ABSTRACT
In this study, we have tried to find new targets and effective drugs for imatinib-resistant chronic myelogenous leukemia (CML) cells displaying loss of Bcr-Abl kinase target dependence. The imatinib-resistant K562/R1, -R2 and -R3 cells showed profound declines of Bcr-Abl level and concurrently exhibited up-regulation of Bcl-2 and Ku70/80, and down-regulation of Bax, DNA-PKcs and BRCA1, suggesting that loss of Bcr-Abl after exposure to imatinib might be accompanied by other cell survival mechanism. K562/R3 cells were more sensitive to camptothecin (CPT)- and radiation-induced apoptosis than K562 cells, indicating hypersensitivity of imatinib-resistant cells to DNA damaging agents. Moreover, when K562 cells were treated with the combination of imatinib with CPT, the level of Bax and the cleavage of PARP-1 and DNA-PK were significantly increased in comparison with the effects of each drug. Therefore, our study suggests that CPT can be used to treat CML with loss of Bcr-Abl expression.
Subject(s)
Antineoplastic Agents/pharmacology , Camptothecin/pharmacology , Drug Resistance, Neoplasm/drug effects , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism , Piperazines/pharmacology , Protein-Tyrosine Kinases/antagonists & inhibitors , Pyrimidines/pharmacology , Antigens, Nuclear/metabolism , BRCA1 Protein/antagonists & inhibitors , Benzamides , Cell Line, Tumor , DNA Repair Enzymes/metabolism , DNA-Activated Protein Kinase/antagonists & inhibitors , DNA-Activated Protein Kinase/metabolism , DNA-Binding Proteins/metabolism , Drug Synergism , Fusion Proteins, bcr-abl , Humans , Imatinib Mesylate , Ku Autoantigen , Nuclear Proteins/antagonists & inhibitors , Nuclear Proteins/metabolism , Poly (ADP-Ribose) Polymerase-1 , Poly(ADP-ribose) Polymerase Inhibitors , Poly(ADP-ribose) Polymerases/metabolism , Proto-Oncogene Proteins c-bcl-2 , Radiation Tolerance , bcl-2-Associated X Protein/antagonists & inhibitors , bcl-2-Associated X Protein/metabolismABSTRACT
The failure to treat metastatic cancer with multidrug resistance is a major problem for successful cancer therapy, and the molecular basis for the association of metastatic phenotype with resistance to therapy is still unclear. In this study, we revealed that various metastatic cancer cells showed consistently higher levels of antiapoptotic proteins, including Bcl-2, nuclear factor-kappaB, MDM2, DNA-dependent protein kinase (DNA-PK), and epidermal growth factor receptor (EGFR), and lower levels of proapoptotic proteins, including Bax and p53 than low metastatic parental cells. This was followed by chemo- and radioresistance in metastatic cancer cells compared with their parental cells. EGFR and DNA-PK activity, which are known to be associated with chemo- and radioresistance, were demonstrated to be mutually regulated by each other. Treatment with PKI166, an EGFR inhibitor, suppressed etoposide-induced activation of DNA-PK in A375SM metastatic melanoma cells. In addition, PKI166 enhanced markedly the chemosensitivities of metastatic cancer cell sublines to various anticancer drugs in comparison with those of low metastatic cancer cells. These results suggest that the activities of DNA-PK and EGFR, which is positively correlated with each other, may contribute to metastatic phenotype as well as therapy resistance, and the EGFR inhibitor enhances the effect of anticancer drugs against therapy-resistant metastatic cancer cells via suppression of stress responses, including activation of DNA-PK.