Chronic Myeloid Leukemia (CML) is characterized by increased and unregulated growth of myeloid cells in the bone marrow and accumulation of these cells in the blood. Most CML is caused by a chromosomal abnormality that results in a fusion between Abl tyrosine kinase and BCR gene on chromosome 2, which results in a constitutively active tyrosine kinase. Most CMLs are treated with tyrosine kinase inhibitors (TKI) such as imatinib. Some forms of CML, however, are resistant to TKI treatment and proceed independent of BCR-Abl1 activity. A recent colloborative study utilizing Cellecta’s unique platform in paired imatinib-resistant and imatininb-sensitive K-562 CML cell lines to identify other genes whose knockdown might play a role in the survival of the imatinib-resistant cells. This loss–of-function shRNA library screen identified RAN and XPO1, which are components of the nucleocytoplasmic transport complex.
When these genes were knocked down and the cells were treated with imatinib, the cells were more sensitive to imatinib. The shRNA screen also identified other pathways that are involved in TKI resistance, including ubiquitination and proteasomal protein degradation, chromatin remodeling, apoptosis, DNA repair and cell cycle regulation, apoptosis, and antioxidation. These other pathways have yet to be experimentally validated. This study shows that loss-of-function screens are a useful procedure for finding alternative mechanisms of drug resistance in CML. More information on use of RNAi screens in uncovering drug resistance mechanism is available in this review by Diehl et al.
The figure below shows the mechanisms of oncogene-kinase-independent resistance to TKI therapy in CML. (From Rassool and Perrotti, Blood, (2015) Vol 125:1686-1688.)
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