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Molecular mechanisms underlying epothilone-induced apoptotic cell death were investigated in SW620 human colon cancer cells. Treatment with epothilone B and D at different concentrations (1–100 nmol/L) dose-dependently inhibited cell growth and caused cell cycle arrest at G2-M, which was followed by apoptosis. Consistent with this induction of apoptotic cell death, epothilone B and D enhanced the constitutional activation of nuclear factor-κB (NF-κB) via IκB degradation through IκB kinase (IKKα and IKKβ) activation, and this resulted in p50 and p65 translocation to the nucleus. Moreover, cells treated with sodium salicylic acid, an IKK inhibitor, or transiently transfected with mutant IKKα and β did not show epothilone-induced cell growth inhibition or p50 translocation, although p65 was still translocated to the nucleus. Treatment with epothilone B and D also enhanced β-tubulin polymerization and the formation of p50/β-tubulin complex. However, β-tubulin polymerization was not inhibited in the cells treated by sodium salicylic acid or transiently transfected with mutant IKKα and β. Moreover, epothilone B and D increased the expressions of NF-κB–dependent apoptotic cell death regulatory genes, i.e., Bax, p53, and the active form of caspase-3, but reduced Bcl-2 expression, and these actions were partially reversed by salicylic acid. In addition, caspase-3 inhibitor reduced epothilone B–induced cell death and NF-κB activation. These findings suggest that the activation of NF-κB/IKK signals plays an important role in the epothilone-induced apoptotic cell death of SW620 colon cancer cells in a tubulin polymerization–independent manner. [Mol Cancer Ther 2007;6(10):2786–97]

PPARγ ligands have been reported to reduce proliferation of human prostate cancer cells. However, the molecular mechanism of PPARγ agonist-induced cell growth inhibition of prostate cancer cells is not clear. GSK-3β expression and NFκB activity have important roles in prostate cancer development. To investigate the mechanisms of the PPARγ agonist-induced prostate cancer cell growth inhibition, we examined the effect of troglitazone on the expression of PPARγ, GSK-3β and activity of NFκB as well as on the prostate cancer cell growth. Troglitazone induced the expression of PPARγ in the nuclear of PC-3 cells, but not in LNCaP cells. Troglitazone (0-16 uM) inhibited cancer cell growth in a similar extend between both cells accompanied by the induction of cell cycle arrest in G(0)/G(1) phase and an increased in the similar extent of apoptotic cell death in concentration dependent manner. Troglitazone inhibited the constitutive expression of GSK-3β and activation of NFκB. Co-treatment of troglitazone with a GSK-3β inhibitor (AR-a014418) or GSK-3β siRNA significantly augmented the inhibitory effect of troglitazone on the NFκB activity and on prostate cancer cell growth inhibition and apoptotic cell death. However, overexpression of GSK-3β hindered troglitazone-induced cell growth inhibition and NFκB inactivation. These results suggest that PPARγ agonist, troglitazone, inhibits prostate cancer cell growth through inactivation of NFκB via suppression of GSK-3β expression.