Studies on the so-called "synchronization therapy" of tumors with vincristine

Cell kinetic studies on the effect of vincristine (VCR) on cells in different cell-cycle phases were carried out using single- and double-labeling methods with 3H- and 14C-thymidine. Studies on mouse L 1210 and JB-1 ascites tumor cells, mouse jejunal crypt cells as well as on HeLa cells have shown that VCR affects cells not only during or prior to mitosis, but also cells that are in S phase at the time of VCR application. These cells are arrested during the next mitosis. Cells arrested in mitosis even with small doses of VCR subsequently become necrotic. Thus, it has been shown experimentally that an in vivo synchronization of tumor cells cannot be achieved with VCR and, therefore, the effect of a so-called synchronization therapy with VCR is not due to synchronization of tumor cells.