Abstract 2463: Enhancing the antileukemic activity of venetoclax against leukemia stem cells by targeting oxidative phosphorylation through dual inhibition of PI3K and HDAC (2021)

Abstract Over 40% of acute myeloid leukemia (AML) patients experience relapse after remission from intensive chemotherapy and stem cell transplant. Therefore, novel therapies are in demand to target the root cause of relapse, leukemia stem cells (LSCs). Recently, a selective inhibitor of anti-apoptotic Bcl-2, venetoclax, was FDA approved for treating AML in combination with less intensive therapies for patients with comorbidities. However, anti-apoptotic Mcl-1 overexpression and pro-apoptotic Bim downregulation manifests venetoclax resistance. Our previous work demonstrated that a novel dual inhibitor of PI3K and HDAC, CUDC-907, synergizes with venetoclax by overcoming these resistance mechanisms in bulk AML cells and suppressing c-Myc expression and mTOR activity. Previous literature has reported that Bcl-2 inhibition suppresses oxidative phosphorylation (OXPHOS), which is what LSCs rely on for energy production. This is in contrast to normal HSCs that can readily shift their reliance to glycolysis for ATP production if OXPHOS is inhibited. Since c-Myc and mTOR signaling are also known to support mitochondrial respiration, we hypothesize that the combination of CUDC-907 and venetoclax can selectively target LSCs. Metabolomics analyses revealed that pre-treatment of CUDC-907 followed by venetoclax affects the abundance of intermediates in the TCA cycle of AML cells, prior to apoptosis. RNAseq analyses with the same treatment regimen found that the transcription of the TCA cycle regulator pyruvate dehydrogenase kinase 2 (PDK2) is upregulated, and the transcription of pyruvate carboxylase (PC), aconitase 2 (ACO2) and the glutamine transporter SLC1A5 is downregulated, some of which are known cMyc target genes. These findings were correlated with a reduced oxygen consumption rate, indicating the suppression of OXPHOS. Treatment of patient-derived xenograft (PDX) mice with venetoclax and CUDC-907 reduced primary AML cell engraftment, suggesting both bulk AML cell and LSC suppression. These results suggest that the combination of CUDC-907 with venetoclax may target LSCs by interfering with the TCA cycle. To further establish our hypothesis, C13 glucose flux analysis will assist in following the effected metabolic pathways. Rescue experiments supplementing metabolites that were downregulated in treated AML cells and/or inhibition of PDK2 will confirm the mitochondrial respiration based mechanism of AML cell death by the combination of CUDC-907 and venetoclax. Finally we will confirm that these two drugs when combined, reduce the number of LSCs in primary patient samples with a PDX model and flow cytometry for known LSC markers, CD38, CD34 &amp; CD123. The results of this study will form a solid foundation for the clinical evaluation of this promising combination therapy for the treatment of AML and potentially reduce the incidence of relapse. Citation Format: Katie Hege, Hasini Kalpage, Maik Hüttemann, Holly Pitman, Jeffrey W. Taub, Lisa Polin, Jing Li, Yubin Ge. Enhancing the antileukemic activity of venetoclax against leukemia stem cells by targeting oxidative phosphorylation through dual inhibition of PI3K and HDAC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2463.