ABSTRACT
A t(9;22) chromosomal translocation which forms the chimeric tyrosine kinase breakpoint cluster region (BCR)Abelson murine leukemia viral oncogene homolog 1 (ABL) is a key mechanism underlying the pathogenesis of chronic myelogenous leukemia (CML). Pharmacological inhibition of BCRABL with imatinib (Gleevec) has been reported as an effective targeted therapy; however, mutations (including the kinase domain of ABL) suppress the efficacy of inhibitors. PF114, a derivative of the third generation BCRABL inhibitor ponatinib, demonstrated a high inhibitory activity against wild-type and mutant BCRABL forms, such as the clinically important T315I. Furthermore, PF114 exhibited preferential kinase selectivity, safety, notable pharmacokinetic properties and therapeutic efficacy in a murine model. Investigation into the mechanisms of CML cell death revealed an exceptional potency of PF114 (at low nanomolar concentrations) for the CMLderived K562 cell line, whereas leukemia cell lines that lack the chimeric tyrosine kinase were markedly more refractory. The molecular ordering of events mechanistically associated with K562 cell death included the dephosphorylation of CrkL adaptor protein followed by inhibition of ERK1/2 and Akt, G1 arrest, a decrease of phosphorylated Bcl2associated death promoter, Bcl2like protein 11, BH3 interactingdomain death agonist, Bclextra large and Bcl2 family apoptosis regulator, and reduced mitochondrial transmembrane potential. Increased Annexin V reactivity, activation of caspases and poly(ADPribose)polymerase cleavage were proposed to lead to internucleosomal DNA fragmentation. Thus, PF114 may be a potent inducer of apoptosis in CML cells. Nevertheless, activation of STAT3 phosphorylation in response to PF114 may permit cell rescue; thus, a combination of BCRABL and STAT3 inhibitors should be considered for improved therapeutic outcome. Collectively, the targeted killing of BCRABLpositive cells, along with other beneficial properties, such as in vivo characteristics, suggests PF114 as a potential candidate for analysis in clinical trials with CML patients.