A novel molecular magnetic resonance imaging agent targeting activated leukocyte cell adhesion molecule as demonstrated in mouse brain metastasis models.

Molecular magnetic resonance imaging (MRI) allows visualization of biological processes at the molecular level. Upregulation of endothelial ALCAM (activated leukocyte cell adhesion molecule) is a key element for leukocyte recruitment in neurological disease. The aim of this study, therefore, was to develop a novel molecular MRI contrast agent, by conjugating anti-ALCAM antibodies to microparticles of iron oxide (MPIO), for detection of endothelial ALCAM expression in vivo. Binding specificity of ALCAM-MPIO was demonstrated in vitro under static and flow conditions. Subsequently, in a proof-of-concept study, mouse models of brain metastasis were induced by intracardial injection of brain-tropic human breast carcinoma, lung adenocarcinoma or melanoma cells to upregulate endothelial ALCAM. At selected time-points, mice were injected intravenously with ALCAM-MPIO, and ALCAM-MPIO induced hypointensities were observed on T2*-weighted images in all three models. Post-gadolinium MRI confirmed an intact blood-brain barrier, indicating endoluminal binding. Correlation between endothelial ALCAM expression and ALCAM-MPIO binding was confirmed histologically. Statistical analysis indicated high sensitivity (80-90%) and specificity (79-83%) for detection of endothelial ALCAM in vivo with ALCAM-MPIO. Given reports of endothelial ALCAM upregulation in numerous neurological diseases, this advance in our ability to image ALCAM in vivo may yield substantial improvements for both diagnosis and targeted therapy.

The role of activated leukocyte cell adhesion molecule (ALCAM) in cancer progression, invasion, metastasis and recurrence: A novel cancer stem cell marker and tumor-specific prognostic marker.

Activated leukocyte cell adhesion molecule (ALCAM) or CD166 is a 100 to 105 KDa transmembrane immunoglobulin which is involved in activation of T-cells, hematopoiesis, neutrophils trans-endothelial migration, angiogenesis, inflammation and tumor propagation and invasiveness through formation of homophilic and heterophilic interactions. Recently, many studies have proposed that the expression pattern of ALCAM is highly associated with the grade, stage and invasiveness of tumors. Although ALCAM is a valuable prognostic marker in different carcinomas, similar expression patterns in different tumor types may be associated with completely different prognostic states, making it to be a tumor-type-dependent prognostic marker. In addition, ALCAM isoforms provide ways for primary detection of tumor cells with metastatic potential. More importantly, this prognostic marker has shown to be considerably dependent on the cytoplasmic and membranous expression, indirect and direct regulation of post-transcriptional molecules, pro-apoptotic proteins functionalities and several other oncogenic proteins or signalling pathways. This review mainly focuses on the pathways involved in expression of ALCAM and its prognostic value of in different types of cancers and the way in which it is regulated.

MiR-148b, MiR-152/ALCAM Axis Regulates the Proliferation and Invasion of Pituitary Adenomas Cells.

BACKGROUND/AIMS: Aberrant expression of miRNA has been found in many tumor tissues to regulate the tumorigenesis by binding to the 3`- untranslated region (3`-UTR) of the target genes. The aim of this study is to investigate the role of miR-148b, miR-152/ALCAM axis in human pituitary adenomas (PAs). METHODS: First, we detected the expression level of miR-148b-3p and miR-152 in human PAs samples by using qRT-PCR. Then we studied the role of miR-148b-3p, miR-152 on human PAs cell proliferation, invasion and apoptosis by using MTS assay, Transwell invasion assay and Annexin V/PI Staining Test. To study the relationship between miR-148b-3p, miR-152 and activated leukocyte antigen molecule (ALCAM), we overexpressed miR-148-3p or miR-152 by transfecting specific mimics. Lucifearase reporter assay was then performed to confirm the target. Next, we studied the biological functions of ALCAM in human PAs cells. Finally, the role of miR-148b-3p, miR-152/ALCAM axis in PAs cells was studied. RESULTS: The expression level of miR-148-3p and miR-152 in invasive PAs samples was lower than those in noninvasive samples. Overexpression of miR-148b-3p, miR-152 could repress proliferation and invasion, and promote apoptosis. Moreover, miR-148b-3p and miR-152 could repress activated leukocyte antigen molecule (ALCAM) expression. Knockdown of ALCAM could repress proliferation and invasion and promote apoptosis. By contrary, overexpression of ALCAM promoted proliferation and invasion. Further, the rescue experiments indicated that overexpression of ALCAM significantly restored the proliferation, apoptosis, and invasion influenced by miR-148b-3p and miR-152. CONCLUSIONS: Our study suggests that miR-148b-3p, miR-152 may serve as suppressors in PAs through downregulating ALCAM expression. miR-148b, miR-152/ ALCAM axis may be a new therapeutic target in the future.

Enhanced immunoPET of ALCAM-positive colorectal carcinoma using site-specific 64Cu-DOTA conjugation.

Activated leukocyte cell adhesion molecule (ALCAM) is an immunoglobulin superfamily cell adhesion molecule that is aberrantly expressed in a wide variety of human tumors, including melanoma, prostate cancer, breast cancer, colorectal carcinoma, bladder cancer and pancreatic adenocarcinoma. This wide spectrum of human malignancies makes ALCAM a prospective pan-cancer immunoPET target to aid in detection and diagnosis in multiple malignancies. In this study, we assess site-specific versus non-site-specific conjugation strategies for (64)Cu-DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) immunoPET imaging of a fully human ALCAM cys-diabody (cDb) with a reduced linker length that retains its bivalent binding ability. ALCAM constructs with linker lengths of eight, five and three amino acids were produced to make true non-covalent site-specifically modified cDbs. Characterization by gel electrophoresis, size exclusion chromatography, flow cytometry and mass spectrometry of the various constructs was performed. To demonstrate the increased utility of targeting multiple malignancies expressing ALCAM, we compare the targeting of the site-specific versus non-site-specific conjugated cDbs to the human colorectal cancer xenograft LS174T. Interestingly, the conjugation strategy not only affects tumor targeting but also hepatic and renal uptake/clearance.

CD166/ALCAM mediates proinflammatory effects of S100B in delayed type hypersensitivity.

Promiscuity of pattern recognition receptors, such as receptor for advanced glycation end products (RAGE), allows for a complex regulatory network controlling inflammation. Scavenging of RAGE ligands by soluble RAGE treatment is effective in reducing delayed-type hypersensitivity (DTH), even in RAGE(-/-) mice by 50% (p < 0.001). This has led to the hypothesis that molecules scavenged by soluble RAGE bind to receptors other than RAGE. This study identifies CD166/ALCAM (ALCAM) as a close structural and functional homolog of RAGE, and it shows that binding of S100B to CD166/ALCAM induces dose- and time-dependent expression of members of the NF-κB family in wild type (WT) and RAGE(-/-) mouse endothelial cells. Blocking CD166/ALCAM expression using small interfering RNA completely inhibited S100B-induced NF-κB activation in RAGE(-/-), but not in WT cells. The in vivo significance of these observations was demonstrated by attenuation of DTH in WT and RAGE(-/-) animals pretreated with CD166/ALCAM small interfering RNA by 50% and 40%, respectively (p < 0.001). Experiments in ALCAM(-/-) animals displayed an only slight reduction of 16% in DTH, explained by compensatory reciprocal upregulation of RAGE in animals devoid of CD166/ALCAM, and vice versa. Consistently, ALCAM(-/-) mice, but not WT mice treated with RAGE small interfering RNA show a 35% reduction in DTH, and ALCAM(-/-) RAGE(-/-) double-knockout mice show a 27% reduction in DTH reaction. Thus, S100B is a proinflammatory cytokine bridging RAGE and CD166/ALCAM downstream effector mechanisms, both being compensatory upregulated after genetic deletion of its counterpart.

Multiplexed surface plasmon resonance imaging for protein biomarker analysis.

The reliable detection of ligand and analyte binding is of significant importance for the field of medical diagnostics. Recent advances in proteomics and the rapid expansion in the number of identified protein biomarkers enhance the need for reliable techniques for their identification in complex samples. Surface plasmon resonance imaging (SPRi) provides label-free detection of this binding process in real-time. This chapter details the fabrication of an SPR imaging instrument and its use in analyzing molecular binding interactions with the use of a high-density microfluidic SPRi chip, capable of multiplexed analysis as well as various immobilization chemistries. Controlled recovery of bound biomarkers is demonstrated to enable their identification using mass spectrometry. Finally, activated leukocyte cell adhesion molecule (ALCAM), a protein biomarker associated with a variety of cancers, is identified from human crude cell lysates using the microfluidic surface plasmon resonance imaging (SPRi) instrument.

CD166/activated leukocyte cell adhesion molecule is expressed on glioblastoma progenitor cells and involved in the regulation of tumor cell invasion.

For improvement of prognosis for glioblastoma patients, which remains poor, identification and targeting of glioblastoma progenitor cells are crucial. In this study, we found that the cluster of differentiation (CD)166/activated leukocyte cell adhesion molecule (ALCAM) was highly expressed on CD133+ glioblastoma progenitor cells. ALCAM+ CD133+ cells were highly enriched with tumor sphere-initiating cells in vitro. Among gliomas with isocitrate dehydrogenase-1/R132H mutation, the frequencies of ALCAM+ cells were significantly higher for glioblastomas than for World Health Organization grade II or III gliomas. The function of ALCAM in glioblastoma was then investigated. An in vitro invasion assay showed that transfection of ALCAM small interfering RNA or small hairpin RNA into glioblastoma cells significantly increased cell invasion without affecting cell proliferation. A soluble isoform of ALCAM (sALCAM) was also expressed in all glioblastoma samples and at levels that correlated well with ALCAM expression levels. In vitro invasion of glioblastoma cells was significantly enhanced by administration of purified sALCAM. Furthermore, overexpression of sALCAM in U87MG glioblastoma cells promoted tumor progression in i.c. transplants into immune-deficient mice. In summary, we were able to show that ALCAM constitutes a novel glioblastoma progenitor cell marker. We could also demonstrate that ALCAM and its soluble isoform are involved in the regulation of glioblastoma invasion and progression.

ALCAM/CD166: cancer-related issues.

Activated leucocyte adhesion molecule (ALCAM) was originally identified as a transmembrane receptor which is involved in T-cell activation and has other still unresolved functions in hematopoiesis, development, inflammation and transendothelial migration of neutrophils. ALCAM is a member of a subfamily of immunoglobulin receptors with five immunoglobulin-like domains (VVC2C2C2) in the extracellular domain and is expressed in many types of tumors. The tumor-type-dependent impact of its expression level with respect to prognosis points to a possible context-dependent function. Most functional investigations have focused on malignant melanoma, in which high ALCAM expression at the protein level correlates with a poor prognosis. ALCAM mediates low-affinity homophilic interactions and much stronger interactions with CD6. Modulation of ALCAM function with agents such as transfected dominant negative ALCAM and ligand-binding secreted ALCAM both lead to inhibition of matrix metalloproteinase-2 activation, but their impact with respect to invasion in vitro and metastasis in vivo are different. Single-chain Fv fragments directed against ALCAM are efficiently internalized, paving the way for exploration of immunoconjugates as therapeutic agents. Validation experiments of the target with modulatory agents for possible therapeutic application in oncology are discussed.

Attenuation of melanoma invasion by a secreted variant of activated leukocyte cell adhesion molecule.

Activated leukocyte cell adhesion molecule (ALCAM/CD166/MEMD), a marker of various cancers and mesenchymal stem cells, is involved in melanoma metastasis. We have exploited a secreted NH(2)-terminal fragment, sALCAM, to test the hypothesis that ALCAM coordinates tissue growth and cell migration. Overexpression of sALCAM in metastatic melanoma cells disturbed clustering of endogenous ALCAM and inhibited activation of matrix metalloproteinase-2 (MMP-2). Exposure of HT1080 fibrosarcoma cells to sALCAM similarly inhibited MMP-2, suggesting a broader effect on ALCAM-positive tumor cells. In contrast to the previously reported, promotive effects of an NH(2)-terminally truncated, transmembrane variant (DeltaN-ALCAM), sALCAM impaired the migratory capacity of transfected cells in vitro, reduced basement membrane penetration in reconstituted human skin equivalents, and diminished metastatic capacity in nude mice. Remarkably, L1 neuronal cell adhesion molecule (L1CAM/CD171), another progression marker of several cancers including melanoma, was suppressed upon sALCAM overexpression but was up-regulated by DeltaN-ALCAM. The partially overlapping and opposite effects induced by alternative strategies targeting ALCAM functions collectively attribute an integrative role to ALCAM in orchestrating cell adhesion, growth, invasion, and proteolysis in the tumor tissue microenvironment and disclose a therapeutic potential for sALCAM.

Expression and characterization of a novel CD6 ligand in cells derived from joint and epithelial tissues.

CD6 is a T cell surface glycoprotein that plays an important role in interactions of thymocytes with thymic epithelial cells and in mature T cell interactions with selected nonprofessional tissue APCs. We describe a novel CD6 ligand (CD6L) 3A11 Ag that is distinct from the known CD6L (CD166). The 3A11 protein is expressed on cells derived from human thymus, skin, synovium, and cartilage, and its expression is enhanced by IFN-gamma. mAbs directed against the 3A11 Ag and CD166 exhibit distinct patterns of binding to a panel of cell lines. Confocal microscopy shows that both CD166 and the 3A11 Ag are expressed at the cell surface, and that these proteins colocalize. The 3A11 Ag has a molecular mass of 130 kDa and is immunoprecipitated using either mAb 3A11 or soluble CD6-Ig fusion protein. mAbs directed against individual CD6L were less potent than was soluble CD6-Ig fusion protein in reducing adhesion of T cells to adherent 3A11-positive epithelial cells in vitro, suggesting that these Abs recognize epitopes on the 3A11 Ag and CD166 that are distinct from CD6 binding sites. Finally, transfection of epithelial cells with CD166-specific small interfering RNAs significantly decreased CD166 expression without alteration in 3A11 Ag levels, and thus confirmed that these two CD6L are distinct. Taken together, our data identifies a novel 130-kDa CD6L that may mediate interactions of synovial and epithelial cells with T lymphocytes.

Molecular isolation and characterization of a soluble isoform of activated leukocyte cell adhesion molecule that modulates endothelial cell function.

Cell adhesion molecules regulate a variety of endothelial cell functions such as migration, response to inflammation, and angiogenesis. Recently, activated leukocyte cell adhesion molecule (ALCAM), a member of the Ig superfamily, has been detected in the primitive subsets of hematopoietic cells and endothelial cells during embryogenesis. ALCAM supports the development of hematopoietic cells as well as enhancing capillary tube formation in vitro. Here, we isolated a novel soluble isoform of ALCAM (sALCAM) that is produced via alternative splicing. sALCAM contains the single amino-terminal Ig-like domain of ALCAM and lacks a transmembrane domain. When expressed in cultured cells, sALCAM was properly secreted into the media. Both ALCAM and sALCAM are expressed in a variety of cultured human endothelial cells. Notably, their transcripts were differentially regulated in human microvascular endothelial cells (HMVEC) upon tumor necrosis factor-alpha stimulation. ALCAM significantly enhanced tube formation of endothelial-like yolk sac cells on Matrigel, whereas it inhibited their migration in vitro. sALCAM completely abolished these effects of ALCAM. Furthermore, sALCAM enhanced migration of mock-transfected endothelial-like yolk sac cells that do not express ALCAM, indicating that sALCAM has an independent effect on cell migration in addition to modulating ALCAM function. In addition, sALCAM significantly enhanced migration of HMVEC, whereas it inhibited tube formation of HMVEC on Matrigel. sALCAM demonstrated an ability to bind ALCAM and partially inhibited ALCAM-ALCAM homophilic interactions. Taken together, these data characterize a novel soluble isoform of ALCAM that may have ALCAM-dependent and ALCAM-independent functions, providing further insights regarding the role of this adhesion molecule in the regulation of endothelial cell function.

Evidence for the expression of a second CD6 ligand by synovial fibroblasts.

OBJECTIVE: CD6, a cell surface glycoprotein expressed primarily on T cells, may function as a costimulatory molecule and may play a role in autoreactive immune responses. Recently, a CD6 ligand termed CD166 (previously known as activated leukocyte cell adhesion molecule [ALCAM]) has been identified and shown to be expressed on activated T cells, B cells, thymic epithelium, keratinocytes, and in rheumatoid arthritis synovial tissue. However, the results of functional studies have suggested the existence of a second CD6 ligand. The present study was undertaken to seek evidence for a second CD6 ligand on cultured synovial fibroblasts. METHODS: Flow cytometric and biochemical techniques were applied, using anti-CD166 monoclonal antibody (mAb) and a recombinant CD6 fusion protein, to determine whether cultured synovial fibroblasts and other cell types expressed a non-ALCAM CD6 ligand. RESULTS: CD14- fibroblastic synoviocytes showed greater binding of a recombinant CD6 fusion protein than of anti-ALCAM mAb. With interferon-gamma treatment of synovial fibroblasts, binding of both reagents increased, but this was more marked for binding of CD6 fusion protein. Exposure of synovial fibroblasts to other cytokines or to the superantigen staphylococcal enterotoxin A also regulated binding of CD6 fusion protein and anti-ALCAM mAb in a discordant manner. Immunoprecipitation of proteins from membrane extracts of synovial fibroblasts with a CD6-Ig fusion protein revealed a novel 130-kd band distinct from CD166; an identical molecule was also precipitated from membranes of HBL-100 tumor cells. CONCLUSION: Taken together with previous data regarding CD6 and CD166 function, the present findings strongly suggest the existence of a second CD6 ligand distinct from CD166, which can be expressed by synovial fibroblasts as well as other cells.