Purpose: Although tumor necrosis factor-α (TNF-α) induces a strong cytotoxic effect on cell growth, many authors have reported that various cancer cells are resistant to TNF-α and the basis for this sensitivity or resistance to TNF-α remains to be elucidated. Since nuclear factor kappa B (NF-κB) activation has recently been reported to inhibit TNF-α-induced cell death, we studied whether NF-κB also assumes a protective role in TNF-α-induced cell death in prostate cancer cells. Materials and Methods: We used two human prostate cancer cell lines of DU145 and PC-3. We prepared two different NF-κB inhibitors, pyrrolidine dithiocarbamate (PDTC) and NF-κB decoy. NF-κB DNA binding activity was detected by electrophoretic mobility shift assay (EMSA). Cell survivals were measured by MTT assay. Induction of apoptosis was detected by nuclear staining and measured by fragmented DNA ELISA. Results: EMSA showed that NF-κB inhibitors continuously inhibited TNF-α-induced NF-κB activation. Cell growth was not inhibited by either TNF-α (50 ng./ml. or less) or NF-κB inhibitors. However, both PCA cells treated with TNF-α (20 ng./ml.) plus NF-κB inhibitors showed significant growth inhibition compared with controls (p <0.05). Nuclei of PCA cells appeared severely fragmented by this combination therapy. Furthermore, the levels of DNA fragmentation were significantly elevated in PCA cells treated with TNF-α (20 ng./ml.) plus NF-κB inhibitors compared with controls (p <0.05). Conclusions: NF-κB activation is suggested to produce the resistance of DU145 and PC-3 to TNF-α and that the combination of TNF-α and NF-κB inhibitors could be constituted an effective therapy to TNF-α-resistant human prostate cancer cells.
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