Assessment of azithromycin as an anticancer agent for treatment of imatinib sensitive and resistant CML cells

Abstract

Introduction: Chronic Myeloid Leukemia (CML) is a hematological disease which is characterized by the presence of BCR-ABL fusion protein. Imatinib (IMA), a tyrosine kinase inhibitor of BCR-ABL, is used as a frontline treatment.Although IMA aids in killing a majority of leukemia cells, it may not kill CML stem cells which are the primary roots of disease and therapy resistance. Recently, antimicrobial drugs have been gaining attention because of their selective targeting of cancer cells. Therefore, we now ask if combinational therapy of IMA with a targeted antimicrobial drug Azithromycin (AZT) can enhance the treatment efficiency in IMA resistant CML.

Methods: K562S (IMA sensitive) and K562R (IMA resistant) cells were treated with increasing concentrations of AZT to determine its effects on cell proliferation and apoptosis. Cell viability, apoptosis, caspase3/7 activity and P-glycoprotein (Pgp) function were investigated with spectrophotometric MTT assay and flow cytometric Annexin V staining, caspase 3/7 activity, and Rhodamine123 staining assays respectively. The expression levels of pro-apoptotic (BAX, BAD and BIM), anti- apoptotic (BCL-XL and BCL-2) and drug transporter (MDR-1 and MRP-1) genes were assessed with qRT-PCR.

Results: AZT treatment alone inhibited cell viability, induced apoptosis and enhanced caspase 3/7 activity in both K562S and high MDR-1 (Pgp) expressing K562R cells. Moreover, combination of AZT/IMA suppressed cell viability, induced apoptosis and caspase3/7 activity more effectively and significantly compared to K562R cells treated with only IMA or AZT. Furthermore, AZT and AZT/IMA combination decreased Pgp function in K562R cells in comparison with their controls. Based on qRT-PCR data, single AZT and combined AZT/IMA treatment also induced BAX/BCL-2 ratio significantly in both K562S and K562R cells.

Conclusion: Single AZT and AZT/IMA combinational treatment can be proposed as a promising and effective treatment strategy for CML. One of the mechanisms underlying the potent anticancer effect of combined AZT/IMA could be its ability to inhibit Pgp function and increase intracellular accumulation of IMA which leads to the induction of apoptosis in K562R cells.

Keywords: Apoptosis; Azithromycin; Chronic myeloid leukemia; Imatinib resistance.