Doxycycline inhibits cell proliferation and invasive potential: combination therapy with cyclooxygenase-2 inhibitor in human colorectal cancer cells

Matrix metalloproteinases (MMPs) and cyclooxygenase (COX) enzymes play pivotal roles in the metastatic process of colorectal cancers. Inhibition of both MMPs and COX could be an attractive option for the inhibition of cell growth and invasion. Two human colorectal cancer cell lines, LS174T and HT29, were challenged with MMP inhibitor (doxycycline), selective COX-2 inhibitor (NS-398), or a combination of these agents to evaluate cancer cell proliferation and invasion. Dose-dependent growth inhibition was observed in both cell lines when they were treated with a single therapy. These effects were not related to MMP-2 or MMP-9 expression potential of the cell lines. Doxycycline (10 microg/mL) induced G(0)/G(1) arrest, and 20 microg/mL provoked annexin V positivity and up-regulated caspase-3 activity in HT29 cells. However, 20 microg/mL doxycycline caused no distinct apoptotic change in LS174T cells. Although MMP expression was not inhibited by 5 to 10 microg/mL doxycycline or 50 to 100 micromol/L NS-398, MMPs' activities were down-regulated by these concentrations. Cellular invasion was noticed in LS174T cells, but their capacity for invasion was diminished by these inhibitors. The antiproliferative and antiinvasive effects of the combination therapy were more pronounced. Doxycycline (5 microg/mL) with 50 micromol/L NS-398 inhibited cell proliferation and doxycycline (5 microg/mL) with 100 micromol/L NS-398 attenuated MMP expression and activity, as well as capacity for invasion, compared with single therapy. These data suggest that combination therapy consisting of an MMP inhibitor with a COX-2 inhibitor is an attractive approach to the treatment of colorectal cancers. The use of this treatment regimen for chemoprevention or treatment of colorectal cancers should be considered in future clinical trials.