Retention of 6-mercaptopurine derivatives by intact cells as an index of drug response in human and murine leukemias.

Human and animal leukemias, varying widely in responsive ness to 6-mercaptopurine, were examined to seek determinants of drug sensitivity. Drug-responsive rodent leukemias showed a comparatively high capacity for in vitro conversion of 6-mer captopurine into nondiffusible cellular metabolites, predomi nantly drug nucleotides. A similar study of human leukemia cells indicated that the in vitro capacity for 6-mercaptopurine anabolism can also be a useful predictive measure of drug responsiveness in man.