Effect of N-methylisatin-beta-4':4'-diethylthiosemicarbazone on intracellular Moloney leukemia virus constituents.

N-Methylisatin-beta-4':4'-diethylthiosemicarbazone (M-IBDET) inhibits intracellular production of viral constituents in a mouse cell line, 3T3/MLV, chronically infected with Moloney leukemia virus. Electron microscopic observations confirmed that inhibition of virus production by the drug was not associated with any structural changes in the cell morphology or any damage to the plasma membrane, the site of viral assembly and 'budding'. Treatment of the cells with 17 microM M-IBDET for 6 h inhibited extracellular virus production by 80% but did not affect the level of viral RNA in the cytoplasm or in the plasma membrane. Intracellular reverse transcriptase activity and levels of viral structural proteins were significantly inhibited. Thus, although the drug did not affect viral RNA, it reduced viral protein synthesis.