mTOR Signaling is Involved in Indomethacin and Nimesulide Suppression of Colorectal Cancer Cell Growth via a COX-2 Independent Pathway

Inhibition of mammalian target of rapamycin (mTOR) represents an attractive target for anticancer therapy, but its role in suppression of colorectal cancer (CRC) cell growth by cyclooxygenase-2 (COX-2) inhibitors is unclear. Here, we analyzed the effect of indomethacin (Indo, a nonselective COX-2 inhibitor) and nimesulide (Nim, a selective COX-2 inhibitor) on mTOR signaling in CRC cells in vitro and in vivo to determine the dependence of this effect on COX-2. Human CRC cell lines with varying COX-2 expression levels were treated with Indo and Nim. Western blot test was performed to detect mTOR-related components (mTOR, p70s6 K, and 4EBP1), and cell viability, cell cycle, and apoptosis were assessed. HCT116 and SW1116 cells were injected into athymic nude mice to establish a CRC xenograft model. After treatment with Nim, tumor volume, mTOR signaling, and apoptosis were evaluated in this model. HT29 and SW1116 cells were also treated with Nim after transfection with COX-2-specific small interfering RNA (siRNA) to assess dependence of COX-2 on mTOR signaling under drug treatment. Both Indo and Nim reduced mTOR signaling activity in CRC cells that differ in their COX-2 expression in vitro and in vivo. Additionally, Indo and Nim could reduce the mTOR signaling activity after COX-2 silencing in CRC cells. mTOR signaling is involved in Indo- and Nim-mediated suppression of CRC growth via a COX-2 independent pathway. This study unveils a novel mechanism through which COX-2 inhibitors exerts their anticancer effects and further emphasizes targeting mTOR signaling in anticancer therapy.