Mesenchymal stem cells-derived exosomes: novel carriers for nanoparticle to combat cancer.

BACKGROUND: The advancement in novel cancer therapeutics brought a platform combining the properties of exosomes with nanoparticles to precision medicine. The novel therapeutic approach aim is cancer-targeted therapy. Exosomes from mesenchymal stem cells (MSCs-Exo) exhibit unique properties in cancer therapies, which makes them an ideal tool for delivering therapeutic agents into tumor cells. The key role of natural MSCs-Exo is controversial in cancer therapy; however, they can be engineered at their surface or cargo to serve as a smart drug delivery system for cancer-targeted therapy. In the last few years, researchers harnessed nanotechnology to enforce MSCs-Exo for cancer management including, tumor cell tracking, imaging, and tumor cell killing. Different nanoparticles such as gold nanoparticles have particularly been incorporated into MSCs-Exo, which showed an efficient accumulation at the site of tumor with improved anticancer impact. These findings indicate that a hybrid of exosomes-nanoparticles may serve as combination therapy for the effective removal of cancers. SHORT CONCLUSION: Although exhibiting impressive potential, the use of nanoparticle-loaded MSCs-Exo as a drug-delivery tool has been troubled by some challenges, therefore, translation to clinic prerequisites further scrutiny. In this review, we focus on nanoparticle-loaded MSCs-Exo as a new cancer therapy and discuss engineered MSC-Exo for target therapy.

Length-Dependent Transition from Extended to Folded Shapes in Short Oligomers of an Azetidine-Based α-Amino Acid: The Critical Role of NH···N H-Bonds.

Hydrogen bonds (H-bonds) are ubiquitous in peptides and proteins and are central to the stabilization of their structures. Inter-residue H-bonds between non-adjacent backbone amide NH and C=O motifs lead to the well-known secondary structures of helices, turns and sheets, but it is recognized that other H-bonding modes may be significant, including the weak intra-residue H-bond (called a C5 H-bond) that implicates the NH and C=O motifs of the same amino acid residue. Peptide model compounds that adopt stable C5 H-bonds are not readily available and the so-called 2.05-helix, formed by successive C5 H-bonds, is an elusive secondary structure. Using a combination of theoretical chemistry and spectroscopic studies in both the gas phase and solution phase, we have demonstrated that derivatives of 3-amino-1-methylazetidine-3-carboxylic acid, Aatc(Me) can form sidechain-backbone N-H···N C6γ H-bonds that accompany-and thereby stabilize-C5 H-bonds. In the capped trimer of Aatc(Me), extended C5/C6γ motifs are sufficiently robust to challenge classical 310-helix formation in solution and the fully-extended 2.05-helix conformer has been characterized in the gas phase. Concurrent H-bonding support for successive C5 motifs is a new axiom for stabilizing the extended backbone secondary structure in short peptides.

Non-covalent interactions reveal the protein chain δ conformation in a flexible single-residue model.

The δ conformation is a local secondary structure in proteins that implicates a πamide N-H⋯N interaction between a backbone N atom and the NH of the following residue. Small-molecule models thereof have been limited so far to rigid proline-type compounds. We show here that in derivatives of a cyclic amino acid with a sulphur atom in the γ-position, specific side-chain/backbone N-H⋯S interactions stabilize the δ conformation sufficiently to allow it to compete with classical C5 and C7 H-bonded conformers.

N-H⋯X interactions stabilize intra-residue C5 hydrogen bonded conformations in heterocyclic α-amino acid derivatives.

Nature makes extensive and elaborate use of hydrogen bonding to assemble and stabilize biomolecular structures. The shapes of peptides and proteins rely significantly on N-H⋯O[double bond, length as m-dash]C interactions, which are the linchpins of turns, sheets and helices. The C5 H-bond, in which a single residue provides both donor and acceptor, is generally considered too weak to force the backbone to adopt extended structures. Exploiting the synergy between gas phase (experimental and quantum chemistry) and solution spectroscopies to decipher IR spectroscopic data, this work demonstrates that the extended C5-based conformation in 4-membered ring heterocyclic α-amino acid derivatives is significantly stabilized by the formation of an N-H⋯X H-bond. In this synergic system the strength of the C5 interaction remains constant while the N-H⋯X H-bond strength, and thereby the support provided by it, varies with the heteroatom.

A theoretical and experimental case study of the hydrogen bonding predilection of S-methylcysteine.

S-containing amino acids can lead to two types of local NH···S interactions which bridge backbone NH sites to the side chain to form either intra- or inter-residue H-bonds. The present work reports on the conformational preferences of S-methyl-L-cysteine, Cys(Me), using a variety of investigating tools, ranging from quantum chemistry simulations, gas-phase UV and IR laser spectroscopy, and solution state IR and NMR spectroscopies, on model compounds comprising one or two Cys(Me) residues. We demonstrate that in gas phase and in low polarity solution, the C- and N-capped model compound for one Cys(Me) residue adopts a preferred C5-C6γ conformation which combines an intra-residue N-H···O=C backbone interaction (C5) and an inter-residue N-H···S interaction implicating the side-chain sulfur atom (C6γ). In contrast, the dominant conformation of the C- and N-capped model compound featuring two consecutive Cys(Me) residues is a regular type I ß-turn. This structure is incompatible with concomitant C6γ interactions, which are no longer in evidence. Instead, C5γ interactions occur, that are fully consistent with the turn geometry and additionally stabilize the structure. Comparison with the thietane amino acid Attc, which exhibits a rigid cyclic side chain, pinpoints the significance of side chain flexibility for the specific conformational behavior of Cys(Me).

Local versus Global Control of Helical Folding in ß-Peptide Segments Using Hydrazino Turns.

Rational control of the self-organization of ß-peptides sequences to adopt regular secondary structures is an important challenge in peptidomimetic foldamer science. By replacing the N- and C-terminal residues of homooligomers of trans-2-aminocyclobutanecarboxylic acid (tACBC)n with N-aminoazetidine-2-carboxylic acid, an 8-helical topology is shown to dominate for sequences up to n = 7. This constitutes an atomic-level tool to override locally the preferred global 12-helix secondary structure of the corresponding tACBC homooligomers of the same length.

Conformation control through concurrent N-H⋯S and N-H⋯O[double bond, length as m-dash]C hydrogen bonding and hyperconjugation effects.

In addition to the classical N-H⋯O[double bond, length as m-dash]C non-covalent interaction, less conventional types of hydrogen bonding, such as N-H⋯S, may play a key role in determining the molecular structure. In this work, using theoretical calculations in combination with spectroscopic analysis in both gas phase and solution phase, we demonstrate that both these H-bonding modes exist simultaneously in low-energy conformers of capped derivatives of Attc, a thietane α-amino acid. 6-Membered ring inter-residue N-H⋯S interactions (C6γ), assisted by hyperconjugation between the thietane ring and the backbone, combine with 5-membered ring intra-residue backbone N-H⋯O[double bond, length as m-dash]C interactions (C5) to provide a C5-C6γ feature that stabilizes a planar geometry in the monomer unit. Two contiguous C5-C6γ features in the planar dimer implicate an unprecedented three-centre H-bond of the type C[double bond, length as m-dash]O⋯H(N)⋯SR2, while the trimer adopts two C5-C6γ features separated by a Ramachandran α-type backbone configuration. These low-energy conformers are fully characterized in the gas phase and support is presented for their existence in solution state.

Double quick, double click reversible peptide "stapling".

The development of constrained peptides for inhibition of protein-protein interactions is an emerging strategy in chemical biology and drug discovery. This manuscript introduces a versatile, rapid and reversible approach to constrain peptides in a bioactive helical conformation using BID and RNase S peptides as models. Dibromomaleimide is used to constrain BID and RNase S peptide sequence variants bearing cysteine (Cys) or homocysteine (hCys) amino acids spaced at i and i + 4 positions by double substitution. The constraint can be readily removed by displacement of the maleimide using excess thiol. This new constraining methodology results in enhanced α-helical conformation (BID and RNase S peptide) as demonstrated by circular dichroism and molecular dynamics simulations, resistance to proteolysis (BID) as demonstrated by trypsin proteolysis experiments and retained or enhanced potency of inhibition for Bcl-2 family protein-protein interactions (BID), or greater capability to restore the hydrolytic activity of the RNAse S protein (RNase S peptide). Finally, use of a dibromomaleimide functionalized with an alkyne permits further divergent functionalization through alkyne-azide cycloaddition chemistry on the constrained peptide with fluorescein, oligoethylene glycol or biotin groups to facilitate biophysical and cellular analyses. Hence this methodology may extend the scope and accessibility of peptide stapling.