Nitroso-chloramphenicol: Cell cycle specificity of action

We have examined the ability of the nitroso derivative of chloramphenicol (NOCAP) to inhibit subsequent growth of logarithmically growing or plateau phase cell cultures after short-term drug exposure. Raji cells taken from log growth cultures exhibited complete inhibition after 6-hour preincubation with 2-3 × 10^-5.M NO-CAP, while similarly treated cells taken from plateau populations demonstrated 90-100% of expected growth on replating. Flow-cytometric studies indicate that the irreversible effects of NO-CAP are greatest as cells proceed into and through the DNA synthetic portion (S phase) of the cell cycle.