metastases in recipient mice. Treatment of green fluorescent protein-chimeric animals with fastuosain did not change the number of cells that migrated to the lung, compared to PBS-injected control mice, but the number of positive major histocompatibility complex class II cells increased with fastuosain treatment. Murine antibodies against fastuosain, bromelain, and cathepsins B and L cross-reacted in ELISA and recognized surface and cytoplasmic components expressed on B16F10-Nex2 cells. Anti-fastuosain antibodies were cytotoxic/lytic to B16F10-Nex2 cells. Antitumor effects of fastuosain involve mainly the direct effect of the enzyme and elicitation of protective antibodies.

Modulatory effect of killed Propionibacterium acnes and its purified soluble polysaccharide on peritoneal exudate cells from C57Bl/6 mice: major NKT cell recruitment and increased cytotoxicity

Propionibacterium acnes has been described as a potent adjuvant to immune responses in vitro and in vivo. Presently, we analysed the modulation of peritoneal exudate cells (PEC) by heat-killed P. acnes or its purified soluble polysaccharide (PS), both injected intraperitoneally in C57Bl/6 mice, aiming at their recruitment and cytotoxicity. Both treatments induced an increase in macrophages, immature dendritic cells, B1a lymphocytes and NK1.1(+) CD3(+) cells. The bacterium caused a remarkable increase in a NK1.1(+) CD3(+) CD4(-) CD8(-) cells subpopulation, whereas the PS component seemed responsible for the recruitment of mainly macrophage cells. To assess P. acnes and PS adjuvant effect on PEC cytotoxicity we evaluated their in vitro effect on murine B16F10 melanoma cells. The effector cells from the heat-killed bacteria and PS-treated groups lysed melanoma cells in co-cultures with PEC. Mice genetically deficient in IFN-gamma, when stimulated with P. acnes or PS, had reduced PEC cytotoxicity, and the cytotoxic effect was completely abrogated in PEC from iNOS(-/-) mice. The tumoricidal activity of PEC from P. acnes-treated mice was mediated by macrophages and NKT cells stimulated with IL-12. In PS-treated mice the cytotoxicity was mediated mainly by macrophages. Moreover, both treatments increased IL-4 and IFN-gamma production by NKT cells. In conclusion, we show that P. acnes act mainly by recruiting and activating NKT double-negative cells in PEC, which were shown to be tumoricidal in vitro when induced by IL-12. Macrophages induced by both P. acnes and PS have their antitumour effect dependent on NO production.

Soluble components of Hericium erinaceum induce NK cell activation via production of interleukin-12 in mice splenocytes

AIM

To investigate the immunoregulatory functions of water extracts of Hericium erinaceum (WEHE) focusing on natural killer (NK) cell-based anticancer activities.

METHODS

Mouse splenocytes or purely isolated NK cells were stimulated with 1-100 mg/L WEHE for 24 h followed by co-culture with (51)Cr-labeled Yac-1 cells for 4 h, then NK cell-derived cytolytic activity was measured using a radio-release assay. Neutralizing antibodies against mouse interleukin-12 (IL-12) were added into the WEHE-stimulated splenocytes, thereafter, cytotoxicity was measured to examine the involvement of IL-12. RT-PCR and ELISA analyses were performed to confirm the induction of transcription and the translation of IL-12 and interferon-gamma (IFN-gamma) in the WEHE-treated splenocytes.

RESULTS

WEHE enhanced the cytolytic activity of total splenocytes towards Yac-1 cells in a dose-dependent manner. However, this activation was not observed when the NK cells isolated from the splenocytes were treated with WEHE. Furthermore, the treatment with antibodies against IL-12 abolished the effect of WEHE on splenocyte-derived cytolytic activity. RT-PCR and ELISA analyses showed the induction of IL-12 and IFN-gamma in the WEHE-treated splenocytes.

CONCLUSION

WEHE indirectly activates the cytolytic ability of NK cells via the induction of IL-12 in total splenocytes, and possibly via other immuno-mediators or cellular components.

Analysis of the interaction between IFN-gamma and IFN-gammaR in the effector phase of experimental murine allergic conjunctivitis

IFN-gamma acts to promote the severity of experimental allergic conjunctivitis (EC) during the effector phase. To identify the cell source and cell target of this cytokine in the effector phase of EC, we established mice lacking both IFN-gamma and the IFN-gamma receptor (Dbl-KO). Reciprocal adoptive transfer experiments involving wild-type, Dbl-KO, IFN-gamma-lacking and IFN-gammaR-lacking mice were performed. EC was then induced by RW challenge in eye drops. Analysis of the resulting eosinophil infiltration in the six donor/recipient combinations revealed that IFN-gamma produced by both donor and recipient cells plays an important role in the EC effector phase, and that the targets for this cytokine are also both donor and recipient cells. That EC was attenuated when any of the IFN-gamma-IFN-gammaR interactions were disturbed confirms that IFN-gamma promotes the severity of EC during the effector phase. These observations indicate that Dbl-KO mice will be useful for investigating the role(s) IFN-gamma play in inflammatory diseases.

MEL4B3, a novel mRNA is induced in skin tumors and regulated by TGF-beta and pro-inflammatory cytokines

Tumor-stroma interactions play a decisive role in the growth and metastasis of solid tumors, and involve signalling either by soluble mediators or direct cell-cell interaction. Here, we report the isolation and characterisation of a novel cDNA (MEL4B3), which is induced in cultured dermal fibroblasts exposed to supernatants of melanoma cell lines. MEL4B3 shares high homology with two predicted cDNA sequences for which no activity has so far been described. In situ hybridisation revealed the expression of MEL4B3 in malignant melanoma increasing with tumor depth; in basal cell carcinoma and in squamous cell carcinoma. MEL4B3 was barely detectable in normal skin or non-malignant melanocytic naevi. Furthermore, MEL4B3 was expressed at high level in the epidermis of psoriatic skin. In vitro, the expression of MEL4B3 was found to be induced by the exposure of human dermal fibroblasts to melanoma cell culture supernatants or to transforming growth factor-beta, interleukin-1 and tumor necrosis factor-alpha. The expression MEL4B3 therefore reflects closely cell activation occurring during tumor growth, metastasis and inflammation.

Mice lacking the IFN-gamma receptor or fyn develop severe experimental autoimmune uveoretinitis characterized by different immune responses

Endogenous interferon (IFN)-gamma negatively regulates experimental autoimmune uveoretinitis (EAU), a Th1-mediated disease. Although it is well known that IFN-gamma exerts its effects by binding to the IFN-gamma receptor (IFN-gammaR), the role that IFN-gammaR plays in the development of EAU has not been investigated. Fyn has been reported to inhibit Th2 differentiation. We aimed to investigate how endogenous IFN-gammaR and fyn, which influence Th1/Th2 differentiation, participate in the development of EAU. Sex-matched 6- to 10-week-old C57BL/6 wild-type (WT), IFN-gammaR knockout (GRKO) and fyn knockout (fyn KO) mice were compared. Mice were immunized subcutaneously with human interphotoreceptor retinoid-binding protein peptide 1-20 emulsified in Freund's complete adjuvant together with an intraperitoneal injection of Bordetella pertussis toxin. Three weeks later, mice were sacrificed, and their eyes and spleens were harvested for histopathologic analyses and examination of cellular immune responses, respectively. Cellular immune responses were evaluated by measuring the proliferative responses and cytokine production [interleukin (IL)-4, IL-5, IL-6, IL-13, IFN-gamma and tumor necrosis factor (TNF)-alpha] of splenocytes. The incidence of EAU was 40.0% in WT mice, 59.3% in GRKO mice and 78.6% in fyn KO mice. The average EAU score was 0.294 in WT mice, 0.917 in GRKO mice and 1.063 in fyn KO mice. Upon EAU induction, significant infiltration of eosinophils into the eyes was observed in GRKO and fyn KO mice compared to WT mice. Splenocytes from GRKO mice proliferated against the antigen and a mitogen more vigorously than those from WT and fyn KO mice. Stimulation of splenocytes with the antigen induced a higher production of IL-4, IL-6, IL-13 and IFN-gamma in GRKO mice compared to WT and fyn KO mice. In contrast, IL-5 and TNF-alpha were most abundantly produced by splenocytes from fyn KO mice compared to WT and GRKO mice. The incidence and mean severity of EAU were significantly higher in GRKO and fyn KO mice than in WT mice, suggesting that endogenous IFN-gammaR and fyn negatively regulate the development of EAU. The different cytokine production patterns by the GRKO and fyn KO mice indicate that the negative regulatory mechanism mediated by IFN-gammaR and fyn may differ.

Melanoma heterogeneity: differential, invasive, metastatic properties and profiles of cathepsin B, D and L activities in subclones of the B16F10-NEX2 cell line

Tumour cell lines and in vivo growing tumours are heterogeneous, comprising different cell clones. To understand why some cells primarily invade a tissue, while others are more apt to metastasize, several clones from the established B16F10-Nex2 cell line were isolated and 10 viable cells of each clone were injected intravenously into C57Bl/6 and Balb/c mice. Two cell clones (Nex2B and Nex2D) showed contrasting metastatic abilities. Clone 2D rather than clone 2B colonized the lungs of both mice after intravenous injection. Surprisingly, clone 2B grew more rapidly than 2D after subcutaneous implantation, significantly reducing the survival of injected mice. Clearly, dissociation between subcutaneous growth and metastatic ability was observed in clones from the same tumour cell lineage. Clone Nex2B continuously released proteolytic activity, including cathepsin B, and showed a greater capacity to invade Matrigel than clone Nex2D. Clone Nex2D accumulated cathepsins B, D and L intracellularly and released a moderate proteolytic activity in vitro that was inhibited with the time of incubation. E-64-treated Nex2B cells injected subcutaneously showed a significant delay in tumour development and increased survival of challenged animals. A similar result was obtained on treatment of clone 2B with chagasin, a cysteine proteinase inhibitor from Trypanosoma cruzi, even at 2 microM. Clone Nex2D was less sensitive to pretreatment with inhibitors of cysteine proteases for tumour development in vivo. Our results suggest that, in a tumour cell population, cells dissociate into metastatic and non-metastatic subtypes, and that release or accumulation of cathepsins can be a differential trait of these cells.

A novel approach in the treatment of neuroendocrine gastrointestinal tumors: additive antiproliferative effects of interferon-gamma and meta-iodobenzylguanidine

BACKGROUND

Therapeutic options to effectively inhibit growth and spread of neuroendocrine gastrointestinal tumors are still limited. As both meta-iodobenzylguanidine (MIBG) and interferon-gamma (IFNgamma) cause antineoplastic effects in neuroendocrine gastrointestinal tumor cells, we investigated the antiproliferative effects of the combination of IFNgamma and non-radiolabeled MIBG in neuroendocrine gut STC-1 and pancreatic carcinoid BON tumor cells.

METHODS AND RESULTS

IFNgamma receptors were expressed in both models. IFNgamma dose- and time-dependently inhibited the growth of both STC-1 and of BON tumor cells with IC50-values of 95 +/- 15 U/ml and 135 +/- 10 U/ml, respectively. Above 10 U/ml IFNgamma induced apoptosis-specific caspase-3 activity in a time-dependent manner in either cell line and caused a dose-dependent arrest in the S-phase of the cell cycle. Furthermore, IFNgamma induced cytotoxic effects in NE tumor cells. The NE tumor-targeted drug MIBG is selectively taken up via norepinephrine transporters, thereby specifically inhibiting growth in NE tumor cells. Intriguingly, IFNgamma treatment induced an upregulation of norepinephrine transporter expression in neuroendocrine tumors cells, as determined by semi-quantitative RT-PCR. Co-application of sub-IC50 concentrations of IFNgamma and MIBG led to additive growth inhibitory effects, which were mainly due to increased cytotoxicity and S-phase arrest of the cell cycle.

CONCLUSION

Our data show that IFNgamma exerts antiproliferative effects on neuroendocrine gastrointestinal tumor cells by inducing cell cycle arrest, apoptosis and cytotoxicity. The combination of IFNgamma with the NE tumor-targeted agent MIBG leads to effective growth control at reduced doses of either drug. Thus, the administration of IFNgamma alone and more so, in combination with MIBG, is a promising novel approach in the treatment of neuroendocrine gastrointestinal tumors.