Monitoring insulin fibrillation kinetics using chromatographic analysis.

Insulin is a small protein widely used to treat patients with diabetes and is a commonly used model for protein fibrillation studies. Under specific conditions, such as low pH and high temperature, insulin monomers aggregate to form fibrils. This aggregation is problematic for manufacturing and storage of insulin. The thioflavin T (ThT) assay is commonly used to study amyloid fibrillation but suffers from several limitations, such as the effect of protein concentration, the size of the amyloid fibrillar bundles, competitive binding, and fibril aggregation, all of which hinder precise quantitative analysis. Here, we present a method for studying the kinetics of insulin fibrillation utilizing ultraperformance liquid chromatography (UPLC). This method enables the quantitative detection of soluble insulin components, including chemically modified components. The formation of a deamidated species could be monitored at the early stage of fibrillation, and this species was likely included in the fibrils. In addition, in the presence of inhibitors known to compete with ThT for binding to fibrils, UPLC analysis showed the disappearance of soluble components even though the ThT assay did not indicate the presence of fibrils. These results suggest that the UPLC-based analysis presented here can complement the ThT assay for investigating the kinetics of protein fibrillation.

Fluorocarbon-DNA conjugates for enhanced cellular delivery: Formation of a densely packed DNA nano-assembly.

Forming nano-assemblies is essential for delivering DNA conjugates into cells, with the DNA density in the nano-assembly playing an important role in determining the uptake efficiency. In this study, we developed a strategy for the facile synthesis of DNA strands bearing perfluoroalkyl (RF) groups (RF-DNA conjugates) and investigated how they affect cellular uptake. An RF-DNA conjugate bearing a long RF group at the DNA terminus forms a nano-assembly with a high DNA density, which results in greatly enhanced cellular uptake. The uptake mechanism is mediated by clathrin-dependent endocytosis. The use of RF groups to densely assemble negatively charged DNA is a useful strategy for designing drug delivery carriers.

Synthesis of Short Peptides with Perfluoroalkyl Side Chains and Evaluation of Their Cellular Uptake Efficiency.

With an increasing demand for macromolecular biotherapeutics, the issue of their poor cell-penetrating abilities requires viable and relevant solutions. Herein, we report tripeptides bearing an amino acid with a perfluoroalkyl (RF ) group adjacent to the α-carbon. RF -containing tripeptides were synthesized and evaluated for their ability to transport a conjugated hydrophilic dye (Alexa Fluor 647) into the cells. RF -containing tripeptides with the fluorophore showed high cellular uptake efficiency and none of them were cytotoxic. Interestingly, we demonstrated that the absolute configuration of perfluoroalkylated amino acids (RF -AAs) affects not only nanoparticle formation but also the cell permeability of the tripeptides. These novel RF -containing tripeptides are potentially useful as short and noncationic cell-penetrating peptides (CPPs).

Reconstitution of microtubule into GTP-responsive nanocapsules.

Nanocapsules that collapse in response to guanosine triphosphate (GTP) have the potential as drug carriers for efficiently curing diseases caused by cancer and RNA viruses because GTP is present at high levels in such diseased cells and tissues. However, known GTP-responsive carriers also respond to adenosine triphosphate (ATP), which is abundant in normal cells as well. Here, we report the elaborate reconstitution of microtubule into a nanocapsule that selectively responds to GTP. When the tubulin monomer from microtubule is incubated at 37 °C with a mixture of GTP (17 mol%) and nonhydrolysable GTP* (83 mol%), a tubulin nanosheet forms. Upon addition of photoreactive molecular glue to the resulting dispersion, the nanosheet is transformed into a nanocapsule. Cell death results when a doxorubicin-containing nanocapsule, after photochemically crosslinked for properly stabilizing its shell, is taken up into cancer cells that overexpress GTP.

Photoreactive Molecular Glue for Enhancing the Efficacy of DNA Aptamers by Temporary-to-Permanent Conjugation with Target Proteins.

We developed a photoreactive molecular glue, BPGlue-N3, which can provide a universal strategy to enhance the efficacy of DNA aptamers by temporary-to-permanent stepwise stabilization of their conjugates with target proteins. As a proof-of-concept study, we applied BPGlue-N3 to the SL1 (DNA aptamer)/c-Met (target protein) conjugate system. BPGlue-N3 can adhere to and temporarily stabilize this aptamer/protein conjugate multivalently using its guanidinium ion (Gu+) pendants that form a salt bridge with oxyanionic moieties (e.g., carboxylate and phosphate) and benzophenone (BP) group that is highly affinitive to DNA duplexes. BPGlue-N3 is designed to carry a dual-mode photoreactivity; upon exposure to UV light, the temporarily stabilized aptamer/protein conjugate reacts with the photoexcited BP unit of adhering BPGlue-N3 and also a nitrene species, possibly generated by the BP-to-N3 energy transfer in BPGlue-N3. We confirmed that SL1, covalently conjugated with c-Met, hampered the binding of hepatocyte growth factor (HGF) onto c-Met, even when the SL1/c-Met conjugate was rinsed prior to the treatment with HGF, and suppressed cell migration caused by HGF-induced c-Met phosphorylation.

Transferrin-Appended Nanocaplet for Transcellular siRNA Delivery into Deep Tissues.

Transferrin (Tf) is known to induce transcytosis, which is a consecutive endocytosis/exocytosis event. We developed a Tf-appended nanocaplet (TfNC⊃siRNA) for the purpose of realizing siRNA delivery into deep tissues and RNA interference (RNAi) subsequently. For obtaining TfNC⊃siRNA, a macromonomer (AzGu) bearing multiple guanidinium (Gu+) ion units, azide (N3) groups, and trityl (Trt)-protected thiol groups in the main chain, side chains, and termini, respectively, was newly designed. Because of a multivalent Gu+-phosphate salt-bridge interaction, AzGu can adhere to siRNA along its strand. When I2 was added to a preincubated mixture of AzGu and siRNA, oxidative polymerization of AzGu took place along the siRNA strand, affording AzNC⊃siRNA, the smallest siRNA-containing reactive nanocaplet so far reported. This conjugate was converted into Glue/BPNC⊃siRNA by the click reaction with a Gu+-appended bioadhesive dendron (Glue) followed by a benzophenone derivative (BP). Then, Tf was covalently immobilized onto Glue/BPNC⊃siRNA by Gu+-mediated adhesion followed by photochemical reaction with BP. With the help of Tf-induced transcytosis, TfNC⊃siRNA permeated deeply into a cancer spheroid, a 3D tissue model, at a depth of up to nearly 70 µm, unprecedentedly.