Hydroxyurea-induced inhibition of deoxyribonucleotide synthesis: studies in intact cells.

Abstract

Summary Hydroxyurea-induced inhibition of thymidine incorporation by monolayers of HeLa cells was partially prevented and reversed by addition of deoxyadenosine, deoxyguanosine, and deoxycytidine to the culture medium. All 3 deoxyribonucleosides were required for optimal effect. Hydroxyurea inhibited incorporation of thymidine into DNA of embryos of the sand-dollar species Echinarachnius parma . The onset of inhibition was delayed for 3–4 synthesis ( S ) periods when the drug was added at fertilization, but was evident with the next replication cycle following drug addition between the 5th and 6th S period. Hydroxyurea did not alter rates of leucine incorporation into protein regardless of the time of drug exposure. Echinoderm ova possess significant quantities of preformed deoxyribonucleotides; previous studies with 5-fluorodeoxyuridine have suggested that these stores can supply the embryo with the thymidylate required for DNA replication over 6 S periods following fertilization. These observations, i.e., partial reversal of drug-induced inhibition by exogenous deoxyribonucleosides in HeLa cells, and the insensitivity of sand-dollar embryos to hydroxyurea during initial S periods, are compatible with the postulate that this compound inhibits reduction of ribonucleotides to deoxyribonucleotides.