Complement resistance of human carcinoma cells depends on membrane regulatory proteins, protein kinases and sialic acid

Sweet escape: sialic acids in tumor immune evasion

Sialic acids represent a family of sugar molecules derived from neuraminic acid that frequently terminate glycan chains and contribute to many biological processes. Already five decades ago, aberrantly high expression of sialic acids has been proposed to protect cancer cells from recognition and eradication by the immune system. Today, increased understanding at the molecular level demonstrates the broad immunomodulatory capacity of tumor-derived sialic acids that is, at least in part, mediated through interactions with immunoinhibitory Siglec receptors. Here we will review current studies from a sialic acid sugar perspective showing that tumor-derived sialic acids disable major killing mechanisms of effector immune cells, trigger production of immune suppressive cytokines and dampen activation of antigen-presenting cells and subsequent induction of anti-tumor immune responses. Furthermore, strategies to modulate sialic acid expression in cancer cells to improve cancer immunotherapy will be discussed.

Retinal pigment epithelial cell death by the alternative complement cascade: role of membrane regulatory proteins, calcium, PKC, and oxidative stress

PURPOSE

Retinal pigment epithelial (RPE) cell death is an important feature of the advanced forms of AMD. Complement alternative pathway (AP) activation is associated with RPE cell death in AMD. In this study, we developed a new model to initiate AP activation on RPE cells and investigated the cellular mechanisms modulating AP activation-mediated RPE cell death.

METHODS

An anti-RPE antibody was developed. A spontaneously arising human RPE cell line (ARPE-19) and donor RPE cells were primed with this antibody followed by stimulation with 6% C1q-depleted human serum (C1q-Dep) to activate AP. Complement activation was evaluated by flow cytometry and immunofluorescent staining. Cellular response to complement activation was examined by measurement of intracellular calcium and adenosine triphosphate (ATP) release. Cell viability was assessed by Sytox orange, tetrazolium salt, and lactate dehydrogenase release assays.

RESULTS

Alternative pathway complement-mediated RPE cell death was associated with membrane attack complex formation and a rapid rise in intracellular calcium followed by release of ATP. Downregulation of membrane complement regulatory proteins and protein kinase C (PKC) inhibition increased cell susceptibility to complement attack. Pretreatment of RPE cells with either hydrogen peroxide or hydroquinone enhanced cell death. Chronic repetitive treatment of RPE cells with low levels of oxidants also enhanced complement-mediated cell death.

CONCLUSIONS

Activation of complement through the alternative pathway induces sublytic and lytic phases of complement attack on RPE cells, leading to cell death modulated by extracellular calcium, membrane complement regulatory proteins, and intracellular signaling mechanisms. Single-dose oxidant exposure and low-dose repetitive oxidant exposure rendered RPE cells more susceptible to complement-mediated death.

Complement anaphylatoxins as immune regulators in cancer

The role of the complement system in innate immunity is well characterized. However, a recent body of research implicates the complement anaphylatoxins C3a and C5a as insidious propagators of tumor growth and progression. It is now recognized that certain tumors elaborate C3a and C5a and that complement, as a mediator of chronic inflammation and regulator of immune function, may in fact foster rather than defend against tumor growth. A putative mechanism for this function is complement-mediated suppression of immune effector cells responsible for immunosurveillance within the tumor microenvironment. This paradigm accords with models of immune dysregulation, such as autoimmunity and infectious disease, which have defined a pathophysiological role for abnormal complement signaling. Several types of immune cells express the cognate receptors for the complement anaphylatoxins, C3aR and C5aR, and demonstrate functional modulation in response to complement stimulation. In turn, impairment of antitumor immunity has been intimately tied to tumor progression in animal models of cancer. In this article, the literature was systematically reviewed to identify studies that have characterized the effects of the complement anaphylatoxins on the composition and function of immune cells within the tumor microenvironment. The search identified six studies based upon models of lymphoma and ovarian, cervical, lung, breast, and mammary cancer, which collectively support the paradigm of complement as an immune regulator in the tumor microenvironment.

The role of complement in tumor growth

Complement is a central part of the immune system that has developed as a first defense against non-self cells. Neoplastic transformation is accompanied by an increased capacity of the malignant cells to activate complement. In fact, clinical data demonstrate complement activation in cancer patients. On the basis of the use of protective mechanisms by malignant cells, complement activation has traditionally been considered part of the body's immunosurveillance against cancer. Inhibitory mechanisms of complement activation allow cancer cells to escape from complement-mediated elimination and hamper the clinical efficacy of monoclonal antibody-based cancer immunotherapies. To overcome this limitation, many strategies have been developed with the goal of improving complement-mediated effector mechanisms. However, significant work in recent years has identified new and surprising roles for complement activation within the tumor microenvironment. Recent reports suggest that complement elements can promote tumor growth in the context of chronic inflammation. This chapter reviews the data describing the role of complement activation in cancer immunity, which offers insights that may aid the development of more effective therapeutic approaches to control cancer.

Role of C5b-9 complement complex and response gene to complement-32 (RGC-32) in cancer

Complement system activation plays an important role in both innate and acquired immunity, with the activation of complement and the subsequent formation of C5b-9 terminal complement complex on cell membranes inducing target cell death. Recognition of this role for C5b-9 leads to the assumption that C5b-9 might play an antitumor role. However, sublytic C5b-9 induces cell cycle progression by activating signal transduction pathways and transcription factors in cancer cells, indicating a role in tumor promotion for this complement complex. The induction of the cell cycle by C5b-9 is dependent upon the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/FOXO1 and ERK1 pathways in a Gi protein-dependent manner. C5b-9 also induces response gene to complement (RGC)-32, a gene that plays a role in cell cycle promotion through activation of Akt and the CDC2 kinase. RGC-32 is expressed by tumor cells and plays a dual role in cancers, in that it has both a tumor suppressor role and tumor-promoting activity. Thus, through the activation of tumor cells, the C5b-9-mediated induction of the cell cycle plays an important role in tumor proliferation and oncogenesis.

Serglycin is implicated in the promotion of aggressive phenotype of breast cancer cells

Serglycin is a proteoglycan expressed by some malignant cells. It promotes metastasis and protects some tumor cells from complement system attack. In the present study, we show for the first time the in situ expression of serglycin by breast cancer cells by immunohistochemistry in patients' material. Moreover, we demonstrate high expression and constitutive secretion of serglycin in the aggressive MDA-MB-231 breast cancer cell line. Serglycin exhibited a strong cytoplasmic staining in these cells, observable at the cell periphery in a thread of filaments near the cell membrane, but also in filopodia-like structures. Serglycin was purified from conditioned medium of MDA-MB-231 cells, and represented the major proteoglycan secreted by these cells, having a molecular size of ~ 250 kDa and carrying chondroitin sulfate side chains, mainly composed of 4-sulfated (~ 87%), 6-sulfated (~ 10%) and non-sulfated (~ 3%) disaccharides. Purified serglycin inhibited early steps of both the classical and the lectin pathways of complement by binding to C1q and mannose-binding lectin. Stable expression of serglycin in less aggressive MCF-7 breast cancer cells induced their proliferation, anchorage-independent growth, migration and invasion. Interestingly, over-expression of serglycin lacking the glycosaminoglycan attachment sites failed to promote these cellular functions, suggesting that glycanation of serglycin is a pre-requisite for its oncogenic properties. Our findings suggest that serglycin promotes a more aggressive cancer cell phenotype and may protect breast cancer cells from complement attack supporting their survival and expansion.

Lipoplex mediated silencing of membrane regulators (CD46, CD55 and CD59) enhances complement-dependent anti-tumor activity of trastuzumab and pertuzumab

The therapeutic potential of anticancer antibodies is limited by the resistance of tumor cells to complement-mediated attack, primarily through the over-expression of membrane complement regulatory proteins (mCRPs: CD46, CD55 and CD59). Trastuzumab, an anti- HER2 monoclonal antibody, approved for the treatment of HER2-positive breast and gastric cancers, exerts only minor complement-mediated cytotoxicity (CDC). Pertuzumab is a novel anti-HER2 monoclonal antibody, which blocks HER2 dimerization with other ligand-activated HER family members. Here, we explored the complement-mediated anti-tumor effects of trastuzumab and pertuzumab on HER2-positive tumor cells of various histological origins. Delivery of chemically stabilized anti-mCRP siRNAs using cationic lipoplexes, AtuPLEXes, to HER2-over-expressing BT474, SK-BR-3 (breast), SKOV3 (ovarian) and Calu-3 (lung) cancer cells reduced mCRPs expression by 85-95%. Knockdown of individual complement regulators variably led to increased CDC only upon combined treatment with trastuzumab and pertuzumab. The combined down-regulation of all the three regulators augmented CDC by 48% in BT474, 46% in SK-BR-3 cells, 78% in SKOV3 cells and by 30% in Calu-3 cells and also increased complement-induced apoptosis and caspase activity on mCRP neutralized tumor cells. In addition, antibody-induced C3 opsonization of tumor cells was significantly enhanced after mCRP silencing and further augmented tumor cell killing by macrophages. Our findings suggest that siRNA-induced inhibition of complement regulator expression clearly enhances complement- and macrophage-mediated anti-tumor activity of trastuzumab and pertuzumab on HER2-positive tumor cells. Thus - if selectively targeted to the tumor - siRNA-induced inhibition of complement regulation may serve as an innovative strategy to potentiate the efficacy of antibody-based immunotherapy.

Dynamics and visualization of MCF7 adenocarcinoma cell death by aptamer-C1q-mediated membrane attack

This study was designed to characterize binding of a DNA aptamer to breast cancer cells and to test whether that aptamer could be used to kill target cells in vitro as part of an aptamer-C1q protein conjugate by coupling to the classic complement cascade. A biotinylated DNA aptamer designated MUC1-5TR-1 was shown to decorate the plasma membranes of human breast adenocarcinoma (MCF7) cells via fluorescence confocal microscopy. Biotinylated aptamer binding successfully initiated the classical complement pathway leading to complement fixation on the target cells via a streptavidin-C1q conjugate as previously reported. Förster Resonance Energy Transfer (FRET) measurements demonstrated membrane depolarization upon aptamer binding, providing indirect evidence of membrane attack complex (MAC) formation as a result of aptamer binding. Transmission electron microscopy (TEM) and immunogold labeling confirmed that aptamer-mediated complement fixation results in MAC formation on the plasma membrane, leading to osmotic swelling and cell death. This approach may provide a much less toxic and more precisely targeted "antibody-like" treatment for cancers by coupling to the patient's innate immune system in much the same way as more expensive humanized monoclonal antibodies.

Humoral innate immune response and disease

The humoral innate immune response consists of multiple components, including the naturally occurring antibodies (NAb), pentraxins and the complement and contact cascades. As soluble, plasma components, these innate proteins provide key elements in the prevention and control of disease. However, pathogens and cells with altered self proteins utilize multiple humoral components to evade destruction and promote pathogy. Many studies have examined the relationship between humoral immunity and autoimmune disorders. This review focuses on the interactions between the humoral components and their role in promoting the pathogenesis of bacterial and viral infections and chronic diseases such as atherosclerosis and cancer. Understanding the beneficial and detrimental aspects of the individual components and the interactions between proteins which regulate the innate and adaptive response will provide therapeutic targets for subsequent studies.

Caveolin-1 and dynamin-2 are essential for removal of the complement C5b-9 complex via endocytosis

The complement system, an important element of both innate and adaptive immunity, is executing complement-dependent cytotoxicity (CDC) with its C5b-9 protein complex that is assembled on cell surfaces and transmits to the cell death signals. In turn, cells, and in particular cancer cells, protect themselves from CDC in various ways. Thus, cells actively remove the C5b-9 complexes from their plasma membrane by endocytosis. Inhibition of clathrin by transfection with shRNA or of EPS-15 with a dominant negative plasmid had no effect on C5b-9 endocytosis and on cell death. In contrast, inhibition of caveolin-1 (Cav-1) by transfection with an shRNA or a dominant negative plasmid sensitized cells to CDC and inhibited C5b-9 endocytosis. Similarly, both inhibition of dynamin-2 by transfection with a dominant negative plasmid or by treatment with Dynasore reduced C5b-9 endocytosis and enhanced CDC. C5b-9 endocytosis was also disrupted by pretreatment of the cells with methyl-β-cyclodextrin or Filipin III, hence implicating membrane cholesterol in the process. Analyses by confocal microscopy demonstrated co-localization of Cav-1-EGFP with C5b-9 at the plasma membrane, in early endosomes, at the endocytic recycling compartment and in secreted vesicles. Further investigation of the process of C5b-9 removal by exo-vesiculation demonstrated that inhibition of Cav-1 and cholesterol depletion abrogated C5b-9 exo-vesiculation, whereas, over-expression of Cav-1 increased C5b-9 exo-vesiculation. Our results show that Cav-1 and dynamin-2 (but not clathrin) support cell resistance to CDC, probably by facilitating purging of the C5b-9 complexes by endocytosis and exo-vesiculation.

Anti-Sp17 monoclonal antibody with antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities against human ovarian cancer cells

Sperm protein 17 (Sp17) is a cancer testis antigen that has been shown to be overexpressed in a variety of gynecologic malignancies, in particular ovarian cancer. Emerging evidences indicate that Sp17 is involved in tumorigenesis and in the migration of malignant cells. It has been proposed as a useful target for tumor-vaccine strategies and a novel marker to define tumor subsets and predict drug response. However, the antitumor activity of anti-Sp17 monoclonal antibody (anti-Sp17 mAb) has not been investigated. In this study, the in vitro cytotoxicity, antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) activities of anti-Sp17 mAb were evaluated using Sp17-positive ovarian cancer cells as targets, Sp17-negative ovarian cancer cells as the control, and healthy human peripheral blood monocytes and healthy human serum as effectors. Our preliminary results indicate that the direct cytotoxicity of anti-Sp17 mAb against the investigated ovarian cancer cells was very weak. However, the cytotoxicity of anti-Sp17 mAb, mediated by peripheral blood mononuclear cells (PBMCs), as ADCC, or by human serum, as CDC, was relatively strong in the Sp17-positive ovarian cancer cells. This finding suggested that anti-Sp17 mAb could be a useful tool against ovarian cancer and may provide insight into the development of low side-effect targeting therapy for this malignant disease.

Complement in cancer and cancer immunotherapy

Recently, there has been an increase of interest in the use of biological or immune-based therapies for patients with malignancies. This has been informed by the deeper understanding of the crosstalk between the host immune system and malignant tumours, as well as the potential advantages of immunotherapy-high specificity and less toxicity compared to standard approaches. The particular emphasis of this article is on the role of the complement system in tumour growth and antibody-based cancer immunotherapy. The functional consequences from overexpression of complement regulators by tumours and the development of strategies for overcoming this are discussed in detail. This review discusses these issues with a view to inspiring the development of new agents that could be useful for the treatment of cancer.

The effects of CD59 gene as a target gene on breast cancer cells

The retroviral-vector-targeted CD59 gene (pSUPER-siCD59) was constructed and transfected into breast cells (MCF-7). The results demonstrated that the retroviral vector-mediated RNAi successfully suppressed human CD59 gene. The expression of CD59 decreased at both mRNA and protein levels. Knockdown of CD59 abrogated its protective effect on complement-mediated cytolysis. Fas and caspase-3 were remarkably upregulated, which induced apoptosis and tumor growth suppression in MCF-7 cells. In addition, overexpression of CD59 promoted the proliferation of MCF-7 cells and inhibited anti-apoptotic Bcl-2 expression. In conclusion, CD59 may be a promising target in the gene therapy of breast cancer.

Aptamer–biotin–streptavidin–C1q complexes can trigger the classical complement pathway to kill cancer cells

Nucleic acid aptamers are regarded as rivals for antibodies and as such are being investigated for their therapeutic potential. In the present work, it is shown that two different high-affinity DNA aptamers developed previously by Ferreira et al. against MUC1 antigen (designated MUC1-5TR-1 and MUC1-S1.3/S2.2) on MCF7 breast cancer cells can be linked to the first component of complement (C1q) via a biotin–streptavidin system and induce significant killing of MCF7 cells in vitro. Cell viability was assessed by Trypan blue uptake and absorbance at 590 nm of stained cells following buffer washes and lysis in 1% SDS. While the killing effect is demonstrable versus various controls, dependent on aptamer dose, and reproducible, it appears to kill maximally about half of treated MCF7 cells. Possible reasons for the marginal killing effect include antigenic shedding in vitro and membrane-bound complement regulatory proteins (mCRPs) on the cell surface such as CD46, CD55, and CD59 which act to inhibit complement-mediated lysis of cells. Future in vitro research could benefit from application of mCRP-specific aptamers in combination with anti-MUC1 aptamers to overcome surface protective mechanisms while attacking the plasma membrane of MCF7 cells or other MUC1-expressing cancer cells. However, in vivo such a combination could have deleterious effects on normal MUC1-expressing cells as well.

Dynamic control of the complement system by modulated expression of regulatory proteins

The complement system serves many biological functions, including the eradication of invasive pathogens and the removal of damaged cells and immune-complexes. Uncontrolled complement activation causes injury to host cells, however, so adequate regulation of the system is essential. Control of the complement system is maintained by a group of cell surface and circulating proteins referred to as complement regulatory proteins. The expression of the cell surface complement regulatory proteins varies from tissue to tissue. Furthermore, specific cell types can upregulate or downregulate the expression of these proteins in response to a variety of signals or insults. Altered regulation of the complement regulatory proteins can have important effects on local complement activation. In some circumstances this can be beneficial, such as in the setting of certain infections. In other circumstances, however, this can be a cause of complement-mediated injury of the tissue. A full understanding of the mechanisms by which the complement system is modulated at the local level can have important implications for how we diagnose and treat a wide range of inflammatory diseases.

Cancer and the complement cascade

Despite significant research on the role of inflammation and immunosurveillance in the immunologic microenvironment of tumors, little attention has been given to the oncogenic capabilities of the complement cascade. The recent finding that complement may contribute to tumor growth suggests an insidious relationship between complement and cancer, especially in light of evidence that complement facilitates cellular proliferation and regeneration. We address the hypothesis that complement proteins promote carcinogenesis and suggest mechanisms by which complement can drive the fundamental features of cancer. Evidence shows that this diverse family of innate immune proteins facilitates dysregulation of mitogenic signaling pathways, sustained cellular proliferation, angiogenesis, insensitivity to apoptosis, invasion and migration, and escape from immunosurveillance. Given that the traditionally held functions for the complement system include innate immunity and cancer defense, our review suggests a new way of thinking about the role of complement proteins in neoplasia.

Differential regulation of MRN (Mre11-Rad50-Nbs1) complex subunits and telomerase activity in cancer cells

Several lines of evidence suggest that cancer progression is associated with up-regulation or reactivation of telomerase and the underlying mechanism remains an active area of research. The heterotrimeric MRN complex, consisting of Mre11, Rad50 and Nbs1, which is required for the repair of double-strand breaks, plays a key role in telomere length maintenance. In this study, we show significant differences in the levels of expression of MRN complex subunits among various cancer cells and somatic cells. Notably, siRNA-mediated depletion of any of the subunits of MRN complex led to complete ablation of other subunits of the complex. Treatment of leukemia and prostate cancer cells with etoposide lead to increased expression of MRN complex subunits, with concomitant decrease in the levels of telomerase activity, compared to breast cancer cells. These studies raise the possibility of developing anti-cancer drugs targeting MRN complex subunits to sensitize a subset of cancer cells to radio- and/or chemotherapy.

Cancer biomarker discovery: the entropic hallmark

Background

It is a commonly accepted belief that cancer cells modify their transcriptional state during the progression of the disease. We propose that the progression of cancer cells towards malignant phenotypes can be efficiently tracked using high-throughput technologies that follow the gradual changes observed in the gene expression profiles by employing Shannon's mathematical theory of communication. Methods based on Information Theory can then quantify the divergence of cancer cells' transcriptional profiles from those of normally appearing cells of the originating tissues. The relevance of the proposed methods can be evaluated using microarray datasets available in the public domain but the method is in principle applicable to other high-throughput methods.

Methodology/Principal Findings

Using melanoma and prostate cancer datasets we illustrate how it is possible to employ Shannon Entropy and the Jensen-Shannon divergence to trace the transcriptional changes progression of the disease. We establish how the variations of these two measures correlate with established biomarkers of cancer progression. The Information Theory measures allow us to identify novel biomarkers for both progressive and relatively more sudden transcriptional changes leading to malignant phenotypes. At the same time, the methodology was able to validate a large number of genes and processes that seem to be implicated in the progression of melanoma and prostate cancer.

Conclusions/Significance

We thus present a quantitative guiding rule, a new unifying hallmark of cancer: the cancer cell's transcriptome changes lead to measurable observed transitions of Normalized Shannon Entropy values (as measured by high-througput technologies). At the same time, tumor cells increment their divergence from the normal tissue profile increasing their disorder via creation of states that we might not directly measure. This unifying hallmark allows, via the the Jensen-Shannon divergence, to identify the arrow of time of the processes from the gene expression profiles, and helps to map the phenotypical and molecular hallmarks of specific cancer subtypes. The deep mathematical basis of the approach allows us to suggest that this principle is, hopefully, of general applicability for other diseases.

Soluble iC3b as an early marker for pancreatic adenocarcinoma is superior to CA19.9 and radiology

Pancreatic adenocarcinoma as an aggressive tumor still lacks specific markers. Resection offers the only potential cure, and earlier diagnosis could benefit many patients. Here, we analyzed siC3b as a potential diagnostic marker. Soluble iC3b is generated in the fluid phase after binding of autoantibodies to tumor cells and subsequent inactivation of the complement cascade by interaction with complement regulatory proteins. Two hundred thirty-two plasma samples from patients with adjuvant treatment after resection, from healthy volunteers, and from vulnerable patients were collected prospectively and analyzed for siC3b. Every 3 months, the patients underwent imaging and the results from siC3b enzyme-linked immunosorbent assay were categorized according to radiologically defined recurrence within 4 months after blood withdrawal. Furthermore, the regulatory factors of the complement system were analyzed in tumor cells and in urine. The most important finding was that up to 4 months before radiologically defined recurrence, siC3b plasma level is increased with a sensitivity and specificity resulting in an area under the curve of 0.85, which could be further increased by combining it with CA19.9 (area under the curve=0.92). Complement regulatory proteins are highly expressed in pancreatic carcinoma cells and detectable in the patient's urine. In summary, screening for siC3b in patients with an increased risk for pancreatic ductal adenocarcinoma (patients with chronic pancreatitis, hereditary pancreatitis, after curative resection, and patients with a variety of familial cancer syndromes) allows for early detection with high sensitivity, as siC3b plasma levels are increased up to 4 months before radiologic evidence. Sensitivity could be further increased by combining this approach with CA19.9.

Engineered anti-CD20 antibodies with enhanced complement-activating capacity mediate potent anti-lymphoma activity

One of the major issues in current antibody therapy is insufficient efficacy. Various biological factors relating to the host's immune system or tumor cells have been suggested to reduce the efficacy of anti-CD20 therapy in B-cell malignancies. In this study, we characterized the in vitro anti-lymphoma activity of anti-CD20 antibodies having a novel engineered heavy chain with enhanced complement-dependent cytotoxicity (CDC). Anti-CD20 antibodies having a variant heavy constant region of mixed IgG1/IgG3 isotype, which have previously been found to enhance CDC, were investigated for their in vitro CDC against lymphoma cells and whole blood B-cell depletion activity. Use of the variant constant region greatly increased the CDC of an anti-CD20 antibody having variable regions identical to those of rituximab to the level shown by an IgG1 antibody of ofatumumab. Although the whole blood assay showed different cytotoxicity patterns among individual blood donors, the CDC-enhancing variant of rituximab showed higher activity than the parent IgG1 and consistently showed maximized activity when further combined with antibody-dependent cellular cytotoxicity (ADCC)-enhancing modification by fucose removal from Fc-linked oligosaccharides. In addition, the rituximab variant showed potent CDC against transfectant cells with lower CD20 expression and chronic lymphocytic leukemia-derived cell lines with higher complement regulatory proteins. These findings suggest that CDC enhancement, both alone and in combination with ADCC enhancement, increases the anti-lymphoma activity of anti-CD20 antibodies irrespective of individual differences in effector functions, and renders current anti-CD20 therapy capable of overcoming the potential resistance mechanisms.

Complement regulators and inhibitory proteins

The complement system is important for cellular integrity and tissue homeostasis. Complement activation mediates the removal of microorganisms and the clearance of modified self cells, such as apoptotic cells. Complement regulators control the spontaneously activated complement cascade and any disturbances in this delicate balance can result in damage to tissues and in autoimmune disease. Therefore, insights into the mechanisms of complement regulation are crucial for understanding disease pathology and for enabling the development of diagnostic tools and therapies for complement-associated diseases.

Unwelcome complement

For decades, the complement system has been recognized as an effector arm of the innate immunity system that contributes to the destruction of tumor cells. However, recent studies have challenged this paradigm by demonstrating that a complement component, the anaphylatoxin C5a, promotes the growth of malignant tumors in a mouse model of cervical carcinoma. The effect of C5a on tumor growth was associated with the recruitment of myeloid-derived suppressor cells to tumors, followed by the activation of these cells. These unexpected findings identify the complement system as a potential new target for anticancer immunotherapy.

Is complement good or bad for cancer patients? A new perspective on an old dilemma

Several studies of human cancers have established that chronic and insidious inflammation promotes the process of carcinogenesis and exacerbates the growth of existing tumors. Conversely, acute inflammation seems to have the opposite effect. Recent discoveries indicate that this dualism in the role of inflammation in cancer is mirrored by the effects of the complement system on this disease process. Previous studies have suggested that complement proteins can contribute to the immune surveillance of malignant tumors. However, a very recent study has indicated that complement proteins can also promote tumor growth. Here, we describe our current understanding of the role of complement in tumor development and progression.

Enhanced complement resistance in drug-selected P-glycoprotein expressing multi-drug-resistant ovarian carcinoma cells

Multi-drug resistance (MDR) is a major obstacle in cancer chemotherapy. There are contrasting data on a possible correlation between the level of expression of the drug transporter P-glycoprotein (P-gp) and susceptibility to complement-dependent cytotoxicity (CDC). We therefore investigated the sensitivity of human ovarian carcinoma cells and their P-gp expressing MDR variants to complement. Chemoselected P-gp expressing MDR cells showed increased resistance to CDC associated with overexpression of membrane-bound complement regulatory proteins (mCRP) and increased release of the soluble inhibitors C1 inhibitor and factor I. MDR1 gene transfection alone did not alter the susceptibility of P-gp expressing A2780-MDR and SKOV3-MDR cells to CDC. However, subsequent vincristine treatment conferred an even higher resistance to complement to these cells, again associated with increased expression of mCRP. Blocking the function of P-gp with verapamil, cyclosporine A or the anti-P-gp-antibody MRK16 had no impact on their complement resistance, whereas blocking of mCRP enhanced their susceptibility to complement. These results suggest that enhanced resistance of chemoselected MDR ovarian carcinoma cells to CDC is not conferred by P-gp, but is due at least partly to overexpression of mCRP, probably induced by treatment with the chemotherapeutic agents.

Modulation of the antitumor immune response by complement

The involvement of complement activation products in promoting tumor growth has not yet been recognized. Here we show that generation of complement C5a in the tumor microenvironment enhanced tumor growth by suppressing the anti-tumor CD8⁺ T cell-mediated response. This suppression was associated with the recruitment of myeloid-derived suppressor cells (MDSCs) into tumors and augmentation of their T cell-directed suppressive capabilities. Amplification of MDSC suppressive capacity by C5a occurred through regulation of the production of reactive oxygen and nitrogen species. Pharmacological blockade of C5a receptor significantly impaired tumor growth to a degree comparable to the effect produced by the anti-cancer drug Taxol. Thus, this study demonstrates a therapeutic role for complement inhibition in the treatment of cancer.

Targeting and purification of metabolically biotinylated baculovirus

Targeting viral entry is one of the major goals in the development of vectors for gene therapy. Ideally, the coupling of each new targeting motif would not require changes in vector structure. To achieve this, we developed novel metabolically biotinylated baculoviral vectors by displaying a small biotin acceptor peptide (BAP) fused either to different sites in the baculovirus glycoprotein gp64 or to the transmembrane anchor of vesicular stomatitis virus G protein. Baculoviral particles were biotinylated during vector production by coexpression of Escherichia coli biotin ligase (BirA). The insertion of BAP at amino acid position 283 of gp64 resulted in the most efficient biotin display. Unlike vectors with lower biotin display, these vectors also showed improved transduction when retargeted to transferrin, epidermal growth factor, and CD46 receptors overexpressed on rat glioma and human ovarian carcinoma cells. Biotinylated baculoviral vectors could also be concentrated by one-step magnetic particle-based capture to reach titers up to 10(10) plaque-forming units/ml. These results demonstrate the utility of metabolically biotinylated baculovirus for vector targeting and viral purification applications.

Potent oncolytic activity of human enteroviruses against human prostate cancer

BACKGROUND

Oncolytic virotherapy offers a unique treatment modality for prostate cancer, especially stages that are resistant to current therapies, with the additional benefit of preferentially targeting tumor cells amongst an environment of healthy tissue. Herein, the low pathogenic enteroviruses; Coxsackievirus A21 (CVA21), as well as a bio-selected variant of Coxsackievirus A21 (CVA21-DAFv) and Echovirus 1 (EV1) are evaluated as novel oncolytic agents against human prostate cancer.

METHODS

The surface expression of viral receptors required for enterovirus cell attachment/entry, including intercellular adhesion molecule-1 (ICAM-1), decay-accelerating factor (DAF) and integrin alpha(2)beta(1) on a number of human prostate cancer lines was assessed by flow cytometry. Susceptibility to viral oncolysis was determined via in vitro cell lysis assays performed on cell monolayers cultured in micro titer plates. The in vivo oncolytic efficacy of the enteroviruses was assessed using xenograft models in immune compromised SCID-mice following systemic challenge.

RESULTS

The majority of prostate cancer lines tested expressed surface ICAM-1 and/or DAF, or alpha(2)beta(1), facilitating significant degrees of oncolysis following in vitro viral challenge. Systemic delivery of each of the three viruses induced reduction of xenograft tumor burdens in vivo, and a therapeutic dose-response was demonstrated for escalating doses of EV1 in the LNCaP animal model.

CONCLUSION

Enteroviruses CVA21, CVA21-DAFv, and EV1 are potentially potent oncolytic agents against human prostate cancer.

Non-small cell lung cancer cells produce a functional set of complement factor I and its soluble cofactors

The complement system is important for protection from invading pathogens, removal of waste products and guidance of the immune response. Furthermore, complement can be also targeted to cancer cells. However, membrane-bound inhibitors over-expressed by certain types of tumor cells restrict the cytotoxic activity of complement. Herein we report that non-small cell lung cancer (NSCLC) cells produce soluble complement inhibitors factor I (FI) and C4b-binding protein (C4BP). FI is a serine protease capable of degrading the activated complement components C3b and C4b, whilst C4BP acts as its cofactor. Furthermore, NSCLC cells express membrane-bound regulators and shed membrane cofactor protein (MCP), which shares cofactor function with C4BP. Secretion of FI from NSCLC cells was higher than previously reported for any non-hepatic source and FI produced by these cells could efficiently support cleavage of C3b and C4b. In vitro functional assays revealed that additional FI significantly decreased C3 deposition and complement-dependent lysis, particularly when cofactors were added. Our results demonstrate that soluble inhibitors produced by NSCLC cells may provide further protection from complement beyond the level ensured by membrane-bound inhibitors and, as such, contribute to the aggressive phenotype of these lung cancer cells.

Down-regulation of CD55 and CD46 expression by anti-sense phosphorothioate oligonucleotides (S-ODNs) sensitizes tumour cells to complement attack

Overexpression of one or more membrane-bound complement regulatory proteins (mCRPs) protects tumour cells against complement-mediated clearance by the autologous humoral immune response and is also considered as a barrier for successful immunotherapy with monoclonal anti-tumour antibodies. Neutralization of mCRPs by blocking antibodies, enzymatic removal or cytokine-mediated down-regulation has been shown to sensitize tumour cells to complement attack. In our study we applied, for the first time, anti-sense phosphorothioate oligonucleotides (S-ODNs) to knock down the expression of the mCRPs CD55 and CD46 with the aim of exploiting complement more effectively for tumour cell damage. Potent anti-sense oligonucleotides against CD55 and CD46 were identified by screening various target sequences (n = 10) for each regulator. S-ODN anti-CD55(687) reduced CD55 protein expression up to 84% and CD46 protein expression was inhibited up to 76% by S-ODN anti-CD46(85). Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed a similar reduction of the CD55 and CD46 mRNA levels, which argues for an RNAse H-dependent anti-sense mechanism. T47D, A549 and PC3 cells, representing breast, lung and prostate carcinoma, were used for functional studies. Dependent on the particular cell line, anti-sense-based inhibition of mCRP expression enhanced complement-dependent cytolysis (CDC) up to 42% for CD55 and up to 40% for CD46, and the combined inhibition of both regulators yielded further additive effects in T47D cells. C3 opsonization of CD55/CD46-deficient tumour cells was also clearly enhanced upon mCRP suppression. Due to the clinical applicability of S-ODNs, the anti-sense approach described in this study may offer an additional alternative to improve the efficacy of antibody- and complement-based cancer immunotherapy.

Complement susceptibility in glutamine deprived breast cancer cells

Background

Membrane complement regulatory proteins (mCRPs) inhibit complement-mediated killing of human cells by human complement, a property that confers protection from complement to malignant breast cancer cells and that thwarts some immunotherapies. Metabolic mechanisms may come into play in protecting cancer cells from the complement system subsequent to relatively low levels of complement deposition.

Results

In differentiating these mechanisms, two types of human breast cancer cell lines, MCF7 (adenocarcinoma) and Bcap37 (medullary carcinoma) were cell-cycle synchronized using glutamine-deprivation followed by restoration. These cells were examined for the expression of two mCRPs (CD59 and CD55), and for subsequent susceptibility to antibody-mediated complement-induced membrane damage. After glutamine restoration, MCF7 and Bcap37 cells were synchronized into the G2/M phase and an average increased expression of CD59 and CD55 occurred with a corresponding resistance to complement-mediated damage. Blocking CD59 inhibitory function with monoclonal antibody revealed that CD59 played a key role in protecting unsynchronized Bcap37 and MCF7 cancer cells from the complement membrane attack complex. Interestingly, glutamine-deprivation did not significantly affect the expression of proteins e.g., the surface level of CD59 or CD55, but did increase the susceptibility to complement-mediated killing. One possible explanation is that glutamine-deprivation may have slowed the turnover rate of mCRPs, preventing the cells from replacing pre-existing mCRPs, as they became neutralized by covalent C4b and C3b depositions.

Conclusion

Taken together the findings are consistent with the conclusion that future immunotherapies should aim to achieve a highly specific and profound activation and deposition of complement as well as to disrupt the synthesis and expression of CD59 and CD55 by the cancer cells.

Inhibition of decay-accelerating factor (CD55) attenuates prostate cancer growth and survival in vivo

Decay-accelerating factor (CD55) is a member of membrane-bound complement-regulatory proteins. CD55 expression correlates with poor survival in patients with colorectal cancer and has been implicated in the survival and tumorigenesis of blood-borne malignancies. Histologic analysis of clinical specimens from patients with advanced prostate cancer revealed an increase in CD55 expression in prostate tumor epithelial cells. CD55 was shown to be functionally active and to inhibit complement-mediated lysis in PC-3 and DU145 cells. The percentage of lysis was correlative with the CD55 expression profile observed in these prostate cancer cell lines. These data suggest that CD55 is an important regulator of prostate cancer cell survival. As a result, we have hypothesized that CD55 expression on prostate cancer cells promotes cell survival and contributes to the metastatic potential of prostate cancer cells. To determine the role of CD55 in prostate cancer tumorigenesis and metastasis, we generated PC-3(Luc) prostate cancer cells with CD55 siRNA-targeted disruption. We found that PC-3(Luc)/CD55 siRNA constructs in SCID mice resulted in a significant attenuation of overall tumor burden. Further investigation into the mechanisms of CD55-mediated tumor cell/microenvironment interaction is necessary to understand the role of CD55 in tumor cell survival and metastatic lesion formation.

Interference with the complement system by tumor cell membrane type-1 matrix metalloproteinase plays a significant role in promoting metastasis in mice

Neoplasms have developed strategies to protect themselves against the complement-mediated host immunity. Invasion- and metastasis-promoting membrane type-1 (MT1) matrix metalloproteinase (MMP) is strongly associated with many metastatic cancer types. The relative importance of the individual functions of MT1-MMP in metastasis was, however, unknown. We have now determined that the expression of murine MT1-MMP in murine melanoma B16F1 cells strongly increased the number of metastatic loci in the lungs of syngeneic C57BL/6 mice. In contrast, MT1-MMP did not affect the number of metastatic loci in complement-deficient C57BL/6-C3-/- mice. Our results indicated, for the first time, that the anticomplement activity of MT1-MMP played a significant role in promoting metastasis in vivo and determined the relative importance of the anticomplement activity in the total metastatic effect of this multifunctional proteolytic enzyme. We believe that our results shed additional light on the functions of MT1-MMP in cancer and clearly make this protease a promising drug target in metastatic malignancies.

Expression of the membrane complement regulatory protein CD59 (protectin) is associated with reduced survival in colorectal cancer patients

It has been known for some time that the immune system can recognise growing tumours, and that tumours may respond by modulation of molecules, which make them resistant to further attack. Expression, over-expression, or loss of these molecules may function as markers of tumour progression and prognosis. Among such molecules are the membrane-bound complement regulatory proteins (mCRP), which protect cells from bystander attack by autologous complement. These include CD59 (protectin), which prevents formation of the MAC complex in the terminal stages of complement activation. In the present study, we evaluated immunohistochemical expression of CD59 in a series of over 460 well-characterised colorectal cancers using tissue microarrays (TMA), and related this information to known tumour and patient variables and to survival. The CD59 expression was observed in 69 (15%) of cases overall, and was significantly associated with tumour grade. In contrast, no associations were noted with tumour site, stage or histological type. On survival analysis, a further correlation was observed between expression of CD59 by the colorectal tumours and a reduction in disease-specific patient survival. This observation was strongest for patients with early stage disease. However, a negative impact on survival was also seen in those patients with late stage disease. These results indicate that TMA linked to good clinicopathological databases with good long term follow up are useful tools for determining new prognostic indicators that can be used in future patient management. Immune surveillance may result in immune-editing that induces variable expression of a range of target antigens, and these may be useful prognostic markers. This study has identified CD59 expression as a marker of poor prognosis in colorectal cancer patients.

Myeloid precursors and acute myeloid leukemia cells express multiple CD33-related Siglecs

OBJECTIVES

CD33 is a cell surface marker of committed myelomonocytic precursors and circulating monocytes, and is also found on acute myeloid leukemia (AML) cells. CD33 belongs to a family of sialic acid-binding cell surface proteins named Siglecs, among which there are 7 other functional CD33-related Siglecs (CD33rSiglecs). We sought to characterize the spectrum of expression of the other CD33rSiglecs on bone marrow precursors and AML cells and asked if they can potentially serve as targets for therapy.

METHODS

Cell surface CD33rSiglecs were analyzed by flow cytometry. The ability of certain anti-Siglec antibodies to target toxin-mediated cell killing of Siglec-expressing cell lines was characterized and compared.

RESULTS

We demonstrate that Siglecs-3, -5, -6, -7, and -9 are expressed on subsets of normal bone marrow precursors, including promonocytes and myelocytes. Furthermore, most AML (but not ALL) cells express these Siglecs. There is substantial variability in Siglec type and expression level between cases, with each having a unique "CD33rSiglec fingerprint." Individual anti-Siglec antibodies along with a saporin toxin-conjugated secondary antibody can target myelomonocytic leukemia cells for death, and targeting of multiple Siglecs improves cell killing. Cytotoxicity was further enhanced by sialidase treatment of target cells, which improves antibody binding. We also confirmed that antibody binding induced rapid internalization of Siglecs from the cell surface, which is a requirement for cell killing via saporin.

CONCLUSIONS

Multiple CD33rSiglecs are expressed on normal and malignant myelomonoyctic cells. Targeting these Siglecs, possibly in combinations, could improve anti-CD33 antibody therapy or be used as an alternative to anti-CD33.

Neoplastic transformation of the thyroid gland is accompanied by changes in cellular sialylation

Cancer of the thyroid gland is one of the most common endocrine diseases. Histological evaluation is often complicated by difficulty in distinguishing between benign and malignant lesions. Abnormal glycosylation of cell structures, including changes in sialylation, is a feature of the neoplastic transformation process. The aim of this study was to evaluate associations between neoplastic changes in the thyroid gland and changes in sialylation, with reference to its terminal linkage type. Lectin histochemistry using three sialic acid-binding lectins: Tritrichomonas mobilensis lectin (TML), which recognizes sialic acid without linkage preference; Maackia amurensis leukoagglutinin (MAL), which preferentially binds alpha-2,3-linked sialic acid; and Sambucus nigra agglutinin (SNA), which preferentially binds alpha-2,6-linked sialic acid, were used for detection of sialylated glycoconjugates in 50 human thyroid gland specimens. These included papillary, follicular, oncocytic, medullary and anaplastic carcinomas, follicular adenomas and benign follicular and parenchymatous goiter. The luminal surface of follicular cells in normal thyroid glands, adenomas and goiters showed weak or absent labelling for sialic acid. Malignant transformation of the gland was accompanied by an increase of sialic acid positivity on follicular epithelial cells, especially of alpha-2,3-linked sialic acid. Strong luminal positivity for sialic acid was found in papillary carcinomas, whereas moderate positivity was seen in follicular carcinomas. Inconsistent, weak positivity for sialic acid was documented in medullary and anaplastic carcinomas. Increased membrane sialic acid on thyroid gland cells may be an important diagnostic pathological finding, that could be useful in distinction of malignant from benign thyroid lesions, especially with respect to aspiration cytology diagnostics.

Minimal residual disease in ovarian cancer as a target for complement-mediated mAb immunotherapy

Ovarian cancer is potentially well suited for local monoclonal antibody (mAb) immunotherapy, because it remains within the peritoneal cavity for a long period of time before giving rise to distant metastases. At the stage of minimal residual disease, the cells appear to be in a state of dormancy (G(0)) or at least have lower rates of tumour cell proliferation. They should be a promising target for immunotherapy. Here we first examined the cell-cycle expression of CD59 and decay-accelerating factor (DAF; CD55) on four different ovarian carcinoma cell lines, using simultaneous flow cytometric analysis of DNA content or the cell-cycle-specific nuclear proliferation protein Ki67 and CD59 or DAF surface expression. We found that CD59 and DAF are stably expressed throughout the cell cycle. The polyvalent approach to target-independent antigens to improve the efficiency of mAb complement (C)-mediated damages was promising, and tumour cells become sensitive to C damage, when incubated with cross-linked mAb against different tumour-associated antigens. Although, such immune complex-mediated C activation was rather ineffective in killing the cells, it could be potentiated by the addition of blocking mAb against CD59 and DAF. Our results suggest that the activities of intrinsic C regulators must be neutralized to make minimal residual disease a promising target for antibody therapy.

Overexpression of ecto-protein kinases in prostasomes of metastatic cell origin

BACKGROUND

Prostasomes are secretory granules produced, stored, and released by the glandular epithelial cells of the prostate. They express numerous enzymes whose physiological roles have so far not been fully evaluated. In this study, we investigated the expression and function of prostasomal protein kinases and ATPase.

METHODS

The protein kinase activities of prostasomes isolated from seminal fluid and malignant prostate cell lines (PC-3, DU145, and LNCaP) were investigated using the model phosphorylation substrates histone and casein, as well as the plasma proteins C3 and fibrinogen, in combination with specific protein kinase inhibitors. The prostasomal ATPase activity was also evaluated. The expression of protein kinases and ATPase on prostasomes was verified by flow cytometry.

RESULTS

Prostasomes (intact or solubilized with octylglucoside or saponin) from prostate cancer cells had higher expression of protein kinases A, C, and casein kinase II compared to prostasomes isolated from seminal plasma, resulting in higher phosphorylation of both exogenous and endogenous substrates. Using intact prostasomes, it was found that prostasomes of metastatic origin had lower ATPase activity, resulting in higher residual ATP available for the phosphorylation reaction. Finally, complement component C3 and fibrinogen (two proteins whose activities are modulated by phosphorylation) were identified as physiologically relevant phosphorylation substrates.

CONCLUSIONS

These results indicate that prostasomes are capable of modifying proteins possibly involved in the innate response by extracellular phosphorylation mediated by ecto-kinases. This is a novel mechanism by which prostatic malignant cells may interact with their environment.

Transcriptomic analysis of an in vitro murine model of ovarian carcinoma: functional similarity to the human disease and identification of prospective tumoral markers and targets

Ovarian cancer is an aggressive disease of poor prognostic when detected at advanced stage. It is widely accepted that the ovarian surface epithelium plays a central role in disease etiology, but little is known about disease progression at the molecular level. To identify genes involved in ovarian tumorigenesis, we carried out a genome-wide transcriptomic analysis of six spontaneously transformed mouse ovarian surface epithelial (MOSE) cell lines, an in vitro model for human ovarian carcinoma. Loess normalization followed by statistical analysis with control of multiple testing resulted in 509 differentially expressed genes using an adjusted P-value < or = 0.05 as cut-off. The top 20 differentially expressed genes included 10 genes (Spp1, Cyp1b1, Btg1, Cfh, Mt1, Mt2, Igfbp5, Gstm1, Gstm2, and Esr1) implicated in various aspects of ovarian carcinomas, and other 3 genes (Gsto1, Lcn7, and Alcam) associated to breast cancer. Upon functional analysis, the majority of alterations affected genes involved in glutathione metabolism and MAPK signaling pathways. Interestingly, over 20% of the aberrantly expressed genes were related to extracellular components, suggestive of potential markers of disease progression. In addition, we identified the genes Pura, Cnn3, Arpc1b, Map4k4, Tgfb1i4, and Crsp2 correlated to in vivo tumorigenic parameters previously reported for these cells. Taken together, our findings support the utility of MOSE cells in studying ovarian cancer biology and as a source of novel diagnostic and therapeutic targets.

Inhibiting complement regulators in cancer immunotherapy with bispecific mAbs

Although monoclonal antibody (mAb)-mediated immunotherapy of cancer has been proven to be feasible for clinical use, success rates until now have been disappointing. One reason for this might be the overexpression of membrane-bound complement regulatory proteins (mCRPs) by tumour cells. As complement activation is an important effector mechanism induced by therapeutic mAbs, inhibition of complement activation by tumour cells might reduce therapeutic efficacy by decreasing direct complement-mediated lysis as well as complement-dependent cellular cytotoxicity. Modulation of the function of these mCRPs might be achieved with therapeutic bispecific (bi-)mAbs that target a tumour antigen and simultaneously block a major mCRP. Clinical results will probably increase with such bi-mAbs compared with monovalent antitumour mAbs. In this review the feasibility of this approach is discussed.

Extracellular phosphorylation of C9 by protein kinase CK2 regulates complement-mediated lysis

Ecto-protein kinases (ecto-PK) are expressed on many cell types, both normal and malignant, yet their functions are largely unknown. An ecto-PK capable of phosphorylating the C9 component of the complement system is described. This C9 ecto-PK could be inhibited by TBB, Emodin and DRB, selective inhibitors of protein kinase CK2. Treatment of Raji human B lymphoma cells with these CK2 inhibitors augmented cell killing by Rituximab (anti-CD20 antibodies) and human complement. Analysis of C5b-7-bearing Raji cells showed that extracellular inhibition of the ecto-CK2 enhanced cell lysis by C8 and C9. Blocking of the membrane complement regulator CD59 with monoclonal antibodies further enhanced the effect of the CK2 inhibitors on Raji cell death by complement. C9 ecto-CK2 activity was increased on cancer cells relative to normal fibroblasts and blood cells. Therefore, ecto-CK2 appears to be an additional factor protecting cells from complement-mediated lysis, probably by phosphorylation/inhibition of complement C9.

Oncolytic activities of approved mumps and measles vaccines for therapy of ovarian cancer

Oncolytic viruses are promising cytoreductive agents for cancer treatment but extensive human testing will be required before they are made commercially available. Here, we investigated the oncolytic potential of two commercially available live attenuated vaccines, Moraten measles and Jeryl-Lynn mumps, in a murine model of intraperitoneal human ovarian cancer and compared their efficacies against a recombinant oncolytic measles virus (MV-CEA) that is being tested in a phase I clinical trial. The common feature of these viruses is that they express hemagglutinin and fusion therapeutic proteins that can induce extensive fusion of the infected cell with its neighbors, resulting in death of the cell monolayer. In vitro, the three viruses caused intercellular fusion in human ovarian cancer cells but with marked differences in fusion kinetics. MV-CEA was the fastest followed by Jeryl-Lynn mumps virus while Moraten measles virus was the slowest, although all viruses eventually caused comparable cell death 6 days postinfection. Tumor-bearing mice treated with 10(6) or 10(7) pfu (one thousand times the vaccine dose) of each of the three viruses responded favorably to therapy with significant prolongations in survival. All three viruses demonstrated equivalent antitumor potency. Commercially available Moraten measles and Jeryl-Lynn mumps vaccines warrant further investigation as potential anticancer agents.

Increased CD59 protein expression predicts a PSA relapse in patients after radical prostatectomy

BACKGROUND

Human protectin (CD59) is a regulator of complement activation that inhibits complement-mediated cell lysis, and thus might confer immune resistance to tumor cells. CD59 expression has been described in a variety of human malignancies, including breast cancer. Since a comprehensive investigation of CD59 expression in prostate cancer has not been conducted yet, we aimed to determine the significance of CD59 expression in prostate cancer.

METHODS

Eighty-six primary adenocarcinomas of the prostate were immunostained using a monoclonal CD59 antibody (clone MEM-43) and a standard detection system. The immunoreactivity of the tumor was evaluated as low versus high for statistical analysis. Additionally, CD59 mRNA levels were determined by real-time PCR in matched (tumor/normal) microdissected tissues from 26 cases.

RESULTS

Cytoplasmic CD59 immunoreactivity was found in epithelia of prostate cancer, prostatic intraepithelial neoplasia, benign hyperplasia, atrophic, and normal glands. High rates of CD59 expression were noted in 36% of prostate cancer cases and were significantly associated with tumor pT stage (P = 0.043), Gleason grade (P = 0.013) and earlier biochemical (PSA) relapse in Kaplan-Meier analysis (P = 0.0013). On RNA level, we found an upregulation in 19.2% (five cases), although the general rate of CD59 transcript was significantly lower in tumor tissue (P = 0.03).

CONCLUSION

CD59 protein is strongly expressed in 36% of adenocarcinomas of the prostate and and is associated with disease progression and adverse patient prognosis.

Transfer of functional prostasomal CD59 of metastatic prostatic cancer cell origin protects cells against complement attack

BACKGROUND

Prostasomes are secretory granules produced, stored, and released, by the glandular epithelial cells of the prostate. They express the glycosylphosphatidylinositol (GPI)-anchored complement regulatory protein CD59, which has been shown to be transferred to spermatozoa and erythrocytes.

METHODS

The CD59 content of prostasomes isolated from seminal fluid and malignant prostate cells (PC-3, DU145, and LNCaP) and the transfer of prostasomal CD59 to rabbit erythrocytes (RE) and to PIPLC-treated and unmanipulated cancer cells were investigated using FACS. All prostasomes were also incubated with RE and tested in a hemolytic assay.

RESULTS

Prostasomes from cancer cells had higher expression of CD59 than those of normal cells. Prostasomal CD59 of different origin could be transferred to RE, malignant cell lines stripped of CD59 by PIPLC, or unmanipulated LNCaP cells. Malignant cell prostasomes had an increased ability to inhibit complement-mediated lysis compared to those from non-malignant cells.

CONCLUSIONS

These results point to a novel mechanism by which prostasomes can protect prostatic malignant cells from complement attack.