Enhancement of docetaxel anticancer activity by a novel diindolylmethane compound in human non- small cell lung cancer

Purpose: This study was conducted to examine the cytotoxic effects of a peroxisome proliferator-activated receptor γ (PPAR-γ) agonist, 1,1-bis (3′-indolyl)-1-(p-biphenyl) methane (DIM-C-pPhC ₆H ₅), alone and in combination with docetaxel in vitro in A549 lung cancer cells and in vivo in nude mice bearing A549 orthotopic lung tumors. Experimental Design: Isobolographic method was used to calculate combination index values from cell viability data. Apoptosis was evaluated in A549 cells by terminal deoxynucleotidyl transferase-mediated nick end labeling assay and measurement of cleaved poly(ADP-ribose) polymerase level. Expression of proteins was studied by Western blotting. A549 ceils were implanted to induce orthotopic lung tumors in nude mice and the efficacy of docetaxel, DiM-C-pPhC ₆H _5, or combination was determined. Apoptosis and cleaved caspase-3 expression in the harvested tissues were studied by terminal deoxynucleotidyl transferase-mediated nick end labeling and immunohistochemistry, respectively. Results: The combination index values (0.36-0.9) suggested synergistic to additive effects of docetaxel + DIM-C-pPhC ₆H ₅ and resulted in the highest increase in percentage of apoptotic cells and expression of cleaved poly(ADP-ribose) polymerase, Bax, and N-cadherin compared with treatment with either agent. The combination also enhanced procaspase-3 and -9 cleavage. In vivo, docetaxel + DIM-C-pPhC ₆H ₅ reduced lung weights by 57% compared with 39% by docetaxel or 22% by DIM-C-pPhC ₆H ₅ alone, induced apoptosis in 43% of the tumor cells compared with 29% and 22% in tumors treated with docetaxel and DIM-C-pPhC ₆H _5, respectively, and increased procaspase-3 cleavage compared with either agent alone. Conclusions: These findings suggest potential benefit for use of docetaxel and DIM-C-pPhC ₆H ₅ combination in lung cancer treatment.