Retinoic acid receptor-ß gene reexpression and biological activity in SHI-1 cells after combined treatment with 5-aza-2'-deoxycytidine and all-trans retinoic acid.

ABSTRACT

BACKGROUND: This study was conducted to determine the antineoplastic activities of 5-aza-2'-deoxycytidine (decitabine; DAC) and all-trans retinoic acid (ATRA), administered either alone or in combination, on in vitro cultured SHI-1 cells as well as their effects on the expression of the tumor suppressor gene p16(INK4a) (p16) and the retinoic acid receptor (RAR)-ß. METHODS: Cell growth inhibition, differentiation and apoptosis were determined in SHI-1 cells treated with DAC and/or ATRA, and the combination index of the two compounds was calculated. Methylation of the p16 and RAR-ß genes in SHI-1 cells was detected by methylation-specific polymerase chain reaction (PCR). Real-time quantitative reverse transcriptase PCR was used to detect mRNA expression of the p16 and RAR-ß genes, and Western blot analysis was performed for protein expression. RESULTS: The drug combination had a synergistic effect on growth inhibition, differentiation and apoptosis of SHI-1 cells, and the effects of DAC and ATRA were dependent on time. DAC, either alone or in combination with ATRA, induced demethylation of the genes p16 and RAR-ß, whereas ATRA alone had no effect on methylation. The RAR-ß gene was reexpressed following DAC-ATRA combination treatment, and both agents had no effect on p16 expression. CONCLUSION: The results revealed that DAC used in combination with ATRA has significant clinical potential in the treatment of acute monocytic leukemia.