Synergistic effect of all-trans-retinoic acid and arsenic trioxide on growth inhibition and apoptosis in human hepatoma, breast cancer, and lung cancer cellsin vitro

AIM: To investigate the effect of all-trans-retinoic acid (ATRA) on arsenic trioxide (As(2)O(3))-induced apoptosis of human hepatoma, breast cancer, and lung cancer cells in an attempt to find a better combination therapy for solid tumors. METHODS: Human hepatoma cell lines HepG2, Hep3B, human breast cancer cell line MCF-7, and human lung adenocarcinoma cell line AGZY-83-a were treated with As(2)O(3) together with ATRA. Cell survival fraction was determined by MTT assay, cell viability and apoptosis were measured by annexin V-fluorescein isothiocyanate (FITC) and PI staining, and intracellular glutathione (GSH) and glutathione-S-transferase (GST) activities were determined using commercial kits. RESULTS: Cytotoxicity of ATRA was low. ATRA (0.1, 1, and 10 micromol/L) could synergistically potentiate As(2)O(3) to exert a dose-dependent inhibition of growth and to induce apoptosis in each of the cell lines. HepG2 and Hep3B with low intracellular GSH or GST activities were remarkably sensitive to As(2)O(3) or As(2)O(3)+ATRA, while AGZY-83-a with higher GSH or GST activities was less sensitive to As(2)O(3) or As(2)O(3)+ATRA. Treatment with 2 micromol/L As(2)O(3) for 72 h significantly decreased intracellular GSH and GST levels in each of the cell lines, and 1 micromol/L ATRA alone reduced minimal intracellular GSH and GST levels. ATRA potentiated the effect of As(2)O(3) on intracellular GSH levels, but intracellular GST levels were not significantly affected by the combination of As(2)O(3) and ATRA for 72 h as compared to As(2)O(3) alone. CONCLUSION: ATRA can strongly potentiate As(2)O(3)-induced growth-inhibition and apoptosis in each of the cell lines, and two drugs can produce a significant synergic effect. The sensitivity to As(2)O(3) or As(2)O(3)+ATRA is inversely proportional to intracellular GSH or GST levels in each of the cell lines. The GSH redox system may be the possible mechanism by which ATRA synergistically potentiates As(2)O(3) to exert a dose-dependent inhibition of growth and to induce apoptosis.