Chemical Zymogens and Transmembrane Activation of Transcription in Synthetic Cells

In this work, synthetic cells equipped with an artificial signaling pathway that connects an extracellular trigger event to the activation of intracellular transcription are engineered. Learning from nature, this is done via an engineering of responsive enzymes, such that activation of enzymatic activity can be triggered by an external biochemical stimulus. Reversibly deactivated creatine kinase to achieve triggered production of adenosine triphosphate, and a reversibly deactivated nucleic acid polymerase for on-demand synthesis of RNA are engineered. An extracellular, enzyme-activated production of a diffusible zymogen activator is also designed. The key achievement of this work is that the importance of cellularity is illustrated whereby the separation of biochemical partners is essential to resolve their incompatibility, to enable transcription within the confines of a synthetic cell. The herein designed biochemical pathway and the engineered synthetic cells are arguably primitive compared to their natural counterpart. Nevertheless, the results present a significant step toward the design of synthetic cells with responsive behavior, en route from abiotic to life-like cell mimics.

Development of N-Terminally Modified Variants of the CXCR4-Antagonistic Peptide EPI-X4 for Enhanced Plasma Stability

EPI-X4, a natural peptide CXCR4 antagonist, shows potential for treating inflammation and cancer, but its short plasma stability limits its clinical application. We aimed to improve the plasma stability of EPI-X4 analogues without compromising CXCR4 antagonism. Our findings revealed that only the peptide N-terminus is prone to degradation. Consequently, incorporating d-amino acids or acetyl groups in this region enhanced peptide stability in plasma. Notably, EPI-X4 leads 5, 27, and 28 not only retained their CXCR4 binding and antagonism but also remained stable in plasma for over 8 h. Molecular dynamic simulations showed that these modified analogues bind similarly to CXCR4 as the original peptide. To further increase their systemic half-lives, we conjugated these stabilized analogues with large polymers and albumin binders. These advances highlight the potential of the optimized EPI-X4 analogues as promising CXCR4-targeted therapeutics and set the stage for more detailed preclinical assessments.

Antibody-Drug Conjugates to Treat Bacterial Biofilms via Targeting and Extracellular Drug Release

The treatment of implant-associated bacterial infections and biofilms is an urgent medical need and a grand challenge because biofilms protect bacteria from the immune system and harbor antibiotic-tolerant persister cells. This need is addressed herein through an engineering of antibody-drug conjugates (ADCs) that contain an anti-neoplastic drug mitomycin C, which is also a potent antimicrobial against biofilms. The ADCs designed herein release the conjugated drug without cell entry, via a novel mechanism of drug release which likely involves an interaction of ADC with the thiols on the bacterial cell surface. ADCs targeted toward bacteria are superior by the afforded antimicrobial effects compared to the non-specific counterpart, in suspension and within biofilms, in vitro, and in an implant-associated murine osteomyelitis model in vivo. The results are important in developing ADC for a new area of application with a significant translational potential, and in addressing an urgent medical need of designing a treatment of bacterial biofilms.

Mechanisms of Degradation for Polydisulfides: Main Chain Scission, Self-Immolation, Or Chain Transfer Depolymerization

Organic polydisulfides hold immense potential for the design of recyclable materials. Of these, polymers based on lipoic acid are attractive, as they are based on a natural, renewable resource. Herein, we demonstrate that reductive degradation of lipoic acid polydisulfides is a rapid process whereby the quantity of added initiator relative to the polymer content defines the mechanism of polymer degradation, through the main chain scission, self-immolation, or "chain transfer" depolymerization. The latter mechanism is defined as the one during which a thiol group released through the decomposition of one polydisulfide chain initiates depolymerization of the neighbor macromolecule. The chain transfer mechanism afforded the highest yields of recovery of the monomer in its pristine form, and just one molecule of the reducing agent to initiate polymer degradation afforded recovery of over 50% of the monomer. These data are important to facilitate the development of polymer recycling and monomer reuse schemes.

Chemical zymogens: specificity and steroidal control of reactivation

Activation and masking of enzymatic activity on demand is of the highest importance in nature. It is achieved via chemical interconversion of enzymes and the corresponding zymogens through, for example, proteolytic processing or reversible phosphorylation, and affords on-demand activation of enzymes, controlled in space and/or time. In stark contrast, examples of chemical zymogens are very few, and in most cases these are based on the disulfide chemistry, which is largely indiscriminate to the nature of the activating thiol. In this work, we address an outstanding challenge of specificity of reactivation of chemical zymogens. We achieve this through engineering affinity between the chemical zymogen and the activator. Additional, higher level control over zymogen reactivation is installed in a nature-mimicking approach using steroidal hormones. Taken together, results of this study take a step towards establishing specificity of reactivation of synthetic, chemical zymogens. We anticipate that results of this study contribute significantly to the development of chemical zymogens as tools for diverse use in chemical biology and biotechnology.

Transmembrane signaling by a synthetic receptor in artificial cells

Signal transduction across biological membranes is among the most important evolutionary achievements. Herein, for the design of artificial cells, we engineer fully synthetic receptors with the capacity of transmembrane signaling, using tools of chemistry. Our receptors exhibit similarity with their natural counterparts in having an exofacial ligand for signal capture, being membrane anchored, and featuring a releasable messenger molecule that performs enzyme activation as a downstream signaling event. The main difference from natural receptors is the mechanism of signal transduction, which is achieved using a self-immolative linker. The receptor scaffold is modular and can readily be re-designed to respond to diverse activation signals including biological or chemical stimuli. We demonstrate an artificial signaling cascade that achieves transmembrane enzyme activation, a hallmark of natural signaling receptors. Results of this work are relevant for engineering responsive artificial cells and interfacing them and/or biological counterparts in co-cultures.

Chemical zymogens for the protein cysteinome

We present three classes of chemical zymogens established around the protein cysteinome. In each case, the cysteine thiol group was converted into a mixed disulfide: with a small molecule, a non-degradable polymer, or with a fast-depolymerizing fuse polymer (Z_LA). The latter was a polydisulfide based on naturally occurring molecule, lipoic acid. Zymogen designs were applied to cysteine proteases and a kinase. In each case, enzymatic activity was successfully masked in full and reactivated by small molecule reducing agents. However, only Z_LA could be reactivated by protein activators, demonstrating that the macromolecular fuse escapes the steric bulk created by the protein globule, collects activation signal in solution, and relays it to the active site of the enzyme. This afforded first-in-class chemical zymogens that are activated via protein-protein interactions. We also document zymogen exchange reactions whereby the polydisulfide is transferred between the interacting proteins via the "chain transfer" bioconjugation mechanism.

Macromolecular Viral Entry Inhibitors as Broad-Spectrum First-Line Antivirals with Activity against SARS-CoV-2

Inhibitors of viral cell entry based on poly(styrene sulfonate) and its core-shell nanoformulations based on gold nanoparticles are investigated against a panel of viruses, including clinical isolates of SARS-CoV-2. Macromolecular inhibitors are shown to exhibit the highly sought-after broad-spectrum antiviral activity, which covers most analyzed enveloped viruses and all of the variants of concern for SARS-CoV-2 tested. The inhibitory activity is quantified in vitro in appropriate cell culture models and for respiratory viral pathogens (respiratory syncytial virus and SARS-CoV-2) in mice. Results of this study comprise a significant step along the translational path of macromolecular inhibitors of virus cell entry, specifically against enveloped respiratory viruses.

Dimerization of the Peptide CXCR4-Antagonist on Macromolecular and Supramolecular Protraction Arms Affords Increased Potency and Enhanced Plasma Stability

Peptides are prime drug candidates due to their high specificity of action but are disadvantaged by low proteolytic stability. Here, we focus on the development of stabilized analogues of EPI-X4, an endogenous peptide antagonist of CXCR4. We synthesized macromolecular peptide conjugates and performed side-by-side comparison with their albumin-binding counterparts and considered monovalent conjugates, divalent telechelic conjugates, and Y-shaped peptide dimers. All constructs were tested for competition with the CXCR4 antibody-receptor engagement, inhibition of receptor activation, and inhibition of the CXCR4-tropic human immunodeficiency virus infection. We found that the Y-shaped conjugates were more potent than the parent peptide and at the same time more stable in human plasma, with a favorable outlook for translational studies.

Synthetic Artificial Apoptosis-Inducing Receptor for On-Demand Deactivation of Engineered Cells

The design of a fully synthetic, chemical "apoptosis-inducing receptor" (AIR) molecule is reported that is anchored into the lipid bilayer of cells, is activated by the incoming biological input, and responds with the release of a secondary messenger-a highly potent toxin for cell killing. The AIR molecule has four elements, namely, an exofacial trigger group, a bilayer anchor, a toxin as a secondary messenger, and a self-immolative scaffold as a mechanism for signal transduction. Receptor installation into cells is established via a robust protocol with minimal cell handling. The synthetic receptor remains dormant in the engineered cells, but is effectively triggered externally by the addition of an activating biomolecule (enzyme) or in a mixed cell population through interaction with the surrounding cells. In 3D cell culture (spheroids), receptor activation is accessible for at least 5 days, which compares favorably with other state of the art receptor designs.

Ceria Nanozyme and Phosphate Prodrugs: Drug Synthesis through Enzyme Mimicry

Nanozymes can mimic the activities of diverse enzymes, and this ability finds applications in analytical sciences and industrial chemistry, as well as in biomedical applications. Among the latter, prodrug conversion mediated by nanozymes is investigated as a step toward site-specific drug synthesis, to achieve localized therapeutic effects. In this work, we investigated a ceria nanozyme as a mimic to phosphatase, to mediate conversion of phosphate prodrugs into corresponding therapeutics. To this end, the substrate scope of ceria as a phosphatase mimic was analyzed using a broad range of natural phosphor(di)esters and pyrophosphates. Knowledge of this scope guided the selection of existing phosphate prodrugs that can be converted by ceria into the corresponding therapeutics. "Extended scaffold phosphates" were engineered using self-immolative linkers to accommodate a prodrug design for amine-containing drugs, such as monomethyl auristatin E. Phosphate prodrugs masked activity of the toxin, whereas prodrug conversion mediated by the nanozyme restored drug toxicity, which was validated in mammalian cell culture. The main novelty of this work lies in the rational pairing of the ceria nanozyme with the existing and the de novo designed "extended scaffold" phosphate prodrugs toward their use in nanozyme-prodrug therapy based on the defined nanozyme substrate scope.

Per-glycosylation of the Surface-Accessible Lysines: One-Pot Aqueous Route to Stabilized Proteins with Native Activity

Chemical glycosylation of proteins is a powerful tool applied widely in biomedicine and biotechnology. However, it is a challenging undertaking and typically relies on recombinant proteins and site-specific conjugations. The scope and utility of this nature-inspired methodology would be broadened tremendously by the advent of facile, scalable techniques in glycosylation, which are currently missing. In this work, we investigated a one-pot aqueous protocol to achieve indiscriminate, surface-wide glycosylation of the surface accessible amines (lysines and/or N-terminus). We reveal that this approach afforded minimal if any change in the protein activity and recognition events in biochemical and cell culture assays, but at the same time provided a significant benefit of stabilizing proteins against aggregation and fibrillation - as demonstrated on serum proteins (albumins and immunoglobulin G, IgG), an enzyme (uricase), and proteins involved in neurodegenerative disease (α-synuclein) and diabetes (insulin). Most importantly, this highly advantageous result was achieved via a one-pot aqueous protocol performed on native proteins, bypassing the use of complex chemical methodologies and recombinant proteins.

Nitric Oxide to Fight Viral Infections

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) that has quickly and deeply affected the world, with over 60 million confirmed cases. There has been a great effort worldwide to contain the virus and to search for an effective treatment for patients who become critically ill with COVID-19. A promising therapeutic compound currently undergoing clinical trials for COVID-19 is nitric oxide (NO), which is a free radical that has been previously reported to inhibit the replication of several DNA and RNA viruses, including coronaviruses. Although NO has potent antiviral activity, it has a complex role in the immunological host responses to viral infections, i.e., it can be essential for pathogen control or detrimental for the host, depending on its concentration and the type of virus. In this Essay, the antiviral role of NO against SARS-CoV, SARS-CoV-2, and other human viruses is highlighted, current development of NO-based therapies used in the clinic is summarized, existing challenges are discussed and possible further developments of NO to fight viral infections are suggested.

Broad-Spectrum Antiviral Agents Based on Multivalent Inhibitors of Viral Infectivity

The ongoing pandemic of the coronavirus disease (Covid-19), caused by the spread of the severe acute respiratory syndrome coronavirus 2 (SARS CoV-2), highlights the need for broad-spectrum antiviral drugs. In this Essay, it is argued that such agents already exist and are readily available while highlighting the challenges that remain to translate them into the clinic. Multivalent inhibitors of viral infectivity based on polymers or supramolecular agents and nanoparticles are shown to be broadly acting against diverse pathogens in vitro as well as in vivo. Furthermore, uniquely, such agents can be virucidal. Polymers and nanoparticles are stable, do not require cold chain of transportation and storage, and can be obtained on large scale. Specifically, for the treatment of respiratory viruses and pulmonary diseases, these agents can be administered via inhalation/nebulization, as is currently investigated in clinical trials as a treatment against SARS CoV-2/Covid-19. It is believed that with due optimization and clinical validation, multivalent inhibitors of viral infectivity can claim their rightful position as broad-spectrum antiviral agents.

Nanozymes and Glucuronides: Glucuronidase, Esterase, and/or Transferase Activity

Nanozymes are fundamentally interesting catalysts that are investigated as alternatives to fragile protein-enzymes for applications in biotechnology, for prodrug activation, and use in biomedicine, as well as the catalysts that contributed to the Origin of Life. However, until now, nanozymes mostly have been documented to exhibit activity as red/ox catalysts, whereas examples of activity outside this broad class of reactions are very few. Herein, activity of nanozymes on glucuronide prodrugs is investigated, specifically focusing on the mechanism of prodrug conversion reactions. The main finding of this work is that nanozymes exhibit glucuronide-like activity, but also catalyze prodrug conversion via esterase-like mechanism and facilitate group transfer reactions.

Inhaled and systemic heparin as a repurposed direct antiviral drug for prevention and treatment of COVID-19

Here, we advocate a highly favourable opportunity for the treatment of COVID-19 disease by repurposing a long-serving medical agent with an excellent history of clinical use, namely heparin. Heparin is best known as an anticoagulant, but it also exhibits direct antiviral activity against many enveloped viruses and has anti-inflammatory activity. The high incidence of thromboembolic events in COVID-19 patients suggests that coagulopathy plays an important role in the SARS-CoV-2 pathogenesis. This already makes heparin a unique, potentially curative agent that can be used immediately to help resolve the ongoing crisis associated with SARS-CoV-2 infection and COVID-19 disease. We demonstrate here in vitro that heparin does indeed inhibit SARS-CoV-2 infection. The three concurrent modes of activity of heparin (antiviral, anticoagulant and anti-inflammatory) against SARS-CoV-2/COVID-19 form a unique therapeutic combination. Thus, repurposing of heparin to fight SARS-CoV-2 and COVID-19 appears to be a powerful, readily available measure to address the current pandemic.

Chemical Artificial Internalizing Receptors for Primary T Cells

The newest generation of cell-based technologies relies heavily on methods to communicate to the engineered cells using artificial receptors, specifically to deactivate the cells administered to a patient in the event of adverse effects. Herein, artificial synthetic internalizing receptors are engineered that function in mammalian cells in 2D and in 3D and afford targeted, specific intracellular drug delivery with nanomolar potency in the most challenging cell type, namely primary, donor-derived T cells. Receptor design comprises a lipid bilayer anchor for receptor integration into cell membrane and a small xenobiotic molecule as a recognition ligand. Artificial receptors are successfully targeted by the corresponding antibody-drug conjugate (ADC) and exhibit efficient cargo cell entry with ensuing intracellular effects. Receptor integration into cells is fast and robust and affords targeted cell entry in under 2 h. Through a combination of the receptor design and the use of ADC, combined benefits previously made available by chimeric artificial receptors (performance in T cells) and the chemical counterpart (robustness and simplicity) in a single functional platform is achieved. Artificial synthetic receptors are poised to facilitate the maturation of engineered cells as tools of biotechnology and biomedicine.

Remotely Triggered Liquefaction of Hydrogel Materials

Adaptable behavior such as triggered disintegration affords a broad scope and utility for (bio)materials in diverse applications in materials science and engineering. The impact of such materials continues to grow due to the increased importance of environmental considerations as well as the increased use of implants in medical practices. However, examples of such materials are still few. In this work, we engineer triggered liquefaction of hydrogel biomaterials in response to internal, localized heating, mediated by near-infrared light as external stimulus. This adaptable behavior is engineered into the readily available physical hydrogels based on poly(vinyl alcohol), using gold nanoparticles or an organic photothermal dye as heat generators. Upon laser light irradiation, engineered biomaterials underwent liquefaction within seconds. Pulsed laser light irradiation afforded controlled, on-demand release of the incorporated cargo, successful for small molecules as well as proteins (enzymes) in their biofunctional form.

Enzyme Mimics for the Catalytic Generation of Nitric Oxide from Endogenous Prodrugs

The highly diverse biological roles of nitric oxide (NO) in both physiological and pathophysiological processes have prompted great interest in the use of NO as a therapeutic agent in various biomedical applications. NO can exert either protective or deleterious effects depending on its concentration and the location where it is delivered or generated. This double-edged attribute, together with the short half-life of NO in biological systems, poses a major challenge to the realization of the full therapeutic potential of this molecule. Controlled release strategies show an admirable degree of precision with regard to the spatiotemporal dosing of NO but are disadvantaged by the finite NO deliverable payload. In turn, enzyme-prodrug therapy techniques afford enhanced deliverable payload but are troubled by the inherent low stability of natural enzymes, as well as the requirement to control pharmacokinetics for the exogenous prodrugs. The past decade has seen the advent of a new paradigm in controlled delivery of NO, namely localized bioconversion of the endogenous prodrugs of NO, specifically by enzyme mimics. These early developments are presented, successes of this strategy are highlighted, and possible future work on this avenue of research is critically discussed.

Zinc Oxide Particles Catalytically Generate Nitric Oxide from Endogenous and Exogenous Prodrugs

Nitric oxide (NO) is a potent biological molecule that contributes to a wide spectrum of physiological processes. However, the full potential of NO as a therapeutic agent is significantly complicated by its short half-life and limited diffusion distance in human tissues. Current strategies for NO delivery focus on encapsulation of NO donors into prefabricated scaffolds or an enzyme-prodrug therapy approach. The former is limited by the finite pool of NO donors available, while the latter is challenged by the inherent low stability of natural enzymes. Zinc oxide (ZnO) particles with innate glutathione peroxidase and glycosidase activities, a combination that allows to catalytically decompose both endogenous (S-nitrosoglutathione) and exogenous (β-gal-NONOate) donors to generate NO at physiological conditions are reported. By tuning the concentration of ZnO particles and NO prodrugs, physiologically relevant NO levels are achieved. ZnO preserves its catalytic property for at least 6 months and the activity of ZnO in generating NO from prodrugs in human serum is demonstrated. The ZnO catalytic activity will be beneficial toward generating stable NO release for long-term biomedical applications.

Potent Lymphatic Translocation and Spatial Control Over Innate Immune Activation by Polymer-Lipid Amphiphile Conjugates of Small-Molecule TLR7/8 Agonists

Uncontrolled systemic inflammatory immune triggering has hampered the clinical translation of several classes of small-molecule immunomodulators, such as imidazoquinoline TLR7/8 agonists for vaccine design and cancer immunotherapy. By taking advantage of the inherent serum-protein-binding property of lipid motifs and their tendency to accumulate in lymphoid tissue, we designed amphiphilic lipid-polymer conjugates that suppress systemic inflammation but provoke potent lymph-node immune activation. This work provides a rational basis for the design of lipid-polymer amphiphiles for optimized lymphoid targeting.

Nucleic Acids as a Nature-Inspired Scaffold for Macromolecular Prodrugs of Nucleoside Analogues

Macromolecular prodrugs (MP) built on the natural phosphodiester and deoxyribose backbone are developed using marketed antiviral nucleoside analogues. These MP are synthesized using automated synthesis, have defined molecular composition, and have a natural mechanism for drug release. These unique attributes, coupled to the efficient cell entry and potent antiviral effects, position the prodrugs scaffolded on nucleic acids favorably for translational studies.

Innate glycosidic activity in metallic implants for localized synthesis of antibacterial drugs

The unexpected discovery presented herein is that industrialized metallic wires can perform conversion of the glucuronide prodrugs with ensuing antibacterial effects.

Antifouling properties of layer by layer DNA coatings

Fouling is a major concern for solid/liquid interfaces of materials used in different applications. One approach of fouling control is the use of hydrophilic polymer coatings made from poly-anions and poly-cations using the layer-by-layer (LBL) method. The authors hypothesized that the poly-anionic properties and the poly-phosphate backbone of DNA would provide anti-biofouling and anti-scaling properties. To this end, poly(ethyleneimine)/DNA LBL coatings against microbial and inorganic fouling were developed, characterized and evaluated. DNA LBL coatings reduced inorganic fouling from tap water by 90% when incubated statically or under flow conditions mimicking surfaces in heat exchangers. The coatings also impaired biofilm formation by 93% on stainless steel from tap water, and resulted in a 97% lower adhesion force and reduced initial attachment of the human pathogens Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa on glass. This study demonstrates a proof of concept that LBL coatings with poly-anions harboring phosphate groups can address fouling in several applications.

Extended scaffold glucuronides: en route to the universal synthesis of O-aryl glucuronide prodrugs

An extended scaffold is the key to facile glucuronidation for the synthesis of prodrugs.

Non-covalent hitchhiking on endogenous carriers as a protraction mechanism for antiviral macromolecular prodrugs

Albumin is a highly successful tool of drug delivery providing drastically extended body and blood residence time for the associated cargo, but it only traffics single drug copies at a time. In turn, macromolecular prodrugs (MP) are advantaged in carrying a high drug payload but offering only a modest extension of residence time to the conjugated drugs. In this work, we engineer MP to contain terminal groups that bind to albumin via non-covalent association and reveal that this facile measure affords a significant protraction for the associated polymers. This methodology is applied to MP of acyclovir, a successful drug against herpes simplex virus infection but with poor pharmacokinetics. Resulting albumin-affine MP were efficacious agents against herpes simplex virus type 2 (HSV-2) both in vitro and in vivo. In the latter case, sub-cutaneous administration of MP resulted in local (vaginal) antiviral effects and a systemic protection. Presented benefits of non-covalent association with albumin are readily transferrable to a wide variety of MP in development for drug delivery as anticancer, anti-inflammatory, and anti-viral measures.

Materials and methods for delivery of biological drugs

Biological drugs generated via recombinant techniques are uniquely positioned due to their high potency and high selectivity of action. The major drawback of this class of therapeutics, however, is their poor stability upon oral administration and during subsequent circulation. As a result, biological drugs have very low bioavailability and short therapeutic half-lives. Fortunately, tools of chemistry and biotechnology have been developed into an elaborate arsenal, which can be applied to improve the pharmacokinetics of biological drugs. Depot-type release systems are available to achieve sustained release of drugs over time. Conjugation to synthetic or biological polymers affords long circulating formulations. Administration of biological drugs through non-parenteral routes shows excellent performance and the first products have reached the market. This Review presents the main accomplishments in this field and illustrates the materials and methods behind existing and upcoming successful formulations and delivery strategies for biological drugs.

Combatting implant-associated biofilms through localized drug synthesis

Bacterial contamination of implantable biomaterials is a significant socioeconomic and healthcare burden. Indeed, bacterial colonization of implants after surgery has a high rate of incidence whereas concurrent prophylaxis using systemic antibiotics has limited clinical success. In this work, we develop enzyme-prodrug therapy (EPT) to prevent and to treat bacteria at interfaces. Towards the overall goal, novel prodrugs for fluoroquinolone antibiotics were developed on a privileged glucuronide scaffold. Whereas carbamoyl prodrugs were not stable and not suitable for EPT, glucuronides containing self-immolative linker between glucuronic acid masking group and the antibiotic were stable in solution and readily underwent bioconversion in the presence of β-glucuronidase. Surface coatings for model biomaterials were engineered using sequential polymer deposition technique. Resulting coatings afforded fast prodrug conversion and mediated antibacterial measures against planktonic species as evidenced by pronounced zone of bacterial growth inhibition around the biomaterial surface. These biomaterials coupled with the glucuronide prodrugs also effectively combatted bacteria within established biofilms and also successfully prevented bacterial colonization of the surface. To our knowledge, this is the first report of EPT engineered to the surface of biomaterials to mediate antibacterial measures.

Progress and Promise of Nitric Oxide-Releasing Platforms

Nitric oxide (NO) is a highly potent radical with a wide spectrum of physiological activities. Depending on the concentration, it can enhance endothelial cell proliferation in a growth factor-free medium, mediate angiogenesis, accelerate wound healing, but may also lead to tumor progression or induce inflammation. Due to its multifaceted role, NO must be administered at a right dose and at the specific site. Many efforts have focused on developing NO-releasing biomaterials; however, NO short half-life in human tissues only allows this molecule to diffuse over short distances, and significant challenges remain before the full potential of NO can be realized. Here, an overview of platforms that are engineered to release NO via catalytic or noncatalytic approaches is presented, with a specific emphasis on progress reported in the past five years. A number of NO donors, natural enzymes, and enzyme mimics are highlighted, and recent promising developments of NO-releasing scaffolds, particles, and films are presented. In particular, key parameters of NO delivery are discussed: 1) NO payload, 2) maximum NO flux, 3) NO release half-life, 4) time required to reach maximum flux, and 5) duration of NO release. Advantages and drawbacks are reviewed, and possible further developments are suggested.

Long-Acting, Potent Delivery of Combination Antiretroviral Therapy

Antiretroviral therapy (ART) has revolutionized HIV treatment, yet grand challenges remain: (i) short blood and body residence time of the antiviral drugs, (ii) relative poor antiretroviral drug penetrance into key tissue reservoirs of viral infection, namely, the spleen and lymph nodes, and (iii) obstacles in different pharmacokinetics of the necessary combination drugs. We present a novel drug delivery approach that simultaneously overcomes these limitations. We designed albumin-polymer-drug conjugates where albumin ensures long body residence time as well as lymphatic accumulation of the conjugate. The polymer enabled the delivery of combinations of drugs in precise ratios affording potency superior to the individual antiretroviral drugs and strong protection from HIV infection in primary human T cells.

Macromolecular prodrugs of ribavirin: Polymer backbone defines blood safety, drug release, and efficacy of anti-inflammatory effects

Macromolecular (pro)drugs hold much promise as broad-spectrum antiviral agents as either microbicides or carriers for intracellular delivery of antiviral drugs. Intriguing opportunity exists in combining the two modes of antiviral activity in the same polymer structure such that the same polymer acts as a microbicide and also serves to deliver the conjugated drug (ribavirin) into the cells. We explore this opportunity in detail and focus on the polymer backbone as a decisive constituent of such formulations. Fourteen polyanions (polycarboxylates, polyphosphates and polyphosphonates, and polysulfonates) were analyzed for blood pro/anti coagulation effects, albumin binding and albumin aggregation, inhibitory activity on polymerases, cytotoxicity, and anti-inflammatory activity in stimulated macrophages. Ribavirin containing monomers were designed to accommodate the synthesis of macromolecular prodrugs with disulfide-exchange triggered drug release. Kinetics of drug release was fast in all cases however enhanced hydrophobicity of the polymer significantly slowed release of ribavirin. Results of this study present a comprehensive view on polyanions as backbone for macromolecular prodrugs of ribavirin as broad-spectrum antiviral agents.

Enzyme Prodrug Therapy Achieves Site-Specific, Personalized Physiological Responses to the Locally Produced Nitric Oxide

Nitric oxide (NO) is a highly potent but short-lived endogenous radical with a wide spectrum of physiological activities. In this work, we developed an enzymatic approach to the site-specific synthesis of NO mediated by biocatalytic surface coatings. Multilayered polyelectrolyte films were optimized as host compartments for the immobilized β-galactosidase (β-Gal) enzyme through a screen of eight polycations and eight polyanions. The lead composition was used to achieve localized production of NO through the addition of β-Gal-NONOate, a prodrug that releases NO following enzymatic bioconversion. The resulting coatings afforded physiologically relevant flux of NO matching that of the healthy human endothelium. The antiproliferative effect due to the synthesized NO in cell culture was site-specific: within a multiwell dish with freely shared media and nutrients, a 10-fold inhibition of cell growth was achieved on top of the biocatalytic coatings compared to the immediately adjacent enzyme-free microwells. The physiological effect of NO produced via the enzyme prodrug therapy was validated ex vivo in isolated arteries through the measurement of vasodilation. Biocatalytic coatings were deposited on wires produced using alloys used in clinical practice and successfully mediated a NONOate concentration-dependent vasodilation in the small arteries of rats. The results of this study present an exciting opportunity to manufacture implantable biomaterials with physiological responses controlled to the desired level for personalized treatment.

The molecular tweezer CLR01 inhibits Ebola and Zika virus infection

Ebola (EBOV) and Zika viruses (ZIKV) are responsible for recent global health threats. As no preventive vaccines or antiviral drugs against these two re-emerging pathogens are available, we evaluated whether the molecular tweezer CLR01 may inhibit EBOV and ZIKV infection. This small molecule has previously been shown to inactivate HIV-1 and herpes viruses through a selective interaction with lipid-raft-rich regions in the viral envelope, which results in membrane disruption and loss of infectivity. We found that CLR01 indeed blocked infection of EBOV and ZIKV in a dose-dependent manner. The tweezer inhibited infection of epidemic ZIKV strains in cells derived from the anogenital tract and the central nervous system, and remained antivirally active in the presence of semen, saliva, urine and cerebrospinal fluid. Our findings show that CLR01 is a broad-spectrum inhibitor of enveloped viruses with prospects as a preventative microbicide or antiviral agent.

Macromolecular Antiviral Agents against Zika, Ebola, SARS, and Other Pathogenic Viruses

Viral pathogens continue to constitute a heavy burden on healthcare and socioeconomic systems. Efforts to create antiviral drugs repeatedly lag behind the advent of pathogens and growing understanding is that broad‐spectrum antiviral agents will make strongest impact in future antiviral efforts. This work performs selection of synthetic polymers as novel broadly active agents and demonstrates activity of these polymers against Zika, Ebola, Lassa, Lyssa, Rabies, Marburg, Ebola, influenza, herpes simplex, and human immunodeficiency viruses. Results presented herein offer structure–activity relationships for these pathogens in terms of their susceptibility to inhibition by polymers, and for polymers in terms of their anionic charge and hydrophobicity that make up broad‐spectrum antiviral agents. The identified leads cannot be predicted based on prior data on polymer‐based antivirals and represent promising candidates for further development as preventive microbicides.

Synthetic Polymer with a Structure-Driven Hepatic Deposition and Curative Pharmacological Activity in Hepatic Cells

Synthetic polymers make strong contributions as tools for delivery of biological drugs and chemotherapeutics. The most praised characteristic of polymers in these applications is complete lack of pharmacological function such as to minimize the side effects within the human body. In contrast, synthetic polymers with curative pharmacological activity are truly rare. Moreover, such activity is typically nonspecific rather than structure-defined. In this work, we present the discovery of poly(ethylacrylic acid) (PEAA) as a polymer with a suit of structure-defined, unexpected, pharmacological, and pharmacokinetic properties not observed in close structural analogues. Specifically, PEAA reveals capacity to bind to albumin with ensuing natural hepatic deposition in vivo and exhibits concurrent inhibitory activity against the hepatitis C virus and inflammation in hepatic cells. Our findings provide a view on synthetic polymers as curative, functional agents and present PEAA as a unique biomedical tool with applications related to health of the human liver.

Prodrugs in medicinal chemistry and enzyme prodrug therapies

Prodrugs are cunning derivatives of therapeutic agents designed to improve the pharmacokinetics profile of the drug. Within a prodrug, pharmacological activity of the drug is masked and is recovered within the human body upon bioconversion of the prodrug, a process that is typically mediated by enzymes. This concept is highly successful and a significant fraction of marketed therapeutic formulations is based on prodrugs. An advanced subset of prodrugs can be engineered such as to achieve site-specific bioconversion of the prodrug - to comprise the highly advantageous "enzyme prodrug therapy", EPT. Design of prodrugs for EPT is similar to the prodrugs in general medicinal use in that the pharmacological activity of the drug is masked, but differs significantly in that site-specific bioconversion is a prime consideration, and the enzymes typically used for EPT are non-mammalian and/or with low systemic abundance in the human body. This review focuses on the design of prodrugs for EPT in terms of the choice of an enzyme and the corresponding prodrug for bioconversion. We also discuss the recent success of "self immolative linkers" which significantly empower and diversify the prodrug design, and present methodologies for the design of prodrugs with extended blood residence time. The review aims to be of specific interest for medicinal chemists, biomedical engineers, and pharmaceutical scientists.

Enzyme Prodrug Therapy Engineered into Electrospun Fibers with Embedded Liposomes for Controlled, Localized Synthesis of Therapeutics

Enzyme prodrug therapy (EPT) enables localized conversion of inert prodrugs to active drugs by enzymes. Performance of EPT necessitates that the enzyme remains active throughout the time frame of the envisioned therapeutic application. β-glucuronidase is an enzyme with historically validated performance in EPT, however it retains its activity in biomaterials for an insufficiently long period of time, typically not exceeding 7 d. Herein, the encapsulation of β-glucuronidase in liposomal subcompartments within poly(vinyl alcohol) electrospun fibers is reported, leading to the assembly of biocatalytically active materials with activity of the enzyme sustained over at least seven weeks. It is further shown that liposomes provide the highly beneficial stabilization of the enzyme when incubated in cell culture media. The assembled biocatalytic materials successfully produce antiproliferative drugs (SN-38) using externally administered prodrugs (SN-38-glucuronide) and effectively suppress cell proliferation, with envisioned utility in the design of cardiovascular grafts.