Enhancement of pyrimidine nucleoside uptake into K562 and YAC-1 cells by cadeguomycin.

Cadeguomycin markedly stimulated the uptake of thymidine, deoxycytidine and uridine into the acid-insoluble fraction of K562 human leukemic cells, but did not significantly affect adenosine incorporation. The enhancement of pyrimidine nucleoside uptake was 6-17 fold over the control. Aspartate incorporation into nucleic acid was not significantly blocked by the antibiotic, suggesting that the stimulation of pyrimidine nucleoside incorporation is not due to the inhibition of de novo pyrimidine nucleotide synthesis. Net DNA and RNA syntheses, observed by [32P]phosphate uptake, were not significantly affected by cadeguomycin. The enzymatic activity of thymidine, deoxycytidine and uridine kinases was higher in cadeguomycin-treated cells than in untreated cells, suggesting that the enhancement of pyrimidine nucleoside uptake occurs in the phosphorylation process. The stimulatory activity of cadeguomycin of thymidine uptake was reversed by guanosine and deoxyguanosine, but not by adenosine and deoxyadenosine, suggesting that intracellular metabolism and/or action of cadeguomycin is related to that of guanosine and deoxyguanosine. The stimulation of pyrimidine nucleoside incorporation by cadeguomycin was also found with YAC-1 cells, but not with the other cell lines. The enhancement effect of the antibiotic seems to be not directly related to its cytotoxicity.