Cell and environment interactions in tumor microregions: the multicell spheroid model

Abnormal vascularization of malignant tumors is associated with the development of microregions of heterogeneous cells and environments. Experimental models such as multicell spheroids and a variety of new techniques are being used to determine the characteristics of these microregions and to study the interactions of the cells and microenvironments. The special cellular microecology of tumors influences responsiveness to therapeutic agents and has implications for future directions in cancer research.

Ubiquitous cell-surface glycoprotein on tumor cells is proliferation-associated receptor for transferrin

A murine monoclonal antibody (OKT9) raised against human leukemic cells binds to a wide variety of leukemia and tumor cell lines and to a minority of leukemia cells taken directly from patients. Fetal thymus and liver are strongly reactive as are some normal, immature hemopoietic cells and activated lymphocytes. Reactivity with OKT9 appears to correlate with proliferation status in both normal and malignant populations. Biochemical analysis indicates that this structure is a approximately equal to 180,000-dalton glycoprotein with two disulfide-bonded subunits of approximately equal to 90,000-daltons. Isolation of the transferrin receptor from a T-cell line (MOLT-4) indicates that it also has a dimeric approximately equal to 180,000-dalton structure. Radio-labeled transferrin bound to its receptors can be specifically precipitated by the monoclonal OKT9, although the latter does not bind transferrin itself, indicating that the antigenic structure defined by this antibody is likely to be the transferrin receptor.

P-24: a human leukemia-associated and lymphohemopoietic progenitor cell surface structure identified with monoclonal antibody

This study was directed at surface structures that are found on human lymphohemopoietic progenitor cells in normal and leukemic bone marrow. A monoclonal antibody was produced against an acute lymphoblastic leukemia (ALL) cell line of the pre-B phenotype; this antibody (BA-2) was used to demonstrate a cell surface polypeptide of approximately 24,000 mol wt that migrates similarly in both reduced and nonreduced form. This polypeptide, p24/BA-2, was shown by immune precipitation and gel electrophoresis and cell distribution studies to be different from HLA-DR and gp 100/cALLa. p24/BA-2 was present on the surface of 77% (54/70) of cases of non-T, non-B ALL; BA-2 staining was less bright or nondetectable in surface Ig+ (SIg+) chronic lymphocytic leukemia (CLL) and T ALL and nondetectable on peripheral T and B lymphocytes. Approximately 3% of bone marrow mononuclear cells were p24/BA-2+, and these cells were E rosette-, surface (SIg-), and nonphagocytic. Marrow TdT+ progenitor cells were frequently p 24/BA-2+. Results suggest that p24/BA-2 represents a surface structure present on lymphohemopoietic bone marrow progenitor cells and that most common types of ALL bear the p25/BA-2 structure.

Antibacterial activity of mupirocin (pseudomonic acid), a new antibiotic for topical use

Mupirocin (pseudomonic acid A), an antibiotic produced by Pseudomonas fluorescens, showed a high level of activity against staphylococci and streptococci and against certain gram-negative bacteria, including Haemophilus influenzae and Neisseria gonorrhoeae, but was much less active against most gram-negative bacilli an anaerobes. Nearly all clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis, including multiply resistant strains, were susceptible (mupirocin MIC, less than or equal to 0.5 microgram/ml). There was no cross-resistance between mupirocin and clinically available antibiotics, and the selection of resistant variants in vitro occurred at a low frequency. Mupirocin was highly bound (95% bound) to the protein of human serum, and activity was reduced 10- to 20-fold in the presence of human serum. The activity of mupirocin was not greatly influenced by inoculum size but was significantly enhanced in acid medium. In tests of bactericidal activity, MBCs were 8- to 32-fold higher than MICs and the antibiotic demonstrated a slow bactericidal action in time-kill tests, resulting in 90 to 99% killing after 24 h at 37 degrees C.

Cell-associated ovalbumin is cross-presented much more efficiently than soluble ovalbumin in vivo

To better understand the antigenic requirements for cross-presentation, we compared the in vivo efficiency of presentation of cell-associated vs soluble OVA with the OT-I (CD8) and OT-II (CD4) TCR transgenic lines. Cross-presentation of cell-associated OVA was very efficient, requiring as little as 21 ng of OVA to activate OT-II cells and 100-fold less to activate OT-I cells. In contrast, soluble OVA was presented inefficiently, requiring at least 10,000 ng OVA for activation of either T cell subset. Thus, cell-associated OVA was presented 500-fold more efficiently than soluble OVA to CD4 T cells and 50,000-fold more efficiently to CD8 T cells. These data, which represent the first quantitative in vivo analysis of cross-presentation, show that cell-associated OVA is very efficiently presented via the class I pathway.

Variations in tumor cell growth rates and metabolism with oxygen concentration, glucose concentration, and extracellular pH

Tumors and multicellular tumor spheroids can develop gradients in oxygen concentration, glucose concentration, and extracellular pH as they grow. In order to calculate these gradients and assess their impact on tumor growth, it is necessary to quantify the effect of these variables on tumor cell metabolism and growth. In this work, the oxygen consumption rates, glucose consumption rates, and growth rates of EMT6/Ro mouse mammary tumor cells were measured at a variety of oxygen concentrations, glucose concentrations, and extracellular pH levels. At an extracellular pH of 7.25, the oxygen consumption rate of EMT6/Ro cells increased by nearly a factor of 2 as the glucose concentration was decreased from 5.5 mM to 0.4 mM. This effect of glucose concentration on oxygen consumption rate, however, was slight at an extracellular pH of 6.95 and disappeared completely at an extracellular pH of 6.60. The glucose consumption rate of EMT6/Ro cells increased by roughly 40% when the oxygen concentration was reduced from 0.21 mM to 0.023 mM and decreased by roughly 60% when the extracellular pH was decreased from 7.25 to 6.95. The growth rate of EMT6/Ro cells decreased with decreasing oxygen concentration and extracellular pH; however, severe conditions were required to stop cell growth (0.0082 mM oxygen and an extracellular pH of 6.60). Empirical correlations were developed from these data to express EMT6/Ro cell growth rates, oxygen consumption rates, and glucose consumption rates, as functions of oxygen concentration, glucose concentration, and extracellular pH. These empirical correlations make it possible to mathematically model the gradients in oxygen concentration, glucose concentration, and extracellular pH in EMT6/Ro multicellular spheroids by solution of the diffusion/reaction equations. Computations such as these, along with oxygen and pH microelectrode measurements in EMT6/Ro multicellular spheroids, indicated that nutrient concentration and pH levels in the inner regions of spheroids were low enough to cause significant changes in nutrient consumption rates and cell growth rates. However, pH and oxygen concentrations measured or calculated in EMT6/Ro spheroids where quiescent cells have been observed were not low enough to cause the cessation of cell growth, indicating that the observed quiescence must have been due to factors other than acidic pH, oxygen depletion, or glucose depletion.

CD8 T cell ignorance or tolerance to islet antigens depends on antigen dose

There are two major mechanisms reported to prevent the autoreactivity of islet-specific CD8(+) T cells: ignorance and tolerance. When ignorance is operative, naïve autoreactive CD8(+) T cells ignore islet antigens and recirculate without causing damage, unless activated by an external stimulus. In the case of tolerance, CD8(+) T cells are deleted. Which factor(s) contributes to each particular outcome was previously unknown. Here, we demonstrate that the concentration of self antigen determines which mechanism operates. When ovalbumin (OVA) was expressed at a relatively low concentration in the pancreatic islets of transgenic mice, there was no detectable cross-presentation, and the CD8(+) T cell compartment remained ignorant of OVA. In mice expressing higher doses of OVA, cross-presentation was detectable and led to peripheral deletion of OVA-specific CD8(+) T cells. When cross-presentation was prevented by reconstituting the bone marrow compartment with cells incapable of presenting OVA, deletional tolerance was converted to ignorance. Thus, the immune system uses two strategies to avoid CD8(+) T cell-mediated autoimmunity: for high dose antigens, it deletes autoreactive T cells, whereas for lower dose antigens, it relies on ignorance.

T cell signaling. Antigen affinity, costimulation, and cytokine inputs sum linearly to amplify T cell expansion

T cell responses are initiated by antigen and promoted by a range of costimulatory signals. Understanding how T cells integrate alternative signal combinations and make decisions affecting immune response strength or tolerance poses a considerable theoretical challenge. Here, we report that T cell receptor (TCR) and costimulatory signals imprint an early, cell-intrinsic, division fate, whereby cells effectively count through generations before returning automatically to a quiescent state. This autonomous program can be extended by cytokines. Signals from the TCR, costimulatory receptors, and cytokines add together using a linear division calculus, allowing the strength of a T cell response to be predicted from the sum of the underlying signal components. These data resolve a long-standing costimulation paradox and provide a quantitative paradigm for therapeutically manipulating immune response strength.

Serologic response to treatment of infectious syphilis

OBJECTIVE

To evaluate the serologic response to treatment of patients with infectious syphilis.

DESIGN

Historical cohort study of all cases of infectious syphilis in Alberta from 1981 to 1987.

PATIENTS

A total of 1090 patients were entered; 857 with primary syphilis, 183 with secondary syphilis, and 50 with early latent disease. Two hundred and eight patients were excluded who either were pregnant, had negative serologic results before treatment, had clinical relapse, were treatment failures, or were lost to follow-up.

INTERVENTIONS

All 882 evaluable patients were treated with a recommended antibiotic regimen for infectious syphilis and returned for re-assessment including repeat serologic testing.

MEASUREMENTS AND MAIN RESULTS

Seventy-two percent (95% CI, 66% to 77%) and 56% (CI, 43% to 70%) of patients with initial episodes of primary or secondary syphilis had seroreverted according to rapid plasma reagin (RPR) test results by 36 months. A 2- and 3-tube decline was seen by 6 and 12 months in primary and secondary syphilis. Early latent syphilis resulted in only a 2-tube decrease at 12 months. Serologic response was not affected by sex, age, race, or sexual orientation. Patients with their first infection were more likely to experience RPR seroreversal than those with repeat infections. The RPR reversal rates also depended on the pretreatment titer and stage of disease. At 36 months, 24% (CI, 20% to 28%) of patients had nonreactive fluorescent treponemal antibody absorption tests (FTA-Abs), and 13% (CI, 11% to 15%) had nonreactive microhemoglutination tests for Treponema pallidum (MHA-TP).

CONCLUSIONS

Adequate therapeutic response for syphilis must be based on illness episode and the pretreatment RPR titer. Treponemal tests can demonstrate seroreversion after 36 months, and a negative treponemal test does not rule out a past history of syphilis.

Mathematical modelling of microenvironment and growth in EMT6/Ro multicellular tumour spheroids

In order to determine the role of micromilieu in tumour spheroid growth, a mathematical model was developed to predict EMT6/Ro spheroid growth and microenvironment based upon numerical solution of the diffusion/reaction equation for oxygen, glucose, lactate ion, carbon dioxide, bicarbonate ion, chlorine ion and hydrogen ion along with the equation of electroneutrality. This model takes into account the effects of oxygen concentration, glucose concentration and extracellular pH on cell growth and metabolism. Since independent measurements of EMT6/Ro single cell growth and metabolic rates, spheroid diffusion constants, and spinner flask mass transfer coefficients are available, model predictions using these parameters were compared with published data on EMT6/Ro spheroid growth and micro-environment. The model predictions of reduced spheroid growth due to reduced cell growth rates and cell shedding fit experimental spheroid growth data below 700 microns, but overestimated the spheroid growth rate at larger diameters. Predicted viable rim thicknesses based on predicted near zero glucose concentrations fit published viable rim thickness data for 1000 microns spheroids grown at medium glucose concentrations of 5.5 mM or less. However, the model did not accurately predict the onset of necrosis. Moreover, the model could not predict the observed decreases in oxygen and glucose metabolism seen in spheroids with time, nor could it predict the observed growth plateau. This suggests that other unknown factors, such as inhibitors or cell-cell contact effects, must also be important in affecting spheroid growth and cellular metabolism.

Influence of glucose and oxygen supply conditions on the oxygenation of multicellular spheroids

The interrelationship among external O2 and glucose supply, oxygenation status, oxygen consumption rates and cellular viability in tumour microregions was studied using the multicellular spheroid model. For chronic exposure to various supply conditions multicellular EMT6/Ro spheroids were cultured in stirred media equilibrated either with 20% (v/v) or 5% (v/v) oxygen and containing four different glucose concentrations ranging from 0.8 mM to 16.5 mM. Spheroids were investigated using histology and O2-sensitive microelectrodes for measuring oxygen tension (PO2) values. A chronic decrease of the glucose concentration in the medium is associated with a substantial reduction in the thickness of the viable rim of cells and with a persistent increase in the cellular respiration rate. In general, both viable rim size and respiration are decreased through restriction of O2 supply during spheroid growth at a given external glucose concentration. The O2 consumption in spheroids appears to decrease with increasing spheroid size under most of the growth conditions investigated. These findings provide evidence for a large capacity of the spheroid cells to chronically adapt their metabolic rates to different supply situations. The experimental data and theoretical considerations indicate that necrosis may develop in the centre of these spheroids due to the lack of O2 and/or glucose under some of the growth conditions, but central necrosis can also occur despite sufficient O2 and glucose supply. Consequently, cellular metabolism and viability in tumour microregions may not be determined by the diffusion limitation of O2 or specific substrates alone, such as glucose, but may be influenced by a complex interaction of factors in the micromilieu the majority of which are still unknown.

A reduction in the in situ rates of oxygen and glucose consumption of cells in EMT6/Ro spheroids during growth

The rates of consumption of oxygen and glucose by EMT6/Ro cells in multicellular spheroids were measured at various times during normal growth. In situ spheroid cellular consumption rates were similar to those of exponentially growing single cells up to a spheroid diameter of 150 micron. Further growth resulted in decreases in the rates of both oxygen and glucose consumption which were correlated with the increase in spheroid diameter and cell number. At a diameter of 1300 micron, both rates of cellular consumption had decreased by a factor of 2.5. The rates of consumption per unit of nonnecrotic spheroid volume decreased in a similar manner. Measurements with single cells demonstrated that the rate of oxygen consumption was coupled with glucose concentration, and vice versa. The rates of consumption for cells dissociated from small spheroids indicated that there was some effect of the spheroid environment. As the spheroids grew, however, association in the spheroid structure accounted for a smaller proportion of the total observed reduction in the rates of nutrient consumption. The presence of central necrosis also appeared to have no effect on the rates of consumption of these nutrients. Spheroid-derived cells showed a decrease in cell volume with growth as the cells accumulated in a quiescent state. Measurements with single cells demonstrated that oxygen and glucose consumption were correlated with cell volume and with the development of nonproliferating cells. We conclude that the observed decrease in oxygen and glucose consumption with growth in spheroids is largely due to the progressive accumulation of cells in a quiescent state characterized by an inherently lower cellular rate of nutrient utilization.

Amoxycillin: a new semi-synthetic penicillin

Amoxycillin (alpha-amino-p-hydroxybenzylpenicillin) is a new semi-synthetic penicillin with a broad spectrum of antibacterial activity similar to that of ampicillin. Penicillin-sensitive strains of staphylococci, streptococci, and pneumococci were sensitive to concentrations of 0.1 mug or less of amoxycillin/ml. Strains of Haemophilus influenzae were inhibited by a level of 0.5 mug/ml, and most strains of Escherichia coli, Proteus mirabilis, Shigella sonnei, Salmonella species, and Streptococcus faecalis were sensitive to a concentration of 5 mug or less of amoxycillin/ml. Penicillinase-producing strains of Staphylococcus aureus and strains of Pseudomonas aeruginosa, indole-positive Proteus, Klebsiella, and Enterobacter were insensitive to amoxycillin. The new penicillin was bactericidal in activity, as with other penicillins, and its antibacterial activity was not reduced in the presence of serum. After oral administration to volunteer subjects amoxycillin produced serum concentrations twice as high as those obtained with similar doses of ampicillin, and the penicillin was recovered unchanged in high concentrations in the urine. The absorption of amoxycillin was not greatly influenced by food, and administration of probenecid resulted in increased and more prolonged concentrations of amoxycillin in serum.

Flucloxacillin, a new isoxazolyl penicillin, compared with oxacillin, cloxacillin, and dicloxacillin

Flucloxacillin, a new isoxazole penicillin, is active against penicillinase-producing strains of Staphylococcus aureus and is well absorbed in man after oral and intramuscular administration. Compared with isoxazole penicillins in current clinical use-namely, oxacillin, cloxacillin, and dicloxacillin-flucloxacillin has proved as active against Gram-positive cocci, including penicillin-resistant staphylococci. The extent of binding of flucloxacillin to the protein of human serum was similar to that of oxacillin and cloxacillin and less than that of dicloxacillin. In man flucloxacillin given orally produced total and free serum levels higher than those obtained with oxacillin and cloxacillin; total serum levels similar to those of dicloxacillin, and free levels greater than those of dicloxacillin. Similarly, after intramuscular injection the free serum levels of flucloxacillin were higher than those of oxacillin, cloxacillin, and dicloxacillin.

Oxygen tensions in multicell spheroids of two cell lines

O2 tensions (Po2) were measured with microelectrodes in multicellular spheroids from EMT6/Ro and V-79-171-B cells. The measurements were performed in spheroids kept in flowing growth medium that was equilibrated with 5% CO2 and air at a temperature of 37 degrees C and contained 5.5 mM glucose. The recorded Po2 profiles are characterized by a diffusion-depleted zone surrounding the spheroids and by a steep drop in Po2 within the spheroids over mean distance of 220 and 188 micrometer from the surface of EMT6/Ro and V-79-171B spheroids over mean distance of 220 and 188 micrometer from the surface of EMT6/Ro and V-79-171B spheroids respectively. Smaller spheroid exhibit parabolic Po2 profiles, larger ones show a central plateau. The region of the steep decrease in Po2 corresponds to the thickness of the viable rim: the plateau region is created by the absence of O2 consumption in the central necrotic area. Po2 in the centre of EMT6/Ro spheroids decreased from 66 mmHg at a diameter of 400 micrometer to 13 mmHg at a diameter of 1000 micrometer. Under the present conditions during growth and in the experiments, values below 5 mmHg were recorded only in spheroids 1200 micrometer. Comparably low Po2 was recorded in V-79 spheroids with diameters of 650 micrometer +. In spheroids of this cell type with a diameter of 400 micrometer, Po2 was 42 mmHg. The findings provide evidence that necrosis may arise at average Po2 of 57 and 42 mmHg in EMT6/Ro and V-79-171B spheroids, respectively, grown under the conditions described.

Optical detection of antibody-antigen reactions at a glass-liquid interface

We describe an optical technique for detecting and monitoring antibody-antigen reactions at a solid-liquid interface. The antibody is covalently immobilized onto the surface of either a planar (microscope slide) or cylindrical (fibre optic) waveguide made of fused quartz. The reaction of immobilized antibody with antigen in solution is detected through use of the evanescent wave component of a light beam, which has a characteristic depth of penetration of a fraction of a wavelength into the aqueous phase, thus optically interacting primarily with substances bound (or located very close) to the interface and only minimally with the bulk solution. This resulting in-situ spatial separation of the antibody-bound from free antigen precludes a formal separation step and allows the reaction to be monitored kinetically. An immunoassay for methotrexate by absorption spectrometry achieved a detection limit of about 270 nmol/L; binding of methotrexate by immobilized antibody was monitored by the decrease in transmittance at 310 nm. A two-site immunofluorometric assay for human IgG could detect as little as 30 nmol/L; binding of fluorescein-labeled antibody was monitored by the increase in signal above 520 nm (lambda ex = 495 nm). With both immunoassays the signal-generating phase was monitored kinetically and was completed within 15 min.

The identification of heme oxygenase as a major hypoxic stress protein in Chinese hamster ovary cells

Chronic hypoxia increases the expression of a set of stress proteins (oxygen regulated proteins or ORPs) which is implicated in the development of drug resistance and radiation sensitivity in tumour cells. Five major ORPs have been documented, and two, ORP 80 and ORP 100, are considered to be identical to the glucose regulated stress proteins GRP78 and GRP94, respectively. We report here that ORP 33 is a form of the heme catabolic enzyme, heme oxygenase, using evidence obtained from northern blotting, two-dimensional polyacrylamide gel electrophoresis and western analysis. Heme oxygenase is believed to be an important component of the cellular response to oxidative stress. The significance of heme oxygenase as a hypoxia-induced stress protein is discussed.