Objective: To study the inhibitory effects of ciglitazone, a synthetic ligand of peroxisome proliferator-activated receptors (PPAR), on human lung cancer growth in vitro and in vivo and its mechanisms.
Methods: Human lung cancer A549 cells cultured in vitro were treated with different concentrations of ciglitazone. The proliferative activity and cell cycle of A549 cells were determined by MTT assay and flow cytometry. Expression of PPARgamma protein was detected by Western blot. A549 cells (1 x 10(6) cells/nude mouse) were inoculated subcutaneously into nude mice, which were randomly divided into two groups, 10 in each: control group (group A) and ciglitazone treated group (group B). When the tumors grew to a size with diameter around 1 cm, ciglitazone 100 microl (100 micromol/L) was intratumorally injected every other day in group B mice. A total of 15 injections were given. Mice in group A were similarly treated with normal saline. One month later, tumors were excised and weighed. Expression of cyclin D1 and p21 protein were detected by immunohistochemistry and Western blot.
Results: Growth of A549 cells was significantly inhibited in group B in a dose-dependent and time-dependent fashion as compared with that in group A. Most of the ciglitazone-treated cells arrested in G(1)/G(0) phase and the expression of PPARgamma protein was markedly up-regulated. The tumor weights in group A was (2.79 +/- 0.33) g and that in group B was (1.51 +/- 0.40) g, with an inhibition rate of 47.0%. The expression level of cyclin D1 in group A was significantly higher than that in group B, while the expression level of p21 protein in group A was significantly lower than that in group B.
Conclusion: Ciglitazone can effectively inhibit the growth of human lung cancer A549 and induce its differentiation by cell cycle arrest via PPARgamma activation.