ASCENT1: A Phase 2 Trial to Evaluate the Efficacy and Safety of Oral Decitabine-Tetrahydrouridine (NDec) in Patients with Sickle Cell Disease

Background: Sickle cell disease (SCD) is driven by the polymerization of mutated hemoglobin (HbS) in red blood cells (RBCs). Fetal hemoglobin (HbF) mitigates the effects of HbS polymerization, but the HbF gene expression is silenced in infancy by DNA methyltransferase 1 (DNMT1). Decitabine induces HbF expression by direct inhibition of DNMT1. NDec is an innovative combination treatment with decitabine, the active component, and the pharmacokinetic enhancer tetrahydrouridine (THU). Hydroxyurea (HU), the current standard of SCD care, indirectly induces HbF by inducing bone marrow stress. As the indirect effect of HU on HbF is clinically variable, the direct HbF induction of NDec is hypothesized to provide a sustainable treatment option for patients with SCD.

In a previous trial in high-risk patients with SCD by Molokie R et al. (2017), oral decitabine (0.16 mg/kg) and THU vs placebo significantly increased total Hb, HbF, proportion of HbF-enriched RBCs (%F-cells) and improved RBC health markers, without triggering grade ≥3 non-hematologic toxicity. NDec formulations were further investigated in 2 phase 1 trials in healthy people. The ASCENT1 trial (NCT05405114) aims to study the efficacy and safety of once- or twice-weekly NDec vs placebo in patients with SCD. This study will provide proof of concept and determine the optimal dose for future trials.

Study design: ASCENT1 is a randomized, placebo-controlled phase 2 trial with an additional exploratory open-label HU block (Figure). To ease the operational aspects for patients and sites, trial design, visit schedule and trial materials were developed together with patient groups, study nurses and coordinators. The HU non-eligible block will include those who are HU-naïve or who cannot be treated with HU for any reason. Participants randomized to NDec in the HU active block will discontinue HU during a 4-week washout period.

Study population: All SCD genotypes are eligible for inclusion; other criteria are ≥18 years of age, 2-10 documented vaso-occlusive crises (VOCs) ≤12 months before screening, Hb ≥5.0-≤10.5 g/dL and reticulocyte count >1.5x upper limit of normal at screening. HU active participants are eligible only if deemed inadequately controlled by investigators despite being prescribed HU in the preceding 6 months and being on a stable dose >3 months.

Exclusion criteria include chronic transfusion therapy or treatment 28 days before screening/during trial with hematopoietic growth factors and treatment with voxelotor, crizanlizumab or L-glutamine 12 weeks before signing informed consent.

Study treatment and endpoints: HU non-eligible (n=60) and HU active (n=24) participants will be randomized 1:1:1 to NDec once weekly, NDec twice weekly (2 consecutive days) or placebo/open-label HU. The trial consists of a main and extension phase (24 weeks each). NDec will be administered orally, with a meal, according to body weight intervals to attain a decitabine dose level of 0.16−0.25 mg/kg and THU dose level of 8−12.5 mg/kg.

The primary endpoint is change in total Hb (g/dL) from baseline (BL) to Week 24. Secondary efficacy endpoints include change in HbF (g/dL and %HbF of total Hb), change in %F-cells of total RBCs, and change in hemolysis markers from BL to Week 24. Secondary efficacy endpoints also include numbers of VOCs, acute chest syndrome and transfused RBC units from BL to Week 48. The secondary safety endpoint is the number of adverse events (grade ≥3) from BL to Week 52. Changes in patient-reported outcomes from BL to Week 48 will be assessed using 5 validated questionnaires for SCD.

Statistical analysis: The primary endpoint will be analyzed using an ANCOVA model with treatment, historical VOC rate and sex as fixed factors, and BL Hb as covariate. Treatment policy estimand will be used to handle intercurrent events.

Considerations: In this trial, VOCs are defined as ≥1 predefined clinical events requiring a medical visit, including home and telemedicine visits, for those with limited regular access to medical management at a clinic/hospital.

NDec and HU both induce HbF and will not be given together due to a theoretical potentiation of hematologic toxicity. The exploratory HU active block enables preliminary comparisons of the efficacy and safety between NDec and HU. The extension phase allows for analyses that may require longer follow-up to show clinical benefits and sustainability of NDec in SCD. The recruitment to ASCENT1 started in summer 2022.

Andemariam:Forma Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Emmaus: Consultancy, Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi Genzyme: Consultancy, Membership on an entity's Board of Directors or advisory committees; CRISPR Therapeutics AG: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Hemanext: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novo Nordisk A/S: 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; Aruvant: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees; Terumo BCT: Consultancy, Membership on an entity's Board of Directors or advisory committees; Shenox: Consultancy, Membership on an entity's Board of Directors or advisory committees; Vertex: Consultancy, Membership on an entity's Board of Directors or advisory committees. Højlund Nielsen:Novo Nordisk A/S: Current Employment. Zillmer:Novo Nordisk A/S: Current Employment. Derving Karsbøl:Novo Nordisk A/S: Current Employment.