A Triazole Disulfide Compound Increases the Affinity of Hemoglobin for Oxygen and Reduces the Sickling of Human Sickle Cells

Finding the Ajoene Sweet-Spot: Structure-Activity Relations that Govern its Blood Stability and Cancer Cytotoxicity

Ajoene is an organosulfur compound found in crushed garlic that exerts its anti-cancer activity by S-thiolating cysteine residues on proteins. Its development is hampered due to limited bioavailability, so in this study, we synthesised analogues of ajoene to probe the significance of the ajoene vinyl disulfide/sulfoxide core with respect to cytotoxicity and blood stability. Polar side groups were also incorporated to improve aqueous solubility. It was found that derivatives containing a vinyl disulfide functional group (4-7, as in ajoene), were more cytotoxic compared to analogues in which the double bond was removed, although the latter showed superior blood stability. It was also found that the allyl-S sulfur of the disulfide was more electrophilic to S-thiolysis based on the global electrophilicity index (ω) and the condensed electrophilic Fukui functionf k + ${{ f}_{\rm{k}}^{\rm{ + }} }$ . S-Thiolysis was found to be exergonic for the vinyl disulfides based on entropy and enthalpy computations with a deprotonated thiolate. Derivatisation to the dihydro (10, 12) and deoxydihydroajoenes (9, 11) produced analogues that were slightly less potent but with greatly improved blood stability. Taken together, the deoxydihydroajoenes present themselves as good candidates for further therapeutic development.

Targeted modification of furan-2-carboxaldehydes into Michael acceptor analogs yielded long-acting hemoglobin modulators with dual antisickling activities

Sickle cell disease (SCD) is the most common genetic disorder, affecting millions of people worldwide. Aromatic aldehydes, which increase the oxygen affinity of human hemoglobin to prevent polymerization of sickle hemoglobin and inhibit red blood cell (RBC) sickling, have been the subject of keen interest for the development of effective treatment against SCD. However, the aldehyde functional group metabolic instability has severly hampered their development, except for voxelotor, which was approved in 2019 for SCD treatment. To improve the metabolic stability of aromatic aldehydes, we designed and synthesized novel molecules by incorporating Michael acceptor reactive centers into the previously clinically studied aromatic aldehyde, 5-hydroxymethylfurfural (5-HMF). Eight such derivatives, referred to as MMA compounds were synthesized and studied for their functional and biological activities. Unlike 5-HMF, which forms Schiff-base interaction with αVal1 nitrogen of hemoglobin, the MMA compounds covalently interacted with βCys93, as evidenced by reverse-phase HPLC and disulfide exchange reaction, explaining their RBC sickling inhibitory activities, which at 2 mM and 5 mM, range from 0% to 21% and 9% to 64%, respectively. Additionally, the MMA compounds showed a second mechanism of sickling inhibition (12%-41% and 13%-62% at 2 mM and 5 mM, respectively) by directly destabilizing the sickle hemoglobin polymer. In vitro studies demonstrated sustained pharmacologic activities of the compounds compared to 5-HMF. These findings hold promise for advancing SCD therapeutics.

Cefmetazole sodium as an allosteric effector that regulates the oxygen supply efficiency of adult hemoglobin

Allosteric effectors play an important role in regulating the oxygen supply efficiency of hemoglobin for blood storage and disease treatment. However, allosteric effectors that are approved by the US FDA are limited. In this study, cefmetazole sodium (CS) was found to bind adult hemoglobin (HbA) from FDA library (1338 compounds) using surface plasmon resonance imaging high-throughput screening. Using surface plasmon resonance (SPR), the interaction between CS and HbA was verified. The oxygen dissociation curve of HbA after CS interaction showed a significant increase in P50 and theoretical oxygen-release capacity. Acid-base sensitivity (SI) exhibited a decreasing trend, although not significantly different. An oxygen dissociation assay indicated that CS accelerated HbA deoxygenation. Microfluidic modulated spectroscopy showed that CS changed the ratio of the alpha-helix to the beta-sheet of HbA. Molecular docking suggested CS bound to HbA's β-chains via hydrogen bonds, with key amino acids being N282, K225, H545, K625, K675, and V544.The results of molecular dynamics simulations (MD) revealed a stable orientation of the HbA-CS complex. CS did not significantly affect the P50 of bovine hemoglobin, possibly due to the lack of Valβ1 and Hisβ2, indicating that these were the crucial amino acids involved in HbA's oxygen affinity. Competition between the 2,3-Diphosphoglycerate (2,3-DPG) and CS in the HbA interaction was also determined by SPR, molecular docking and MD. In summary, CS could interact with HbA and regulate the oxygen supply efficiency via forming stable hydrogen bonds with the β-chains of HbA, and showed competition with 2,3-DPG.Communicated by Ramaswamy H. Sarma.

Process-Divergent Syntheses of 4- and 5-Sulfur-Functionalized 1,2,3-Triazoles via Copper-Catalyzed Azide-Alkyne Cycloadditions of 1-Phosphinyl-2-sulfanylethynes

4-Sulfanyl-substituted 1,2,3-triazoles were provided regioselectively with good yields and broad scope via consecutive t-BuOK-promoted dephosphinylation of 1-phosphinyl-2-sulfanylethynes and copper-catalyzed azide-alkyne cycloadditions (CuAAC) with alkyl azides. Unsymmetrically substituted ditriazoles were successfully obtained using a tandem dephosphinylative CuAAC protocol with diazides. Direct CuAAC of the 1-phosphinyl-2-sulfanylethynes with azides afforded regioisomeric mixtures of 4-phosphinyl-5-sulfanyl- and 5-phosphinyl-4-sulfanyl-1,2,3-triazoles that were easily separable from one another. When the phosphinyl- and sulfanyl-substituted triazoles were treated with t-BuOK, the dephosphination proceeded smoothly, yielding the corresponding 5- and 4-sulfanyltriazoles, respectively. 5-(1-Aryl-1-hydroxymethyl)-4-sulfanyltriazoles were synthesized by stepwise treatment of 5-phosphinyl-4-sulfanyltriazole with MeMgBr and arylaldehydes. Additionally, Ph₂P(O) and RS groups in the triazoles were easily converted to Ph₂P and RSO₂ by PhSiH₃-reduction and m-CPBA-oxidation, respectively. Following the dephosphinylative CuAAC of 1-phosphinyl-2-(4-t-butylphenylsulfanyl)ethyne with aryl azides and m-CPBA-oxidation, potent antagonists of pregnane X receptor LC-58 and LC-59 were successfully produced.

Resveratrol, a New Allosteric Effector of Hemoglobin, Enhances Oxygen Supply Efficiency and Improves Adaption to Acute Severe Hypoxia

Acute altitude hypoxia represents the cause of multiple adverse consequences. Current treatments are limited by side effects. Recent studies have shown the protective effects of resveratrol (RSV), but the mechanism remains unknown. To address this, the effects of RSV on the structure and function of hemoglobin of adult (HbA) were preliminarily analyzed using surface plasmon resonance (SPR) and oxygen dissociation assays (ODA). Molecular docking was conducted to specifically analyze the binding regions between RSV and HbA. The thermal stability was characterized to further validate the authenticity and effect of binding. Changes in the oxygen supply efficiency of HbA and rat RBCs incubated with RSV were detected ex vivo. The effect of RSV on the anti-hypoxic capacity under acute hypoxic conditions in vivo was evaluated. We found that RSV binds to the heme region of HbA following a concentration gradient and affects the structural stability and rate of oxygen release of HbA. RSV enhances the oxygen supply efficiency of HbA and rat RBCs ex vivo. RSV prolongs the tolerance times of mice suffering from acute asphyxia. By enhancing the oxygen supply efficiency, it alleviates the detrimental effects of acute severe hypoxia. In conclusion, RSV binds to HbA and regulates its conformation, which enhances oxygen supply efficiency and improves adaption to acute severe hypoxia.

High-Throughput Assay to Screen Small Molecules for Their Ability to Prevent Sickling of Red Blood Cells

Sickle cell disease (SCD) is an inherited disorder of hemoglobin (Hb); approximately 300,000 babies are born worldwide with SCD each year. In SCD, fibers of polymerized sickle Hb (HbS) form in red blood cells (RBCs), which cause RBCs to develop their characteristic "sickled" shape, resulting in hemolytic anemia and numerous vascular complications including vaso-occlusive crises. The development of novel antisickling compounds will provide new therapeutic options for patients with SCD. We developed a high-throughput "sickling assay" that is based on an automated high-content imaging system to quantify the effects of hypoxia on the shape and size of RBCs from HbSS SCD patients (SS RBCs). We used this assay to screen thousands of compounds for their ability to inhibit sickling. In the assay, voxelotor (an FDA-approved medication used to treat SCD) prevented sickling with a z'-factor > 0.4, suggesting that the assay is capable of identifying compounds that inhibit sickling. We screened the Broad Repurposing Library of 5393 compounds for their ability to prevent sickling in 4% oxygen/96% nitrogen. We identified two compounds, SNS-314 mesylate and voxelotor itself, that successfully prevented sickling. SNS-314 mesylate prevented sickling in the absence of oxygen, while voxelotor did not, suggesting that SNS-314 mesylate acts by a mechanism that is different from that of voxelotor. The sickling assay described in this study will permit the identification of additional, novel antisickling compounds, which will potentially expand the therapeutic options for SCD.

Modulating hemoglobin allostery for treatment of sickle cell disease: current progress and intellectual property

INTRODUCTION

Sickle cell disease (SCD) is a debilitating inherited disorder that affects millions worldwide. Four novel SCD therapeutics have been approved, including the hemoglobin (Hb) modulator Voxelotor.

AREAS COVERED

This review provides an overview of discovery efforts toward modulating Hb allosteric behavior as a treatment for SCD, with a focus on aromatic aldehydes that increase Hb oxygen affinity to prevent the primary pathophysiology of hypoxia-induce erythrocyte sickling.

EXPERT OPINION

The quest to develop small molecules, especially aromatic aldehydes, to modulate Hb allosteric properties for SCD began in the 1970s; however, early promise was dogged by concerns that stalled support for research efforts. Persistent efforts eventually culminated in the discovery of the anti-sickling agent 5-HMF in the 2000s, and reinvigorated interest that led to the discovery of vanillin analogs, including Voxelotor, the first FDA approved Hb modulator for the treatment of SCD. With burgeoning interest in the field of Hb modulation, there is a growing landscape of intellectual property, including drug candidates at various stages of preclinical and clinical investigations. Hb modulators could provide not only the best chance for a highly effective oral therapy for SCD, especially in the under-developed world, but also a way to treat a variety of other human conditions.

Advances in Sickle Cell Disease Treatments

Sickle Cell Disease (SCD) is an inherited disorder of red blood cells that is caused by a single mutation in the β -globin gene. The disease, which afflicts millions of patients worldwide mainly in low income countries, is characterized by high morbidity, mortality and low life expectancy. The new pharmacological and non-pharmacological strategies for SCD is urgent in order to promote treatments able to reduce patient's suffering and improve their quality of life. Since the FDA approval of HU in 1998, there have been few advances in discovering new drugs; however, in the last three years voxelotor, crizanlizumab, and glutamine have been approved as new therapeutic alternatives. In addition, new promising compounds have been described to treat the main SCD symptoms. Herein, focusing on drug discovery, we discuss new strategies to treat SCD that have been carried out in the last ten years to discover new, safe, and effective treatments. Moreover, non-pharmacological approaches, including red blood cell exchange, gene therapy and hematopoietic stem cell transplantation will be presented.

Antioxidant and anti-sickling activity of glucal-based triazoles compounds - An in vitro and in silico study

The sickle cell disease (SCD) has a genetic cause, characterized by a replacement of glutamic acid to valine in the β-chain of hemoglobin. The disease has no effective treatment so far, and patients suffer a range from acute to chronic complications that include chronic hemolytic anemia, vaso-occlusive ischemia, pain, acute thoracic syndrome, cerebrovascular accident, nephropathy, osteonecrosis and reduced lifetime. The oxidation in certain regions of the hemoglobin favors the reactive oxygen species (ROS) formation, which is the cause of many clinical manifestations. Antioxidants have been studied to reduce the hemoglobin ROS levels, and in this sense, we have searched for new antioxidants glucal-based triazoles compounds with anti-sickling activity. Thirty analogues were synthetized and tested in in vitro antioxidant assays. Two of them were selected based in their effects and concentration-response activity and conducted to in cell assays. Both molecules did not cause any hemolysis and could reduce the red blood cell damage caused by hydrogen peroxide, in a model of oxidative stress induction that mimics the SCD. Moreover, one molecule (termed 11m), besides reducing the hemolysis, was able to prevent the cell damage caused by the hydrogen peroxide. Later on, by in silico pharmacokinetics analysis, we could see that 11m has appropriated proprieties for druggability and the probable mechanism of action is the binding to Peroxiredoxin-5, an antioxidant enzyme that reduces the hydrogen peroxide levels, verified after molecular docking assays. Thus, starting from 30 glucal-based triazoles molecules in a structure-activity relationship, we could select one with antioxidant proprieties that could act on RBC to reduce the oxidative stress, being useful for the treatment of SCD.

βCysteine 93 in human hemoglobin: a gateway to oxidative stability in health and disease

βcysteine 93 residue plays a key role in oxygen (O2)-linked conformational changes in the hemoglobin (Hb) molecule. This solvent accessible residue is also a target for binding of thiol reagents that can remotely alter O2 affinity, cooperativity, and Hb's sensitivity to changes in pH. In recent years, βCys93 was assigned a new physiological role in the transport of nitric oxide (NO) through a process of S-nitrosylation as red blood cells (RBCs) travel from lungs to tissues. βCys93 is readily and irreversibly oxidized in the presence of a mild oxidant to cysteic acid, which causes destabilization of Hb resulting in improper protein folding and the loss of heme. Under these oxidative conditions, ferryl heme (HbFe4+), a higher oxidation state of Hb is formed together with its protein radical (.HbFe4+). This radical migrates to βCys93 and interacts with other "hotspot" amino acids that are highly susceptible to oxidative modifications. Oxidized βCys93 may therefore be used as a biomarker of oxidative stress, reflecting the deterioration of Hb within RBCs intended for transfusion or RBCs from patients with hemoglobinopathies. Site specific mutation of a redox active amino acid(s) to reduce the ferryl heme or direct chemical modifications that can shield βCys93 have been proposed to improve oxidative resistance of Hb and may offer a protective therapeutic strategy.

An Investigation of Structure-Activity Relationships of Azolylacryloyl Derivatives Yielded Potent and Long-Acting Hemoglobin Modulators for Reversing Erythrocyte Sickling

Aromatic aldehydes that bind to sickle hemoglobin (HbS) to increase the protein oxygen affinity and/or directly inhibit HbS polymer formation to prevent the pathological hypoxia-induced HbS polymerization and the subsequent erythrocyte sickling have for several years been studied for the treatment of sickle cell disease (SCD). With the exception of Voxelotor, which was recently approved by the U.S. Food and Drug Administration (FDA) to treat the disease, several other promising antisickling aromatic aldehydes have not fared well in the clinic because of metabolic instability of the aldehyde moiety, which is critical for the pharmacologic activity of these compounds. Over the years, our group has rationally developed analogs of aromatic aldehydes that incorporate a stable Michael addition reactive center that we hypothesized would form covalent interactions with Hb to increase the protein affinity for oxygen and prevent erythrocyte sickling. Although, these compounds have proven to be metabolically stable, unfortunately they showed weak to no antisickling activity. In this study, through additional targeted modifications of our lead Michael addition compounds, we have discovered other novel antisickling agents. These compounds, designated MMA, bind to the α-globin and/or β-globin to increase Hb affinity for oxygen and concomitantly inhibit erythrocyte sickling with significantly enhanced and sustained pharmacologic activities in vitro.

Hemoglobin: Structure, Function and Allostery

This chapter reviews how allosteric (heterotrophic) effectors and natural mutations impact hemoglobin (Hb) primary physiological function of oxygen binding and transport. First, an introduction about the structure of Hb is provided, including the ensemble of tense and relaxed Hb states and the dynamic equilibrium of Hb multistate. This is followed by a brief review of Hb variants with altered Hb structure and oxygen binding properties. Finally, a review of different endogenous and exogenous allosteric effectors of Hb is presented with particular emphasis on the atomic interactions of synthetic ligands with altered allosteric function of Hb that could potentially be harnessed for the treatment of diseases.

[Research progress on mechanism in adaptation of hemoglobin to plateau hypoxia]

Low oxygen partial pressure is the main cause of acute mountain sickness.Hemoglobin plays a crucial physiological role in the binding, utilization, transportation and release of oxygen in the body. To increase the capacity of oxygen binding of hemoglobin or the capacity of oxygen supply in tissues can help alleviate altitude sickness. However, increasing hemoglobin content has certain limitations. Using techniques from molecular biology, researchers are looking for endogenous or exogenous substances that can regulate the conformation of hemoglobin to increase oxygen uptake in the alveoli, or the availability of alveolar oxygen in the tissues. At present, the research on allosteric modulators to improve the affinity of hemoglobin has made some progress, and research on applying this mechanism to plateau hypoxia is also underway. This article reviews the relationship between hemoglobin and hypoxia, the structure of hemoglobin and the role of various allosteric modulators in hypoxia, which would provide information for finding new substances regulating the conformation of hemoglobin.

100 years of sickle cell disease research: etiology, pathophysiology and rational drug design (part 1)

Background

Sickle cell disease (SCD) is a chronic hemolytic disease caused by an altered hemoglobin molecule (HbS) and was first termed as a molecular disease. Glutamic acid in the normal hemoglobin molecule (HbA), was replaced by valine in HbS at the sixth position of both β-chains. This alteration was proved to be due to a single point mutation GTG instead of GAG in the genetic code. Since the discovery of sickle cell disease in 1910, great efforts have been done to study this disease on a molecular level. These efforts aimed to identify the disease etiology, pathophysiology, and finally to discover efficient treatment. Despite the tremendous work of many research groups all over the world, the only approved drug up to this moment, for the treatment of SCD is the hydroxyurea.

Main text

In this review, the antisickling pharmaco-therapeutics will be classified into two major groups: hemoglobin site directed modifiers and ex-hemoglobin effectors. The first class will be discussed in details, here in, focusing on the most important figures in the way of the rational drug design for SCD treatment aiming to help scientists solve the mystery of this problem and to get clear vision toward possible required therapy for SCD.

Conclusion

Despite the large number of the antisickling candidates that have been reached clinical studies yet, none of them has been introduced to the market. This may be due to the fact that hemoglobin is a large molecule with different target sites, which requires highly potent therapeutic agent. With this potency, these drugs should be safe, with acceptable oral pharmacokinetic and pharmacodynamic properties. Such ideal drug candidate needs more efforts to be developed.

Antisickling Drugs Targeting βCys93 Reduce Iron Oxidation and Oxidative Changes in Sickle Cell Hemoglobin

Sickle cell disease is a genetic blood disorder caused by a single point mutation in the β globin gene where glutamic acid is replaced by valine at the sixth position of the β chain of hemoglobin (Hb). At low oxygen tension, the polymerization of deoxyHbS into fibers occurs in red blood cells (RBCs) leading to an impaired blood vessel transit. Sickle cell hemoglobin (HbS), when oxidized with hydrogen peroxide (H₂O₂), stays longer in a highly oxidizing ferryl (Fe⁴⁺) form causing irreversible oxidation of βCys93 to a destabilizing cysteic acid. We have previously reported that an antisickling drug can be designed to bind specifically to βCys93 and effectively protect against its irreversible oxidation by H₂O₂. Here, we report oxygen dissociation, oxidation, and polymerization kinetic reactions for four antisickling drugs (under different preclinical/clinical developmental stages) that either site-specifically target βCys93 or other sites on the HbS molecule. Molecules that specifically bind to or modify βCys93, such as 4,4′-di(1,2,3-triazolyl) disulfide (TD-3) and hydroxyurea (HU) were contrasted with molecules that target other sites on Hb including 5-hydroxymethyl-2-furfural (5-HMF) and L-glutamine. All reagents induced a left shift in the oxygen dissociation curve (ODC) except L-glutamine. In the presence of H₂O₂ (2.5:1, H₂O₂:heme), both TD-3 and HU reduced the ferryl heme by 22 and 37%, respectively, which corresponded to a 3- to 2-fold reduction in the levels of βCys93 oxidation as verified by mass spectrometry. Increases in the delay times prior to polymerization of HbS under hypoxia were in the following order: TD-3 > HU > 5-HMF = L-glutamine. Designing antisickling agents that can specifically target βCys93 may provide a dual antioxidant and antisickling therapeutic benefits in treating this disease.