A novel molecular diagnostic of glioblastomas: detection of an extracellular fragment of protein tyrosine phosphatase mu

Unveiling Alterations of Epigenetic Modifications and Chromatin Architecture Leading to Lipid Metabolic Reprogramming during the Evolutionary Trastuzumab Adaptation of HER2-Positive Breast Cancer

Secondary trastuzumab resistance represents an evolutionary adaptation of HER2-positive breast cancer during anti-HER2 treatment. Most current studies have tended to prioritize HER2 and its associated signaling pathways, often overlooking broader but seemingly less relevant cellular processes, along with their associated genetic and epigenetic mechanisms. Here, transcriptome data is not only characterized but also examined epigenomic and 3D genome architecture information in both trastuzumab-sensitive and secondary-resistant breast cancer cells. The findings reveal that the global metabolic reprogramming associated with trastuzumab resistance may stem from genome-wide alterations in both histone modifications and chromatin structure. Specifically, the transcriptional activities of key genes involved in lipid metabolism appear to be regulated by variant promoter H3K27me3 and H3K4me3 modifications, as well as promoter-enhancer interactions. These discoveries offer valuable insights into how cancer cells adapt to anti-tumor drugs and have the potential to impact future diagnostic and treatment strategies.

Manipulating PTPRD function with ectodomain antibodies

Protein tyrosine phosphatases (PTPs) are critical regulators of signal transduction but have yet to be exploited fully for drug development. Receptor protein tyrosine phosphatase δ (RPTPδ/PTPRD) has been shown to elicit tumor-promoting functions, including elevating SRC activity and promoting metastasis in certain cell contexts. Dimerization has been implicated in the inhibition of receptor protein tyrosine phosphatases (RPTPs). We have generated antibodies targeting PTPRD ectodomains with the goal of manipulating their dimerization status ectopically, thereby regulating intracellular signaling. We have validated antibody binding to endogenous PTPRD in a metastatic breast cancer cell line, CAL51, and demonstrated that a monoclonal antibody, RD-43, inhibited phosphatase activity and induced the degradation of PTPRD. Similar effects were observed following chemically induced dimerization of its phosphatase domain. Mechanistically, RD-43 triggered the formation of PTPRD dimers in which the phosphatase activity was impaired. Subsequently, the mAb-PTPRD dimer complex was degraded through lysosomal and proteasomal pathways, independently of secretase cleavage. Consequently, treatment with RD-43 inhibited SRC signaling and suppressed PTPRD-dependent cell invasion. Together, these findings demonstrate that manipulating RPTP function via antibodies to the extracellular segments has therapeutic potential.

Small molecule antagonists of PTPmu identified by artificial intelligence-based computational screening block glioma cell migration and growth

PTPmu (PTPμ) is a member of the receptor protein tyrosine phosphatase IIb family that participates in both homophilic cell-cell adhesion and signaling. PTPmu is proteolytically downregulated in glioblastoma generating extracellular and intracellular fragments that have oncogenic activity. The intracellular fragments, in particular, are known to accumulate in the cytoplasm and nucleus where they interact with inappropriate binding partners/substrates generating signals required for glioma cell migration and growth. Thus, interfering with these fragments is an attractive therapeutic strategy. To develop agents that target these fragments, we used the AI-based AtomNetⓇ model, a drug design and discovery tool, to virtually screen molecular libraries for compounds able to target a binding pocket bordered by the wedge domain, a known regulatory motif located within the juxtamembrane portion of the protein. Seventy-four high-scoring and chemically diverse virtual hits were then screened in multiple cell-based assays for effects on glioma cell motility (scratch assays) and growth in 3D culture (sphere assays), and PTPmu-dependent adhesion (Sf9 aggregation). We identified three inhibitors (247678835, 247682206, 247678791) that affected the motility of multiple glioma cell lines (LN229, U87MG, and Gli36delta5), the growth of LN229 and Gli36 spheres, and PTPmu-dependent Sf9 aggregation. Compound 247678791 was further shown to suppress PTPmu enzymatic activity in an in vitro phosphatase assay, and 247678835 was able to inhibit the growth of human glioma tumors in mice. We propose that these three compounds are PTPmu-targeting agents with therapeutic potential for treating glioblastoma.

Artificial Intelligence-Based Computational Screening and Functional Assays Identify Candidate Small Molecule Antagonists of PTPmu-Dependent Adhesion

PTPmu (PTPµ) is a member of the receptor protein tyrosine phosphatase IIb family that participates in cell-cell adhesion and signaling. PTPmu is proteolytically downregulated in glioblastoma (glioma), and the resulting extracellular and intracellular fragments are believed to stimulate cancer cell growth and/or migration. Therefore, drugs targeting these fragments may have therapeutic potential. Here, we used the AtomNet^® platform, the first deep learning neural network for drug design and discovery, to screen a molecular library of several million compounds and identified 76 candidates predicted to interact with a groove between the MAM and Ig extracellular domains required for PTPmu-mediated cell adhesion. These candidates were screened in two cell-based assays: PTPmu-dependent aggregation of Sf9 cells and a tumor growth assay where glioma cells grow in three-dimensional spheres. Four compounds inhibited PTPmu-mediated aggregation of Sf9 cells, six compounds inhibited glioma sphere formation/growth, while two priority compounds were effective in both assays. The stronger of these two compounds inhibited PTPmu aggregation in Sf9 cells and inhibited glioma sphere formation down to 25 micromolar. Additionally, this compound was able to inhibit the aggregation of beads coated with an extracellular fragment of PTPmu, directly demonstrating an interaction. This compound presents an interesting starting point for the development of PTPmu-targeting agents for treating cancer including glioblastoma.

Comparison of Near-Infrared Imaging Agents Targeting the PTPmu Tumor Biomarker

PURPOSE

Maximal, safe resection of solid tumors is considered a critical first step in successful cancer treatment. The advent of fluorescence image-guided surgery (FIGS) using non-specific agents has improved patient outcomes, particularly in the case of glioblastoma. Molecularly targeted agents that recognize specific tumor biomarkers have the potential to augment these gains. Identification of the optimal combination of targeting moiety and fluorophore is needed prior to initiating clinical trials.

PROCEDURES

A 20-amino acid peptide (SBK2) recognizing the receptor protein-tyrosine phosphatase mu (PTPmu)-derived tumor-specific biomarker, with or without a linker, was conjugated to three different near-infrared fluorophores: indocyanine green (ICG), IRDye® 800CW, and Tide Fluor™ 8WS. The in vivo specificity, time course, and biodistribution were evaluated for each using mice with heterotopic human glioma tumors that express the PTPmu biomarker to identify component combinations with optimal properties for FIGS.

RESULTS

SBK2 conjugated to ICG demonstrated excellent specificity for gliomas in heterotopic tumors. SBK2-ICG showed significantly higher in vivo tumor labeling compared to the Scram-ICG control from 10 min to 24 h, p < 0.01 at all timepoints, following injection, as well as a significantly higher ex vivo tumor signal at 24 h, p < 0.001. Inserting a six-amino acid linker between the targeting peptide and ICG increased the clearance rate and resulted in significantly higher in vivo tumor signal relative to its linker-containing Scrambled control from 10 min to 8 h, p < 0.05 at all timepoints, after dosing. Agents made with the more hydrophilic IRDye® 800CW and Tide Fluor™ 8WS showed no specific tumor labeling relative to the controls. The IRDye 800CW-conjugated agents cleared within 1 h, while the non-specific fluorescent tumor signal generated by the Tide Fluor 8WS-conjugated agents persists beyond 24 h.

CONCLUSIONS

The SBK2 PTPmu-targeting peptide conjugated to ICG specifically labels heterotopic human gliomas grown in mice between 10 min and 24 h following injection. Similar molecules constructed with more hydrophilic dyes demonstrated no specificity. These studies present a promising candidate for use in FIGS of PTPmu biomarker-expressing tumors.

Physically-cross-linked poly(vinyl alcohol) cell culture plate coatings facilitate preservation of cell-cell interactions, spheroid formation, and stemness

We employed aqueous solutions of highly-hydrolyzed (>99+%) poly(vinyl alcohol), PVA, to coat plastic dishes as a method to efficiently induce three-dimensional (3D) culturing of cells. The coatings were prepared by simple evaporation of 3 wt/vol% solutions of PVA in water and require no additional processing steps after air drying under sterile conditions. The coating allows spheroids to form in solution. Spheroid formation is usually preferable to two-dimensional (2D) culturing as it creates a more realistic ex vivo model of some human tissues and tumors. Using PVA-coated cell culture plates, we demonstrated that we can grow reproducibly sized spheroids using several human glioma cell lines, including LN229, U87 MG, and Gli36, and the embryonic kidney cell line, 293T. Spheroids formed on PVA-coated plates grow as well as on other commercially-available, low-attachment plates, and have excellent optical imaging properties. As spheroids, LN229 cells express markers of cancer stem cells. Finally, we confirmed that spheroids generated on PVA-coated plates are sensitive to molecular perturbations, as increased expression of the cell adhesion molecule PTPμ significantly increased the size of spheroids. The PVA hydrogel layer is an effective tool for creating a more realistic ex vivo culture system than traditional 2D culture and can be used to generate cell spheroids for potential application in drug screening and personalized medicine for diseases such as cancer.

Ultrasound-Based Molecular Imaging of Tumors with PTPmu Biomarker-Targeted Nanobubble Contrast Agents

Ultrasound imaging is a widely used, readily accessible and safe imaging modality. Molecularly-targeted microbubble- and nanobubble-based contrast agents used in conjunction with ultrasound imaging expand the utility of this modality by specifically targeting and detecting biomarkers associated with different pathologies including cancer. In this study, nanobubbles directed to a cancer biomarker derived from the Receptor Protein Tyrosine Phosphatase mu, PTPmu, were evaluated alongside non-targeted nanobubbles using contrast enhanced ultrasound both in vitro and in vivo in mice. In vitro resonant mass and clinical ultrasound measurements showed gas-core, lipid-shelled nanobubbles conjugated to either a PTPmu-directed peptide or a Scrambled control peptide were equivalent. Mice with heterotopic human tumors expressing the PTPmu-biomarker were injected with PTPmu-targeted or control nanobubbles and dynamic contrast-enhanced ultrasound was performed. Tumor enhancement was more rapid and greater with PTPmu-targeted nanobubbles compared to the non-targeted control nanobubbles. Peak tumor enhancement by the PTPmu-targeted nanobubbles occurred within five minutes of contrast injection and was more than 35% higher than the Scrambled nanobubble signal for the subsequent two minutes. At later time points, the signal in tumors remained higher with PTPmu-targeted nanobubbles demonstrating that PTPmu-targeted nanobubbles recognize tumors using molecular ultrasound imaging and may be useful for diagnostic and therapeutic purposes.

Detection of Tumor-Specific PTPmu in Gynecological Cancer and Patient Derived Xenografts

Background: We developed a fluorophore-conjugated peptide agent, SBK4, that detects a tumor-specific proteolyzed form of the cell adhesion molecule, PTPmu, found in the tumor microenvironment. We previously demonstrated its tissue specific distribution in high-grade brain tumors. To extend those studies to other aggressive solid tumor types, we assessed the tissue distribution of PTPmu/SBK4 in a set of matched gynecologic cancer patient derived xenografts (PDXs) and primary patient tumors, as well as a limited cohort of tumors from gynecological cancer patients. PDXs isolated from the tissues of cancer patients have been shown to yield experimentally manipulatable models that replicate the clinical characteristics of individual patients’ tumors. In this study, gynecological cancer PDXs and patient biopsies were examined to determine if tumor-specific proteolyzed PTPmu was present. Methods: We used the peptide agent SBK4 conjugated to the fluorophore Texas Red (TR) to label tumor tissue microarrays (TMAs) containing patient and/or PDX samples from several high-grade gynecologic cancer types, and quantified the level of staining with Image J. In one TMA, we were able to directly compare the patient and the matched PDX tissue on the same slide. Results: While normal tissue had very little SBK4-TR staining, both primary tumor tissue and PDXs have higher labeling with SBK4-TR. Matched PDXs and patient samples from high-grade endometrial and ovarian cancers demonstrated higher levels of PTPmu by staining with SBK4 than normal tissue. Conclusion: In this sample set, all PDXs and high-grade ovarian cancer samples had increased labeling by SBK4-TR compared with the normal controls. Our results indicate that proteolyzed PTPmu and its novel peptide detection agent, SBK4, allow for the visualization of tumor-specific changes in cell adhesion molecules by tissue-based staining, providing a rationale for further development as an imaging agent in aggressive solid tumors, including gynecological cancers.

PTPmu-targeted nanoparticles label invasive pediatric and adult glioblastoma

Poor prognosis for glioblastoma (GBM) is a consequence of the aggressive and infiltrative nature of gliomas where individual cells migrate away from the main tumor to distant sites, making complete surgical resection and treatment difficult. In this manuscript, we characterize an invasive pediatric glioma model and determine if nanoparticles linked to a peptide recognizing the GBM tumor biomarker PTPmu can specifically target both the main tumor and invasive cancer cells in adult and pediatric glioma models. Using both iron and lipid-based nanoparticles, we demonstrate by magnetic resonance imaging, optical imaging, histology, and iron quantification that PTPmu-targeted nanoparticles effectively label adult gliomas. Using PTPmu-targeted nanoparticles in a newly characterized orthotopic pediatric SJ-GBM2 model, we demonstrate individual tumor cell labeling both within the solid tumor margins and at invasive and dispersive sites.

Dynamic, Simultaneous Concentration Mapping of Multiple MRI Contrast Agents with Dual Contrast - Magnetic Resonance Fingerprinting

Synchronous assessment of multiple MRI contrast agents in a single scanning session would provide a new "multi-color" imaging capability similar to fluorescence imaging but with high spatiotemporal resolution and unlimited imaging depth. This multi-agent MRI technology would enable a whole new class of basic science and clinical MRI experiments that simultaneously explore multiple physiologic/molecular events in vivo. Unfortunately, conventional MRI acquisition techniques are only capable of detecting and quantifying one paramagnetic MRI contrast agent at a time. Herein, the Dual Contrast - Magnetic Resonance Fingerprinting (DC-MRF) methodology was extended for in vivo application and evaluated by simultaneously and dynamically mapping the intra-tumoral concentration of two MRI contrast agents (Gd-BOPTA and Dy-DOTA-azide) in a mouse glioma model. Co-registered gadolinium and dysprosium concentration maps were generated with sub-millimeter spatial resolution and acquired dynamically with just over 2-minute temporal resolution. Mean tumor Gd and Dy concentration measurements from both single agent and dual agent DC-MRF studies demonstrated significant correlations with ex vivo mass spectrometry elemental analyses. This initial in vivo study demonstrates the potential for DC-MRF to provide a useful dual-agent MRI platform.

A PTPmu Biomarker is Associated with Increased Survival in Gliomas

An integrated approach has been adopted by the World Health Organization (WHO) for diagnosing brain tumors. This approach relies on the molecular characterization of biopsied tissue in conjunction with standard histology. Diffuse gliomas (grade II to grade IV malignant brain tumors) have a wide range in overall survival, from months for the worst cases of glioblastoma (GBM) to years for lower grade astrocytic and oligodendroglial tumors. We previously identified a change in the cell adhesion molecule PTPmu in brain tumors that results in the generation of proteolytic fragments. We developed agents to detect this cell surface-associated biomarker of the tumor microenvironment. In the current study, we evaluated the PTPmu biomarker in tissue microarrays and individual tumor samples of adolescent and young adult (n = 25) and adult (n = 69) glioma populations using a fluorescent histochemical reagent, SBK4-TR, that recognizes the PTPmu biomarker. We correlated staining with clinical data and found that high levels of the PTPmu biomarker correlate with increased survival of glioma patients, including those with GBM. Patients with high PTPmu live for 48 months on average, whereas PTPmu low patients live only 22 months. PTPmu high staining indicates a doubling of patient survival. Use of the agent to detect the PTPmu biomarker would allow differentiation of glioma patients with distinct survival outcomes and would complement current molecular approaches used in glioma prognosis.

Targeted Contrast Agents for Molecular MRI

Molecular magnetic resonance imaging (MRI) provides information non-invasively at cellular and molecular levels, for both early diagnosis and monitoring therapeutic follow-up. This imaging technique requires the development of a new class of contrast agents, which signal changes (typically becomes enhanced) when in presence of the cellular or molecular process to be evaluated. Even if molecular MRI has had a prominent role in the advances in medicine over the past two decades, the large majority of the developed probes to date are still in preclinical level, or eventually in phase I or II clinical trials. The development of novel imaging probes is an emergent active research domain. This review focuses on gadolinium-based specific-targeted contrast agents, providing rational design considerations and examples of the strategies recently reported in the literature.

β1,6 GlcNAc branches-modified protein tyrosine phosphatase Mu attenuates its tyrosine phosphatase activity and promotes glioma cell migration through PLCγ-PKC pathways

The metastatic potential of malignant tumor has been shown to be correlated with the increased expression of tri- and tetra-antennary β1,6-N-acetylglucosamine (β1,6-GlcNAc) N-glycans. In this study, We found that GnT-V expression was negatively correlated with receptor protein tyrosine phosphatase type μ(RPTPμ) in human glioma tissues. To study whether RPTPμ is a novel substance of GnT-V which further affect RPTPμ's downstream dephosphorylation function, we preform lentiviral infection with GnT-V gene to construct stably transfected GnT-V glial cell lines. We found RPTPμ undergone severer cleavage in GnT-V transfected glioma cells compare to Mock cells. RPTPμ intracellular domain fragments increased while β1,6-GlcNAc-branched N-glycans increased, in consistent with the decrease of RPTPμ's catalytic activity. The results showed that abnormal glycosylation could decrease the phosphorylation activity of PTP μ, and affect PLCγ-PKC pathways. Both protease inhibitor Furin and N-glycan biosynthesis inhibitor swainsonine could decrease cell mobility in GnT-V-U87 transfectants and other glioma cell lines. All results above suggest increased post-translational modification of RPTPμ N-glycans by GnT-V attenuates its tyrosine phosphatase activity and promotes glioma cell migration through PLCγ-PKC pathways, and that the β1,6-GlcNAc-branched N-glycans of RPTPμ play a crucial role in glioma invasivity.

Fast magnetic resonance fingerprinting for dynamic contrast-enhanced studies in mice

PURPOSE

The goal of this study was to develop a fast MR fingerprinting (MRF) method for simultaneous T₁ and T₂ mapping in DCE-MRI studies in mice.

METHODS

The MRF sequences based on balanced SSFP and fast imaging with steady-state precession were implemented and evaluated on a 7T preclinical scanner. The readout used a zeroth-moment-compensated variable-density spiral trajectory that fully sampled the entire k-space and the inner 10 × 10 k-space with 48 and 4 interleaves, respectively. In vitro and in vivo studies of mouse brain were performed to evaluate the accuracy of MRF measurements with both fully sampled and undersampled data. The application of MRF to dynamic T₁ and T₂ mapping in DCE-MRI studies were demonstrated in a mouse model of heterotopic glioblastoma using gadolinium-based and dysprosium-based contrast agents.

RESULTS

The T₁ and T₂ measurements in phantom showed strong agreement between the MRF and the conventional methods. The MRF with spiral encoding allowed up to 8-fold undersampling without loss of measurement accuracy. This enabled simultaneous T₁ and T₂ mapping with 2-minute temporal resolution in DCE-MRI studies.

CONCLUSION

Magnetic resonance fingerprinting provides the opportunity for dynamic quantification of contrast agent distribution in preclinical tumor models on high-field MRI scanners.

Quantitative Molecular Imaging with a Single Gd-Based Contrast Agent Reveals Specific Tumor Binding and Retention in Vivo

Magnetic resonance imaging (MRI) has become an indispensable tool in the diagnosis and treatment of many diseases, especially cancer. However, the poor sensitivity of MRI relative to other imaging modalities, such as PET, has hindered the development and clinical use of molecular MRI contrast agents that could provide vital diagnostic information by specifically locating a molecular target altered in the disease process. This work describes the specific and sustained in vivo binding and retention of a protein tyrosine phosphatase mu (PTPμ)-targeted, molecular magnetic resonance (MR) contrast agent with a single gadolinium (Gd) chelate using a quantitative MRI T₁ mapping technique in glioma xenografts. Quantitative T₁ mapping is an imaging method used to measure the longitudinal relaxation time, the T₁ relaxation time, of protons in a magnetic field after excitation by a radiofrequency pulse. T₁ relaxation times can in turn be used to calculate the concentration of a gadolinium-containing contrast agent in a region of interest, thereby allowing the retention or clearance of an agent to be quantified. In this context, retention is a measure of molecular contrast agent binding. Using conventional peptide chemistry, a PTPμ-targeted peptide was linked to a chelator that had been conjugated to a lysine residue. Following complexation with Gd, this PTPμ-targeted molecular contrast agent containing a single Gd ion showed significant tumor enhancement and a sustained increase in Gd concentration in both heterotopic and orthotopic tumors using dynamic quantitative MRI. This single Gd-containing PTPμ agent was more effective than our previous version with three Gd ions. Differences between nonspecific and specific agents, due to specific tumor binding, can be determined within the first 30 min after agent administration by examining clearance rates. This more facile chemistry, when combined with quantitative MR techniques, allows for widespread adoption by academic and commercial entities in the field of molecular MRI ultimately leading to improved detection of disease.

Fluorescent-Guided Surgical Resection of Glioma with Targeted Molecular Imaging Agents: A Literature Review

The median life expectancy after a diagnosis of glioblastoma is 15 months. Although chemotherapeutics may someday cure glioblastoma by killing the highly dispersive malignant cells, the most important contribution that clinicians can currently offer to improve survival is by maximizing the extent of resection and providing concurrent chemo-radiation, which has become standard. Strides have been made in this area with the advent and implementation of methods of improved intraoperative tumor visualization. One of these techniques, optical fluorescent imaging with targeted molecular imaging agents, allows the surgeon to view fluorescently labeled tumor tissue during surgery with the use of special microscopy, thereby highlighting where to resect and indicating when tumor-free margins have been obtained. This advantage is especially important at the difficult-to-observe margins where tumor cells infiltrate normal tissue. Targeted fluorescent agents also may be valuable for identifying tumor versus nontumor tissue. In this review, we briefly summarize nontargeted fluorescent tumor imaging agents before discussing several novel targeted fluorescent agents being developed for glioma imaging in the context of fluorescent-guided surgery or live molecular navigation. Many of these agents are currently undergoing preclinical testing. As the agents become available, however, it is necessary to understand the strengths and weaknesses of each.

Molecular Imaging of Tumors Using a Quantitative T 1 Mapping Technique via Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) of glioblastoma multiforme (GBM) with molecular imaging agents would allow for the specific localization of brain tumors. Prior studies using T₁-weighted MR imaging demonstrated that the SBK2-Tris-(Gd-DOTA)₃ molecular imaging agent labeled heterotopic xenograft models of brain tumors more intensely than non-specific contrast agents using conventional T₁-weighted imaging techniques. In this study, we used a dynamic quantitative T₁ mapping strategy to more objectively compare intra-tumoral retention of the SBK2-Tris-(Gd-DOTA)₃ agent over time in comparison to non-targeted control agents. Our results demonstrate that the targeted SBK2-Tris-(Gd-DOTA)₃ agent, a scrambled-Tris-(Gd-DOTA)₃ control agent, and the non-specific clinical contrast agent Optimark™ all enhanced flank tumors of human glioma cells with similar maximal changes on T₁ mapping. However, the retention of the agents differs. The non-specific agents show significant recovery within 20 min by an increase in T₁ while the specific agent SBK2-Tris-(Gd-DOTA)₃ is retained in the tumors and shows little recovery over 60 min. The retention effect is demonstrated by percent change in T₁ values and slope calculations as well as by calculations of gadolinium concentration in tumor compared to muscle. Quantitative T₁ mapping demonstrates the superior binding and retention in tumors of the SBK2-Tris-(Gd-DOTA)₃ agent over time compared to the non-specific contrast agent currently in clinical use.

A protease storm cleaves a cell-cell adhesion molecule in cancer: multiple proteases converge to regulate PTPmu in glioma cells

Cleavage of the cell-cell adhesion molecule, PTPµ, occurs in human glioblastoma multiforme brain tumor tissue and glioma cell lines. PTPµ cleavage is linked to increased cell motility and growth factor independent survival of glioma cells in vitro. Previously, PTPµ was shown to be cleaved by furin in the endoplasmic reticulum to generate membrane associated E- (extracellular) and P- (phosphatase) subunits, and by ADAMs and the gamma secretase complex at the plasma membrane. We also identified the presence of additional extracellular and intracellular PTPµ fragments in brain tumors. We set out to biochemically analyze PTPµ cleavage in cancer cells. We determined that, in addition to the furin-processed form of PTPµ, a pool of 200 kDa full-length PTPµ exists at the plasma membrane that is cleaved directly by ADAM to generate a larger shed form of the PTPµ extracellular segment. Notably, in glioma cells, full-length PTPµ is also subject to calpain cleavage, which generates novel PTPµ fragments not found in other immortalized cells. We also observed glycosylation and phosphorylation differences in the cancer cells. Our data suggest that an additional serine protease also contributes to PTPµ shedding in glioma cells. We hypothesize that a "protease storm" occurs in cancer cells whereby multiple proteases converge to reduce the presence of cell-cell adhesion molecules at the plasma membrane and to generate protein fragments with unique biological functions. As a consequence, the "protease storm" could promote the migration and invasion of tumor cells.

Genetic alterations of protein tyrosine phosphatases in human cancers

Protein tyrosine phosphatases (PTPs) are enzymes that remove phosphate from tyrosine residues in proteins. Recent whole-exome sequencing of human cancer genomes reveals that many PTPs are frequently mutated in a variety of cancers. Among these mutated PTPs, protein tyrosine phosphatase T (PTPRT) appears to be the most frequently mutated PTP in human cancers. Beside PTPN11 which functions as an oncogene in leukemia, genetic and functional studies indicate that most of mutant PTPs are tumor suppressor genes. Identification of the substrates and corresponding kinases of the mutant PTPs may provide novel therapeutic targets for cancers harboring these mutant PTPs.

Regulation of development and cancer by the R2B subfamily of RPTPs and the implications of proteolysis

The initial cloning of receptor protein tyrosine phosphatases (RPTPs) was met with excitement because of their hypothesized function in counterbalancing receptor tyrosine kinase signaling. In recent years, members of a subfamily of RPTPs with homophilic cell-cell adhesion capabilities, known as the R2B subfamily, have been shown to have functions beyond that of counteracting tyrosine kinase activity, by independently influencing cell signaling in their own right and by regulating cell adhesion. The R2B subfamily is composed of four members: PTPmu (PTPRM), PTPrho (PTPRT), PTPkappa (PTPRK), and PCP-2 (PTPRU). The effects of this small subfamily of RPTPs is far reaching, influencing several developmental processes and cancer. In fact, R2B RPTPs are predicted to be tumor suppressors and are among the most frequently mutated protein tyrosine phosphatases (PTPs) in cancer. Confounding these conclusions are more recent studies suggesting that proteolysis of the full-length R2B RPTPs result in oncogenic extracellular and intracellular protein fragments. This review discusses the current knowledge of the role of R2B RPTPs in development and cancer, with special detail given to the mechanisms and implications that proteolysis has on R2B RPTP function. We also touch upon the concept of exploiting R2B proteolysis to develop cancer imaging tools, and consider the effects of R2B proteolysis on axon guidance, perineural invasion and collective cell migration.

MR molecular imaging of prostate cancer with a small molecular CLT1 peptide targeted contrast agent

Tumor extracellular matrix has abundance of cancer related proteins that can be used as biomarkers for cancer molecular imaging. In this work, we demonstrated effective MR cancer molecular imaging with a small molecular peptide targeted Gd-DOTA monoamide complex as a targeted MRI contrast agent specific to clotted plasma proteins in tumor stroma. We performed the experiment of evaluating the effectiveness of the agent for non-invasive detection of prostate tumor with MRI in a mouse orthotopic PC-3 prostate cancer model. The targeted contrast agent was effective to produce significant tumor contrast enhancement at a low dose of 0.03 mmol Gd/kg. The peptide targeted MRI contrast agent is promising for MR molecular imaging of prostate tumor.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.

Molecular Magnetic Resonance Imaging of Tumors with a PTPµ Targeted Contrast Agent

Molecular magnetic resonance imaging (MRI) of tumors improves the specificity of MRI by using targeted probes conjugated to contrast-generating metals. The limitation of this approach is in the identification of a target molecule present in sufficient concentration for visualization and the development of a labeling reagent that can penetrate tumor tissue with the fast kinetics required for use in a clinical setting. The receptor protein tyrosine phosphatase PTPµ is a transmembrane protein that is continuously proteolyzed in the tumor microenvironment to generate a high concentration of extracellular fragment that can be recognized by the SBK2 probe. We conjugated the SBK2 peptide to a gadolinium chelate [SBK2-Tris-(Gd-DOTA)3] to test whether the SBK2 probe could be developed as an MR molecular imaging probe. When intravenously injected into mice bearing flank tumors of human glioma cells, SBK2-Tris-(Gd-DOTA)3 labeled the tumors within 5 minutes with a high level of contrast for up to 2 hours post-injection. The contrast enhancement of SBK2-Tris-(Gd-DOTA)3 was significantly higher than that observed with a current MRI macrocyclic gadolinium chelate (Gadoteridol, ProHance) alone or a scrambled control. These results demonstrate that SBK2-Tris-(Gd-DOTA)3 labeling of the PTPµ extracellular fragment is a more specific MR molecular imaging probe than ProHance or a scrambled control. Consequently, the SBK2 probe may be more useful than the current gold standard reagent for MRI to identify tumors and to co-register tumor borders during surgical resection.

Investigation of serum proteome alterations in human glioblastoma multiforme

Glioblastoma multiforme (GBM) or grade IV astrocytoma is the most common and lethal adult malignant brain tumor. The present study was conducted to investigate the alterations in the serum proteome in GBM patients compared to healthy controls. Comparative proteomic analysis was performed employing classical 2DE and 2D-DIGE combined with MALDI TOF/TOF MS and results were further validated through Western blotting and immunoturbidimetric assay. Comparison of the serum proteome of GBM and healthy subjects revealed 55 differentially expressed and statistically significant (p <0.05) protein spots. Among the identified proteins, haptoglobin, plasminogen precursor, apolipoprotein A-1 and M, and transthyretin are very significant due to their functional consequences in glioma tumor growth and migration, and could further be studied as glioma biomarkers and grade-specific protein signatures. Analysis of the lipoprotein pattern indicated elevated serum levels of cholesterol, triacylglycerol, and low-density lipoproteins in GBM patients. Functional pathway analysis was performed using multiple software including ingenuity pathway analysis (IPA), protein analysis through evolutionary relationships (PANTHER), database for annotation, visualization and integrated discovery (DAVID), and GeneSpring to investigate the biological context of the identified proteins, which revealed the association of candidate proteins in a few essential physiological pathways such as intrinsic prothrombin activation pathway, plasminogen activating cascade, coagulation system, glioma invasiveness signaling, and PI3K signaling in B lymphocytes. A subset of the differentially expressed proteins was applied to build statistical sample class prediction models for discrimination of GBM patients and healthy controls employing partial least squares discriminant analysis (PLS-DA) and other machine learning methods such as support vector machine (SVM), Decision Tree and Naïve Bayes, and excellent discrimination between GBM and control groups was accomplished.

Single cell molecular recognition of migrating and invading tumor cells using a targeted fluorescent probe to receptor PTPmu

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.

Cryo-image analysis of tumor cell migration, invasion, and dispersal in a mouse xenograft model of human glioblastoma multiforme

PURPOSE

The goals of this study were to create cryo-imaging methods to quantify characteristics (size, dispersal, and blood vessel density) of mouse orthotopic models of glioblastoma multiforme (GBM) and to enable studies of tumor biology, targeted imaging agents, and theranostic nanoparticles.

PROCEDURES

Green fluorescent protein-labeled, human glioma LN-229 cells were implanted into mouse brain. At 20-38 days, cryo-imaging gave whole brain, 4-GB, 3D microscopic images of bright field anatomy, including vasculature, and fluorescent tumor. Image analysis/visualization methods were developed.

RESULTS

Vessel visualization and segmentation methods successfully enabled analyses. The main tumor mass volume, the number of dispersed clusters, the number of cells/cluster, and the percent dispersed volume all increase with age of the tumor. Histograms of dispersal distance give a mean and median of 63 and 56 μm, respectively, averaged over all brains. Dispersal distance tends to increase with age of the tumors. Dispersal tends to occur along blood vessels. Blood vessel density did not appear to increase in and around the tumor with this cell line.

CONCLUSION

Cryo-imaging and software allow, for the first time, 3D, whole brain, microscopic characterization of a tumor from a particular cell line. LN-229 exhibits considerable dispersal along blood vessels, a characteristic of human tumors that limits treatment success.

Synthesis and evaluation of a peptide targeted small molecular Gd-DOTA monoamide conjugate for MR molecular imaging of prostate cancer

Tumor extracellular matrix has an abundance of cancer related proteins that can be used as biomarkers for cancer molecular imaging. Innovative design and development of safe and effective targeted contrast agents to these biomarkers would allow effective MR cancer molecular imaging with high spatial resolution. In this study, we synthesized a low molecular weight CLT1 peptide targeted Gd(III) chelate CLT1-dL-(Gd-DOTA)(4) specific to clotted plasma proteins in tumor stroma for cancer MR molecular imaging. CLT1-dL-(Gd-DOTA)(4) was synthesized by conjugating four Gd-DOTA monoamide chelates to a CLT1 peptide via generation 1 lysine dendrimer. The T(1) relaxivity of CLT1-dL-(Gd-DOTA)(4) was 40.4 mM(-1) s(-1) per molecule (10.1 mM(-1) s(-1) per Gd) at 37 °C and 1.5 T. Fluorescence imaging showed high binding specificity of CLT1 to orthotopic PC3 prostate tumor in mice. The contrast agent resulted in improved tumor contrast enhancement in male athymic nude mice bearing orthotopic PC3 prostate tumor xenograft at a dose of 0.03 mmol Gd/kg. The peptide targeted MRI contrast agent is promising for high-resolution MR molecular imaging of prostate tumor.

The malignant social network: cell-cell adhesion and communication in cancer stem cells

Tumors contain a vastly complicated cellular network that relies on local communication to execute malignant programs. The molecular cues that are involved in cell-cell adhesion orchestrate large-scale tumor behaviors such as proliferation and invasion. We have recently begun to appreciate that many tumors contain a high degree of cellular heterogeneity and are organized in a cellular hierarchy, with a cancer stem cell (CSC) population identified at the apex in multiple cancer types. CSCs reside in unique microenvironments or niches that are responsible for directing their behavior through cellular interactions between CSCs and stromal cells, generating a malignant social network. Identifying cell-cell adhesion mechanisms in this network has implications for the basic understanding of tumorigenesis and the development of more effective therapies. In this review, we will discuss our current understanding of cell-cell adhesion mechanisms used by CSCs and how these local interactions have global consequences for tumor biology.

Protein tyrosine phosphatase mu regulates glioblastoma cell growth and survival in vivo

Glioblastoma multiforme (GBM) is the most lethal primary brain tumor. Extensive proliferation and dispersal of GBM tumor cells within the brain limits patient survival to approximately 1 year. Hence, there is a great need for the development of better means to treat GBM. Receptor protein tyrosine phosphatase (PTP)µ is proteolytically cleaved in GBM to yield fragments that promote dispersal of GBM cells. While normal brain tissue retains expression of full-length PTPµ, low-grade human astrocytoma samples have varying amounts of full-length PTPµ and cleaved PTPµ. In the highest-grade astrocytomas (i.e., GBM), PTPµ is completely proteolyzed into fragments. We demonstrate that short hairpin RNA mediated knockdown of full-length PTPµ and PTPµ fragments reduces glioma cell growth and survival in vitro. The reduction in growth and survival following PTPµ knockdown is enhanced when cells are grown in the absence of serum, suggesting that PTPµ may regulate autocrine signaling. Furthermore, we show for the first time that reduction of PTPµ protein expression decreases the growth and survival of glioma cells in vivo using mouse xenograft flank and i.c. tumor models. Inhibitors of PTPµ could be used to reduce the growth and survival of GBM cells in the brain, representing a promising therapeutic target for GBM.

Tumour suppressor function of protein tyrosine phosphatase receptor-T

It has long been thought that PTPs (protein tyrosine phosphatases) normally function as tumour suppressors. Recent high-throughput mutational analysis identified loss-of-function mutations in six PTPs in human colon cancers, providing critical cancer genetics evidence that PTPs can act as tumour suppressor genes. PTPRT (protein tyrosine phosphatase receptor-T), a member of the family of type IIB receptor-like PTPs, is the most frequently mutated PTP among them. Consistent with the notion that PTPRT is a tumour suppressor, PTPRT knockout mice are hypersensitive to AOM (azoxymethane)-induced colon cancer. The present review focuses on the physiological and pathological functions of PTPRT as well as the cellular pathways regulated by this phosphatase.

Cadherin-11, a marker of the mesenchymal phenotype, regulates glioblastoma cell migration and survival in vivo

Glioblastoma multiforme (GBM) is the most malignant and lethal form of astrocytoma. The GBM patient survival time of approximately 1 year necessitates the identification of novel molecular targets and more effective therapeutics. Cadherin-11, a calcium-dependent cell-cell adhesion molecule and mesenchymal marker, plays a role in both normal tissue development and in cancer cell migration. The functional significance of cadherin-11 in GBM has not been investigated. Here, we show that cadherin-11 is expressed in human GBM tumors and human glioma stem-like cells by immunohistochemical labeling. In addition, we show that cadherin-11 is expressed in human glioma cell lines by immunoblotting. Short hairpin RNA-mediated knockdown of cadherin-11 expression in human glioma cell lines results in decreased migration and growth factor-independent cell survival in vitro. More importantly, knockdown of cadherin-11 inhibits glioma cell survival in heterotopic and orthotopic mouse xenograft models. Together, our results show the functional significance of cadherin-11 expression in GBM and provide evidence for a novel role of cadherin-11 in promoting glioma cell survival in an in vivo environment. Thus, our studies suggest cadherin-11 is a viable molecular target for therapeutic intervention in GBM.

The interconnectedness of cancer cell signaling

The elegance of fundamental and applied research activities have begun to reveal a myriad of spatial and temporal alterations in downstream signaling networks affected by cell surface receptor stimulation including G protein-coupled receptors and receptor tyrosine kinases. Interconnected biochemical pathways serve to integrate and distribute the signaling information throughout the cell by orchestration of complex biochemical circuits consisting of protein interactions and covalent modification processes. It is clear that scientific literature summarizing results from both fundamental and applied scientific research activities has served to provide a broad foundational biologic database that has been instrumental in advancing our continued understanding of underlying cancer biology. This article reflects on historical advances and the role of innovation in the competitive world of grant-sponsored research.

Novel cryo-imaging of the glioma tumor microenvironment reveals migration and dispersal pathways in vivid three-dimensional detail

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.

Identification of phospholipase C gamma1 as a protein tyrosine phosphatase mu substrate that regulates cell migration

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.

Dinosaurs and ancient civilizations: reflections on the treatment of cancer

Research efforts in the area of palaeopathology have been seen as an avenue to improve our understanding of the pathogenesis of cancer. Answers to questions of whether dinosaurs had cancer, or if cancer plagued ancient civilizations, have captured the imagination as well as the popular media. Evidence for dinosaurian cancer may indicate that cancer may have been with us from the dawn of time. Ancient recorded history suggests that past civilizations attempted to fight cancer with a variety of interventions. When contemplating the issue why a generalized cure for cancer has not been found, it might prove useful to reflect on the relatively limited time that this issue has been an agenda item of governmental attention as well as continued introduction of an every evolving myriad of manmade carcinogens relative to the total time cancer has been present on planet Earth. This article reflects on the history of cancer and the progress made following the initiation of the "era of cancer chemotherapy."

Cancer cells cut homophilic cell adhesion molecules and run

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.