ALTERATIONS IN GLIAL AND MESENCHYMAL TUMOR CELL MEMBRANE RESISTANCE WITH HETEROIMMUNE AND AUTOLOGOUS SERA

Electrophysiological and biochemical characterization of a continuous human astrocytoma cell line with many properties of well-differentiated astrocytes

Astrocytes comprise about 25% of the cellular volume of the brain, and their main function is to maintain homeostasis of the neuronal environment. These cells are commonly identified on the basis of their membrane electrical properties and the presence of specific proteins. We have characterized the human astrocytoma cell line designated UC-11MG and have shown these cells have many of the traits of differentiated astrocytes. Many of the UC-11MG cells have a large resting membrane potential, averaging -74 mV. The slope of the Em vs log [K]o cuve was 58.5 mV per decade [K]o. The cells were inexcitable when exposed to brief depolarizing current pulses. The astrocytoma traits are virtually identical to those previously reported for normal astrocytes. The astrocytoma cells also express glutamine synthetase activity which is considered specific to astrocytes among brain cells. Previous work had also demonstrated the presence of other astrocyte markers glial fibrillary acidic protein and S-100 protein in the UC-11MG cells. The steady-state ion transport properties of Na+, Cl-, and K+ were also characterized in these cells, and the rates of efflux were found to be similar to those in other astrocytes, with the major difference being the presence of a second kinetic compartment in the UC-11MG cells. From this work, we conclude that the UC-11MG cell line displays prominent features associated with differentiated astrocytes, and may provide an excellent model system for the study of human astrocytes.

Microcytotoxicity blocking assay for the detection and isolation of soluble astrocytoma association antigen

A blocking microcytotoxicity assay was used to detect soluble astrocytoma-associated antigen. The richest source of soluble antigen was found in spent culture media from an established glioblastoma (GF) tissue culture line. Also assayed were fractions of sonicated membrane antigen from another (GM) glioblastoma and pellets of GF and GM cultured glioblastoma tissue. Blocking by media conditioned by cultured normal human brain, breast cancer, neuroblastoma, meningioma, or 2-year-old astrocytoma cell lines was 41-82% lower. A monomer was isolated that blocked cytotoxicity and migrated in molecular exclusion chromatography with alpha-macroglobulins rather than the beta-2-microglobulins usually associated with histocompatibility antigens.

Autologous serologic responses in glioma patients. Correlation with tumor grade and survival

The serologic responses of 42 patients with gliomas have been evaluated in a quantitative microcytotoxicity assay utilizing autologous cultured glioma cells. Forty-five percent of patients had detectable cytotoxic antibody apparently directed to their own cultured cells. When tumor grade was correlated with immune response, 15/20 patients with Grade I, II and III astrocytomas had antigens detectable in autologous sera whereas only 5/22 patients with Grade IV astrocytomas had such responses. None of the autologous fibroblasts from the 15 patients with paired gliomas and fibroblast lines had membrane antigens detectable using autologous sera and fibroblast absorption did not reduce antiglioma activity. Thus, the cytotoxicity observed in this assay appears to be restricted to tumor cells, suggesting reactivity against tumor-associated antigen. In addition, it appears that these immune responses are highly correlated with survival in primary malignant brain tumor patients.

Membrane and cytoplasmic changes in 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU)-sensitive and resistant human malignant glioma-derived cell lines

Human glioma-derived cell lines previously determined by a microtiter chemotherapy assay to be either 'sensitive' or 'resistant' to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) were treated with BCNU (1-80 micrograms/ml) and observed using microcinematography, scanning electron microscopy, and transmission electron microscopy. Striking bleb formation and cell retraction were observed to occur in a dose-dependent relationship within minutes in the cells known to be BCNU-sensitive. At 15 micrograms/ml, 69% of cells showed blebs by 30 min, 87% by 90 min, and 100% by 4 hr. This activity was not seen in BCNU-resistant cells. These morphological changes occur at a time too early to be accounted for by the known BCNU mechanism of DNA alkylation and cross-link formation and suggest that cytoplasmic and/or membrane events may be significant initial events in the cytotoxic actions of BCNU.

Immunological, biochemical, ultrastructural, and electrophysiological characteristics of a human glioblastoma-derived cell culture line

This report presents the results of a study using multiple techniques of the established human cell line, LM, which has been developed in culture medium from a patient with a right temporoparietal glioblastoma. This cell line has human subtetraploid karyotype and has several features of a transformed line in culture. These include continuous propagation for 10 years, ability to form tumor nodules when transplanted into immunologically suppressed hamsters, and pleomorphic appearance. Ultrastructurally, it is characterized by multiple nuclei, few actin cables, and numerous surface-membrane microvilli, as well as abundant 9- to 10-nm cytoplasmic filaments. By its immunological reactivity, the line can be shown to contain glial fibrillary acidic protein at low levels, consistent with its glial origin and continued nature. Dibutyryl cyclic adenosine monophosphate (db-cAMP) induces formation of long astrocytic-like processes as well. Its membrane electrical characteristics include a low resting membrane potential and short time constant. Used in a microtiter antiglioma antibody cytotoxicity assay, LM yields a positive reaction to antibodies in the sera of 80% of patients with astrocytomas and only 9% of normal blood-bank donors, suggesting that it shares common antigens with other astrocytic tumor lines. The varied characteristics of this glioblastoma-derived line emphasize the "multiforme" nature on the neoplasm and suggest that for characterization of any such line, multiple parameters are necessary to allow comparison with other long-term glioblastoma lines in the literature. The usefulness of the LM line in in vitro cell biological, immunological, chemotherapeutic, and radiobiological studies of gliomas makes such efforts very worthwhile.

The utilization of native glioma antigens in the assessment of cellular and humoral immune responses in malignant glioma patients

Cellular and humoral components of the immune response have been studied preoperatively, concurrently, and serially in patients with malignant glial neoplasms. In order to assess titres of circulating antibodies to tumour cell constituents an indirect immunofluorescent technique was applied to single cell suspensions and snap frozen cell smears. In an allogeneic system, 49% of 47 test and 7% of 124 control sera gave a positive response to cytoplasmic components. The leucocyte adherence inhibition assay was applied to study 39 test and 64 control patients. Significant non-adherence of leukocytes was observed in 77% of test cases. Control parameters indicated specificity of the response. Simultaneous assessment in 28 test patients yielded a positive response for one or both assays in 89% of cases..

Glial membrane potentials and their relationship to [K+]o in man and guinea pig. A comparative study of intracellularly marked normal, reactive, and neoplastic glia

✓ Glial cells were studied in vitro in physiologically viable brain slices prepared from tissues obtained during operations for focal epilepsy and brain tumors. The results from human normal and reactive cerebral cortex and glial tumors were compared with those obtained in guinea pig cortex. The resting membrane potential (RMP) or the relationship of RMP to changes in extracellular potassium concentration ([K+]o) were recorded, and the cell was injected iontophoretically with horseradish peroxidase (HRP) for later visualization and correlation with the physiological data. In normal cortex, the marked cells were protoplasmic astrocytes; in reactive cortex, fibrous astrocytes with abnormal processes predominated. The majority of neoplastic glia resembled the reactive astrocytes, except that they showed a pleomorphism that increased with the degree of malignancy. The mean RMP's of glia from normal human and guinea pig cortex, human reactive cortex, and well differentiated astrocytomas were comparable, about −70 mV. In the less differentiated gliomas, the mean RMP's were lower, with the glioblastoma multiforme having the lowest value, −40 ± 7 mV. When the [K+]o was manipulated over a range of 2 to 40 mM/liter, the mean slope of RMP plotted against [K+]o indicated that normal human and guinea pig glia were exclusively permeable to K+ between [K+]o of 4 to 40 mM/liter. In contrast, the mean slope of reactive glia at these [K+]o's was less, suggesting a permeability to one or more additional ions. Below 4 mM/liter, the slopes of both normal and reactive glia showed changes in RMP smaller than the values expected of cells that are permeable only to K+. Like the reactive glia, the slopes derived for neoplastic cells did not indicate an exclusive permeability to K+, and some cells from the glioblastoma multiforme showed no change in RMP when [K+]o was varied.

Immunological aspects of intrinsic glial tumors

✓ Fundamental concepts of general tumor immunology and modes of immunotherapy are presented. Significant work dealing with the relationship of the immune system to intrinsic glial neoplasms is reviewed in relation to therapeutic applications and future investigative efforts.

Response of cultured human brain tumors to nitrosoureas: correlation with clinical data

An in vitro microcytotoxicity assay was utilized to determine the sensitivity of 58 cultured human malignant gliomas to the chemotherapy agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Of 58 such tumors, 42 (72%) showed a statistically significant cytotoxic response to BCNU in this assay. For those responding tumor lines, the cytotoxic index ranged from 0.25 to 0.76, with most clustered at the 0.40 level. To determine the therapeutic predictive relevance of such microcytotoxicity testing, the clinical course of patients receiving postoperative radiation therapy plus two or more doses of nitrosourea chemotherapy, as well as two or more computerized tomographic scans, was evaluated. In the 14 patients meeting all these criteria, tumor size increased in all five patients whose tumors did not respond to BCNU in the microcytotoxicity test. Six of the nine patients whose tumors in culture showed significant sensitivity to BCNU in vitro showed a clear decrease in tumor size over periods ranging from 17 to 48 months. Tumors in two patients increased in size, and one remained unchanged over the interval studied. These data support the concept that in vitro microcytotoxicity testing can be predictive of clinical response. Further study of this correlation seems warranted.

Biophysical properties of human astrocytic brain tumor cells in cell culture

For malignant cells cultured from a human astrocytoma, electrophysiological characteristics of the plasma membrane included specific resistivity of 446.82 +/- 279.5 ohm . cm2, specific capacitance of 0.758 +/- 0.52 microfarads/cm2, time constant 0.318 +/- 0.10 msec. The resting membrane potential averaged--14.07 +/- 7.4 mV; the mean input resistance 8.1 +/- 4.0 megohms. The average cell area was 1638 +/- 585 mu2 for contactual and and 1919 +/- 989 mu2 for noncontactual cells. Changes in input resistance and resting membrane potential were observed with increasing time in culture, possibly reflecting cel cycling. There did not appear to be electrical coupling in this cell line.

Cytotoxic antibody responses in astrocytoma patients. An improved allogeneic assay

Early diagnosis of brain tumors may be facilitated by a microcytotoxicity assay which the authors have used to detect a humoral immune response against an allogeneic glioblastoma cell line. Sixty-seven of 82 serum samples (82%) from astrocytoma patients elicited significant cytotoxicity, while only six of 65 samples (9%) from normal blood-bank donors demonstrated a similar response. Positive results were more frequently obtained in lower-grade astrocytomas. Meningiomas, acoustic schwannomas, pituitary adenomas, and metastatic tumors were positive in variable numbers of cases. A small series of serum samples were platelet-absorbed to insure that cytotoxicity was not merely due to histocompatibility antigens, and seven of eight samples, when retested on the target cell line, remained significantly positive. The assays were performed under strictly monitored conditions that afforded optimum reliability and minimal experimental variability. As the specificity of this test increases, it may lead to early detection of astrocytomas.

Detection of humoral immune response to human brain tumors: specificity and reliability of microcytotoxicity assay

A humoral microcytotoxicity assay has been used to study the immune response to human malignant astrocytic tumors. Two series are described. When the assay was performed under uniform, ideal conditions, the sera from 36 of 45 patients with these tumors (80%) produced significant cytotoxicity against allogeneic astrocytoma cells. Only 4 of 55 (7%) normal sera tested demonstrated cytotoxicity. The second series describes a five year study of over 400 sera with several sera assayed each week. The assay was found to vary in specificity and reliability over this five year period. The reasons for this variability are discussed and methods of standardizing the technique are proposed. Recent information concerning the mechanisms of the humoral microcytotoxicity assay offer promise of improved reliability and clinical utility.

Variations in response of human brain tumors to BCNU in vitro

A microtiter assay was used to study the sensitivity of 24 cultured human astrocytomas to the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1 nitrosourea (BCNU). The tumor cell lines testes originated from patients who were being treated with post-operative chemotherapy within the past 24 months. At a dose level comparable to the maximum in vivo therapeutic dose level, 18 of the 24 cell lines tested showed a significant response to the drug. If in vitro response can eventually be correlated with clinical response, this microtiter assay could help to form a basis for planning more specific chemotherapeutic treatment.

Immunobiology of primary intracranial tumors. Part 3: Microcytotoxicity assays of specific immune responses of brain tumor patients

Fifty-six in vitro microcytotoxicity assays were conducted on 30 patients with intracranial tumors at various times during the postoperative course. Significant specific cellular cytotoxic responses were found in nine of 56 assays, humoral cytotoxic responses in nine of 54 assays, and host effector cell-dependent, antibody-dependent cytotoxic responses in four of 28 assays. Variables that might influence the occurrence of cytotoxicity were studied, and the relationship of these findings to other immune parameters was discussed.

Procedure for the embedment and ultrastructural visualization of cells cultured on plastic microtest plates

The polystyrene Microtest plate has served as an excellent means of quantitation in the interaction of immunological, chemotherapeutic and radiobiological treatments with cultured cells. In order to assess the accompanying ultrastructural changes it was necessary to develop a technique which allowed cells grown in the wells of the plates to be embedded for electron microscopy. Conventional epoxy resin embedding techniques require the use of propylene oxide as a clearing agent. Unfortunately propylene oxide is a solvent of the polystyrene plates. By the substitution of absolute ethanol for propylene oxide, toluidine blue staining during the procedure and other preparative techniques it was feasible to prepare reacted cells grown in Microtest plates for electron microscopy.

Relationship between membrane potential and external potassium in human glioblastoma cells in tissue culture

Cells from a human glioblastoma (TC 526) maintained in tissue culture for ten years had a mean membrane potential of 27 +/- 0.9 mV at an external potassium concentration [Ko] of 5.3 mM. When [Ko] was varied between 2.5 and 5.3 mM, membrane potential changes were close to those predicted by the Nernst equation. At higher [Ko], the Nernstian slope was approached only in the presence of 10(-5) M ouabain, which did not affect membrane potential at a [Ko] of 5.3 mM. An electrogenic sodium pump activated by high [Ko] could explain these findings; such a mechanism has been demonstrated in other tissues.