Activity of STAMP inhibitors in ABL2 rearranged acute lymphoblastic leukemia is dependent on the Abl2 SH3 domain

<i>ABL2</i> rearranged (<i>ABL2r</i>) acute lymphoblastic leukemia (ALL) is a subtype of high-risk Philadelphia chromosome-like ALL. Patients with <i>ABL2r</i> ALL are treated with high-dose multiagent chemotherapy, and the addition of tyrosine kinase inhibitors to their treatment regimen is currently being explored. We have previously demonstrated the in vitro sensitivity of cells harboring the <i>ZC3HAV1</i>::<i>ABL2</i> fusion to asciminib, the first inhibitor that specifically targets the Abl myristate pocket (STAMP). In this study, we extended these in vitro findings to demonstrate similar sensitivity to the second-generation STAMP inhibitor, TERN-701, using <i>ZC3HAV1</i>::<i>ABL2</i> ALL cells. In addition, using truncated <i>ZC3HAV1</i>::<i>ABL2</i> isoforms, we identified that exon 3 of Abl2 (encoded by <i>ABL2</i>) is essential for the efficacy of both STAMP inhibitors. In an in silico model, we further demonstrated that different myristate pocket residues impact the effective binding of asciminib to Abl2 compared to Abl. Importantly, this suggests that, in the clinical setting, different asciminib binding site mutations may be anticipated with STAMP treatment for <i>ABL2r</i> ALL. Finally, we demonstrated the efficacy of both STAMP inhibitors against cells from patients with <i>ZC3HAV1</i>::<i>ABL2</i> and asciminib as a novel treatment for <i>ZC3HAV1</i>::<i>ABL2</i> disease in a preclinical in vivo study.