Factor IXa as a target for anticoagulation in thrombotic disorders and conditions

Structure and pharmacokinetics/pharmacodynamics of the anticoagulant tetradecasaccharide oHG-14 as an intrinsic tenase inhibitor

The intrinsic tenase complex (iXase) is an attractive antithrombotic target to treat or prevent pathological thrombosis with negligible bleeding risk. Fucosylated glycosaminoglycan (FG) is a promising anticoagulant by inhibiting iXase. A depolymerized FG (dHG-5) as an anticoagulant has been approved for clinical trials. Given that dHG-5 is a multi-component drug candidate consisting of a homologous series of oligosaccharides, it is difficult to predict a clear pharmacokinetics. Here, as a major oligosaccharide component, the tetradecasaccharide (oHG-14) was purified from dHG-5 and its structure was defined as L-Fuc3S4S-α(1,3)-L-Δ4,5GlcA-α(1,3)-{D-GalNAc4S6S-β(1,4)-[L-Fuc3S4S-α(1,]3)-D-GlcA-β(1,3)-}3-D-GalNAc4S6S-β(1,4)-[L-Fuc3S4S-α(1,]3)-D-GlcA-ol. oHG-14 showed potent iXase inhibitory activity in vitro and antithrombotic effect in vivo comparable to dHG-5. After single subcutaneous administration of oHG-14 at 8, 14.4 and 32.4 mg/kg to rats, the absolute bioavailability was 71.6 %-80.9 % determined by the validated bioanalytical methods. The maximum concentration (Cmax) was 3.73, 8.07, and 11.95 μg/mL, respectively, and the time reaching Cmax (Tmax) was about 1 h. oHG-14 was mainly excreted by kidney as the parent compound with the elimination kinetics of first-order linear model. Anticoagulant activity of oHG-14 was positively correlated with its concentration in rat plasma. The pharmacokinetics/pharmacodynamics (PK/PD) of oHG-14 is similar to that of dHG-5. This study could provide supportive data for the clinical trial of dHG-5 and further development of pure oligosaccharide as an antithrombotic drug candidate.

Potential anticoagulant of traditional chinese medicine and novel targets for anticoagulant drugs

BACKGROUND

Anticoagulants are the main drugs used for the prevention and treatment of thrombosis. Currently, anticoagulant drugs are primarily multitarget heparin drugs, single-target FXa inhibitors and FIIa inhibitors. In addition, some traditional Chinese drugs also have anticoagulant effects, but they are not the main direction of treatment at present. But the anticoagulant drugs mentioned above, all have a common side effect is bleeding. Many other anticoagulation targets are under investigation. With further exploration of coagulation mechanism, how to further determine new anticoagulant targets and how to make traditional Chinese medicine play anticoagulant role have become a new field of exploration.

PURPOSE

The purpose of the study was to summarize the recent research progress on coagulation mechanisms, new anticoagulant targets and traditional Chinese medicine.

METHODS

A comprehensive literature search was conducted using four electronic databases, including PubMed, Embase, CNKI, Wanfang database and ClinicalTrials.gov, from the inception of the study to 28 Feb 2023. Key words used in the literature search were "anticoagulation", "anticoagulant targets", "new targets", "coagulation mechanisms", "potential anticoagulant", "herb medicine", "botanical medicine", "Chinese medicine", "traditional Chinese medicine", "blood coagulation factor", keywords are linked with AND/OR. Recent findings on coagulation mechanisms, potential anticoagulant targets and traditional Chinese medicine were studied.

RESULTS

The active components extracted from the Chinese medicinal herbs, Salvia miltiorrhiza, Chuanxiong rhizoma, safflower and Panax notoginseng have obvious anticoagulant effects and can be used as potential anticoagulant drugs, but the risk of bleeding is unclear. TF/FVIIa, FVIII, FIX, FXI, FXII, and FXIII have all been evaluated as targets in animal studies or clinical trials. FIX and FXI are the most studied anticoagulant targets, but FXI inhibitors have shown stronger advantages.

CONCLUSION

This review of potential anticoagulants provides a comprehensive resource. Literature analysis suggests that FXI inhibitors can be used as potential anticoagulant candidates. In addition, we should not ignore the anticoagulant effect of traditional Chinese medicine, and look forward to more research and the emergence of new drugs.

Discovery of Benzyl Tetraphosphonate Derivative as Inhibitor of Human Factor Xia

The inhibition of factor XIa (FXIa) is a trending paradigm for the development of new generations of anticoagulants without a substantial risk of bleeding. In this report, we present the discovery of a benzyl tetra-phosphonate derivative as a potent and selective inhibitor of human FXIa. Biochemical screening of four phosphonate/phosphate derivatives has led to the identification of the molecule that inhibited human FXIa with an IC50 value of ∼7.4 μM and a submaximal efficacy of ∼68 %. The inhibitor was at least 14-fold more selective to FXIa over thrombin, factor IXa, factor Xa, and factor XIIIa. It also inhibited FXIa-mediated activation of factor IX and prolonged the activated partial thromboplastin time of human plasma. In Michaelis-Menten kinetics experiment, inhibitor 1 reduced the VMAX of FXIa hydrolysis of a chromogenic substrate without significantly affecting its KM suggesting an allosteric mechanism of inhibition. The inhibitor also disrupted the formation of FXIa - antithrombin complex and inhibited thrombin-mediated and factor XIIa-mediated formation of FXIa from its zymogen factor XI. Inhibitor 1 has been proposed to bind to or near the heparin/polyphosphate-binding site in the catalytic domain of FXIa. Overall, inhibitor 1 is the first benzyl tetraphosphonate small molecule that allosterically inhibits human FXIa, blocks its physiological function, and prevents its zymogen activation by other clotting factors under in vitro conditions. Thus, we put forward benzyl tetra-phosphonate 1 as a novel lead inhibitor of human FXIa to guide future efforts in the development of allosteric anticoagulants.

A synthetic heparin mimetic that allosterically inhibits factor XIa and reduces thrombosis in vivo without enhanced risk of bleeding

BACKGROUND

Human factor XIa (FXIa) is an actively pursued target for development of safer anticoagulants. Our long-standing hypothesis has been that allosterism originating from heparin-binding site(s) on coagulation enzymes is a promising approach to yield safer agents.

OBJECTIVES

To develop a synthetic heparin mimetic as an inhibitor of FXIa so as to reduce clot formation in vivo but not carry high bleeding risk.

METHODS

We employed a gamut of methods involving synthetic chemistry, biophysical biochemistry, enzyme assays, blood and plasma coagulation assays, and in vivo thrombosis models in this work.

RESULTS

Sulfated chiro-inositol (SCI), a non-saccharide mimetic of heparin, was synthesized in three steps in overall yields of >50%. SCI inhibited FXIa with potency of 280 nmol/L and preferentially engaged FXIa's heparin-binding site to conformationally alter its active site. SCI inhibition of FXIa could be rapidly reversed by common antidotes, such as protamine. SCI preferentially prolonged plasma clotting initiated with recalcification, rather than thromboplastin, alluding to its intrinsic pathway-based mechanism. Human blood thromboelastography indicated good ex vivo anticoagulation properties of SCI. Rat tail bleeding and maximum-dose-tolerated studies indicated that no major bleeding or toxicity concerns for SCI suggesting a potentially safer anticoagulation outcome. FeCl3 -induced arterial and thromboplastin-induced venous thrombosis model studies in the rat showed reduced thrombus formation by SCI at 250 μg/animal, which matched enoxaparin at 2500 μg/animal.

CONCLUSIONS

Overall, SCI is a highly promising, allosteric inhibitor of FXIa that induces potent anticoagulation in vivo. Further studies are necessary to assess SCI in animal models mimicking human clinical indications.

Computer Design of Low-Molecular-Weight Inhibitors of Coagulation Factors

The review discusses main approaches to searching for new low-molecular-weight inhibitors of coagulation factors IIa, Xa, IXa, and XIa and the results of such studies conducted from 2015 to 2018. For each of these factors, several inhibitors with IC₅₀ < 10 nM have been found, some of which are now tested in clinical trials. However, none of the identified inhibitors meets the requirements for an "ideal" anticoagulant, so further studies are required.

Aptamers in the Therapeutics and Diagnostics Pipelines

Aptamers are short single-stranded DNA or RNA oligonucleotides that can selectively bind to small molecular ligands or protein targets with high affinity and specificity, by acquiring unique three-dimensional structures. Aptamers have the advantage of being highly specific, relatively small in size, non-immunogenic and can be easily stabilized by chemical modifications, thus allowing expansion of their diagnostic and therapeutic potential. Since the invention of aptamers in the early 1990s, great efforts have been made to make them clinically relevant for diseases like macular degeneration, cancer, thrombosis and inflammatory diseases. Furthermore, owing to the aforementioned advantages and unique adaptability of aptamers to point-of-care platforms, aptamer technology has created a stable niche in the field of in vitro diagnostics by enhancing the speed and accuracy of diagnoses. The aim of this review is to give an overview on aptamers, highlight the inherent therapeutic and diagnostic opportunities and challenges associated with them and present various aptamers that have reached therapeutic clinical trials, diagnostic markets or that have immediate translational potential for therapeutics and diagnostics applications.

Aptamers as targeted therapeutics: current potential and challenges

Nucleic acid aptamers, often termed 'chemical antibodies', are functionally comparable to traditional antibodies, but offer several advantages, including their relatively small physical size, flexible structure, quick chemical production, versatile chemical modification, high stability and lack of immunogenicity. In addition, many aptamers are internalized upon binding to cellular receptors, making them useful targeted delivery agents for small interfering RNAs (siRNAs), microRNAs and conventional drugs. However, several crucial factors have delayed the clinical translation of therapeutic aptamers, such as their inherent physicochemical characteristics and lack of safety data. This Review discusses these challenges, highlighting recent clinical developments and technological advances that have revived the impetus for this promising class of therapeutics.

Preclinical and translational evaluation of coagulation factor IXa as a novel therapeutic target

The benefits of novel oral anticoagulants are hampered by bleeding. Since coagulation factor IX (fIX) lies upstream of fX in the coagulation cascade, and intermediate levels have been associated with reduced incidence of thrombotic events, we evaluated the viability of fIXa as an antithrombotic target. We applied translational pharmacokinetics/pharmacodynamics (PK/PD) principles to predict the therapeutic window (TW) associated with a selective small molecule inhibitor (SMi) of fIXa, compound 1 (CPD1, rat fIXa inhibition constant (Ki, 21 nmol/L) relative to clinically relevant exposures of apixaban (rat fXa Ki 4.3 nmol/L). Concentrations encompassing the minimal clinical plasma concentration (C min) of the 5 mg twice daily (BID) dose of apixaban were tested in rat arteriovenous shunt (AVS/thrombosis) and cuticle bleeding time (CBT) models. An I max and a linear model were used to fit clot weight (CW) and CBT. The following differences in biology were observed: (1) antithrombotic activity and bleeding increased in parallel for apixaban, but to a lesser extent for CPD1 and (2) antithrombotic activity occurred at high (>99%) enzyme occupancy (EO) for fXa or moderate (>65% EO) for fIXa. translational PK/PD analysis indicated that noninferiority was observed for concentrations of CPD1 that provided between 86% and 96% EO and that superior TW existed between 86% and 90% EO. These findings were confirmed in a study comparing short interfering (si)RNA-mediated knockdown (KD) modulation of fIX and fX mRNA. In summary, using principles of translational biology to relate preclinical markers of efficacy and safety to clinical doses of apixaban, we found that modulation of fIXa can be superior to apixaban.