GBT440 increases haemoglobin oxygen affinity, reduces sickling and prolongs RBC half-life in a murine model of sickle cell disease

Identification of human in vitro metabolites of the haemoglobin S polymerization inhibitor voxelotor for doping control purposes

Voxelotor (GBT440) is a haemoglobin S polymerization inhibitor used to treat anaemia in sickle cell disease. Due to an increase of arterial oxygen saturation as well as serum erythropoietin and haemoglobin, the World Anti-Doping Agency included voxelotor in the list of prohibited substances and methods in 2023. The objective of the present study was to identify and characterize metabolites of voxelotor to detect a potential misuse by athletes. The biotransformation was studied in vitro using the human hepatocellular cell line HepG2 and pooled human liver microsomes. The metabolites were analysed using high-performance liquid chromatography (high-resolution) mass spectrometry. In total, three phase I metabolites and six phase II metabolites (resulting from glucuro-conjugation and O-methylation) were formed by the HepG2 cells in a time-dependent manner, and two phase I metabolites were generated by the liver microsomes, among them one also found in the HepG2 incubations. A reduced metabolite and the glucuro-conjugate of a reduced metabolite were the most abundant formed by HepG2 cells. In addition, metabolites resulting from mono-hydroxylation, reduction and O-methylation in different combinations were identified. Voxelotor was also found as glucuro-conjugate with a low abundance. With the spectrometric behaviour of voxelotor and its in vitro metabolites described herein, an implementation in doping control screening and, consequently, a detection of an abuse in an athlete urine sample might be possible.

Design, Synthesis, and Evaluation of Allosteric Effectors for Hemoglobin

ConspectusSickle cell disease (SCD) is an inherited blood disorder caused by a point mutation in hemoglobin (Hb), the protein in the red blood cell (RBC) responsible for the transport of oxygen (O₂) throughout the body. The mutation leads to the expression of sickle cell hemoglobin (HbS). Both Hb and HbS exist in equilibrium between oxygenated and deoxygenated forms; however, deoxygenated HbS can polymerize to form long fibers which distort the shape of RBCs into the characteristic sickled shape. The misshapen RBCs can obstruct blood vessels and capillaries, resulting in a vaso-occlusive crisis. Vaso-occulsion deprives tissues and organs of O₂ and can cause intense pain which often results in hospitalization. Chronic organ damage is a major cause of reduced life expectancy for SCD patients.Allosteric effectors are molecules which regulate protein function. HbS allosteric effectors can be used to decrease polymerization by stabilizing the oxygenated form of HbS, which leads to an increase in O₂ uptake and a decrease in the sickling of RBCs. Allosteric effectors that have been evaluated for the treatment of SCD include vanillin, 5-hydroxymethyl furfural (5-HMF), and voxelotor, which was approved by the U.S. Food and Drug Administration (FDA) for the treatment of SCD in 2019. 5-HMF did not progress to phase III clinical trials since it suffered from rapid metabolic degradation. However, several derivatives of 5-HMF and vanillin have been synthesized and evaluated as potential candidates for SCD treatment. Derivatives of these compounds have shown promise, but their shortcomings, such as high levels of oxidative metabolism, have prevented them from progressing into marketable drugs. Our efforts have produced multiple 5-HMF derivatives which have been evaluated for their potential to treat SCD. Each derivative was evaluated for its ability to increase O₂ affinity (i.e., P₅₀, the partial pressure at which hemoglobin is 50% saturated with O₂). The synthesized aryl ether derivatives were evaluated, and results suggest that compounds with multiple aromatic aldehydes may have enhanced biological properties. One such derivative, compound 5, which features two furan aldehyde rings, exhibited increased O₂ affinity (P₅₀ = 8.82 ± 1.87 mmHg) over that of unmodified Hb (P₅₀ = 13.67 ± 0.22 mmHg). Future studies include obtaining crystal structures of the 5-HMF derivatives complexed with HbS to confirm the protein-allosteric effector interactions.

Investigating the Potential Use of Andrographolide as a Coadjuvant in Sickle Cell Anemia Therapy

Andrographolide is one of the main active principles of Andrographolide paniculata and has been extensively explored for its therapeutic use. Current studies focus on phytotherapeutics-based adjuvant therapy to symptomatically treat sickle cell anemia (SCA) as there is no specific drug/gene therapy available to date. The present study aimed to explore the potential of andrographolide as an adjuvant therapy for SCA in the presence or absence of hydroxyurea (HU), a key drug for SCA treatment. A panel of ex vivo and in vivo experimentations was performed to explore the antisickling activity of andrographolide, followed by evaluating pharmacokinetic and pharmacodynamic (PK/PD) activities in the presence of HU. Andrographolide showed significant antisickling activity using blood from SCA patients (ex vivo) and did not show any deleterious effect to cause hemolysis using rat blood (ex vivo). It displayed a substantial decrease in HU-induced decline in splenic lymphocyte proliferation and cytokine level (TNF-α and IFN-γ) using rat splenocytes (ex vivo). Concomitant oral administration of andrographolide with HU in rats for 15 days exhibited a noticeable improvement in the RBC count and hemoglobin levels comparable to the efficacy of l-glutamine (in vivo). Simultaneous administration of andrographolide with HU caused no marked effect on any pharmacokinetic parameters of HU except the highest plasma concentration of HU and its corresponding time point, which significantly dropped and delayed, respectively (in vivo). No considerable effect of andrographolide was observed on urease and horseradish peroxidase activity (in vitro). Overall, results suggest that andrographolide has several beneficial actions to be an adjuvant therapy to symptomatically manage SCA, but it should be avoided during the prescribed therapy of HU.

Treatment of sickle cell disease by increasing oxygen affinity of hemoglobin

The issue of treating sickle cell disease with drugs that increase hemoglobin oxygen affinity has come to the fore with the FDA approval in 2019 of voxelotor, the only anti-sickling drug approved since hydroxyurea in 1998. Voxelotor reduces sickling by increasing the concentration of the non-polymerizing, high oxygen affinity R (oxy) conformation of HbS. Treatment of sickle cell patients with voxelotor increases Hb levels and decreases indicators of hemolysis, but with no indication as yet that it reduces the frequency of pain episodes. Here we use the allosteric model of Monod, Wyman, and Changeux to simulate whole blood oxygen dissociation curves and red cell sickling in the absence and presence of voxelotor under the in vivo conditions of rapid oxygen pressure decreases. Our modeling agrees with experiments using a new robust assay, which shows the very large, expected decrease in sickling from the drug. The modeling indicates, however, that the increase in oxygen delivery from reduced sickling is largely offset by the increase in oxygen affinity. The net result is that the drug increases overall oxygen delivery only at the very lowest oxygen pressures. Reduction of sickling does, however, mitigate against red cell damage and explains the observed decrease in hemolysis. More importantly, our modeling of in vivo oxygen dissociation, sickling, and oxygen delivery suggests that drugs that increase fetal hemoglobin or decrease MCHC, should be more therapeutically effective than drugs that increase oxygen affinity.

MWC allosteric model explains unusual hemoglobin-oxygen binding curves from sickle cell drug binding

An oxygen-affinity-modifying drug, voxelotor, has very recently been approved by the FDA for treatment of sickle cell disease. The proposed mechanism of action is by preferential binding of the drug to the R quaternary conformation, which cannot copolymerize with the T conformation to form sickle fibers. Here, we report widely different oxygen dissociation and oxygen association curves for normal blood in the presence of voxelotor and interpret the results in terms of the allosteric model of Monod, Wyman, and Changeux with the addition of drug binding. The model does remarkably well in quantitatively explaining a complex data set with just the addition of drug binding and dissociation rates for the R and T conformations. Whereas slow dissociation of the drug from R results in time-independent dissociation curves, the changing association curves result from slow dissociation of the drug from T, as well as extremely slow binding of the drug to T. By calculating true equilibrium curves from the model parameters, we show that there would be a smaller decrease in oxygen delivery from the left shift in the dissociation curve caused by drug binding if drug binding and dissociation for both R and T were rapid. Our application of the Monod, Wyman, and Changeux model demonstrates once more its enormous power in explaining many different kinds of experimental results for hemoglobin. It should also be helpful in analyzing oxygen binding and in vivo delivery in future investigations of oxygen-affinity-modifying drugs for sickle cell disease.

Exploration of Structure-Activity Relationship of Aromatic Aldehydes Bearing Pyridinylmethoxy-Methyl Esters as Novel Antisickling Agents

Aromatic aldehydes elicit their antisickling effects primarily by increasing the affinity of hemoglobin (Hb) for oxygen (O₂). However, challenges related to weak potency and poor pharmacokinetic properties have hampered their development to treat sickle cell disease (SCD). Herein, we report our efforts to enhance the pharmacological profile of our previously reported compounds. These compounds showed enhanced effects on Hb modification, Hb-O₂ affinity, and sickling inhibition, with sustained pharmacological effects in vitro. Importantly, some compounds exhibited unusually high antisickling activity despite moderate effects on the Hb-O₂ affinity, which we attribute to an O₂-independent antisickling activity, in addition to the O₂-dependent activity. Structural studies are consistent with our hypothesis, which revealed the compounds interacting strongly with the polymer-stabilizing αF-helix could potentially weaken the polymer. In vivo studies with wild-type mice demonstrated significant pharmacologic effects. Our structure-based efforts have identified promising leads to be developed as novel therapeutic agents for SCD.

Sickle Cell Clinical Research and Intervention Program (SCCRIP): A lifespan cohort study for sickle cell disease progression from the pediatric stage into adulthood

BACKGROUND

Previous natural history studies have advanced the understanding of sickle cell disease (SCD), but generally have not included sufficient lifespan data or investigation of the role of genetics in clinical outcomes, and have often occurred before the widespread use of disease-modifying therapies, such as hydroxyurea and chronic erythrocyte transfusions. To further advance knowledge of SCD, St. Jude Children's Research Hospital established the Sickle Cell Clinical Research and Intervention Program (SCCRIP), to conduct research in a clinically evaluated cohort of individuals with SCD across their lifetime.

PROCEDURES

Initiated in 2014, the SCCRIP study prospectively recruits patients diagnosed with SCD and includes retrospective and longitudinal collection of clinical, neurocognitive, geospatial, psychosocial, and health outcomes data. Biological samples are banked for future genomics and proteomics studies. The organizational structure of SCCRIP is based upon organ/system-specific working groups and is opened to the research community for partnerships.

RESULTS

As of August 2017, 1,044 (92.3% of eligible) patients with SCD have enrolled in the study (860 children and 184 adults), with 11,915 person-years of observation. Population demographics included mean age at last visit of 11.3 years (range 0.7-30.1), 49.8% females, 57.7% treated with hydroxyurea, 8.5% treated with monthly transfusions, and 62.9% hemoglobin (Hb) SS or HbSB⁰ -thalassemia, 25.7% HbSC, 8.4% HbsB⁺ -Thalassemia, 1.7% HbS/HPFH, and 1.2% other.

CONCLUSIONS

The SCCRIP cohort will provide a rich resource for the conduct of high impact multidisciplinary research in SCD.