3 research outputs found
Measuring the Adhesion Forces for the Multivalent Binding of Vancomycin-Conjugated Dendrimer to Bacterial Cell-Wall Peptide
Multivalent
ligand–receptor interaction provides the fundamental
basis for the hypothetical notion that high binding avidity relates
to the strong force of adhesion. Despite its increasing importance
in the design of targeted nanoconjugates, an understanding of the
physical forces underlying the multivalent interaction remains a subject
of urgent investigation. In this study, we designed three vancomycin
(Van)-conjugated dendrimers G5Â(Van)<sub><i>n</i></sub> (<i>n</i> = mean valency = 0, 1, 4) for bacterial targeting with
generation 5 (G5) polyÂ(amidoamine) dendrimer as a multivalent scaffold
and evaluated both their binding avidity and physical force of adhesion
to a bacterial model surface by employing surface plasmon resonance
(SPR) spectroscopy and atomic force microscopy. The SPR experiment
for these conjugates was performed in a biosensor chip surface immobilized
with a bacterial cell-wall peptide Lys-d-Ala-d-Ala.
Of these, G5Â(Van)<sub>4</sub> bound most tightly with a <i>K</i><sub>D</sub> of 0.34 nM, which represents an increase in avidity
by 2 or 3 orders of magnitude relative to a monovalent conjugate G5Â(Van)<sub>1</sub> or free vancomycin, respectively. By single-molecule force
spectroscopy, we measured the adhesion force between G5Â(Van)<sub><i>n</i></sub> and the same cell-wall peptide immobilized on the
surface. The distribution of adhesion forces increased in proportion
to vancomycin valency with the mean force of 134 pN at <i>n</i> = 4 greater than 96 pN at <i>n</i> = 1 at a loading rate
of 5200 pN/s. In summary, our results are strongly supportive of the
positive correlation between the avidity and adhesion force in the
multivalent interaction of vancomycin nanoconjugates
Control of an Unusual Photo-Claisen Rearrangement in Coumarin Caged Tamoxifen through an Extended Spacer
The use of coumarin
caged molecules has been well documented in
numerous photocaging applications including for the spatiotemporal
control of Cre-estrogen receptor (Cre-ERT2) recombinase activity.
In this article, we report that 4-hydroxytamoxifen (4OHT) caged with
coumarin <i>via</i> a conventional ether linkage led to
an unexpected photo-Claisen rearrangement which significantly competed
with the release of free 4OHT. The basis for this unwanted reaction
appears to be related to the coumarin structure and its radical-based
mechanism of uncaging, as it did not occur in <i>ortho</i>-nitrobenzyl (ONB) caged 4OHT that was otherwise linked in the same
manner. In an effort to perform design optimization, we introduced
a self-immolative linker longer than the ether linkage and identified
an optimal linker which allowed rapid 4OHT release by both single-photon
and two-photon absorption mechanisms. The ability of this construct
to actively control Cre-ERT2 mediated gene modifications was investigated
in mouse embryonic fibroblasts (MEFs) in which the expression of a
green fluorescent protein (GFP) reporter dependent gene recombination
was controlled by 4OHT release and measured by confocal fluorescence
microscopy and flow cytometry. In summary, we report the implications
of this photo-Claisen rearrangement in coumarin caged compounds and
demonstrate a rational linker strategy for addressing this unwanted
side reaction
Photocontrolled Release of Doxorubicin Conjugated through a Thioacetal Photocage in Folate-Targeted Nanodelivery Systems
Despite
their proven ability for precise and targeted release,
nanoplatform systems for photocontrolled delivery often face formidable
synthetic challenges, in part due to the paucity of advanced linker
strategies. Here, we report on a novel linker strategy using a thioacetal <i>ortho</i>-nitrobenzaldehyde (TNB) cage, demonstrating its application
for delivery of doxorubicin (Dox) in two nanoscale systems. This photocleavable
linker, TNBÂ(OH), which presents two identical arms, each terminated
with a hydroxyl functionality, was prepared in a single step from
6-nitroveratraldehyde. TNBÂ(OH) was used to cross-link Dox to a folate
receptor (FAR)-targeting polyÂ(amidoamine) dendrimer conjugate G5Â(FA)<sub><i>n</i>=5.4</sub>(Dox)<sub><i>m</i>=5.1</sub>, and also used to prepare an upconversion nanocrystal (UCN) conjugate,
UCN–PPIX@(Dox)Â(G5FA), a larger core/shell nanostructure. In
this core/shell nanostructure, the UCN core emits UV and visible light
luminescence upon near-infrared (NIR) excitation, allowing for the
photocleavage of the TNB linker as well as the photostimulation of
protoporphyrin IX (PPIX) coupled as a cytotoxic photosensitizer. Drug-release
experiments performed in aqueous solutions with long-wavelength ultraviolet
A (UVA) light showed that Dox release occurred rapidly from its TNB
linked form or from its dendrimer conjugated form with comparable
decay kinetics. Cellular toxicity studies in FAR-overexpressing KB
carcinoma cells demonstrated that each nanoconjugate lacked intrinsic
cytotoxicity until exposed to UVA or NIR (980 nm) (for the UCN nanoconjugate),
which resulted in induction of potent cytotoxicity. In summary, this
new TNB strategy offers synthetic convenience in drug conjugation
chemistry with the ability for the temporal control of drug activation
at the delivery site