Inhibition of estrogen receptor negative breast cancer cell growth by a new class of peroxisome proliferator-activated receptor γ agonists

Proc Amer Assoc Cancer Res, Volume 45, 2004 3856 A series of 1,1-bis(3’-indolyl)-1-(p-substituted phenyl)methanes activate peroxisome proliferator-activated receptor γ (PPARγ) and inhibit growth of estrogen receptor (ER)-positive breast cancer cells. The most active methylene-substituted diindolylmethane (DIM) compounds contained p-CF3 (DIM-p-pPhCF3), p-tbutyl (DIM-C-pPhtBu) and p-C6H5 (DIM-C-pPhC6H5) substituents and the effects of these compounds on proliferation of ER-negative MDA-MB-231 and MDA-MB-453 breast cancer cells were investigated. The PPARγ-active methylene substituted DIMs inhibited growth of both ER-negative cell lines and the concentrations required for 50% growth inhibition (IC50) were 1-5 μM. MDA-MB-453 cells were treated for 96 hours with DMSO, 1 or 5 uM DIM-C-pPhC6H5. FACS analysis showed that the percentage of cells in G0/G1, G2/M and S phase was 73.8, 7.54 and 18.7% respectively in DMSO (solvent) treated cells whereas these percentages were 86.3, 5.46 and 8.23% respectively after treatment with 5 μM DIM-C-pPhC6H5. No significant changes were observed in cells treated with 1 μM DIM-C-pPhC6H5, however the higher concentration significantly blocked G0/G1 to S phase progression. MDA-MB-231 cells treated for 12 hours with 1-10 μM DIM-C-pPhCF3 were also investigated in cell cycle progression studies. The percentage of cells in G0/G1, G2/M and S phase with DMSO treatment were 57.3, 14.8, 27.9% respectively and 71.5, 13.7, 14.7% with 10 μM DIM-C-pPhCF3 treatment. No substantial differences were seen with 1 or 5 μM treatment of DIM-C-pPhCF3 in MDA-MB-231 cells. The PPARγ-active compounds had minimal effects on expression of cyclin D1 and cyclin-dependent kinase inhibitors p21 and p27 in MDA-MB-453 cells whereas both p21 and p27 protein were induced in MDA-MB-231 cells. Other cell context-dependent mechanisms of growth inhibition are currently being investigated.