Inactivation by the mitotic inhibitor NY 3170 of human cells in vitro.

Inactivation of NHIK 3025 cells ny the mitotic inhibitor NY 3170 (1-propargyl-5-chloropyrimidin-2-one) was measured as loss of colony-forming ability. NY 3170 at a concentration of 0.15 nM allowed no formation of colonies after 12 days of continuous exposure to the drug. Metaphase arrest after treatment with NY 3170 was reversible if the drug was removed immediately after the onset of the arrest. When the cells were kept in mitosis by the presence of NY 3170, inactivation was complete after 8h incubation of mitotic cells with 0.4 nM NY 3170. Using synchronized cell populations, it was shown that mitosis is by far the most sensitive stage of the cell cycle to inactivation by NY 3170. This leads to the suggestion that there is a connection between the inactivating and the metaphase-arresting effect of this drug. The age response curves show that after mitosis the stages in order of decreasing sensitivity to NY3170 are: G2, late S, early S and G1. This is a similar age response to that reported for proliferating cells treated with bleomycin, whereas the mitotic inhibitors vincristine and vinblastine have shown qhite different age response curves.