In vitro growth inhibition by indomethacin on human oral squamous cell carcinoma lines synergistically suppressed by all-trans retinoic acid correlating to apoptosis

Abstract

Background: Indomethacin, an NSAID capable of inhibiting the effect of both cyclooxygenase and lipooxygenase, has been reported to repress the growth of breast cancer, skin cancer and head & neck cancer, etc. Inhibition in the some cell lines of oral squamous cell carcinoma (OSCC) has also been reported. The purpose of this study was primarily to explore the cellular response of human OSCC lines after indomethacin or retinoic acid (RA) treatment and its correlation to apoptosis phenomenon.

Methods: Five human OSCC cell lines--KB, SCC15, SCC25, OEC-M1 and OC2--were used for this in vitro study. By direct cell number counting, the cellular response was observed under incremental indomethacin concentrations of 50 microM, 100 microM, 200 microM and 400 microM, in order to select the most appropriate concentration for further study. Then 200 microM indomethacin and all-trans RA at 1 microM were used in the 2nd experiment to explore the intensity of their inhibitory effects individually and potential synergistic inhibition when exerted together. While in the 3rd part, TdT-mediated-dUTP nick-end labeling (TUNEL) method was used for in situ apoptosis assay to see if the apoptosis rate varied with these two agents.

Results: All 5 cell lines constantly showed growth suppression with positive dosage effect of indomethacin. Synergistic inhibition by combined treatment of indomethacin and RA was seen in RA responsive lines of SCC15 and SCC25, whereas other RA-resistant clones showed no synergism of this combined treatment. The in situ detection of apoptosis by TUNEL assay revealed a significantly higher ratio of apoptotic cells in the indomethacin/RA treated SCC15 and SCC25 than in controls.

Conclusions: The study provides the value of further exploration on the mechanism of how indomethacin inhibiting cancer cell growth and how RA-sensitive OSCC cell lines are synergistically suppressed by conjoint treatment of RA and indomethacin. This study also highlights the value to see how the apoptotic pathway responds differently to the indomethacin/RA treatment.