Allosteric Inhibition of Factor XIIIa. Non-Saccharide Glycosaminoglycan Mimetics, but Not Glycosaminoglycans, Exhibit Promising Inhibition Profile

Factor XIIIa (FXIIIa) is a transglutaminase that catalyzes the last step in the coagulation process. Orthostery is the only approach that has been exploited to design FXIIIa inhibitors. Yet, allosteric inhibition of FXIIIa is a paradigm that may offer a key advantage of controlled inhibition over orthosteric inhibition. Such an approach is likely to lead to novel FXIIIa inhibitors that do not carry bleeding risks. We reasoned that targeting a collection of basic amino acid residues distant from FXIIIa’s active site by using sulfated glycosaminoglycans (GAGs) or non-saccharide GAG mimetics (NSGMs) would lead to the discovery of the first allosteric FXIIIa inhibitors. We tested a library of 22 variably sulfated GAGs and NSGMs against human FXIIIa to discover promising hits. Interestingly, although some GAGs bound to FXIIIa better than NSGMs, no GAG displayed any inhibition. An undecasulfated quercetin analog was found to inhibit FXIIIa with reasonable potency (efficacy of 98%). Michaelis-Menten kinetic studies revealed an allosteric mechanism of inhibition. Fluorescence studies confirmed close correspondence between binding affinity and inhibition potency, as expected for an allosteric process. The inhibitor was reversible and at least 9-fold- and 26-fold selective over two GAG-binding proteins factor Xa (efficacy of 71%) and thrombin, respectively, and at least 27-fold selective over a cysteine protease papain. The inhibitor also inhibited the FXIIIa-mediated polymerization of fibrin in vitro. Overall, our work presents the proof-of-principle that FXIIIa can be allosterically modulated by sulfated non-saccharide agents much smaller than GAGs, which should enable the design of selective and safe anticoagulants

Plasmin Regulation through Allosteric, Sulfated, Small Molecules

Plasmin, a key serine protease, plays a major role in clot lysis and extracellular matrix remodeling. Heparin, a natural polydisperse sulfated glycosaminoglycan, is known to allosterically modulate plasmin activity. No small allosteric inhibitor of plasmin has been discovered to date. We screened an in-house library of 55 sulfated, small glycosaminoglycan mimetics based on nine distinct scaffolds and varying number and positions of sulfate groups to discover several promising hits. Of these, a pentasulfated flavonoid-quinazolinone dimer 32 was found to be the most potent sulfated small inhibitor of plasmin (IC50 = 45 μM, efficacy = 100%). Michaelis-Menten kinetic studies revealed an allosteric inhibition of plasmin by these inhibitors. Studies also indicated that the most potent inhibitors are selective for plasmin over thrombin and factor Xa, two serine proteases in coagulation cascade. Interestingly, different inhibitors exhibited different levels of efficacy (40%–100%), an observation alluding to the unique advantage offered by an allosteric process. Overall, our work presents the first small, synthetic allosteric plasmin inhibitors for further rational design

Potential Anti-SARS-CoV-2 Therapeutics That Target the Post-Entry Stages of the Viral Life Cycle: A Comprehensive Review

The coronavirus disease-2019 (COVID-19) pandemic continues to challenge health care systems around the world. Scientists and pharmaceutical companies have promptly responded by advancing potential therapeutics into clinical trials at an exponential rate. Initial encouraging results have been realized using remdesivir and dexamethasone. Yet, the research continues so as to identify better clinically relevant therapeutics that act either as prophylactics to prevent the infection or as treatments to limit the severity of COVID-19 and substantially decrease the mortality rate. Previously, we reviewed the potential therapeutics in clinical trials that block the early stage of the viral life cycle. In this review, we summarize potential anti-COVID-19 therapeutics that block/inhibit the post-entry stages of the viral life cycle. The review presents not only the chemical structures and mechanisms of the potential therapeutics under clinical investigation, i.e., listed in clinicaltrials.gov, but it also describes the relevant results of clinical trials. Their anti-inflammatory/immune-modulatory effects are also described. The reviewed therapeutics include small molecules, polypeptides, and monoclonal antibodies. At the molecular level, the therapeutics target viral proteins or processes that facilitate the post-entry stages of the viral infection. Frequent targets are the viral RNA-dependent RNA polymerase (RdRp) and the viral proteases such as papain-like protease (PLpro) and main protease (Mpro). Overall, we aim at presenting up-to-date details of anti-COVID-19 therapeutics so as to catalyze their potential effective use in fighting the pandemic

Vericiguat: A New Hope for Heart Failure Patients

Heart failure with reduced ejection fraction (HFrEF) is the inability of the heart to adequately contract or eject blood. This heart is unable to produce adequate cardiac output to perfuse vital tissues. At a fundamental level, it is known that the cardioprotective pathway of nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate is impaired in heart failure patients. Vericiguat is a novel, orally used, small molecule, and direct stimulator of the soluble guanylate cyclase, and thus, it enhances the production of cyclic guanosine monophosphate. Vericiguat was approved by the FDA in January of 2021 to reduce the risk of cardiovascular death and heart failure hospitalization following a hospitalization for heart failure or need for outpatient IV diuretics, in adults with symptomatic chronic heart failure and ejection fraction less than 45%. In this review, we describe the chemical and mechanistic aspects, pharmacokinetics, adverse effects, and contraindications of vericiguat so as to facilitate its optimal therapeutic use

First Therapeutic Approval for Eosinophilic Esophagitis

Eosinophilic esophagitis (EE) is a chronic, immune-mediated or antigen-mediated esophageal disease. Treatment for patients with EE can be challenging with no previously approved medications. Current management strategies follow the four D’s paradigm of drugs, dietary elimination, dilation, and disease anxiety and hypervigilance therapy. On 20 May 2022, dupilumab was approved by FDA for EE. A dose of 300 mg dupilumab weekly significantly improved signs and symptoms of EE compared to placebo in a phase 3 trial. The approval of dupilumab will fulfill an unmet need for the increasing number of patients with EE

Venous Thromboembolism Prophylaxis in Major Orthopedic Surgeries and Factor XIa Inhibitors

Venous thromboembolism (VTE), comprising pulmonary embolism (PE) and deep vein thrombosis (DVT), poses a significant risk during and after hospitalization, particularly for surgical patients. Among various patient groups, those undergoing major orthopedic surgeries are considered to have a higher susceptibility to PE and DVT. Major lower-extremity orthopedic procedures carry a higher risk of symptomatic VTE compared to most other surgeries, with an estimated incidence of ~4%. The greatest risk period occurs within the first 7–14 days following surgery. Major bleeding is also more prevalent in these surgeries compared to others, with rates estimated between 2% and 4%. For patients undergoing major lower-extremity orthopedic surgery who have a low bleeding risk, it is recommended to use pharmacological thromboprophylaxis with or without mechanical devices. The choice of the initial agent depends on the specific surgery and patient comorbidities. First-line options include low-molecular-weight heparins (LMWHs), direct oral anticoagulants, and aspirin. Second-line options consist of unfractionated heparin (UFH), fondaparinux, and warfarin. For most patients undergoing knee or hip arthroplasty, the initial agents recommended for the early perioperative period are LMWHs (enoxaparin or dalteparin) or direct oral anticoagulants (rivaroxaban or apixaban). In the case of hip fracture surgery, LMWH is recommended as the preferred agent for the entire duration of prophylaxis. However, emerging factor XI(a) inhibitors, as revealed by a recent meta-analysis, have shown a substantial decrease in the occurrence of VTE and bleeding events among patients undergoing major orthopedic surgery. This discovery poses a challenge to the existing paradigm of anticoagulant therapy in this specific patient population and indicates that factor XI(a) inhibitors hold great promise as a potential strategy to be taken into serious consideration

Sulfated Non-Saccharide Glycosaminoglycan Mimetics as Novel Drug Discovery Platform for Various Pathologies.

Glycosaminoglycans (GAGs) are very complex, natural anionic polysaccharides. They are polymers of repeating disaccharide units of uronic acid and hexosamine residues. Owing to their template-free, spatiotemporally-controlled, and enzyme-mediated biosyntheses, GAGs possess enormous polydispersity, heterogeneity, and structural diversity which often translate into multiple biological roles. It is well documented that GAGs contribute to physiological and pathological processes by binding to proteins including serine proteases, serpins, chemokines, growth factors, and microbial proteins. Despite advances in the GAG field, the GAG-protein interface remains largely unexploited by drug discovery programs. Thus, Non-Saccharide Glycosaminoglycan Mimetics (NSGMs) have been rationally developed as a novel class of sulfated molecules that modulate GAG-protein interface to promote various biological outcomes of substantial benefit to human health. In this review, we describe the chemical, biochemical, and pharmacological aspects of re-cently reported NSGMs and highlight their therapeutic potentials as structurally and mechanistically novel anti-coagulants, anti-cancer agents, anti-emphysema agents, and anti-viral agents. We also describe the challenges that complicate their advancement and describe ongoing efforts to overcome these challenges with the aim of advancing the novel platform of NSGMs to clinical use

New Small Molecule Drugs for Thrombocytopenia: Chemical, Pharmacological, and Therapeutic Use Considerations

This review provides details about three small molecules that were recently approved by the FDA for the treatment of thrombocytopenia. The new treatments include lusutrombopag, avatrombopag, and fostamatinib. The first two drugs are orally active thrombopoietin receptor (TPO-R) agonists which are FDA-approved for the treatment of thrombocytopenia in adult patients with chronic liver disease who are scheduled to undergo a procedure. Fostamatinib is orally active prodrug that, after activation, becomes spleen tyrosine kinase (SYK) inhibitor. Fostamatinib is currently used to treat chronic and refractory immune thrombocytopenia in patients who have had insufficient response to previous treatment. Chemical structures, available dosage forms, recommended dosing, pharmacokinetics, results of toxicity studies in animals, most frequent adverse effects, significant outcomes of the corresponding clinical trials, and their use in specific patient populations are thoroughly described. Described also is a comparative summary of the different aspects of five currently available therapies targeting TPO-R or SYK for the treatment of thrombocytopenia

Designing Allosteric Inhibitors of Factor XIa. Lessons from the Interactions of Sulfated Pentagalloylglucopyranosides

We recently introduced sulfated pentagalloylglucopyranoside (SPGG) as an allosteric inhibitor of factor XIa (FXIa) (Al-Horani et al., J. Med Chem. 2013, 56, 867–878). To better understand the SPGG–FXIa interaction, we utilized eight SPGG variants and a range of biochemical techniques. The results reveal that SPGG’s sulfation level moderately affected FXIa inhibition potency and selectivity over thrombin and factor Xa. Variation in the anomeric configuration did not affect potency. Interestingly, zymogen factor XI bound SPGG with high affinity, suggesting its possible use as an antidote. Acrylamide quenching experiments suggested that SPGG induced significant conformational changes in the active site of FXIa. Inhibition studies in the presence of heparin showed marginal competition with highly sulfated SPGG variants but robust competition with less sulfated variants. Resolution of energetic contributions revealed that nonionic forces contribute nearly 87% of binding energy suggesting a strong possibility of specific interaction. Overall, the results indicate that SPGG may recognize more than one anion-binding, allosteric site on FXIa. An SPGG molecule containing approximately 10 sulfate groups on positions 2 through 6 of the pentagalloylglucopyranosyl scaffold may be the optimal FXIa inhibitor for further preclinical studies