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The Role of Periodic and Interrupted Treatment of Newborn and Infant Mice with Urethan on Leukemogenesis¹

Division of Oncology, Institute for Medical Research, Chicago Medical School, Chicago, Illinois

The significance of the number of urethan injections and the length of interruption of treatment on the leukemogenesis in newborn mice were studied. Five-tenths mg of urethan was injected i.p./gm of body weight to C57BL x C3H F₁ mice for a total of 3, 5, or 6 times. The 1st injection was given when the mice were less than 24 hr of age, while others followed at 3-day intervals. This periodicity was interrupted in 2 groups for 9 or 21 days following the 3rd treatment.

The group that received all 6 injections of urethan at 3-day intervals developed leukemia in significantly higher proportion of mice than the groups in which similar treatment was interrupted for 9 or 21 days, or which received 3 or 5 injections continuously.

The results demonstrated that continuous and periodic treatment with urethan starting at newborn age was significantly more efficient in inducing leukemogenesis than if such a treatment was interrupted for varied periods of time. It was postulated that the presence or absence of the immature cells in the thymus during the urethan treatment may be causally related to these results.

¹ This investigation was supported by Contract Ph 43-65-67 from the National Cancer Institute, NIH, USPHS.

Received 6/ 2/66. Accepted 9/12/66.