Nonspecific inhibition of precursor uptake by alkyl-substituted purines and prednisolone

Of 43 compounds, encompassing a wide variety of biological activities, only the same six (9-cyclopentyladenine, 9-benzyladenine,9-n-butyladenine, 6-benzylthiopurine, 9-cyclopentyl-6-mercaptopurine, and prednisolone), at concentrations less than 10 times the toxic amounts, inhibited precursor incorporation into lipids, glycoproteins, and DNA of logarithmically-growing adenocarcinoma 755 and leukemia LI 210 cells in culture. For adenocarcinoma 755 cells, each of the six agents, added subsequent to choline, had little effect on the incorporation of choline into lipids, an indication that their action was on uptake of the precursor rather than on a bio-synthetic step. Direct measurements of choline and thymidine uptake into cells of both types showed that each of the six agents apparently blocked choline incorporation into lipids and thymidine incorporation into nucleic acids by inhibiting uptake of the precursors.