Implication of NAG-1 in synergistic induction of apoptosis by combined treatment of sodium salicylate and PI3K/MEK1/2 inhibitors in A549 human lung adenocarcinoma cells.

Aspirin is used as chemopreventive agents in a variety of human cancer cells including those of colon, lung, breast, and leukemia. Sodium salicylate (NaSal, the natural deacetylated form of aspirin) induced cell cycle arrest and apoptosis in a dose-dependent manner in A549 cells; high dose (20mM) of NaSal-induced apoptosis, whereas low dose (2-10mM) induced cell cycle arrest. We found that NaSal-activated Akt/PKB, ERK1/2, and p38MAPK signal cascades. Twenty micromolar of NaSal-induced apoptotic response of A549 cells was enhanced by the PI3K inhibitors (LY294002 and wortmannin) and in a less extent by the MEK1/2 inhibitors (U0126 and PD98059), whereas it was suppressed by the p38MAPK inhibitor (SB203580). Furthermore, simultaneous inhibition of the Akt/PKB and ERK1/2 signal cascades could lower the dose of NaSal to induce apoptosis to 2mM in A549 lung cancer cells. Similar enhancement was observed in cells treated with 2mM NaSal and 100muM genistein, an inhibitor of receptor tyrosine kinases (RTKs) that are upstream of PI3K and MEK1/2 signaling. We further demonstrated that NAG-1 plays a key role in apoptosis by NaSal-based combined treatment. Collectively, our findings indicate that inhibition of the pro-survival Akt/PKB and ERK1/2 signaling may increase the chemopreventive effects of NaSal and combined treatment of two natural compounds (NaSal and genistein) results in a highly synergistic induction of apoptosis, thereby increasing the chemopreventive effects of NaSal against cancer.