Frequent methylation of RASSF1A in synovial sarcoma and the anti-tumor effects of 5-aza-2'-deoxycytidine against synovial sarcoma cell lines

In this study, the methylation status of RASSF1A in synovial sarcomas and the effect of de-methylation on synovial sarcoma were examined. The methylation status in 74 soft tissue sarcomas (STSs) including 21 synovial sarcomas was determined by methylation specific PCR. The effect of the de-methylating agent 5-aza-2'-deoxycytidine (5-Aza-dC) on synovial sarcoma was examined using synovial sarcoma cell lines (SYO-1 and HS-SY-II). RASSF1A methylation was observed in 10 (47.6%) of 21 synovial sarcomas and in 10 (18.9%) of 53 the other STSs (P = 0.0295). De-methylation of the cells by treatment with 5-Aza-dC induced re-expression of RASSF1A and growth suppression of the cells. The calculated IC50 of 5-Aza-dC against the SYO-1 and the HS-SY-II cells were 0.9 and 1.3 mu M (96 h), respectively. With twice weekly administration of 1 or 10 mg/kg 5-Aza-dC, the growth of the mouse xenograft tumors of SYO-1 was significantly suppressed in comparison to the controls (P < 0.01). This is the first report showing the anti-tumor effect of 5-Aza-dC on synovial sarcoma. 5-Aza-dC is suggested to have a good therapeutic potential against synovial sarcoma.