The presence in mammalian liver and blood of substances which inhibit the mitotic activity of human cells grown in vitro

Multipolar mitotic cells in the human cell line NHIK 3025 following treatment with the mitotic inhibitor NY 4137

Treatment of human NHIK 3025 cells during interphase with the mitotic inhibitor 2-(2-thenyl) sulfonyl-5-bromopyrimidine (NY 4137) induced the formation of multipolar mitotic cells. A 4 h pulse treatment with 0.010 mM NY 4137 induced the formation of such cells regardless of whether treatment occurred in G1 or S phase. Approximately 35% of the cells originating from such multipolar mitotic divisions had less-than-normal G1 DNA content. Recordings of the DNA content of these small cells by means of flow cytometry showed that the amount of DNA per cell varied randomly. Subpopulations were separated by centrifugal elutriation on the basis of differences in cellular volume. Simultaneous two-parametric recordings of DNA versus total cellular protein showed that even though cells contained an amount of DNA less than G1 cells, there was a proportionality between DNA content and protein content despite variations in cell size.

Effects of the new mitotic inhibitor pyrimidinsulfone NY 4137 on human cells in vitro and on colchicine binding to tubulin

The effect of 2-(2-thenyl)sulfonyl-5-bromopyrimidine (NY 4137) on cells of the human line NHIK 3025 was investigated. It was shown that NY 4137 induces cell cycle specific inhibition in metaphase. A dose-dependent prolongation of metaphase was found and the fraction of cells able to escape metaphase arrest declined gradually as the concentration of NY 4137 increased. A total block in metaphase was achieved with 0.016 mM and higher concentrations of NY 4137. Interphase was also prolonged in cells treated with 0.016 mM. Inhibition of valine incorporation by NY 4137 was also found to be dose-dependent. Following a 2-h exposure to 0.2 mM NY 4137 valine incorporation was inhibited by 80-85%. Inhibition of colchicine and vincristine binding to purified tubulin was also investigated. Double reciprocal plot and gel filtration chromatography showed that NY 4137 competitively inhibited colchicine binding to DEAE-cellulose purified tubulin. NY 4137 had no effect on vincristine binding to tubulin. The binding of NY 4137 to tubulin at or near the colchicine binding site may be responsible for the metaphase arrest.

Mitotic arrest and interphase inhibition induced by the pyrimidine sulfoxide NY 4138

Phase-specific cell-cycle inhibitory effects of the sulfoxide 5-bromo-2-(2-thienylmethyl)sulfinyl-pyrimidine (NY 4138) was studied on synchronized human NHIK 3025 cells cultivated in vitro. When added to exponentially growing cells, NY 4138 induced an accumulation of metaphases. The metaphase arrest was, however, not efficient immediately after addition of the compound. While a few telophases were still present 3 h after addition of 0.1 mM, no telophases were seen 6 h after addition. Most cells exposed to metaphase arrest by NY 4138 lost their ability to form colonies. We therefore characterize the metaphase arrest induced by this drug as irreversible. For concentrations above 0.5 mM phase specific cell cycle inhibition was also observed during interphase. Cells treated in G1 only were not delayed in G1 but were delayed in S and in G2. Cells treated in S only were also delayed in S, but to a smaller extent than the cells treated in G1 only. Cells treated with 0.1 mM NY 4138 for a period of 4 h in either G1 or in S showed no significant prolongation of the subsequent mitosis (i.e. the drug was in this case not present during mitosis). However, about 20% of the cells in this case divided to form 3 daughter cells of which 1 had a normal G1 DNA-content, 1 had 1/3 and 1 had 2/3 of a normal G1 DNA-content.

Structure-activity relationship of 1-propargyl-5-halopyrimidin-2-ones. Metaphase arresting properties and competitive inhibition of colchicine binding to tubulin

The structure-activity relationship of 1-propargyl-5-halopyrimidin-2-ones with respect to mitotic inhibitory potential and inhibition of colchicine binding to tubulin was investigated. A correlation between accumulation in metaphase of cultured human NHIK 3025 cells and drug competition with colchicine binding to tubulin was found for each compound. Effects on division of NHIK 3025 cells were determined in stained preparations following a 6 h treatment with drugs. The four halogen-substituted compounds displayed metaphase arresting ability while the H-substituted 1-propargylpyrimidin-2-one did not. 1-Propargyl-5-fluoropyrimidin-2-one was active at 1.5 and 0.75 mM while the 5-chloro, 5-bromo and 5-iodo compounds caused metaphase arrest at 0.375 and 0.18 mM. The ability of these drugs to compete with colchicine binding to DEAE-cellulose purified tubulin was also investigated. 1-Propargylpyrimidin-2-one at 5 mM did not inhibit (3H)colchicine binding to tubulin as determined by Sephadex G-50 gel filtration. The halogen-substituted pyrimidones, however, demonstrated competitive inhibition of colchicine binding to tubulin. Five mM 1-propargyl-5-iodopyrimidin-2-one inhibited colchicine binding by 43.2%, the highest value obtained within the metahalone group. The drugs tested had no effect on vincristine binding to tubulin. With respect to the halogen substitution, the increasing order of mitotic inhibitory potential and competition with colchicine binding to tubulin is H less than less than F less than Cl less than or equal to Br less than or equal to I.

Standardization of human diploid cell cultivation

Human embryonic diploid lung fibroblasts grown in Eagle's medium were exposed continually to a variety of environmental conditions over a large number of passages to observe how these conditions affected the growth and longevity of these cells in vitro. The cells grew well at temperatures between 34 and 37 C and some cells could be adapted to grow at 40 C. Very limited growth occurred at 30 to 31 C; however, confluent monolayers of cells could be maintained for months at 30 C and still give rise to actively growing cultures. Increasing the amino acid concentration in Eagle's medium or the calf serum concentration above 10% had no effect on the growth rate or longevity. One per cent calf serum could not support prolonged active growth. Trypsin concentrations between 1 and 0.1% and crystalline trypsin at 50 mug/ml showed no influence on cell growth. Ethylenediaminetetraacetic acid treatment and scraping, however, destroyed many of the cells, and the survivors grew poorly. The clonal morphology varied with age. Young cells frequently gave rise to densely packed clones, whereas older cells gave rise to clones with widely scattered cells. The cloning efficiency was high when the cells were young but decreased rapidly with successive passage. It was relatively constant from the 7th to 20th passage at about 15%.