2012 – N/KRAS-MUTANT AML LSCS ORIGINATE FROM COMMITTED MYELOMONOCYTIC PROGENITORS AND DRIVE CLINICAL RESISTANCE TO VENETOCLAX

Driver mutations in hematologic malignancies often show distinct temporal acquisition patterns, but the biological basis for this, if any, remains unknown. RAS mutations occur invariably late in the course of acute myeloid leukemia (AML), as well as upon progression or relapsed/refractory disease. We developed synthetic leukemogenesis models in induced pluripotent stem cell (iPSC)-derived and primary human hematopoietic stem/progenitor cells (HSPCs) by introduction of the prototypical NRAS G12D mutation alone or with other mutational combinations and engraftment of a transplantable leukemia as the readout. We first show that RAS mutations are obligatory late events that need to succeed earlier cooperating mutations. We provide the mechanistic explanation for this in a requirement for mutant (MT) RAS to specifically transform committed progenitors of the myelomonocytic lineage (granulocyte-monocyte progenitors, GMPs) harboring previously acquired driver mutations, revealing that advanced leukemic clones originate from a different cell type than ancestral clones. Furthermore, we demonstrate that RAS-MT leukemia stem cells (LSCs) give rise to monocytic disease, as frequently observed in patients with poor responses to treatment with the BCL2 inhibitor drug Venetoclax (VEN). We show that this is because RAS-MT LSCs, in contrast to RAS-WT LSCs, have altered BCL2 family gene expression profiles and are resistant to VEN, driving clinical resistance and relapse with monocytic features. Our findings demonstrate that a specific genetic driver shapes the non-genetic cellular hierarchy of AML and critically impacts therapeutic outcomes in patients by imposing a specific LSC target cell restriction. Importantly, our results also indicate that VEN treatment can accelerate disease progression in AML patients through selection of preexisting subclonal RAS-MT LSCs.