The glucose distribution in 9L rat brain multicell tumor spheroids and its effect on cell necrosis

L-glutamine: a major substrate for tumor cells in vivo?

From 65 human breast cancer xenografts investigated, a net glutamine uptake was found in 13 tumors (mean +/- SE: 15.7 +/- 4.5 nmol/g per min) whereas a net release (22.5 +/- 3.3 nmol/g per min) was observed in 40 tumors. In 12 tumors neither a significant net uptake nor a net release was obvious. There is experimental evidence that glutamine is taken up by cancer cells only at arterial concentrations greater than 0.5 mM. Another parameter determining glutamine utilization by tumor cells may be the tissue oxygenation. In hypoxic or anoxic tumor areas, glutamine oxidation is unlikely since oxygen is required for the reoxidation of coenzymes which are reduced in the course of this metabolic pathway. The pronounced net release could be due to proteolysis within the tumors investigated. In ascitic fluid (DS-carcinosarcoma), glutamine accumulated during growth, implicating a reduction in the glutamine consumption rate, proposedly also due to a worsening of the oxygen supply to the suspended tumor cells. Thus, the generally held opinion that L-glutamine is a (if not the) major substrate for the energy metabolism of rapidly growing tumor cells should be reconsidered since evidence for this hypothesis has been derived mainly from in vitro systems with abundant oxygen.

Effect of cytochalasin B, nocodazole and irradiation on migration and internalization of cells and microspheres in tumor cell spheroids

The effect of cytochalasin B (CB), nocodazole, and irradiation on the adherence and internalization of 3H-labeled EMT6 spheroid-derived single cells and inert microspheres in unlabeled, intact EMT6 multicellular spheroids has been examined. CB inhibited adhesion and internal migration, whereas nocodazole did not stop adhesion but did prevent later internalization. Treatment of labeled cells with 5, 15 and 25 Gy 250 kV X-rays before adherence did not effect their adherence or later internalization. The same radiation treatments administered to the spheroids either immediately before or after the introduction of unirradiated single cells did not affect adherence, but the depths reached by labeled cells and microspheres were reduced largely because of the consequent reduction in spheroid growth. Microsphere size (9, 15, or 25 microns) and surface charge (negative, or non-ionic) had minimal, if any, effect on the adherence and internalization of these particles.

Dynamics of cell kinetic parameters during 9L spheroid growth

Cell population kinetics were followed in 9L tumour spheroids as they grew from aggregates of about 80 micron in diameter to over 800 micron. The kinetic parameters measured were cell cycle time, spheroid-doubling time, and growth fraction; from these the cell loss factor phi was calculated. The rate of cell shedding from the surface was also measured, so that the contribution of shedding to the overall cell loss could be evaluated. The major findings include significant elongation of the cell cycle, a low rate of cell death in spheroids below 500 micron in diameter, and a relatively high GF in large spheroids. The results also indicated that 9L spheroid kinetic parameters may be strongly influenced by the culture methodology.

Growth and characterization of multicellular tumor spheroids of human bladder carcinoma origin

We have examined the MGH-U1 human bladder carcinoma cell line and 12 primary bladder carcinoma biopsies for their ability to form spheroids in suspension culture and in multiwell dishes. MGH-U1 cells formed tightly packed spheroids with a necrotic center and viable rim whereas three sublines formed loose aggregates only. Spheroids formed from as few as 100 MGH-U1 cells placed into multiwells. MGH-U1 cells derived from spheroids formed new spheroids more rapidly and and consistently than cells derived from monolayer culture. Spheroid diameter increased at a rapid rate of approximately 100 microns/d in multiwell dishes, and necrosis occurred only in spheroids of diameter greater than 1 mm. Spheroids placed in spinner culture at a higher concentration (approximately 1.5 spheroids/ml) grew more slowly and developed necrosis at smaller diameters. The width of the viable rim of spheroids grown in spinner culture was maintained at approximately 190 microns over a wide range of spheroid diameters (400 to 1000 microns). Sequential trypsinization of spheroids, which stripped layers of cells from the spheroids, demonstrated no difference in the plating efficiency of cells derived from varying depths into the spheroid. Only one of the 12 primary bladder biopsy specimens demonstrated an ability to form spheroids. This biopsy, designated HB-10, formed spheroids that grew linearly over 40 d, formed colonies in methylcellulose culture and grew as xenografts in immune-deprived mice. These studies characterize the MGH-U1 spheroids that are useful in vitro models to study the effects of various treatments for solid tumors and demonstrate the limited capacity of cells from primary human bladder biopsies to form spheroids.

Variation of pO2 in the growth medium of spheroids: interaction with glucose to influence spheroid growth and necrosis

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Potential applications of therapeutic drug monitoring in treatment of neoplastic disease by antineoplastic agents

Therapeutic drug monitoring of antineoplastic agents must be considered in terms of cytotoxicity to stem cells and toxicity of normal tissues. The dose-limiting toxicity which is myelosuppression is believed to be a necessary effect for maximal antitumour effect. The areas in which therapeutic drug monitoring can play a role include: predicting patients at risk of toxicity, e.g. high dose methotrexate therapy; low bioavailability, e.g. oral 6-mercaptopurine; identifying patients at risk of treatment failure, e.g. methotrexate clearance in acute lymphoblastic leukemia. Although therapeutic drug monitoring is not clinically useful at present, the potential role it can play is illustrated for cytosine arabinoside, adriamycin and cyclophosphamide. Two problems encountered with drug monitoring of antineoplastic disease are tumour heterogeneity manifested by clonal, nutritional and physical characteristics and the common practice of combination chemotherapy. These problems must be addressed in order to make therapeutic drug monitoring a practical tool in cancer chemotherapy. Future applications of therapeutic drug monitoring will require more studies to define therapeutic ranges for single agents, patient-to-patient variation, course-to-course variation and the effects of drug combinations on pharmacokinetic profiles of the drugs used.

Two-dimensional diffusion limited system for cell growth

A new cell system, designed to supplement multicellular spheroids as tumour analogues, was analysed theoretically and experimentally. This 'sandwich' system is a single layer of cells, subject to self-created gradients of nutrients and metabolic products. Due to these gradients the sandwich system develops a border of viable cells and an inner region of necrotic cells corresponding to the viable rim and the necrotic center of a spheroid. However, sandwiches differ from spheroids in several ways. All the cells in the sandwich can be microscopically viewed during the entire experiment. In sandwiches there is no three-dimensional cell to cell contact. Also, the gradients are less steep in our sandwich system, so the width of the viable region in a sandwich is about 10 times as large as the width of the viable rim in a spheroid. Indeed, in sandwiches the experimenter has some control over the steepness of the gradients and thus can vary the width of this viable border. We used DNA labelling studies and flow cytometry along with visual observation to analyse the system. Our experiments show that the observed cell necrosis, similar to that found in spheroids, is due to diffusion limitations. The results are consistent with the idea that oxygen deprivation stops cell cycling and, when extreme and prolonged, leads to necrosis. The possibility that substances other than oxygen are involved is not excluded by the data. The data also suggests that in the final, near-equilibrium state the average overall oxygen consumption rate for the viable sandwich population may be about one-quarter of that for an exponentially growing population of the same cell line.

Growth and cellular characteristics of multicell spheroids

The data reviewed here demonstrate that there are many similarities in growth and cellular characteristics for different types of tumor cells grown as multicell spheroids. Furthermore, where comparisons have been made many of the features of spheroids also occur in tumors in vivo. However, as for tumors, there are also many characteristics of individual types of spheroids which are relatively specific and cannot be generalized as properties of all spheroid model systems. The results also demonstrate the marked influence which cellular microenvironments regulated by a supply of oxygen and nutrients may have on the development of cellular heterogeneity. Furthermore, using spheroids it was shown that dynamic cellular and metabolic interactions exist in regulating the development of cellular subpopulations and microenvironments. Spheroids are more sensitive to alterations in culture environment than are monolayer or single-cell suspension cultures. Consequently, researchers who use this model system must characterize, optimize, and standardize the growth conditions for the spheroid cell type being investigated. This information then provides a base from which to undertake detailed studies, which are not possible in experimental tumors, of controlled manipulation of microenvironments in spheroids. The ranges of cellular microenvironments and cellular heterogeneity which exist at different stages of spheroid growth provide a model, at least in part, for coexisting size ranges of microregions in many solid tumors. Thus, spheroids provide a model, which at different stages of growth is readily manipulated and controlled experimentally, to facilitate studies of contributions of individual environmental factors, or concomitant changes in these, on cellular phenotypic expression. It is probable that the cellular changes which can be demonstrated to occur during spheroid growth, also occur in vivo. Modulation of cellular characteristics revealed by research with spheroids requires much more study to determine the mechanisms and effects on tumor cell behavior, as well as response to therapeutic agents and their relevance to tumors in vivo.

The role of glucose in the growth of 9L multicell tumor spheroids

Monolayer-cultured 9L rat brain tumor cells grew optimally in culture media containing glucose concentrations greater than 0.07 mg/ml, but growth ceased at concentrations lower than this value. Assuming that this glucose concentration defines the proliferating fraction of cells in 9L multicell tumor spheroids, it is possible to simulate spheroid growth based on the intraspheroid glucose distribution derived by the author earlier. An excellent fit to experimental growth data was obtained by assigning the proliferating fraction a growth rate constant equal to 40% of that of monolayer-cultured cells. This definition is in accord with our observation that the colony-forming efficiency (CFE) of spheroid-derived cells is 40% of the CFE of cells maintained in monolayer. This suggests that the role of glucose in 9L cell growth is similar in spheroids and in monolayer culture.