Abstract: Background: Sickle cell disease (SCD) is a lifelong, inherited blood disorder, resulting from a mutation in the hemoglobin (Hb) subunit β gene, that leads to sickle hemoglobin (HbS) formation. Polymerization of HbS causes red blood cell sickling and damage, leading to hemolysis, chronic anemia, and vaso-occlusive crises (VOCs). Patients with SCD are at higher risk of end-organ damage, increased morbidity, and early mortality as a result of low Hb and increased hemolysis. Voxelotor (Oxbryta ®) tablets, a HbS polymerization inhibitor, are approved in the US for treatment of SCD in adults and adolescent patients aged ≥12 years. The randomized, placebo-controlled HOPE trial showed that significantly more patients treated with voxelotor 1500 mg achieved a & gt;1 g/dL Hb increase compared with placebo (89% vs 25%, respectively) at any time up to week 72. These Hb increases were associated with reductions in markers of hemolysis (eg, indirect bilirubin, reticulocyte percentage). To confirm the safety and efficacy of long-term voxelotor use, we report an interim analysis of an ongoing open-label extension (OLE) of the HOPE trial. Methods: Patients who completed the phase 3 HOPE trial were eligible to enroll in the multicenter OLE study and receive treatment as long as they continued to receive clinical benefit and/or until they had access to voxelotor through commercialization or a managed access program. All patients, including those who previously received placebo or voxelotor 900 mg, received voxelotor 1500 mg as ongoing treatment. Adverse event data were collected beginning on the date of informed consent through 28 days after discontinuation of voxelotor. Measurements of Hb and clinical markers of hemolysis are ongoing and summarized here for 48 weeks of treatment in the OLE. Central laboratory assessments were used for the US and Europe, and local laboratory assessments were used for the rest of the world. Data presented are based on an interim data cut (December 31, 2020). Results: Of the 199 patients who completed the HOPE trial, 178 (89.4%) were enrolled and dosed in the OLE. Median age at enrollment was 25 years (15.7% adolescents, 84.3% adults). At the cutoff date, the median duration of voxelotor exposure the OLE was 69.9 weeks (range: 1.9-102.0 weeks), with 78 patients treated for ≥72 weeks. Of these 78 patients, 52 had previously received voxelotor in the randomized part of the study, for a combined exposure duration of ≥144 weeks. Among those who previously received placebo, the mean (SD) change in Hb from baseline (ie, the start of the OLE) to week 48 was 1.3 (1.51) g/dL, consistent with the HOPE trial results. Mean (SD) Hb changes for patients who previously received voxelotor 900 mg and 1500 mg were 0.7 (1.48) g/dL and 0.2 (1.15) g/dL, respectively, indicating durability of response. Markers of hemolysis improved from baseline to week 48 in patients who received placebo in the HOPE trial (-39.5% indirect bilirubin; -28.6% reticulocyte percentage). Patients who received voxelotor during the HOPE trial showed a stable response at week 48 (-2.0% and 1.1% indirect bilirubin, -14.6% and -21.0% reticulocytes for voxelotor 900 mg and 1500 mg, respectively). The annualized incidence rate of VOCs was 1.3 (95% CI: 1.1-1.4) events per year across all patients. A total of 83.7% of patients (149/178) experienced a non-SCD-related treatment-emergent adverse event (TEAE), with the most commonly reported being arthralgia, headache, pain, nausea, and pain in extremity (Table). Most non-SCD-related TEAEs were grade 1 or 2 in severity. Eleven patients (6.2%) had an adverse event that led to treatment discontinuation. No TEAEs consistent with lack of tissue oxygenation were observed. Conclusions: In this OLE study, treatment with voxelotor 1500 mg resulted in improvements in Hb and clinical measures of hemolysis at 48 weeks in patients who received placebo in the HOPE trial. Treatment with voxelotor 1500 mg showed durability of response in patients previously treated with voxelotor of any dosage in the HOPE trial. The safety profile in the OLE was consistent with the findings from the HOPE trial, and no new safety signals were identified with exposure through a combined 144 weeks of treatment. Based on these results, long-term use of voxelotor is safe, well tolerated, and effective in reducing anemia and hemolysis, with a low rate of VOCs, in patients with SCD. Funding: This study was supported by Global Blood Therapeutics. Figure 1 Figure 1. Disclosures Achebe: Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pharmacosmos: Membership on an entity's Board of Directors or advisory committees; Fulcrum Therapeutics: Consultancy. Hassab: Global Blood Therapeutics: Research Funding. Alkindi: Global Blood Therapeutics: Speakers Bureau; Emmaus: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Brown: Global Blood Therapeutics: Consultancy, Research Funding; Imara: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Novo Nordisk: Consultancy; Forma Therapeutics: Research Funding; Pfizer: Research Funding. Telfer: BlueBirdBio: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Addmedica: Membership on an entity's Board of Directors or advisory committees; Emmaus: Membership on an entity's Board of Directors or advisory committees; Terumo: Honoraria; ApoPharma: Membership on an entity's Board of Directors or advisory committees. Biemond: Sanquin: Research Funding; Global Blood Therapeutics: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria; Novo Nordisk: Honoraria; Novartis: Honoraria, Research Funding, Speakers Bureau; CSL Behring: Honoraria. Gordeuk: Modus Therapeutics: Consultancy; Global Blood Therapeutics: Consultancy, Research Funding; Emmaus: Consultancy, Research Funding; Incyte: Research Funding; Novartis: Research Funding; CSL Behring: Consultancy. Lipato: Global Blood Therapeutics: Speakers Bureau. Tonda: Global Blood Therapeutics: Current Employment, Current equity holder in publicly-traded company. Gray: Global Blood Therapeutics: Current Employment, Current equity holder in publicly-traded company. Howard: Resonance Health: Honoraria; Bluebird Bio: Research Funding; Agios Pharmaceuticals: Consultancy; Forma Therapeutics: Consultancy; Novo Nordisk: Consultancy; Novartis: Consultancy, Honoraria; Global Blood Therapeutics: Consultancy; Imara: Consultancy, Honoraria.

Abstract: The hallmark of sickle cell disease (SCD) is polymerization of deoxygenated hemoglobin S (HbS), resulting in red blood cell (RBC) sickling, oxidative and membrane damage, hemolysis, vaso-occlusion, and end-organ damage. Exacerbating the pathogenesis of SCD, the sickle RBC (sRBC) has increased 2,3-DPG levels with decreased oxygen (O 2) affinity (increased P 50) and decreased ATP. Etavopivat, a small molecule activator of erythrocyte pyruvate kinase (PKR), increases PKR activity, resulting in decreased 2,3-DPG levels and increased ATP levels in RBCs. In a Phase 1 study in patients with SCD [NCT03815695], etavopivat significantly improved anemia and hemolysis after 2 weeks of treatment (Brown et al. Blood 2020). To evaluate the potential of etavopivat to reduce vaso-occlusive crises, exploratory studies were conducted to characterize the sRBC specific (intrinsic) and systemic effects of PKR activation. Patients with SCD received once daily etavopivat 300 or 600 mg for 2 weeks or 400 mg for up to 12 weeks. Peripheral blood was collected prior to treatment (ie, baseline), on treatment and 7-28 days post treatment. Studies to assess the sRBC intrinsic effects of PKR activation included evaluation of RBC parameters and reticulocyte counts (ADVIA ®), membrane deformability (Lorrca ®), enzyme function studies, and membrane markers by flow cytometry. Studies to assess the systemic effects of PKR activation included markers of coagulation, inflammation, and hypoxia in the 12-week cohort only. As of May 24, 2021, 15 patients who completed the 2-week dose cohorts and 7 patients treated in the 12-week dose cohort were evaluable for this analysis. The intrinsic effects of etavopivat on the sRBCs of patients receiving 2 weeks of treatment are summarized in Table 1. Etavopivat significantly increased Hb and reduced reticulocytes, including immature reticulocytes (CD71 +), suggesting that an etavopivat-mediated increase in sRBC lifespan is accompanied by a decrease in erythropoietic stress. In addition, etavopivat reduced 2,3-DPG levels thereby increasing HbS O 2 affinity (decreased P 50) resulting in a significant shift in the point of sickling (PoS) to a lower partial O 2 pressure. The deformability (EI max) of the sRBCs as measured by oxygenscan and osmoscan was significantly improved with etavopivat treatment, consistent with reduced membrane damage due to decreased HbS polymerization and improved membrane repair enabled by increased ATP production, collectively improving the health of the sRBC membrane. This improvement in membrane health was further supported by a significant reduction in the external expression of phosphatidylserine (PS) following etavopivat treatment. Finally, etavopivat significantly improved enzymatic activity not only of PKR but also superoxide dismutase and glutathione reductase, enzymes involved in reducing oxidative stress in sRBCs. This suggests that etavopivat-treated sRBCs may have an improved ability to inhibit and repair damage caused by reactive O 2 species, thereby improving overall sRBC health and function. Initial results on the effect of etavopivat on systemic biomarkers that are commonly elevated in SCD are shown in Table 2. In patients receiving etavopivat 400 mg once daily for up to 12 weeks, tumor necrosis factor-a and prothrombin 1.2, as systemic markers of inflammation and hypercoagulability, respectively, showed a significant decrease compared with baseline. Furthermore, a trend towards reduced erythropoietin levels suggests that etavopivat treatment may reduce tissue hypoxia. Patients with SCD treated with etavopivat for at least 2 weeks demonstrated a significant increase in RBC membrane deformability and improved antioxidant capacity that resulted in increased sRBC survival and decreased anemia. The reduced reticulocyte count and lowered PS surface membrane expression suggest that etavopivat-treated sRBC may have reduced adhesive properties and may thus be less likely to promote vaso-occlusion. Initial studies evaluating the downstream effects of up to 12 weeks of etavopivat treatment once daily provided evidence for a reduction in markers of inflammation and hypercoagulability, with improved O 2 delivery capacity. These initial results suggest that the multimodal effects of decreased 2,3-DPG and increased ATP by PKR activation with etavopivat may have an impact on both the anemia and vaso-occlusive events that characterize SCD. Figure 1 Figure 1. Disclosures Kalfa: Agios Pharmaceuticals, Inc.: Other: Steering Committee, Research Funding; FORMA Therapeutics, Inc: Research Funding. Telen: GlycoMimetics, Inc.: Consultancy; Novartis, Inc.: Other: Data Safety Monitoring Board; Forma Therapeutics, Inc.: Consultancy, Research Funding; CSL Behring, Inc.: Research Funding; Doris Duke Charitable Foundation: Research Funding; National Institutes of Health: Research Funding. Saraf: Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding. Brown: Novo Nordisk: Consultancy; Imara: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Global Blood Therapeutics: Consultancy, Research Funding; Pfizer: Research Funding; Forma Therapeutics: Research Funding. Larkin: Forma Therapeutics, Inc.: Research Funding. Ribadeneira: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Schroeder: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Wu: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Kelly: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Kuypers: Forma Therapeutics, Inc.: Research Funding.

Abstract: Background: Sickle cell disease (SCD) is caused by polymerization of sickle hemoglobin (HbS), resulting in red blood cell (RBC) sickling, RBC destruction, vaso-occlusion and end-organ damage. GBT021601 is an oral, small molecule, next-generation HbS polymerization inhibitor. Similar to voxelotor, the first generation HbS polymerization inhibitor, GBT021601 increases hemoglobin-oxygen (Hb-O2) affinity and stabilizes hemoglobin (Hb) in the oxy-hemoglobin (oxyHb) state, thereby inhibiting polymerization of HbS in RBCs. The fraction of Hb bound to drug - (Hb occupancy) approximates the oxyHb molecules per RBC. Compared to voxelotor, GBT021601 has the potential to achieve higher Hb occupancies. GBT021601 achieves greater exposures per dose and is more potent as measured by improvements in hematological parameters in an in vivo SCD mouse model (Dufu, Kobina 2020). We hypothesized that GBT021601 would achieve a substantial reduction in RBC hemolysis and increase in hemoglobin while maintaining a favorable safety profile. We therefore explored safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) in healthy volunteer participants (HVs) and adults living with SCD. Methods: Two studies are in progress: 1) the first in human (FIH), randomized, double-blind, placebo-controlled, parallel group phase 1 study for HVs ages 18-55 years; and 2) a single arm, intrapatient single dose and multiple ascending dose study in homozygous HbSS SCD patients ages 18-60 years with baseline Hb levels ≥5.5 g/dL and ≤10.5 g/dL and without vaso-occlusive crisis or transfusion within 30 days of screening. The HV study tests single ascending doses (SAD) with a 6:2 randomization ratio. Doses administered to HV cohorts ranged from 50 mg to 2200 mg. The SCD patient study tests a single dose (100 mg) followed by multiple ascending doses of the study drug in the same patients to reach a % Hb occupancy of & gt;20-30% over 7 weeks. The primary endpoints for both studies are safety and tolerability. Secondary endpoints include PK and PD. For the patient study, additional secondary endpoints are confirmation of the relationship between time matched GBT021601 concentrations and the change from baseline of clinical measures of anemia and hemolysis. Hb occupancy is calculated as a percentage of the molar ratio of drug concentrations in RBCs to the estimated Hb concentrations (using MCHC) in RBCs. Results: As of July 22, 2021, 63 HVs and 6 adults with SCD were enrolled. Thirty-nine HVs completed the study; one discontinued due to moving to a new geographical area and 23 were in follow-up. GBT021601 was generally well-tolerated, most adverse events (AE) were Grade 1 and 2, there were no deaths, and there was one serious adverse event in a HV that was not related to the study drug. There were no AEs indicative of tissue hypoxia. GBT021601 showed linear PK, high partitioning into RBCs, and a dose dependent increase in percent hemoglobin occupancy in HVs (Figure 1). From single doses of 50 to 1400 mg, the mean preliminary % Hb occupancy ranged from 0.88 to 25%, respectively, exceeding the Hb occupancies reported for HV receiving single doses of voxelotor over a similar range (Putz, 2017). Six adults with SCD have received a single 100 mg dose of GBT021601 and the dose has been well tolerated. Multiple-dose data in adults will be presented. Conclusions: Single doses of GBT021601 are well tolerated in HV and adults with SCD. Given its drug exposure, GBT021601 has the capacity to achieve a targeted Hb occupancy and attain the desired hematological effect at low doses, therefore reducing pill burden and improving clinical outcomes for individuals living with SCD. Forthcoming multiple-dose data will help to evaluate GBT021601's potential as a best-in-class, oral, disease-modifying therapy for SCD. Funding: This study was supported by Global Blood Therapeutics. Figure 1 Figure 1. Disclosures Brown: Pfizer: Research Funding; Imara: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Forma Therapeutics: Research Funding; Novo Nordisk: Consultancy; Global Blood Therapeutics: Consultancy, Research Funding. Redfern: Eisai: Other: Advisory Board; Linear Clinical Research: Current Employment; Pfizer: Other: Advisory Board; Novartis: Other: Advisory Board; Astra Zeneca: Other: Advisory Board; Roche: Other: Advisory Board. Lisbon: Global Blood Therapeutics: Current Employment. Washington: Global Blood Therapeutics: Consultancy. Agodoa: Global Blood Therapeutics: Current Employment, Current equity holder in publicly-traded company. Smith-Whitley: Global Blood Therapeutics: Current Employment.

Abstract: Background: Vaso-occlusive crises (VOCs) are the hallmark of SCD. The cell adhesion molecule P-selectin plays a key role in the multicellular interactions that can lead to VOCs. In the SUSTAIN trial in adults, crizanlizumab 5.0 mg/kg, a humanized monoclonal antibody that blocks P-selectin, significantly reduced the median annualized rate of VOCs vs placebo and had a favorable safety profile (Ataga et al. N Engl J Med 2017). Aim: To describe initial safety and efficacy results for patients (pts) with SCD aged 12- & lt;18 yr treated with crizanlizumab 5.0 mg/kg, with or without hydroxyurea (HU), in the SOLACE-kids trial (ClinicalTrials.gov NCT03474965). Methods: SOLACE-kids is a Phase II study to confirm and establish appropriate dosing and evaluate safety of crizanlizumab in pediatric pts with SCD (any genotype) and ≥1 VOC leading to a healthcare (HC) visit within 12 mo prior to screening. Pts (N≥100) are stratified by age: Group 1 (G1; 12- & lt;18 yr), Group 2 (6- & lt;12 yr) and Group 3 (6 mo- & lt;6 yr). Part A of the trial will confirm and establish crizanlizumab dosing based on first-dose and multiple-dose pharmacokinetic (PK) results (targeting similar exposure to adults) and safety in each group; Part B will expand recruitment for pts and evaluate long-term safety and efficacy of the PK-confirmed dose. Crizanlizumab is administered on Day 1, Day 15, then every 4 wk (up to 2 yr). Primary endpoints are PK and pharmacodynamic parameters (after starting dose and multiple doses) and frequency of adverse events (AEs). Secondary endpoints include the annualized rate of VOCs leading to HC visit, annualized rate of hospitalizations/emergency room (ER) visits and additional safety measures. This analysis focuses on safety and efficacy data of G1 pts receiving crizanlizumab 5 mg/kg. Results: As of 28 August 2020, 50 pts were enrolled in G1 of SOLACE-kids. Mean (SD) age of pts was 15.0 (1.92) yr, 29 (58%) were female, 44 (88%) had the HbSS genotype, 32 (64%) were Black/African American and 42 (84%) were receiving HU. Median (range) duration of exposure to crizanlizumab was 36.6 (6-98) wk; 44 (88%) pts received treatment for ≥26 wk. The most commonly reported AEs were headache (n=14 [28%]), vomiting (n=12 [24%] ) and back pain (n=9 [18%]). Grade ≥3 AEs were reported in 13 (26%) pts; most common were anemia (n=3 [6%] ) and back pain (n=2 [4%]). Serious AEs were reported in 11 (22%) pts; none were deemed related to treatment. Incidence of AEs of special interest (AESI) is shown in Table 1. No AESI led to treatment discontinuation except 1 pt who died of meningitis (not related to treatment). No infusion-related reactions were serious; all had resolved at data cut-off (except for 1 case of Grade 1 dizziness). No case of anaphylactic reaction to crizanlizumab was reported. Pain events on the day of crizanlizumab infusion suspected to be related to treatment were reported in 3 (6%) pts. All pain events, regardless of relationship to treatment, were Grade 1/2, except for two Grade 3 events reported in the same pt (back pain and pain in extremity), which resolved on day of onset. All hemorrhage events were mild and not considered related to treatment. Increase from baseline (BL) in total bilirubin, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was reported in 29 (58%), 17 (34%) and 20 (40%) pts, respectively. 2 (4%) pts had Grade 4 total bilirubin significantly above normal (1 pt was Grade 4 and 1 pt was Grade 3 at BL); 21 (42%) pts had Grade 3 total bilirubin significantly above normal (5 pts were Grade 3 at BL). Grade 3 increase in ALT and AST was reported in 2 (4%) pts each. All reported liver function parameters did not meet study criteria for severe drug-induced liver injury. The median (range) number of VOCs leading to a HC visit was 3.0 (1.0-26.0) at BL and 1.6 (0.0-12.7) on treatment (median absolute reduction: 1.0 [range: -13.3 to 5.8]). 18 (36%) pts did not experience a VOC leading to a HC visit while on treatment. The median (range) annualized rate of hospitalizations/ER visits at BL was 4.0 (1.0-36.0) vs 1.54 (0.0-14.3) on treatment (median reduction: 2.35 [range: -21.7 to 5.3] ) (Table 2). Conclusion: This initial analysis of SOLACE-kids shows crizanlizumab 5.0 mg/kg is safe and well tolerated in pts aged 12- & lt;18 yr, consistent with the established profile of crizanlizumab in adult pts. No new safety signals were identified. Compared with BL, crizanlizumab 5.0 mg/kg treatment led to a median reduction of 1 VOC leading to a HC visit/year in this pt population. Figure 1 Figure 1. Disclosures Heeney: FORMA: Consultancy, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Vertex / Crispr Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: DSMB; bluebird bio: Consultancy; Keros: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: DSMB; Cyclerion: 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. Rees: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Addmedica: Honoraria; TauRx: Membership on an entity's Board of Directors or advisory committees. De Montalembert: Vertex: Membership on an entity's Board of Directors or advisory committees; bluebird bio: Membership on an entity's Board of Directors or advisory committees; Addmedica: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Odame: Novo Nordisk: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Steering Committee; Global Blood Therapeutics: Other: DSMB. Brown: Imara: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Novo Nordisk: Consultancy; Forma Therapeutics: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Consultancy, Research Funding. Wali: Novatis Oncology: Research Funding. Nguyen: Novartis: Current Employment. Lam: Novartis Pharmaceuticals Corporation: Current Employment, Current equity holder in publicly-traded company. Pfender: Novartis: Current Employment, Current equity holder in publicly-traded company. Kanter: Fulcrum Therapeutics, Inc.: Consultancy; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Forma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios: Honoraria, Membership on an entity's Board of Directors or advisory committees; Beam: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Graphite Bio: Consultancy; GuidePoint Global: Honoraria; Fulcrum Tx: Consultancy.

Abstract: Background Sickle cell disease (SCD) and thalassemia are inherited hemoglobinopathies characterized by lifelong anemia. In SCD, a single mutation in the β-globin gene results in sickle hemoglobin (HbS) that polymerizes upon deoxygenation, causing red blood cells (RBCs) to sickle leading to a variety of complications. In thalassemia, mutation(s) in α- or β-globin genes result in reduced or absent adult Hb causing ineffective erythropoiesis and downstream complications. The resultant anemias are exacerbated by impaired RBC function due to decreased ATP content. Supportive care and agents like hydroxyurea are used most in SCD, with a subset of patients (pts) on regular transfusions. Regular or episodic transfusions, with their own set of complications, are the mainstay of treatment for thalassemias. Etavopivat, a potent, selective, oral, small molecule activator of erythrocyte pyruvate kinase (PKR) increases ATP and decreases 2,3 diphosphoglycerate (2,3-DPG). In a Phase 1 study, etavopivat 300‒600 mg once daily in pts with SCD not regularly transfused was well-tolerated, improved hematological markers, decreased hemolysis, and improved markers of RBC functional health (Brown et al. EHA 2021 # EP1202). Etavopivat 200 and 400 mg once daily (dose levels predicted to provide the desired pharmacodynamic response profiles) is being evaluated in a Phase 2/3 study of pts with SCD who are not on chronic transfusions (The Hibiscus Study, NCT04624659). Herein we describe the design of a Phase 2, open-label, multicenter study (NCT04987489) evaluating the efficacy and safety of etavopivat in pts with: SCD on chronic transfusions (Cohort A), transfusion-dependent thalassemia (Cohort B), and non-transfusion-dependent thalassemia (Cohort C). Study Design and Methods Up to 20 pts aged 12-65 years will be enrolled in each of the three cohorts described above. Pts will receive etavopivat 400 mg once daily for 48-wks (Figure). In cohorts A and B, pts must have received ≥6 RBC units in the 24 wks before the first dose of etavopivat without a & gt;35-day transfusion-free period during that period and be on iron chelation therapy for & gt;3 months before enrollment. Additionally, pts in Cohort A should have received ≥24 monthly transfusions for the prevention or treatment of primary stroke. Pts in Cohort C should have a Hb ≤10 g/dL. Key exclusion criteria include significant infection, hepatic/renal dysfunction, history of malignancy/cardiac/pulmonary disease, a drug malabsorption disorder, prior/concomitant therapies ≤3 months before the first dose (eg, chronic systemic glucocorticoids, new chelation therapy). Baseline assessments will include medical, disease, transfusion, and medication histories. Transfusions received during the study (every ~3-5 wks) will be recorded and include Hb values before and ≥15 minutes after transfusion, number of RBC units, and volume of packed RBCs. If a pt has an increase in pre-transfusion Hb of ≥1.0 g/dL compared with their baseline pre-transfusion Hb, the Investigator may delay transfusion by 1 wk or reduce the number of RBC units transfused. In pts with SCD, RBC exchange may also be performed. The primary endpoint for Cohorts A/B is erythroid response defined as the proportion of pts with ≥20% reduction in transfusions over a continuous 12-wk treatment period versus baseline, and for Cohort C is Hb response at Wk 12 defined as an increase in Hb of ≥1.0 g/dL from baseline. For Cohorts A/B, secondary and exploratory endpoints include the proportion of pts with a reduction in transfusions over 12 wks of ≥33% and ≥50%, respectively, and a reduction in transfusions over 12, 24, and 48 wks; and for Cohort C, Hb response at Wks 24 and 48, and changes from baseline in Hb over 12, 24, and 48 wks. The following additional endpoints will be assessed for all cohorts: changes from baseline in quality of life as assessed via the Short Form Health Survey and Patient-Reported Outcome Measurement Information System Fatigue Scale; changes from baseline in the levels of serum ferritin at 12, 24, and 48 wks; liver iron at 48 wks; 2,3-DPG and ATP; pharmacokinetics; and safety. All primary endpoints will be analyzed using a 1-sided test at α=0.025. Summary Etavopivat is a novel, investigational, PKR activator designed to improve the functional health of RBCs. This Phase 2 study will assess the safety of etavopivat and its impact on Hb levels and transfusion burden in pts with SCD or thalassemia. Figure 1 Figure 1. Disclosures Lal: Chiesi: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; bluebird bio, Inc.: Research Funding; Protagonist Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios Pharmaceuticals: Consultancy; Insight Magnetics: Research Funding; Novartis: Research Funding; Terumo Corporations: Research Funding; La Jolla Pharmaceutical Company: Research Funding. Brown: Novo Nordisk: Consultancy; Novartis: Consultancy, Research Funding; Imara: Consultancy, Research Funding; Forma Therapeutics: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Consultancy, Research Funding. Coates: Apo Pharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: 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; Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Chiesi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Research Funding; Forma Pharma: Consultancy; Sangamo: Consultancy; UpToDate: Patents & Royalties; Vifor Pharma: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees. Kalfa: Agios Pharmaceuticals, Inc.: Other: Steering Committee, Research Funding; FORMA Therapeutics, Inc: Research Funding. Kwiatkowski: Bioverativ: Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; CRISPR: Research Funding; Imara: Consultancy, Research Funding; Silence Therapeutics: Consultancy; Sangamo: Research Funding; bluebird bio: Consultancy, Research Funding; Chiesi: Research Funding; Vertex: Research Funding. Brevard: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of stock options in a privately-held company. Potter: Forma Therapeutics, Inc: Current Employment, Current equity holder in publicly-traded company; Bristol Myers Squibb: Ended employment in the past 24 months. Wood: Forma Therapeutics, Inc: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. Sheth: Bluebird bio: Consultancy; CRISPR: Consultancy; Bristol Myers Squibb: Consultancy, Research Funding; Imara: Research Funding; Chiesi: Consultancy; Agios: Consultancy; Dispersol: Research Funding.

Abstract: Etavopivat is a small molecule activator of erythrocyte pyruvate kinase (PKR), that increases PKR activity, resulting in decreased 2,3-DPG and increased ATP in red blood cells (RBCs) of healthy volunteers (HV) and patients (pts) with sickle cell disease (SCD) (Kalfa 2019, Brown 2020). Based on initial safety, pharmacokinetic (PK) and pharmacodynamic (PD) data for HVs and pts with SCD, we performed multiple-dose studies in pts with SCD (NCT03815695): 2-wk multiple ascending dose (MD) cohorts to identify the once daily etavopivat dose that provides maximum PD activity with an acceptable safety profile and a 12-wk open label (OL) study to further characterize the safety and clinical activity at the maximum PD dose. These data are presented here. In the completed MD cohorts, 20 pts with SCD were randomized 8:2 to receive etavopivat (300 mg, then 600 mg) or placebo (PBO) once daily for 2 wks. In the ongoing OL cohort, up to 20 pts will receive etavopivat 400 mg once daily for 12 wks. Safety assessments included adverse events (AEs), vital signs, electrocardiograms, and peripheral blood laboratory parameters. PK/PD blood sampling was performed for up to 72 h after last dose and at end of study visit. RBC function studies were performed to assess membrane deformability (Lorrca ®). Enrollment in the MD cohorts (n=17 HbSS, n=2 HbSβ+thalassemia, n=1 HbSC) is complete and data unblinded (n=8: 300 mg etavopivat; n=8: 600 mg etavopivat; n=4: PBO). As of July 13, 2021, 11 pts (n=10 HbSS, 1 HbSC) have been treated in the OL cohort: median treatment duration was 12 (range 1-12) wks, 6 pts completed 12 wks of treatment. In MD pts, etavopivat demonstrated dose-proportional PK with overlapping PD responses (decreased 2,3-DPG and increased ATP), confirming prior results in HVs that etavopivat 400 mg once daily provides near maximal PD activity. Etavopivat was well tolerated in both MD and OL cohorts. AEs were reported in 1 of 4 (25%) MD PBO pts, most were grade (gr) ≤3, with 1 gr 4 blood creatine phosphokinase (CPK) increase. 13 of 16 (81%) etavopivat-treated MD pts reported AEs, most were gr 1/2 and commonly ( & gt;2 pts) included sickle cell pain (n=6 [38%]), headache (n=5 [31%] ), and nausea (n=3 [19%]). One pt had a serious AE (SAE) of gr 3 vaso-occlusive crisis (VOC) after completion of etavopivat (considered unrelated). In the OL cohort, AEs were reported in 7 of 11 (64%) pts who received at least 1 wk of etavopivat. AEs reported in & gt;1 pt were headache and VOC (n=2 [18%] each). Most AEs were gr 1/2; one pt had SAEs of gr 3 acute chest syndrome and VOC (unrelated), one pt had an SAE of gr 3 deep vein thrombosis (possibly related), and one pt had an AE of gr 4 transient blood CPK increase (unrelated). Hematologic and hemolytic parameters were significantly improved at end of treatment in both MD and OL cohorts (Table 1); 11 of 15 (73%) evaluable MD pts achieved a Hb increase ≥1g/dL over baseline (mean 1.1 g/dL, P & lt;0.004). Decreases in absolute reticulocyte count (ARC), indirect bilirubin and lactate dehydrogenase (LDH) were observed (Table 1). These initial observations were sustained in pts receiving up to 12 wks of etavopivat in the OL cohort (Table 1, Fig. 1). Of 6 pts who completed 12 wks of etavopivat treatment, 5 (83%) achieved & gt;1g/dL Hb increase over baseline (mean 1.39 g/dL). Reductions in ARC, indirect bilirubin and LDH were also observed. Of 9 pts on etavopivat for at least 4 wks, 8 (89%) reported an increase in Hb & gt;1g/dL, and the highest mean Hb increase was 1.81 g/dL during active treatment. Etavopivat-treated RBCs from MD pts (n=14) demonstrated improved functional health, including point of sickling and deformability. The improved deformability persisted up to 1 wk after etavopivat treatment in 36% of pts. Similar results were observed in the initial OL pts. Data on additional treated pts will be presented. Etavopivat 400 mg once daily for up to 12 wks was well-tolerated, with a safety profile consistent with underlying SCD. Increases in Hb & gt;1 g/dL were observed in 89% of pts and maintained throughout 12 wks of treatment in the majority (83%) of pts. Increased Hb and a significant reduction in ARC indicated that etavopivat enhanced survival of sickle RBCs and significantly improved the severe anemia associated with SCD. These longer-living sickle RBCs have improved membrane health that may further reduce the risk of VOCs and end-organ damage. These results support further evaluation of etavopivat in the ongoing Phase 2/3 Hibiscus Study in pts with SCD (NCT04624659). Figure 1 Figure 1. Disclosures Brown: Imara: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Novo Nordisk: Consultancy; Forma Therapeutics: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Consultancy, Research Funding. Saraf: Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding. Idowu: Pfizer: Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Forma Therapeutics, Inc.: Research Funding; Ironwood: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding. Kalfa: Agios Pharmaceuticals, Inc.: Other: Steering Committee, Research Funding; FORMA Therapeutics, Inc: Research Funding. Geib: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Forsyth: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Schroeder: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Wu: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Kelly: Forma Therapeutics, Inc.: Current Employment, Current equity holder in publicly-traded company. Telen: GlycoMimetics, Inc.: Consultancy; Novartis, Inc.: Other: Data Safety Monitoring Board; Forma Therapeutics, Inc.: Consultancy, Research Funding; CSL Behring, Inc.: Research Funding; Doris Duke Charitable Foundation: Research Funding; National Institutes of Health: Research Funding.

Abstract: Background: Pulmonary function is particularly susceptible to acute and chronic injury occurring in patients with sickle cell anemia (SCA). Acute Chest Syndrome (ACS), a common and potentially fatal complication of SCA, can be the cause or the consequence of abnormal pulmonary function (Siddiqui & Ahmed, 2003). Use of hydroxyurea therapy (HU) is increasing for children with recurrent pulmonary complications, following the findings that HU reduces risk of ACS in adults (Charache et al, 1995). How HU may improve pulmonary function in children with SCA is still ill-defined. The purpose of this study was to assess the change observed on serial pulmonary function tests (PFT) for children prescribed HU for abnormal pulmonary function. Methods: Over 240 children with pulmonary complications, such as acute chest syndrome, reactive airway disease, and chronic hypoxia, have been evaluated in the Sickle Cell Pulmonary Clinic at Children’s Healthcare of Atlanta since beginning in July 2000. As part of the Clinic’s standard of care, PFT were routinely attempted on children over the age of 5. A retrospective review of PFT results was done for the children with SCA and prior abnormal PFT. Children were included in the HU cohort (+HU) if repeat PFTs were available following & gt; 3 months on HU therapy and if time on HU did not include frequent RBC transfusions. Children without history of HU therapy (−HU) were selected for comparison. PFTs were performed on a standard plethysmograph. Paired t-test was used to evaluate observed differences. Results: Thirty-one children with prior abnormal PFT had test before and following prescription of HU. Their mean age was 12.6 (range 6–20) years and mean duration of HU was 21 (range 4–47) months at the time of the repeat PFT. Hematologic changes expected on HU occurred for all 31 children. Twenty-four children followed for abnormal PFT had no history of HU (−HU) and matched the +HU group by gender, age (mean 12.3, range 7–19 years), duration followed at time of repeat PFT (mean 19, range 3–66 months; p=0.36), and initial hematologic parameters. Spirometry findings changed for +HU group, and remained stable for −HU group. Mean FVC and FEV1 values improved significantly on HU, when compared to initial (PreHU) PFT and to −HU controls. Conversion to a normal PFT, as interpreted by a pediatric pulmonologist masked to treatment status, occurred in 18 (58%) and 2 (8%) children in the +HU and −HU groups, respectively. Table 1: Serial PFT and hematologic parameters according to HU exposure −HU (n=24) +HU (n=31) Initial Repeat # PreHU Repeat 1 % predicted value for age, sex and height of subject. 2Mean (SD) #No significant changes compared to Initial, p & gt; 0.05. *P value & lt; 0.001 compared to PreHU; ++P value & lt; 0.001 compared to −HU repeat. PFT parameter 1 TLC 88 (13.6)2 85 (11.7) 85 (13.4) 90 (13.5) FVC 78 (9.8) 79 (9.9) 75 (12.6) 90 (13.2)*,++ FEV1 75 (9.6) 74 (12.2) 72 (11.4) 86 (10.2)*,++ FEF 25-75 75 (22) 72 (28.0) 77 (23.4) 79 (26.8) FEV1/FVC (%) 85(6.7) 82 (9.8) 87 (11.8) 86 (11.1) Pulse oximetry (%) 95 (3.1) 96 (2.4) 94 (4.4) 97 (2.8)* WBC (x103/ul) 14 (3.8) 13 (2.9) 13.02 (2.9) 9.0 (2.1) *,++ Hb (g/dl) 8.0 (0.1) 8.0 (0.9) 7.8 (1.1) 9.1 (1.3) *,++ MCV (fl) 84 (9.2) 85 (10.0) 87.3 (8.1) 101.2 (10.1) *,++ HbF (%) 4.3 (1.5) 5.2 (5.2) 6.0 (3.8) 14.0 (7.3) *,++ Conclusions: Serial PFTs showed improved pulmonary function, following initiation of HU therapy in children with prior abnormal PFT. Routine PFT assessments of children prescribed HU may serve as an objective measure of clinical response in children with SCA and pulmonary complications. These results will help in the design of future prospective studies examining the clinical benefits of HU therapy for children at risk for long-term pulmonary complications.

Abstract: Vaso-Occlusive Crises (VOCs) in patients with SCD cause acute and chronic morbidity including disabling pain, hospitalizations, missed school and work, end-organ damage, and early mortality. VOC prophylaxis, while beneficial, does not address the disabling pain and morbidity of breakthrough VOC events that still occur. E-selectin upregulation on vascular endothelium leads to leukocyte trapping, activation and aggregation and is a critical driver of acute VOC (Morikis et al, Blood 2017). Rivipansel, a pan-selectin inhibitor with potent activity against E-selectin, prevents interaction between leukocytes and vascular endothelium (Morikis et al, Blood 2017) and increases blood flow by reducing cell-cell aggregates and vascular occlusion in a SCD mouse model (Chang et al, Blood 2010). A phase 2 study of rivipansel in VOC demonstrated shorter hospital stays and reduced opioid use (Telen et al Blood, 2015). The RESET trial (NCT02187003) was a phase 3, randomized, double-blind, placebo-controlled, study of the efficacy and safety of rivipansel for VOC requiring hospitalization. Three hundred forty-five patients (204 patients ≥18 and 141 patients 6-17 years of age) were randomized to an intravenous rivipansel loading dose, followed by up to 14 additional doses Q 12 hr, or placebo, in addition to standard care. Overall, 320 were treated: 162 with rivipansel, 158 with placebo. Pre-treatment variables were well balanced, including concomitant hydroxyurea use, genotype, chronic opioid use, gender, and country. The primary endpoint was time to readiness for discharge (TTRFD), and key secondary endpoints were time to discharge (TTD), time to discontinuation of IV opioids (TTDIVO), and cumulative IV opioid use (CIVO). Hazard ratios or ratios of medians, and confidence intervals were calculated for each. Both study arms had comparable baseline soluble E-selectin (sE-sel) levels and inflammatory/coagulation biomarkers. Median sE-sel in the rivipansel group decreased by 59% from baseline after a loading dose while increasing by 9% in the placebo group. Although the RESET study did not show statistically significant improvements in outcomes for the total population, additional analysis demonstrated that rivipansel treatment within 26.4 hr of pain onset (earliest quartile of duration of VOC until treatment) reduced median TTRFD by 56.3 hrs (from 122.0 to 65.7 hrs), reduced median TTD by 41.5 hrs (from 112.8 to 71.3 hrs), and reduced median TTDIVO by 50.5 hrs (from 104.0 to 53.5 hrs), compared to placebo. There was also a consistent trend for lower hazard ratios for rivipansel treatment earlier during VOC (up to ~36 hr from onset) for all endpoints (Figure 1). Pediatric subjects (6-17 yrs, n = 141) were 41% of patients treated in the RESET trial (71 in rivipansel arm, 70 in placebo arm). As in the overall population the observed benefit with rivipansel in pediatric subjects depended on duration of VOC prior to treatment. Children 6-17 yrs of age treated with rivipansel within 30 hrs of onset of VOC experienced reduction in median TTRFD by 29.3 hrs (from 94.1 to 64.8 hrs), reduction in median TTD by 23.2 hrs (from 92.8 to 69.6 hrs), and reduction in median TTDIVO by 15.4 hrs (from 68.9 to 53.5 hrs). Early treatment with rivipansel decreased median TTRFD by more than one day and led to more children ready for discharge by 24, 48, and 72 hrs, compared to patients receiving placebo (Table 1). Additionally, pain scale assessments (VAS and Faces scale) showed a substantial reduction in the time to first clinically meaningful reduction in pain (data not shown). Thus, the hazard ratios for the efficacy endpoints favored early rivipansel treatment over placebo in the overall population and the pediatric population (Table 2). Summary: Rivipansel administered early in VOC results in clinically meaningful benefit for adults and children with SCD, shortening IV opioid use and hospital stay. Biomarker data confirm on-target effect, suggesting that the diminishing effect of later rivipansel treatment results from downstream pathophysiology. These findings suggest the utility of early treatment to shorten or interrupt acute VOCs, analogous to thrombolysis for heart attack or stroke. This could change the VOC treatment paradigm from deferral of hospitalization to one of early intervention to reduce length of hospitalization and IV opioid requirement, relieve VOC symptoms, and possibly mitigate end-organ damage from tissue ischemia. Disclosures Dampier: Merck: Research Funding; Hudson Publishing Company: Consultancy, Research Funding; CLS Behring: Consultancy, Other: DSMB Chair; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Micelle Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cyclerion: Consultancy, Other: DSMB Chair; Novartis: Research Funding. Telen:GlycoMimetics Inc.: Consultancy; Forma Therapeutics: Research Funding; CSL Behring: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Wun:GlycoMimetics, Inc.: Consultancy; Pfizer, Inc.: Other: Steering Committee for clinical study, Research Funding. Smith:Incyte: Other: Investigator; Pfizer: Consultancy; Ironwood: Consultancy; Novo Nordisk: Consultancy; Imara: Research Funding; Shire: Research Funding; NHLBI: Research Funding; Patient-Centered Outcomes Research Institute: Other: Investigator, Research Funding; Health Resources and Services Administration: Other: Investigator, Research Funding; Shire, Inc.: Other: Investigator, Research Funding; Global Blood Therapeutics, Inc.: Consultancy, Research Funding; Novartis, Inc.: Consultancy, Other: Investigator, Research Funding; Emmaeus Pharmaceuticals, Inc.: Consultancy; GlycoMimetics, Inc.: Consultancy. Brown:Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Forma Therapeutics, Inc,: Research Funding; Imara, Inc.: Consultancy, Research Funding; Novartis, Inc.: Consultancy, Research Funding. Desai:Pfizer, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; GBT, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Ironwood Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees; Rockpointe Continuing Medical Education Company: Consultancy. El Rassi:Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Cyclerion: Research Funding; Pfizer: Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bluebird bio: Membership on an entity's Board of Directors or advisory committees. Kanter:Wells Fargo: Honoraria; Medscape: Honoraria; Guidepoint Global: Honoraria; NHLBI Sickle Cell Advisory Board: Membership on an entity's Board of Directors or advisory committees; SCDAA Medical and Research Advisory Board: Membership on an entity's Board of Directors or advisory committees; AGIOS: Membership on an entity's Board of Directors or advisory committees; BEAM: Membership on an entity's Board of Directors or advisory committees; Jeffries: Honoraria; GLG: Honoraria; Sanofi: Consultancy; bluebird bio, inc: Consultancy, Honoraria; Novartis: Consultancy; Cowen: Honoraria. Pastore:Pfizer: Honoraria. Rothman:Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Agios Pharmaceuticals: Honoraria, Research Funding. Readett:Pfizer, Inc.: Current Employment. Lozier:GlycoMimetics, Inc.: Current Employment, Current equity holder in publicly-traded company. Magnani:GlycoMimetics, Inc.: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Thackray:GlycoMimetics, Inc.: Current Employment. Hassell:Pfizer, Inc.: Other: RESET Study Steering Committee; Pfizer, Inc.: Research Funding.