Anemia in patients with sickle cell disease (SCD) increases 2,3-diphosphoglycerate (2,3-DPG), decreasing hemoglobin-oxygen (HbO2) affinity to improve oxygen offloading and promote hemoglobin polymerization (sickling) of red blood cells (RBCs). We report the discovery of FT-4202, an investigational, selective pyruvate kinase type-R (PKR) activator with a multimodal mechanism of action and potential to increase ATP and decrease 2,3-DPG, resulting in increased HbO2 affinity, decreased Hb polymerization, and improved RBC health. FT-4202 was identified via structure-enabled lead optimization medicinal chemistry using X-ray crystallography, molecular modeling, and thermal shift assays. FT-4202, an allosteric PKR activator, stabilizes the tetrameric enzyme and increases PKR activity in human and mouse RBCs in vitro. Seven-day oral administration of FT-4202 in Berkeley SCD mice reduced 2,3-DPG, increased HbO2 affinity, and reduced RBC sickling versus control. There were no adverse in vitro safety findings. FT-4202 offers a therapeutic opportunity to modify the course of SCD. (c) 2024 International Society for Experimental Hematology. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/)

Presentation Date: 6/9/2024 Presentation Start Time: 2:27:00 PM Fetal hemoglobin (HbF) is established as a potent modulator of severity in sickle cell disease (SCD); any increment has been shown to be beneficial. Hydroxyurea maintains HbF at high levels in children with SCD, with some decline at age 10 years. HU reduces widespread organ damage, and a HbF level > 8.6% corrects survival. Proportions of RBCs containing HbF (F-cells) and amount of HbF/cell are both considered important parameters for benefit, with >70% F-cells and 10 pg F/cell proposed as targets. As many adults do not tolerate optimal doses due to myelosuppression, additional therapies which can be used with HU are considered desirable. Benserazide (PB-04) was discovered in a high throughput screen to induce the fetal globin gene promoter, and to suppress or displace 4 repressors associated with HPFH, including Bcl-11A, KLF-1, LSD-1, and HDAC-3. In a Ph1b dose-ranging Study of PK, Safety, and preliminary efficacy (NCT04432631) which first enrolled beta thalassemia patients, active doses were identified which induced F-reticulocytes up to 14.8-fold, F-cells up to 7-fold, HbF/cell up to 11-fold, and HbF up to 14% >baseline. In a prior report, PB-04 treatment restored myelopoiesis which was profoundly suppressed by HU in sickle mice and reduced organ damage. Accordingly, 2 single daily doses were explored in 7 individual subjects with SCD, of whom 3 were taking HU at MTD. Patients with HbSS or S-beta thalassemia were enrolled sequentially to receive either 3 or 5 mg/kg/dose to a maximum dose of 350 mg, once/day, 3 days/week (QOD) for 24 wks. Baseline chemistry and CBC laboratory values, medical history, QOL assessments, and assays of HbF, F-cells, F-reticulocytes, and mean HbF/cell by flow cytometry were obtained during screening, every 4 weeks during the treatment period, and at 4-8 weeks afterwards. PK studies were performed on day 1 and at/ after week 4. Sickling of F-cells, F-reticulocytes after 20 minutes of deoxygenation was assessed by ImageMaster for round or sickled cells, and whole blood adhesion to VCAM were performed every 3 months. Although not powered to detect statistical significance, signed rank non-parametric tests or t-tests were preliminarily performed to assess potential early trends. Seven individual subjects (ages 31-51 years, mean 37 years; 4 female) enrolled on 8 treatment courses. There were no drug-related SAEs. Significant increases in F-cells (from mean BL 48.9% to 62.9% (p = 0.03), F-reticulocytes (mean increase 20%, p < 0.001), and HbF (up to 13.8% above BL) were observed. In HU-treated subjects, F-cells increased from mean 63% to 80%. A dose-proportional increase was observed in 3 subjects who were taking HU at MTD. Addition of PB-04 to 2/2 subjects at 5 mg/kg increased HbF further to levels >30% and F-cells >80%, and to 13% HbF, 94.7% F-cells in the subject who received the 3 mg/kg dose. The mean proportion of RBCs with normal morphology after prolonged deoxygenation increased from BL 50.9% to 82% (p = 0.043). Whole blood adhesion to VCAM declined in 3 subjects. Responses are illustrated in Figure 1. Preliminary investigation on a Ph1b safety study strongly suggests that PB-04 increases HbF expression assessed by F-cell proportions, amount of HbF/cell, and total HbF levels, has additive activity with HU, achieving targets for reducing disease severity. The findings support further investigation of this therapeutic and additional dosing regimens in larger numbers of patients with sickle cell disease. HbF Expression with PB-04 Baseline values are shown in blue; peak values with PB-04 are shown in yellow. Left panel: F-reticulocytes The top three subjects in the left panel were taking HU at MTD. Right panel: HbF/cell (MFI)

Exposure to both oxidative and shear stress, a condition that the red blood cell (RBC) continuously experiences in the circulation in vivo can be mimicked in a Couette type viscometer and monitored by ektacytometry. RBCs maintain their deformation and orientation under shear stress and oxidative stress until a threshold is reached at which these conditions appear to overwhelm the elaborate and complex pathways that maintain a proper redox environment in the cell. Oxidative stress under shear alters the ability of the cell to deform, changes cell morphology, its orientation in the shear stress field, and appears to alter intracellular and membrane characteristics. The application of the RoxyScan technology allows the comparison of oxidant effects and the role of antioxidant systems. This provides the opportunity to study the ability of RBC to deal with oxidative stress in various conditions, including RBC disorders such as sickle cell disease (SCD).

Etavopivat is an investigational, once-daily, oral, selective erythrocyte pyruvate kinase (PKR) activator. A multicenter, randomized, placebo-controlled, double-blind, 3-part, phase 1 study (https://clinicaltrials.gov/study/NCT03815695) was conducted to characterize the safety and clinical activity of etavopivat. Thirty-six patients with sickle cell disease (SCD) were enrolled into 4 cohorts: one single-dose; two multiple ascending doses; one open-label [OL]. In the OL cohort, 15 patients (median age 33.0 [range, 17‒55] years received 400-mg etavopivat once daily for 12 weeks; 14 completed treatment. Consistent with the mechanism of PKR activation, increases in ATP and decreases in 2,3-diphosphoglycerate were observed and sustained over 12 weeks’ treatment. This translated clinically to an increase in hemoglobin (mean maximal increase 1.6 [range, 0.8‒2.8] g/dL), with >1 g/dL increase in 11 (73%) patients during treatment. Additionally, oxygen tension at which hemoglobin is 50% saturated was reduced (P=.0007) with concomitant shift in point-of-sickling (P=.0034) to lower oxygen tension in oxygen-gradient ektacytometry. Hemolysis markers (absolute reticulocyte count, indirect bilirubin, lactate dehydrogenase) decreased from baseline, along with matrix metalloproteinase-9 and erythropoietin. In the OL cohort, adverse events (AEs) were mostly grade 1/2, consistent with underlying SCD; 5 patients had serious AEs. Vaso-occlusive pain episode was the most common treatment-emergent AE (n=7) in the OL cohort. In this first study of etavopivat in SCD, 400 mg once daily for 12 weeks was well-tolerated, resulting in rapid and sustained increases in hemoglobin, improved RBC physiology, and decreased hemolysis.

BackgroundIndividuals with sickle cell anemia (SCA) exhibit decreased exercise capacity. Anemia limits oxygen-carrying capacity and affects cardiopulmonary fitness. The drug voxelotor raises hemoglobin in SCA. We hypothesized that voxelotor improves exercise capacity in youths with SCA. MethodsIn a single-center, open-label, single-arm, longitudinal interventional pilot study (NCT04581356), SCA patients aged 12 and older, stably maintained on hydroxyurea, were treated with 1500 mg voxelotor daily, and performed cardiopulmonary exercise testing before (CPET#1) and after voxelotor (CPET#2). A modified Bruce Protocol was performed on a motorized treadmill, and breath-by-breath gas exchange data were collected. Peak oxygen consumption (peak VO2), anaerobic threshold, O-2 pulse, VE/VCO2 slope, and time exercised were compared for each participant. The primary endpoint was change in peak VO2. Hematologic parameters were measured before each CPET. Patient Global Impression of Change (PGIC) and Clinician Global Impression of Change (CGIC) surveys were collected. ResultsTen hemoglobin SS patients aged 12-24 completed the study. All demonstrated expected hemoglobin rise, with average +1.6 g/dL (p = .003) and P-50 left shift of average -11 mmHg (p < .0001) with decreased oxygen off-loading at low pO(2). The change in % predicted peak VO2 from CPET#1 to CPET#2 ranged from -12.8% to +11.3%, with significant improvement of more than 5% in one subject, more than 5% decrease in five subjects, and insignificant change of less than 5% in four subjects. All 10 CGIC and seven of 10 PGIC responses were positive. ConclusionIn a plot study of 10 youths with SCA, voxelotor treatment did not improve peak VO2 in 9 out of 10 patients.

Extensive evidence has shown fetal hemoglobin (HbF) is a major modulator of sickle cell disease (SCD) phenotype. Clinical benefit with any increment of HbF was shown in the NIH-sponsored Natural History Study and the Multicenter Study of Hydroxyurea (HU), with mean HbF increases of 3.6% above baseline (BL), to improve survival, reduce painful vaso-occlusive crises, and recently stroke prevention and improved cardiac and neurocognitive function with HU are reported. As some patients do not tolerate optimal HU doses due to cytopenias, additional inducers suitable for combined use are desirable. Proportions of F-cells and HbF-quantity/cell have been cited as important. PB-04, a repurposed drug with a well-known safety profile, is an oral fetal globin stimulant identified in high throughput screening, which suppresses 4 repressors of the HMG gene promoter, ( BCL-11A, LSD-1, HDAC-3, KLF-1). PB-04 induces fetal globin in nonhuman primates, transgenic mice, with additive effect when combined with HU in SCD erythroid progenitors, and was shown to reduce infarcts in multiple organs with preserved splenic function in transgenic sickle mice. An ongoing Phase 1b trial in beta thalassemia intermedia (BTI) ( NCT04432623) of 3 doses (1,3, or 5 mg/kg QD) given 3 (TIW) or 5 times/week (Wk) for 12 or 24 Wks in 18 courses in 10 subjects demonstrates a favorable safety profile, dose-proportional PK with 5 >3 mg/kg doses and 5 >3 doses/Wk, Median fold-increases from baseline (BL) in F-cells of 4.4x BL (range 2.3-7x), 2.8x F-reticulocytes (1.6-14.8x), and 6.5x (range 3-11x) increases in mean fluorescence intensity (MFI, representing amount of HbF/RBC). Mean increases in % HbF were 6.5%. Evaluation of PB-04 has now begun in 7 subjects with SCD, 19-51 yrs; 3 were receiving HU with HbF responses (12-22%). Adverse events, F-cells, F-reticulocytes, MFI (amount of HbF/RBC or HbF/reticulocyte) by FACS and ImageStream Analysis and % HbF are assessed Q 4 wks; flow adhesion of whole blood to VCAM-1 (FA-WB-VCAM) and sickling kinetics are assessed q 12 wks. In 4 subjects on 3 mg/kg QD TIW for 24 wks, changes observed from BL values included mean increases of 6% F-cells and 27% F-reticulocytes (2-fold) . In 3 ongoing subjects receiving 5 mg/kg QD TIW for 12 wks mean changes above BL are currently 13% F-cells, 15% F-reticulocytes; HbF/cell or HbF/reticulocyte have increased up to 10-fold. Mean % HbF has increased above HU effects in 2/3 pts on the second dose by 5-12.6% (mean 8.8%), producing 81-95% F-cells, and 35-38% HbF. Decline in FA-WB-VCAM) was observed ± HU and with both doses in 3 subjects. Correlation of HbF quantity/cell with RBC survival and sickling dynamics is being explored. These early results with not-yet-optimized doses of PB-04 suggest additive activity with HU, producing significant HbF and F-cell levels, and support further PK-optimized studies in patients with SCD.

Peroxisomes and the endoplasmic reticulum (ER) are intimately linked subcellular organelles, physically connected at membrane contact sites. While collaborating in lipid metabolism, for example, of very long-chain fatty acids (VLCFAs) and plasmalogens, the ER also plays a role in peroxisome biogenesis. Recent work identified tethering complexes on the ER and peroxisome membranes that connect the organelles. These include membrane contacts formed via interactions between the ER protein VAPB (vesicle-associated membrane protein-associated protein B) and the peroxisomal proteins ACBD4 and ACBD5 (acyl-coenzyme A-binding domain protein). Loss of ACBD5 has been shown to cause a significant reduction in peroxisome-ER contacts and accumulation of VLCFAs. However, the role of ACBD4 and the relative contribution these two proteins make to contact site formation and recruitment of VLCFAs to peroxisomes remain unclear. Here, we address these questions using a combination of molecular cell biology, biochemical, and lipidomics analyses following loss of ACBD4 or ACBD5 in HEK293 cells. We show that the tethering function of ACBD5 is not absolutely required for efficient peroxisomal β-oxidation of VLCFAs. We demonstrate that loss of ACBD4 does not reduce peroxisome-ER connections or result in the accumulation of VLCFAs. Instead, the loss of ACBD4 resulted in an increase in the rate of β-oxidation of VLCFAs. Finally, we observe an interaction between ACBD5 and ACBD4, independent of VAPB binding. Overall, our findings suggest that ACBD5 may act as a primary tether and VLCFA recruitment factor, whereas ACBD4 may have regulatory functions in peroxisomal lipid metabolism at the peroxisome-ER interface.

Background: Red blood cells (RBCs) are biconcave-shaped cells with viscoelastic membranes that are optimally adapted for oxygen delivery and gas exchange during their normal lifespan of 120 days. Reactive oxygen species (ROS) continuously challenge the viability of RBCs. Despite an arsenal of compounds to protect the RBC, including Glutathione (GSH), Vitamin E, superoxide dismutase (SOD) and Catalase, damage can easily be inflicted that will disrupt cellular deformability, structure, and membrane properties. The susceptibility to oxidative stress in individuals with Sickle Cell Disease (SCD) is believed to be linked to multiple factors. These include the release of heme and iron during hemolysis, inflammation processes, and a reduction in antioxidant defenses. Methods:Susceptibility of RBCs to oxidative stress was assessed with the RoxyScan. This novel application of the Lorrca MaxSis (RR Mechatronics) measures rheological behavior of RBCs in response to cumene hydroperoxide (CuHP, 100 µM) exposure during continuous shear (30 Pa). For this we used the Lorrca's peristaltic pump and suction needle, directing the blood and CuHP to the instrument's cup and mixing them for 30 seconds (s) before starting the run. Deformability of RBCs (EI, elongation index) was measured over time. PoX is defined as the time where a 10% decrease in EI is reached. EI start: EI t=0. EI final: EI t=1600s, ΔEI (EIstart-EIfinal). RoxyScan measurements were performed on blood samples from 16 adult SCD patients (HbSS, HbS/β0 or HbS/β+) and 19 healthy controls (HC). Outcome measurement PoX (calculated from curve fitted data) was correlated to laboratory parameters from complete blood count (Cell Dyn Sapphire, Abbott), RBC sickling tendency (Point of Sickling, PoS, as assessed by oxygen gradient ektacytometry on the Lorrca MaxSis), and levels of HbF/HbS (Tosoh G8). Results:RBCs from untreated HC show a stable EI over time (Fig 1A). Upon exposure to CuHP a similar decrease in EI is seen in 19 HC (Fig 1A), mean decrease 0.055, range (0.017 to 0.10). The mean and median calculated PoX in HC is 1723s and 1702s respectively. In contrast, SCD RBC showed an earlier and more pronounced decrease in EI in response to CuHP exposure (representative example, Fig 1A). Comparing the PoX between HC and SCD revealed significant differences: mean PoX HC: 1723s (SD 329s), SCD: 725s (SD 472s), ***p<0.0001, indicating that SCD RBCs are more susceptible to oxidative stress. Correlating PoX to routine laboratory parameters identified a correlation with Hb levels (***p=0.002), inverse correlation with reticulocyte count (***p=0.0014) and hemoglobin distribution width (HDW, ***p<0.001) (Fig 1B). Similarly strong inverse correlations were found for EI start and EI end (***p<0.001) (Fig 1B). PoX also showed an inverse correlation with red cell distribution width (RDW, ns p=0.07) and mean corpuscular volume (MCV, ns p=0.77). Interestingly, PoX showed a significant inverse correlation with PoS (***p=0.004), indicating that SCD RBCs which are more susceptible to oxidative stress tend to sickle at a higher oxygen tension. PoX showed no significant correlations with HbS/HbF levels (Fig 1B). Conclusion: In this study we demonstrate the applicability of the RoxyScan as a novel method to assess RBC resilience to oxidative stress. When applied to SCD, RBCs show an earlier and more pronounced response to oxidative stress than RBCs from HC. The inverse correlation of PoX, the major outcome parameter of this technique, with reticulocyte count could indicate a generally increased susceptibility to oxidative stress due to a higher level of hemolysis. The correlation with Hb levels affirms this. PoX showed other strong and significant correlations with routine laboratory parameters, such as HDW, implying that the greater variability in hemoglobin content is associated with higher susceptibility to oxidative stress. On a functional level, it is interesting to find strong correlations of PoX with PoS, showing a direct link between RBC sickling tendency and ability to withstand oxidative stress. On the other hand, HbS and HbF levels did not correlate significantly to PoX. Overall, our study highlights the potential use of the RoxyScan and its associated biomarkers in the analysis of the RBC's response to oxidative stress. Further research is in progress to investigate the clinical applicability of this new technique.

Background/Aims Cells adapt to chronic extracellular hypotonicity by altering metabolism. Corresponding effects of sustained hypotonic exposure at the whole-person level remain to be confirmed and characterized in clinical and population-based studies. This analysis aimed to 1) describe changes in urine and serum metabolomic profiles associated with four weeks of sustained > +1 L/d drinking water in healthy, normal weight, young men, 2) identify metabolic pathways potentially impacted by chronic hypotonicity, and 3) explore if effects of chronic hypotonicity differ by type of specimen and/or acute hydration condition. Materials Untargeted metabolomic assays were completed for specimen stored from Week 1 and Week 6 of the Adapt Study for four men (20-25 years) who changed hydration classification during that period. Each week, first-morning urine was collected after overnight food and water restriction, and urine (t+60 min) and serum (t+90 min) were collected after a 750 mL bolus of drinking water. Metaboanalyst 5.0 was used to compare metabolomic profiles. Results In association with four weeks of > + 1 L/d drinking water, urine osmolality decreased below 800 mOsm/kg H2O and saliva osmolality decreased below 100 mOsm/kg H2O. Between Week 1 and Week 6, 325 of 562 metabolic features in serum changed by 2-fold or more relative to creatinine. Based on hypergeometric test p-value <0.05 or Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway impact factor >0.2, the sustained > + 1 L/d of drinking water was associated with concurrent changes in carbohydrate, protein, lipid, and micronutrient metabolism, a metabolomic pattern of carbohydrate oxidation via the tricarboxylic acid (TCA) cycle, instead of glycolysis to lactate, and a reduction of chronic disease risk factors in Week 6. Similar metabolic pathways appeared potentially impacted in urine, but the directions of impact differed by specimen type. Conclusion In healthy, normal weight, young men with initial total water intake below 2 L/d, sustained > + 1 L/d drinking water was associated with profound changes in serum and urine metabolomic profile, which suggested normalization of an aestivation-like metabolic pattern and a switch away from a Warburg-like pattern. Further research is warranted to pursue whole-body effects of chronic hypotonicity that reflect cell-level effects and potential beneficial effects of drinking water on chronic disease risk.

Intravascular hemolysis results in the release of cell-free hemoglobin and heme in plasma. In sickle cell disease, the fragility of the sickle red blood cell leads to chronic hemolysis, which can contribute to oxidative damage and activation of inflammatory pathways. The scavenger proteins haptoglobin and hemopexin provide pathways to remove hemoglobin and heme, respectively, from the circulation. Heme also intercalates in membranes of blood cells and endothelial cells in the vasculature and associates with other plasma components such as albumin and lipoproteins. Hemopexin has a much higher affinity and can strip heme from the other pools and detoxify plasma from cell-free circulatory heme. However, due to chronic hemolysis, hemopexin is depleted in individuals with sickle cell disease. Thus, cell-free unbound heme is expected to accumulate in plasma. We developed a methodology for the accurate quantification of the fraction of heme, which is pathologically relevant in sickle cell disease, that does not appear to be sequestered to a plasma compartment. Our data show significant variation in the concentration of unbound heme, and rather unexpectedly, the size of the unbound fraction does not correlate to the degree of hemolysis, as measured by the concentration of bound heme. Very high heme concentrations (>150 µM) were obtained in some plasma with unbound concentrations that were several fold lower than in plasma with much lower hemolysis (<50 µM). These findings underscore the long-term effects of chronic hemolysis on the blood components and of the disruption of the essential equilibrium between release of hemoproteins/heme in the circulation and adaptative response of the scavenging/removal mechanisms. Understanding the clinical implications of this loss of response may provide insights into diagnostic and therapeutic targets in patients with sickle cell disease.

ObjectivesL-Glutamine is FDA-approved for sickle cell disease (SCD), yet the mechanism(s)-of-action are poorly understood. We performed a pharmacokinetics (pK) study to determine the metabolic fate of glutamine supplementation on plasma and erythrocyte amino acids in patients with SCD.DesignA pK study was performed where patients with SCD fasting for > 8 h received oral L-glutamine (10 g). Blood was analyzed at baseline, 30/60/90 min/2/3/4/8 hrs. A standardized diet was administered to all participants at 3 established time-points (after 2/5/7hrs). A subset of patients also had pK studies performed without glutamine supplementation to follow normal diurnal fluctuations in amino acids.SettingComprehensive SCD Center in Oakland, CaliforniaResultsFive patients with SCD were included, three of whom performed pK studies both with and without glutamine supplementation. Average age was 50.6 ± 5.6 years, 60% were female, 40% SS, 60% SC. Plasma glutamine levels increased significantly after oral glutamine supplementation, compared to minimal fluctuations with diet. Plasma glutamine concentration peaked within 30-min of ingestion (p = 0.01) before decreasing to a plateau by 2-h that remained higher than baseline by 8 h. Oral glutamine also increased plasma arginine concentration, which peaked by 4-h (p = 0.03) and remained elevated through 8-h. Erythrocyte glutamine levels began to increase by 8-h, while erythrocyte arginine concentration peaked at 4-h.ConclusionsOral glutamine supplementation acutely improved glutamine and arginine bioavailability in both plasma and erythrocytes. This is the first study to demonstrate that glutamine therapy increases arginine bioavailability and may provide insight into shared mechanisms-of-action between these conditionally-essential amino acids.

OBJECTIVES:Validation of the measurement of erythrocyte deformability as a useful prognostic, rheological biomarker for patients with sickle cell disease (SCD). METHODS:The degree of reduced deformability was based on the value of the maximum elongation index (EImax ) of the deformability curve of an osmotic gradient ektacytometer. The performance of this technique was analytically and clinically validated by analysing 200 normal subjects and 100 patients with well-documented thalassemia's and Hb variants in relation to their clinical condition. RESULTS:In this study, we show that EImax is a reproducible parameter with a small inter-individual coefficient of (Biological) variation (CV)=1.6% and a small intra-individual CV=3.5%. We demonstrate that loss of deformability correlates with the clinical condition and the various mutations underlying sickle cell disease and thalassemia. For SCD patients, a strongly reduced EImax with a cut-off =0.360 is a signal for future vaso-occlusive (VOC) events requiring hospitalisation with a specificity=85%, sensitivity=80%, PPV=81% and NPV=84% based on a ROC curve (AUC=0.89). CONCLUSION:This study validated the clinical utility of EImax as a prognostic marker for future clinical problems in individual high-risk SCD patients. In addition, EImax may help to achieve an adequate personal transfusion policy for an optimal blood flow in anaemic patients with SCD.

[This corrects the article DOI: 10.1371/journal.pone.0229718.].

The cytokine storm (CS) in hyperinflammation is characterized by high levels of cytokines, extreme activation of innate as well as adaptive immune cells and initiation of apoptosis. High levels of apoptotic cells overwhelm the proper recognition and removal system of these cells. Phosphatidylserine on the apoptotic cell surface, which normally provides a recognition signal for removal, becomes a target for hemostatic proteins and secretory phospholipase A2. The dysregulation of these normal pathways in hemostasis and the inflammasome result in a prothrombotic state, cellular death, and end-organ damage. In this review, we provide the argument that this imbalance in recognition and removal is a common denominator regardless of the inflammatory trigger. The complex reaction of the immune defense system in hyperinflammation leads to self-inflicted damage. This common endpoint may provide additional options to monitor the progression of the inflammatory syndrome, predict severity, and may add to possible treatment strategies.

The transfer of acyl chains to proteins and lipids from acyl-CoA donor molecules is achieved by the actions of diverse enzymes and proteins, including the acyl-CoA binding domain-containing protein ACBD6. N-myristoyl-transferase (NMT) enzymes catalyze the covalent attachment of a 14-carbon acyl chain from the relatively rare myristoyl-CoA to the N-terminal glycine residue of myr-proteins. The interaction of the ankyrin-repeat domain of ACBD6 with NMT produces an active enzymatic complex for the use of myristoyl-CoA protected from competitive inhibition by acyl donor competitors. The absence of the ACBD6/NMT complex in ACBD6.KO cells increased the sensitivity of the cells to competitors and significantly reduced myristoylation of proteins. Protein palmitoylation was not altered in those cells. The specific defect in myristoyl-transferase activity of the ACBD6.KO cells provided further evidence of the essential functional role of the interaction of ACBD6 with the NMT enzymes. Acyl-CoAs bound to the acyl-CoA binding domain of ACBD6 are acyl donors for the lysophospholipid acyl-transferase enzymes (LPLAT), which acylate single acyl-chain lipids, such as the bioactive molecules LPA and LPC. Whereas the formation of acyl-CoAs was not altered in ACBD6.KO cells, lipid acylation processes were significantly reduced. The defect in PC formation from LPC by the LPCAT enzymes resulted in reduced lipid droplets content. The diversity of the processes affected by ACBD6 highlight its dual function as a carrier and a regulator of acyl-CoA dependent reactions. The unique role of ACBD6 represents an essential common feature of (acyl-CoA)-dependent modification pathways controlling the lipid and protein composition of human cell membranes.

Background: Etavopivat, an investigational, once-daily, selective, activator of erythrocyte pyruvate kinase (PKR) increases PKR activity, resulting in decreased 2,3-DPG and increased ATP in red blood cells (RBCs) of healthy volunteers and patients (pts) with sickle cell disease (SCD).1,2 Aims: We report results of an open-label (OL) extension cohort from a Phase 1 study (NCT03815695) designed to characterize the safety and clinical activity of etavopivat at a maximal pharmacodynamic dose in pts with SCD. Methods: 15 pts were enrolled to receive etavopivat 400 mg once daily for 12 wks, followed by a 4-wk follow-up. Assessments included safety, pharmacokinetics, pharmacodynamics, RBC health parameters and systemic markers of SCD pathophysiology. Results: Of 15 pts (age 32.3 ±10.1 yr; HbSS/SC n=13/2), 14 completed 12-wks of treatment (tx); 1 pt discontinued tx after ~2 wks. Etavopivat 400 mg once daily was generally well tolerated. Adverse events (AEs) reported during tx and follow-up were commonly low grade (Gr) and consistent with pts’ SCD. Gr1-2 AEs in >2 pts (n [%]) were sickle cell pain events (9 [60%]); headache (5 [33%]); and upper respiratory tract infection (3 [20%]). The Gr3-4 AE in >1 pt was sickle cell vaso-occlusion (VOC; 4 [27%]). On-tx serious adverse events (SAEs; 1 pt each) were Gr3 VOC post Gr3 COVID (not tx-related) and Gr3 left femoral deep vein thrombosis (possibly related, resulting in tx discontinuation as stated above). SAEs (1 pt each) during the 4-wk follow-up were Gr3 acute chest syndrome + Gr3 VOC, Gr3 non-cardiac chest pain and Gr3 syncope (all unrelated). Observed increases in ATP and decreases in 2,3-DPG were durable over 12 wks of etavopivat tx. Etavopivat tx normalized hemoglobin (Hb)S-oxygen affinity to that of HbA. Etavopivat tx over 12 wks improved overall sickle RBC health, demonstrated by a reduction in point of sickling as well as improved measures of deformability and hydration of sickle RBCs (all P<0.01; Figure). Etavopivat tx over 12 wks was associated with a sustained significant increase in Hb compared with baseline (BL; P<0.0001), with mean maximal increase of 1.5 (range 0.7-2.3) g/dL. On-tx increase in Hb >1g/dL was achieved in 11 (73%) pts, for whom the mean maximal Hb increase was 1.8 (1.2-2.3) g/dL. Absolute reticulocytes, indirect bilirubin and lactate dehydrogenase significantly decreased from BL and were sustained over the 12wk period (all P<0.05), indicative of increased RBC lifespan and decreased hemolysis. Several markers of disease activity significantly decreased from BL during daily etavopivat tx, including the inflammatory marker tumor necrosis factor-α, which decreased by 35% (P<0.001). Based on preliminary exploratory analysis with an aggregate duration of etavopivat exposure of 3.32 pt-yrs in the OL cohort, a decrease in the trend for VOC hospitalizations was observed: annualized historical and on-tx VOC hospitalization rates were 0.93 and 0.30, respectively; the 1 on-tx VOC hospitalization was COVID-related. Image:Summary/Conclusion: Etavopivat 400 mg once daily for up to 12 wks demonstrated a tolerable safety profile and showed improvements in various markers of RBC health in pts with SCD. Rapid and sustained increases in Hb were associated with decreases in reticulocyte counts and markers of hemolysis, supporting increased sickle RBC lifespan and improved anemia. Together, these results support further evaluation of etavopivat in the Phase 2/3 Hibiscus Study (NCT04624659) currently enrolling pts. 1Kalfa et al, Blood 2019. 2Brown et al, Blood 2020.

Anemia is a continuing global public health concern and a priority for international action. The prevalence of anemia is estimated from the hemoglobin (Hb) levels within target populations, yet the procedures for measuring Hb are not standardized and different approaches may result in discrepancies. Several analytical variables have been proposed to influence Hb measurements, but it is difficult to understand the impact on specific variables from large population or field studies. Therefore, we designed a highly controlled protocol that minimized most technical parameters to specifically investigate the impact of blood draw site and analytic device on Hb measurements. A diverse cohort of sixty healthy adults each provided a sequential capillary and venous blood sample that were measured for Hb using an automated hematology analyzer (ADVIA-2120) and two point-of-care devices (HemoCue 201+ and HemoCue 301). Comparing blood draw sites, the mean Hb content was 0.32-0.47 g/dL (2-4%) higher in capillary compared to venous blood from the same donors. Comparing different Hb measuring instruments, the mean Hb content was 0.19-0.46 g/dL (1-4%) higher measured with HemoCue devices compared to ADVIA-2120 in both capillary and venous blood from the same donors. The maximum variance in measurement was also higher with HemoCue devices using blood from venous (5-6% CV) and capillary (21-25% CV) sites compared to ADVIA-2120 (0.6-2% CV). Other variables including blood collection tube manufacturer did not affect mean Hb content. These results demonstrate that even when most technical variables are minimized, the blood draw site and the analytical device can have a small but statistically significant effect on the mean and dispersion of Hb measurements. Even in this study, the few participants identified as mildly anemic using venous blood measured by ADVIA-2120 would not have been classified as anemic using their capillary blood samples or point-of-care analyzers. Thus, caution is warranted when comparing Hb values between studies having differences in blood draw site and Hb measuring device. Future anemia testing should maintain consistency in these analytical variables.

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.