Age Responses to X Rays, Vinca Alkaloids, and Hydroxyurea of Murine Lymphoma Cells Synchronized In Vivo2

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Abstract
A method is described for the induction of partial synchrony by means of hydroxyurea in a population of murine lymphoma cells in vivo. Three hours after lymphoma-bearing animals were each given a single intraperitoneal injection of hydroxyurea, the survival of femoral lymphoma colony-forming cells, as measured by the spleen-colony technique, was reduced to a plateau level of about 20%. The drug disappeared from both plasma and femoral marrow fluid between 3 and 4 hours after injection. The lymphoma cells surviving this treatment comprised a partially synchronized population. With this synchronization method, the survival of lymphoma cells treated, in different phases of the generation cycle in vivo, to X rays (374, 562, or 750 rads), vinblastine (1 mg/mouse, 3-hour exposure) vincristine (0.3,3 mg/mouse, 3-hour exposure) or hydroxyurea (a second challenge; 5 mg/mouse, 3-hour exposure) was determined. The lymphoma cells showed a peak in sensitivity to X rays at the G1/S transition and then grew more radioresistant as they passed through the S phase of the cell cycle. They had a maximal sensitivity to the two Vinca alkaloids as well as to hydroxyurea, when treated in the S phase. These age responses were similar to those of Chinese hamster or HeLa cells in vitro. The age response to X rays was analyzed in terms of variations in dose-survival curve parameters through the cycle; in addition, dose-fractionation studies indicated repair of sublethal damage at certain positions in the cell cycle.

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