Purpose: Although tumor necrosis factor-alpha (TNF-alpha) induces a strong cytotoxic effect on cell growth, many authors have reported that various cancer cells are resistant to TNF-alpha and the basis for this sensitivity or resistance to TNF-alpha remains to be elucidated. Since nuclear factor kappa B (NF-kappaB) activation has recently been reported to inhibit TNF-alpha-induced cell death, we studied whether NF-kappaB also assumes a protective role in TNF-alpha-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-kappaB inhibitors, pyrrolidine dithiocarbamate (PDTC) and NF-kappaB decoy. NF-kappaB 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-kappaB inhibitors continuously inhibited TNF-alpha-induced NF-kappaB activation. Cell growth was not inhibited by either TNF-alpha (50 ng./ml. or less) or NF-kappaB inhibitors. However, both PCA cells treated with TNF-alpha (20 ng./ml.) plus NF-kappaB 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-alpha (20 ng./ml.) plus NF-kappaB inhibitors compared with controls (p<0.05).
Conclusions: NF-kappaB activation is suggested to produce the resistance of DU145 and PC-3 to TNF-alpha and that the combination of TNF-alpha and NF-kappaB inhibitors could be constituted an effective therapy to TNF-alpha-resistant human prostate cancer cells.