Kinetics of cell proliferation and polyamine synthesis during Ehrlich ascites tumor growth

The kinetics of cell proliferation and polyamine synthesis during Ehrlich ascites tumor growth were studied. The steady deceleration of the specific growth rate with increasing tumor mass that was observed was attributable to a prolongation of the cell cycle, particularly of the S and G2 phases. The cell cycle time (Tc) was 43.3 hr (TG1 equals 10.8, TS equals 26.8, and TG2 equals 5.7 hr) on the seventh day of growth and 76.0 hr (TG1 equals 14.0, TS equals 52.0, and TG2 equals 10.0 hr) on the tenth day of growth. The growth fraction showed a decrease from 0.77 to 0.60 during the 7- to 10-day tumor growth interval. The cell death rate remained low and essentially unchanged during this period. A high correlation was found between polyamine synthesis (ornithine decarboxylase activity) and the specific growth rate; the correlation coefficient was 0.985. There was also a high positive correlation between the cellular polyamine (spermidine and spermine) and nucleic acid content (spermidine: DNA equals 0.916, spermine: DNA equals 0.947, spermidine:RNA equals 0.907, and spermine: RNA equals 0.881). These observations suggest that there may be a functional coupling between polyamines and nucleic acids, and they support the hypothesis that polyamines play an important role in DNA replication and cell division.