High caspase 3 and vulnerability to dual BCL2 family inhibition define ETO2::GLIS2 pediatric leukemia

Pediatric acute myeloid leukemia expressing the ETO2::GLIS2 fusion oncogene is associated with dismal prognosis. Previous studies have shown that ETO2::GLIS2 can efficiently induce leukemia development associated with strong transcriptional changes but those amenable to pharmacological targeting remained to be identified. By studying an inducible ETO2::GLIS2 cellular model, we uncovered that de novo ETO2::GLIS2 expression in human cells led to increased CASP3 transcription, CASP3 activation, and cell death. Patient-derived ETO2::GLIS2(+) leukemic cells expressed both high CASP3 and high BCL2. While BCL2 inhibition partly inhibited ETO2::GLIS2(+) leukemic cell proliferation, BH3 profiling revealed that it also sensitized these cells to MCL1 inhibition indicating a functional redundancy between BCL2 and MCL1. We further show that combined inhibition of BCL2 and MCL1 is mandatory to abrogate disease progression using in vivo patient-derived xenograft models. These data reveal that a transcriptional consequence of ETO2::GLIS2 expression includes a positive regulation of the pro-apoptotic CASP3 and associates with a vulnerability to combined targeting of two BCL2 family members providing a novel therapeutic perspective for this aggressive pediatric AML subgroup.