Nitroso-chloramphenicol: cell cycle specificity of action

We have examined the ability of the nitroso derivative of chloramphenicol (NO-CAP) 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 x 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.