Dithiocarbamates and iron chelators were recently considered for the treatment of AIDS and neurodegenerative diseases. In this study, we show that dithiocarbamates and metal chelators can potently block the activation of nuclear factor kappa B (NF-kappa B), a transcription factor involved in human immunodeficiency virus type 1 (HIV-1) expression, signaling, and immediate early gene activation during inflammatory processes. Using cell cultures, the pyrrolidine derivative of dithiocarbamate (PDTC) was investigated in detail. Micromolar amounts of PDTC reversibly suppressed the release of the inhibitory subunit I kappa B from the latent cytoplasmic form of NF-kappa B in cells treated with phorbol ester, interleukin 1, and tumor necrosis factor alpha. Other DNA binding activities and the induction of AP-1 by phorbol ester were not affected. The antioxidant PDTC also blocked the activation of NF-kappa B by bacterial lipopolysaccharide (LPS), suggesting a role of oxygen radicals in the intracellular signaling of LPS. This idea was supported by demonstrating that treatment of pre-B and B cells with LPS induced the production of O2- and H2O2. PDTC prevented specifically the kappa B-dependent transactivation of reporter genes under the control of the HIV-1 long terminal repeat and simian virus 40 enhancer. The results from this study lend further support to the idea that oxygen radicals play an important role in the activation of NF-kappa B and HIV-1.