ASXL1 mutations are associated with distinct epigenomic alterations that lead to sensitivity to venetoclax and azacytidine

Abstract

The BCL2-inhibitor, Venetoclax (VEN), has shown significant anti-leukemic efficacy in combination with the DNMT-inhibitor, Azacytidine (AZA). To explore the mechanisms underlying the selective sensitivity of mutant leukemia cells to VEN and AZA, we used cell-based isogenic models containing a common leukemia-associated mutation in the epigenetic regulator ASXL1. KBM5 cells with CRISPR/Cas9-mediated correction of the ASXL1G710X mutation showed reduced leukemic growth, increased myeloid differentiation, and decreased HOXA and BCL2 gene expression in vitro compared to uncorrected KBM5 cells. Increased expression of the anti-apoptotic gene, BCL2, was also observed in bone marrow CD34+ cells from ASXL1 mutant MDS patients compared to CD34+ cells from wild-type MDS cases. ATAC-sequencing demonstrated open chromatin at the BCL2 promoter in the ASXL1 mutant KBM5 cells. BH3 profiling demonstrated increased dependence of mutant cells on BCL2. Upon treatment with VEN, mutant cells demonstrated increased growth inhibition. In addition, genome-wide methylome analysis of primary MDS samples and isogenic cell lines demonstrated increased gene-body methylation in ASXL1 mutant cells, with consequently increased sensitivity to AZA. These data mechanistically link the common leukemia-associated mutation ASXL1 to enhanced sensitivity to VEN and AZA via epigenetic upregulation of BCL2 expression and widespread alterations in DNA methylation.

Mitochondria and Their Relationship with Common Genetic Abnormalities in Hematologic Malignancies

“…Leukemic cells with ASXL1 mutation have been shown to overexpress anti-apoptotic Bcl-2 and have increased global cytosine methylation levels. It is not surprising that these cells were sensitive to both the Bcl-2 inhibitor venetoclax and the DNMT-inhibitor azacytidine [258]. In addition, clinical trials have shown the efficacy of venetoclax combined with hypomethylating agents or low-dose cytarabine in a subgroup of AML patients [259].…”

Venetoclax resistance: mechanistic insights and future strategies

“…ASXL1 mutation was recently found to drive response to Venetoclax in vitro . ASXL1 acts as an epigenetic regulator via PRC2-mediated chromatin modification to keep various genes in a repressed state [ 34 ] . Thus, ASXL1 mutation leads to aberrant activation of its target genes, including BCL2 [ 34 ] .…”

“…ASXL1 acts as an epigenetic regulator via PRC2-mediated chromatin modification to keep various genes in a repressed state [ 34 ] . Thus, ASXL1 mutation leads to aberrant activation of its target genes, including BCL2 [ 34 ] . In preclinical study of Rahmani et al .…”

“…[ 34 ] , ATAC-sequencing analysis suggested higher chromatin accessibility on the BCL-2 locus of ASXL1 mutant KBM5 cells due to failure of PRC2 complex recruitment, resulting in BCL-2 overexpression [ 34 ] . BH3 profiling further showed higher BCL2 anti-apoptotic protein dependency in ASXL1 mutant cells, which explained ASXL1 sensitivity to Venetoclax in vitro [ 34 ] . Rahmani et al [ 34 ] also demonstrated enhanced global cytosine methylation, which led to sensitivity to Azacitidine, a DNMT inhibitor.…”

The venetoclax/azacitidine combination targets the disease clone in Acute Myeloid Leukemia, being effective and safe in a patient with COVID

“… 4 However, the clone composition may impact on the probability of response and its duration. 5 – 6 Patients with AML and NPM1 and/or IDH2 mutations have the highest probability of response to VEN/HMA combinations, but also RUNX1 mutations appear to be associated with favorable responses. On the other hand, activating kinase mutations such as FLT3-ITD , N/KRAS , CBL , or KIT have been associated with treatment resistance.…”