Epigenetics in etoposide-resistant tumor cells

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 13670848
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Pediatrics
• Research Institution: Nippon Medical School
• Principal Investigator: ASANO Takeshi Nippon Medical School, Assis Prof, 医学部, 助教授 (70277490)
• Project Period (FY): 2001 – 2003
• Keywords: Topoisomerase / drug resistance / epigenetic / etoposide

Research Abstract

K562/MX2 cells were more resistant to MX2 than the parent cells, also showed cross-resistance to etoposide, and doxorubicin. P-glycoprotein expression was identical to K562/P and K562/MX2. MRP1 expression in K562/MX2 is slightly higher than in K562/P. Accumulation of MX2 was slightly lower than in K562/P. Topoisomerase (Topo) IIα protein in K562/MX2 cells were lower of those in K562/P cells by immunoblot analysis as well as decreased expression of the Topo IIα mRNA in K562/MX2 cells. Topo II catalytic activity was also reduced in the nuclear extract from K562/MX2 cells compared with K562/P cells. Increased methylated CpG of Topo IIα gene was observed in K562/MX2 cells compared to parent line by bisulfite modified sequence and methylation specific restriction enzyme analysis. To overcome the drug resistance to MX2, and etoposide, we examined 5-Aza-2'-deoxycytidine(5AZ), which is a demethylating agent, treatment in K562/MX2 cells. 5AZ treatment increased Topo IIα mRNA expression in K562/MX2 cells, but not in K562/P cells, as well as increased cytotoxicity against MX2 and etoposide. The methylated CpG was decreased in K562/MX2 cells after 5AZ treatment. We concluded that the mechanism of drug resistance to MX2 as well as etoposide in K562/MX2 cells might contribute to decreased expression of Topo IIα gene with increased methylation of the gene and 5AZ treatment could be a novel treatment in etoposide resistant cell line, K562/MX2.