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958 The Novel Dihydroorotate Dehydrogenase (DHODH) Inhibitor PTC299 Inhibit De Novo Pyrimidine Synthesis with Broad Anti-Leukemic Activity Against Acute Myeloid Leukemia

Program: Oral and Poster Abstracts
Session: 604. Molecular Pharmacology and Drug Resistance in Myeloid Diseases: Poster I
Hematology Disease Topics & Pathways:
AML, apoptosis, Diseases, Non-Biological, Therapies, chemical interactions, cellular interactions, Biological Processes, DNA damage, Technology and Procedures, cell expansion, Lymphoid Malignancies, Myeloid Malignancies, flow cytometry, mass cytometry, metabolomics, pathways, signal transduction
Saturday, December 5, 2020, 7:00 AM-3:30 PM

Sujan Piya, PhD1, Marla Weetall, PhD2*, Josephine Sheedy, BS, MSc2*, Balmiki Ray, PhD3*, Huaxian Ma, MS4*, Kensuke Kojima, MD, PhD5, Vivian Ruvolo, MS6*, Mahesh Basyal, BS6*, Marina Konopleva, MD, PhD4, Michael Andreeff, MD, PhD6 and Gautam Borthakur, MD7

1Department of Leukemia, The University of Texas MD Anderson Cancer Center, Pearland, TX
2PTC Therapeutics Inc., South Plainfield, NJ
3PTC Therapeutics Inc., South Plainsfield, NJ
4Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX
5Division of Hematology, Respiratory Medicine and Oncology, Department of Internal Medicine, Faculty of Medicine, Saga University, Saga, Japan
6Section of Molecular Hematology and Therapy, Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX
7Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, TX

Introduction: Acute myeloid leukemia (AML) is characterized by both aberrant proliferation and differentiation arrest at hematopoietic progenitor stages 1, 2. AML relies upon de novo nucleotide synthesis to meet a dynamic metabolic landscape and to provide a sufficient supply of nucleotides and other macromolecules 3,4. Hence, we hypothesized that inhibition of de novo nucleotide synthesis would lead to depletion of the nucleotide pool and pyrimidine starvation in leukemic cells compared to their non-malignant counterparts and impact proliferative and differentiation inhibition pathways. PTC299 is an inhibitor of dihydroorotate dehydrogenase (DHODH), a rate limiting enzyme for de novo pyrimidine nucleotide synthesis that is currently in a clinical trial for the treatment of AML.

Aim: We investigated the pre-clinical activity of PTC299 against AML in primary AML blasts and cytarabine-resistant cell lines. To confirm that PTC299 effects are due to inhibition of de novo pyrimidine nucleotide synthesis for leukemic growth, we specifically tested the impact of uridine and orotate rescue. In addition, a comprehensive analysis of alteration of metabolic signaling in PI3K/AKT pathways, apoptotic signatures and DNA damage responses were analyzed by Mass cytometry based proteomic analysis (CyTOF) and immunoblotting. The potential clinical relevance of DHODH inhibition was confirmed in an AML-PDX model.

Results: The IC50s for all tested cell lines (at 3 day) and primary blasts (at 5-7 day) were in a very low nanomolar range: OCI-AML3 -4.43 nM, HL60 -59.7 nM and primary samples -18-90 nM. Treatment of AML in cytarabine-resistant cells demonstrated that PTC299 induced apoptosis, differentiation, and reduced proliferation with corresponding increase in Annexin V and CD14 positive cells (Fig.1). PTC299-induced apoptosis and inhibition of proliferation was rescued by uridine and orotate. To gain more mechanistic insights, we used an immunoblotting and mass cytometry (CyTOF) based approach to analyze changes in apoptotic and cell signaling proteins in OCI-AML3 cells. Apoptotic pathways were induced (cleaved PARP, cleaved Caspase-3) and DNA damage responses (TP53, γH2AX) and the PI3/AKT pathway were downregulated in response to PTC299. In isogenic cell lines, p53‑wildtype cells were sustained and an increased DNA damage response with corresponding increase in apoptosis in comparison to p53-deficient cells was shown. (Fig.2)

In a PDX mouse model of human AML, PTC299 treatment improved survival compared to mice treated with vehicle (median survival 40 days vs. 30 days, P=0.0002) (Fig.3). This corresponded with a reduction in the bone marrow burden of leukemia with increased expression of differentiation markers in mice treated with PTC299 (Fig.3).

Conclusion: PTC299 is a novel dihydroorotate dehydrogenase (DHODH) inhibitor that triggers differentiation, apoptosis and/or inhibition of proliferation in AML and is being tested in a clinical trials for the treatment of acute myeloid malignancies.


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Disclosures: Weetall: PTC Therapeutic: Current Employment. Sheedy: PTC therapeutics: Current Employment. Ray: PTC Therapeutics Inc.: Current Employment. Konopleva: Genentech: Consultancy, Research Funding; Rafael Pharmaceutical: Research Funding; Ablynx: Research Funding; Ascentage: Research Funding; Agios: Research Funding; Kisoji: Consultancy; Eli Lilly: Research Funding; AstraZeneca: Research Funding; Reata Pharmaceutical Inc.;: Patents & Royalties: patents and royalties with patent US 7,795,305 B2 on CDDO-compounds and combination therapies, licensed to Reata Pharmaceutical; AbbVie: Consultancy, Research Funding; Calithera: Research Funding; Cellectis: Research Funding; Amgen: Consultancy; Stemline Therapeutics: Consultancy, Research Funding; Forty-Seven: Consultancy, Research Funding; F. Hoffmann La-Roche: Consultancy, Research Funding; Sanofi: Research Funding. Andreeff: Amgen: Research Funding; 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. Borthakur: BioLine Rx: Consultancy; BioTherix: Consultancy; Nkarta Therapeutics: Consultancy; Treadwell Therapeutics: Consultancy; Xbiotech USA: Research Funding; Polaris: Research Funding; AstraZeneca: Research Funding; BMS: Research Funding; BioLine Rx: Research Funding; Cyclacel: Research Funding; GSK: Research Funding; Jannsen: Research Funding; Abbvie: Research Funding; Novartis: Research Funding; Incyte: Research Funding; PTC Therapeutics: Research Funding; FTC Therapeutics: Consultancy; Curio Science LLC: Consultancy; PTC Therapeutics: Consultancy; Argenx: Consultancy; Oncoceutics: Research Funding.

*signifies non-member of ASH