CELL-CYCLE ARREST BY COLCEMID DIFFERS IN HUMAN NORMAL AND TUMOR-CELLS

In the continuous presence of Colcemid, the mitotic index in cultures of nine human tumor cell lines began to increase immediately upon addi tion of the drug. For 12 human normal (nontumorigenic) cell lines, the mitotic index did not begin to increase for some 2 to 3 h after the a ddition of Colcemid. The effect was independent of whether the cells w ere of fibroblast or epithelial origin and occurred over a 1000-fold r ange of Colcemid concentrations. No such differential effect was seen with single concentrations of either Taxol or nocodazole, but a simila r delayed effect was seen for two concentrations of vinblastine. These observations suggest a fundamental difference between human normal an d human tumor cells involving a cell cycle checkpoint in G(2), about 1 to 2 h before mitosis.