Chronic myeloid leukemia (CML) is effectively treated with imatinib. However, reactivation of Bcr-Abl via kinase domain mutations that reduce sensitivity to imatinib can cause relapse. As combination therapy is frequently used to prevent emergence of resistance, the combination of imatinib with an inhibitor of imatinib-resistant Bcr-Abl mutants (e.g., Src/Abl inhibitors AP23848 and BMS-354825) was investigated. To test this approach, cellular proliferation and Bcr-Abl tyrosine phosphorylation assays were done on Ba/F3 cells expressing wild-type (WT) Bcr-Abl and four common imatinib-resistant mutants (Y253F, E255K, T315I, and M351T). Colony-forming assays with primary CML cells were also done. Both Src/Abl inhibitors retained full inhibitory capacity when coadministered with imatinib at concentrations above typical clinical levels. For cells expressing WT Bcr-Abl or the marginally imatinib-resistant mutant M351T, inclusion of imatinib at therapeutic levels enhanced the effects of the Src/Abl inhibitors. By comparison, for the highly imatinib-resistant mutants Y253F and E255K, inclusion of imatinib at clinical levels resulted in only a slight enhancement beyond the effects of the Src/Abl inhibitors. None of the inhibitors affected Bcr-Abl T315I cells. Colony-forming assays with primary CML cells yielded analogous results. Our results indicate that Src/Abl inhibitors are compatible with imatinib and suggest that combined Abl inhibitor therapy is a feasible treatment strategy for patients with CML.
Combined Abl inhibitor therapy for minimizing drug resistance in chronic myeloid leukemia: Src/Abl inhibitors are compatible with imatinib.
Clinical cancer research : an official journal of the American Association for Cancer Research, Oct 2005
The deregulated, oncogenic tyrosine kinase Bcr-Abl causes chronic myeloid leukemia (CML). Imatinib mesylate (Gleevec, STI571), a Bcr-Abl kinase inhibitor, selectively inhibits proliferation and promotes apoptosis of CML cells. Despite the success of imatinib mesylate in the treatment of CML, resistance is observed, particularly in advanced disease. The most common imatinib mesylate resistance mechanism involves Bcr-Abl kinase domain mutations that impart varying degrees of drug insensitivity. AP23464, a potent adenosine 5'-triphosphate (ATP)-based inhibitor of Src and Abl kinases, displays antiproliferative activity against a human CML cell line and Bcr-Abl-transduced Ba/F3 cells (IC(50) = 14 nM; imatinib mesylate IC(50) = 350 nM). AP23464 ablates Bcr-Abl tyrosine phosphorylation, blocks cell cycle progression, and promotes apoptosis of Bcr-Abl-expressing cells. Biochemical assays with purified glutathione S transferase (GST)-Abl kinase domain confirmed that AP23464 directly inhibits Abl activity. Importantly, the low nanomolar cellular and biochemical inhibitory properties of AP23464 extend to frequently observed imatinib mesylate-resistant Bcr-Abl mutants, including nucleotide binding P-loop mutants Q252H, Y253F, E255K, C-terminal loop mutant M351T, and activation loop mutant H396P. AP23464 was ineffective against mutant T315I, an imatinib mesylate contact residue. The potency of AP23464 against imatinib mesylate-refractory Bcr-Abl and its distinct binding mode relative to imatinib mesylate warrant further investigation of AP23464 for the treatment of CML.
Inhibition of wild-type and mutant Bcr-Abl by AP23464, a potent ATP-based oncogenic protein kinase inhibitor: implications for CML.
Blood, Oct 2004
BCR-ABL kinase domain mutations are infrequently detected in newly diagnosed chronic-phase chronic myeloid leukemia (CML) patients. Recent studies indicate the presence of pre-existing BCR-ABL mutations in a higher percentage of CML patients when CD34+ stem/progenitor cells are investigated using sensitive techniques, and these mutations are associated with imatinib resistance and disease progression. However, such studies were limited to smaller number of patients. We investigated BCR-ABL kinase domain mutations in CD34+ cells from 100 chronic-phase CML patients by multiplex allele-specific PCR and sequencing at diagnosis. Mutations were re-investigated upon manifestation of imatinib resistance using allele-specific PCR and direct sequencing of BCR-ABL kinase domain. Pre-existing BCR-ABL mutations were detected in 32/100 patients and included F311L, M351T, and T315I. After a median follow-up of 30 months (range 8-48), all patients with pre-existing BCR-ABL mutations exhibited imatinib resistance. Of the 68 patients without pre-existing BCR-ABL mutations, 24 developed imatinib resistance; allele-specific PCR and BCR-ABL kinase domain sequencing detected mutations in 22 of these patients. All 32 patients with pre-existing BCR-ABL mutations had the same mutations after manifestation of imatinib-resistance. In imatinib-resistant patients without pre-existing BCR-ABL mutations, we detected F311L, M351T, Y253F, and T315I mutations. All imatinib-resistant patients except T315I and Y253F mutations responded to imatinib dose escalation. Pre-existing BCR-ABL mutations can be detected in a substantial number of chronic-phase CML patients by sensitive allele-specific PCR technique using CD34+ cells. These mutations are associated with imatinib resistance if affecting drug binding directly or indirectly. After the recent approval of nilotinib, dasatinib, bosutinib and ponatinib for treatment of chronic myeloid leukemia along with imatinib, all of which vary in their effectiveness against mutated BCR-ABL forms, detection of pre-existing BCR-ABL mutations can help in selection of appropriate first-line drug therapy. Thus, mutation testing using CD34+ cells may facilitate improved, patient-tailored treatment.
Sensitive detection of pre-existing BCR-ABL kinase domain mutations in CD34+ cells of newly diagnosed chronic-phase chronic myeloid leukemia patients is associated with imatinib resistance: implications in the post-imatinib era.
PloS one, 2013