Neutrophil Extracellular Traps are Increased in Chronic Myeloid Leukemia and are Differentially Affected by Tyrosine Kinase Inhibitors

Cardiovascular (CVS) and thrombotic complications are increasingly reported with the use of the tyrosine kinase inhibitor (TKI) ponatinib, for the treatment of chronic myeloid leukemia (CML).

In response to various stimuli, neutrophils can expel neutrophil extracellular traps (NETs). These structures have the ability to ensnare microbes but are also implicated in the pathogenesis of thrombosis.

To study a possible association between NET formation and CVS and thrombotic complications in CML patients, we used treatment-naïve CML patient blood samples and prepared BCR-ABL1 retroviral transduced HoxB8-immortalized mouse hematopoietic progenitors which differentiate into neutrophils.

CML neutrophils revealed NETosis characteristic morphological features and displayed NETosis characteristic markers such as increased presence of DNA-associated neutrophil elastase, increased H3cit & PAD4 expression and elevated ROS generation compared to normal neutrophils.

Ponatinib treatment of CML neutrophils augmented DNA-associated neutrophil elastase and increased ROS levels compared to control and other TKI-treated neutrophils.

BCR-ABL1-transduced HoxB8 neutrophils also showed NET-characteristic nuclear morphology and increased H3cit & PAD4 expression compared to empty-vector transduced HoxB8 neutrophils. These were significantly reduced by Cl-amidine, a PAD4 inhibitor. As was seen with the CML patient`s neutrophils, ponatinib increased H3cit expression in BCR-ABL1-HoxB8- cells as well.

Our findings support the hypothesis that CML is associated with increased NET formation which is further augmented by ponatinib. Therefore the utility of NET related biomarkers for prediction of thrombosis in CML may be useful. Further studies are needed to assess the possible role of increased NET formation in CML in CVS associated with BCR-ABL1 and TKIs exposure.