Variable duration of vincristine-induced metaphase block in leukemic and nornal bone marrow cells of children.

In four children with previously untreated acute leukemia the stathmokinetic effect of a single IV dose of vincristine (in two children with AML), or of a single IV dose of vincristine combined with daily prednisone (in one child with AMMoL and one with ALL), were investigated. The kinetics of bone marrow blast cells from all patients, and of red cell precursors from the patient with ALL, were studied by conventional methods (determinations of mitotic index and pro-+metaphase/ana-+telophase ratios). In two of the four patients (one AML and one AMMoL) the progression of cells through S, the incorporation pattern of tritiated thymidine, and the nuclear projection area changes during S were analyzed by a combination of autoradiographic and cytophotometric techniques. The results suggest that the doses of vincristine used (0.05 and 0.075mg/kg body weight) did not influence the progression of cells from G0/G1 into S nor from S into G2, and had no effect on the incorporation pattern of tritiated thymidine or on the nuclear projection area changes during S. The results suggests, however, that the duration of the metaphase block induced by vincristine varied from one cell system to another. Differences in the time course of regeneration processes in neoplastic and normal cell systems might be one of the mechanisms responsible for the anti-neoplastic effect of vincristine in man.