Synergistic down-regulation of telomerase by all-trans retinoic acid and antisense oligonucleotide in oral squamous cell carcinoma cell line (Tca8113).

Human telomerase, activated in about 90% of cancers, is mainly composed of hTR, hTERT and TP1. The exposed RNA template of hTR is an ideal target for antisense oligonucleotides (As-ODN); while recent findings indicate all-trans retinoid acid (ATRA) could effectively inhibit the expression of catalytic subunit-hTERT. The aim of this study was to investigate the effect of ATRA and As-ODN in oral squamous cell carcinoma and whether telomerase activity could be synergistically inhibited by them and thus therapeutically exploited in the future. As-ODN-hTR was transfected into human tongue squamous cell carcinoma cell line (Tca8113) with or without ATRA. Telomerase activity was examined by PCR-Elisa; viability was compared with growth curve; apoptotic rate was analyzed by Annexin V/PI double staining and hTERT expression was tested with western blot. Tca8113 cells displayed significant growth inhibition during the 9-day exposure to ATRA/As-ODN, especially to a combination of As-ODN-hTR and 5muM ATRA, correlating with the inhibition of telomerase expression. The relative telomerase activity was inhibited during treated with As-ODN-hTR alone, ATRA alone, or a combination of them. While without ATRA, the effect of As-ODN would disappear at 96h after transfection. As-ODN-hTR alone or combined with ATRA also significantly increase the apoptotic rate. Our findings provided direct evidence, in oral squamous cell carcinoma, As-ODN-hTR and ATRA could synergistically inhibit telomerase activity and telomerase protein in human tongue squamous cell carcinoma cells, which correlated with the induction of growth arrest.