BCR: a new target in resistance mediated by BCR/ABL-315I?

Targeting BCR/ABL with Tyrosine kinase inhibitors (TKIs) is a proven concept for the treatment of Philadelphia chromosome-positive (Ph+) leukemias. The most important mechanism of resistance against TKIs is the selection of leukemic clones driven by BCR/ABL harboring point mutations. The “gatekeeper”mutation T315I confers resistance against all approved TKIs, with the only exception of ponatinib, a multi-targeted kinase inhibitor. Besides resistance to TKIs, T315I also confers additional features to the leukemogenic potential of BCR/ABL, involving endogenous BCR. Therefore we studied the role of BCR for the effects of T315I on BCR/ABL mutants lacking functional domains indispensable for the oncogenic activity of BCR/ABL. As models we used the factor independent growth of murine myeloid progenitor 32D cells and the transformation of Rat-1 fibroblasts both mediated by BCR/ABL. Here we report that T315I restores the capacity to mediate factor-independent growth and transformation potential of loss-of-function mutants of BCR/ABL. Targeting endogenous Bcr abrogated the capacity of oligomerization deficient mutant of BCR/ ABL-T315I to mediate factor independent growth of 32D cells and strongly reduced their transformation potential in Rat-1 cells, as well as led to the up-regulation of mitogen activated protein kinase (MAPK) pathway. Our data show that the T315I restores the capacity of loss-of-function mutants to transform cells which is dependent on the transphosphorylation of endogenous Bcr, which becomes a putative therapeutic target to overcome resistance by T315I

BCR: a new target in resistance mediated by BCR/ABL-315I?

Targeting BCR/ABL with Tyrosine kinase inhibitors (TKIs) is a proven concept for the treatment of Philadelphia chromosome-positive (Ph+) leukemias. The most important mechanism of resistance against TKIs is the selection of leukemic clones driven by BCR/ABL harboring point mutations. The “gatekeeper”mutation T315I confers resistance against all approved TKIs, with the only exception of ponatinib, a multi-targeted kinase inhibitor. Besides resistance to TKIs, T315I also confers additional features to the leukemogenic potential of BCR/ABL, involving endogenous BCR. Therefore we studied the role of BCR for the effects of T315I on BCR/ABL mutants lacking functional domains indispensable for the oncogenic activity of BCR/ABL. As models we used the factor independent growth of murine myeloid progenitor 32D cells and the transformation of Rat-1 fibroblasts both mediated by BCR/ABL. Here we report that T315I restores the capacity to mediate factor-independent growth and transformation potential of loss-of-function mutants of BCR/ABL. Targeting endogenous Bcr abrogated the capacity of oligomerization deficient mutant of BCR/ ABL-T315I to mediate factor independent growth of 32D cells and strongly reduced their transformation potential in Rat-1 cells, as well as led to the up-regulation of mitogen activated protein kinase (MAPK) pathway. Our data show that the T315I restores the capacity of loss-of-function mutants to transform cells which is dependent on the transphosphorylation of endogenous Bcr, which becomes a putative therapeutic target to overcome resistance by T315I

Crizotinib acts as ABL1 inhibitor combining ATP-binding with allosteric inhibition and is active against native BCR-ABL1 and its resistance and compound mutants BCR-ABL1 T315I and BCR-ABL1 T315I-E255K

Resistance remains the major clinical challenge for the therapy of Philadelphia chromosome-positive (Ph+) leukemia. With the exception of ponatinib, all approved tyrosine kinase inhibitors (TKIs) are unable to inhibit the common gatekeeper mutation T315I. Here we investigated the therapeutic potential of crizotinib, a TKI approved for targeting ALK and ROS1 in non-small cell lung cancer patients, which inhibited also the ABL1 kinase in cell-free systems, for the treatment of advanced and therapy-resistant Ph+ leukemia. By inhibiting the BCR-ABL1 kinase, crizotinib efficiently suppressed growth of Ph+ cells without affecting growth of Ph- cells. It was also active in Ph+ patient-derived long-term cultures (PD-LTCs) independently of the responsiveness/resistance to other TKIs. The efficacy of crizotinib was confirmed in vivo in syngeneic mouse models of BCR-ABL1- or BCR-ABL1T315I-driven chronic myeloid leukemia-like disease and in BCR-ABL1-driven acute lymphoblastic leukemia (ALL). Although crizotinib binds to the ATP-binding site, it also allosterically affected the myristol binding pocket, the binding site of GNF2 and asciminib (former ABL001). Therefore, crizotinib has a seemingly unique double mechanism of action, on the ATP-binding site and on the myristoylation binding pocket. These findings strongly suggest the clinical evaluation of crizotinib for the treatment of advanced and therapy-resistant Ph+ leukemia