6 research outputs found
Acetalated Dextran: A Tunable and Acid-Labile Biopolymer with Facile Synthesis and a Range of Applications
Acetalated dextran
(Ac-DEX) is a tunable acid-labile biopolymer
with facile synthesis, aptly designed for the formulation of microparticles
for vaccines and immune modulation. Tunability of degradation is achieved
based on the kinetics of reaction and the molecular weight of the
parent dextran polymer. This tunability translated to differential
rates of activation of CD8+ T cells in an <i>in vitro</i> ovalbumin model and illustrated that acid-labile polymer can activate
CD8+ T cells at an increased rate compared to acid-insensitive polymers.
In addition, Ac-DEX has been used to encapsulate small molecules,
deliver nucleotides, transport inorganic molecules, formulate immune
modulating therapies and vaccines, and trigger pH responsive constructs
for therapy. Here we highlight the properties and results of Ac-DEX
nano-/microparticles as well as the use of the polymer in other constructs
and chemistries
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
Synthesis, Optimization, and Characterization of Camptothecin-Loaded Acetalated Dextran Porous Microparticles for Pulmonary Delivery
We propose the use of a new biopolymer, acetalated dextran
(Ac-DEX),
to synthesize porous microparticles for pulmonary drug delivery. Ac-DEX
is derived from the polysaccharide dextran and, unlike polyesters,
has tunable degradation from days to months and pH neutral degradation
products. Ac-DEX microparticles fabricated through emulsion techniques
were optimized using a variety of postprocessing techniques to enhance
the respirable fraction for pulmonary delivery. Tangential flow filtration
resulted in a maximum 37% respirable fraction for Ac-DEX porous microparticles,
compared to a 10% respirable fraction for polyÂ(lactic-co-glycolic
acid) (PLGA) porous microparticles. Ac-DEX microparticles were of
an optimum diameter to minimize macrophage clearance but had a low
enough theoretical density for deep lung penetration. Transepithelial
electrical resistance (TEER) measurements showed that the particles
did not impinge on a monolayer of lung epithelial cells in either
air or liquid conditions. Also, the release of the chemotherapeutic
camptothecin was shown to be tunable depending on Ac-DEX degradation
time and molecular weight, and drug release was shown to be bioactive
over a range of concentrations. Our results indicate that both release
kinetics and fraction of burst release of drug from Ac-DEX porous
microparticles can be tuned by simply changing the Ac-DEX polymer
properties, affording a large range of formulation options for drug
delivery to the pulmonary cavity. Overall, Ac-DEX porous microparticles
show promise as an emerging carrier for pulmonary delivery of drugs
to the alveolar region of the lung, particularly for the treatment
of lung diseases
Electrospray Encapsulation of Toll-Like Receptor Agonist Resiquimod in Polymer Microparticles for the Treatment of Visceral Leishmaniasis
Leishmaniasis is a disease caused by the intracellular
protozoan, <i>Leishmania</i>. A current treatment for cutaneous
leishmaniasis
involves the delivery of imidazoquinolines via a topical cream. However,
there are no parenteral formulations of imidazoquinolines for the
most deadly version of the disease, visceral leishmaniasis. This work
investigates the use of electrospray to encapsulate the imidazoquinoline
adjuvant resiquimod in acid sensitive microparticles composed of acetalated
dextran (Ac-DEX) or Ac-DEX/Tween blends. The particles were characterized
and tested both <i>in vitro</i> and <i>in vivo</i>. Solutions of Ac-DEX and resiquimod in ethanol were electrosprayed
to generate approximately 2 μm Ac-DEX particles containing resiquimod
with an encapsulation efficiency of 85%. To prevent particle aggregation,
blends of Ac-DEX with Tween 20 and Tween 80 were investigated. Tween
80 was then blended with the Ac-DEX at ∼10% (w/w) of total
polymer and particles containing resiquimod were formed via electrospray
with encapsulation efficiencies between 40% and 60%. <i>In vitro</i> release profiles of resiquimod from Ac-DEX/Tween 80 particles exhibited
the acid-sensitive nature of Ac-DEX, with 100% drug release after
8 h at pH 5 (phagosomal pH) and after 48 h at pH 7.4 (physiological
pH). Treatment with Ac-DEX/Tween 80 particles elicited significantly
greater immune response in RAW macrophages over free drug. When injected
intravenously into mice inoculated with <i>Leishmania</i>, parasite load reduced significantly in the bone marrow compared
to blank particles and phosphate-buffered saline controls. Overall,
electrospray appears to offer an elegant, scalable way to encapsulate
adjuvant into an acid sensitive delivery vehicle for use in treating
visceral leishmaniasis
Efficient Delivery of the Toll-like Receptor Agonists Polyinosinic:Polycytidylic Acid and CpG to Macrophages by Acetalated Dextran Microparticles
To
enhance the immune activity of vaccine adjuvants polyinosinic:polycytidylic
acid (poly I:C) and CpG acetalated dextran (Ac-DEX) microparticles
can be used. Ac-DEX is a biodegradable and water-insoluble polymer
that degrades significantly faster at pH 5.0 (phagosomal pH) than
at pH 7.4 and has tunable degradation rates that can range from hours
to months. This is an ideal characteristic for delivery of an antigen
and adjuvant within the lysosomal compartment of a phagocytic cell.
We evaluated poly I:C and CpG encapsulated in Ac-DEX microparticles
using RAW macrophages as a model antigen-presenting cell. These cells
were cultured with poly I:C or CpG in their free form, encapsulated
in a fast degrading Ac-DEX, in slow degrading Ac-DEX, or in the Food
and Drug Administration-approved polymer polyÂ(lactic-<i>co</i>-glycolic acid) (PLGA). Ac-DEX had higher encapsulation efficiencies
for both poly I:C and CpG than PLGA. Furthermore, poly I:C or CpG
encapsulated in Ac-DEX also showed, in general, a significantly stronger
immunostimulatory response than PLGA and unencapsulated CpG or poly
I:C, which was indicated by a higher rate of nitric oxide release
and increased levels of cytokines such as TNF-α, IL-6, IL-10,
and IFN-γ. Overall, we have illustrated a method for enhancing
the delivery of these vaccine adjuvants to further enhance the development
of Ac-DEX vaccine formulations
Electrospun Acetalated Dextran Scaffolds for Temporal Release of Therapeutics
Electrospun acetalated dextran (Ac-DEX)
scaffolds were fabricated
to encapsulate resiquimod, an immunomodulatory toll-like-receptor
(TLR) agonist. Ac-DEX has been used to fabricate scaffolds for sustained
and temporal delivery of therapeutics because it has tunable degradation
rates that are dependent on its synthesis reaction time or the molecular
weight of dextran. Additionally, as opposed to commonly electrospun
polyesters that shift the local pH upon degradation, the degradation
products of Ac-DEX are pH-neutral: dextran, an alcohol, and the metabolic
byproduct acetone. Formulations of Ac-DEX with two different degradation
rates were used in this study. The effects of electrospinning conditions
on the scaffold size and morphology were examined as well as fibroblast
adhesion as imaged with fluorescence microcopy and scanning electron
microscopy. Macrophage (MΦ) viability further indicates that
the scaffolds are cytocompatible. Also, the controlled release profiles
of resiquimod from loaded scaffolds and nitric oxide (NO) production
by MΦ incubated with these scaffolds show the potential for
Ac-DEX scaffolds to be used to temporally and efficiently deliver
therapeutics. Overall, we present a novel scaffold that can have tunable
and unique drug release rates for tissue engineering, drug delivery,
immunomodulation, and wound healing applications