Targeting leukemic stem and progenitor cells expressing different BCR::ABL1 levels: antileukemic activity of asciminib with or without TKIs

Tyrosine kinase inhibitors (TKIs) targeting ABL1 catalytic activity have markedly improved Chronic Myeloid Leukemia (CML) outcomes, inducing unprecedented and durable therapeutic responses. However, while TKIs efficiently target committed leukemic progenitors, they fail to eradicate leukemic stem cells (LSCs), which may drive disease relapse. High BCR::ABL1 transcripts at diagnosis confer a proliferative and survival advantage and are associated with a higher risk of CML progression to the acute phase. Specifically Targeting the ABL Myristoyl Pocket (STAMP) compounds, including asciminib (ASC), provide a novel mechanism to inhibit BCR::ABL1 catalytic activity. ASC is FDA-approved for patients who have failed one or more TKIs, and its efficacy has been evaluated as monotherapy, and in combination with different TKIs, in T315I-positive or advanced-phase CML. We investigated the cytotoxic effects of ASC, alone or with imatinib (IM) or nilotinib (NIL), on committed progenitors and LSCs from CML patients expressing high or low BCR::ABL1 at diagnosis. ASC reduced BCR::ABL1-dependent survival and impaired clonogenicity in committed progenitors with low, but not high, BCR::ABL1 transcripts. ASC also disrupted LSC self-renewal, reducing both frequency and number of Long-Term Culture-Initiating Cells (LTC-ICs). When combined with IM or NIL, ASC restored TKI activity against LTC-ICs expressing high BCR::ABL1 transcripts, with the association of ASC and NIL reducing both LTC-IC division rates and LTC-IC-derived CFUs. These findings suggest that ASC, alone or with NIL, may target LSCs and improve outcomes in patients with high BCR::ABL1 expression at diagnosis.