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The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) alone or in combination with an NF-kappaB inhibitor, (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY 11-7082; BAY), on the growth and apoptosis of human prostate cancer PC-3 cells cultured in vitro or grown in immunodeficient mice were studied. Treatment of cultured PC-3 cells with TPA (0.2-10 ng/ml) for 96 h resulted in growth inhibition and apoptosis in a concentration-dependent manner. BAY inhibited NF-kappaB activity in PC-3 cells as determined by a luciferase reporter assay and enhanced TPA-induced growth inhibition and apoptosis in cultured PC-3 cells. In animal studies, NCr immunodeficient mice were injected subcutaneously with PC-3 cells in Matrigel. Mice with well-established tumors received daily i.p. injections with TPA (100 ng/g body weight/day), BAY (4 microg/g/day), or a combination of TPA (100 ng/g/day) and BAY (4 microg/g/day) for 36 days. Tumor growth occurred in all of the vehicle-treated control mice. The percent of animals with some tumor regression after 36 days of treatment was 0% for the control group, 40% for the TPA group, 50% for the BAY group and 100% for the TPA + BAY group. Mechanistic studies indicated that treatment of the mice with TPA or TPA + BAY decreased proliferation and increased apoptosis in the tumors. Results from our studies indicate that inhibition of NF-kappaB activity is associated with enhanced TPA-induced growth inhibition and apoptosis in PC-3 cells. Inhibition of NF-kappaB activity by suitable pharmacological inhibitors may be an effective strategy for improving the therapeutic efficacy of TPA in prostate cancer.

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) is a potent stimulator of differentiation and apoptosis in myeloid leukemia cells. In the present study, we investigated the role of the transcription factor NF-kappaB in TPA-induced growth inhibition and apoptosis in the myeloid leukemia HL-60 cell line and its TPA-resistant cell variant HL-525. Unlike the parental cell line, HL-525 cells are protein kinase C (PKC)-beta deficient and resistant to TPA-induced differentiation and apoptosis. We found that treatment of HL-60 cells with TPA resulted in a concentration-dependent growth inhibition and an increase in apoptotic cells. TPA only had a small effect on growth and apoptosis in HL-525 cells. Treatment of HL-60 cells with TPA (0.64-3.2 nM) caused a rapid activation of NF-kappaB as determined by electrophoresis mobility shift assay (EMSA) and immunocytochemistry. Although the basal level of NF-kappaB activity was low in HL-60 cells, TPA-resistant HL-525 cells had a high basal level of NF-kappaB activity. Treatment of HL-525 cells with higher concentrations of TPA (16-80 nM) resulted in a further increase in NF-kappaB activity. (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY 11-7082; BAY), which inhibits IkappaB alpha phosphorylation and thus decreases NF-kappaB activation, was found to decrease TPA-induced nuclear translocation of NF-kappaB. Furthermore, BAY enhanced TPA-induced growth inhibition and apoptosis in both HL-60 and HL-525 cells. Results from the present study indicate that inhibition of NF-kappaB by BAY was associated with enhanced TPA-induced growth inhibition and apoptosis in human myeloid leukemia cells. TPA in combination with pharmacological inhibitors of NF-kappaB may improve the therapeutic efficacy of TPA and overcome the resistance to TPA in some myeloid leukemia patients.