Further studies on the self-limitation of growth of JB-1 ascites tumours

L.H. Gray Medal lecture: cell kinetics and radiation oncology

Development of the study of human tumor cell kinetics during the past decades has deepened our understanding of the natural history of human cancers. Mathematical models based on the data which have been accumulated may help to evaluate, for the various types of human tumors, the time during their growth that the dissemination process occurred and to calculate the size distribution of the subclinical metastases at the time of treatment of the primary tumor. The perturbations caused by radiotherapy and chemotherapy are complex and include reassortment of surviving cells and repopulation. Currently it appears difficult in clinical practice to take advantage of cell reassortment while the differences in the rate and in the duration of repopulation between normal and neoplastic tissues are exploited in most therapeutic regimens. A better knowledge of cell and tissue kinetics following treatment may help to optimize the treatment scheduling in particular during combined administration of radiotherapy and chemotherapy. The study of the kinetics of proliferation in normal tissue has shown the existence of several types of inhibitory and stimulatory humoral factors. These, when purified, can be used to manipulate the proliferation of critical normal tissues in order to protect them during the administration of cell cycle specific drug or to accelerate their regeneration after treatment.

Lack of evidence of chalone activity in used medium and extract of JB-1 tumor cells in vitro. A flow cytometry study

In cell-free mouse ascites fluid from the JB-1 ascites tumor in the plateau phase of growth low-molecular chalone substances have been found which reversibly and specifically arrest JB-1 cells in the G1 and G2 phase of the cell cycle. The aim of this study was to investigate whether chalones were involved in the regulation of in vitro growth of JB-1 tumor cells. Used medium and cell extract from confluent, stationary JB-1 cell cultures were investigated for proliferation-inhibitory properties. JB-1 cells from stationary cultures were explanted in test cultures and the traverse of cells through the S phase was investigated by means of flow cytometry (FCM). Inhibition--expressed as a delay of the traverse of cells through the S phase--was not observed when a surplus of used medium, concentrated and fractionated used medium or concentrated and fractionated cell extract from JB-1 cells in vitro was added to test cultures. On the contrary, used medium and concentrated and fractionated used medium stimulated growth. Thus, no involvement of chalones in the growth regulation of JB-1 tumor cells in vitro was detected.

The identification of a cell culture inhibitor in a tumour extract

An extract of Harding-Passey mouse melanoma was found to inhibit the proliferation of the same cell line grown in culture when measured by both thymidine incorporation and by the increase in cell number. The active ingredient was purified by ultrafiltration, column chromatography and preparative electrophoresis. The purified material was identified by mass spectrometry and by gas chromatography as spermidine. The partially purified material reversed the methylglyoxal Bis-guanyl hydrazone (Methyl-GAG) inhibition of cultured cells to the same extent as spermidine. Very low concentrations of Methyl-GAG were found to suppress the spermidine inhibition of thymidine incorporation into cells. The inhibitor extracted from melanoma tumours behaved in the same way as spermidine at all Methyl-GAG concentrations. Thus, it is unlikely that the active ingredient in the biological extract is anything other than spermidine.

Specific chalone inhibition of the regeneration of the JB-1 ascites tumour studied by flow microfluorometry

The variation in the DNA distribution in the JB-1 and the Lla2 ascites tumour was investigated by means of flow microfluorometry (FMF) in the plateau stage and during the initiation of the regenerative growth induced by percutaneous aspiration. The study showed that a considerable influx of cells with G1DNA content into the S phase occurred in both tumours about 10 hr after aspiration. In the JB-1 tumour, these initial regenerative changes could be reversibly blocked by injections of cell-free plateau JB-1 ascitic fluid or an ultrafiltrate of this ascites. In contrast to these observations no delay in the regenerative changes was observed in the L1a2 tumour after treatment with JB-1 ascites or the ultrafiltrate. The study supports the assumption of a specific growth regulation of the JB-1 ascites tumour and emphasizes the suitability of FMF analyses in cell-kinetic studies in which short-term fluctuations take place in the distribution of cells with different DNA content.

DNA-binding proteins in Yoshida ascites tumor fluid

DNA-binding proteins were isolated from Yoshida ascites tumor fluid by chromatography on DNA-cellulose. This fraction represents 1-2% of the total ascites protein. Most of the DNA-binding proteins will bind to phosphocellulose as well. The proteins migrate by agarose gel electrophoresis at pH 8.6 as alpha and beta globulins. Quantitative immunoelectrophoresis revealed the presence of 12-18 proteins. SDS-polyacrylamide electrophoresis indicated molecular weights ranging from 3-10(4) to 10(6). Seven of the proteins were identified by specific immunoprecipitation as beta1-Eglobulin, beta2-glycoprotein I, fibrinogen split product E (fibrinogen E), coagulation factor XIII (factor XIII), alpha2-macroglobulin, IgG and IgM. Alpha1-antichymotrypsin might also be represented. In nuclear extracts of the tumor cells only factor XIII was present. With the exception of fibrinogen E and P5 all recognized DNA-binding proteins are present in normal rat plasma. With increasing tumor age the concentration of fibrinogen E, factor XIII, P5 and IgM increased both in ascites fluid and in plasma, while the concentration of other DNA-binding-proteins decreased or remained constant. Evidence is presented that the DNA- and phosphocellulose binding ascites protein fraction inhibit tumor cell growth. No inhibition was induced by corresponding protein fractions isolated from normal rat plasma.

Cell proliferation in Walker tumour growing in the stomach wall

Tumour cells from a Walker carcinosarcoma 256 were implanted in the gastric mucosa in rats. The tumour grew and infiltrated the lamina propria and the submucosal space after 7 days. It appeared to grow faster in the submucosal space than in the lamina propria. The cell proliferation was therefore studied separately in: (1) the tumour in the lamina propria, (2) the main tumour mass and (3) the tumour periphery, defined as the cells located within the outer 100-120 mum of the tumour. Mitoses arrested with vinblastine, cells labelled with tritiated thymidine and the grain count per labelled cell were studied at the three different sites. The rate of cell proliferation in the tumour was highest in the lamina propria, lower in the centre of the main tumour mass, and lowest at the periphery. Cell loss might explain the discrepancy between the rate of cell proliferation and the actual tumour growth. The factors that influence tumour cell proliferation in the different parts of the tumour are discussed.

Kinetic analysis of cell size and DNA content distributions during tumor cell proliferation: Ehrlich ascites tumor study

In order to study the growth dynamics of proliferating and non-proliferating cells utilizing discrete-time state equations, the cell cycle was divided into a finite number of age compartments. In analysing tumor growth, the kinetic parameters associated with a retardation in the growth rate of tumors were characterized by computer simulation in which the simulated results of the growth curve, the growth fraction, and the mean generation time were adjusted to fit the experimental data. The cell age distibution during the period of growth was obtained and by a linear transformation of the state transition matrices, was employed to specify the cell size and DNA content distributions. In an application of the model, the time-course behavior of cell cycle parameters of Ehrlich ascites tumor is illustrated, and the parameters important for the transition of cells in the proliferating compartment to the non-proliferating compartment are discussed, particularly in relation to the G1-G0 and G2-G0 transitions of non-cycling cells as revealed by the variation of cell size distribution.