Changes in DNA distributions and ploidy of CHO cells as a function of time in culture.

Chinese hamster ovary (CHO) cells maintained in continuous culture for 3 to 5 months may undergo subtle changes in drug sensitivity response, growth kinetics, plating efficiencies, et cetera. Our studies done independently in two different laboratories, using flow cytometry, indicate that the DNA histogram patterns change at about 11 wk, from populations with an approximate diploid DNA content to populations also composed of triploid and tetraploid cells. Chromosome counts also change from distributions of 21 to 22 to populations of cells having 21 to 22, 34 to 35 and 44 to 46 chromosomes. These alterations occur earlier (at 8 to 9 wk) in cell populations previously treated with anticancer drugs.