Detection of amino-terminal extracellular domain of somatostatin receptor 2 by specific monoclonal antibodies and quantification of receptor density in medulloblastoma.

Abstract

Somatostatin receptor 2 (SSTR2) is expressed by most medulloblastomas (MEDs). We isolated monoclonal antibodies (MAbs) to the 12-mer (33)QTEPYYDLTSNA(44), which resides in the extracellular domain of the SSTR2 amino terminus, screened the peptide-bound MAbs by fluorescence microassay on D341 and D283 MED cells, and demonstrated homogeneous cell-surface binding, indicating that all cells expressed cell surface-detectable epitopes. Five radiolabeled MAbs were tested for immunoreactive fraction (IRF), affinity (KA) (Scatchard analysis vs. D341 MED cells), and internalization by MED cells. One IgG(3) MAb exhibited a 50-100% IRF, but low KA. Four IgG(2a) MAbs had 46-94% IRFs and modest KAs versus intact cells (0.21-1.2 x 10(8) M(-1)). Following binding of radiolabeled MAbs to D341 MED at 4 degrees C, no significant internalization was observed, which is consistent with results obtained in the absence of ligand. However, all MAbs exhibited long-term association with the cells; binding at 37 degrees C after 2 h was 65-66%, and after 24 h, 52-64%. In tests with MAbs C10 and H5, the number of cell surface receptors per cell, estimated by Scatchard and quantitative FACS analyses, was 3.9 x 10(4) for the "glial" phenotype DAOY MED cell line and 0.6-8.8 x 10(5) for four neuronal phenotype MED cell lines. Our results indicate a potential immunotherapeutic application for these MAbs.

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Citation

Published Version (Please cite this version)

10.1089/hyb.2009.0049

Publication Info

Kuan, Chien-Tsun, Carol J Wikstrand, Roger E McLendon, Michael R Zalutsky, Ujendra Kumar and Darell D Bigner (2009). Detection of amino-terminal extracellular domain of somatostatin receptor 2 by specific monoclonal antibodies and quantification of receptor density in medulloblastoma. Hybridoma (Larchmt), 28(6). pp. 389–403. 10.1089/hyb.2009.0049 Retrieved from https://hdl.handle.net/10161/3241.

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Scholars@Duke

Chien-Tsun Kuan

Adjunct Associate Professor in the Department of Pathology

Research Interests:
Conventional therapy for malignant brain tumors is ineffective. Targeted therapy using tumor-specific antibodies (MAb) alone or MAbs armed with radionuclides or toxins is a promising alternative approach for increasing therapeutic efficacy and decreasing toxicity to normal tissue. The major factors that influence antibody-targeted therapy for cancer treatment, including glioma therapy, are specificity, affinity, tumor penetration, toxicity and immunogenicity. The effective use of radioimmunotherapy (RAIT) for the treatment of solid malignancies has been limited by inadequate tumor penetration and non-targeted myelotoxicity resulting from the presence of radioimmunoconjugates in circulation. We believe that these limitations to direct RAIT can be overcome by using smaller engineered antibody-based molecules as vehicles and by selecting therapeutic radioisotopes with physical properties that complement the pharmacokinetics and pharmacodynamics of the antibody.

Our research is focused upon exploiting engineered antibody fragments to treat brain tumors by targeting to glioma-associated, oncofetal epitopes such as tenascin, glioma variant epidermal growth factor variant III (EGFRvIII), medulloblastoma-associated developmental markers, as well as the newly identified glioma-associated antigens, GPNMB and MRP3, by serial analysis of gene expression (SAGE). Projects performed in the current years have: 1) produced and evaluated the monovalent single-chain Fv (scFv) against EGRvIII in athymic mice bearing human glioma xenografts; 2) begun the development of divalent form of scFv, including diabody and minibody, to increase the efficacy of therapeutic agents in vivo; 3) generated CH2 domain-deleted Ch81C6 vs tenascin and evaluated the pharmacokinetics in mice and canines; 4) begun an extensive analysis of GPNMB and MRP3 protein expression correlated with measurement of RNA transcript levels and degree of DNA amplification.

Unarmed antibody can be effective against both subcutaneous and intracranial tumor models. The unarmed antibody approach with Mab Y10 vs EGFRvIII is very similar to the successful use of HerceptinTM. The mechanism is most likely both a direct antiproliferative effect with the induction of apoptosis and an indirect effect through the mobilization of antibody-mediated immune effector functions, such as complement and antibody-dependent cell-mediated cytotoxicity (ADCC). We also have begun to construct human/mouse chimeric Y10 to reduce immunogenicity of the Mab reagent and possibly enhance ADCC.

Our objectives for the coming years are to continue the optimization of engineered-antibody systems for in vivo application, namely; a) development of human/mouse chimeric anti-EGFRvIII murine Y10 with the same affinity and specificity but reduced immunogenicity and enhanced ADCC for in vivo application; b) to generate a totally human scFv specific to EGFRvIII but with anti-proliferative activity via screening from human phage libraries; c) generation of monomeric and dimeric anti-GPNMB/MRP3 scFvs and construction of immunoconjugate toxins or radiolabeled to determine the efficacy of therapeutic reagents in athymic rodent in athymic rodent in vivo models of intracranial glioma.

McLendon

Roger Edwin McLendon

Professor of Pathology

Brain tumors are diagnosed in more than 20,000 Americans annually. The most malignant neoplasm, glioblastoma, is also the most common. Similarly, brain tumors constitute the most common solid neoplasm in children and include astrocytomas of the cerebellum, brain stem and cerebrum as well as medulloblastomas of the cerebellum.  My colleagues and I have endeavored to translate the bench discoveries of genetic mutations and aberrant protein expressions found in brain tumors to better understand the processes involved in the etiology, pathogenesis, and treatment of brain tumors.  Using the resources of the Preston Robert Brain Tumor Biorepository at Duke, our team, consisting of Henry Friedman, Allan Friedman, and Hai Yan and lead by Darell Bigner, have helped to identify mutations in Isocitrate Dehydrogenase (IDH1 and IDH2) as a marker of good prognosis in gliomas of adults.  This test is now offered at Duke as a clinical test.  Working with the Molecular Pathology Laboratory at Duke, we have also brought testing for TERT promoter region mutations as another major test for classifying gliomas in adults.  Our collaboration with the Toronto Sick Kids Hospital has resulted in prognostic testing for childhood medulloblastomas, primitive neuroectodermal tumors, and ependymomas at Duke.

Zalutsky

Michael Rod Zalutsky

Jonathan Spicehandler, M.D. Distinguished Professor of Neuro Oncology, in the School of Medicine

The overall objective of our laboratory is the development of novel radioactive compounds for improving the diagnosis and treatment of cancer. This work primarily involves radiohalo-genation of biomolecules via site-specific approaches, generally via demetallation reactions. Radionuclides utilized for imaging include I-123, I-124 and F-18, the later two being of particular interest because they can be used for the quantification of biochemical and physiological processes in the living human through positron emission tomography. For therapy, astatine-211 decays by the emission of alpha-particles, a type of radiation considerably more cytotoxic that the beta-particles used in conventional endoradiotherapy. The range of At-211 alpha particles is only a few cell diameters, offering the possibility of extremely focal irradiation of malignant cells while leaving neighboring cells intact. Highlights of recent work include: a)
development of reagents for protein and peptide radioiodination that decrease deiodination in vivo by up to 100-fold, b) demonstration that At-211 labeled monoclonal antibodies are effective in the treatment of a rat model of neoplastic meningitis, c) synthesis of a thymidine analogue labeled with At-211 and the demonstration that this molecule is taken up in cellular DNA with highly cytotoxicity even at levels of only one atom bound per cell and d) development of
radiohalobenzylguanidines which are specifically cytotoxic for human neuroblastoma cells.

Bigner

Darell Doty Bigner

E. L. and Lucille F. Jones Cancer Distinguished Research Professor, in the School of Medicine

The Causes, Mechanisms of Transformation and Altered Growth Control and New Therapy for Primary and Metastatic Tumors of the Central Nervous System (CNS).

There are over 16,000 deaths in the United States each year from primary brain tumors such as malignant gliomas and medulloblastomas, and metastatic tumors to the CNS and its covering from systemic tumors such as carcinoma of the lung, breast, colon, and melanoma. An estimated 80,000 cases of primary brain tumors were expected to be diagnosed last year. Of that number, approximately 4,600 diagnosed will be children less than 19 years of age. During the last 20 years, however, there has been a significant increase in survival rates for those with primary malignant brain tumors.

For the last 44 years my research has involved the investigation of the causes, mechanism of transformation and altered growth control, and development of new methods of therapy for primary brain tumors and those metastasizing to the CNS and its coverings. In collaboration with my colleagues in the Preston Robert Tisch Brain Tumor Center, new drugs and those not previously thought to be active against CNS tumors have been identified. Overcoming mechanisms of drug resistance in primary brain tumors are also being pursued.

As the founding Director of the Preston Robert Tisch Brain Tumor Center, I help coordinate the research activities of all 37 faculty members in the Brain Tumor Center. These faculty members have projects ranging from very basic research into molecular etiology, molecular epidemiology, signal transduction; translational research performing pre-clinical evaluation of new therapies, and many clinical investigative efforts. I can describe any of the Brain Tumor Center faculty member’s research to third year students and then direct them to specific faculty members with whom the students would like a discussion.

We have identified through genome-wide screening methodology several new target molecules selectively expressed on malignant brain tumors, but not on normal brain. These include EGFRwt, EGFRvIII, and two lacto series gangliosides, 3'-isoLM1 and 3',6'-isoLD1 and chondroitin proteoglycan sulfate. We raised conventional and fully human monoclonal antibodies against most of these targets as well as having developed single fragment chain molecules from naïve human libraries.

My personal research focuses on molecularly targeted therapies of primary and metastatic CNS tumors with monoclonal antibodies and their fragments. Our study we conducted was with a molecule we discovered many years ago, the extracellular matrix molecule, Tenascin. We have treated over 150 malignant brain tumor patients with excellent results with a radiolabeled antibody we developed against Tenascin. We are collaborating with Dr. Ira Pastan at NIH to develop tumor-targeted therapies by fusing single fragment chain molecules from monoclonal antibodies or from naïve human libraries to the truncated fragment of pseudomonas exotoxin A. One example of this is the pseudomonas exotoxin conjugated to a single fragment chain antibody that reacts with wild type EGFR and EGFRvIII, two overexpressed proteins on glioblastoma. The immunotoxin, called D2C7-IT, is currently being investigated in an FDA dose-escalation study, in which patients undergoing treatment of this investigational new drug are showing positive responses. My laboratory is also working with Matthias Gromeier, creator of the oncolytic poliovirus - a re-engineered poliovirus that is lethal to cancer cells, but not lethal to normal cells. The oncolytic poliovirus therapeutic approach has shown such promising results in patients with glioblastoma, that it was recently featured on a on a special two-segment program of 60 Minutes. The next clinical step will be to combine both the virus and the immunotoxin with anti-PD1, an immune checkpoint blockade inhibitor and with anti-CD40, a fully human monoclonal antibody which converts tumor stimulant macrophages into tumor suppressive macrophages. We believe that regional tumor-targeted cytotoxic therapies, such as oncolytic poliovirus and the D2C7 immunotoxin, not only specifically target and destroy tumor cells, but in the process, initiate immune events that promote an in situ vaccine effect. That immune response can be amplified by human checkpoint blockade to engender a long-term systemic immune response that effectively eliminates recurrent and disseminated GBM cells. Ultimately, all three agents may be used together, providing different antigenic targets and cytotoxicity mechanisms.

We have identified through genome-wide screening methodology several new target molecules selectively expressed on malignant brain tumors, but not on normal brain. These include glycoprotein non-metastatic B (GPNMB), a molecule shared with malignant melanoma; MRP3, a member of the multidrug resistant family; and two lacto series gangliosides, 3'-isoLM1 and 3',6'-isoLD1 and chondroitin proteoglycan sulfate. We are raising conventional monoclonal antibodies against all of these targets as well as developing single fragment chain molecules from naïve human libraries. When necessary, affinity maturation in vitro is carried out and the antibodies and fragments are armed either with radioactive iodine, radioactive lutetium, or radioactive Astatine-211. Other constructs are evaluated for unarmed activity and some are armed with Pseudomonas exotoxin. After development of the constructs, they are evaluated in human malignant glioma xenograft systems and then all studies necessary for Investigational New Drug Permits from the Food and Drug Administration are carried out prior to actual clinical trial.

I was senior author on a New England Journal of Medicine paper that was the first to show markedly increased survival in low to intermediate grade gliomas with an isocitrate dehydrogenase mutation.

The first fully funded Specialized Research Center on Primary and Metastatic Tumors to the CNS funded by the National Institutes of Health, of which I was Principal Investigator, was funded for 30 years at which time the type of grant was discontinued. My NCI MERIT Award, which ranked in the upper 1.2 percentile of all NIH grants at the time of its last review, is currently in its 40th year of continuous funding. It is one of the few MERIT awards awarded three consecutive times, and it is the longest continually funded grant of the NCI Division of Cancer Diagnosis and Treatment. My last NCI Award was an Outstanding Investigator Award from 2014 to 2022.

In addition to the representative publications listed, I have made national presentations and international presentations during the past year.

My laboratory has trained over 50 third year medical students, residents, Ph.D. students, and postdoctoral fellows and I have a great deal of experience in career development with some students having advanced all the way from fellowship status to endowed professorships. A major goal with third year medical students is to perform work that can be presented in abstract form at national or international meetings and to obtain publication in major peer-reviewed journals.


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