| Multidrug resistance ( MDR) is characterized by cross-resistance to a variety of drugs with different structure and function. Despite improvement in chemotherapy strategies, the development of MDR remains the major problem in chemotherapy to cure acute leukemia. MDR is mainly associated with the overexpres-sion of P-glycoprotein. Furthermore, the topoisomerase II , glutathione S-trans-ferase,bcl-2 and DNA repair mechanism may also play an important role in MDR.DNA topoisomerases are essential nuclear enzymes that regulate DNA topology. These enzymes are crucial for cellular genetic process such as DNA replication , transcription and recombination. There are two isoenzymes of Topo II , Topo Ⅱ α and Topo Ⅱ $. Topo Ⅱ α is the primary target for several cytostatic drugs, such as anthracyclines, epipodophyllotoxins and amsacrine. These drugs convert the reversible double-strand break into an irreversible one and eventually lead to apoptosis. It has been shown that low levels of Topo Ⅱ α lead to drug resistance. In response to the threat of DNA double strand breaks ( DSBs) , cells have evolved pathway for repairing DSBs. DNA-dependent protein kinase (DNA-PK) is activated by DSBs and participates in DNA repair. It consists of regulatory subunit, Ku autoantigen and catalytic subunit ( DNA-PKcs). It has been shown that defects in DNA-PK subunits result in a reduced capacity to repair DNA DSBs and consequently hypersensitivity to radiation and anticancer drugs. On the contrary, an enhanced expression of DNA-PK participates in the development of drug resistance.The aim of this study is to investigate the expression of Topo Ⅱ α and DNA-PKcs in acute leukemia patients and their correlation with clinical drug resistance. The results showed that the lower expression of Topo Ⅱ α and the higherexpression of DNA-PKcs had closely relation with clinical drug resistance.Materials and methods62 acute leukemia patients were classified according to FAB-types, 45 cases of AML (M1 case, M 5 cases, M27 cases, M36 cases, M45 cases, M516 cases, M6 3 cases, M7 2 cases) , 17 cases of ALL (L12 cases, L2 14 cases, L3 1 case). The median age of the patients was 39 years.Bone marrow samples were collected in heparinized tubes. Mononuclear cells were isolated by Ficoll Hypaque density gradient centrifugation. The expression of Topo II a and DNA-PKcs were measured by SP immunohistochemistry method. PBS substitute for primary antibodies were used as negative controls. MCF-7 and U937 cell lines were used as positive controls of Topo and DNA-PKcs , respectively. Positive expression cases were defined as at least 15% of the leukemia cells were positively stained.Statistical methods x test, Fisher' s exact test and Spearman rank correlation test were used.ResultsThe expression rates of Topo II a and DNA-PKcs in 62 acute leukemia patients were 50% and 37. 1% , in control group were 10% and 30% ,respective-ly. The expression rate of Topo in the treatment resistant group (33. 3% ) was significantly lower than that in the sensitive group (69% ) ( P <0.01). The expression rate of DNA-PKcs in the treatment resistant group (51.5%) was significantly higher than that in the sensitive group (20.7% ) (P <0.05).In the positive expression cases of Topo , the drug resistance rate in the DNA-PKcs positive expression group (61. 5%) was significandy higher than that in DNA-PKcs negative expression group (16.7%)(P<0.05). In the negative expression cases of DNA-PKcs, the drug resistance rate in the Topo negative expression group (61.9% ) was significandy higher than that in Topo positive expression group ( 16. 7% ) ( P <0.01). The lowest drug resistancerate was in the group of Topo Ⅱα positive expression and DNA-PKcs negativeexpression (16.7%) . The highest drug resistance rate was in the group of TopoⅡα negative expression and DNA-PKcs positive expression (90%) ( P <0.001) . There was no correlation between Topo Ⅱ α and DNA-PKcs expression.ConclusionThe lower expression of Topo Ⅱ α and t...
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