1,1-Bis(3'-indolyl)-1-(p-substitutedphenyl)methanes: A new class of mechanism-based anticancer drugs

1,1-Bis(3'-indolyl)-1-(p-trifluoromethylphenyl)methane (DIM-C-pPhCF3) and troglitazone activate peroxisome proliferator-activated receptor gamma(PPARgamma) in Panc-28 pancreatic cancer cells and also inhibit cell proliferation. DIM-C-pPhCF3 was more active than troglitazone and was used as a model to investigate the mechanism of PPARgamma-dependent inhibition of Panc-28 cell growth. DIM-C-pPhCF3 significantly inhibited G0/G1→S phase progression, as determined by FACS analysis, and this was associated with decreased retinoblastoma protein phosphorylation and increased p21 protein and mRNA expression, but no change in p27 or cyclin D1. PPARgamma antagonists blocked DIM-C-pPhCF3-induced growth inhibition and induction of p21 protein, and similar inhibitory effects were observed in Panc-28 cells transfected with a construct (pWWP) containing a -2325 to +8 p21 promoter insert. Deletion analysis of the p21 promoter indicated that PPARgamma-dependent activation of p21 promoter constructs by DIM-C-pPhCF 3 required GC-rich sites 3 and 4 in the proximal region (-124 to -60) of the p21 promoter. The results of RNA interference and protein expression/DNA binding assays suggest that DIM-C-pPhCF3 induced p21 expression through a novel mechanism that involves PPARgamma interactions with both Sp1 and Sp4 proteins bound to the proximal GC-rich region of the p21 promoter.;1,1-Bis (3'-indolyl)-1-(p-substitutedphenyl)-methanes, including the p-t-butylphenyl (DIM-C-pPhtBu) and biphenyl (DIM-C-pPhC6H5) derivatives, activate PPARgamma in HEC1A endometrial cancer cells. However, like other structural classes of PPARgamma agonists, DIM-C-pPhtBu-induced growth inhibition and cell death in cancer cells was PPARgamma-independent. In HEC1A cells, DIM-C-pPhtBu decreased mitochondrial membrane potential (DeltaPsim), promoted the release of cytochrome c, and the nuclear uptake of endonuclease G leading to apoptosis. DIM-C-pPhtBu specifically targeted the mitochondrial permeability transition pore complex since all of the DIM-C-pPhtBu-induced pro-apoptotic responses were specifically inhibited by atractyloside (Atra), a pharmacologic inhibitor of the mitochondrial adenine nucleotide transport (ANT) protein. In vitro labeling experiments revealed that DIM-C-pPhtBu/DIM-C-pPhC 6H5 and Atra differentially affected the ability of eosin-5-maleimide to alkylate Cys160 in the ANT protein, and Atra, but not DIM-C-pPhtBu, inhibited the exchange of ATP/ADP in isolated mitochondria suggesting that these pharmacophores act on different sites on the ANT protein. Thus, the receptor-independent actions of the PPARgamma-active DIM-C-pPhtBu/DIM-C-pPhC6H 5 are related to novel mitochondriotoxic activities which involve inner mitochondrial ANT proteins.