Multidomain Targeting of Bcr-Abl by Disruption of Oligomerization and Tyrosine Kinase Inhibition: Toward Eradication of CML

The oncoprotein Bcr-Abl, the causative agent of chronic myeloid leukemia (CML), requires homo-oligomerization via a coiled-coil domain to function [Bartram, C. R.; et al. Nature 1983, 306 (5940), 277–280; and Zhao, X.; et al. Nat. Struct. Biol. 2002, 9(2), 117–120]. While tyrosine kinase inhibitors (TKIs) have shown great efficacy as treatment options for CML, their use may cause an acquisition of mutations in the tyrosine kinase domain, which prevent TKI binding and lead to a loss in activity [Woessner, D. W.; et al. Cancer J. 2011, 17(6), 477–486]. Previously, we have shown that a rationally modified coiled-coil domain (CCmut3) can disrupt this oligomerization, inhibit proliferation, and induce apoptosis in CML cells [Dixon, A. S.; et al. Mol. Pharmaceutics 2012, 9(1), 187–195]. Here, we show that using the most recently approved TKI, ponatinib (Iclusig), in combination with CCmut3 allows a dose reduction of ponatinib and increased therapeutic efficacy in vitro measured by reduction in kinase activity, induction of apoptosis via caspase-3/7 and 7-AAD/Annexin V assays, and reduced transformative ability measured by a colony forming assay. The combination was effective not only in cells containing wild-type Bcr-Abl (K562, Ba/F3-p210) but also cells with Bcr-Abl containing the T315I mutation (Ba/F3-p210-T315I). In addition, we report for the first time the ability of CCmut3 alone to inhibit the T315I mutant form of Bcr-Abl. This novel combination may prove to be more potent than single agent therapies and should be further explored for clinical use.