Antitumor activity of a folate-cleaving enzyme, carboxypeptidase G 1 .

We have studied the antitumor activity of a folate-cleaving bacterial enzyme, carboxypeptidà se G, (CPD G,), which hydrolyzes the C-terminal glutamate residue from folie acid analogs. CPD GÌcompletely inhibited the growth of all murine leukemic cell lines tested in tissue culture at enzyme levels of 0.02 to 0.025 unit/ml. A decrease in cell number was apparent after 12 hr of exposure to the enzyme, while a decrease in cell viability, as determined by soft-agar cloning, was evident after 6 hr. The biochemical effect of CPD GÌ in blocking incorporation of labeled deoxynucleosides into DNA was detected after 1 hr of incubation with the agent. Inhibition of DNA synthesis by CPD G! was characterized by a fall in the incorporation of both thymidine-3H and deoxyuridine-3H into DNA, rather than the selective depression of deoxyuridine-3H