BACKGROUNDTo study the proliferation inhibition and anti-invasion of retinoic acid (RA) and 18β-glycyrrhetinic acid (GA) in highly metastasized lung cancer cell line (PGCL3), and to observe the combined effects of RA and GA.

METHODSThe proliferation inhibitive rate, the colony-formation rate in semi-solid agar, the invasive ability to reconstituted basement membrane, the chemotatic migration ability, the laminin adhesion ability, and the activity of cathepsin B (CB) were tested.

RESULTSTreated with RA and GA, the proliferation of PGCL3 cells were inhibited obviously, and the inhibition degree was related to the dosage of the drugs. IC₅₀ of the proliferation inhibition were 12.58 μmol/L and 145.3 μmol/L respectively. Treated with 5.0 μmol/L RA, 25 μmol/L and 50 μmol/L GA, the invasive ability was decreased significantly (P < 0.01 and P < 0.001), and the inhibition was in a dose dependent manner. In combined treatment with 5.0 μmol/L RA and 25 μmol/L GA, the inhibition of invasion was greater than the sum of them used alone. Treated with GA of above concentrations and 10 μmol/L RA, the adhesion and migration ability and the secretion of CB of the PGCL3 cells were decreased significantly (P < 0.001). Treated with GA of above concentation, the colony formation rate in semi-solid agar was decreased significantly (P < 0.001)..

CONCLUSIONSRA and GA can inhibit the proliferation and invasion of the PGCL3 human lung cancer cells and have the anti-invasion synergism. The mechanism of anti-invasion of RA and GA is to inhibit many points of invasive process.