Monoclonal antibody ONS-M21 recognizes integrin alpha3 in gliomas and medulloblastomas

Novel monoclonal antibody against integrin α3 shows therapeutic potential for ovarian cancer

Ovarian cancer has a high recurrence rate after platinum‐based chemotherapy. To improve the treatment of ovarian cancer and identify ovarian cancer‐specific antibodies, we immunized mice with the human ovarian carcinoma cell line, SKOV‐3, and generated hybridoma clones. Several rounds of screening yielded 30 monoclonal antibodies (mAbs) with no cross‐reactivity to normal cells. Among these mAbs, OV‐Ab 30‐7 was found to target integrin α3 and upregulate p53 and p21, while stimulating the apoptosis of cancer cells. We further found that binding of integrin α3 by OV‐Ab 30‐7 impaired laminin‐induced focal adhesion kinase phosphorylation. The mAb alone or in combination with carboplatin and paclitaxel inhibited tumor progression and prolonged survival of tumor‐bearing mice. Moreover, immunohistochemical staining of ovarian patient specimens revealed higher levels of integrin α3 in cancer cells compared with normal cells. By querying online clinical databases, we found that elevated ITGA3 expression in ovarian cancer is associated with poor prognosis. Taken together, our data suggest that the novel mAb, OV‐Ab 30‐7, may be considered as a potential therapeutic for ovarian cancer.

Challenges and Recent Advances in Medulloblastoma Therapy

Medulloblastoma (MB) is the most common childhood brain tumor, which occurs in the posterior fossa. MB tumors are highly heterogeneous and have diverse genetic make-ups, with differential microRNA (miRNA) expression profiles and variable prognoses. MB can be classified into four subgroups, each with different origins, pathogenesis, and potential therapeutic targets. miRNA and small-molecule targeted therapies have emerged as a potential new therapeutic paradigm in MB treatment. However, the development of chemoresistance due to surviving cancer stem cells and dysregulation of miRNAs remains a challenge. Combination therapies using multiple drugs and miRNAs could be effective approaches. In this review we discuss various MB subtypes, barriers, and novel therapeutic options which may be less toxic than current standard treatments.

Carboxymethylcellulose hydrogels support central nervous system-derived tumor-cell chemotactic migration: Comparison with conventional extracellular matrix macromolecules

The local microenvironment plays an important role in maintaining the dynamics of the extracellular matrix and the cell–extracellular matrix relationship. The extracellular matrix is a complex network of macromolecules with distinct mechanical and biochemical characteristics. Disruptions in extracellular matrix homeostasis are associated with the onset of cancer. The extracellular matrix becomes highly disorganized, and the cell–matrix relationship changes, resulting in altered cell-signaling processes and metastasis. Medulloblastoma is one of the most common malignant pediatric brain tumors in the United States. In order to gain a better understanding of the interplay between cell–extracellular matrix interactions and cell-migratory responses in tumors, eight different matrix macromolecule formulations were investigated using a medulloblastoma-derived cell line: poly-d-lysine, matrigel, laminin, collagen 1, fibronectin, a 10% blend of laminin–collagen 1, a 20% blend of laminin–collagen 1, and a cellulose-derived hydrogel, carboxymethylcellulose. Over time, the average changes in cell morphology were quantified in 2D and 3D, as was migration in the presence and absence of the chemoattractant, epidermal growth factor. Data revealed that carboxymethylcellulose allowed for a cell–extracellular matrix relationship typically believed to be present in tumors, with cells exhibiting a rounded, amoeboid morphology consistent with chemotactic migration, while the other matrices promoted an elongated cell shape as well as both haptotactic and chemotactic motile processes. Therefore, carboxymethylcellulose hydrogels may serve as effective platforms for investigating central nervous system-derived tumor-cell migration in response to soluble factors.

WT1 expression distinguishes astrocytic tumor cells from normal and reactive astrocytes

Particularly in small brain biopsies, it might be difficult to distinguish reactive astrogliosis from low-grade or infiltration zones of high-grade astrocytomas. So far no immunohistochemical marker allows a reliable distinction. Recently, the over-expression of Wilms' tumor gene product WT1 was reported in astrocytic tumor cells. However, no sufficient data on WT1 expression in normal or reactive astrocytes are available. Therefore, we investigated WT1 expression in paraffin-embedded brain sections from 28 controls, 48 cases with astrogliosis of various etiology and 219 astrocytomas [World Health Organization (WHO) grades I-IV] by immunohistochemistry. In normal brains and in astrogliosis, expression of WT1 was restricted to endothelial cells. In astrocytomas, WT1-positive tumor cells were found in pilocytic astrocytomas (66.7% of cases), diffuse astrocytomas (52.7%) WHO grade II (52.7%), anaplastic astrocytomas (83.4%) and glioblastomas (98.1%). Overall, the majority of all astrocytic neoplasms (84.5%) expressed WT1. Establishing a cut-off value of 0% immunoreactive tumor cells served to recognize neoplastic astrocytes with 100% specificity and 68% sensitivity and was associated with positive and negative predictive values of 1 and 0.68, respectively. Therefore, WT1 expression in astrocytes indicates a neoplastic origin and might represent an important diagnostic tool to differentiate reactive from neoplastic astrocytes by immunohistochemistry.

Changes in adhesive and migratory characteristics of hepatocellular carcinoma (HCC) cells induced by expression of alpha3beta1 integrin

The invasive and metastatic potentials of hepatocellular carcinoma are positively correlated with the expression level of alpha3beta1 integrin, a high-affinity adhesion receptor for laminin isoforms including laminin-5. In this study, we investigated changes in the adhesive and invasive behaviors of human HCC HepG2 cells after transfection with cDNA for alpha3 integrin in order to elucidate the direct involvement of this integrin in these cellular processes. We introduced cDNA for splice variants of alpha3 integrin (alpha3A and alpha3B) into the cells, and selected two transfectant clones (HepG2-3A and HepG2-3B), which express the alpha3A and alpha3B integrins, respectively. Both transfectant cells adhered almost equally to laminin-5-coated plates in an alpha3 integrin-dependent manner, indicating that transfected alpha3Abeta1 and alpha3Bbeta1 integrins were functionally active in these cells. The migratory and invasive potentials of the transfectant cells were assessed by scratch wound assay and in vitro chemoinvasion assay. The results demonstrated that the migration of HepG2-3A and HepG2-3B cells but not of mock transfectant (HepG2-M) cells was stimulated on the plates coated with laminin-5. Furthermore, HepG2-3A and HepG2-3B cells were found to be more invasive into laminin-5-containing matrices than were HepG2-M cells. These results strongly suggest that enhanced expression of alpha3beta1 integrin on HCC cells is directly involved in their malignant phenotypes such as invasion and metastasis.

Possible involvement of TWIST in enhanced peritoneal metastasis of epithelial ovarian carcinoma

Loss of E-cadherin triggers peritoneal dissemination, leading to an adverse prognosis for most patients with epithelial ovarian carcinoma (EOC). Because TWIST mainly regulates the epithelial-to-mesenchymal transition and is one of the E-cadherin repressors, we investigated the possibility that TWIST expression affects peritoneal metastasis of EOC using siRNA technique. In the present study, we showed a correlation between TWIST expression and EOC cellular morphology. Furthermore, we demonstrated that the suppression of TWIST expression in EOC cells (HEY) alters the cellular morphology from a fibroblastic and motile phenotype to an epithelial phenotype, and inhibits the adhesion of these cells to mesothelial monolayers. To investigate the mechanism by which down-regulation of TWIST leads to inhibition of adhesion to mesothelial cells (MCs), expression of adhesion molecules (CD29, CD44 and CD54) were observed. Moreover, matrix metalloproteinase 2 and membrane type 1 matrix metalloproteinase, important markers associated with invasive and metastatic potential, were remarkably reduced. This findings suggests that reduced expression of TWIST suppresses the multistep process of peritoneal dissemination (detachment from the primary lesion, adhesion to MCs and invasion of MCs) and may be a potential therapeutic target for the treatment of this carcinoma.

Characterization of the promoter for the alpha3 integrin gene in various tumor cell lines: roles of the Ets- and Sp-family of transcription factors

The alpha3beta1 integrin is an adhesion receptor for extracellular matrix proteins, including laminin isoforms, and plays crucial roles in the organization of epithelial and endothelial tissues. The aberrant expression of this adhesion molecule on tumor cells is associated with their invasive and metastatic potentials. In the present study, we analyzed the elements essential for alpha3 integrin gene expression in various tumor cell lines with different tissue origins by luciferase assay. An approximately 0.3 kb fragment of the 5'-flanking region of the mouse alpha3 integrin gene (-260/+84, relative to the major transcription start site) showed strong promoter activity in all six examined tumor cell lines. However, we found that these cell lines could be divided into two groups according to the level of dependency on the putative Ets-transcription factor binding motif located at -133. This motif was previously shown to be crucial for alpha3 integrin expression in MKN1 gastric carcinoma cells. The gene expression in one group of cell lines was upregulated mainly by the Ets motif, whereas that in the other group was less dependent on the Ets motif. We then postulated that additional regulatory elements were responsible for the expression of alpha3 integrin, and found that a GC-rich motif at -69 was another important element. An electrophoretic mobility shift assay using specific antibodies and a Western blot analysis of nuclear proteins revealed that the Sp3-transcription factor bound to this GC-rich motif. These results suggest that the Sp3 and Ets transcription factors cooperatively regulate alpha3 integrin gene expression and that the contribution of each element depends on the type of tumor cells.

Transforming growth factor-beta1 upregulates transcription of alpha3 integrin gene in hepatocellular carcinoma cells via Ets-transcription factor-binding motif in the promoter region

The invasive and metastatic potentials of hepatocellular carcinoma (HCC) are positively correlated with the expression level of alpha3beta1 integrin, a high-affinity adhesion receptor for laminin isoforms. Transforming growth factor (TGF)-beta1 stimulates non-invasive HCC cells to acquire invasive phenotypes in association with the enhanced expression of alpha3 integrin. In this study, we investigated the molecular mechanism underlying the upregulation of alpha3beta1 integrin by TGF-beta1 in non-invasive HepG2 HCC cells. The treatment of HepG2 cells with TGF-beta1 induced the expression of alpha3 integrin and potentiated these cells to adhere to laminin-5 and to migrate through laminin-5-coated membranes. The promoter activity was measured by luciferase assay with a series of deletion constructs of the 5'-flanking region of the mouse alpha3 integrin gene, and the results showed that the -260/-119 region (relative to the major transcription start site) contained elements responsive to TGF-beta1 stimulation. The introduction of mutations into the putative consensus binding sequence for the Ets-family of transcription factors located at -133 greatly decreased the promoter activity responding to TGF-beta1 stimulation. The nuclear proteins extracted from TGF-beta1-stimulated HepG2 cells yielded a larger amount of DNA-nuclear protein complexes than did those extracted from unstimulated cells, as determined by an electrophoretic mobility shift assay using an oligonucleotide containing the Ets-site as a probe. These results suggest that TGF-beta1 stimulates HepG2 cells to express a higher level of alpha3 integrin by transcriptional upregulation via Ets transcription factors and to exhibit a more invasive phenotype.

alpha(v)beta(3) Integrin in central nervous system tumors

alpha(v)beta(3) Is an integrin specifically expressed in endothelial cells of newly forming blood vessels. Integrin-mediated angiogenesis is hypothesized to play a central role in the development and the progression of central nervous system neoplasms. Accordingly, it is considered a potential target for antiangiogenic therapy. In the current study, we compare the expression of alpha(v)beta(3) in ependymomas, oligodendrogliomas, pilocytic astrocytomas, medulloblastomas, and vestibular schwannomas (acoustic neuromas). Samples of 5 tumors of each of the 5 tumor types were harvested surgically and frozen. After the pathological diagnosis was confirmed, immunohistochemistry was performed using an anti- alpha(v)beta(3) monoclonal antibody (LM609). The expression of alpha(v)beta(3) was assessed using a 4-tiered (0-3) grading scheme reflecting the percentage of positively staining vessels. All vestibular schwannomas demonstrated strong (grade 3) alpha(v)beta(3) expression. The expression was uniformly prominent in Antoni B regions of the tumors. Of 5 ependymomas, 4 demonstrated uniformly strong alpha(v)beta(3). Oligodendrogliomas, medulloblastomas, and pilocytic astrocytomas demonstrated more variable alpha(v)beta(3). alpha(v)beta(3) may contribute significantly to angiogenesis in vestibular schwannomas and ependymomas. Despite the high vascular density of oligodendrogliomas, pilocytic astrocytomas, and medulloblastomas, these tumors had variable moderate alpha(v)beta(3) expression. This discrepancy suggests temporal and/or regional variability in the angiogenesis in these types of tumor. This study provides the first demonstration of alpha(v)beta(3) expression in vestibular schwannomas, medulloblastomas, and pilocytic astrocytomas.

Adhesion of gastric carcinoma cells to peritoneum mediated by alpha3beta1 integrin (VLA-3)

The interaction between gastric carcinoma cells and the peritoneal lining is a key step in peritoneal dissemination. In this study, we examined the roles of the beta1 family of integrin receptors in the adhesion of such cells to the peritoneum. The adhesion of several gastric carcinoma cell lines to peritonea excised from mice was inhibited most by an anti-alpha3 integrin antibody and to a lesser extent by an anti-alpha2 integrin antibody. In the peritoneal implantation of NUGC-4 human gastric carcinoma cells in athymic mice, treatment of the cells with anti-alpha2 or anti-alpha3 integrin antibody reduced the number of disseminated nodules; suppression by the anti-alpha3 integrin antibody was stronger than that by the anti-alpha2 integrin antibody. The cDNAs to human alpha2 and alpha3 integrins were introduced into K562 leukemic cells, which were positive for the integrin beta1 subunit but negative for the alpha2 or alpha3 subunit. The alpha3 integrin-transfected cells adhered to excised peritoneum and to a monolayer of peritoneal mesothelial cells more firmly than did the alpha2 integrin-transfected cells or the mock transfectant. Reverse transcription-PCR was used to analyze the expression of laminin-5 and laminin-10/11, which have been reported to serve as high-affinity ligands for alpha3beta1 integrin. mRNA for these laminin isoforms was found in mesothelial cells from the diaphragm and parietal peritoneum. These results strongly suggest that alpha3beta1 integrin plays an essential role in mediating the initial attachment of cancer cells to the peritoneum, leading to the formation of peritoneal metastasis.

Physiological and Pathological Roles of α3β1 Integrin

Alpha3beta1 integrin has been considered to be a mysterious adhesion molecule due to the pleiotropy in its ligand-binding specificity. However, recent studies have identified laminin isoforms as high-affinity ligands for this integrin, and demonstrated that alpha3beta1 integrin plays a number of essential roles in development and differentiation, mainly by mediating the establishment and maintenance of epithelial tissues. Furthermore, alpha3beta1 integrin is also implicated in many other biological phenomena, including cell growth and apoptosis, angiogenesis and neural functions. This integrin receptor forms complexes with various other membrane proteins, such as the transmembrane-4 superfamily proteins (tetraspanins), cytoskeletal proteins and signaling molecules. Recently, lines of evidence have been reported showing that complex formation regulates integrin functions in cell adhesion and migration, signal transduction across cell membranes, and cytoskeletal organization. In addition to these roles in physiological processes, alpha3beta1 integrin performs crucial functions in various pathological processes, especially in wound healing, tumor invasion and metastasis, and infection by pathogenic microorganisms.

Characterization of the promoter for the mouse alpha 3 integrin gene

The alpha 3 beta 1 integrin is an adhesion receptor for extracellular matrix proteins including isoforms of laminin, and the changes of its expression level in various cancer cells are thought to cause their malignant phenotypes. We have cloned an approximately 4 kb DNA fragment of the 5'-flanking region of the murine alpha 3 integrin gene and analyzed its promoter activity. Transfection of MKN1 gastric carcinoma cells with serially truncated segments of the 5'-flanking region linked to a luciferase gene indicated that a 537-bp SalI/SacI fragment upstream of exon 1 was sufficient to promote high level gene expression. By 5'-rapid amplification of cDNA ends (5'-RACE) using a cap site-labeled cDNA library, we determined one major and one minor transcription start sites in this region. The murine alpha 3 integrin gene was found to contain a CCAAT box, but to lack a TATA box. Luciferase assay following transfection with a series of deletion constructs of the SalI/SacI fragment revealed that the sequence between positions -260 and -119 bp (relative to the major transcription start site) is required for efficient transcription in gastric carcinoma cells. The sequence analysis of this segment showed the presence of several consensus sequences for transcription factors including Ets, GATA and MyoD/E-box binding factors. The introduction of mutation in one of the Ets-binding sequences greatly decreased its promoter activity, suggesting that the transcription of the alpha 3 integrin gene in these cells is regulated by the Ets-family of transcription factors.

Functions of alpha3beta1 integrin

alpha3beta1 integrin is a laminin receptor with apparently diverse functions. In epithelial cells it acts as a receptor for the basement membrane, whereas in neuronal and possibly tumor cells it mediates migration. Interactions of alpha3beta1 integrin with tetraspanin proteins may provide clues to how it transduces signals that affect cell behavior.