Identification of a tumor inhibitory factor in rat ascites fluid

A polypeptide which inhibits the growth of human carcinoma cells has been characterized from Novikoff rat ascites fluid. This tumor inhibitory factor co-purified with transforming growth factor activity through acid/ethanol extraction and Bio-Gel chromatography. The two activities were completely separated by reverse phase HPLC. The tumor inhibitory factor is heat stable and requires disulfide bonds for bioactivity. This factor inhibited the anchorage independent growth of the more differentiated human colon carcinoma cell lines but did not affect the less differentiated carcinoma cells. The presence of stimulatory and inhibitory activities in the same extracts suggests that the relative concentrations of these factors may be important in the control of cell growth.     

The effect of various seleno-compounds on ehrlich ascites tumor cells

The effect of various concentrations and forms of selenium on in vitro viability of Ehrlich Ascites Tumor Cells (EATC) was investigated. Sodium selenite, selenium dioxide, seleno-dl-cystine, and seleno-dl-methionine, dramatically decreased EATC viability as measured by dye exclusion. Sodium selenate only marginally decreased EATC viability. Cell viabilities decreased with increasing selenium in the incubation media and as a function of time. Viabilities determined by dye exclusion did not correlate with the inhibition of tumor growth observed after treatment with selenium. Intraperitoneal injections of selenite in mice previously inoculated with EATC significantly inhibited tumor development. Delaying intraperitoneal injections of selenite to 5 and 7 days after inoculation of mice with EATC reduced the effectiveness of this nutrient on the inhibition of EATC growth. Incubation of EATC in vitro with supplemental selenium prior to injection of mice completely inhibited EATC development in vivo before any appreciable alteration in cell viability was observed.     

Phosphate transport in Ehrlich ascites tumor cells and the effect of arsenate

The effect of extracellular Pi and arsenate on Pi-transport in Ehrlich ascites tumor cells has been studied. Pi-transport can be described by Michaelis-Menten kinetics; the maximal flux equal to 44 mmoles (kg cell water)^?1 hour^?1 and K_m equal to 3.3 × 10^?4 M . Arsenate is a competitive inhibitor of Pi-transport with an inhibition constant (K_i) equal to 2.41 × 10^?3 M . The data support the hypothesis that cellular Pi is regulated by the cell membrane through the mediation of a carrier system.     

On the mechanism of the Crabtree effect in mouse ascites tumor cells

The addition of glucose to ELD and ELT/B1 mouse ascites tumor cell suspensions caused a 2.3-fold increase in the phosphorylation state ratio, (ATP)/(ADP) (Pi), because of a decrease in the intracellular Pi concentration. The addition of glucose to these cell suspensions has been reported by Chance and Hess ('59) to cause an increase in the study state reduction of cytochrome b and an increase in the steady state oxidation of cytochrome c. On a quantitative basis these two independent measurements suggest that a near equilibrium exists between the oxidation-reduction state of the mitochondrial electron carriers and the reactions of ATP synthesis (as expressed by the phosphorylation state ratio) both before and after glucose addition. We conclude that the mechanism of the inhibition of respiration by glycolysis (the Crabtree effect) is a decrease in the rate of electron transport caused by the mass action effect of the elevated phosphorylation state ratio.     

Analysis of RNA synthesized in isolated nuclei of Ehrlich ascites tumor cells

The molecular size and poly-A content of RNA synthesized in isolated nuclei of Ehrlich ascites tumor cells were measured. KCl was found to be essential for synthesis of high molecular weight RNA: when 0.4 M KCl was added to the reaction mixture, the average molecular size of the RNA formed was 14S; without KCl the average molecular size was 5S. A significant amount of poly-A sequences was found in RNA synthesized in the presence of alpha-amanitin, suggesting that RNA polymerase I and/or III may synthesized some RNA containing poly-A in isolated nuclei.     

Further observations on the effect of calcium ionophores on ascites tumor cells

The effect of the Ca2+ ionophore ionomycin on neoplastic thymocytes in comparison to its effect on normal thymus cells was studied. Ionomycin increases intracellular Ca2+ in normal lymphocytes but fails to increase Ca2+ in neoplastic thymocytes. In these cells the ionophore causes a transient increase in cytosolic free Ca2+. The lack of effect of ionomycin reproduces that of A23187, but it does not depend on reduced availability of intracellular Mg2+ to exchange with Ca2+; it appears to depend on the strong activity of the plasma membrane Ca2+-extruding pump that counteracts ionomycin permeabilization and that can be partly inhibited by the calmodulin inhibitor R24571 (calmidazolium). Neoplastic thymocytes show a high content of magnesium, the intracellular binding of which is efficiently regulated by endogenous ATP. The data show also an interesting correlation between the regulation of energy metabolism (aerobic glycolysis) and cation homeostasis in the neoplastic cells studied.