DNA damage response in imatinib resistant chronic myeloid leukemia K562 cells

Abstract

Resistance to imatinib in patients with chronic myeloid leukemia can lead to advanced disease and blast crisis. Conventional chemotherapy with DNA damaging agents is then used, alone or in combination with other tyrosine kinase inhibitors (TKIs). Our aim was to assess whether imatinib resistant K562 cells were also resistant to DNA damaging agents. After treatment with H₂O₂ and doxorubicin, but not camptothecin, cell survival was higher in imatinib resistant cells compared to parental cells. DNA damage, measured by comet and γ-H2AX assays, was lower in imatinib resistant cells. mRNA expression levels of 50 genes of the DNA damage response pathway showed increased expression of the base excision repair (BER) genes MBD4 and NTHL1. Knockdown of MBD4 and NTHL1 expression in resistant cells using siRNA decreased cell survival after treatment with H₂O₂ and doxorubicin. Our results indicate that imatinib resistant cells display cross-resistance to oxidative agents, partly through up-regulation of BER genes. Expression of these genes in imatinib resistant patients was not significantly different compared to sensitive patients. However, the strategy followed in this study could help identify chemotherapeutic agents that are more effective as alternative agents in cases of resistance to TKIs.

Keywords::

• Chronic myeloid leukemia
• resistance to imatinib
• genotoxicity
• DNA repair
• oxidative damage

Acknowledgements

This work had the financial support of Fundação para a Ciência e a Tecnologia through project PTDC/SAU-GMG/71720/2006 and through grant SFRH/BPD/39046/2007 and Programa Ciência 2008 to M.G.

Potential conflict of interest:

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