Evaluation of anti-leukemic activity and underlying mechanisms of the novel GSPT1 degrader AB138 in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a relapsing and drug-resistant hematologic malignancy. We report AB138, a novel molecular glue degrader that recruits G1-to-S phase transition protein 1 (GSPT1) to cereblon (CRBN). In AML cell lines, AB138 induces rapid, sustained GSPT1 degradation. qPCR and immunoblotting revealed activation of the integrated stress response, as evidenced by eIF2α phosphorylation and the upregulation of ATF3 and CHOP. The subsequent depletion of the oncoproteins MCL1 and c-Myc coincides with the accumulation of cleaved caspase-3 and cleaved PARP and marked apoptosis. Flow cytometric analysis confirmed pronounced S-phase arrest together with an increase in the number of Annexin V-positive cells. Oral administration of AB138 significantly reduces the tumor burden in an MV-4-11-Luc xenograft model without overt toxicity. These findings demonstrate that efficient GSPT1 degradation by AB138 promtoes integrated stress signaling and downregulates the survival-promoting BCL-2 family member MCL1 and the oncogenic driver c-Myc, leading to potent antileukemic activity in vitro and in vivo and supporting further development of AB138 for AML therapy.