Direct determination of the influence of the cell cycle on the survival of tumor cells exposed to cytotoxic antibodies.

Abstract

We have developed a direct method for measuring the influence of the cell cycle on the survival of tumor cells exposed to antibody and complement. Asynchronous, exponentially growing S107 myeloma cells were exposed to antisera reactive with either histocompatibility, viral, or other surface antigens. The resulting mixtures of live and dead cells were simultaneously analyzed for viability and DNA content using a modified fluorescence-activated cell sorter, which was adjusted to record only the DNA content of the tumor cells surviving antibody treatment. The cell cycle analysis of the tumor cells surviving exposure to either of the three antisera indicated that there was no major loss of cells from a single phase of the cell cycle prior to the death of cells in other phases. The relative risk of cell death was only 1.03 times higher for G1 cells than for either S or G2 + M cells. Even when myeloma cells were exposed to a concentration of antihistocompatibility serum that killed 96% of the cells, there was only a small decrease in the proportion of cells in G1. These studies were extended to populations of cells which had altered sensitivity to cytotoxic antibody after being treated with the chemotherapeutic agents melphalan or actinomycin D. Using the method described above, we demonstrated that the drug-induced changes in susceptibility were not due to the cell cycle effects of the two drugs. The method of analysis described here should also be useful for directly determining how the changes that occur during the cell cycle can affect the susceptibility of tumor cells to other lethal agents.