A2A adenosine receptor protects tumors from antitumor T cells

The A2A adenosine receptor (A2AR) has been shown to be a critical and nonredundant negative regulator of immune cells in protecting normal tissues from inflammatory damage. We hypothesized that A2AR also protects cancerous tissues by inhibiting incoming antitumor T lymphocytes. Here we confirm this hypothesis by showing that genetic deletion of A2AR in the host resulted in rejection of established immunogenic tumors in approximately 60% of A2AR-deficient mice with no rejection observed in control WT mice. The use of antagonists, including caffeine, or targeting the A2 receptors by siRNA pretreatment of T cells improved the inhibition of tumor growth, destruction of metastases, and prevention of neovascularization by antitumor T cells. The data suggest that effects of A2AR are T cell autonomous. The inhibition of antitumor T cells via their A2AR in the adenosine-rich tumor microenvironment may explain the paradoxical coexistence of tumors and antitumor immune cells in some cancer patients (the "Hellstrom paradox"). We propose to target the hypoxia-->adenosine-->A2AR pathway as a cancer immunotherapy strategy to prevent the inhibition of antitumor T cells in the tumor microenvironment. The same strategy may prevent the premature termination of immune response and improve the vaccine-induced development of antitumor and antiviral T cells. The observations of autoimmunity during melanoma rejection in A2AR-deficient mice suggest that A2AR in T cells is also important in preventing autoimmunity. Thus, although using the hypoxia-->adenosine-->A2AR pathway inhibitors may improve antitumor immunity, the recruitment of this pathway by selective drugs is expected to attenuate the autoimmune tissue damage.

Drug-selected human lung cancer stem cells: cytokine network, tumorigenic and metastatic properties

Background

Cancer stem cells (CSCs) are thought to be responsible for tumor regeneration after chemotherapy, although direct confirmation of this remains forthcoming. We therefore investigated whether drug treatment could enrich and maintain CSCs and whether the high tumorogenic and metastatic abilities of CSCs were based on their marked ability to produce growth and angiogenic factors and express their cognate receptors to stimulate tumor cell proliferation and stroma formation.

Methodology/Findings

Treatment of lung tumor cells with doxorubicin, cisplatin, or etoposide resulted in the selection of drug surviving cells (DSCs). These cells expressed CD133, CD117, SSEA-3, TRA1-81, Oct-4, and nuclear β-catenin and lost expression of the differentiation markers cytokeratins 8/18 (CK 8/18). DSCs were able to grow as tumor spheres, maintain self-renewal capacity, and differentiate. Differentiated progenitors lost expression of CD133, gained CK 8/18 and acquired drug sensitivity. In the presence of drugs, differentiation of DSCs was abrogated allowing propagation of cells with CSC-like characteristics. Lung DSCs demonstrated high tumorogenic and metastatic potential following inoculation into SCID mice, which supported their classification as CSCs. Luminex analysis of human and murine cytokines in sonicated lysates of parental- and CSC-derived tumors revealed that CSC-derived tumors contained two- to three-fold higher levels of human angiogenic and growth factors (VEGF, bFGF, IL-6, IL-8, HGF, PDGF-BB, G-CSF, and SCGF-β). CSCs also showed elevated levels of expression of human VEGFR2, FGFR2, CXCR1, 2 and 4 receptors. Moreover, human CSCs growing in SCID mice stimulated murine stroma to produce elevated levels of angiogenic and growth factors.

Conclusions/Significance

These findings suggest that chemotherapy can lead to propagation of CSCs and prevention of their differentiation. The high tumorigenic and metastatic potentials of CSCs are associated with efficient cytokine network production that may represent a target for increased efficacy of cancer therapy.

Generation and accumulation of immunosuppressive adenosine by human CD4+CD25highFOXP3+ regulatory T cells

Naturally occurring regulatory T cells (nTreg) are crucial for maintaining tolerance to self and thus preventing autoimmune diseases and allograft rejections. In cancer, Treg down-regulate antitumor responses by several distinct mechanisms. This study analyzes the role the adenosinergic pathway plays in suppressive activities of human nTreg. Human CD4(+)CD25(high)FOXP3(+) Treg overexpress CD39 and CD73, ectonucleotidases sequentially converting ATP into AMP and adenosine, which then binds to A(2a) receptors on effector T cells, suppressing their functions. CD4(+)CD39(+) and CD4(+)CD25(high) T cells express low levels of adenosine deaminase (ADA), the enzyme responsible for adenosine breakdown, and of CD26, a surface-bound glycoprotein associated with ADA. In contrast, T effector cells are enriched in CD26/ADA but express low levels of CD39 and CD73. Inhibitors of ectonucleotidase activity (e.g. ARL67156) and antagonists of the A(2a) receptor (e.g. ZM241385) blocked Treg-mediated immunosuppression. The inhibition of ADA activity on effector T cells enhanced Treg-mediated immunosuppression. Thus, human nTreg characterized by the presence of CD39 and the low expression of CD26/ADA are responsible for the generation of adenosine, which plays a major role in Treg-mediated immunosuppression. The data suggest that the adenosinergic pathway represents a potential therapeutic target for regulation of immunosuppression in a broad variety of human diseases.

Role of NK cells in the control of metastatic spread and growth of tumor cells in mice

The ability of BALB/c nude and C57BL/6 mice to eliminate tumor cells from the blood stream was severely impaired after a single inoculation of 0.2 ml of anti-asialo BMI (asGMI) serum, diluted 1:40 to 1:320. The number of i.v.-inoculated YAC-I cells surviving in the lungs of BALB/c nude mice pretreated with anti-asGMI serum was 28 times higher than in the control nude mice. In this respect, nude mice treated with anti-asGMI behaved similarly to beige mice. The increase in the initial survival of tumor cells in the mice that was induced by pre-treatment with anti-asGMI resulted in a substantial increase in the number of artificial lung metastases that developed. In C57BL/6 +/+ mice treated with anti-asGMI and in C57BL/6 beige mice, i.v. inoculation of B16 melanoma cells induced 10 times more metastatic foci in the lungs than in the control C57BL/6 +/+ mice. In contrast, in nude mice which possess higher levels of NK reactivity, metastatic growth was suppressed 7-fold in comparison with intact C57BL/6 +/+ mice. In beige mice and in C57BL/6 +/+ mice treated with anti-asGMI, multiple metastatic foci developed in the liver, whereas in control C57BL/6 +/+ and nude mice, no extrapulmonary metastases were found. These data indicate that B16 melanoma cells are able to grow in the liver, but their growth is ordinarily prevented by NK cells. The antimetastatic defense of C57BL/6 mice treated by anti-asGMI could be restored by transplantation of 40 X 10(6) normal spleen cells. This antimetastatic effect of transplanted spleen cells was mediated by asGMI-bearing cells, since after in vitro pre-treatment of normal spleen cells with anti-asGMI and complement, they lost their ability to inhibit the development of artificial metastases in the lungs of C57BL/6 mice. Suppression of NK reactivity by multiple injections of anti-asGMI (every 4 to 5 days), in C57BL/6 mice inoculated intrafootpad (i.f.p.) with B16 melanoma or 3LL tumor cells, did not influence the growth of local tumors, but dramatically accelerated the development of spontaneous pulmonary metastases. These data demonstrate that NK cells may play an important role in resistance to the dissemination of tumor cells, and therefore contribute to the control of metastasis formation in mice.

Multiplexed immunobead-based cytokine profiling for early detection of ovarian cancer

Early detection of ovarian cancer might improve clinical outcome. Some studies have shown the role of cytokines as a new group of tumor markers for ovarian cancer. We hypothesized that a panel comprised of multiple cytokines, which individually may not show strong correlation with the disease, might provide higher diagnostic power. To evaluate the diagnostic utility of cytokine panel, we used a novel multianalyte LabMAP profiling technology that allows simultaneous measurement of multiple markers. Concentrations of 24 cytokines (cytokines/chemokines, growth, and angiogenic factors) in combination with cancer antigen-125 (CA-125), were measured in sera of 44 patients with early-stage ovarian cancer, 45 healthy women, and 37 patients with benign pelvic tumors. Six markers, i.e., interleukin (IL)-6, IL-8, epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), monocyte chemoattractant protein-1 (MCP-1), and CA-125, showed significant differences in serum concentrations between ovarian cancer and control groups. Out of this group, IL-6, IL-8, VEGF, EGF, and CA-125, were used in a classification tree analysis that resulted in 84% sensitivity at 95% specificity. The receiver operator characteristic curve created using the combination of markers produced sensitivities between 90% and 100% in the area of 80% to 90% specificity, whereas the receiver operator characteristic curve for CA-125 alone resulted in sensitivities of 70% to 80%. The classification tree analysis for discrimination of benign condition from ovarian cancer used CA-125, granulocyte colony-stimulating factor (G-CSF), IL-6, EGF, and VEGF resulting in 86.5% sensitivity and 93.0% specificity. The presented data show that simultaneous testing of a panel of serum cytokines and CA-125 using LabMAP technology may present a promising approach for ovarian cancer detection.

On the role of cell surface carbohydrates and their binding proteins (lectins) in tumor metastasis

This review focuses on the recent advances in investigations of the role of cell surface carbohydrates in tumor metastasis. It also summarizes the results of extensive studies of endogenous lectins, their structure, carbohydrate specificity and biological functions with the major emphasis on the significance of lectin-cell surface carbohydrate interactions in a metastatic process. Numerous data demonstrate that malignant transformation is associated with various and complex alterations in the glycosylation process. Some of these changes might provide a selective advantage for tumor cells during their progression to more invasive and metastatic phenotype. Cell glycosylation depends on the expression and function of various glycosyltransferases and glycosidases. Recently, transfection of genes encoding various glysosyltransferases gene in sense and antisense orientation helped to bring direct evidence that changes in cell surface carbohydrates are important for the metastatic behavior of tumor cells. Cell surface carbohydrates affect tumor cell interactions with normal cells or with the extracellular matrix during metastatic spread and growth. These interactions can be mediated via tumor cell carbohydrates and their binding proteins known as endogenous lectins. The family of the discovered endogenous lectins is rapidly expanding. The number of C-type lectins has reached 50 and at least 10 galectins have been identified. The biological significance of the endogenous lectins and their possible role in tumor growth and metastasis formation has started to unravel. Some lectins recognize the 'foreign' patterns of cell surface carbohydrates expressed by microorganisms and tumor cells, and play a role in innate and adaptive immunity. It was shown that lectins affect tumor cell survival, adhesion to the endothelium or extracellular matrix, as well as tumor vascularization and other processes that are crucial for metastatic spread and growth.

Development of a multimarker assay for early detection of ovarian cancer

PURPOSE

Early detection of ovarian cancer has great promise to improve clinical outcome.

PATIENTS AND METHODS

Ninety-six serum biomarkers were analyzed in sera from healthy women and from patients with ovarian cancer, benign pelvic tumors, and breast, colorectal, and lung cancers, using multiplex xMAP bead-based immunoassays. A Metropolis algorithm with Monte Carlo simulation (MMC) was used for analysis of the data.

RESULTS

A training set, including sera from 139 patients with early-stage ovarian cancer, 149 patients with late-stage ovarian cancer, and 1,102 healthy women, was analyzed with MMC algorithm and cross validation to identify an optimal biomarker panel discriminating early-stage cancer from healthy controls. The four-biomarker panel providing the highest diagnostic power of 86% sensitivity (SN) for early-stage and 93% SN for late-stage ovarian cancer at 98% specificity (SP) was comprised of CA-125, HE4, CEA, and VCAM-1. This model was applied to an independent blinded validation set consisting of sera from 44 patients with early-stage ovarian cancer, 124 patients with late-stage ovarian cancer, and 929 healthy women, providing unbiased estimates of 86% SN for stage I and II and 95% SN for stage III and IV disease at 98% SP. This panel was selective for ovarian cancer showing SN of 33% for benign pelvic disease, SN of 6% for breast cancer, SN of 0% for colorectal cancer, and SN of 36% for lung cancer.

CONCLUSION

A panel of CA-125, HE4, CEA, and VCAM-1, after additional validation, could serve as an initial stage in a screening strategy for epithelial ovarian cancer.

Multiplex analysis of serum cytokines in melanoma patients treated with interferon-alpha2b

PURPOSE

Interferon (IFN)-alpha2b is the only Food and Drug Administration-approved treatment for operable high-risk melanoma that has been shown to significantly and durably prolong relapse-free survival (RFS) of patients with stage IIB-III melanoma. Development of reliable serum assays may contribute to the development of methods for earlier detection of melanoma and the selection of patients who may be most susceptible to current available interventions with IFNalpha.

EXPERIMENTAL DESIGN

A powerful high-throughput xMAP multiplex immunobead assay technology (Luminex Corp., Austin, TX) was used to simultaneously test 29 cytokines, chemokines, angiogenic as well as growth factors, and soluble receptors in the sera of 179 patients with high-risk melanoma and 378 healthy individuals.

RESULTS

Serum concentrations of interleukin (IL)-1alpha, IL-1beta, IL-6, IL-8, IL-12p40, IL-13, granulocyte colony-stimulating factor, monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, IFNalpha, tumor necrosis factor (TNF)-alpha, epidermal growth factor, vascular endothelial growth factor (VEGF), and TNF receptor II were found to be significantly higher in patients with resected high-risk melanoma compared with healthy controls. Bayesian Network algorithm classification of the data offered 90% sensitivity at 98% specificity with 96.5% of melanoma patients distinguished from healthy individuals. IFN-alpha2b therapy resulted in a significant decrease of serum levels of immunosuppressive and tumor angiogenic/growth stimulatory factors (VEGF, epidermal growth factor, and hepatocyte growth factor) and increased levels of antiangiogenic IFN-gamma inducible protein 10 (IP-10) and IFN-alpha. Pretreatment levels of proinflammatory cytokines IL-1beta, IL-1alpha, IL-6, TNF-alpha, and chemokines MIP-1alpha and MIP-1beta were found to be significantly higher in the serum of patients with longer RFS values of 1 to 5 and >5 years when compared with patients with shorter RFS of <1 year.

CONCLUSION

These data show that multiplexed analysis of serum biomarkers is useful for the evaluation of prognostic markers of clinical outcome and potential predictive markers of response to IFN-alpha2b in patients with high-risk operable melanoma.

Increased ectonucleotidase expression and activity in regulatory T cells of patients with head and neck cancer

PURPOSE

Regulatory T cell (Treg) frequency and activity are increased in cancer patients and play a major role in tumor escape. Although disease progression is favored by the presence of Treg, mechanisms used by Treg to suppress antitumor immunity are unknown. The ectonucleotidases CD39 and CD73 are expressed in Treg and convert ATP into immunosuppressive adenosine. In this study, the involvement of the adenosinergic pathway in Treg-mediated suppression in head and neck squamous cell carcinoma (HNSCC) patients was evaluated.

EXPERIMENTAL DESIGN

HNSCC patients with an active disease (n = 19) and patients with no evident disease after therapy (n = 14) were studied. Ectonucleotidase expression on CD4(+) T cells and CD4(+)CD25(high) Treg was evaluated by flow cytometry and compared with normal controls. Ectonucleotidase activity was also compared within these three groups. The data were analyzed for associations of ectonucleotidase expression/function with disease stage.

RESULTS

The percentages and expression levels of CD39 and CD73 in CD4(+) T cells and Treg were greater in HNSCC than in normal controls and highest in patients with no evident disease. Patients' Treg hydrolyzed ATP at higher rates and produced higher levels of adenosine than normal controls' Treg. The increased frequency and enzymatic activity of CD4(+)CD39(+) cells corresponded to increased adenosine-mediated suppression of effector T cells, which was partly inhibited by ARL67156, an ectonucleotidase inhibitor, and by ZM241385, a selective A(2a)/A(2b) receptor antagonist.

CONCLUSIONS

CD39(+) Treg frequency and adenosine-mediated suppression are significantly increased in HNSCC patients. The adenosinergic pathway is involved in Treg-mediated immunosuppression in cancer and its attenuation could be a promising immunotherapeutic strategy for patients with HNSCC.

Gs protein-coupled adenosine receptor signaling and lytic function of activated NK cells

The effect of adenosine and its analogues on the cytotoxic activity of IL-2-activated NK cells was investigated. Adenosine is an endogenous ligand for four different adenosine receptor (AdoR) subtypes (AdoRA1, AdoRA2A, AdoRA2B, and AdoRA3). Increased concentrations of adenosine were found in ascites of MethA sarcoma or in culture medium of 3LL Lewis lung carcinoma growing under hypoxic conditions. We hypothesize that intratumor adenosine impairs the ability of lymphokine-activated killer (LAK) cells to kill tumor cells. The effect of AdoR engagement on LAK cells cytotoxic activity was analyzed using AdoR agonists and antagonists as well as LAK cells generated from AdoR knockout mice. Adenosine and its analogues efficiently inhibited the cytotoxic activity of LAK cells. CGS21680 (AdoRA2A agonist) and 5-N-ethylcarboxamide adenosine (NECA) (AdoRA2A/ADoRA2B agonist) inhibited LAK cell cytotoxicity in parallel with their ability to increase cAMP production. The inhibitory effects of stable adenosine analog 2-chloroadenosine (CADO) and AdoRA2 agonists were blocked by AdoRA2 antagonist ZM 241385. Adenosine and its analogues impair LAK cell function by interfering with both perforin-mediated and Fas ligand-mediated killing pathways. Studies with LAK cells generated from AdoRA1-/- and AdoRA3-/- mice ruled out any involvement of these AdoRs in the inhibitory effects of adenosine. LAK cells with genetically disrupted AdoRA2A were resistant to the inhibitory effects of adenosine, CADO and NECA. However, with extremely high concentrations of CADO or NECA, mild inhibition of LAK cytotoxicity was observed that was probably mediated via AdoRA2B signaling. Thus, by using pharmacological and genetic blockage of AdoRs, our results clearly indicate the prime importance of cAMP elevating AdoR2A in the inhibitory effect of adenosine on LAK cell cytotoxicity. The elevated intratumor levels of adenosine might inhibit the antitumor effects of activated NK cells.

Adenosine and prostaglandin E2 cooperate in the suppression of immune responses mediated by adaptive regulatory T cells

Adaptive regulatory T cells (Tr1) are induced in the periphery upon encountering cognate antigens. In cancer, their frequency is increased; however, Tr1-mediated suppression mechanisms are not yet defined. Here, we evaluate the simultaneous involvement of ectonucleotidases (CD39/CD73) and cyclooxygenase 2 (COX-2) in Tr1-mediated suppression. Human Tr1 cells were generated from peripheral blood mononuclear cell-derived, sorted CD4(+)CD25(-) T cells and incubated with autologous immature dendritic cells, irradiated COX-2(+) or COX-2(-) tumor cells, and IL-2, IL-10, and IL-15 (each at 10-15 IU/ml) for 10 days as described (Bergmann, C., Strauss, L., Zeidler, R., Lang, S., and Whiteside, T. L. (2007) Cancer Immunol. Immunother. 56, 1429-1442). Tr1 were phenotyped by multicolor flow cytometry, and suppression of proliferating responder cells was assessed in carboxyfluorescein diacetate succinimidyl ester-based assays. ATP hydrolysis was measured using a luciferase detection assay, and levels of adenosine or prostaglandin E(2) (PGE(2)) in cell supernatants were analyzed by mass spectrometry or ELISA, respectively. Intracellular cAMP levels were measured by enzyme immunoassay. The COX-2(+) tumor induced a greater number of Tr1 than COX-2(-) tumor (p < 0.05). Tr1 induced by COX-2(+) tumor were more suppressive, hydrolyzed more exogenous ATP (p < 0.05), and produced higher levels of adenosine and PGE(2) (p < 0.05) than Tr1 induced by COX-2(-) tumor. Inhibitors of ectonucleotidase activity, A(2A) and EP(2) receptor antagonists, or an inhibitor of the PKA type I decreased Tr1-mediated suppression (p < 0.05), whereas rolipram, a PDE(4) inhibitor, increased the intracellular cAMP level in responder cells and their susceptibility to Tr1-mediated suppression. Tr1 present in tumors or the peripheral blood of head and neck squamous cell carcinoma patients co-expressed COX-2, CD39, and CD73. A concomitant inhibition of PGE(2) and adenosine via the common intracellular cAMP pathway might be a novel approach for improving results of immune therapies for cancer.

Isolation of functional human regulatory T cells (Treg) from the peripheral blood based on the CD39 expression

Human regulatory T cells (Treg) have been variously defined as CD4(+)CD25(+), CD4(+)CD25(high) or CD4(+)CD25(high)FOXP3(+) cells which are responsible for maintaining peripheral tolerance. Their isolation from human peripheral blood or tissues depends on the expression level of CD25(IL-2Ralpha) - a surface marker which is also expressed on activated effector helper T cells. CD39, a cell surface associated ectonucleotidase, can be used to purify Treg with strong suppressor functions. The CD4(+)CD39(+) T cells catalyze cleavage of adenosine triphosphate (ATP) to adenosine monophosphate (AMP), which is then further cleaved to adenosine. CD4(+)CD39(+) T cells largely overlap with CD4(+)CD25(high)FOXP3(+) but not CD4(+)CD25(+) T cell subset, and mediate equally potent immune suppression. Thus, CD39 surface marker can be successfully used for routine isolation of functionally-active human Treg from the peripheral blood of healthy donors or patients with cancer for studies of their role in health and disease.

Differential expression of H-2 gene products in tumour cells in associated with their metastatogenic properties

Many neoplasms seem to be heterogeneous in nature, producing metastases by pre-existing variant cells with inherent biochemical and biological properties. The survival and proliferation of metastatic cells depend on various biological properties, such as enzymes which degrade basement membranes, resistance to various host defence systems, association with host cellular components, adhesiveness and expression of certain membrane glycoproteins. Recent studies have indicated that metastatic cells may differ from the local tumour cells in the expression of immune recognizable membrane-associated antigens. Such antigenic differences may result from an immunoselection of cells with distinct antigenic properties due to a specific immune response evoked against the local tumour. In view of the role of the major histocompatibility complex (MHC) system in controlling and restricting the function of immune effector cells against modified self-components, one could assume that the modulation of the expression of MHC-encoded antigens on the membrane of tumour cells influenced the interclonal relationship within a local heterogeneous tumour cell population and the subsequent generation of metastasis. The modulation of the expression of H-2 antigens on several murine tumours is well documented; however, practically no attempts were made to relate H-2 modulation with invasiveness. We now describe principal differences in the expression of H-2 parental haplotypes between a local F1 methylcholanthrene-induced tumour and its descendant pulmonary metastases. These results suggest that both the expression and the immunogenicity of MHC products strongly influence the immune relationship between the tumour and the host's immune system, thus determining the generation and dissemination of metastases.

Elimination of human lung cancer stem cells through targeting of the stem cell factor-c-kit autocrine signaling loop

Cancer stem cells (CSC) are thought to be responsible for tumor initiation and tumor regeneration after chemotherapy. Previously, we showed that chemotherapy of non-small cell lung cancer (NSCLC) cells lines can select for outgrowth of highly tumorigenic and metastatic CSCs. The high malignancy of lung CSCs was associated with an efficient cytokine network. In this study, we provide evidence that blocking stem cell factor (SCF)-c-kit signaling is sufficient to inhibit CSC proliferation and survival promoted by chemotherapy. CSCs were isolated from NSCLC cell lines as tumor spheres under CSC-selective conditions and their stem properties were confirmed. In contrast to other tumor cells, CSCs expressed c-kit receptors and produced SCF. Proliferation of CSCs was inhibited by SCF-neutralizing antibodies or by imatinib (Gleevec), an inhibitor of c-kit. Although cisplatin treatment eliminated the majority of tumor cells, it did not eliminate CSCs, whereas imatinib or anti-SCF antibody destroyed CSCs. Significantly, combining cisplatin with imatinib or anti-SCF antibody prevented the growth of both tumor cell subpopulations. Our findings reveal an important role for the SCF-c-kit signaling axis in self-renewal and proliferation of lung CSCs, and they suggest that SCF-c-kit signaling blockade could improve the antitumor efficacy of chemotherapy of human NSCLC.

Recombination of retrotransposon and exogenous RNA virus results in nonretroviral cDNA integration

Retroviruses have the potential to acquire host cell-derived genetic material during reverse transcription and can integrate into the genomes of larger, more complex DNA viruses. In contrast, RNA viruses were believed not to integrate into the host's genome under any circumstances. We found that illegitimate recombination between an exogenous nonretroviral RNA virus, lymphocytic choriomeningitis virus, and the endogenous intracisternal A-type particle (IAP) retrotransposon occurred and led to reverse transcription of exogenous viral RNA. The resulting complementary DNA was integrated into the host's genome with an IAP element. Thus, RNA viruses should be closely scrutinized for any capacity to interact with endogenous retroviral elements before their approval for therapeutic use in humans.

Adenosine-Mediated Inhibition of the Cytotoxic Activity and Cytokine Production by Activated Natural Killer Cells

Adenosine is an important signaling molecule that regulates multiple physiologic processes and exerts major anti-inflammatory actions. Tumors have high concentrations of adenosine, which could inhibit the function of tumor-infiltrating lymphoid cells. We investigated the ability of adenosine and its stable analogue 2-chloroadenosine (CADO) to inhibit cytokine production and cytotoxic activity of lymphokine-activated killer (LAK) cells and determined whether both these effects are initiated via a common pathway. CADO strongly inhibited cytotoxic activity of LAK cells and attenuated the production of IFN-gamma, granulocyte macrophage colony-stimulating factor, tumor necrosis factor alpha, and macrophage inflammatory protein-1alpha by LAK cells stimulated by cross-linking of the Ly49D receptor. These inhibitory effects were associated with the ability of CADO to stimulate cyclic AMP (cAMP) production and activate protein kinase A (PKA). Using cAMP analogues with different affinities for the A and B sites of the regulatory subunits of PKA types I and II, we found that activation of PKA I, but not PKA II, mimicked the inhibitory effects of CADO on LAK cell cytotoxic activity and cytokine production. Inhibitors of the PKA catalytic subunits (H89 and PKI(14-22) peptide) failed to abrogate the inhibitory effects of CADO whereas Rp-8-Br-cAMPS, an antagonist of the RI subunit, blocked the inhibitory effects of CADO. We conclude that the inhibitory effects of adenosine are probably mediated via cAMP-dependent activation of the RI subunits of PKA I but are independent of the catalytic activity of PKA. Tumor-produced adenosine could be a potent tumor microenvironmental factor inhibiting the functional activity of tumor-infiltrating immune cells.

Circulating IL-8 and anti-IL-8 autoantibody in patients with ovarian cancer

OBJECTIVES

In an ongoing effort to identify diagnostic ovarian cancer biomarkers, SEREX (serological analysis of recombinant cDNA expression libraries) technique was employed resulting in detection of 20 known genes, nine ESTs and one novel sequence. Interleukin-8 (IL-8) was one of ovarian cancer-associated antigens identified by SEREX screening. The objective of this study was, therefore, to evaluate the potential importance of circulating anti-IL-8 antibody as ovarian cancer biomarker.

METHODS

We developed and optimized a new immunofluorescent bead-based assay for detection of anti-IL-8 antibody in blood serum. Circulating IL-8 and anti-IL-8 IgG concentrations were measured in blood sera from 44 patients with early stage (I-II) ovarian cancer, 50 patients with late stage (III-IV) ovarian cancer, 37 patients with benign pelvic masses, and 80 healthy women using the bead-based assay.

RESULTS

Our data indicate that serum contains IL-8 cytokine, anti-IL-8 antibody, and IL-8:anti-IL-8 complexes. We found that concentrations of IL-8 and anti-IL-8 antibody were elevated in sera of patients with ovarian cancer as compared with healthy controls. Logistic regression analysis of circulating concentrations of anti-IL-8 IgG in patients with stages I-II ovarian cancer versus healthy controls allowed for prediction of early ovarian cancer with 98% specificity, 65.5% sensitivity, 80.3% of patients correctly classified. Combining IL-8 and anti-IL-8 IgG with CA 125 resulted in increased classification power as compared to individual markers analyzed separately.

CONCLUSION

Thus, IL-8 and anti-IL-8 autoantibody might potentially serve as additional biomarkers for ovarian cancer.

Inhibition of cytokine production and cytotoxic activity of human antimelanoma specific CD8+ and CD4+ T lymphocytes by adenosine-protein kinase A type I signaling

The goal of this study was to investigate the effects of adenosine and its stable analogue 2-chloroadenosine (CADO) on the cytotoxic activity and cytokine production by human antimelanoma specific CD8+ and CD4+ T-helper type 1 (Th1) clones. The cytotoxic activity of CD8+ T cells was inhibited by adenosine and CADO. Using Lab MAP multiplex technology, we found that adenosine inhibits production of various cytokines and chemokines by CD8+ and CD4+ T cells. Studies with CGS21680, a specific agonist of adenosine A2A receptor (AdoRA2A), and ZM241385, an AdoRA2-selective antagonist, indicate that the inhibitory effects of adenosine are mediated via cyclic AMP (cAMP)-elevating AdoRA2A, leading to protein kinase A (PKA) activation. Using cAMP analogues with different affinities for the A and B sites of the regulatory subunits of PKAI and PKAII, we found that activation of PKAI, but not of PKAII, mimicked the inhibitory effects of adenosine on T-cell cytotoxic activity and cytokine production. Inhibitors of the PKA catalytic subunits (H89 and PKA inhibitor peptide 14-22) failed to abrogate the inhibitory effects of CADO. In contrast, Rp-8-Br-cAMPS that antagonizes binding of cAMP to the regulatory I subunit and PKA activation was efficient in blocking the inhibitory effect of adenosine on the functional activity of T cells. Our findings on the ability of adenosine to inhibit the effector function of antimelanoma specific T cells suggest that intratumor-produced adenosine could impair the function of tumor-infiltrating T lymphocytes. Thus, blocking the inhibitory activity of tumor-produced adenosine might represent a new strategy for improvement of cancer immunotherapy.

Adenosine-Mediated Inhibition of Cytotoxic Activity and Cytokine Production by IL-2/NKp46-Activated NK cells: Involvement of Protein Kinase A Isozyme I (PKA I)

Adenosine suppresses the production of various cytokines/ chemokines and inhibits the cytotoxic activity of murine and human NK cells activated with IL-2 or Ly49D, NKp46-receptor crosslinking, respectively. These effects are mediated by the type A2A adenosine receptor via stimulation of adenylyl cyclase, increased production of cAMP, and activation of PKA. PKA I, but not PKA II, participates in the inhibitory effects of adenosine. Blocking regulatory, but not catalytic, subunits of PKA I abrogates the inhibitory effects of adenosine. These findings suggest that tumor-produced adenosine inhibits the activity of NK and other effector cells and thereby protects tumors from immune-mediated destruction.

Role of NK cells in the antimetastatic effect of anticoagulant drugs

The antimetastatic effects of heparin (40 units) and prostacyclin (PGI2, 100 microgram)1 were investigated in normal mice and in mice with depressed or activated natural killer (NK) cell activity. Both anticoagulants inhibited the formation of lung metastases after inoculation of the FI or F10 sublines of B16 melanoma. Inhibition of NK activity by treatment of mice with anti-asialo GM1 serum abrogated the antimetastatic effects of PGI2 or heparin. Conversely, augmentation of NK-cell activity by poly I:C plus treatment with anticoagulants produced synergistic antimetastatic effects. A similar pattern of results was obtained with heparin treatment of mice challenged with the Madison lung carcinoma (M109), but PGI2 alone or in combination with theophylline had little or no detectable antimetastatic effect on M109 or on the parental B16 melanoma. Studies of the mechanism of the interaction between heparin nd NK cells revealed that the anticoagulant treatment did not affect splenic NK activity in vitro. However, heparin treatment caused a significant increase in the clearance of radiolabelled tumor cells from the lungs of normal mice. Combined treatment of mice with poly I:C and heparin synergistically accelerated the elimination of radiolabelled tumor cells. In contrast, heparin did not affect the clearance of tumor cells from the lungs of mice with depressed NK activity. Thus the antimetastatic effects of heparin and PGI2 are dependent on levels of NK activity in the host. Platelet aggregation and fibrin coating of the surface of tumor cells may be among the mechanisms by which hematogenously spread tumor cells are protected from destruction by NK cells. Anticoagulant drugs may exert antimetastatic effects by making tumor cells more vulnerable to the cytotoxic effects of NK cells, rather than by blocking adherence of tumor cells to vascular endothelium.

Differences in cell surface antigens of tumor metastases and those of the local tumor

Tests were made to determine whether cell surface tumor antigens of metastases differed from the tumor antigens of the cell population of the local tumor growth. C57BL/6 mouse spleen lymphocytes sensitized against monolayers of the local growth of the 3LL Lewis lung carcinoma (L-3LL) in the presence of syngeneic serum generated lymphocytes that were cytotoxic to L-3LL but significantly less cytotoxic to target cells derived from lung metastases (M-3LL). Lymphocytes sensitized against M-3LL were significantly more cytotoxic against M-3LL than against L-3LL cells. Anti-M-3LL cytotoxic lymphocytes but not anti-L-3LL, admixed with either L-3LL cells or M-3LL tumor cells, when injected into syngeneic recipients reduced lung metastasis significantly. Results indicated that cells with high metastatic capacity and distinct antigenic properties exist within the tumor cell population and that immunoselection might be involved in the production of lung metastases.

Biological significance of prolactin in gynecologic cancers

There is increasing evidence that prolactin (PRL), a hormone/cytokine, plays a role in breast, prostate, and colorectal cancers via local production or accumulation. Elevated levels of serum PRL in ovarian and endometrial cancers have been reported, indicating a potential role for PRL in endometrial and ovarian carcinogenesis. In this study, we show that serum PRL levels are significantly elevated in women with a strong family history of ovarian cancer. We show dramatically increased expression of PRL receptor in ovarian and endometrial tumors as well as in endometrial hyperplasia, signifying the importance of PRL signaling in malignant and premalignant conditions. PRL mRNA was expressed in ovarian and endometrial tumors, indicating the presence of an autocrine loop. PRL potently induced proliferation in several ovarian and endometrial cancer cell lines. Binding of PRL to its receptor was followed by rapid phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, mitogen-activated protein kinase/ERK kinase 1, signal transducer and activator of transcription 3, CREB, ATF-2, and p53 and activation of 37 transcription factors in ovarian and endometrial carcinoma cells. PRL also activated Ras oncogene in these cells. When human immortalized normal ovarian epithelial cells were chronically exposed to PRL, a malignant transformation occurred manifested by the acquired ability of transformed cells to form clones, grow in soft agar, and form tumors in severe combined immunodeficient-beige mice. Transformation efficiency was diminished by a Ras inhibitor, providing proof that PRL-induced transformation uses the Ras pathway. In summary, we present findings that indicate an important role for PRL in ovarian and endometrial tumorigenesis. PRL may represent a risk factor for ovarian and endometrial cancers.

Lectin-induced apoptosis of tumour cells

The mechanisms of cytotoxic activity of Griffonia simplicifolia 1-B4 (GS1B4) and wheat germ agglutinin (WGA) lectins against various murine tumour cell lines were studied. Tumour cells that lack lectin-binding carbohydrates were resistant to lysis by these lectins. However, YAC-1 cells that expressed GS1B4 lectin-binding sites showed low sensitivity to lysis. To further analyse the relative importance of cell surface carbohydrates in lectin cytotoxicity, BL6-8 melanoma cells, which do not express the alpha 1,3 galactosyltransferase (alpha 1,3GT) gene and cell surface alpha-galactosyl epitopes reacting with GS1B4 lectin, were transfected with cDNA encoding alpha 1,3GT. After transfection, BL6-8 cells expressed high levels of GS1B4-binding alpha-galactosyl epitopes, but remained resistant to lysis by GS1B4 lectin, suggesting that the presence of lectin-binding epitopes, while essential, is not sufficient for tumour cell lysis and probably some intracellular mechanisms are involved in the regulation of lectin-mediated cytotoxicity. We found that the GS1B4 and WGA lectins induced apoptosis with DNA fragmentation of sensitive, but not resistant, tumour cell lines. DNA fragmentation, as well as tumour cell lysis, was blocked in the presence of the specific inhibitory sugar. To determine whether binding of the lectin to cell surface carbohydrates is sufficient to trigger tumour cell lysis, lectin-sensitive CL8-1 melanoma cells were incubated with GS1B4 lectin immobilized on agarose beads. Although these tumour cells bind to the immobilized lectin, it failed to trigger tumour cell death, suggesting that only soluble lectin is capable of tumour cell lysis and lectin internalization is probably required for their lysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of eotaxin-1 signaling in ovarian cancer

PURPOSE

Tumor cell growth and migration can be directly regulated by chemokines. In the present study, the association of CCL11 with ovarian cancer has been investigated.

EXPERIMENTAL DESIGN AND RESULTS

Circulating levels of CCL11 in sera of patients with ovarian cancer were significantly lower than those in healthy women or women with breast, lung, liver, pancreatic, or colon cancer. Cultured ovarian carcinoma cells absorbed soluble CCL11, indicating that absorption by tumor cells could be responsible for the observed reduction of serum level of CCL11 in ovarian cancer. Postoperative CCL11 levels in women with ovarian cancer negatively correlated with relapse-free survival. Ovarian tumors overexpressed three known cognate receptors of CCL11, CC chemokine receptors (CCR) 2, 3, and 5. Strong positive correlation was observed between expression of individual receptors and tumor grade. CCL11 potently stimulated proliferation and migration/invasion of ovarian carcinoma cell lines, and these effects were inhibited by neutralizing antibodies against CCR2, CCR3, and CCR5. The growth-stimulatory effects of CCL11 were likely associated with activation of extracellular signal-regulated kinase 1/2, MEK1, and STAT3 phosphoproteins and with increased production of multiple cytokines, growth factors, and angiogenic factors. Inhibition of CCL11 signaling by the combination of neutralizing antibodies against the ligand and its receptors significantly increased sensitivity to cisplatin in ovarian carcinoma cells.

CONCLUSION

We conclude that CCL11 signaling plays an important role in proliferation and invasion of ovarian carcinoma cells and CCL11 pathway could be targeted for therapy in ovarian cancer. Furthermore, CCL11 could be used as a biomarker and a prognostic factor of relapse-free survival in ovarian cancer.