Azacitidine + venetoclax, decitabine + venetoclax, and low-dose cytarabine + venetoclax are now standard treatments for newly diagnosed older or unfit patients with acute myeloid leukemia (AML). Although these combinations are also commonly used in relapsed or refractory AML (RR-AML), clinical and molecular predictors of response and survival in RR-AML are incompletely understood. We retrospectively analyzed clinical and molecular characteristics and outcomes for 86 patients with RR-AML who were treated with venetoclax combinations. The complete remission (CR) or CR with incomplete hematologic recovery (CRi) rate was 24%, and the overall response rate was 31% with the inclusion of a morphologic leukemia-free state. Azacitidine + venetoclax resulted in higher response rates compared with low-dose cytarabine + venetoclax (49% vs 15%; P = .008). Median overall survival (OS) was 6.1 months, but it was significantly longer with azacitidine + venetoclax compared with low-dose cytarabine + venetoclax (25 vs 3.9 months; P = .003). This survival advantage of azacitidine + venetoclax over low-dose cytarabine + venetoclax persisted when patients were censored for subsequent allogeneic stem cell transplantation (8.1 vs 3.9 months; P = .035). Mutations in NPM1 were associated with higher response rates, whereas adverse cytogenetics and mutations in TP53, KRAS/NRAS, and SF3B1 were associated with worse OS. Relapse was driven by diverse mechanisms, including acquisition of novel mutations and an increase in cytogenetic complexity. Venetoclax combination therapy is effective in many patients with RR-AML, and pretreatment molecular characteristics may predict outcomes. Trials that evaluate novel agents in combination with venetoclax therapy in patients with RR-AML that have adverse risk genomic features are warranted.

Plasmacytoid dendritic cells (pDCs) are the principal natural type I interferon–producing dendritic cells. Neoplastic expansion of pDCs and pDC precursors leads to blastic plasmacytoid dendritic cell neoplasm (BPDCN), and clonal expansion of mature pDCs has been described in chronic myelomonocytic leukemia. The role of pDC expansion in acute myeloid leukemia (AML) is poorly studied. Here, we characterize patients with AML with pDC expansion (pDC-AML), which we observe in ∼5% of AML cases. pDC-AMLs often possess cross-lineage antigen expression and have adverse risk stratification with poor outcome. RUNX1 mutations are the most common somatic alterations in pDC-AML (>70%) and are much more common than in AML without pDC expansion and BPDCN. We demonstrate that pDCs are clonally related to, as well as originate from, leukemic blasts in pDC-AML. We further demonstrate that leukemic blasts from RUNX1-mutated AML upregulate a pDC transcriptional program, poising the cells toward pDC differentiation and expansion. Finally, tagraxofusp, a targeted therapy directed to CD123, reduces leukemic burden and eliminates pDCs in a patient-derived xenograft model. In conclusion, pDC-AML is characterized by a high frequency of RUNX1 mutations and increased expression of a pDC transcriptional program. CD123 targeting represents a potential treatment approach for pDC-AML.

Accumulating evidence indicates that the β-arrestins act as scaffold molecules that couple G-protein-coupled receptors to mitogen-activated protein (MAP) kinase signaling pathways. Recently, we identified the c-Jun N-terminal kinase 3 (JNK3) as a β-arrestin2-interacting protein in yeast-two hybrid and co-immunoprecipitation studies. β-Arrestin2 acts as a scaffold to enhance signaling to JNK3 stimulated by overexpression of the MAP3 kinase ASK1 or by agonist activation of the angiotensin 1A receptor. Whereas β-arrestin2 is a very strong activator of JNK3 signaling, β-arrestin1 is very weak in this regard. The data also indicate that the specific step enhanced by β-arrestin2 involves phosphorylation of JNK3 by the MAP2 kinase MKK4. We reasoned that defining the region (or domain) in β-arrestin2 responsible for high level JNK3 activation would provide insight into the mechanism by which β-arrestin2 enhances the activity of this signaling pathway. Using chimeric β-arrestins, we have determined that sequences in the carboxyl-terminal region of β-arrestin2 are important for the enhancement of JNK3 phosphorylation. More detailed analysis of the carboxyl-terminal domains of the β-arrestins indicated that β-arrestin2, but not β-arrestin1, contains a sequence (RRSLHL) highly homologous to the conserved docking motif present in many MAP kinase-binding proteins. Replacement of the β-arrestin2 RRS residues with the corresponding KP residues present in β-arrestin1 dramatically reduced both JNK3 interaction and enhancement of JNK3 phosphorylation. Conversely, replacement of the KP residues in β-arrestin1 with RRS significantly increased both JNK3 binding and enhancement of JNK3 phosphorylation. These results delineate a mechanism by which β-arrestin2 functions as a scaffold protein in the JNK3 signaling pathway and implicate the conserved docking site in β-arrestin2 as an important factor in binding JNK3 and stimulating the phosphorylation of JNK3 by MKK4.