Effect of Orally Administered 3′,5′-Dichloroamethopterin on Formate-C¹⁴ Incorporation in Leukemic Mice^*

The influence of the route of administration on the inhibition by 3′,5′-dichloroamethopterin (DCM) and amethopterin (MTX) of formate-C¹⁴ incorporation in vivo into acid-soluble adenine of mouse spleens infiltrated with leukemia L1210 was investigated. At equal dose levels, oral treatment was less effective than subcutaneous administration in inhibiting formate incorporation. Maximum inhibition occurred within ½ hour after subcutaneous, and about 2 hours after oral, administration of DCM. The extensive inhibition produced by parenterally administered DCM was not obtained with oral administration, even at much higher dose levels.