Sterilization of leukemic cells in vivo and in vitro.

Certain 4-amino derivatives of pteroylglutamic acid (PGA), as well as various nitrogen mustards and ethylenimines, have shown chemothenapeutic activity in screening tests against transplanted mouse leukemia (8—7, 1@,14, 15). In an attempt to differentiate between the modes of action of these compounds, a technic has been employed (4, 11) which evaluates the ability of compounds to affect in vivo the transplantability of leukemic cells. A somewhatsimilartechnichas been employed previously to test the in vivo effect of certain agents against tumor cells. Sugiura (16—is)demonstrated that irradiation has an inactivating effect in vivo on Sarcoma 180 in the mouse. Karnofsky (11) has shown a similar effect with x-ray and methyl bis(@-chloroethyl)amine (IIN@) on Sarcoma 180 when grown on the chlonioallantoic membrane of the developing chick embryo, whereas the 4-amino derivatives of PGA tested by the same technic had no effect.' Results of preliminary experiments on the ability of a nitrogen mustard and two 4-amino derivatives of PGA to inactivate leukemic cells in vivo showed that HN@ had a definite sterilizing effect, while the two derivatives of PGA were without this effect (4). Although the 4-amino derivatives of PGA were demonstrated by Biesele (1) to be inactive in tissue culture, @,6-diamino punine, an adenine antagonist (10), damaged mouse sarcoma cells in this technic at concentra tions which were well tolerated by normal mouse tissue (1). On the basis of these preliminary results, six nitrogen mustards, two ethylenimines, five an tagonists of PGA, and @,6-diaminopunine were evaluated for their ability to sterilize leukcmic cells in vivo and so prevent the transmission of the disease on bioassay into normal mice. Similar studies were done with 4-amino-N'°-methyl-PGA