Activity of STAMP inhibitors in ABL2 rearranged Acute Lymphoblastic Leukemia is dependent on the Abl2 SH3 domain

1. Asciminib inhibits Abl2 (Abelson-related gene) by interacting with different myristate pocket residues compared to Abl.

2. ABL2 exon 3-encoded region of the SH3 domain is critical for STAMP inhibitor activity against ABL2 rearrangements in vitro and in vivo.

ABL2 rearranged (ABL2r) acute lymphoblastic leukemia (ALL) is a subtype of high-risk Ph-like ALL. ABL2r patients are treated with high-dose multiagent chemotherapy while the addition of TKIs to their treatment regimen is currently being explored. We have previously demonstrated in vitro sensitivity of cells harboring the ZC3HAV1::ABL2 fusion to the first STAMP inhibitor, asciminib. Here, we extend these in vitro findings to demonstrate similar sensitivity to second-generation STAMP inhibitor, TERN-701, using ZC3HAV1::ABL2 ALL cells. Additionally, using truncated ZC3HAV1::ABL2 isoforms, we identified that exon 3 of Abl2 (encoded by ABL2) is essential for the efficacy of both STAMP inhibitors. In an in-silico model, we further demonstrate 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 ABL2r ALL. Finally, we demonstrate the efficacy of both STAMP inhibitors against ZC3HAV1::ABL2 patient cells and asciminib as a novel treatment of ZC3HAV1::ABL2 disease in a preclinical in vivo study.