Antibacterial Nanoplatelets via Crystallization-Driven Self-Assembly of Poly(l-lactide)-Based Block Copolymers

Membrane-active antimicrobial materials are promising substances to fight antimicrobial resistance. Herein, crystallization-driven self-assembly (CDSA) is employed for the preparation of nanoparticles with different morphologies, and their bioactivity is explored. Block copolymers (BCPs) featuring a crystallizable and antimicrobial block were synthesized using a combination of ring-opening and photoiniferter RAFT polymerizations. Subsequently formed nanostructures formed by CDSA could not be deprotected without degradation of the structures. CDSA of deprotected BCPs yielded 2D diamond-shaped nanoplatelets in MeOH, while spherical nanostructures were observed for assembly in water. Platelets exhibited improved antibacterial capabilities against two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) compared to their spherical counterparts. The absence of hemolytic activity leads to the excellent selectivity of platelets. A mechanism based on membrane permeabilization was confirmed via dye-leakage assays. This study emphasized the impact of the shape of nanostructures on their interaction with bacterial cells and how a controlled assembly can improve bioactivity.

Semisynthesis and characterization of versatile azide intermediates using sodium alginate and its homopolymeric derivatives as starting material

Alginate, a polyuronic biopolymer composed of mannuronic and guluronic acid units, contain hydroxyl and carboxyl groups as targeting modification sites to obtain structures with new and/or improved biological properties. The copper-catalyzed azide-alkyne cycloaddition (CuAAC) is a versatile click reaction for polymer functionalization, but it typically requires a "pre-click" modification to introduce azide or alkyne groups. Here, we described a straightforward chemical path to selectively modify alginate carboxyl groups producing versatile azido derivatives through N-acylation using 3-azydopropylamine. The resulting azide-functionalized polysaccharides underwent click chemistry to yield amino derivatives, confirmed by NMR and FTIR analyses. The 1H NMR spectrum reveals a characteristic triazole group signal at 8.15 ppm. The absence of the azide FTIR band for all amino derivatives, previously observed for the N-acylation products, indicated reaction success. Antibacterial and antioxidant assessments revealed that the initial polysaccharide lacks E. coli inhibition, while the click chemistry-derived amine products exhibit growth inhibition at 5.0 mg/mL. Lower molecular weight derivatives demonstrate superior DPPH scavenging ability, particularly amino-derivatives (24-33 % at 1.2 mg/mL). This innovative chemical pathway offers a promising strategy for developing polysaccharide structures with enhanced properties, demonstrating potential applications in various fields.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

Polysarcosine-Coated liposomes attenuating immune response induction and prolonging blood circulation

HYPOTHESIS

Liposomes coated with long polysarcosine (PSar) chains at a high density might enable long blood circulation and attenuate accelerated blood clearance (ABC) phenomenon.

EXPERIMENTS

In this study, we controlled the length (23, 45, 68 mers) and density (5, 10, 15 mol%) of PSar on liposomal coatings and, furthermore, investigated the effects of PSar length and density on the blood circulation time, biodistribution, immune response, and ABC phenomenon induction. Length-controlled PSar-bound lipids (PSar-PEs) were synthesized using a click reaction and inserted into bare liposomes at different combinations of chain lengths and proportions.

FINDINGS

Although all PSar-coated liposomes (PSar-lipos) had similar morphological, physical, and chemical properties, they had different blood circulation times and biodistribution, and exerted varied effects on the immune system. All PSar-lipos with different PSar length and density showed a similar anti-PSar IgM response. Liposomes modified with the longest PSar chain (68 mers) at a high density (15 mol%) showed the longest blood circulation time and, additionally, attenuated ABC phenomenon compared with PEG-lipo. The ex vivo analysis of the biodistribution of liposomes revealed that a thick PSar layer enhanced the blood circulation time of liposomes due to the reduction of the accumulation of liposomes in the liver and spleen. These findings provide new insights into the relationship between IgM expression and ABC phenomenon inhibition.

A Survey of Strain-Promoted Azide-Alkyne Cycloaddition in Polymer Chemistry

Highly efficient reactions that enable the assembly of molecules into complex structures have driven extensive progress in synthetic chemistry. In particular, reactions that occur under mild conditions and in benign solvents, while producing no by-products and rapidly reach completion are attracting significant attention. Amongst these, the strain-promoted azide-alkyne cycloaddition, involving various cyclooctyne derivatives reacting with azide-bearing molecules, has gained extensive popularity in organic synthesis and bioorthogonal chemistry. This reaction has also recently gained momentum in polymer chemistry, where it has been used to decorate, link, crosslink, and even prepare polymer chains. This survey highlights key achievements in the use of this reaction to produce a variety of polymeric constructs for disparate applications.

Tetrazine- and trans-cyclooctene-functionalised polypept(o)ides for fast bioorthogonal tetrazine ligation

Tetrazine- and trans-cyclooctene-functionalised polypeptides and polypetoids were prepared by ring-opening polymerisation of N-carboxyanhydrides using the respective functional initiators and shown to react in fast bioorthogonal tetrazine ligations.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Multifunctional Cationic PeptoStars as siRNA Carrier: Influence of Architecture and Histidine Modification on Knockdown Potential

RNA interference provides enormous potential for the treatment of several diseases, including cancer. Nevertheless, successful therapies based on siRNA require overcoming various challenges, such as poor pharmacokinetic characteristics of the small RNA molecule and inefficient cytosolic accumulation. In this respect, the development of functional siRNA carrier systems is a major task in biomedical research. To provide such a desired system, the synthesis of 3-arm and 6-arm PeptoStars is aimed for. The different branched polypept(o)idic architectures share a stealth-like polysarcosine corona for efficient shielding and a multifunctional polylysine core, which can be independently varied in size and functionality for siRNA complexation-, transport and intra cellular release. The special feature of star-like polypept(o)ides is in their uniform small size (<20 nm) and a core-shell structure, which implies a high stability and stealth-like properties and thus, they may combine long circulation times and a deep penetration of cancerous tissue. Initial toxicity and complement studies demonstrate well tolerated cationic PeptoStars with high complexation capability toward siRNA (N/P ratio up to 3:1), which can lead to potent RNAi for optimized systems. Here, the synthetic development of 3-arm and 6-arm polypept(o)idic star polymers, their modification with endosomolytic moieties, and first in vitro insights on RNA interference are reported on.

Thermoresponsive polysarcosine-based nanoparticles

Polysarcosine modified with limited molar amounts of (N-(2-hydroxypropyl)methacrylamide) yields a block copolymer capable of forming thermoresponsive nanoparticles that are suitable for controlled release applications.

A sequential native chemical ligation – thiol-Michael addition strategy for polymer–polymer ligation

Native Chemical Ligation (NCL) between cysteine-terminated polymers and functional thioesters has been employed to prepare functional (co)polymers. The retained thiol functionality at the NCL junction can be exploited for thiol-Michael addition.

Efficient Shielding of Polyplexes Using Heterotelechelic Polysarcosines

Shielding agents are commonly used to shield polyelectrolyte complexes, e.g., polyplexes, from agglomeration and precipitation in complex media like blood, and thus enhance their in vivo circulation times. Since up to now primarily poly(ethylene glycol) (PEG) has been investigated to shield non-viral carriers for systemic delivery, we report on the use of polysarcosine (pSar) as a potential alternative for steric stabilization. A redox-sensitive, cationizable lipo-oligomer structure (containing two cholanic acids attached via a bioreducible disulfide linker to an oligoaminoamide backbone in T-shape configuration) was equipped with azide-functionality by solid phase supported synthesis. After mixing with small interfering RNA (siRNA), lipopolyplexes formed spontaneously and were further surface-functionalized with polysarcosines. Polysarcosine was synthesized by living controlled ring-opening polymerization using an azide-reactive dibenzo-aza-cyclooctyne-amine as an initiator. The shielding ability of the resulting formulations was investigated with biophysical assays and by near-infrared fluorescence bioimaging in mice. The modification of ~100 nm lipopolyplexes was only slightly increased upon functionalization. Cellular uptake into cells was strongly reduced by the pSar shielding. Moreover, polysarcosine-shielded polyplexes showed enhanced blood circulation times in bioimaging studies compared to unshielded polyplexes and similar to PEG-shielded polyplexes. Therefore, polysarcosine is a promising alternative for the shielding of non-viral, lipo-cationic polyplexes.

Combining Orthogonal Reactive Groups in Block Copolymers for Functional Nanoparticle Synthesis in a Single Step

We report on the synthesis of polysarcosine-block-poly(S-alkylsulfonyl)-l-cysteine block copolymers, which combine three orthogonal addressable groups enabling site-specific conversion of all reactive entities in a single step. The polymers are readily obtained by ring-opening polymerization (ROP) of corresponding α-amino acid N-carboxyanhydrides (NCAs) combining azide and amine chain ends, with a thiol-reactive S-alkylsulfonyl cysteine. Functional group interconversion of chain ends using strain-promoted azide-alkyne cycloaddition (SPAAC) and activated ester chemistry with NHS- and DBCO-containing fluorescent dyes could be readily performed without affecting the cross-linking reaction between thiols and S-alkylsulfonyl protective groups. Eventually, all three functionalities can be combined in the formation of multifunctional disulfide core cross-linked nanoparticles bearing spatially separated functionalities. The simultaneous attachment of dyes in core and corona during the formation of core-cross-linked nanostructures with controlled morphology is confirmed by fluorescence cross-correlation spectroscopy (FCCS).

Orthogonally reactive amino acids and end groups in NCA polymerization

We summarize recent strategies for the synthesis of orthogonally reactive polypeptides and polypeptoids by direct and post-polymerization approaches.

Synthesis and application of a novel poly-l-phenylalanine electroactive macromonomer as matrix for the biosensing of ‘Abused Drug’ model

The synthesis and biosensing application of a novel poly-l-phenylalanine-bearing electroactive macromonomer has been carried out.

Polypept(o)ides: Hybrid Systems Based on Polypeptides and Polypeptoids

Polypept(o)ides combine the multifunctionality and intrinsic stimuli-responsiveness of synthetic polypeptides with the "stealth"-like properties of the polypeptoid polysarcosine (poly(N-methyl glycine)). This class of block copolymers can be synthesized by sequential ring opening polymerization of α-amino acid N-carboxy-anhydrides (NCAs) and correspondingly of the N-substituted glycine N-carboxyanhydride (NNCA). The resulting block copolymers are characterized by Poisson-like molecular weight distributions, full end group integrity, and dispersities below 1.2. While polysarcosine may be able to tackle the currently arising issues regarding the gold standard PEG, including storage diseases in vivo and immune responses, the polypeptidic block provides the functionalities for a specific task. Additionally, polypeptides are able to form secondary structure motives, e.g., α-helix or β-sheets, which can be used to direct self-assembly in solution. In this feature article, we review the relatively new field of polypept(o)ides with respect to synthesis, characterization, and first data on the application of block copolypept(o)ides in nanomedicine. The summarized data already indicates the great potential of polypept(o)ides.