Troglitazone (TGZ) is a synthetic thiazolidinedione drug belonging to a group of potent peroxisome proliferator-activated receptor γ (PPARγ) agonists known to inhibit proliferation, alter cell cycle regulation, and induce apoptosis in various cancer cell types. TGZ is an oral anti-type II diabetes drug that can reverse insulin resistance. For more then 100 yr, aspirin, a nonselective cyclooxygenase (COX) inhibitor, has been successfully used as an anti-inflammatory drug. Recently, Aspirin (ASA) and some other nonsteroidal anti-inflammatory drugs (NSAIDs) have drawn much attention for their protective effects against colon cancer and cardiovascular disease; it has been observed that ASA's anti-tumor effect can be attributed to inhibition of cell cycle progression, induction of apoptosis, and inhibition of angiogenesis. In this report we demonstrate for the first time that, when administered in combination, TGZ and ASA can produce a strong synergistic effect in growth inhibition and G 1 arrest in lung cancer CL1-0 and A549 cells. Examination by colony formation assay revealed an even more profound synergy. In Western blot, combined TGZ and ASA also could downregulate Cdk2, E2F-1, cyclin B1, cyclin D3 protein, and the ratio of phospho-Rb/Rb. Importantly, apoptosis was synergistically induced by the combination treatment, as evidenced by caspase-3 activation and PARP cleavage. The involvement of PI3K/Akt inhibition and p27 upregulation, as well as hypophosphorylation of Rac1 at ser71, were demonstrated. Taken together, these results suggest that clinically achievable concentrations of TGZ and ASA used in combination may produce a strong anticancer synergy that warrants further investigation for its clinical applications.
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