[show abstract][hide abstract] ABSTRACT: Detection of an extracellular cleaved fragment of a cell-cell adhesion molecule represents a new paradigm in molecular recognition and imaging of tumors. We previously demonstrated that probes that recognize the cleaved extracellular domain of receptor protein tyrosine phosphatase mu (PTPmu) label human glioblastoma brain tumor sections and the main tumor mass of intracranial xenograft gliomas. In this article, we examine whether one of these probes, SBK2, can label dispersed glioma cells that are no longer connected to the main tumor mass. Live mice with highly dispersive glioma tumors were injected intravenously with the fluorescent PTPmu probe to test the ability of the probe to label the dispersive glioma cells in vivo. Analysis was performed using a unique three-dimensional (3D) cryo-imaging technique to reveal highly migratory and invasive glioma cell dispersal within the brain and the extent of colabeling by the PTPmu probe. The PTPmu probe labeled the main tumor site and dispersed cells up to 3.5 mm away. The cryo-images of tumors labeled with the PTPmu probe provide a novel, high-resolution view of molecular tumor recognition, with excellent 3D detail regarding the pathways of tumor cell migration. Our data demonstrate that the PTPmu probe recognizes distant tumor cells even in parts of the brain where the blood-brain barrier is likely intact. The PTPmu probe has potential translational significance for recognizing tumor cells to facilitate molecular imaging, a more complete tumor resection and to serve as a molecular targeting agent to deliver chemotherapeutics to the main tumor mass and distant dispersive tumor cells.
International Journal of Cancer 09/2012; · 6.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: Traditional methods of imaging cell migration in the tumor microenvironment include serial sections of xenografts and standard histologic stains. Current molecular imaging techniques suffer from low resolution and difficulty in imaging through the skull. Here we show how computer algorithms can be used to reconstruct images from tissue sections obtained from mouse xenograft models of human glioma and can be rendered into three-dimensional images offering exquisite anatomic detail of tumor cell dispersal. Our findings identify human LN-229 and rodent CNS-1 glioma cells as valid systems to study the highly dispersive nature of glioma tumor cells along blood vessels and white matter tracts in vivo. This novel cryo-imaging technique provides a valuable tool to evaluate therapeutic interventions targeted at limiting tumor cell invasion and dispersal.
Cancer Research 08/2011; 71(17):5932-40. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Dissolution of cell-cell adhesive contacts and increased cell-extracellular matrix adhesion are hallmarks of the migratory and invasive phenotype of cancer cells. These changes are facilitated by growth factor binding to receptor protein tyrosine kinases (RTKs). In normal cells, cell-cell adhesion molecules (CAMs), including some receptor protein tyrosine phosphatases (RPTPs), antagonize RTK signaling by promoting adhesion over migration. In cancer, RTK signaling is constitutive due to mutated or amplified RTKs, which leads to growth factor independence, or autonomy. An alternative route for a tumor cell to achieve autonomy is to inactivate cell-cell CAMs such as RPTPs. RPTPs directly mediate cell adhesion and regulate both cadherin-dependent adhesion and signaling. In addition, RPTPs antagonize RTK signaling by dephosphorylating molecules activated following ligand binding. Both RPTPs and cadherins are downregulated in tumor cells by cleavage at the cell surface. This results in shedding of the extracellular, adhesive segment and displacement of the intracellular segment, altering its subcellular localization and access to substrates or binding partners. In this commentary we discuss the signals that are altered following RPTP and cadherin cleavage to promote cell migration. Tumor cells both step on the gas (RTKs) and disconnect the brakes (RPTPs and cadherins) during their invasive and metastatic journey.
[show abstract][hide abstract] ABSTRACT: The receptor protein tyrosine phosphatase PTPµ has a cell-adhesion molecule-like extracellular segment and a catalytically active intracellular segment. This structure gives PTPµ the ability to transduce signals in response to cell-cell adhesion. Full-length PTPµ is down-regulated in glioma cells by proteolysis which is linked to increased migration of these cells in the brain. To gain insight into the substrates PTPµ may be dephosphorylating to suppress glioma cell migration, we used a substrate trapping method to identify PTPµ substrates in tumor cell lines. We identified both PKCδ and PLCγ1 as PTPµ substrates. As PLCγ1 activation is linked to increased invasion of cancer cells, we set out to determine whether PTPµ may be upstream of PLCγ1 in regulating glioma cell migration. We conducted brain slice assays using U87-MG human glioma cells in which PTPµ expression was reduced by shRNA to induce migration. Treatment of the same cells with PTPµ shRNA and a PLCγ1 inhibitor prevented migration of the cells within the brain slice. These data suggest that PLCγ1 is downstream of PTPµ and that dephosphorylation of PLCγ1 is likely to be a major pathway through which PTPµ suppresses glioma cell migration.
Journal of Cellular Biochemistry 01/2011; 112(1):39-48. · 3.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: Receptor protein tyrosine phosphatase (RPTPs) are involved in many cellular processes, including the regulation of adhesion, migration and cellular signaling. Many RPTPs are putative tumor suppressors because of the transcriptional and translational changes observed in their expression during tumorigenesis. Recently, RPTPs were shown to be post-translationally regulated during tumorigenesis by proteolysis in a manner similar to proteolysis of the Notch receptor. There is accumulating evidence that proteolysis of RPTPs influence their cellular function and that RPTP fragments may function as oncogenes. By exploiting what is known about RPTP ligand binding domains and crystal structures of ligand-RPTP interfaces, we describe novel molecular diagnostics that have been or can be developed to identify tumor margins and target tumor tissues.
Anti-cancer agents in medicinal chemistry 01/2011; 11(1):133-40.
[show abstract][hide abstract] ABSTRACT: The term contact inhibition (CI) encompasses the cellular changes that result in cessation of cell migration and of proliferation due to signals transduced when one cell comes into physical contact with another cell. Cancer cells, however, do not contact inhibit. A molecular understanding of the loss of CI in cancer cells is important for understanding tumor progression. In this Perspective, we propose that the loss of CI observed in cancer cells is the result of extracellular proteolysis of transmembrane cell-cell cell adhesion molecules (CAM) in the tumor microenvironment. Proteolysis of homophilic cell-cell CAMs results in a shed extracellular fragment and released cytoplasmic fragment(s) that disrupts adhesion and induces signals that promote proliferation and/or migration. The importance of this observation in tumor progression is supported by the presence of the shed extracellular fragments of homophilic cell-cell CAMs in serum and tumor tissue of cancer patients suggesting that instead of acting as tumor suppressors, the shed CAM extracellular and cytoplasmic fragments actually function as oncogenes. The study of cell-cell CAM cleavage will provide important and novel means of diagnosing, imaging, and treating tumor progression.
Cancer Research 11/2010; 71(2):303-9. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Receptor protein tyrosine phosphatases (RPTPs) have cell adhesion molecule-like extracellular domains coupled to cytoplasmic tyrosine phosphatase domains. PTPmu is the prototypical member of the type IIb subfamily of RPTPs, which includes PTPrho, PTPkappa, and PCP-2. The authors performed the first comprehensive analysis of the subfamily in one system, examining adhesion and antibody recognition. The authors evaluated if antibodies that they developed to detect PTPmu also recognized other subfamily members. Notably, each antibody recognizes distinct subsets of type IIb RPTPs. PTPmu, PTPrho, and PTPkappa have all been shown to mediate cell-cell aggregation, and prior work with PCP-2 indicated that it can mediate bead aggregation in vitro. This study reveals that PCP-2 is unique among the type IIb RPTPs in that it does not mediate cell-cell aggregation via homophilic binding. The authors conclude from these experiments that PCP-2 is likely to have a distinct biological function other than cell-cell aggregation.
Cell Communication & Adhesion 04/2010; 17(2):34-47. · 1.05 Impact Factor
[show abstract][hide abstract] ABSTRACT: Abstract The receptor protein tyrosine phosphatase T PTPrho is the most frequently mutated tyrosine phosphatase in human cancer. PTPrho mediates homophilic cell-cell aggregation. In its extracellular region, PTPrho has cell adhesion molecule-like motifs, including a MAM domain, an immunoglobulin domain, and four fibronectin type III (FNIII) repeats. Tumor-derived mutations have been identified in all of these extracellular domains. Previously, the authors determined that tumor-derived mutations in the MAM and immunoglobulin domains of PTPrho reduce homophilic cell-cell aggregation. In this paper, the authors describe experiments in which the contribution of the FNIII repeats to PTPrho-mediated cell-cell adhesion was evaluated. The results demonstrate that deletion of the FNIII repeats of PTPrho result in defective cell-cell aggregation. Furthermore, all of the tumor-derived mutations in the FNIII repeats of PTPrho also disrupt cell-cell aggregation. These results further support the hypothesis that mutational inactivation of PTPrho may lead to cancer progression by disrupting cell-cell adhesion.
Cell Communication & Adhesion 03/2010; 16(5-6):146-53. · 1.05 Impact Factor
[show abstract][hide abstract] ABSTRACT: N-cadherin is a cell adhesion molecule that promotes axon outgrowth and synapse formation during the development of the central nervous system. In addition, N-cadherin promotes glial cell adhesion and myelination of axons. Therefore, stimulating N-cadherin function with N-cadherin agonists could be used therapeutically to promote regeneration of the nervous system and remyelination after injury or disease. In the extracellular domain of N-cadherin, the amino acid sequence HAV is required for N-cadherin-mediated adhesion and neurite outgrowth. The ADH-1 cyclic peptide, derived from the N-cadherin HAV site, is an effective antagonist of N-cadherin-mediated neurite outgrowth and is currently being tested in clinical trials for cancer chemotherapy. Of interest, a dimeric version of this cyclic peptide, N-Ac-CHAVDINGHAVDIC-NH(2), functions as an N-cadherin agonist. This dimeric peptide agonist and the peptide antagonist ADH-1 both have limitations as drugs due to their metabolic instability and lack of oral delivery. To address this issue Adherex Technologies Inc. generated a small molecule library of peptidomimetics to the HAV region of N-cadherin, which would be more amenable to therapeutic use. We screened the Adherex library for compounds that altered neurite outgrowth and identified eight N-cadherin agonists that stimulated N-cadherin-dependent neurite outgrowth. Five of these agonists also stimulated retinal cell migration. These small molecule agonists may be effective reagents for promoting axon growth and remyelination after injury or disease.
[show abstract][hide abstract] ABSTRACT: The cell adhesion molecule, N-cadherin, stabilizes cell-cell junctions and promotes cellular migration during tissue morphogenesis in development. N-cadherin is also implicated in mediating tumor progression and metastasis in cancer. Therefore, developing antagonists of N-cadherin adhesion may be of therapeutic value in cancer treatment. The amino acid sequence HAV in the extracellular domain of N-cadherin is required for N-cadherin-mediated adhesion and migration. A cyclic peptide, ADH-1, derived from the N-cadherin HAV site is an effective antagonist of N-cadherin-mediated processes and is now in clinical trials for cancer chemotherapy. Because it is a peptide, ADH-1 has certain limitations as a drug, namely its metabolic instability and lack of oral delivery. Adherex set out to identify small molecule antagonists of N-cadherin, which would be more amenable to therapeutic use. Using three-dimensional computational screening, Adherex identified a set of small molecules as potential antagonists with sufficient structural similarity to the HAV region of N-cadherin. We tested the ability of these small molecules to interfere with two N-cadherin-dependent processes: neurite outgrowth (axonal migration) and N-cadherin-dependent cell adhesion. We identified 21 N-cadherin antagonists of varying potency. More importantly, our studies demonstrate that these compounds are significantly more potent than ADH-1 at perturbing N-cadherin-mediated processes. The IC(50) of ADH-1 is 2.33 mM while the IC(50) of the small molecules ranges from 4.5 to 30 microM. Given the efficacy of ADH-1 for treating cancer, these small molecule antagonists will be highly effective in treatment of cancer metastasis and conditions of aberrant neurite outgrowth, such as neuropathic pain.