Compared effects of N-hydroxyurethan, urethan and hydroxyurea on DNA synthesis. In vivo and in vitro studies.

The effect of N-hydroxyurethan (HUR) on DNA synthesis has been tested both in vivo on various tissues and in vitro on concanavalin A (ConA)-stimulated rat thymocytes and compared with the action of urethan and hydroxyurea. HUR suppresses scheduled DNA synthesis, except that of non-stimulated spleen cells in vitro. The inhibition is efficient and rapid and takes place immediately if the drug is administered at the peak of the S-phase. UR inhibits DNA synthesis in vitro only at much higher doses and with different time course. It is effective or slightly effective if it is administered at the peak of the S-phase. A conversion of urethan into HUR the latter depressing DNA synthesis could partly explain the differences observed. No toxicity was found after treatment with drugs at the concentration employed. Finally, the relationships between drug doses and cell responses have been particularly observed in vivo.