In-depth structural characterization of pentosan polysulfate sodium complex drug using orthogonal analytical tools

Chemical approaches to the sulfation of small molecules: current progress and future directions

Sulfation is one of the most important modifications that occur to a wide range of bioactive small molecules including polysaccharides, proteins, flavonoids, and steroids. In turn, these sulfated molecules have significant biological and pharmacological roles in diverse processes including cell signalling, modulation of immune and inflammation response, anti-coagulation, anti-atherosclerosis, and anti-adhesive properties. This Essay summarises the most encountered chemical sulfation methods of small molecules. Sulfation reactions using sulfur trioxide amine/amide complexes are the most used method for alcohol and phenol groups in carbohydrates, steroids, proteins, and related scaffolds. Despite the effectiveness of these methods, they suffer from issues including multiple-purification steps, toxicity issues (e.g., pyridine contamination), purification challenges, stoichiometric excess of reagents which leads to an increase in reaction cost, and intrinsic stability issues of both the reagent and product. Recent advances including SuFEx, the in situ reagent approach, and TBSAB show the widespread appeal of novel sulfating approaches that will enable a larger exploration of the field in the years to come by simplifying the purification and isolation process to access bespoke sulfated small molecules.

Chemical and biological differences between original and mimetic pentosan polysulfates

Pentosan polysulfate sodium (PPS) is a semi-synthetic, heparin-like polysaccharide with manifold therapeutic actions. It is approved for treatment of bladder pain syndrome / interstitial cystitis in humans and treatment of musculoskeletal diseases in animals. PPS is produced by a complex procedure using beech wood as starting material. It consists of a mixture of sulfated glucuronoxylans, whose structural composition cannot be fully characterized by physicochemical analysis. The question arises whether PPS follow-on products are identical with the original and thus meet the requirement for generic drug application. The aim of this study was to investigate whether commercially available PPS products differ in physicochemical characteristics and biological effects from the original. Ten PPS preparations from different manufactures were analyzed using orthogonal analytical techniques including, inter alia, size exclusion chromatography with triple detection, nuclear magnetic resonance spectroscopy, and high-resolution mid-infrared spectroscopy in aqueous solution with chemometric evaluation. For functional analysis, we measured the plasma kallikrein generation in human plasma and FXII activation. The study revealed significant structural and biological differences between PPS from different sources. Therefore, follow-on products cannot be considered identical but at best similar to original PPS. However, their similar efficacy and safety have still to be proven by comprehensive studies.

Further advances in identification of pentosan polysulfate monosaccharide composition by NMR

Several publications have recently proposed NMR spectroscopy to evaluate the critical quality attributes (CQA) of pentosan polysulfate sodium (PPS), the active ingredient of Elmiron™ approved to treat interstitial cystitis. PPS is a polymer of sulfated β(1-4)-d-xylopyranose residues randomly substituted by 4-O-methyl-glucopyranosyluronic acid, containing, beyond the main xylose-2,3-O-disulfate repetitive unit, some minor residues that can be marker of both the starting material and preparation process. In the present study we assigned some previously unknown cross-peaks in 1H-13C HSQC NMR of PPS related to its minor sequences adding additional details to its CQA. Four anomeric cross-peaks related to glucuronate-branched xylose and different sulfation pattern as well as the preceding xyloses were identified. Two minor process-related signals of monosulfated xyloses (unsubstituted in position 2 or 3) were also assigned. The isolation of a disaccharide fraction allowed the assignment of the reducing end xylose-α/β as well as the preceding xylose residues to be corrected. Additionally, the oversulfation of PPS allowed detection of the reducing end xylose-tri-1,2,3-O-sulfate. The newly identified cross-peaks were integrated into an updated quantitative NMR method. Finally, we demonstrated that an in-depth PPS analysis can be obtained using NMR instruments at medium magnetic fields (500 MHz/600 MHz), commonly available in pharmaceutical industries.

A Precise qNMR Method for the Rapid Quantification of Lot-to-Lot Variations in Multiple Quality Attributes of Pentosan Polysulfate Sodium

Pentosan polysulfate sodium (PPS) is an orphan drug with anticoagulant activity. PPS is prepared from the chemical processing of xylan extracted from beechwood tree to yield a mixture of 4-6 kDa polysaccharides. The chain is mainly composed of sulfated xylose (Xyl) with branched 4-O-methyl-glucuronate (MGA). During generic drug development, the quality attributes (QAs) including monosaccharide composition, modification, and length need to be comparable to those found in the reference list drug (RLD). However, the range of QA variation of the RLD PPS has not been well characterized. Here, multiple PPS RLD lots were studied using quantitative NMR (qNMR) and diffusion ordered spectroscopy (DOSY) to quantitate the components in the mixture and to probe both inter- and intra-lot precision variability. The DOSY precision assessed using coefficient of variation (CV) was 6%, comparable to PPS inter-lot CV of 5%. The QAs obtained from 1D qNMR were highly precise with a precision CV < 1%. The inter-lot MGA content was 4.8 ± 0.1%, indicating a very consistent botanical raw material source. Other process-related chemical modification including aldehyde at 0.51 ± 0.04%, acetylation at 3.3 ± 0.2% and pyridine at 2.08 ± 0.06%, varied more than MGA content. The study demonstrated that 1D qNMR is a quick and precise method to reveal ranges of variation in multiple attributes of RLD PPS which can be used to assess equivalency with generic formulations. Interestingly, the synthetic process appeared to introduce more variations to the PPS product than the botanical source of the material.

Pharmacology of Heparin and Related Drugs: An Update

Heparin has been used extensively as an antithrombotic and anticoagulant for close to 100 years. This anticoagulant activity is attributed mainly to the pentasaccharide sequence, which potentiates the inhibitory action of antithrombin, a major inhibitor of the coagulation cascade. More recently it has been elucidated that heparin exhibits anti-inflammatory effect via interference of the formation of neutrophil extracellular traps and this may also contribute to heparin's antithrombotic activity. This illustrates that heparin interacts with a broad range of biomolecules, exerting both anticoagulant and nonanticoagulant actions. Since our previous review, there has been an increased interest in these nonanticoagulant effects of heparin, with the beneficial role in patients infected with SARS2-coronavirus a highly topical example. This article provides an update on our previous review with more recent developments and observations made for these novel uses of heparin and an overview of the development status of heparin-based drugs. SIGNIFICANCE STATEMENT: This state-of-the-art review covers recent developments in the use of heparin and heparin-like materials as anticoagulant, now including immunothrombosis observations, and as nonanticoagulant including a role in the treatment of SARS-coronavirus and inflammatory conditions.

Pentosan polysulfate inhibits attachment and infection by SARS-CoV-2 in vitro: insights into structural requirements for binding

Two years since the outbreak of the novel coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) pandemic, there remain few clinically effective drugs to complement vaccines. One is the anticoagulant, heparin, which in 2004 was found able to inhibit invasion of SARS-CoV (CoV-1) and which has been employed during the current pandemic to prevent thromboembolic complications and moderate potentially damaging inflammation. Heparin has also been shown experimentally to inhibit SARS-CoV-2 attachment and infection in susceptible cells. At high therapeutic doses however, heparin increases the risk of bleeding and prolonged use can cause heparin-induced thrombocytopenia, a serious side effect. One alternative, with structural similarities to heparin, is the plant-derived, semi-synthetic polysaccharide, pentosan polysulfate (PPS). PPS is an established drug for the oral treatment of interstitial cystitis, is well-tolerated, and exhibits weaker anticoagulant effects than heparin. In an established Vero cell model, PPS and its fractions of varying molecular weights inhibited invasion by SARS-CoV-2. Intact PPS and its size-defined fractions were characterized by molecular weight distribution and chemical structure using nuclear magnetic resonance spectroscopy and liquid chromatography–mass spectrometry, then employed to explore the structural basis of interactions with SARS-CoV-2 spike protein receptor-binding domain (S1 RBD) and the inhibition of Vero cell invasion. PPS was as effective as unfractionated heparin, but more effective in inhibiting cell infection than low-molecular-weight heparin (on a weight/volume basis). Isothermal titration calorimetry and viral plaque-forming assays demonstrated size-dependent binding to S1 RBD and inhibition of Vero cell invasion, suggesting the potential application of PPS as a novel inhibitor of SARS-CoV-2 infection.

Pentosan Polysulphate (PPS), a Semi-Synthetic Heparinoid DMOAD With Roles in Intervertebral Disc Repair Biology emulating The Stem Cell Instructive and Tissue Reparative Properties of Heparan Sulphate

This review highlights the attributes of pentosan polysulphate (PPS) in the promotion of intervertebral disc (IVD) repair processes. PPS has been classified as a disease modifying osteoarthritic drug (DMOAD) and many studies have demonstrated its positive attributes in the countering of degenerative changes occurring in cartilaginous tissues during the development of osteoarthritis (OA). Degenerative changes in the IVD also involve inflammatory cytokines, degradative proteases and cell signalling pathways similar to those operative in the development of OA in articular cartilage. PPS acts as a heparan sulphate (HS) mimetic to effect its beneficial effects in cartilage. The IVD contains small cell membrane HS-proteoglycans (HSPGs) such as syndecan, and glypican and a large multifunctional HS/chondroitin sulphate (CS) hybrid proteoglycan (HSPG2/perlecan) that have important matrix stabilising properties and sequester, control and present growth factors from the FGF, VEGF, PDGF and BMP families to cellular receptors to promote cell proliferation, differentiation and matrix synthesis. HSPG2 also has chondrogenic properties and stimulates the synthesis of extracellular matrix (ECM) components, expansion of cartilaginous rudiments and has roles in matrix stabilisation and repair. Perlecan is a perinuclear and nuclear proteoglycan in IVD cells with roles in chromatin organisation and control of transcription factor activity, immunolocalises to stem cell niches in cartilage, promotes escape of stem cells from quiescent recycling, differentiation and attainment of pluripotency and migratory properties. These participate in tissue development and morphogenesis, ECM remodelling and repair. PPS also localises in the nucleus of stromal stem cells, promotes development of chondroprogenitor cell lineages, ECM synthesis and repair and discal repair by resident disc cells. The availability of recombinant perlecan and PPS offer new opportunities in repair biology. These multifunctional agents offer welcome new developments in repair strategies for the IVD.

2D NMR peak profiling to compare chemical differences between batches of pentosan polysulfate sodium

Pentosan Polysulfate Sodium (PPS) is a semi-synthetic polysulfated xylan sourced from beechwood tree barks. PPS, which is mainly composed of a xylose chain with branched O-methyl-glucuronate (MGA), can have heterogeneity in monosaccharide species, sequence and chemical modifications including sulfation and acetylation. The monosaccharide composition in polysaccharide therapeutics is a frequently quoted quality attribute (QA), which has been assessed using two-dimensional (2D) ¹H-¹³C HSQC NMR. However, the sensitivity of 2D NMR for the assessment of PPS inter-lot variability from the same manufacturer was unclear and questions remained whether 2D NMR had sufficient sensitivity to distinguish normal batch to batch variations in this QA. Here, a 2D peak profile method was applied to compare high-resolution semi-quantitative (semi-q) HSQC spectra with the inclusion of intermediate precision spectra collected on two PPS drug lots released 29 months apart (where one of the lots was expired). The semi-q HSQC NMR confirmed the mass equivalence of total polysaccharides, O-Methyl and acetyl groups between the two lots. The 2D spectral peak profile results readily identified significant lot-to-lot differences (p < 0.05) in relative distribution among most monosaccharide species, in addition to heterogeneity in MGA distribution and acetyl transfer from PPS to free acetate in the expired lot. Precisely measured chemical QAs are prerequisites to establish normal batch variation in the innovator product, providing important reference ranges for complex generic drug developers. Overall, high-resolution semi-q HSQC NMR may provide a sensitive tool to measure fine chemical differences in polysaccharide therapeutics needed to establish chemical QAs and compare batches without concerns of intrinsic NMR method variation.

A Rapid and Mild Sulfation Strategy Reveals Conformational Preferences in Therapeutically Relevant Sulfated Xylooligosaccharides

Although sulfated xylooligosaccharides are promising therapeutic leads for a multitude of afflictions, the structural complexity and heterogeneity of commercially deployed forms (e. g. Pentosan polysulfate 1) complicates their path to further clinical development. We describe herein the synthesis of the largest homogeneous persulfated xylooligomers prepared to date, comprising up to eight xylose residues, as standards for biological studies. Near quantitative sulfation was accomplished using a remarkably mild and operationally simple protocol which avoids the need for high temperatures and a large excess of the sulfating reagent. Moreover, the sulfated xylooligomer standards so obtained enabled definitive identification of a pyridinium contaminant in a sample of a commercially prepared Pentosan drug and provided significant insights into the conformational preferences of the constituent persulfated monosaccharide residues. As the spatial distribution of sulfates is a key determinant of the binding of sulfated oligosaccharides to endogenous targets, these findings have broad implications for the advancement of Pentosan-based treatments.

Supramolecular Structuring of Hyaluronan-Lactose-Modified Chitosan Matrix: Towards High-Performance Biopolymers with Excellent Biodegradation

Non-covalent interactions in supramolecular chemistry provide useful systems to understand biological processes, and self-assembly systems are suitable assets to build-up innovative products for biomedical applications. In this field, polyelectrolyte complexes are interesting, especially when polysaccharides are involved, due to their non-toxicity and bio-absorbability. In this work, we investigated a polyelectrolyte formed by hyaluronic acid (HA), a negatively charged linear polysaccharide, with Chitlac (Ch), a positively charged lactose-modified chitosan. The aim of the study was the investigation of a novel Ch–HA polyelectrolyte complex, to understand the interaction between the two polysaccharides and the stability towards enzymatic activity. By means of gel permeation chromatography–triple detector array (GPC–TDA), nuclear magnetic resonance (NMR), dynamic viscosity, Zeta Potential and scanning electron microscopy (SEM), the polyelectrolyte complex properties were identified and compared to individual polysaccharides. The complex showed monodisperse molecular weight distribution, high viscosity, negative charge, and could be degraded by specific enzymes, such as hyaluronidase and lysozyme. The results suggest a close interaction between the two polysaccharides in the complex, which could be considered a self-assembly system.

Minor N-Glycan Mapping of Monoclonal Antibody Therapeutics Using Middle-Down NMR Spectroscopy

The N-glycosylation pattern of Asn-297 may have impacts on monoclonal antibody (mAb) drug plasma clearance, antibody-dependent cell mediated cytotoxicity (ADCC), and complement-dependent cytotoxicity (CDC). Notably, the changes in the relative abundance of certain minor glycans, like the afucosylation, high-mannose, or galactosylation are known to change mAb properties and functions. Here, a middle-down NMR spectroscopy based analytical procedure was applied to assess the composition and structure of glycans on adalimumab and trastuzumab without glycan cleavage from the mAbs. The anomeric 2D ¹H-¹³C spectra showed distinct patterns that could be used to profile and differentiate mAb glycan compositions. Specifically, the anomeric C1/H1 resonances from N-acetylglucosamine (GlcNAc2 and -5) and mannose (Man4) were identified as characteristic peaks for key glycan anomeric linkages and branching states. They were also utilized for measuring the relative abundance of minor glycans of total afucosylation (aFuc%), high mannose (HM%), and branch specific galactosylation (Gal_1-3% and Gal_1-6%). The obtained total aFuc% value of 11-12% was similar between the two mAbs; however, trastuzumab had significantly lower level of high mannose and a higher level of galactosylation than adalimumab. Overall, the 2D-NMR measurements provided functionally relevant mAb glycan composition and structure information. The method was deemed fit-for-purpose for assessment of these mAb quality attributes and involved fewer chemical preparation steps than the classical approaches that cleave glycans prior to making measurements.

Pentosan polysulfate to control hepcidin expression in vitro and in vivo

Hepcidin peptide is crucial in the regulation of systemic iron availability controlling its uptake from the diet and its release from the body storage tissues. Hepcidin dysregulation causes different human disorders ranging from iron overload (e.g. hemochromatosis) to iron deficiency (e.g. anemia). Hepcidin excess is common in the Anemia of Chronic Diseases or Anemia of Inflammation and in the genetic form of anemia named IRIDA; the pharmacological downregulation of hepcidin in these disorders could improve the anemia. Commercial heparins were shown to be strong inhibitors of hepcidin expression, by interfering with BMP6/SMAD pathway. The non-anti-coagulant heparins, modified to abolish the anti-thrombin binding site, were equally potent and could be used to improve iron status. To perform its anti-hepcidin activity heparin needs 2O- and 6O-sulfation and an average molecular weight (MW) up to 4000-8000 Dalton, depending on the sulfation level. The pentosane polysulfate (PPS), which shares with heparin a high degree of sulfation, is a compound with low anti-coagulant activity that is already in use for pharmaceutical treatment. In the present work we analyzed the anti-hepcidin activity of PPS in vitro and in vivo. We found that it acts as a strong inhibitor of hepcidin expression in HepG2 cells with an effect already visible after 2-3 h of treatment. It also suppressed hepcidin in mice in a dose dependent manner after 3 h and with a significant redistribution of systemic iron without evident side effects. PPS is also able to abolish the LPS dependent hepcidin upregulation similarly to that showed for heparin derivatives. These results suggest PPS as an interesting compound to control hepcidin in vivo.