Uptake of cytosine arabinoside (Ara-C) by LSA lymphoma after irradiation in the stationary phase of growth.

An in vitro system was used to assess uptake of cytosine arabinoside by LSA ascites tumor cells growing in vivo. Changes in tumor uptake with aging after depopulation and perturbation of the cell population with 1,000 rad were studied. Both DNA synthesis and drug uptake were highest during early rapid tumor growth and decreased with aging and the stationary phase of growth. However, irradiation caused a second peak of cellular activity and drug uptake. These results indicate that irradiation stimulates regrowth of tumor.