Although BCR-ABL tyrosine kinase inhibitors (TKIs) are highly effective in treating CML at chronic phase, a number of patients develop drug resistance due to the inability of TKIs to kill leukemia stem cells (LSCs).
Although strategies to overcome resistance-mediated T315I mutation may improve the survival of BCR-ABL-positive leukemia patients, there is little information on cell-based studies.
Although tyrosine kinase inhibitors, such as the BCR-ABL inhibitor imatinib, have demonstrated remarkable efficacy in the clinic, drug-resistant leukemias emerge in some patients because of either the acquisition of point mutations or amplification of the tyrosine kinase, resulting in a poor long-term prognosis.
An emerging problem in patients with Philadelphia (Ph)-positive leukaemias is the occurrence of cells with multiple mutations in the BCR-ABL1 tyrosine kinase domain (TKD) associated with high resistance to different tyrosine kinase inhibitors.
An etiological connection between BCR/ABL and leukemia is indicated by the observation that transgenic mice bearing a BCR/ABL DNA construct develop leukemia of B, T, and myeloid cell origin.
As an oral, nontoxic compound with a mechanism of action distinct from that of ABL tyrosine kinase inhibition, FTI SCH66336 shows promise for the treatment of BCR/ABL-induced leukemia.
BCR-ABL1-negative myeloproliferative neoplasms (MPNs) are clonal stem cell disorders defined by proliferation of one or more myeloid lineages, and carry an increased risk of vascular events and progression to myelofibrosis and leukemia.
BCR-ABL1 point mutation-mediated resistance to tyrosine kinase inhibitor (TKI) therapy in Philadelphia chromosome-positive (Ph<sup>+</sup>) leukemia is effectively managed with several approved drugs, including ponatinib for BCR-ABL1<sup>T315I</sup>-mutant disease.
Because the BCR-ABL fusion gene appears to be the result of cytogenetic rearrangement in all cases of these leukemias, the causes and mechanism of chromosome rearrangement will be relevant to the development of leukemia in man.
Because the propensity for on- versus off-target resistance varies across cancer types, a deeper understanding of the mutational burden in drug targets could rationalize treatment outcomes and prioritize pan-target inhibitors for indications where on-target mutations are most likely.<b>Experimental Design:</b> To measure and model the mutational landscape of a drug target at high resolution, we integrated single-molecule Duplex Sequencing of the ABL1 gene in Philadelphia-positive (Ph<sup>+</sup>) leukemias with computational simulations.<b>Results:</b> A combination of drug target mutational burden and tumor-initiating cell fraction is sufficient to predict that most patients with chronic myeloid leukemia are unlikely to harbor ABL1 resistance mutations at the time of diagnosis, rationalizing the exceptional success of targeted therapy in this setting.
Because these two chromosomes are translocated with breakpoints within the BCR and ABL genes in Philadelphia chromosome-positive leukemias, knowledge of these sequences also might provide insight into the validity of various theories of chromosomal rearrangements.
Besides, the results of BCR-ABL quantification in the follow-up of patients clearly confirm that real-time PCR with HybProbes is a reliable and sensitive method for monitoring minimal residual leukemia after HSCT in CML patients.