Potent, p53-independent induction of NOXA sensitizes MLL-rearranged B-cell acute lymphoblastic leukemia cells to venetoclax [RNA-Seq]

The prognosis for B cell precursor acute lymphoblastic leukemia patients with Mixed-Lineage Leukemia (MLL) gene rearrangements (MLLr BCP-ALL) is still extremely poor. Inhibition of anti-apoptotic protein BCL-2 with venetoclax emerged as a promising strategy for this subtype of BCP-ALL, however lack of sufficient responses in pre-clinical models and possibility of developing resistance exclude using venetoclax as monotherapy. Herein, we aimed to uncover potential mechanisms responsible for limited venetoclax activity in MLLr BCP-ALL and to identify drugs that could be used in combination therapy. Using RNA-seq, we observed that long-term exposure to venetoclax in vivo in patient derived xenograft model leads to downregulation of particular p53-related genes. Interestingly, addition of auranofin, a thioredoxin system inhibitor, sensitized MLLr BCP-ALL to venetoclax in various in vitro and in vivo models, independently on the p53 pathway functionality. Synergistic activity of these drugs resulted from auranofin-mediated upregulation of NOXA pro-apoptotic protein and potent induction of apoptotic cell death. More specifically, we observed that auranofin orchestrates upregulation of NOXA-encoding gene (PMAIP1) by chromatin remodeling and increased transcriptional accessibility. Altogether, these results present novel, promising drug combination that could be exploited for the treatment of MLLr BCP-ALL patients, including those with TP53 mutations. RNA-seq in MLL-AF4+ patient derived xenograft ALL cells isolated from control (n=3) and venetoclax-treated (n=3) NSG mice