항암제 내성 백혈병 및 폐암 세포주에서 방사선에 대한 교차내성 기전의 규명

Abstract

This study was attempted to explore the cross resistance of chemoresistant cancer cells to radiation and its resistance mechanisms. Cytotoxicity and mRNA expression were determined by MTT assay and cDNA microarray and/or RT-PCR method, respectively. Two doxorubicin -resistant cells, AML-2/DX100 and SK-MES-1/DX1000, and a paclitaxel-resistant cell, SK-MES-1/PT4000, showed the multidrug resistance phenotypes by overexpressing multidrug resistant associated protein (MRP) in AML-2/DX100 and P-glycoprotein in other cells. Three resistant cells showed cross resistance to radiation. The radioresistance of AML-2/DX100 were not influenced by an MRP inhibitor (probenecid), Pgp inhibitor (PSC833), an inhibitor of metallothionein sythesis (propargylglycine), an inhibitor of glutathione S-transferase (buthionine sulfoxamine) and adhesion with fibronectin. AML-2/DX100 cells showed increased defense mechanisms against endogenous reactive oxygen species (ROS) even though they are supersensitive to exogenous hydrogen peroxide when compared to AML-2/WT, suggesting that an anti-oxidant adaptation against ROS occurred. cDNA microarrays for 8000 human genes revealed that among 21 anti-oxidant genes, each four gene was up- and down-regulated more than 1.5-fold in AML-2/DX100 as compared to AML-2/WT. The mRNA expression of glutathione S -transferase Pi, peroxiredoxin 2, thioredoxin 2, and glutaredoxin was elevated whereas that of peroxiredoxin 3, metallothionein-1F, superoxide dismutase 2, and thioredoxin reductase 1 was depressed. Radiation increased bax but not bcl-2 translocation into the mitochondria of AML-2/WT cells, thereby induced cytochrome c release from the mitochondria and consequently caspase 3 activation whereas it increased more bcl-2 but not bax translocation into the mitochondria of AML-2/DX100 cells than those of AML-2/WT cells. Interestingly, AML-2 /DX100 cells showed higher expression of melanoma antigens (MAGEA2, MAGEA4, MAGEB2 and MAGEA6) than that of AML-2/DX100 cells. The SK-MES-1/Rad cells that have been repeatedly irradiated for 6 months did not show radioresistance but chemosensitivity. Overall, it appears that the radioresistance mechanisms of AML-2 /DX100 cells may have nothing to do with MRP, P-glycoprotein, metallothionein and glutathione S-transferase but something to do with altered mitochondrial translocation of Bax and up-regulation of MAGE expression. It is thought that radiotherapy if possible should be done before chemotherapy.