In vivo analysis of the role of BAALC overexpression in AML

Abstract

The upregulation of the Brain and acute leukemia, cytoplasmic (BAALC) gene expression is considered to be a significant negative prognostic factor in acute myeloid leukemia (AML). Patients with BAALC overexpression are less likely to achieve complete remission and have shorter disease free and overall survival rates (Langer et al., Blood 2008; Weber et al., Blood 2013; Xiao et al., Molecular and Clinical Oncology 2015). In this study, we aimed to analyze the role of BAALC overexpression on leukemogenesis and the behavior of leukemic blasts in vitro and in vivo. For our experiments, we used two BAALC high AML cell lines, three BAALC high AML primary patient samples, and one BAALC high CN/AML patient sample. We established CRISPR/Cas9-mediated BAALC knockout (KO) in these cells and investigated the proliferation of the cells in vitro. We could not find a significant difference in the proliferation rate between both groups. In vivo, we compared the engraftment capacity of AML cells with and without BAALC KO in zebrafish embryos and NSG mice. In the zebrafish xenotransplantation model, we observed a significant difference between BAALC KO Kasumi-1 and the respective WT cells. The engraftment capacity of BAALC KO cells was significantly reduced compared to BAALC WT cells. In mice, however, BAALC KO in KG-1a cells and two out of three AML patient samples showed no difference compared to their wild type counterparts. The Kasumi-1 cell line, one of the three AML patient samples, and the CN/AML patient sample did not engraft in the mouse model. Our results could not support the hypothesis that BAALC KO would reduce proliferation in BAALC high AML in vitro or engraftment capacity in vivo unconditionally. Considering the positive results regarding our experiments with Kasumi-1 (a BAALC high AML cell line with RUNX1 mutation) in zebrafish embryos and the relevant results achieved by our colleagues Dannenmann et al. regarding BAALC KO in CN/AML with RUNX1 mutation (Dannenmann et al., Cell stem cell. May 2021) we suspect that the role of BAALC overexpression in leukemogenesis and consequently cell behavior may depend on the cooperativity with RUNX1 mutations. In search of treatment options for patients with BAALC high AML, we conducted experiments with three drugs selected to intervene in the signal cascade downstream of BAALC. We treated the BAALC high AML cells with CMPD1, an M2Ka inhibitor, and MEK1 and MEK2-inhibitors U0126 and AZD6244. We found that CMPD1 and AZD6244 reduced the cell viability of BAALC high AML cells compared to healthy donor cells. The interference of drugs in the downstream pathway of BAALC could be an approach for further studies for the therapy of BAALC high AML patients.