Modelling ponatinib resistance in tyrosine kinase inhibitor-naïve and dasatinib resistant BCR-ABL1+ cell lines

TKI resistance remains a major impediment to successful treatment of CML.In this study, we investigated the emerging modes of ponatinib resistance in TKInaïve and dasatinib resistant BCR-ABL1+ cell lines. To investigate potential resistancemechanisms, ponatinib resistance was generated in BCR-ABL1+ cell-lines by longterm exposure to increasing concentrations of ponatinib. Two cell lines with priordasatinib resistance demonstrated BCR-ABL1 kinase domain (KD) mutation(s) uponexposure to ponatinib. In one of these cell lines the T315I mutation had emergedduring dasatinib exposure. When further cultured with ponatinib, the T315I mutationlevel and BCR-ABL1 mRNA expression level were increased. In the other cell line,compound mutations G250E/E255K developed with ponatinib exposure. In contrast,the ponatinib resistant cell lines that had no prior exposure to other TKIs (TKI-naïve)did not develop BCR-ABL1 KD mutations. Rather, both of these cell lines demonstratedBcr-Abl-independent resistance via Axl overexpression. Axl, a receptor tyrosine kinase,has previously been associated with imatinib and nilotinib resistance. Ponatinibsensitivity was restored following Axl inhibition or shRNA-mediated-knockdown ofAxl, suggesting that Axl was the primary driver of resistance and a potential targetfor therapy in this setting.