Action of demecolcine (colcemid) in the murine sarcoma 180 tumor.

Iv infusions of demecolcine (Colcemid) were established in mice bearing the Sarcoma 180 tumor. During demecolcine infusion at a rate of 6 microgram/hr, the tumor labeling index following 3H-thymidine administration and the mean grain count per labeled cell did not differ significantly from control values. Cells in anaphase and telophase disappeared from the tumor sections, and the net number of cells in the earlier stages of mitosis increased for 20 hrs. The rate of mitotic accumulation during the initial 8 hrs of demecolcine infusion was about one third of what would be expected from the known cell cycle values for this tumor. This reduced rate of accumulation does not appear to result from death of mitotic cells, escape of cells from metaphase blockade, or S-phase arrest secondary to inhibition of DNA synthesis; it is suggested that the reduced accumulation rate is secondary to demecolcine damage to interphase cells. Tumor cells that have been gathered by 4-hr demecolcine infusions may be released in synchronous fashion following the end of the infusion. A small proportion of these cells will recycle synchronously during the following mitotic period.