Chemoselective
reactions with thiols have long held promise for
the site-specific bioconjugation of antibodies and antibody fragments.
Yet bifunctional probes bearing monovalent maleimideslong
the “gold standard” for thiol-based ligationsare
hampered by two intrinsic issues: the in vivo instability
of the maleimide–thiol bond and the need to permanently disrupt
disulfide linkages in order to facilitate bioconjugation. Herein,
we present the synthesis, characterization, and validation of DiPODS,
a novel bioconjugation reagent containing a pair of oxadiazolyl methyl
sulfone moieties capable of irreversibly forming covalent bonds with
two thiolate groups while simultaneously rebridging disulfide linkages.
The reagent was synthesized from commercially available starting materials
in 8 steps, during which rotamers were encountered and investigated
both experimentally and computationally. DiPODS is designed to be
modular and can thus be conjugated to any payload through a pendant
terminal primary amine (DiPODS–PEG4–NH2). Subsequently, the modification of a HER2-targeting Fab
with a fluorescein-conjugated variant of DiPODS (DiPODS–PEG4–FITC) reinforced the site-specificity of the reagent,
illustrated its ability to rebridge disulfide linkages, and produced
an immunoconjugate with in vitro properties superior
to those of an analogous construct created using traditional stochastic
bioconjugation techniques. Ultimately, we believe that this work has
particularly important implications for the synthesis of immunoconjugates,
specifically for ensuring that the attachment of cargoes to immunoglobulins
is robust, irreversible, and biologically and structurally benign.
[18F]FPEB is a positron emission tomography (PET) radiopharmaceutical used for imaging the abundance and distribution of mGluR5 in the central nervous system (CNS). Efficient radiolabeling of the aromatic ring of [18F]FPEB has been an ongoing challenge. Herein, five metal-free precursors for the radiofluorination of [18F]FPEB were compared, namely, a chloro-, nitro-, sulfonium salt, and two spirocyclic iodonium ylide (SCIDY) precursors bearing a cyclopentyl (SPI5) and a new adamantyl (SPIAd) auxiliary. The chloro- and nitro-precursors resulted in a low radiochemical yield (<10% RCY), whereas both SCIDY precursors and the sulfonium salt precursor produced [18F]FPEB in the highest RCYs of 25% and 36%, respectively. Preliminary PET/CT imaging studies with [18F]FPEB were conducted in a transgenic model of Alzheimer’s Disease (AD) using B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J (APP/PS1) mice, and data were compared with age-matched wild-type (WT) B6C3F1/J control mice. In APP/PS1 mice, whole brain distribution at 5 min post-injection showed a slightly higher uptake (SUV = 4.8 ± 0.4) than in age-matched controls (SUV = 4.0 ± 0.2). Further studies to explore mGluR5 as an early biomarker for AD are underway.
Effective bioremediation
of hydrocarbons requires innovative approaches
to minimize phosphate precipitation in soils of different buffering
capacities. Understanding the mechanisms underlying sustained stimulation
of bacterial activity remains a key challenge for optimizing bioremediationparticularly
in northern regions. Positron emission tomography (PET) can trace
microbial activity within the naturally occurring soil structure of
intact soils. Here, we use PET to test two hypotheses: (1) optimizing
phosphate bioavailability in soil will outperform a generic biostimulatory
solution in promoting hydrocarbon remediation and (2) oligotrophic
biostimulation will be more effective than eutrophic approaches. In
so doing, we highlight the key bacterial taxa that underlie aerobic
and anaerobic hydrocarbon degradation in subarctic soils. In particular,
we showed that (i) optimized phosphate bioavailability outperformed
generic biostimulatory solutions in promoting hydrocarbon degradation,
(ii) oligotrophic biostimulation is more effective than eutrophic
approaches, and (iii) optimized biostimulatory solutions stimulated
specific soil regions and bacterial consortia. The knowledge gleaned
from this study will be crucial in developing field-scale biodegradation
treatments for sustained stimulation of bacterial activity in northern
regions.
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