Quercetin suppresses the metastatic ability of lung cancer through inhibiting Snail-dependent Akt activation and Snail-independent ADAM9 expression pathways

Metastasis is the major cause of death from lung cancer. Quercetin, a widely distributed bioflavonoid, is well known to induce growth inhibition in a variety of human cancer cells, but how it affects lung cancer cell invasion and metastasis is unclear. Herein, we found that quercetin inhibited the migration/invasion of non-small cell lung cancer (NSCLC) cell lines and bone metastasis in an orthotopic A549 xenograft model by suppressing the Snail-mediated epithelial-to-mesenchymal transition (EMT). Moreover, survival times of animals were also prolonged after quercetin treatment. Mechanistic investigations found that quercetin suppressed Snail-dependent Akt activation by upregulating maspin and Snail-independent a disintegrin and metalloproteinase (ADAM) 9 expression pathways to modulate the invasive ability of NSCLC cells. In clinical samples, we observed that patients with Snail^high/p-Akt^high tumors had the shortest survival times. In addition, a lower survival rate was also found in ADAM9^high patients than in ADAM9^low patients. Overall, our results provide new insights into the role of quercetin-induced molecular regulation in suppressing NSCLC metastasis and suggest that quercetin has potential therapeutic applications for metastatic NSCLC.