Applications of monoclonal antibodies in the diagnosis and treatment of primary brain tumors

Single low-dose targeted bevacizumab infusion in adult patients with steroid-refractory radiation necrosis of the brain: a phase II open-label prospective clinical trial

OBJECTIVE

There is an unmet need for safe and rapidly effective therapies for refractory brain radiation necrosis (RN). The aim of this prospective single-arm phase II trial was to evaluate the safety and efficacy of a single low-dose targeted bevacizumab infusion after blood-brain barrier disruption (BBBD) in adult patients with steroid-refractory brain RN.

METHODS

Ten adults with steroid-refractory, imaging-confirmed brain RN were enrolled between November 2016 and January 2018 and followed for 12 months after treatment. Bevacizumab 2.5 mg/kg was administered as a one-time targeted intra-arterial infusion immediately after BBBD. Primary outcomes included safety and > 25% decrease in lesion volume. Images were analyzed by a board-certified neuroradiologist blinded to pretrial diagnosis and treatment status. Secondary outcomes included changes in headache, steroid use, and functional status and absence of neurocognitive sequelae. Comparisons were analyzed using the Fisher exact test, Mann-Whitney U-test, linear mixed models, Wilcoxon signed-rank test, and repeated-measures 1-way ANOVA.

RESULTS

Ten adults (mean ± SD [range] age 35 ± 15 [22–62] years) participated in this study. No patients died or exhibited serious adverse effects of systemic bevacizumab. At 3 months, 80% (95% CI 44%–98%) and 90% (95% CI 56%–100%) of patients demonstrated > 25% decrease in RN and vasogenic edema volume, respectively. At 12 months, RN volume decreased by 74% (median [range] 76% [53%–96%], p = 0.012), edema volume decreased by 50% (median [range] 70% [−11% to 83%], p = 0.086), and headache decreased by 84% (median [range] 92% [58%–100%], p = 0.022) among the 8 patients without RN recurrence. Only 1 (10%) patient was steroid dependent at the end of the trial. Scores on 12 of 16 (75%) neurocognitive indices increased, thereby supporting a pattern of cerebral white matter recovery. Two (20%) patients exhibited RN recurrence that required further treatment at 10 and 11 months, respectively, after bevacizumab infusion.

CONCLUSIONS

For the first time, to the authors’ knowledge, the authors demonstrated that a single low-dose targeted bevacizumab infusion resulted in durable clinical and imaging improvements in 80% of patients at 12 months after treatment without adverse events attributed to bevacizumab alone. These findings highlight that targeted bevacizumab may be an efficient one-time treatment for adults with brain RN. Further confirmation with a randomized controlled trial is needed to compare the intra-arterial approach with the conventional multicycle intravenous regimen.

Clinical trial registration no.: NCT02819479 (ClinicalTrials.gov)

Identification of a Type-Specific Epitope in the ORF2 Protein of Duck Astrovirus Type 1

Simple Summary

Duck astrovirus type 1 (DAstV-1) infection constitutes a cause of viral hepatitis in ducklings and little is known about the B-cell epitope of DAstV-1. In this study, using a monoclonal antibody (mAb) 3D2 against ORF2 protein of DAstV-1, a highly conserved linear B-cell epitope of ⁴⁵⁴ STTESA⁴⁵⁹ in DAstV-1 ORF2 was identified. The mAb 3D2 showed no neutralizing activity to DAstV-1 and had no cross-reactivity with other DAstV serotypes.

Abstract

Duck astrovirus type 1 (DAstV-1) infection constitutes a cause of viral hepatitis in ducklings and little is known about the B-cell epitope of DAstV-1. In this study, a monoclonal antibody (mAb) 3D2 against open reading frame 2 (ORF2) protein of DAstV-1 was used to identify the possible epitope in the four serotypes of DAstV. The mAb 3D2 showed no neutralization activity to DAstV-1, and reacted with the conserved linear B-cell epitopes of ⁴⁵⁴STTESA⁴⁵⁹ in DAstV-1 ORF2 protein. Sequence analysis, dot blot assay, and cross-reactivity test indicated that the epitope peptide was highly conserved in DAstV-1 sequence and mAb 3D2 had no cross-reactivity with other DAstV serotypes. To the best of our knowledge, this is the first report about identification of the specific conserved linear B-cell epitope of DAstV-1, which will facilitate the serologic diagnosis of DAstV-1 infection.

Targeted intraarterial anti-VEGF therapy for medically refractory radiation necrosis in the brain

Radiation necrosis (RN) is a serious complication that can occur in up to 10% of brain radiotherapy cases, with the incidence dependent on both dose and brain location. Available medical treatment for RN includes steroids, vitamin E, pentoxifylline, and hyperbaric oxygen. In a significant number of patients, however, RN is medically refractory and the patients experience progressive neurological decline, disabling headaches, and decreased quality of life. Vascular endothelial growth factor (VEGF) is a known mediator of cerebral edema in RN. Recent reports have shown successful treatment of RN with intravenous bevacizumab, a monoclonal antibody for VEGF. Bevacizumab, however, is associated with significant systemic complications including sinus thrombosis, pulmonary embolus, gastrointestinal tract perforation, wound dehiscence, and severe hypertension. Using lower drug doses may decrease systemic exposure and reduce complication rates. By using an intraarterial route for drug administration following blood-brain barrier disruption (BBBD), the authors aim to lower the bevacizumab dose while increasing target delivery. In the present report, the authors present the cases of 2 pediatric patients with cerebral arteriovenous malformations, who presented with medically intractable RN following stereotactic radiosurgery. They received a single intraarterial infusion of 2.5 mg/kg bevacizumab after hyperosmotic BBBD. At mean follow-up duration of 8.5 months, the patients had significant and durable clinical and radiographic response. Both patients experienced resolution of their previously intractable headaches and reversal of cushingoid features as they were successfully weaned off steroids. One of the patients regained significant motor strength. There was an associated greater than 70% reduction in cerebral edema. Intraarterial administration of a single low dose of bevacizumab after BBBD was safe and resulted in durable clinical and radiographic improvements at concentrations well below those required for the typical systemic intravenous route. Advantages over the intravenous route may include higher concentration of drug delivery to the affected brain, decreased systemic toxicity, and a significantly lower cost.

Antibody, T-cell and dendritic cell immunotherapy for malignant brain tumors

Modest improvement in brain tumor patient survival has been achieved through advances in surgical, adjuvant radiation and chemotherapeutic strategies. However, these traditional approaches have been unsuccessful in permanently controlling these aggressive tumors, with recurrence being quite common. Hence, there is a need for novel therapeutic approaches that specifically target the molecularly diverse brain tumor cell population. The ability of the immune system to recognize altered tumor cells while avoiding surrounding normal cells offers an enormous advantage over the nonspecific nature of the conventional treatment schemes. Therefore, immunotherapy represents a promising approach that may supplement the standard therapies in eliminating the residual brain tumor cells. This review summarizes different immunotherapeutic approaches currently being tested for malignant brain tumor treatment.

Recombinant anti-podoplanin (NZ-1) immunotoxin for the treatment of malignant brain tumors

Our study demonstrates the glioma tumor antigen podoplanin to be present at very high levels (>90%) in both glioblastoma (D2159MG, D08-0308MG and D08-0493MG) and medulloblastoma (D283MED, D425MED and DAOY) xenografts and cell line. We constructed a novel recombinant single-chain antibody variable region fragment (scFv), NZ-1, specific for podoplanin from the NZ-1 hybridoma. NZ-1-scFv was then fused to Pseudomonas exotoxin A, carrying a C-terminal KDEL peptide (NZ-1-PE38KDEL). The immunotoxin (IT) was further stabilized by a disulfide (ds) bond between the heavy-chain and light-chain variable regions as the construct NZ-1-(scdsFv)-PE38KDEL. NZ-1-(scdsFv)-PE38KDEL exhibited significant reactivity to glioblastoma and medulloblastoma cells. The affinity of NZ-1-(scdsFv), NZ-1-(scdsFv)-PE38KDEL and NZ-1 antibody for podoplanin peptide was 2.1 × 10(-8) M, 8.0 × 10(-8) M and 3.9 × 10(-10) M, respectively. In a protein stability assay, NZ-1-(scdsFv)-PE38KDEL retained 33-98% of its activity, whereas that of NZ-1-PE38KDEL declined to 13% of its initial levels after incubation at 37°C for 3 days. In vitro cytotoxicity of the NZ-1-(scdsFv)-PE38KDEL was measured in cells isolated from glioblastoma xenografts, D2159MG, D08-0308MG and D08-0493MG, and in the medulloblastoma D283MED, D425MED and DOAY xenografts and cell line. The NZ-1-(scdsFv)-PE38KDEL IT was highly cytotoxic, with an 50% inhibitory concentration in the range of 1.6-29 ng/ml. Significantly, NZ-1-(scdsFv)-PE38KDEL demonstrated tumor growth delay, averaging 24 days (p < 0.001) and 21 days (p < 0.001) in D2159MG and D283MED in vivo tumor models, respectively. Crucially, in the D425MED intracranial tumor model, NZ-1-(scdsFv)-PE38KDEL caused a 41% increase in survival (p ≤ 0.001). In preclinical studies, NZ-1-(scdsFv)-PE38KDEL exhibited significant potential as a targeting agent for malignant brain tumors.

Toxin-based targeted therapy for malignant brain tumors

Despite advances in conventional treatment modalities for malignant brain tumors-surgery, radiotherapy, and chemotherapy-the prognosis for patients with high-grade astrocytic tumor remains dismal. The highly heterogeneous and diffuse nature of astrocytic tumors calls for the development of novel therapies. Advances in genomic and proteomic research indicate that treatment of brain tumor patients can be increasingly personalized according to the characteristics of the targeted tumor and its environment. Consequently, during the last two decades, a novel class of investigative drug candidates for the treatment of central nervous system neoplasia has emerged: recombinant fusion protein conjugates armed with cytotoxic agents targeting tumor-specific antigens. The clinical applicability of the tumor-antigen-directed cytotoxic proteins as a safe and viable therapy for brain tumors is being investigated. Thus far, results from ongoing clinical trials are encouraging, as disease stabilization and patient survival prolongation have been observed in at least 109 cases. This paper summarizes the major findings pertaining to treatment with the different antiglioma cytotoxins at the preclinical and clinical stages.

Reconstruction of the middle cerebral artery after excision of a giant fusiform aneurysm

A patients with a giant fusiform aneurysm of the left inferior trunkus of the middle cerebral artery (MCA) is presented. The size of the aneurysm was 5 cm at its largest diameter. Retrograde flow was well developed. After the application of temporary clips the aneurysm was excised and microsurgical reconstructions were undertaken. Adequate flow in the reconstructed MCA trunkus was maintained. This rare case is discussed in the light of the literature.

Biodistribution of 125I-MAb 425 in a human glioma xenograft model: effect of chloroquine

Chloroquine has been shown to increase the cellular retention and nuclear incorporation of 125I-labeled monoclonal antibody (MAb) 425, a murine anti-epidermal growth factor receptor monoclonal antibody, in human high-grade glioma cells in vitro. The objective of this study was to examine the effect of chloroquine on the biodistribution of 125I-MAb 425 in an intracerebral xenogeneic transplant of glioma cells. Nude rats were stereotaxically implanted in the right hemisphere with A1207 human high-grade glioma cells. After 14 days, animals were injected i.v. with chloroquine (40 mg/kg) followed 2 h later by an 125I-MAb 425 (9 MBq) infusion. Tissue distributions were performed up to 168 h post 125I-MAb 425 injection. From 24 to 168 h, tumor-to-contralateral left brain ratios increased from 9 to 15 for 125I-MAb 425 alone, and 7 to 13 for the 125I-MAb 425/chloroquine combination, respectively. A single administration of chloroquine did not result in any significant difference in radiolabeled MAb accumulation in either the tumor site or other tissues. We conclude that chloroquine did not increase the amount of 125I-MAb 425 into the tumor; however, it is safe to administer i.v. at the 40 mg/kg dose. Under these experimental conditions, the increased radioactive accumulation observed for in vitro data did not translate into similar in vivo results.

Intralesional administration of I-131 labelled monoclonal antibodies in the treatment of malignant gliomas

The authors report their preliminary experience with the use of radiolabelled monoclonal antibodies (MAb) as an adjuvant treatment for 33 malignant gliomas. MAbs employed in this study are raised against Tenascin (TN) which is an antigen of the extracellular matrix of the tumour. It has also been found in neoplastic cells but never in normal brain tissue. This therapy is aimed to give a local high dose radiation (boost) while sparing healthy brain structures. This treatment has always been well tolerated and no adverse reactions at the level of CNS or major extraneural organs has been observed. Significant improvement of median survival has been obtained but this result should be cautiously evaluate since the study is non-randomized. Comparison with other current adjuvant technique is briefly discussed.

Characterization of a glial associated antigen GA-1 by monoclonal antibody

A glial antigen (GA-1) was identified by monoclonal antibodies (MAb) raised against C6 rat glioma cells. MAb-7D3 (IgG2a kappa) revealed GA-1 as a single protein band with a Rf value of 0.09 by the use of basic-PAGE Western blot. SDS-PAGE Western blot and radioimmunoprecipitation (RIP) further resolved GA-1 into two subunits with a molecular weight of 200 and 78 kDa respectively. Subcellular localization by immunocytochemical staining revealed its cytosolic presence with a punctate pattern perinuclearly. Significant expression of GA-1 may be detected in 4 glioma or glial cell lines derived from rat brain. However, no expression may be detected in the rest of the 18 mammalian cell lines or primary neural cell cultures examined. All of the above data thereby suggest that GA-1 may be glial specific whereas the epitope of GA-1 defined by MAb-7D3 is species (rat) specific.

In vitro efficacy of transferrin-toxin conjugates against glioblastoma multiforme

The cytotoxic activity of immunotoxins constructed with human diferric transferrin (Tfn) as the carrier ligand and an abrin variant Pseudomonas exotoxin A (PE) and the diphtheria toxin mutant cross-reacting material (CRM) 107 as the toxin moieties were studied in vitro. Three malignant human cell lines, the glioblastomas multiforme SNB19 and SF295 and the LOX melanoma, and a nonhuman control murine melanoma cell line B16 were assessed. The presence of transferrin receptors on the cell lines was confirmed by direct 125I-Tfn binding assays. The 50% protein synthesis inhibitory concentration (IC50) values for all cell lines demonstrated that Tfn-abrin variant and Tfn-PE had comparable potency and were both more effective than Tfn-CRM 107. Monensin, a carboxylic ionophore, potentiated the effect of Tfn-abrin variant against glioma cells approximately 35-fold with IC50 values of 4.0 x 10(-13) M and 4.7 x 10(-12) M for SNB19 and SF295, respectively. Cytotoxic activity of Tfn-abrin variant (with or without monensin) and Tfn-PE was correlated with the degree of Tfn receptor expression measured on the cell lines. The exquisite in vitro cytotoxicity of Tfn-abrin variant and Tfn-PE immunotoxins against glioma and melanoma cells warrants further in vivo evaluation and future consideration of these agents for potential clinical application against glioblastoma multiforme and leptomeningeal neoplasia.

Tumours in Iceland. 15. Ependymoma. A clinicopathological and immunohistological study

Thirteen ependymomas reported to the Icelandic Cancer Registry during a 32-year period (1955-1986) were histologically reviewed and reclassified according to the WHO Histological Typing of Tumours of the Central Nervous System. The annual incidence rate of ependymoma was 0.20/100.000. Clinical observations and data on biological behaviour and immunohistochemistry are presented. Four tumours were supratentorial, six infratentorial and three intraspinal. There were ten males and three females with a mean age of 32 years (range 2.5-68). The mean postoperative survival of nine surgically treated patients was 35.5 months. Histologically, eight tumours were classical ependymomas, three anaplastic and two myxopapillary. Of 11 tumours stained for GFAP, nine were positive. Nine of 10 tumours tested were positive for vimentin, five for NSE and four for S-100. None of the 10 tumours showed reactivity with AFP, CEA, chromogranin, desmin, factor VIII, keratin or neurofilament.

Immunotoxins and central nervous system neoplasia

The poor prognosis associated with central nervous system (CNS) malignancy has led investigators to seek new, innovative treatment modalities. Immunotoxins, carrier molecules linked to toxic agents, combine high specificity for tumor-associated antigens with extreme potency. The rationale for both the development of these compounds and for their application to CNS neoplasia is explained. This report discusses the design and construction of immunoconjugates, using toxins that differ in their mechanism of action bound to ligands directed against various antigens. A comparison is made between the in vitro efficacy of standard chemotherapy and immunotoxins in glioblastoma- and medulloblastoma-derived cell lines. A review is included of the results of experiments in animals with leptomeningeal neoplasia, where prolongation of survival following intrathecal administration of immunotoxins has been reported. The obstacles encountered in clinical trials with other types of cancer are addressed and approaches to optimize the use of these novel agents in the context of treating malignant disease of the CNS are suggested.

Immunohistological characterisation of retinoblastoma and related ocular tissue

The immunohistological reactivity of six retinoblastomas was investigated by means of 18 monoclonal antibodies and compared with that of adult and fetal retina. The antigenic profiles were found to be characteristic for each cell type studied and indicated that a panel of monoclonal antibodies could achieve a specific immunolocalisation not afforded by any single antibody. Immunohistological comparison between retinoblastoma and adult and fetal retinal cells provided evidence of the histogenesis of the tumour. The data suggest that the tumour arises from an early multipotential cell, which retains the capacity to develop differentiation characteristics associated with inner or outer retinal cell types, resulting in a heterogeneous tumour cell population. A cell with such differentiation potential predominates in the retina prior to the primitive neuroepithelial layer division at eight weeks' gestation.

Monoclonal antibodies in neuro-oncology

Many studies have suggested the possible existence of tumor-associated antigens in brain gliomas. Strong evidence for the existence of such cell determinants was provided by recent investigations using hybridoma technology. The possibility of obtaining monoclonal antibodies (MAbs) against glioma-associated antigens should help to allow their identification, purification, and characterization. Utilizing MAbs as reagents of predefined specificity, a number of central and peripheral nervous system antigens could be detected. The molecules recognized by MAbs in glioma cells can be subdivided into four categories: [1] biochemical defined proteins, [2] specificities shared by nervous system-lymphoid cells, [3] oncoembryonic-oncofetal determinants, and [4] tumor-restricted antigens. Of greater significance is the heterogeneity of antigen expression among various individual glioma cells observed in frozen sections of tumor biopsies. Using a panel of MAbs, the phenotypic heterogeneity, i.e., the variation in antigen expression can be documented within and among malignant gliomas and cell lines derived from them. In spite of this the characteristic pattern of antibody binding to brain tumors makes MAbs the potentially best reagents for immuno-histochemical application in surgical neuropathology. Moreover, immuno-cytological screening of tumor cells in the cerebrospinal fluid has also proved to be valuable. The localization of radio-labelled MAbs in experimental and human gliomas growing subcutaneously and intracranially in athymic nude mice were explored by radioscintigraphy and autoradiography. Imaging experiments with 131I-labelled MAbs recognizing epitopes on the glioma cell surface showed high levels of specific activity in xenografts. Preliminary data indicate that administration of 131I-MAbs as well as drug conjugates (daunomycin-MAbs) causes a depression of glioma cell proliferation in vitro as well as delayed tumor growth and thus prolonged survival time of tumor-bearing mice. The mechanisms of antibody delivery and transport of "immunotoxins" from the vascular compartment to intracerebral tumor tissue are presently a subject of discussion. The complexity of this area necessitates comprehensive experimental work in order to define the factors involved in the delivery of MAbs to brain to tumor tissue and thus optimize the rate of blood-to-tumor transport. Current investigations have shown that it is possible to image malignant human gliomas using radio-labelled antibodies. The next step will be to attain target immunotherapy. The use of MAbs as carrier molecules for clinical applications might soon be possible.

Immunology of central nervous system tumors

With progress in cellular immunology and the development of hybridoma technology, the idea of manipulating host-tumor immune interactions to improve the prognosis of brain tumors has aroused renewed interest. Although no brain tumor-specific antigens have been found, and in spite of the wide antigenic heterogeneity of brain tumor cells, some monoclonal antibodies possessing restricted specificity have been isolated and their potential clinical applications investigated. One of the most pronounced changes in the cellular immune responses of brain tumor patients is a profound depression of the T4-helper lymphocytes. Clinical and laboratory trials are under way to assess the ability of lymphokines, such as gamma-interferon or interleukin-2, to restore immunologic competence in these patients and potentiate a specific anti-tumor immunologic response. Recent work suggests that the endothelium-astrocyte complex may have a pivotal role in assisting the escape of brain tumors from the host's immunologic responses, since it is responsible for the intracerebral sequestration of antigens and local anti-tumor responses. In this review, the data on the antigenic properties of central nervous system tumors and the host's humoral and cellular immune responses to them are analyzed and potential immunologic therapies are discussed.

Monoclonal antibodies with cytotoxic reactivities against human gliomas

Monoclonal antibodies (MAb's) reactive with human malignant glioma cells were derived from mice inoculated with cells from fresh glioma tissue. Seven MAb's were selected for study based on their high-level binding in immunoperoxidase and immunofluorescence assay to most of the glioma tissues derived from various patients and based on the absence of binding to normal bone marrow cells. Four of the seven MAb's did not bind to any of the four normal brain tissues tested, whereas three MAb's bound to one or two of these tissues. Two MAb's bound to the surfaces of cultured glioma cells in radioimmunoassay. One of these MAb's (AS-AY1, immunoglobulin (Ig)(G1) lysed cultured glioma cells with human lymphocytes or murine macrophages as effector cells; the other MAb (AS-AY2, IgM) was reactive in complement-dependent cytotoxicity assay. These two MAb's therefore seem especially promising reagents in approaches to immunotherapy of human malignant glioma.

Surgery of brain neoplasms using 32-P tumour marker

In a series of 60 patients 62 intraoperative measurements with the 32-P (radiophosphorus) tumour marker were performed. Using miniature semiconductor probes a reliable discrimination between normal brain and neoplastic tissue was possible in nearly all brain tumours. The best results were found in meningiomas, where even small, visually hardly discernible tumour resides within the matrix zone could be reliably detected. Only in low-grade gliomas the application of the 32-P marker was impossible due to count rates similar to or below the basic rates of normal brain. This simple to use, non-invasive method proved its usefulness in all situations where a local radical tumour removal was important.

A Preliminary Study of Brain Gliomas with H17E2 Monoclonal Antibody: Immunoscintigraphy and Pharmacokinetics

Ten patients with relapsing high grade brain gliomas and one patient with low grade glioma were studied with a monoclonal antibody (H17E2) against placental alkaline phosphatase. In addition 2 patients with relapsing high grade glioma were studied with a non specific antibody (4D513/2118). 1 mCi of Iodine-131-labelled H17E2 was administered intracarotidly (i.c.) in two, and intravenously (i.v.) in 9 patients. Immunoscintigrams were taken at 0, 2, 24, 48 and 72 hours. Radioactivity was monitored in blood and urine. Tumour/non-tumour ratios were estimated (max. 2.45). All high grade gliomas receiving specific antibody irrespective of the route of administration, gave a positive immunoscintigraphic pattern, increasing in intensity with time.

Disappearance of radioactivity in blood was biexpontential with a long component over 30 hours. Urinary excretion of radioactivity ranged from 3.7–21.7% of administered dose/day. The patient with low grade glioma and the patients receiving non specific monoclonal antibody showed a negative pattern, a fast blood clearance and a high urinary excretion. We conclude that a) Iodine-131 labelled H17E2 proved to be stable in vivo and produced satisfactory tumour localisation and b) i.v. route was as good as i.c.

The mononuclear cell infiltrate compared with survival in high-grade astrocytomas

Frozen samples from 92 malignant astrocytomas were stained with a panel of monoclonal antibodies directed against macrophages and lymphocytes. A follow-up to death was available on 68 cases which form the basis of this study. Large numbers of macrophages were found in all cases; T lymphocytes, mostly of the CD8 phenotype were also seen in moderate numbers in 70% of cases. CD4-positive cells were present in small numbers in 32% and B cells were seen in only 8% of cases. Analysis of the survival showed no demonstrable correlation between the numbers of macrophages or CD4 lymphocytes and survival. The survival curves for parenchymal CD8 infiltration diverged after 9 months suggesting increased survival for those patients without such an infiltration but the difference failed to reach statistical significance (P = 0.37). No correlation between lymphocytic cuffing and survival was seen after studying all paraffin-embedded material. We conclude that there is no significant statistical correlation between survival and the various types of mononuclear cell infiltrating malignant astrocytomas.

Oncogenes and neuro-oncology

The application of molecular biological techniques to the study of lympho-erythroid neoplasms, colo-rectal carcinoma and neuroblastoma has led to fundamental insights into the nature of cellular proliferation, transformation and immortalisation as well as providing prognostic information about the biological behaviour of certain tumours. The study of the molecular genetics of central nervous system tumours with particular reference to oncogenes is however in its infancy. Most of the current literature concerns studies of small numbers of glial tumours or of glial tumour cell lines. In this review the results of these studies are analysed and compared with relevant oncogene findings in experimental cerebral neoplasia, extracranial tumours and postulated mechanisms of oncogene activation. The role of proto-oncogenes in the development of the brain, and the clinical relevance of advances in molecular biology to central nervous system neoplasia are discussed.

Diagnostic markers in human neurooncology. A progress report

In this progress report, some of the most commonly used antibodies are discussed in regard to their immunohistochemical application to human neurooncology. The importance of determining the spectrum of antibody immunoreactivity in a wide panel of normal, reactive, and neoplastic tissues is stressed. in atypical and aberrant cases, immunopositivity needs to be interpreted with caution and in the context of all other available data. The demonstration of a well-characterized, cell type-specific marker in a tumor reflects not so much its cytogenesis as its differentiation potential and its capacity for metaplasia. The relation of an abnormal or aberrant expression of antigenic determinants to the process of neoplasia raises a number of intriguing questions to which research in the next few years will likely provide answers.

Efficacy of intrathecal immunotoxin therapy in an animal model of leptomeningeal neoplasia

Immunotoxins comprise a new class of cell-type specific cytotoxic reagents which consist of a monoclonal antibody linked to a protein toxin. This report examines the efficacy of intrathecal immunotoxin therapy for the treatment of tumors of the cerebrospinal fluid compartment. A syngeneic animal model of leptomeningeal neoplasia was developed in which percutaneous inoculation of L2C tumor cells into the cisterna magna of Strain 2 guinea pigs produced disseminated leptomeningeal and intraventricular leukemia and death. Percutaneous intracisternal injection of 2 micrograms of an anti-idiotype monoclonal antibody (M6)-intact ricin immunotoxin 24 hours following intracisternal inoculation of 10(5) L2C cells (10,000 times the lethal dose) produced prolonged survival (p less than 0.005) of tumor-bearing animals. The immunotoxin therapy caused no detectable toxicity. Intracisternal injection of either M6 monoclonal antibody alone or a nonspecific control immunotoxin had no therapeutic effect. The observed extension of survival times in immunotoxin-treated animals corresponds to a median 2- to 3-log (99% to 99.9%) and, in some animals, possibly a 5-log (99.999%) or greater kill of tumor cells. These results support a possible role for immunotoxins in the clinical treatment of central nervous system neoplastic disease involving compartments (intrathecal, intraventricular, or cystic tumor).

The computer and stereotactic surgery in neurological surgery

The technical aspects, current uses, and future clinical applications of stereotactic surgery and three-dimensional imaging in neurological surgery are reviewed.

Radioimmunodetection of cancer with monoclonal antibodies: current status, problems, and future directions

Early studies of immunoscintography with affinity-purified 131I-labeled polyclonal antibodies reactive against oncofetal antigens such as carcinoembryonic antigen (CEA) were moderately successful in detecting metastatic colorectal carcinoma. However, because of low tumor to background ratios of isotope, background subtraction techniques using 99Tc-labeled albumin were required to visualize small lesions. Antisera were often of low titer and lacked specificity. These problems could be overcome for the most part following the development of highly specific monoclonal antibodies (MoAb) against a variety of tumor-associated antigens. A number of clinical trials using 131I- or 111In-labeled MoAb to image tumors have demonstrated successful localization without the use of subtraction techniques. Variables limiting the usefulness of murine MoAb for diagnosis have included increased localization in liver and spleen, tumor vascularity and heterogeneity of antigen expression, and development of human antimurine globulins. Methods to overcome some of these problems are discussed. Radiolabeled MoAb appear useful as an adjunct to conventional diagnostic techniques both as a means to predict which antibodies might be useful for treatment and, in select patients, as a basis for treatment decisions.

Monoclonal antibodies against human astrocytomas and their reactivity pattern

The establishment of hybridomas after fusion of X63-Ag8.653 mouse myeloma cells and splenocytes from BALB/c mice hyperimmunized against human astrocytomas is presented. The animals were primed with 5 X 10(6) chemically modified uncultured or cultured glioma cells. Six weeks after the last immunization step an intrasplenal booster injection was administrated and 3 days later the spleen cells were prepared for fusion experiments. According to the specificity analysis of the generated antibodies 7 hybridoma products (MUC 7-22, MUC 8-22, MUC 10-22, MUC 11-22, MUC 14-22, MUC 15-22 and MUC 2-63) react with gliomas, neuroblastomas and melanomas as well as with embryonic and fetal cells but do not recognize non-neurogenic tumors. The selected monoclonal antibodies (McAbs) of IgG1 and IgG2a isotypes are not extensively characterized but these antibodies have been demonstrated to be reactive with a panel of glioma cell lines with varying patterns of antigen distribution. Using the McAbs described above and a series of cryosections of glioma biopsies and paraffin sections of the same material as well as glioma cultures established from these, variable antigenic profiles among glioma cell populations could be demonstrated. From these results it is evident that there is not only a distinct degree of antigenic heterogeneity among and within brain tumors, but also that the pattern of antigenic expression can change continuously. Some of the glioma associated antigens recognized by the selected antibodies persist after fixation with methanol/acetone and Karnovsky's fixative and probably are oncoembryonic/oncofetal antigen(s). The data suggest that the use of McAbs recognizing tumor associated oncofetal antigens in immunohistochemistry facilitates objective typing of intracranial malignancies and precise analysis of fine needle brain/tumor biopsies in a sensitive and reproducible manner.

Monoclonal antibodies and immobilized antibodies. Patents and literature

Antibodies in both their free and immobilized state have been the object of considerable industrial and academic interest. A variety of methods are used for preparing and immobilizing antibodies. Applications for monoclonal antibodies include the preparation of therapeutics, diagnostics, and in affinity fractionation. Recent US patents on monoclonal and immobilized antibodies and scientific literature on monoclonal antibodies are surveyed. A description of these patents and a list of references are given.

Magnetic resonance imaging of gadolinium-labeled monoclonal antibody polymers directed at human T lymphocytes implanted in canine brain

Two different murine monoclonal anti-human T cell antibodies, that were coupled to gadolinium (Gd), bind specifically to human T lymphocyte cells implanted in canine brain. This binding was at a concentration of Gd sufficient to detect the implanted cells and to distinguish them from the surrounding brain tissue with magnetic resonance imaging (MRI) at a field strength of 1.5 Tesla. These Gd-labeled immunoglobulin preparations did not bind bovine T cells at a concentration sufficient to be detected on MRI. A protein solution containing the immunoglobulins (100 micrograms), gelatin (2 mg), and bovine serum albumin (2.5 mg) was reacted with the dianhydride of diethylenetriaminepentaacetic acid (DTPA); the DTPA serves as a metal chelator and as a protein crosslinking agent. The DTPA-protein complex was reacted with Gd chloride. There were approximately 10 DTPA residues per protein molecule in the modified protein mixture. Isolated human or bovine monocytes (approximately 12 million cells) were implanted in the brains of anesthetized dogs in a volume of 40 microliters. The blood-brain barrier was then disrupted by the intra-arterial injection of hyperosmotic mannitol, and the Gd-labeled antibodies were injected through a catheter placed at the branch of the internal and external carotid arteries. The brains were imaged 48 to 72 hours later. The MRI scans revealed a markedly decreased T1 relaxation time with a high signal intensity (TE = 25 msec, TR = 200 msec) related to the human T cell implants. There was no evidence of decreased T1 at the site of the bovine T cells. Neither control murine gamma globulin coupled to Gd-DTPA nor anti-human T cell antibodies uncoupled to Gd modified the MRI contrast of the human T cells in the brain.

Potent and specific killing of human malignant brain tumor cells by an anti-transferrin receptor antibody-ricin immunotoxin

Immunotoxins are hybrid molecules which combine the exquisite selectivity of monoclonal antibodies with the potent toxicity of protein toxins. An immunotoxin was constructed by linking a murine monoclonal antibody against the human transferrin receptor (TR) to the plant toxin, ricin. The cytotoxic activity of the anti-TR-ricin immunotoxin was tested in vitro and demonstrated highly potent and cell type-specific killing of cells derived from human glioblastoma, medulloblastoma, and leukemia. The anti-TR-ricin immunotoxin killed more than 50% of "target" cells at a concentration of 5.6 X 10(-13) M after an 18-hour incubation with the ionophore, monensin. This potency exceeds that of any other anti-TR immunotoxin reported in the literature. When the activity of the anti-TR-ricin immunotoxin against "target" tumor-derived cells was compared with the immunotoxin's activity against "non-target" cells, it could be predicted that a selective toxicity of anti-TR-ricin immunotoxin between tumor cells and normal brain was more than 150- to 1380-fold. Solid-phase indirect radioimmunoassay techniques were used to demonstrate significantly higher levels of TR in the glioblastoma- and medulloblastoma-derived cell lines, as well as in surgical tissue samples of medulloblastoma and glioblastoma, as compared to normal brain. Immunotoxins targeted to the TR may possess sufficient specificity to be of therapeutic importance, particularly to treat neoplastic disease of the central nervous system involving compartments (such as intrathecal, intraventricular, or cystic) where delivery of immunotoxins to tumor would not require transvascular transport.

Imaging of a glioma using peripheral benzodiazepine receptor ligands

Two types of benzodiazepine receptors have been demonstrated in mammalian tissues, one which is localized on neuronal elements in brain and the other, on glial cells and in peripheral tissues such as kidney. In vivo administration of 3H-labeled PK 11195 [1-(2-chlorophenyl-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide] or [3H]flunitrazepam with 5 mg of clonazepam per kg to rats with intracranial C6 gliomas resulted in high levels of tritiated-drug binding to the tumor as shown by quantitative autoradiography. Pharmacological studies indicated that the bound drugs labeled the peripheral benzodiazepine binding site. Binding to the peripheral benzodiazepine site was confirmed primarily to malignant cells with little binding to adjacent normal brain tissue or to necrotic tissue. Tumor cell binding was completely inhibited by preadministration of the peripheral benzodiazepine blocking agent PK 11195 at 5 mg/kg. The centrally selective benzodiazepine ligand clonazepam had no effect on PK 11195 binding to the tumor cells. When binding to other tumor cell lines grown in nude mice and nude athymic rats was evaluated, little or no peripheral benzodiazepine binding was detected on human pheochromocytoma (RN1) and neuroblastoma (SK-N-MC, SK-N-SH) tumor cells, respectively. However, high densities of peripheral benzodiazepine binding sites were observed on tumors derived from a human glioma cell line (ATCC HTB 14, U-87 MG). The presence of high concentrations of specific peripheral benzodiazepine receptors on glial tumors suggests that human primary central nervous system tumors could be imaged and diagnosed using peripheral benzodiazepine ligands labeled with positron- or gamma-emitting isotopes.

Growth inhibition of experimental glioma grafts by monoclonal antibody treatment

The effects of 14AC1 monoclonal antibody (McAb) on 79FR-G-41 rat glioma cells in vitro, on the formation of metastases in lung by antibody coated glioma cells, and on the growth of glioma grafts in BALB/c-nu/nu mice were investigated. The 14AC1 antibodies - isotyped as IgG2a - were obtained from a hybridoma clone established after fusion of X63-Ag8.653 myeloma cells and spleen cells of BALB/c mice hyperimmunized with 79FR-G-41 glioma cells. Antibody treatment of glioma cells in vitro caused evident cell surface alterations and pronounced growth depression of most cells. However, a few tumor cells remained unchanged in morphology and continued to proliferate. Moreover, 14AC1 antibodies drastically reduced lung metastasis by pretreated and i.v. delivered glioma cells. Additionally, 14AC1 antibodies suppressed the growth of transplanted rat gliomas in nude mice as evidenced by a longer latency period and a smaller volume of glioma grafts in treated than in control tumor bearers. Nevertheless, glioma grafts showed accelerated growth after termination of antibody treatment. Further experimental investigation is required in order to identify the precise mechanisms of the effects of McAbs on tumor cells in vitro and in vivo.

Enolase isoenzymes in human gliomas

Gamma-enolase (one of the three possible subunits of the dimeric enzyme enolase (EC 4.2.1.11)) has been reported as a marker for human neurons. Studies investigating the presence of gamma-enolase in human gliomas have given conflicting results, but a definite finding is important for further studies of the biology of these tumors and the possible use of gamma-enolase as a marker for tumors originating in nervous tissue or for neuronal damage. Using electrophoresis of tumor tissue extracts as well as immunohistochemistry the authors have demonstrated the presence of gamma-enolase in human gliomas. Analysis of the gamma-enolase content in the plasma of patients with brain neoplasms further revealed that, although this enzyme may be present in the tumor itself, its concentration in blood is not a reliable marker for a tumor of the human central nervous system.

In vivo imaging of intracranial human glioma xenografts comparing specific with nonspecific radiolabeled monoclonal antibodies

Current diagnostic and therapeutic modalities for malignant human gliomas are largely nonspecific. The development of monoclonal antibodies (MA's) with their high degree of specificity may allow precise tumor imaging and selective administration of therapeutic agents. However, the ability of these antibodies to specifically localize tumor tissue in vivo remains speculative. This study compares the localization and imaging properties of two MA's: a specific human glioma-associated extracellular matrix glycoprotein MA, 81C6, and a nonspecific control MA, 45.6, against a human glioma cell line, D-54 MG, intracranially inoculated into athymic rats. Forty-one animals received MA's labeled with iodine-131 (131I) or 125I and underwent imaging with a gamma camera. The images were independently evaluated and compared to tissue radioactivity levels. Radiolabeled antiglioma MA 81C6 specifically localized in intracranial xenografts. The percent of injected dose per gram of tissue for tumor was 1.707 +/- 0.405/gm for 81C6 and 0.118 +/- 0.056/gm for 45.6. All other organs had equivalent levels of specific and nonspecific MA's. For brain, these were 0.004 +/- 0.002/gm and 0.005 +/- 0.005/gm, respectively, and for the other organs, the range was from 0.053 to 0.284/gm. Statistically, 45.6 achieved levels in tumor that were significantly higher than normal brain (p less than 0.05) but significantly less than that achieved with 81C6 (p less than 0.005). With 81C6, the degree of localization was high enough to allow imaging of intracranial tumors at sizes as small as 20 mg. Intracranial tumors were imaged with 45.6 only when they achieved sizes greater than 300 mg. In this imaging study, radiolabeled 81C6, a specific antiglioma MA, proved to be significantly better for imaging small and intermediate-sized tumors than the control MA's. Large tumors were visualized by both MA's, although higher quality scans were obtained earlier and more frequently with specific MA's than with nonspecific immunoglobulin G. These data suggest that specific MA's have a role to play in both the diagnosis and treatment of primary intracranial human tumors.