The effect of 6-mercaptopurine on the incorporation of labeled amino acids into cellular protein of chronic granulocytic leukemia leukocytes.

F RANTZ afl(l Zamecnik’ I)oiIlLe(l out that in vitro incorporation of C’4-leucine and C’4-alanine into white cell proteins was about six times greater in acute leukemic cells, as compared with normal leukecytes. Similar findings were obtained by \Veisberger et ;il23 using S35LcyTstii e and S 5-L-methionine. Baker, Zaniecnik and Stephenson4 showed that cells from cases of chronic’ Invelogenous leukemia were able to incorporate significantly greater amounts of amino acid and to maintain incorporation capacity longer than control cells. It was suggested that amino acid incorporation into cellular pr tei11 coul(I l)e lmSe(l to test viability of leukocytes. \Vinzler et al.5 stu(lied the in vitro metabolism of human normal and lemikemic leukocytes in the presence of various anti-tumor drugs. Radioactive glycine incorporation into cellular I)rotein was used fo measure cellular activity. Their (lata showed tluat the rate of glycine incorporation was 1pproximately five times greater in chronic granulocytic leukemic cells than in normal leukocytes. In vitro addition of 6-mercaptopurine to fresh cells did not always inhibit uptake of rtdioactive amino acid. It was concluded that a four-luour incubation with labeled amino ac:(l could not he used as a screening test for anti-tumor drugs. Observations iii our Ial)oratOry using 1()O , g./ml. of 6-niercal)toPurine indicate that this drug gives erratic effects on tlue rate of lai)eled leucine incorporation, usually causing some inhibition but occasionally causing stimulation. The question of whether 6-mercaptopurine htys any role in vivo which might alter amino amid incorporation into cellular protein has not been answered. The purpose of this paper is to report out’ observations on two hospitalized cases of cluronic gra:iulocytic leukemia treated with 6-mercapto-