Depression of DNA synthesis and mitotic index by colchicine in cultured human lymphocytes

Abstract Colchicine, at concentrations of 5 μg/ml to 15 μg/ml administered for 1 h to 6 h caused significant depressions of DNA synthesis and of the mitotic index in PHA-stimulated human lymphocytes. Colchicine appeared both to prevent cells from beginning DNA synthesis and to reduce the rate of synthesis of cells already in S. The reduced mitotic index probably resulted to a large extent from depressed DNA synthesis, but there was evidence that colchicine also slowed the progress of cells throught G2. The use of colchicine at these concentrations can be a source of serious error in determinations of the duration of cell cycle phases and in kinetic studies based on metaphase counts after a mitotic block.