Mechanisms of Amethopterin Resistance in Leukemia II. Effect of Cortisone on Sensitive and Resistant Mouse Leukemias

(1) The administration of large single doses of cortisone to mice with advanced transplanted leukemia of strains Ak4 (amethopterin sensitive) and Ak4R (amethopterin resistant) caused a fall in the elevated leukocyte count. (2) This leukotoxic effect was considerably more marked and occurred at lower cortisone dosage with the Ak4R than with the parent Ak4 strain, and demonstrates the lack of cross resistance to cortisone in this amethopterin-fast strain (Ak4R) of mouse leukemia.