1,1-Bis(3′-indolyl)-1-(p-substituted phenyl)methanes inhibit ovarian cancer cell growth through peroxisome proliferator-activated receptor-dependent and independent pathways

1,1-Bis(3′-indolyl)-1-(p-t-butylphenyl)methane (DIM-C-pPhtBu) is a peroxisome proliferator - activated receptor γ (PPARγ) agonist, and treatment of SKOV3 ovarian cancer cells with this compound (5 μmol/L) inhibits cell proliferation, whereas up to 15 μmol/L rosiglitazone had no effect on cell growth. DIM-C-pPhtBu also inhibits G₀-G₁ to S phase cell cycle progression and this is linked, in part, to PPARγ-dependent induction of the cyclin-dependent kinase inhibitor p21. DIM-C-pPhtBu induces PPARγ-independent down-regulation of cyclin D1 and we therefore further investigated activation of receptor-independent pathways. DIM-C-pPhtBu also induced apoptosis in SKOV3 cells and this was related to induction of glucose-related protein 78, which is typically up-regulated as part of the unfolded protein response during endoplasmic reticulum (ER) stress. Activation of ER stress was also observed in other ovarian cancer cell lines treated with DIM-C-pPhtBu. In addition, DIM-C-pPhtBu induced CCAAT/enhancer binding protein homologous protein through both ER stress and c-jun NH₂-terminal kinase-dependent pathways, and CCAAT/enhancer binding protein homologous protein activated death receptor 5 and the extrinsic pathway of apoptosis. These results show that DIM-C-pPhtBu inhibits growth and induces apoptosis in ovarian cancer cells through both PPARγ-dependent and PPARγ-independent pathways, and this complex mechanism of action will be advantageous for future clinical development of these compounds for treatment of ovarian cancer.