[Effect of N-nitroso-N'-methylurea on the cellular kinetics in tumors]

Single intrafemoral injection of NMU in the dosage of 80 mg/Kh in mice with ascites leucemia L1210 induced considerable disorders in the tumor cell cycle. The passage of phase S by cells was markedly retarded during the period from 1 hour to 6 days, while after injection of the substance under study a maximum duration of phase G2 increased from 4 to 12 hours. Inhibition of phase S onset was provisional, and already 6 hours following NMU injection all cells entered phase S. In mice mammary tumors the label index fell markedly (by 90%) during the period from 6 hours to 8 days after NMU injection. The intensity of 3H-thymidine incorporation during the whole period of observation was approximately twice reduced.