Abstract
Abstract
Cultured cell populations, derived from lymphocytic leukemia L1210 resistant to 6-mercaptopurine (6-MP; L1210/6-MP) and sensitive lymphocytic leukemia (L1210/0), were propagated in Dulbecco's modified Eagle's minimum essential medium supplemented with 10% horse serum and 5 μm 2-mercaptoethanol. The population doubling times (mean ± SD) were 16.6 ± 1.9 hr (L1210/0) and 16.1 ± 1.8 hr (L1210/6-MP) between cell densities of 7 × 104 − 1.0 × 105 and 2.0 × 106 cells/ml. Cultured L1210/6-MP cell populations were significantly resistant to 6-MP (1.7 to 170 μg/ml for exposure periods of 24 or 48 hr). Cultured L1210/6-MP cell populations were also collaterally sensitive to methotrexate (0.055 to 5.5 μg/ml for an exposure period of 24 hr) or to dichloromethotrexate (1.0-100 μg/ml for an exposure period of 24 hr). The results indicate that resistance to 6-MP and collateral sensitivity to the folate analogs are properties of the L1210/6-MP cells and are independent of any host factors.
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