Acetalated dextran is a chemically and biologically tunable material for particulate immunotherapy

Multi-COBRA hemagglutinin formulated with cGAMP microparticles elicits protective immune responses against influenza viruses

In humans, seasonal influenza viruses cause epidemics. Avian influenza viruses are of particular concern because they can infect multiple species and lead to unpredictable and severe disease. Therefore, there is an urgent need for a universal influenza vaccine that provides protection against all influenza strains. The cyclic GMP-AMP (cGAMP) is a promising adjuvant for subunit vaccines, which promotes type I interferons' production through the stimulator of interferon genes (STING) pathway. The encapsulation of cGAMP in acetalated dextran (Ace-DEX) microparticles (MPs) enhances its intracellular delivery. In this study, the Computationally Optimized Broadly Reactive Antigen (COBRA) methodology was used to generate H1, H3, and H5 vaccine candidates. Monovalent and multivalent COBRA HA vaccines formulated with cGAMP Ace-DEX MPs were evaluated in mice for protective antibody responses. cGAMP MPs adjuvanted COBRA HA vaccines elicited robust antigen-specific antibodies following vaccination. Compared with COBRA HA vaccine groups with no adjuvant or blank MPs, the cGAMP MPs enhanced HAI activity elicited by COBRA HA vaccines. The HAI activity was not significantly different between cGAMP MPs adjuvanted monovalent or multivalent COBRA HA vaccines. The cGAMP MPs adjuvanted COBRA vaccine groups had higher antigen-specific IgG2a-binding titers than the COBRA vaccine groups with no adjuvant or blank MPs. The COBRA vaccines formulated with cGAMP MPs mitigated diseases caused by influenza viral challenge and decreased pulmonary viral titers in mice. Therefore, the formulation of COBRA vaccines plus cGAMP MPs is a promising universal influenza vaccine that elicits protective immune responses against human seasonal and pre-pandemic strains.

IMPORTANCE

Influenza viruses cause severe respiratory disease, particularly in the very young and the elderly. Next-generation influenza vaccines are needed to protect against new influenza variants. This report used a promising adjuvant, cyclic GMP-AMP (cGAMP), to enhance the elicited antibodies by an improved influenza hemagglutinin candidate and protect against influenza virus infection. Overall, adding adjuvants to influenza vaccines is an effective method to improve vaccines.

Development, characterization, and evaluation of withaferin-A and artesunate-loaded pH-responsive acetal-dextran polymeric nanoparticles for the management of malaria

Artemisinin and its derivatives have been commonly used to treat malaria. However, the emergence of resistance against artemisinin derivatives has posed a critical challenge in malaria management. In the present study, we have proposed a combinatorial approach, utilizing pH-responsive acetal-dextran nanoparticles (Ac-Dex NPs) as carriers for the delivery of withaferin-A (WS-3) and artesunate (Art) to improve treatment efficacy of malaria. The optimized WS-3 and Art Ac-Dex NPs demonstrated enhanced pH-responsive release profiles under parasitophorous mimetic conditions (pH 5.5). Computational molecular modeling reveals that Ac-Dex's polymeric backbone strongly interacts with merozoite surface protein-1 (MSP-1), preventing erythrocyte invasion. In-vitro antimalarial activity of drug-loaded Ac-Dex NPs reveals a 1-1.5-fold reduction in IC50 values compared to pure drug against the 3D7 strain of Plasmodium falciparum. Treatment with WS-3 Ac-Dex NPs (100 mg/kg) and Art Ac-Dex NPs (30 mg/kg) to Plasmodium berghei-infected mice resulted in 78.11 % and 100 % inhibition of parasitemia. Notably, the combination therapy comprised of Art and WS-3 Ac-Dex NPs achieved complete inhibition of parasitemia even at a half dose of Art, indicating the synergistic potential of the combinations. However, further investigations are necessary to confirm the safety and effectiveness of WS-3 and Art Ac-Dex NPs for their successful clinical implications.

GFPBW1, a β-glucan from Grifola frondosa as vaccine adjuvant: APCs activation and maturation

Adjuvants for vaccines with characteristics of improving adaptive immunity particularly via leverage of antigen presenting cells (APCs) are currently lacking. In a previous work we obtained a new soluble 300 kDa homogeneous β-glucan named GFPBW1 from the fruit bodies of Granola frondosa. GFPBW1 could activate macrophages by targeting dendritic cell associated C-type lectin 1 (Dectin-1)/Syk/NF-κB signaling to achieve antitumour effects. In this study the adjuvant effects of GFPBW1 were explored with OVA-antigen and B16-OVA tumor model. We showed that GFPBW1 (5, 50, 500 μg/mL) dose-dependently promoted activation and maturation of APCs in vitro by increasing CD80, CD86 and MHC II expression. We immunized female mice with OVA in combination with GFPBW1 (50 or 300 μg) twice with an interval of two weeks. GFPBW1 markedly and dose-dependently increased OVA-specific antibody titers of different subtypes including IgG1, IgG2a, IgG2b and IgG3, suggesting that it could serve as an adjuvant for both Th1 and Th2 type immune responses. Furthermore, GFPBW1 in combination with aluminum significantly increased the titers of OVA-specific IgG2a and IgG2b, but not those of IgG1, suggesting that GFPBW1 could be used as a co-adjuvant of aluminum to compensate for Th1 deficiency. For mice immunized with OVA plus GFPBW1, no obvious pathological injury was observed in either major organs or injection sites, and no abnormalities were noted for any of the hematological parameters. When GFPBW1 served as an adjuvant in the B16-OVA cancer vaccine models, it could accomplish entire tumor suppression with preventive vaccines, and enhance antitumour efficacy with therapeutic vaccines. Differentially expressed genes were found to be enriched in antigen processing process, specifically increased tumor infiltration of DCs, B1 cells and plasma cells in the OVA plus GFPBW1 group, in accordance with its activation and maturation function of APCs. Collectively, this study systematically describes the properties of GFPBW1 as a novel potent and safe adjuvant and highlights its great potential in vaccine development.

Dynamic Release from Acetalated Dextran Nanoparticles for Precision Therapy of Inflammation

Polymer-based nanoparticles (NPs) that react to altered physiological characteristics have the potential to enhance the delivery of therapeutics to a specific area. These materials can utilize biochemical triggers, such as low pH, which is prone to happen locally in an inflammatory microenvironment due to increased cellular activity. This reduced pH is neutralized when inflammation subsides. For precise delivery of therapeutics to match this dynamic reaction, drug delivery systems (DDS) need to not only release the drug (ON) but also stop the release (OFF) autonomously. In this study, we use a systematic approach to optimize the composition of acetalated dextran (AcDex) NPs to start (ON) and stop (OFF) releasing model cargo, depending on local pH changes. By mixing ratios of AcDex polymers (mixed NPs), we achieved a highly sensitive material that was able to rapidly release cargo when going from pH 7.4 to pH 6.0. At the same time, the mix also offered a stable composition that enabled a rapid ON/OFF/ON/OFF switching within this narrow pH range in only 90 min. These mixed NPs were also sensitive to biological pH changes, with increased release in the presence of inflammatory cells compared to healthy cells. Such precise and controllable characteristics of a DDS position mixed NPs as a potential treatment platform to inhibit disease flare-ups, reducing both systemic and local side effects to offer a superior treatment option for inflammation compared to conventional systems.

Immunogenicity of an adjuvanted broadly active influenza vaccine in immunocompromised and diverse populations

Influenza virus outbreaks are a major burden worldwide each year. Current vaccination strategies are inadequate due to antigenic drift/shift of the virus and the elicitation of low immune responses. The use of computationally optimized broadly reactive antigen (COBRA) hemagglutinin (HA) immunogens subvert the constantly mutating viruses; however, they are poorly immunogenic on their own. To increase the immunogenicity of subunit vaccines such as this, adjuvants can be delivered with the vaccine. For example, agonists of the stimulator of interferon genes (STING) have proven efficacy as vaccine adjuvants. However, their use in high-risk populations most vulnerable to influenza virus infection has not been closely examined. Here, we utilize a vaccine platform consisting of acetalated dextran microparticles loaded with COBRA HA and the STING agonist cyclic GMP-AMP. We examine the immunogenicity of this platform in mouse models of obesity, aging, and chemotherapy-induced immunosuppression. Further, we examine vaccine efficacy in collaborative cross mice, a genetically diverse population that mimics human genetic heterogeneity. Overall, this vaccine platform had variable efficacy in these populations supporting work to better tailor adjuvants to specific populations.

Multi-COBRA hemagglutinin formulated with cGAMP microparticles elicit protective immune responses against influenza viruses

Influenza viruses cause a common respiratory disease known as influenza. In humans, seasonal influenza viruses can lead to epidemics, with avian influenza viruses of particular concern because they can infect multiple species and lead to unpredictable and severe disease. Therefore, there is an urgent need for a universal influenza vaccine that provides protection against seasonal and pre-pandemic influenza virus strains. The cyclic GMP-AMP (cGAMP) is a promising adjuvant for subunit vaccines that promotes type I interferons production through the stimulator of interferon genes (STING) pathway. The encapsulation of cGAMP in acetalated dextran (Ace-DEX) microparticles (MPs) enhances its intracellular delivery. In this study, the Computationally Optimized Broadly Reactive Antigen (COBRA) methodology was used to generate H1, H3, and H5 vaccine candidates. Monovalent and multivalent COBRA HA vaccines formulated with cGAMP Ace-DEX MPs were evaluated in a mouse model for antibody responses and protection against viral challenge. Serological analysis showed that cGAMP MPs adjuvanted monovalent and multivalent COBRA vaccines elicited robust antigen-specific antibody responses after a prime-boost vaccination and antibody titers were further enhanced after second boost. Compared to COBRA vaccine groups with no adjuvant or blank MPs, the cGAMP MPs enhanced HAI antibody responses against COBRA vaccination. The HAI antibody titers were not significantly different between cGAMP MPs adjuvanted monovalent and multivalent COBRA vaccine groups for most of the viruses tested in panels. The cGAMP MPs adjuvanted COBRA vaccines groups had higher antigen-specific IgG2a binding titers than the COBRA vaccine groups with no adjuvant or blank MPs. The COBRA vaccines formulated with cGAMP MPs mitigated disease caused by influenza viral challenge and decreased pulmonary viral titers in mice. Therefore, the formulation of COBRA vaccines plus cGAMP MPs is a promising universal influenza vaccine that elicits protective immune responses against human seasonal and pre-pandemic strains.

Flash nanoprecipitation allows easy fabrication of pH-responsive acetalated dextran nanoparticles for intracellular release of payloads

Acetalated dextran (Ac-Dex) nanoparticles are currently of immense interest due to their sharp pH-responsive nature and high biodegradability. Ac-Dex nanoparticles are often formulated through single- or double-emulsion methods utilizing polyvinyl alcohol as the stabilizer. The emulsion methods utilize toxic organic solvents such as dichloromethane or chloroform and require multi-step processing to form stable Ac-Dex nanoparticles. Here, we introduce a simple flash nanoprecipitation (FNP) approach that utilizes a confined impinging jet mixer and a non-toxic solvent, ethanol, to form Ac-Dex nanoparticles rapidly. Ac-Dex nanoparticles were stabilized using nonionic PEGylated surfactants, D-α-Tocopherol polyethylene glycol succinate (TPGS), or Pluronic (F-127). Ac-Dex nanoparticles formed using FNP were highly monodisperse and stably encapsulated a wide range of payloads, including hydrophobic, hydrophilic, and macromolecules. When lyophilized, Ac-Dex TPGS nanoparticles remained stable for at least one year with greater than 80% payload retention. Ac-Dex nanoparticles were non-toxic to cells and achieved intracellular release of payloads into the cytoplasm. In vivo studies demonstrated a predominant biodistribution of Ac-Dex TPGS nanoparticles in the liver, lungs, and spleen after intravenous administration. Taken together, the FNP technique allows easy fabrication and loading of Ac-Dex nanoparticles that can precisely release payloads into intracellular environments for diverse therapeutic applications. pH-responsive Acetalateddextran can be formulated using nonionic surfactants, such as TPGS or F-127, for intracellular release of payloads. Highly monodisperse and stable nanoparticles can be created through the simple, scalable flash nanoprecipitation technique, which utilizes a confined impingement jet mixer.

Delivery of Agarose-aided Sprays to the Posterior Nose for Mucosa Immunization and Short-term Protection against Infectious Respiratory Diseases

AIM

The study aimed to deliver sprays to the posterior nose for mucosa immunization or short-term protection.

BACKGROUND

Respiratory infectious diseases often enter the human body through the nose. Sars- Cov-2 virus preferentially binds to the ACE2-rich tissue cells in the Nasopharynx (NP). Delivering medications to the nose, especially to the NP region, provides either a short-term protective/ therapeutic layer or long-term mucosa immunization. Hydrogel-aided medications can assist film formation, prolong film life, and control drug release. However, conventional nasal sprays have failed to dispense mediations to the posterior nose, with most sprays lost in the nasal valve and front turbinate.

OBJECTIVE

The objective of the study was to develop a practical delivery system targeting the posterior nose and quantify the dosimetry distribution of agarose-saline solutions in the nasal cavity.

METHODS

The solution viscosities with various hydrogel concentrations (0.1-1%) were measured at different temperatures. Dripping tests on a vertical plate were conducted to understand the hydrogel concentration effects on the liquid film stability and mobility. Transparent nasal airway models were used to visualize the nasal spray deposition and liquid film translocation.

RESULTS

Spray dosimetry with different hydrogel concentrations and inhalation flow rates was quantified on a total and regional basis. The solution viscosity increased with decreasing temperature, particularly in the range of 60-40oC. The liquid viscosity, nasal spray atomization, and liquid film mobility were highly sensitive to the hydrogel concentration. Liquid film translocations significantly enhanced delivered doses to the caudal turbinate and nasopharynx when the sprays were administered at 60oC under an inhalation flow rate of 11 L/min with hydrogel concentrations no more than 0.5%. On the other hand, sprays with 1% hydrogel or administered at 40oC would significantly compromise the delivered doses to the posterior nose.

CONCLUSION

Delivering sufficient doses of hydrogel sprays to the posterior nose is feasible by leveraging the post-administration liquid film translocation.

Glycovaccinology: The design and engineering of carbohydrate-based vaccine components

Vaccines remain one of the most important pillars in preventative medicine, providing protection against a wide array of diseases by inducing humoral and/or cellular immunity. Of the many possible candidate antigens for subunit vaccine development, carbohydrates are particularly appealing because of their ubiquitous presence on the surface of all living cells, viruses, and parasites as well as their known interactions with both innate and adaptive immune cells. Indeed, several licensed vaccines leverage bacterial cell-surface carbohydrates as antigens for inducing antigen-specific plasma cells secreting protective antibodies and the development of memory T and B cells. Carbohydrates have also garnered attention in other aspects of vaccine development, for example, as adjuvants that enhance the immune response by either activating innate immune responses or targeting specific immune cells. Additionally, carbohydrates can function as immunomodulators that dampen undesired humoral immune responses to entire protein antigens or specific, conserved regions on antigenic proteins. In this review, we highlight how the interplay between carbohydrates and the adaptive and innate arms of the immune response is guiding the development of glycans as vaccine components that act as antigens, adjuvants, and immunomodulators. We also discuss how advances in the field of synthetic glycobiology are enabling the design, engineering, and production of this new generation of carbohydrate-containing vaccine formulations with the potential to prevent infectious diseases, malignancies, and complex immune disorders.

Humoral Response to the Acetalated Dextran M2e Vaccine is Enhanced by Antigen Surface Conjugation

The influenza A virus causes substantial morbidity and mortality worldwide every year and poses a constant threat of an emergent pandemic. Seasonal influenza vaccination strategies fail to provide complete protection against infection due to antigenic drift and shift. A universal vaccine targeting a conserved influenza epitope could substantially improve current vaccination strategies. The ectodomain of the matrix 2 protein (M2e) of influenza is a highly conserved epitope between virus strains but is also poorly immunogenic. Administration of M2e and the immunostimulatory stimulator of interferon genes (STING) agonist 3'3'-cyclic guanosine-adenosine monophosphate (cGAMP) encapsulated in microparticles made of acetalated dextran (Ace-DEX) has previously been shown to be effective for increasing the immunogenicity of M2e, primarily through T-cell-mediated responses. Here, the immunogenicity of Ace-DEX MPs delivering M2e was further improved by conjugating the M2e peptide to the particle surface in an effort to affect B-cell responses more directly. Conjugated or encapsulated M2e co-administered with Ace-DEX MPs containing cGAMP were used to vaccinate mice, and it was shown that two or three vaccinations could fully protect against a lethal influenza challenge, while only the surface-conjugated antigen constructs could provide some protection against lethal challenge with only one vaccination. Additionally, the use of a reducible linker augmented the T-cell response to the antigen. These results show the utility of conjugating M2e to the surface of a particle carrier to increase its immunogenicity for use as the antigen in a universal influenza vaccine.

Non-Invasive Vaccines: Challenges in Formulation and Vaccine Adjuvants

Given the limitations of conventional invasive vaccines, such as the requirement for a cold chain system and trained personnel, needle-based injuries, and limited immunogenicity, non-invasive vaccines have gained significant attention. Although numerous approaches for formulating and administrating non-invasive vaccines have emerged, each of them faces its own challenges associated with vaccine bioavailability, toxicity, and other issues. To overcome such limitations, researchers have created novel supplementary materials and delivery systems. The goal of this review article is to provide vaccine formulation researchers with the most up-to-date information on vaccine formulation and the immunological mechanisms available, to identify the technical challenges associated with the commercialization of non-invasive vaccines, and to guide future research and development efforts.

An antigen self-assembled and dendritic cell-targeted nanovaccine for enhanced immunity against cancer

The rise of nanotechnology has opened new horizons for cancer immunotherapy. However, most nanovaccines fabricated with nanomaterials suffer from carrier-related concerns, including low drug loading capacity, unpredictable metabolism, and potential systemic toxicity, which bring obstacles for their clinical translation. Herein, we developed an antigen self-assembled nanovaccine, which was resulted from a simple acryloyl modification of the antigen to induce self-assembly. Furthermore, a dendritic cell targeting head mannose monomer and a mevalonate pathway inhibitor zoledronic acid (Zol) were integrated or absorbed onto the nanoparticles (denoted as MEAO-Z) to intensify the immune response. The synthesized nanovaccine with a diameter of around 70 nm showed successful lymph node transportation, high dendritic cell internalization, promoted costimulatory molecule expression, and preferable antigen cross-presentation. In virtue of the above superiorities, MEAO-Z induced remarkably higher titers of serum antibody, stronger cytotoxic T lymphocyte immune responses and IFN-γ secretion than free antigen and adjuvants. In vivo, MEAO-Z significantly suppressed EG7-OVA tumor growth and prolonged the survival time of tumor-bearing mice. These results indicated the translation promise of our self-assembled nanovaccine for immune potentiation and cancer immunotherapy.

A New Biomaterial Derived from Aloe vera-Acemannan from Basic Studies to Clinical Application

Aloe vera is a kind of herb rich in polysaccharides. Acemannan (AC) is considered to be a natural polysaccharide with good biodegradability and biocompatibility extracted from Aloe vera and has a wide range of applications in the biomedical field due to excellent immunomodulatory, antiviral, antitumor, and tissue regeneration effects. In recent years, clinical case reports on the application of AC as a novel biomedical material in tissue regenerative medicine have emerged; it is mainly used in bone tissue engineering, pulp-dentin complex regeneration engineering, and soft tissue repair, among other operations. In addition, multiple studies have proved that the new composite products formed by the combination of AC and other compounds have excellent biological and physical properties and have broader research prospects. This paper introduces the preparation process, surface structure, and application forms of AC; summarizes the influence of acetyl functional group content in AC on its functions; and provides a detailed review of the functional properties, laboratory studies, clinical cutting-edge applications, and combined applications of AC. Finally, the current application status of AC from basic research to clinical treatment is analyzed and its prospects are discussed.

Targeting endosomal receptors, a new direction for polymers in nanomedicine

In this perspective, we outline a new opportunity for exploiting nanoparticle delivery of antagonists to target G-protein coupled receptors localized in intracellular compartments. We discuss the specific example of antagonizing endosomal receptors involved in pain to develop long-lasting analgesics but also outline the broader application potential of this delivery approach. We discuss the materials used to target endosomal receptors and indicate the design requirements for future successful applications.

Acetalized starch-based nanoparticles stabilized acid-sensitive Pickering emulsion as a potential antitumor drug carrier

Pickering emulsions are attracting increased attention owing to their therapeutic applications. However, the slow-release property of Pickering emulsions and the in vivo solid particle accumulation caused by the solid particle stabilizer film limit their applications in therapeutic delivery. In this study, drug-loaded, acid-sensitive Pickering emulsions were prepared using acetal-modified starch-based nanoparticles as stabilizers. The acetalized starch-based nanoparticles (Ace-SNPs) not only act as a solid-particle emulsifier to stabilize Pickering emulsions but also exhibit acid sensitivity and degradability, conducive to the destabilization of Pickering emulsions to release the drug and reduce the effect of particle accumulation in an acidic therapeutic environment. In vitro drug release profiles show that 50 % of curcumin was released in 12 h in an acidic medium (pH 5.4), whereas only 14 % of curcumin was released in 12 h at higher pH (7.4), indicating that the Ace-SNP stabilized Pickering emulsion possess good acid-responsive release characteristics in acidic environments. Moreover, acetalized starch-based nanoparticles and their degradation products showed good biocompatibility, and the resulting curcumin-loaded Pickering emulsions exhibited significant anticancer activity. These features suggest that the acetalized starch-based nanoparticle-stabilized Pickering emulsion has the potential for application as an antitumor drug carrier to enhance therapeutic effects.

Nanoparticle surface decoration mediated efficient protein and peptide co-encapsulation with precise ratiometric control for self-regulated drug release

Accuratly controlling drug release from a smart "self-regulated" drug delivery system is still an ongoing challenge. Herein, we developed a surface decoration strategy to achieve an efficient drug encapsulation with precise ratiometric control. Thanks to the surface decoration with cationic carrier materials by electrostatic attraction, the surface properties of different protein and peptide nanoparticles were uniformed to those adsorbed carrier materials. These carrier materials endowed protein and peptide nanoparticles with good dispersity in the oil phase and significantly inhibited the drug transfer from oil to water. With uniform surface properties, we realized the co-encapsulation of multiple types of proteins and peptides with precise ratiometric control. The encapsulation efficiency was higher than 87.8% for insulin. After solidification, the adsorbed materials on the surface of nanoparticles formed a solid protection layer, which prolonged the mean residence time of insulin from 3.3 ± 0.1 h (for insulin solution) to 47.5 ± 1.3 h. In type 1 diabetes, the spermine-modified acetalated dextran microparticle co-loaded with insulin, glucose oxidase and catalase maintained the blood glucose level within the normal range for 7 days.

Vinyl Sulfone-functionalized Acetalated Dextran Microparticles as a Subunit Broadly Acting Influenza Vaccine

Influenza is a global health concern with millions of infections occurring yearly. Seasonal flu vaccines are one way to combat this virus; however, they are poorly protective against influenza as the virus is constantly mutating, particularly at the immunodominant hemagglutinin (HA) head group. A more broadly acting approach involves Computationally Optimized Broadly Reactive Antigen (COBRA). COBRA HA generates a broad immune response that is capable of protecting against mutating strains. Unfortunately, protein-based vaccines are often weekly immunogenic, so to help boost the immune response, we employed the use of acetalated dextran (Ace-DEX) microparticles (MPs) two ways: one to conjugate COBRA HA to the surface and a second to encapsulate cGAMP. To conjugate the COBRA HA to the surface of the Ace-DEX MPs, a poly(L-lactide)-polyethylene glycol co-polymer with a vinyl sulfone terminal group (PLLA-PEG-VS) was used. MPs encapsulating the STING agonist cGAMP were co-delivered with the antigen to form a broadly active influenza vaccine. This vaccine approach was evaluated in vivo with a prime-boost-boost vaccination schedule and illustrated generation of a humoral and cellular response that could protect against a lethal challenge of A/California/07/2009 in BALB/c mice.

Particle-Based therapies for antigen specific treatment of type 1 diabetes

Type 1 diabetes mellitus (T1D) is the leading metabolic disorder in children worldwide. Over time, incidence rates have continued to rise with 20 million individuals affected globally by the autoimmune disease. The current standard of care is costly and time-consuming requiring daily injections of exogenous insulin. T1D is mediated by autoimmune effector responses targeting autoantigens expressed on pancreatic islet β-cells. One approach to treat T1D is to skew the immune system away from an effector response by taking an antigen-specific approach to heighten a regulatory response through a therapeutic vaccine. An antigen-specific approach has been shown with soluble agents, but the effects have been limited. Micro or nanoparticles have been used to deliver a variety of therapeutic agents including peptides and immunomodulatory therapies to immune cells. Particle-based systems can be used to deliver cargo into the cell and microparticles can passively target phagocytic cells. Further, surface modification and controlled release of encapsulated cargo can enhance delivery over soluble agents. The induction of antigen-specific immune tolerance is imperative for the treatment of autoimmune diseases such as T1D. This review highlights studies that utilize particle-based platforms for the treatment of T1D.

Sustained delivery of CpG oligodeoxynucleotide by acetalated dextran microparticles augments effector response to Computationally Optimized Broadly Reactive Antigen (COBRA) influenza hemagglutinin

A subunit or protein-based influenza vaccine can be a safer alternative to live attenuated vaccine (Flumist) and require fewer boosts than an inactivated vaccine (e.g. Fluzone). However, to form an effective subunit vaccine, an adjuvant is often needed. In this work we used electrospray to encapsulate the hydrophilic adjuvant CpG into microparticles made from the hydrophobic biodegradable polymer acetalated dextran. To understand the rate of particle degradation on CpG release, polymer that was slow (21 h at phagosomal pH 5) and fast (0.25 h at pH 5) degrading was used to encapsulate the adjuvant. The slow-degrading particles exhibited the greatest degree of innate immune stimulation of antigen-presenting cells in vitro. In mice, the broadly acting Computationally Optimized Broadly Reactive Antigen (COBRA) Y2 influenza hemagglutinin (HA) antigen was used with CpG particles, soluble CpG, or MF-59 like adjuvant Addavax. Particles and soluble CpG elicited similar induction of anti-HA antibodies and protection against lethal influenza challenge, but the sustained release particles elicited the highest levels antibody effector functions. These results demonstrate a suitable method for encapsulation of CpG oligonucleotide in a hydrophobic particle matrix, and suggest that sustained release of CpG from Ace-DEX microparticles could potentially be used to induce potent antibody effector functions.

Developing Next-Generation Protein-Based Vaccines Using High-Affinity Glycan Ligand-Decorated Glyconanoparticles

Major diseases, such as cancer and COVID-19, are frightening global health problems, and sustained action is necessary to develop vaccines. Here, for the first time, ethoxy acetalated dextran nanoparticles (Ace-Dex-NPs) are functionalized with 9-N-(4H-thieno[3,2-c]chromene-2-carbamoyl)-Siaα2-3Galβ1-4GlcNAc (TCC Sia-LacNAc) targeting macrophages as a universal vaccine design platform. First, azide-containing oxidized Ace-Dex-NPs are synthesized. After the NPs are conjugated with ovalbumin (OVA) and resiquimod (Rd), they are coupled to TCC Sia-LacNAc-DBCO to produce TCC Sia-Ace-Dex-OVA-Rd, which induce a potent, long-lasting OVA-specific cytotoxic T-lymphocyte (CTL) response and high anti-OVA IgG, providing mice with superior protection against tumors. Next, this strategy is exploited to develop vaccines against infection by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is the main target for neutralizing antibodies. The TCC Sia-Ace-Dex platform is preferentially used for designing an RBD-based vaccine. Strikingly, the synthetic TCC Sia-Ace-Dex-RBD-Rd elicited potent RBD-neutralizing antibodies against live SARS-CoV-2 infected Vero E6 cells. To develop a universal SARS-CoV-2 vaccine, the TCC Sia-Ace-Dex-N-Rd vaccine carrying SARS-CoV-2 nucleocapsid protein (N) is also prepared, which is highly conserved among SARS-CoV-2 and its variants of concern (VOCs), including Omicron (BA.1 to BA.5); this vaccine can trigger strong N-specific CTL responses against target cells infected with SARS-CoV-2 and its VOCs.

A predictive mechanistic model of drug release from surface eroding polymeric nanoparticles

Effective drug delivery requires ample dosing at the target tissue while minimizing negative side effects. Drug delivery vehicles such as polymeric nanoparticles (NPs) are often employed to accomplish this challenge. In this work, drug release of numerous drugs from surface eroding polymeric NPs was evaluated in vitro in physiologically relevant pH 5 and neutral buffers. NPs were loaded with paclitaxel, rapamycin, resiquimod, or doxorubicin and made from an FDA approved polyanhydride or from acetalated dextran (Ace-DEX), which has tunable degradation rates based on cyclic acetal coverage (CAC). By varying encapsulate, pH condition, and polymer, a range of distinct drug release profiles were achieved. To model the obtained drug release curves, a mechanistic mathematical model was constructed based on drug diffusion and polymer degradation. The resulting diffusion-erosion model accurately described drug release from the variety of surface eroding NPs. For drug release from varied CAC Ace-DEX NPs, the goodness of fit of the developed diffusion-erosion model was compared to several conventional drug release models. The diffusion-erosion model maintained optimal fit compared to conventional models across a range of conditions. Machine learning was then employed to estimate effective diffusion coefficients for the diffusion-erosion model, resulting in accurate prediction of in vitro release of dexamethasone and 3'3'-cyclic guanosine monophosphate-adenosine monophosphate from Ace-DEX NPs. This predictive modeling has potential to aid in the design of future Ace-DEX formulations where optimized drug release kinetics can lead to a desired therapeutic effect.

Metal-Organic Coordination Polymer for Delivery of a Subunit Broadly Acting Influenza Vaccine

A zinc-carnosine (ZnCar) metal-organic coordination polymer was fabricated in biologically relevant N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) buffer for use as a vaccine platform. In vitro, ZnCar exhibited significantly less cytotoxicity than a well-established zeolitic imidazolate framework (ZIF-8). Adsorption of CpG on the ZnCar surface resulted in enhanced innate immune activation compared to soluble CpG. The model antigen ovalbumin (OVA) was encapsulated in ZnCar and exhibited acid-sensitive release in vitro. When injected intramuscularly on days 0 and 21 in C57BL/6 mice, OVA-specific serum total IgG and IgG1 were significantly greater in all groups with ZnCar and antigen compared to soluble controls. Th1-skewed IgG2c antibodies were significantly greater in OVA and CpG groups delivered with ZnCar for all time points, regardless of whether the antigen and adjuvant were co-formulated in one material or co-delivered in separate materials. When broadly acting Computationally Optimized Broadly Reactive Antigen (COBRA) P1 influenza hemagglutinin (HA) was ligated to ZnCar via its His-tag, significantly greater antibody levels were observed at all time points compared to soluble antigen and CpG. ZnCar-formulated antigen elicited increased peptide presentation to B3Z T cells in vitro and production of IL-2 after ex vivo antigen recall of splenocytes isolated from vaccinated mice. Overall, this work displays the formation of a zinc-carnosine metal-organic coordination polymer that can be applied as a platform for recombinant protein-based vaccines.

Multiplexed electrospray enables high throughput production of cGAMP microparticles to serve as an adjuvant for a broadly acting influenza vaccine

Subunit vaccines employing designer antigens such as Computationally Optimized Broadly Reactive Antigen (COBRA) hemagglutinin (HA) hold the potential to direct the immune response toward more effective and broadly-neutralizing targets on the Influenza virus. However, subunit vaccines generally require coadministration with an adjuvant to elicit a robust immune response. One such adjuvant is the stimulator of interferon genes (STING) agonist cyclic dinucleotide 3'3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP). We have shown that encapsulation of cGAMP in acetalated dextran (Ace-DEX) microparticles through electrospray results in significantly greater biological activity. Electrospray is a continuous manufacturing process which achieves excellent encapsulation efficiency. However, the throughput of electrospray with a single spray head is limited. Here we report the development of a multiplexed electrospray apparatus with an order of magnitude greater throughput than a single-head apparatus. Physicochemical characterization and evaluation of adjuvant activity in vitro and in vivo indicated that microparticles produced with the higher throughput process are equally suited for use as a potent vaccine adjuvant to induce a balanced immune response to COBRA HA antigens.

Flower-like mesoporous silica nanoparticles as an antigen delivery platform to promote systemic immune response

Virus-like particles (VLPs), a kind of superior subunit vaccine, are assembled from the viral structural proteins with similar capsids to viruses. However, the efficiency of cell uptake is not satisfactory. We prepared flower-like mesoporous silica nanoparticles (SiNPs) with large pore channels and interior cavities to solve the problem. The highly loaded VLPs-SiNPs composites not only enhanced the stability of VLPs, but also delivered antigen to cells and improved the cellular uptake efficiency. Compared with naked VLPs, mice intramuscularly immunized with the VLPs-SiNPs composite induced higher specific antibodies, greater lymphocyte activation and higher level of cytokine secretion. Moreover, the VLPs-SiNPs composite as vaccine also promoted mucosal immune response through intranasal immune pathway. Therefore, the VLPs-SiNPs enable to induce strong cellular, humoral, and slight mucosal immune response through different immunization routes. These results are potentially useful for vaccine formulations and may provide further reference for vaccine design and delivery systems.

STING agonist-containing microparticles improve seasonal influenza vaccine efficacy and durability in ferrets over standard adjuvant

The current pandemic highlights the need for effective vaccines against respiratory viruses. An ideal vaccine should induce robust and long-lasting responses with high manufacturing scalability. We use an adjuvant comprised of a Stimulator of Interferon Genes (STING) agonist incorporated in a scalable microparticle platform to achieve durable protection against the influenza virus. This formulation overcomes the challenges presented by the cytosolic localization of STING and the hydrophilicity of its agonists. We evaluated a monoaxial formulation of polymeric acetalated dextran microparticles (MPs) to deliver the STING agonist cyclic GMP-AMP (cGAMP) which achieved >10× dose-sparing effects compared to other published work. Efficacy was evaluated in ferrets, a larger animal model of choice for influenza vaccines. cGAMP MPs with recombinant hemagglutinin reduced viral shedding and improved vaccine outcomes compared to a seasonal influenza vaccine. Importantly, sustained protection against a lethal influenza infection was detected a year after a single dose of the vaccine-adjuvant.

A Toll-like Receptor-Activating, Self-Adjuvant Glycan Nanocarrier

The global pandemic of COVID-19 highlights the importance of vaccination, which remains the most efficient measure against many diseases. Despite the progress in vaccine design, concerns with suboptimal antigen immunogenicity and delivery efficiency prevail. Self-adjuvant carriers–vehicles that can simultaneously deliver antigens and act as adjuvants–may improve efficacies in these aspects. Here, we developed a self-adjuvant carrier based on an acetyl glucomannan (acGM), which can activate toll-like receptor 2 (TLR2) and encapsulate the model antigen ovalbumin (OVA) via a double-emulsion process. In vitro tests showed that these OVA@acGM-8k nanoparticles (NPs) enhanced cellular uptake and activated TLR2 on the surface of dendritic cells (DCs), with increased expression of co-stimulatory molecules (e.g. CD80 and CD86) and pro-inflammatory cytokines (e.g. TNF-α and IL12p70). In vivo experiments in mice demonstrated that OVA@acGM-8k NPs accumulated in the lymph nodes and promoted DCs’ maturation. The immunization also boosted the humoral and cellular immune responses. Our findings suggest that this self-adjuvant polysaccharide carrier could be a promising approach for vaccine development.

Cyclodextrin-Derived ROS-Generating Nanomedicine with pH-Modulated Degradability to Enhance Tumor Ferroptosis Therapy and Chemotherapy

Nowadays, destruction of redox homeostasis to induce cancer cell death is an emerging anti-cancer strategy. Here, the authors utilized pH-sensitive acetalated β-cyclodextrin (Ac-β-CD) to efficiently deliver dihydroartemisinin (DHA) for tumor ferroptosis therapy and chemodynamic therapy in a synergistic manner. The Ac-β-CD-DHA based nanoparticles are coated by an iron-containing polyphenol network. In response to the tumor microenvironment, Fe²⁺ /Fe³⁺ can consume glutathione (GSH) and trigger the Fenton reaction in the presence of hydrogen peroxide (H₂ O₂ ), leading to the generation of lethal reactive oxygen species (ROS). Meanwhile, the OO bridge bonds of DHA are also disintegrated to enable ferroptosis of cancer cells. Their results demonstrate that these nanoparticles acted as a ROS generator to break the redox balance of cancer cells, showing an effective anticancer efficacy, which is different from traditional approaches.

Hydrogel Transformed from Nanoparticles for Prevention of Tissue Injury and Treatment of Inflammatory Diseases

Functional hydrogels responsive to physiological and pathological signals have extensive biomedical applications owing to their multiple advanced attributes. Herein, engineering of functional hydrogels is reported via transformable nanoparticles in response to the physiologically and pathologically acidic microenvironment. These nanoparticles are assembled by a multivalent hydrophobic, pH-responsive cyclodextrin host material and a multivalent hydrophilic guest macromolecule. Driven by protons, the pH-responsive host-guest nanoparticles can be transformed into hydrogel, resulting from proton-triggered hydrolysis of the host material, generation of a hydrophilic multivalent host compound, and simultaneously enhanced inclusion interactions between host and guest molecules. By in situ forming a hydrogel barrier, the orally delivered transformable nanoparticles protect mice from ethanol- or drug-induced gastric injury. In addition, this type of nanoparticles can serve as responsive and transformable nanovehicles for therapeutic agents to achieve triggerable and sustained drug delivery, thereby effectively treating typical inflammatory diseases, including periodontitis and arthritis in rats. With combined advantages of nanoparticles and hydrogels, together with their good in vivo safety, the engineered transformable nanoparticles hold great promise in tissue injury protection and site-specific/local delivery of molecular and cellular therapeutic agents.

Lung cell membrane-coated nanoparticles capable of enhanced internalization and translocation in pulmonary epithelial cells

Cell membrane-coated nanoparticles (CMCNP), which involve coating a core nanoparticle (NP) with cell membranes, have been gaining attention due to their ability to mimic the properties of the cells, allowing for enhanced delivery and efficacy of therapeutics. Two CMCNP systems comprised of an acetalated dextran-based NP core loaded with curcumin (CUR) coated with cell membranes derived from pulmonary epithelial cells were developed. The NP were approximately 200 nm and their surface charges varied based on their coating, where CMCNP systems exhibited negative surface charge like natural cell membranes. The NP were smooth, spherical, and homogeneous with distinct coatings on their cores. Minimal in vitro toxicity was observed for the NP and controlled release of CUR was observed. The CMCNP internalized into and translocated across an in vitro pulmonary epithelial monolayer significantly more than the control NP. Blocking endocytosis pathways reduced the transcytosis of NP, indicating a relationship between endocytosis and transcytosis. These newly developed CMCNP have the potential to be used in pulmonary drug delivery applications to potentially enhance NP internalization and transport into and across the pulmonary epithelium.

Polysaccharide-based formulations as potential carriers for pulmonary delivery - A review of their properties and fates

Polysaccharides can be elite carriers for therapeutic molecules due to their versatility and low probability to trigger toxicity and immunogenic responses. Local and systemic therapies can be achieved through particle pulmonary delivery, a promising non-invasive alternative. Successful pulmonary delivery requires particles with appropriate flowability to reach alveoli and avoid premature clearance mechanisms. Polysaccharides can form micro-, nano-in-micro-, and large porous particles, aerogels, and hydrogels. Herein, the characteristics of polysaccharides used in drug formulations for pulmonary delivery are reviewed, providing insights into structure-function relationships. Charged polysaccharides can confer mucoadhesion, whereas the ability for specific sugar recognition may confer targeting capacity for alveolar macrophages. The method of particle preparation must be chosen considering the properties of the components and the delivery device to be utilized. The fate of polysaccharide-based carriers is dependent on enzyme-triggered hydrolytic and/or oxidative mechanisms, allowing their complete degradation and elimination through urine or reutilization of released monosaccharides.

Anti-MicroRNA-21 Oligonucleotide Loaded Spermine-Modified Acetalated Dextran Nanoparticles for B1 Receptor-Targeted Gene Therapy and Antiangiogenesis Therapy

The use of nanoparticles (NPs) to deliver small inhibiting microRNAs (miRNAs) has shown great promise for treating cancer. However, constructing a miRNA delivery system that targets brain cancers, such as glioblastoma multiforme (GBM), remains technically challenging due to the existence of the blood-tumor barrier (BTB). In this work, a novel targeted antisense miRNA-21 oligonucleotide (ATMO-21) delivery system is developed for GBM treatment. Bradykinin ligand agonist-decorated spermine-modified acetalated dextran NPs (SpAcDex NPs) could temporarily open the BTB by activating G-protein-coupled receptors that are expressed in tumor blood vessels and tumor cells, which increase transportation to and accumulation in tumor sites. ATMO-21 achieves high loading in the SpAcDex NPs (over 90%) and undergoes gradual controlled release with the degradation of the NPs in acidic lysosomal compartments. This allows for cell apoptosis and inhibition of the expression of vascular endothelial growth factor by downregulating hypoxia-inducible factor (HIF-1α) protein. An in vivo orthotopic U87MG glioma model confirms that the released ATMO-21 shows significant therapeutic efficacy in inhibiting tumor growth and angiogenesis, demonstrating that agonist-modified SpAcDex NPs represent a promising strategy for GBM treatment combining targeted gene therapy and antiangiogenic therapy.

Nano/microparticle Formulations for Universal Influenza Vaccines

Influenza affects millions of people worldwide and can result in severe sickness and even death. The best method of prevention is vaccination; however, the seasonal influenza vaccine often suffers from low efficacy and requires yearly vaccination due to changes in strain and viral mutations. More conserved universal influenza antigens like M2 ectodomain (M2e) and the stalk region of hemagglutinin (HA stalk) have been used clinically but often suffer from low antigenicity. To increase antigenicity, universal antigens have been formulated using nano/microparticles as vaccine carriers against influenza. Utilizing polymers, liposomes, metal, and protein-based particles, indicators of immunity and protection in mouse, pig, ferrets, and chicken models of influenza have been shown. In this review, seasonal and universal influenza vaccine formulations comprised of these materials including their physiochemical properties, fabrication, characterization, and biologic responses in vivo are highlighted. The review is concluded with future perspectives for nano/microparticles as carrier systems and other considerations within the universal influenza vaccine delivery landscape.

Ethoxy acetalated dextran-based nanocarriers accomplish efficient inhibition of leukotriene formation by a novel FLAP antagonist in human leukocytes and blood

Leukotrienes are pro-inflammatory lipid mediators generated by 5-lipoxygenase aided by the 5-lipoxygenase-activating protein (FLAP). BRP-201, a novel benzimidazole-based FLAP antagonist, inhibits leukotriene biosynthesis in isolated leukocytes. However, like other FLAP antagonists, BRP-201 fails to effectively suppress leukotriene formation in blood, which limits its therapeutic value. Here, we describe the encapsulation of BRP-201 into poly(lactide-co-glycolide) (PLGA) and ethoxy acetalated dextran (Ace-DEX) nanoparticles (NPs), aiming to overcome these detrimental pharmacokinetic limitations and to enhance the bioactivity of BRP-201. NPs loaded with BRP-201 were produced via nanoprecipitation and the physicochemical properties of the NPs were analyzed in-depth using dynamic light scattering (size, dispersity, degradation), electrophoretic light scattering (effective charge), NP tracking analysis (size, dispersity), scanning electron microscopy (size and morphology), UV-VIS spectroscopy (drug loading), an analytical ultracentrifuge (drug release, degradation kinetics), and Raman spectroscopy (chemical attributes). Biological assays were performed to study cytotoxicity, cellular uptake, and efficiency of BRP-201-loaded NPs versus free BRP-201 to suppress leukotriene formation in primary human leukocytes and whole blood. Both PLGA- and Ace-DEX-based NPs were significantly more efficient to inhibit leukotriene formation in neutrophils versus free drug. Whole blood experiments revealed that encapsulation of BRP-201 into Ace-DEX NPs strongly increases its potency, especially upon pro-longed (≥ 5 h) incubations and upon lipopolysaccharide-challenge of blood. Finally, intravenous injection of BRP-201-loaded NPs significantly suppressed leukotriene levels in blood of mice in vivo. These results reveal the feasibility of our pharmacological approach using a novel FLAP antagonist encapsulated into Ace-DEX-based NPs with improved efficiency in blood to suppress leukotriene biosynthesis.

Chemically Tuning the Antigen Release Kinetics from Spherical Nucleic Acids Maximizes Immune Stimulation

Cancer vaccine structure is emerging as an important design factor that offers tunable parameters to enhance the targeted immune response. We report the impact of altering the antigen release rate from spherical nucleic acid (SNA) vaccines-nanoparticles with a liposomal core and surface-anchored adjuvant DNA-on immune stimulation. Peptide antigens were incorporated into SNAs using either a nonreducible linker or one of a series of reduction-triggered traceless linkers that release the native peptide at rates controlled by their substitution pattern. Compared with a nonreducible linkage, the traceless attachment of antigens resulted in lower EC50 of T cell proliferation in vitro and greater dendritic cell (DC) activation and higher T cell killing ability in vivo. Traceless linker fragmentation rates affected the rates of antigen presentation by DCs and were correlated with the in vitro potencies of SNAs. Antigen release was correlated with the ex vivo -log(EC50), and more rapid antigen release resulted in an order of magnitude improvement in the EC50 and earlier and greater antigen presentation over the same time-period. In vivo, increasing the rate of antigen release resulted in higher T cell activation and target killing. These findings provide fundamental insights into and underscore the importance of vaccine structure.

Considerations for the delivery of STING ligands in cancer immunotherapy

Several studies have shown the importance of the cGAS-STING pathway in antigen-presenting cells for anti-cancer immunity. Cyclic GMP-AMP (cGAMP) - STING ligand is a negatively charged dinucleotide prone to degradation by hydrolases. Once administered in its soluble form, high doses are needed which in turn may cause side effects such as T cell apoptosis. Moreover, due to its negative charge, transfection of cGAMP into negatively-charged membrane cells is hampered. In order to achieve successful transfection and protection from enzymatic degradation there is a need for a suitable carrier for cGAMP. In this review, we therefore describe currently reported carriers for cGAMP, and correlate their characteristics to the effect they cause. To achieve targeted delivery to the tumor microenvironment, the route of administration and physicochemical parameters of the particles (containing a carrier and cGAMP) such as size and charge need to be determined. Therefore, the choice of the particle formulation and its impact on the preclinical outcome will be discussed.

Screening and Quantification of the Encapsulation of Dyes in Supramolecular Particles

The encapsulation of therapeutic agents, such as drugs and vaccines, into colloidal particles offers an attractive strategy to enhance their efficacy. Previously, we reported the development of guanosine-based supramolecular colloidal particles suitable for encapsulating a broad array of guests ranging from small molecule drugs, like doxorubicin, to proteins, like GFP. Many biomedical applications of such particles require a precise determination of the amount of encapsulated therapeutic agents. Despite many studies describing the development of particle-based delivery systems, a general method for the precise and quick quantification of the encapsulated payload is still lacking. Here, we report a method based on flow cytometry measurements for complexes made from guanosine-based particles and a variety of commercially available fluorescent dyes. This method allows us to determine the apparent affinities of such dyes for two variants of these particles, which in turn provides insightful structure-affinity relationships. In contrast to the current methods, such as those that rely on fluorescence microscopy based on measurements of absorption/fluorescence of dissolved particles or on the supernatant of the solution, the reported method is suitable for high-throughput screening and more reproducible results. The protocol described here should be applicable to a wide variety of colloidal particles being developed around the world. Our group is currently expanding the scope to quantify the encapsulation of other molecules of biomedical interest, such as proteins and nucleic acids.

Modular ketal-linked prodrugs and biomaterials enabled by organocatalytic transisopropenylation of alcohols

Isopropenyl ethers are critical intermediates for accessing medicinally valuable ketal-based prodrugs and biomaterials, but traditional approaches for the synthesis of isopropenyl ethers suffer from poor functional group compatibility and harsh reaction conditions. Here, we develop an organocatalytic transisopropenylation approach to solve these challenges, enabling the synthesis of isopropenyl ethers from various hydroxyl-group-containing small-molecule drugs, polymers, and functional building blocks. The method provides a straightforward and versatile synthesis of isopropenyl ethers, features excellent tolerance of diverse functional groups, applies to a wide range of substrates, and allows scalable synthesis. The development of this organocatalytic transisopropenylation approach enables access to modular preparation of various acid-sensitive ketal-linked prodrugs and functionalized ketalated biomaterials. We expect our syntheses and transformations of isopropenyl ethers will find utility in several diverse fields, including medicinal chemistry, drug delivery, and biomaterials.

Isopropenyl ethers (IPPEs) are essential intermediates for obtaining ketal-based prodrugs and biomaterials, but traditional approaches for their synthesis are limited by poor functional group compatibility and harsh reaction conditions. Here, the authors report an organocatalytic transisopropenylation approach for IPPE synthesis in mild reaction conditions and with wide range of substrates, and use it to prepare acid-sensitive ketal-linked prodrugs and biomaterials.

Hydrolysis-Driven Viscoelastic Transition in Triblock Copolyether Hydrogels with Acetal Pendants

While the hydrolytic cleavage of ester groups is widely exploited in degradable hydrogels, the scission in the midst of chain backbones can bring dramatic changes in the mechanical properties of the hydrogels. However, the predictive design of the mechanical profile of the hydrogels is a complex task, mainly due to the randomness of the location of chain scission. To overcome this challenge, we herein present degradable ABA triblock poly(ethylene oxide)-based hydrogels containing an A-block bearing acetal pendant, which provides systematically tunable mechano-temporal properties of the hydrogels. In particular, hydrophobic endocyclic tetrahydropyranyl or exocyclic 1-(cyclohexyloxy)ethyl acetal pendants are gradually cleaved by acidic hydrolysis, leading to the gel-to-sol transition at room temperature. Most importantly, a series of dynamic mechanical analyses coupled with ex situ NMR spectroscopy revealed that the hydrolysis rate can be orthogonally and precisely tuned by changing the chemical structure and hydrophobicity of acetal pendants. This study provides a platform for the development of versatile degradable hydrogels in a highly controllable manner.

Stimuli-responsive nanobubbles for biomedical applications

Stimuli-responsive nanobubbles have received increased attention for their application in spatial and temporal resolution of diagnostic techniques and therapies, particularly in multiple imaging methods, and they thus have significant potential for applications in the field of biomedicine. This review presents an overview of the recent advances in the development of stimuli-responsive nanobubbles and their novel applications. Properties of both internal- and external-stimuli responsive nanobubbles are highlighted and discussed considering the potential features required for biomedical applications. Furthermore, the methods used for synthesis and characterization of nanobubbles are outlined. Finally, novel biomedical applications are proposed alongside the advantages and shortcomings inherent to stimuli-responsive nanobubbles.

Geminal Diheteroatomic Motifs: Some Applications of Acetals, Ketals, and Their Sulfur and Nitrogen Homologues in Medicinal Chemistry and Drug Design

Acetals and ketals and their nitrogen and sulfur homologues are often considered to be unconventional and potentially problematic scaffolding elements or pharmacophores for the design of orally bioavailable drugs. This opinion is largely a function of the perception that such motifs might be chemically unstable under the acidic conditions of the stomach and upper gastrointestinal tract. However, even simple acetals and ketals, including acyclic molecules, can be sufficiently robust under acidic conditions to be fashioned into orally bioavailable drugs, and these structural elements are embedded in many effective therapeutic agents. The chemical stability of molecules incorporating geminal diheteroatomic motifs can be modulated by physicochemical design principles that include the judicious deployment of proximal electron-withdrawing substituents and conformational restriction. In this Perspective, we exemplify geminal diheteroatomic motifs that have been utilized in the discovery of orally bioavailable drugs or drug candidates against the backdrop of understanding their potential for chemical lability.

Emerging nanomaterials for cancer immunotherapy

Immunotherapy is a unique approach to treat cancer that targets tumours besides triggering the immune cells. It attempts to harness the supremacy and specificity of immune cells for the regression of malignancy. The key strategy of immunotherapy is that it boosts the natural defence and manipulates the immune system at both cellular and molecular levels. Long-lasting anti-tumour response, reduced metastasis, and recurrence can be achieved with immunotherapy than conventional treatments. For example, targeting cytotoxic T-lymphocyte antigen-4 (CTLA4) by monoclonal antibody is reported as an effective strategy against cancer progression in vivo and chimeric antigen receptor (CAR) modified T-cells are known to express a stronger anti-tumour activity. CTLA4 and CAR are, therefore, beneficial in cancer immunotherapy; however, in clinical settings, both are expensive and cause adverse side effects. Nanomaterials have augmented advantages in cancer immunotherapy, besides their utility in effective delivery and diagnostics. In particular, materials based on lipids, polymers, and metals have been sought-after for delivery technologies. Moreover, the surface of nanomaterials can be engineered using ligands, antigens, and antibodies to target immune cells. In this sense, checkpoint inhibitors, cytokines, agonistic antibodies, surface receptors, and engineered T-cells are promising to regulate the immune system against tumours. Therefore, emerging nanomaterials that can be used for the treatment of cancer is the prime focus of this review. The correlation of mode of administration and biodistribution of various nanomaterials is reviewed here. Besides, the acute and chronic side effects and outcome of clinical trials in the context of cancer immunotherapy are discussed.

Collagenase-loaded pH-sensitive nanocarriers efficiently remodeled tumor stroma matrixes and improved the enrichment of nanomedicines

The dense extracellular matrix (ECM) in tumor tissue severely hinders the penetration and enrichment of antitumor nanomedicines, which could significantly affect their efficiency. In this study, we used pH-sensitive nanocarriers loaded with collagenase (Col) to remold the tumor microenvironment (TME). Furthermore, we combined the collagenase delivery system with a nanomedicine to improve its penetration and enrichment in the tumor, thereby improving efficacy. We synthesized acetalated dextran (Ace-DEX) with an ideal pH-sensitivity as the carrier material of collagenase. Under mild preparation conditions, collagenase was loaded into Ace-DEX nanoparticles (NPs) with a high loading capacity (>4%) and remained highly active (>90%). Col-carrying NPs (Col-NPs) significantly reduced the tumor collagen content by 15.1%. Pretreatment with Col-NPs increased the accumulation of doxorubicin (DOX)-loaded liposome (DOX-Lipo) in the tumor by 2.8-fold. There were no safety concerns as the Col-NP showed no significant toxicity and reduced Col-induced damage to healthy tissues. Additionally, the number of circulating tumor cells remained unchanged after Col-NP treatment, suggesting no increased risk of tumor metastasis. Because the Col-NP acts essentially independent of the subsequent treatment, it has considerable potential for enhancing many existing delivery systems and drugs for cancer treatment. It may also be used for treating other collagen-related diseases.

Acetalated dextran based nano- and microparticles: synthesis, fabrication, and therapeutic applications

Acetalated dextran (Ac-DEX) is a pH-responsive dextran derivative polymer. Prepared by a simple acetalation reaction, Ac-DEX has tunable acid-triggered release profile. Despite its relatively short research history, Ac-DEX has shown great potential in various therapeutic applications. Furthermore, the recent functionalization of Ac-DEX makes versatile derivatives with additional properties. Herein, we summarize the cutting-edge development of Ac-DEX and related polymers. Specifically, we focus on the chemical synthesis, nano- and micro-particle fabrication techniques, the controlled-release mechanisms, and the rational design Ac-DEX-based of drug delivery systems in various biomedical applications. Finally, we briefly discuss the challenges and future perspectives in the field.

Engineering Carbohydrate-Based Particles for Biomedical Applications: Strategies to Construct and Modify

Carbohydrate-based micro/nanoparticles have gained significant attention for various biomedical applications such as targeted/triggered/controlled drug delivery, bioimaging, biosensing, etc., because of their prominent characteristics like biocompatibility, biodegradability, hydrophilicity, and nontoxicity as well as nonimmunogenicity. Most importantly, the ability of the nanoparticles to recognize specific cell sites by targeting cell surface receptors makes them a promising candidate for designing a targeted drug delivery system. These particles may either comprise polysaccharides/glycopolymers or be integrated with various polymeric/inorganic nanoparticles such as gold, silver, silica, iron, etc., to reduce the toxicity of the inorganic nanoparticles and thus facilitate their cellular insertion. Various synthetic methods have been developed to fabricate carbohydrate-based or carbohydrate-conjugated inorganic/polymeric nanoparticles. In this review, we have highlighted the recently developed synthetic approaches to afford carbohydrate-based particles along with their significance in various biomedical applications.

A versatile photothermal vaccine based on acid-responsive glyco-nanoplatform for synergistic therapy of cancer

The race is on for therapeutic agents that stop cancer. An effective vaccine offers a safe and promising approach for cancer immunotherapy. However, substantial barriers to immunotherapy in cancer vaccines include the low immunogenicity of cancer antigens and the immunosuppression commonly present in solid tumors, resulting in significant challenges for developing a clinically effective cancer vaccine. Here, the state of the art of synergistic therapy, which includes the photothermal effect combined with immunotherapy, was investigated to target tumors. For the first time, indocyanine green (ICG, referred to as I), imiquimod (R837, referred to as R) and a foreign cytotoxic T lymphocyte antigen peptide (CTL-Ap, referred to as Ap) with the sequence of SIINFEKL from ovalbumin (OVA) were encapsulated by acetalated dextran (AcDEX) to form nanoparticles (NPs) averaging 92 nm in diameter as an immunogen. Administration of the resulting multifunctional vaccine I-R-Ap-AcDEX NPs enhanced antitumor cytotoxic T lymphocyte (CTL) immunotherapy. On the one hand, subcutaneous immunization of the NPs allows foreign Ap to enter the major histocompatibility complex class I (MHC-I) cross-presentation pathway of antigen-presenting cells, thereby presenting Ap and eliciting high levels of Ap-specific CTLs. On the other hand, intratumor/intravenous injections of the NPs allow foreign Ap to enter tumor cells and present Ap through the MHC-I cross-presentation pathway. Ap-specific CTLs can kill Ap-presented tumor cells. Furthermore, the NPs generated near-infrared laser triggered the photothermal killing of tumor cells. To our knowledge, this is the first report of AcDEX NPs in antitumor photothermal therapy. Strikingly, systemic administration of the I-R-Ap-AcDEX NPs combined with near-infrared laser irradiation allowed for complete protection to mice from the tumors when applied to two non-OVA tumor models. This quite impressive result displays the great promise of synergistic therapy by the vaccine I-R-Ap-AcDEX NPs, an approach that harnesses the photothermal effect to boost antitumor immunotherapy.

Considerations for Size, Surface Charge, Polymer Degradation, Co-Delivery, and Manufacturability in the Development of Polymeric Particle Vaccines for Infectious Diseases

Vaccines have advanced human health for centuries. To improve upon the efficacy of subunit vaccines they have been formulated into nano/microparticles for infectious diseases. Much progress in the field of polymeric particles for vaccine formulation has been made since the push for a tetanus vaccine in the 1990s. Modulation of particle properties such as size, surface charge, degradation rate, and the co-delivery of antigen and adjuvant has been used. This review focuses on advances in the understanding of how these properties influence immune responses to injectable polymeric particle vaccines. Consideration is also given to how endotoxin, route of administration, and other factors influence conclusions that can be made. Current manufacturing techniques involved in preserving vaccine efficacy and scale-up are discussed, as well as those for progressing polymeric particle vaccines toward commercialization. Consideration of all these factors should aid the continued development of efficacious and marketable polymeric particle vaccines.

Natural and synthetic carbohydrate-based vaccine adjuvants and their mechanisms of action

Modern subunit vaccines based on homogeneous antigens offer more precise targeting and improved safety compared with traditional whole-pathogen vaccines. However, they are also less immunogenic and require an adjuvant to increase the immunogenicity of the antigen and potentiate the immune response. Unfortunately, few adjuvants have sufficient potency and low enough toxicity for clinical use, highlighting the urgent need for new, potent and safe adjuvants. Notably, a number of natural and synthetic carbohydrate structures have been used as adjuvants in clinical trials, and two have recently been approved in human vaccines. However, naturally derived carbohydrate adjuvants are heterogeneous, difficult to obtain and, in some cases, unstable. In addition, their molecular mechanisms of action are generally not fully understood, partly owing to the lack of tools to elucidate their immune-potentiating effects, thus hampering the rational development of optimized adjuvants. To address these challenges, modification of the natural product structure using synthetic chemistry emerges as an attractive approach to develop well-defined, improved carbohydrate-containing adjuvants and chemical probes for mechanistic investigation. This Review describes selected examples of natural and synthetic carbohydrate-based adjuvants and their application in synthetic self-adjuvanting vaccines, while also discussing current understanding of their molecular mechanisms of action.