Polysaccharide peptide conjugates: Chemistry, properties and applications

The intention of this publication is to give an overview on research related to conjugates of polysaccharides and peptides. Dextran, chitosan, and alginate were selected, to cover four of the most often encountered functional groups known to be present in polysaccharides. These groups are the hydroxyl, the amine, the carboxyl, and the acetal functionality. A collection of the commonly used chemical reactions for conjugation is provided. Conjugation results into distinct properties compared to the parent polysaccharide, and a number of these characteristics are highlighted. This review aims at demonstrating the applicability of said conjugates with a strong emphasis on biomedical applications, drug delivery, biosensing, and tissue engineering. Some suggestions are made for more rigorous chemistries and analytics that could be investigated. Finally, an outlook is given into which direction the field could be developed further. We hope that this survey provides the reader with a comprehensive summary and contributes to the progress of works that aim at synthetically combining two of the main building blocks of life into supramolecular structures with unprecedented biological response.

Reduction-Sensitive Dextran-Paclitaxel Polymer-Drug Conjugate: Synthesis, Self-Assembly into Nanoparticles, and In Vitro Anticancer Efficacy

Delivery systems that can encapsulate a precise amount of drug and offer a spatiotemporally controlled drug release are being actively sought for safe yet effective cancer therapy. Compared to polymer nanoparticle (NP)-based delivery systems that rely on physical drug encapsulation, NPs derived from stimuli-sensitive covalent polymer-drug conjugates (PDCs) have emerged as promising alternatives offering precise control over drug dosage and spatiotemporal drug release. Herein, we report a reduction-sensitive PDC "Dex-SS-PTXL" synthesized by conjugating dextran and paclitaxel (PTXL) through a disulfide bond-bearing linker. The synthesized Dex-SS-PTXL PDC with a precise degree of substitution in terms of the percentage of repeat units of dextran covalently conjugated to PTXL (27 ± 0.6%) and the amount of drug carried by the PDC (39 ± 1.4 wt %) was found to self-assemble into spherical NPs with an average size of 110 ± 34 nm and a ζ-potential of -14.09 ± 8 mV. The reduction-sensitive Dex-SS-PTXL NPs were found to release PTXL exclusively in response to the reducing agent concentration reflective of the intracellular reducing environment of the tumor cells. Challenging BT-549 and MCF-7 cells with Dex-SS-PTXL NPs revealed significant cytotoxicity, while the IC50 values and the mode of action (mitotic arrest) of Dex-SS-PTXL NPs were found to be comparable to those of free PTXL, highlighting the active nature of the intracellularly released drug. The developed PDC with its unique ability to self-assemble into NPs and stimuli-responsive drug release can enhance the success of the NP-based drug delivery systems during clinical translation.

Forward Precision Medicine: Micelles for Active Targeting Driven by Peptides

Precision medicine is based on innovative administration methods of active principles. Drug delivery on tissue of interest allows improving the therapeutic index and reducing the side effects. Active targeting by means of drug-encapsulated micelles decorated with targeting bioactive moieties represents a new frontier. Between the bioactive moieties, peptides, for their versatility, easy synthesis and immunogenicity, can be selected to direct a drug toward a considerable number of molecular targets overexpressed on both cancer vasculature and cancer cells. Moreover, short peptide sequences can facilitate cellular intake. This review focuses on micelles achieved by self-assembling or mixing peptide-grafted surfactants or peptide-decorated amphiphilic copolymers. Nanovectors loaded with hydrophobic or hydrophilic cytotoxic drugs or with gene silence sequences and externally functionalized with natural or synthetic peptides are described based on their formulation and in vitro and in vivo behaviors.

pH-Responsive Nanofibers for Precise and Sequential Delivery of Multiple Payloads

Effective combination therapies can be achieved by programming materials for controlling release sequence, timing, and dose of multiple payloads. Herein, we synthesize dextran esters by coesterification of dextran, which display responsive properties at a precise pH threshold between 5.0 and 7.0. Multilayers electrospun nanofibers are prepared so that three different payloads are entrapped in three different dextran esters. The release of the three drugs can be sequentially and independently activated by a gradual increase of pH value. Because both pH threshold and release kinetics are matching conditions encountered by aliments along the gastrointestinal tract, these dextran ester multilayer nanofibers are promising for oral drug delivery.

Multiphoton fluorescence lifetime imaging microscopy (FLIM) and super-resolution fluorescence imaging with a supramolecular biopolymer for the controlled tagging of polysaccharides

A new supramolecular polysaccharide complex, comprising a functionalised coumarin tag featuring a boronic acid and β-d-glucan (a natural product extract from barley, Hordeum Vulgare) was assembled based on the ability of the boronate motif to specifically recognise and bind to 1,2- or 1,3-diols in water. The complexation ratio of the fluorophore : biopolymer strand was determined from fluorescence titration experiments in aqueous environments and binding isotherms best described this interaction using a 2 : 1 model with estimated association constants of K2:1a1 = 5.0 × 104 M-1 and K2:1a2 = 3.3 × 1011 M-1. The resulting hybrid (denoted 5@β-d-glucan) was evaluated for its cellular uptake as an intact functional biopolymer and its distribution compared to that of the pinacol-protected coumarin boronic acid derivative using two-photon fluorescence lifetime imaging microscopy (FLIM) in living cells. The new fluorescent β-d-glucan conjugate has a high kinetic stability in aqueous environments with respect to the formation of the free boronic acid derivative compound 5 and retains fluorescence emissive properties both in solution and in living cells, as shown by two-photon fluorescence spectroscopy coupled with time-correlated single photon counting (TCSPC). Super-resolution fluorescence imaging using Airyscan detection as well as TM AFM and Raman spectroscopy investigations confirmed the formation of fluorescent and nano-dimensional aggregates of up to 20 nm dimensions which self-assemble on several different inert surfaces, such as borosilicate glass and mica surfaces, and these aggregates can also be observed within living cells with optical imaging techniques. The cytoplasmic distribution of the 5@β-d-glucan complex was demonstrated in several different cancer cell lines (HeLa and PC-3) as well as in healthy cells (J774.2 macrophages and FEK-4). Both new compounds (pinacol protected boronated coumarin) 5-P and its complex hybrid 5@β-d-glucan successfully penetrate cellular membranes with the minimum morphological alterations to cells and distribute evenly in the cytoplasm. The glucan biopolymer retains its activity towards macrophages in the presence of the coumarin tag functionality, demonstrating the potential of this natural β-d-glucan to act as a functional self-assembled theranostic scaffold capable of mediating the delivery of anchored small organic molecules with imaging and drug delivery applications.

Peptide-Based Drug-Delivery Systems in Biotechnological Applications: Recent Advances and Perspectives

Peptides of natural and synthetic sources are compounds operating in a wide range of biological interactions. They play a key role in biotechnological applications as both therapeutic and diagnostic tools. They are easily synthesized thanks to solid-phase peptide devices where the amino acid sequence can be exactly selected at molecular levels, by tuning the basic units. Recently, peptides achieved resounding success in drug delivery and in nanomedicine smart applications. These applications are the most significant challenge of recent decades: they can selectively deliver drugs to only pathological tissues whilst saving the other districts of the body. This specific feature allows a reduction in the drug side effects and increases the drug efficacy. In this context, peptide-based aggregates present many advantages, including biocompatibility, high drug loading capacities, chemical diversity, specific targeting, and stimuli responsive drug delivery. A dual behavior is observed: on the one hand they can fulfill a structural and bioactive role. In this review, we focus on the design and the characterization of drug delivery systems using peptide-based carriers; moreover, we will also highlight the peptide ability to self-assemble and to actively address nanosystems toward specific targets.

Cyclodextrin-based delivery systems for cancer treatment

Cyclodextrins, one of safe excipients, are able to form host-guest complexes with fitted molecules given the unique nature imparted by their structure in result of a number of pharmaceutical applications. On the other hand, targeted or responsive materials are appealing therapeutic platforms for the development of next-generation precision medications. Meanwhile, cyclodextrin-based polymers or assemblies can condense DNA and RNA in result to be used as genetic therapeutic agents. Armed with a better understanding of various pharmaceutical mechanisms, especially for cancer treatment, researchers have made lots of works about cyclodextrin-based drug delivery systems in materials chemistry and pharmaceutical science. This Review highlights recent advances in cyclodextrin-based delivery systems for cancer treatment capable of targeting or responding to the physiological environment. Key design principles, challenges and future directions, including clinical translation, of cyclodextrin-based delivery systems are also discussed.

A novel amphiphilic fluorescent probe BODIPY–O-CMC–cRGD as a biomarker and nanoparticle vector

Fluorescent probes have been demonstrated to be promising candidates as biomarkers and biological carriers. Our study focuses on the development of a novel amphiphilic fluorescent probe with good photostability, high water solubility, excellent specificity and promising loading capability for tumor diagnosis and treatment. At first, BODIPY dye and O-carboxymethyl chitosan were prepared via a chemical reaction. Then, the prepared BODIPY dye and cRGD were bonded to O-carboxymethyl chitosan successively via an acylation reaction. Finally, we obtained the desired amphiphilic fluorescent probe: BODIPY–O-CMC–cRGD, which was based on the fluorescence resonance energy transfer (FRET) principle for selective visualization of tumors in vitro. Through a series of experiments, we found that this fluorescent probe possessed better fluorescence characteristics and tumor targeting properties. Simultaneously, by self-assembly, the amphiphilic probe encapsulated the other flexible structure of BODIPY2 and the rigid structure of porphyrin, which formed distinct nanoparticles with different particle sizes. Hence, we could observe different phagocytosis processes of the two nanoparticles in the tumor cells via the fluorescence of dyes by confocal laser scanning microscopy. Therefore, the results suggest that the fluorescent probe has advantages in tumor detection, and the constructed tumor-specific nanoparticles show high clinical potential to be utilized not only in visual and precise diagnosis but also in excellent drug delivery for tumor treatment. Henceforth, we will prepare new targeted and visualized pharmaceuticals by replacing BODIPY2 and porphyrin with antineoplastic drugs for future tumor treatment.

The amphipathic fluorescence probe, BODIPY–O-CMC–cRGD, can be applied in visualized diagnoses and as drug delivery vehicles of visualized therapies in the future.

Modulating angiogenesis with integrin-targeted nanomedicines

Targeting angiogenesis-related pathologies, which include tumorigenesis and metastatic processes, has become an attractive strategy for the development of efficient guided nanomedicines. In this respect, integrins are cell-adhesion molecules involved in angiogenesis signaling pathways and are overexpressed in many angiogenic processes. Therefore, they represent specific biomarkers not only to monitor disease progression but also to rationally design targeted nanomedicines. Arginine-glycine-aspartic (RGD) containing peptides that bind to specific integrins have been widely utilized to provide ligand-mediated targeting capabilities to small molecules, peptides, proteins, and antibodies, as well as to drug/imaging agent-containing nanomedicines, with the final aim of maximizing their therapeutic index. Within this review, we aim to cover recent and relevant examples of different integrin-assisted nanosystems including polymeric nanoconstructs, liposomes, and inorganic nanoparticles applied in drug/gene therapy as well as imaging and theranostics. We will also critically address the overall benefits of integrin-targeting.