Asciminib antagonizes transplantable BCR::ABL1-positive lymphoid blast crisis in vivo by targeting malignant stem cells.

Philadelphia chromosome-positive (Ph+) lymphoid blast crisis (BC), emanating from chronic myeloid leukemia (CML), is a fatal disease with limited treatment options. Asciminib (ABL001) is a novel selective allosteric inhibitor of the ABL kinase with high efficacy against TKI-resistant BCR::ABL1. In this study, we demonstrate significant suppression of an aggressive B-lymphoblastic disease and restoration of normal hematopoiesis in an inducible transgenic mouse model of p210-BCR::ABL1-positive CML-BC. Molecularly, asciminib treatment significantly reduced BCR::ABL1 transcripts to background levels, demonstrating its ability to suppress BCR::ABL1-induced disease. Furthermore, asciminib treatment normalized the long-term repopulating hematopoietic stem cell (LT-HSC) population in the BM, suggesting the selective targeting of malignant LT-HSCs. This was supported by secondary transplantation experiments, resulting in absence of BC in a proportion of mice. Importantly, none of the secondary transplanted mice that received further asciminib treatment developed leukemia. Sanger sequencing of the BCR::ABL1 myristoyl pocket region of both treatment-naïve and treated mice demonstrated a high mutational load. However, there was no indication of asciminib-specific mutations. These promising findings highlight the potential of asciminib as a drug that targets BC stem cells and as an alternative stand-alone or combinatorial therapy for first-line treatment of CML BC or Ph+ acute lymphoblastic leukemia.