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1052 TET2 and DNMT3A Mutations Exert Divergent Effects on DNA Repair and Sensitivity of Leukemia Cells to PARP Inhibitors

Program: Oral and Poster Abstracts
Session: 616. Acute Myeloid Leukemia: Novel Therapy, excluding Transplantation: Poster I
Hematology Disease Topics & Pathways:
AML, Diseases, CML, Animal models, Therapies, Combinations, MPN, Biological Processes, DNA damage, DNA repair, Study Population, Myeloid Malignancies, pathways, signal transduction
Saturday, December 5, 2020, 7:00 AM-3:30 PM

Silvia Maifrede1*, Bac Viet Le1*, Margaret Nieborowska-Skorska1*, Konstantin Golovine1*, Katherine Sullivan-Reed1*, Wangisa M.B. Dunuwille2*, Joseph Nacson3*, Michael Hulse1*, Lisa Beatrice Caruso1*, Zachary Gazze1*, Zhaorui Lian1*, Antonella Padella4*, Kumaraswamy Chitrala1*, Boris Bartholdy5*, Ksenia Matlawska-Wasowska6*, Daniela Di Marcantonio3, Giorgia Simonetti7*, Georg Greiner8*, Stephen M. Sykes3, Peter Valent, MD9, Elisabeth M. Paietta10*, Hugo F Fernandez11*, Martin S. Tallman, MD 12, Mark Litzow, MD13, Mark D. Minden14, Jian Huang1, Giovanni Martinelli, MD4, George S. Vassiliou, MD, PhD, FRCPath, MRCP15*, Italo Tempera1*, Katarzyna Piwocka16*, Neil Johnson3*, Grant Challen17 and Tomasz Skorski, MD, PhD1

1Temple University School of Medicine, Philadelphia, PA
2Washington University School of Medicine, Saint Louis
3Fox Chase Cancer Center, Philadelphia, PA
4University of Bologna, Meldola, Italy
5Albert Einstein College of Medicine, Bronx, NY
6University of New Mexico, Albuquerque, NM
7University of Bologna, Bologna, Italy
8Medical University of Vienna, Vienna, Austria
9Department of Medicine I, Division of Hematology, Medical University of Vienna, Vienna, Austria
10Albert Einstein College of Medicine, New York, NY
11Moffitt Malignant Hematology & Cellular Therapy at Memorial Healthcare System, Pembroke Pines
12Memorial Sloan-Kettering Cancer Center, New York, NY
13Division of Hematology, Mayo Clinic, Rochester, MN
14Leukemia Program, Division of Medical Oncology and Hematology, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada
15Wellcome Trust Sanger Institute, Cambridge, ENG, United Kingdom
16Nencki Institute of Experimental Biology, Warsaw, Poland
17Washington University School of Medicine, St Louis, MO

Somatic variants in TET2 and DNMT3A are founding mutations in hematological malignancies that both affect the epigenetic regulation of DNA methylation. Although the proteins antagonistically regulate the epigenetic mark of 5-methylcytosine (5-mC), where DNMT3A catalyzes addition of 5-mC while TET2 oxidizes 5-mC as a first step in DNA demethylation, mutations in both genes appear in a similar spectrum of human hematopoietic malignancies. Mutations in both genes often co-occur with activating mutations in oncogenic tyrosine kinases (OTKs) such as FLT3ITD, BCR-ABL1, JAK2V617F, MPLW515L or mutations affecting related signaling pathways such as NRASG12D and CALRdel52. Moreover, while the mutations exert divergent effect on primitive hematopoietic progenitor cells, they lead to similar disease phenotypes, suggesting the roles of these mutations in hematopoietic malignancies may relate to mechanisms outside of DNA methylation.

OTK-positive malignant cells accumulate high numbers of spontaneous and drug-induced DNA double-strand breaks (DSBs) in comparison to normal cells, but they manage to survive because of their enhanced/altered ability to repair these breaks. DSBs, the most lethal DNA lesions, are repaired by two major mechanisms, BRCA1/2-dependent homologous recombination (HR) and DNA-PK –mediated non-homologous end-joining (D-NHEJ). Both HR and D-NHEJ repair DSBs in proliferating cells, while D-NHEJ plays a major role in quiescent cells. PARP1 –dependent alternative NHEJ (Alt-NHEJ) serves as back-up in both proliferating and quiescent cells. The existence of these redundant pathways creates the opportunity to employ a phenomenon called “synthetic lethality”, which was originally applied to eliminate cancer cells with mutations in BRCA1 and BRCA2 by PARP inhibitor (PARPi).

Our previous report [M. Nieborowska-Skorska et al., Gene expression and mutation-guided synthetic lethality eradicates proliferating and quiescent leukemia cells. J Clin Invest 127, 2392-2406 (2017)] suggested that certain leukemias are sensitive to PARPi-triggered synthetic lethality. Here we show that TET2 and DNMT3A mutations exert divergent roles in regulating DNA repair activities in leukemia cells expressing OTKs. Malignant TET2-deficient cells display downregulation of BRCA1 and LIG4 resulting in reduced activity of HR and D-NHEJ, respectively, and rely on Alt-NHEJ to protect them from the toxic effects of replication stress and drug-induced DSBs. Conversely, DNMT3A-deficient cells favor HR/D-NHEJ owing to downregulation of PARP1 and reduction of Alt-NHEJ. Consequently, malignant TET2-deficient cells are sensitive to PARPi treatment in vitro and in vivo, whereas DNMT3A-deficient cells were resistant. Disruption of TET2 dioxygenase activity and/or TET2 - Wilms tumor 1 (WT1) binding ability were responsible for DNA repair defects and sensitivity to PARPi associated with TET2 deficiency. Moreover, mutation or deletion of WT1 mimicked the effect of TET2 mutation on DSB repair activity and sensitivity to PARPi. Our findings reveal that TET2 and WT1 mutations may serve as biomarkers of synthetic lethality triggered by PARPi, which should be explored therapeutically.

Disclosures: Valent: Allcyte GmbH: Research Funding; Pfizer: Honoraria; Cellgene: Honoraria, Research Funding. Tallman: Abbvie: Research Funding; Cellerant: Research Funding; Orsenix: Research Funding; ADC Therapeutics: Research Funding; BioSight: Membership on an entity's Board of Directors or advisory committees, Research Funding; Glycomimetics: Research Funding; Rafael: Research Funding; Amgen: Research Funding; Bioline rx: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; KAHR: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees; Delta Fly Pharma: Membership on an entity's Board of Directors or advisory committees; Oncolyze: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; UpToDate: Patents & Royalties. Martinelli: Roche: Consultancy; Pfizer: Consultancy, Research Funding, Speakers Bureau; Incyte: Consultancy; Jazz: Consultancy; Janssen: Consultancy; Daichii Sankyo: Consultancy, Research Funding; Celgene: Consultancy, Speakers Bureau; Amgen: Consultancy; AbbVie: Consultancy, Research Funding. Vassiliou: Kymab Ltd - Monoclonal antibody company. Currently not working in myeloid cancers or clonal haematopoiesis.: Consultancy.

*signifies non-member of ASH