Targeting Mitochondrial Structure Sensitizes Acute Myeloid Leukemia to Venetoclax Treatment

Abstract

The BCL2 family plays important roles in acute myeloid leukemia (AML). Venetoclax, a selective BCL2 inhibitor, has received FDA approval for the treatment of AML. However, drug resistance ensues after prolonged treatment, highlighting the need for a greater understanding of the underlying mechanisms. Using a genome-wide CRISPR/Cas9 screen in human AML, we identifi ed genes whose inactivation sensitizes AML blasts to venetoclax. Genes involved in mitochondrial organization and function were signifi cantly depleted throughout our screen, including the mitochondrial chaperonin CLPB. We demonstrated that CLPB is upregulated in human AML, it is further induced upon acquisition of venetoclax resistance, and its ablation sensitizes AML to venetoclax. Mechanistically, CLPB maintains the mitochondrial cristae structure via its interaction with the cristae-shaping protein OPA1, whereas its loss promotes apoptosis by inducing cristae remodeling and mitochondrial stress responses. Overall, our data suggest that targeting mitochondrial architecture may provide a promising approach to circumvent venetoclax resistance. SIGNIFICANCE: A genome-wide CRISPR/Cas9 screen reveals genes involved in mitochondrial biological processes participate in the acquisition of venetoclax resistance. Loss of the mitochondrial protein CLPB leads to structural and functional defects of mitochondria, hence sensitizing AML cells to apoptosis. Targeting CLPB synergizes with venetoclax and the venetoclax/azacitidine combination in AML in a p53-independent manner.

MCL1 dependence across MDS subtypes and dual inhibition of MCL1 and BCL2 in MISTRG6 mice

“…Moreover, drug synergy from combining BCL2 and MCL1 inhibitors can be achieved across all subtypes and mutational profiles of MDS in this model, even in the presence of RAS family mutations that are thought to confer resistance to VEN monotherapy (eg. CBL and PTPN11 in this cohort) [14][15][16][17][18] . 38 and in vivo 11 is limited at clinically meaningful doses.…”

“…The data presented here suggest dual BCL2+MCL1 inhibition may be considered for the treatment of all MDS subtypes regardless of mutational status, even those with mutations that may be less likely to respond to VEN monotherapy (eg. TP53 or RAS family mutations) [14][15][16][17][18] MLD is multi-lineage dysplasia; EB1 is excess blasts 5-9%; EB2 is 10-19% blasts; CFU-GEMM is colony-forming unit -granulocyte, erythroid, macrophage, megakaryocyte; CFU-GM is colony-forming unit -granulocyte, macrophage; BFU-E is burst-forming unit -erythroid. n/a n/a n/a n/a n/a n/a n/a DNMTi x12 n/a DNMTi x4 DNMTi x5 DNMTi x1 DNMTi x16 DNMTi x16 n/a n/a DNMTi x3 n/a n/a n/a DNMTi x5 IMID x2…”

“…As expected, we observed an increased number of SF3B1 mutations in the lower blast count MDS patient samples (MDS-RS) 13 . RAS-family mutants, particularly PTPN11-mutated AML have previously been shown to connote resistance to VEN [14][15][16][17][18] . In this small cohort, one of 2 PTPN11 mutant MDS samples, and 2/2 CBL mutant samples were completely resistant to BCL2 inhibition (MDS033, MDS005 and MDS031, respectively).…”

Venetoclax for AML: changing the treatment paradigm

“…60 There are ongoing studies investigating the mechanisms of resistance of these patients, which include loss of BAX and inability of cells to undergo apoptosis, 69 and their dependency on CLBP, a chaperonin involved in maintaining mitochondrial cristae structure. 70 Targeting of these proteins resensitizes cells to venetoclax. Prior therapy with a HMA also appears to be a risk factor for refractory disease 7,64 but more work is necessary to ascertain the biological mechanisms responsible for this nonresponsiveness to venetoclax.…”

Transcriptional Silencing of MCL-1 Through Cyclin-Dependent Kinase Inhibition in Acute Myeloid Leukemia

“…Indeed, increased advances in the understanding of the role of BCL-2 family proteins and their interactors in apoptosis and AML pathogenesis have led to the discovery and clinical development of additional investigational treatments. Recent functional screens using CRISPR/Cas9 approaches highlight the central importance of mitochondrial function/architecture in resistance to BCL-2 inhibitor venetoclax (27,28). Other BCL-2 family protein members may also play a role in AML patients refractory/resistant to BCL-2 inhibition, particularly MCL-1, which is an antiapoptotic multidomain protein regulated by distinct cyclin-dependent kinases (CDKs) in both apoptotic and cell-cycling pathways (8,(29)(30)(31).…”