Session: 802. Chemical Biology and Experimental Therapeutics: Poster III
Hematology Disease Topics & Pathways:
AML, Diseases, Myeloid Malignancies
Acute myeloid leukemia (AML) is a heterogeneous disease associated with high mortality, dependent on molecular subtype and therapy. Bcl-2 family proteins have been established as key mediators of apoptosis in AML with venetoclax, a small molecule BH3 mimetic, selectively inhibiting Bcl-2. Combinatorial therapy of venetoclax and hypomethylating agents (Ven/HMA) has revolutionized the treatment of elderly patients with AML, yielding response rates over 70%, but overall survival remains short. Since PRC2 is required for AML cell survival (Basheer et al., 2019; Neff et al., 2012), targeting both EZH1 and EZH2 (EZH1/2) concomitantly could be efficient in disrupting oncogenic signals. A recent study using a murine AML model demonstrated that genetic deletion of EZH1/2 depleted quiescent leukemic stem cell (LSC) and prolonged survival of leukemia bearing mice (Fujita at al., 2018). AML LSC are located in BM niches and are mainly non-cycling. Thus, overcoming LSC dormancy as well as LSC mobilization from the BM may be critical steps that improve long-term survival of patients with AML. Here, we hypothesized that EZH1/2 is required to regulate LSC dormancy and increase efficacy of Ven/HMA therapy in AML. To test this hypothesis, we utilized pharmacological inhibition of EZH1/2 by a potent and selective EZH1/2 dual inhibitor, DS-3201 (valemetostat; Daiichi Sankyo, Inc.). Granulocyte colony-stimulating factor (G-SCF) has been shown to not only recruit leukemia cells into cell cycle (Andreeff et al, 1990), but also disrupt AML-stromal interactions for stem cell mobilization. Clinically, G-CSF is a critical component of the FLAG-Ida protocol (Petti et al, 1997). Therefore, we hypothesized that G-CSF will also recruit quiescent LSC into cycle, and the alternative mechanism may act synergistically with EZH1/2 inhibition.
To assess if inhibition of EZH1/2 results in recruitment of LSC into the cell cycle and subsequently improves efficacy of Ven/HMA in AML in vitro, we first confirmed the nuclear expression of EZH1/2 in human AML cell lines. All cell lines expressed EZH1/2, although at different levels. These cell lines with various genetic backgrounds were treated with DS-3201 or G-CSF 24 hours prior to their exposure of Ven/HMA. A dual inhibitor of EZH1/2, or G-CSF, in combination with Ven/HMA significantly amplified AML cell death compared to Ven/HMA alone treated counterparts. In a clinical phase 1 trial of DS-3201 in AML, EZH1/2 inhibition promoted cell cycle progression. The proliferative fraction of leukemic cells was assessed by measuring Ki67/DNA in sequential samples obtained from DS-3201 treated patients. Baseline Ki67 positivity of LSC was 11.20%, and the maximized average increased to 59.3% and to over 90% in one patient (Fig 1), validating the concept that EZH1/2 inhibition can indeed recruit leukemia stem cells effectively into cell cycle. Further, a primary sample from a R/R AML patient (resistant to DNR/Ara-C 7+3, Ven/HMA, and Ipilimumab/nivolumab) was ex vivo primed for 5 days with combination of DS-3201 and G-CSF, then exposed to AraC/DNR based treatment. Concomitant treatment of G-CSF and EZH1/2 inhibition increased LSC proliferation and subsequently enhanced AraC/DNR induced apoptosis. Conclusion: we here demonstrate that pharmacological inhibition of EZH1/2 in a clinical trial with DS-3201 resulted in massive recruitment of quiescent AML LSC into the cell cycle. In vitro, EZH1/2 inhibition and G-CSF both enhanced Ven/HMA-induced leukemia cell apoptosis. Experiments are ongoing to test the hypothesis that EZH1/2 inhibition combined with G-CSF receptor activation may sensitize resistant primary AML LSC to apoptosis induction by chemotherapy and/or Bcl-2 inhibition. If successful, this concept could further enhance the activity of FLAG-Ida chemotherapy, which was developed a generation ago along the same concept, and of BH-3 mimetic, apoptosis targeting therapies.
Disclosures: Dos Santos: Daiichi Sankyo, Inc.: Current Employment. Slosberg: Daiichi Sankyo, Inc.: Current Employment. Daver: Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Research Funding; Servier: Research Funding; Genentech: Research Funding; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novimmune: Research Funding; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Trovagene: Research Funding; Fate Therapeutics: Research Funding; ImmunoGen: Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Trillium: Consultancy, Membership on an entity's Board of Directors or advisory committees; Syndax: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Andreeff: Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy; Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding; Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding.
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