5 research outputs found
Traceless Release of Alcohols Using Thiol-Sensitive Oxanorbornadiene Linkers
A class of esterāamide
oxanorbornadiene (EA-OND) molecules
was developed to release alcohol cargos by succinimide formation upon
addition of a thiol reagent. The resulting ring-closed adducts undergo
further fragmentation by retro-DielsāAlder reaction to release
a furan moiety in a manner similar to oxanorbornadiene diesters. The
rates of each of these fragmentation pathways in the same medium were
found to be sensitive to the steric nature of the amide substituent.
Alcohol release was much faster in protic solvents than in aprotic
ones, suggesting that this system may be useful for rapid response
to thiols in biological environments. Accordingly, the attachment
and thiol-dependent release of cholesterol was characterized as an
example of the manipulation of a drug-like cargo
Degradable Conjugates from Oxanorbornadiene Reagents
Oxanorbornadienedicarboxylate (OND) reagents were explored
for
purposes of binding and releasing drugs from serum albumins as representative
macromolecular carriers. Being highly reactive Michael acceptors,
ONDs form adducts with thiols and amines, which then undergo retro-DielsāAlder
fragmentation. A study of more than 30 model adducts revealed a number
of modifications that can be used to influence adduct stability. For
the most reactive OND linkers, the labeling of the single available
bovine serum albumin (BSA) cysteine residue was complete within minutes
at a mid-micromolar concentration of reactants. While a selectivity
of greater than 1000-fold for thiol over amine was observed with model
amino acids, the labeling of protein amines with ONDs is fast enough
to be practical, as demonstrated by the reaction with thiol-depleted
BSA. The ONDāamine adducts were found to be up to 15 times
more stable than ONDāthiol adducts, and to be sensitive to
acid by virtue of a stereochemically dependent acceleration of cycloreversion.
The release rate of fluorescent cargo from serum albumins was tuned
by selecting the coupling partners: the available half-lives ranged
from 40 min to 7 days at 37 Ā°C. Such versatility of release profiles
from protein carriers, controlled by the nature of the OND linkage,
is a useful addition to the drug delivery toolbox
Albumin-Oxanorbornadiene Conjugates Formed <i>ex Vivo</i> for the Extended Circulation of Hydrophilic Cargo
Oxanorbornadiene dicarboxylate (OND)
reagents were explored for the purpose of binding and releasing chemical
cargos from endogenous circulating serum albumins. ONDs bearing gadolinium
chelates as model cargos exhibited variable conjugation efficiencies
with albumin in rat subjects that are consistent with the observed
reactivity of each linker and their observed stability toward serum
hydrolases <i>in vitro</i>. The terminal elimination rate
from circulation was dependent on the identity of the OND used, and
increased circulation time of gadolinium cargo was achieved for linkers
bearing electrophilic fragments designed to react with cysteine-34
of circulating serum albumin. This binding of and release from endogenous
albumin highlights the potential of OND linkers in the context of
optimizing the pharmacokinetic parameters of drugs or diagnostic agents
Modular Degradable Hydrogels Based on Thiol-Reactive Oxanorbornadiene Linkers
Oxanorbornadiene
dicarboxylate (OND) reagents are potent Michael
acceptors, the adducts of which undergo fragmentation by retro-DielsāAlder
reaction at rates that vary with the substitution pattern on the OND
moiety. Rapid conjugate addition between thiol-terminated tetravalent
PEG and multivalent ONDs yielded self-supporting hydrogels within
1 min at physiological temperature and pH. Erosion of representative
hydrogel formulations occurred with predictable and pH-independent
rates on the order of minutes to weeks. These materials could be made
non-degradable by epoxidation of the OND linkers without slowing gelation.
Hydrogels prepared with OND linkers of equal valence had comparable
physical properties, as determined by equilibrium swelling behavior,
indicating similar internal network structure. Diffusion and release
of entrained cargo varied with both the rate of degradation of PEG-OND
hydrogels and the hydrodynamic radius of the entrained species. These
results highlight the utility of OND linkers in the preparation of
degradable network materials with potential applications in sustained
release
Encapsidated Atom-Transfer Radical Polymerization in QĪ² Virus-like Nanoparticles
Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter QĪ² VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA