Synthesis of a novel carboxybetaine copolymer with different spacer lengths and inhibition of nonspecific protein adsorption on its polymer film

Herein, we designed and synthesized a thermally stable carboxybetaine copolymer with a one- or three-carbon spacer between ammonium and carboxylate groups (CBMA1 and CBMA3) to create an anti-nonspecific adsorption surface with the ability to immobilize antibodies. A series of controlled poly(N,N-dimethylaminoethyl methacrylate) was successfully prepared using reversible addition-fragmentation chain-transfer (RAFT) polymerization and was derived to carboxybetaine copolymers of poly(CBMA1-co-CBMA3) [P(CBMA1/CBMA3)] with various CBMA1 contents, including the homopolymers of CBMA1 and CBMA3. Thermal stability of the carboxybetaine (co)polymers was higher than that of the carboxybetaine polymer with a two-carbon spacer (PCBMA2). Further, we also evaluated nonspecific protein adsorption in fetal bovine serum and antibody immobilization on the substrate coated with P(CBMA1/CBMA3) copolymers using surface plasmon resonance (SPR) analysis. As the CBMA1 content increased, nonspecific protein adsorption on the P(CBMA1/CBMA3) copolymer surface decreased. Similarly, the immobilization amount of the antibody decreased as the CBMA1 content increased. However, the figure of merit (FOM), defined as the ratio of the amount of antibody immobilization to that of nonspecific protein adsorption, depended on the CBMA3 content; FOM was higher when the CBMA3 content was 20-40% than those of CBMA1 and CBMA3 homopolymers. These findings will help enhance the sensitivity of the analysis using molecular interaction measurement devices, such as SPR and quartz crystal microbalance.

Cografting of Zwitterionic Sulfobetaines and Cationic Amines on β-Cyclodextrin-Threaded Polyrotaxanes Facilitates Cellular Association and Tissue Accumulation with High Biocompatibility

β-Cyclodextrins (β-CDs) and β-CD-containing polymers have attracted considerable attention as potential candidates for the treatment of cholesterol-related metabolic and intractable diseases. We have advocated the use of β-CD-threaded acid-degradable polyrotaxanes (PRXs) as intracellular delivery carriers for β-CDs. As unmodified PRXs are insoluble in aqueous solutions, chemical modification of PRXs is an essential process to improve their solubility and impart novel functionalities. In this study, we investigated the effect of the modification of zwitterionic sulfobetaines on PRXs due to their excellent solubility, biocompatibility, and bioinert properties. Sulfobetaine-modified PRXs were synthesized by converting the tertiary amino groups of precursor 2-(N,N-dimethylamino)ethyl carbamate-modified PRXs (DMAE-PRXs) using 1,3-propanesultone. The resulting sulfobetaine-modified PRXs showed high solubility in aqueous solutions and no cytotoxicity, while their intracellular uptake levels were low. To further improve this system, we designed PRXs cografted with zwitterionic sulfobetaine and cationic DMAE groups via partial betainization of the DMAE groups. Consequently, the interaction with proteins, intracellular uptake levels, and liver accumulation of partly betainized PRXs were found to be higher than those of completely betainized PRXs. Additionally, partly betainized PRXs showed no toxicity in vitro or in vivo despite the presence of residual cationic DMAE groups. Furthermore, partly betainized PRXs ameliorated the abnormal free cholesterol accumulation in Niemann-Pick type C disease patient-derived cells at lower concentrations than β-CD derivatives and previously designed PRXs. Overall, the cografting of sulfobetaines and amines on PRXs is a promising chemical modification for therapeutic applications due to the high cholesterol-reducing ability and biocompatibility of such modified PRXs. In addition, modification with both zwitterionic and cationic groups can be used for the design of various polymeric materials exhibiting both bioinert and bioactive characteristics.

Synthesis and Hydrogelation of Star-Shaped Graft Copolypetides with Asymmetric Topology

To study the self-assembly and hydrogel formation of the star-shaped graft copolypeptides with asymmetric topology, star-shaped poly(_L-lysine) with various arm numbers were synthesized by using asymmetric polyglycerol dendrimers (PGDs) as the initiators and 1,1,3,3-tetramethylguanidine (TMG) as an activator for OH groups, followed by deprotection and grafting with indole or phenyl group on the side chain. The packing of the grafting moiety via non-covalent interactions not only facilitated the polypeptide segments to adopt more ordered conformations but also triggered the spontaneous hydrogelation. The hydrogelation ability was found to be correlated with polypeptide composition and topology. The star-shaped polypeptides with asymmetric topology exhibited poorer hydrogelation ability than those with symmetric topology due to the less efficient packing of the grafted moiety. The star-shaped polypeptides grafted with indole group on the side chain exhibited better hydrogelation ability than those grafted with phenyl group with the same arm number. This report demonstrated that the grafted moiety and polypeptide topology possessed the potential ability to modulate the polypeptide hydrogelation and hydrogel characteristics.

Construction of Enzyme-Responsive Micelles Based on Theranostic Zwitterionic Conjugated Bottlebrush Copolymers with Brush-on-Brush Architecture for Cell Imaging and Anticancer Drug Delivery

Bottlebrush copolymers with different chemical structures and compositions as well as diverse architectures represent an important kind of material for various applications, such as biomedical devices. To our knowledge, zwitterionic conjugated bottlebrush copolymers integrating fluorescence imaging and tumor microenvironment-specific responsiveness for efficient intracellular drug release have been rarely reported, likely because of the lack of an efficient synthetic approach. For this purpose, in this study, we reported the successful preparation of well-defined theranostic zwitterionic bottlebrush copolymers with unique brush-on-brush architecture. Specifically, the bottlebrush copolymers were composed of a fluorescent backbone of polyfluorene derivate (PFONPN) possessing the fluorescence resonance energy transfer with doxorubicin (DOX), primary brushes of poly(2-hydroxyethyl methacrylate) (PHEMA), and secondary graft brushes of an enzyme-degradable polytyrosine (PTyr) block as well as a zwitterionic poly(oligo (ethylene glycol) monomethyl ether methacrylate-co-sulfobetaine methacrylate) (P(OEGMA-co-SBMA)) chain with super hydrophilicity and highly antifouling ability via elegant integration of Suzuki coupling, NCA ROP and ATRP techniques. Notably, the resulting bottlebrush copolymer, PFONPN9-g-(PHEMA15-g-(PTyr16-b-P(OEGMA6-co-SBMA6)2)) (P2) with a lower MW ratio of the hydrophobic side chains of PTyr and hydrophilic side chains of P(OEGMA-co-SBMA) could self-assemble into stabilized unimolecular micelles in an aqueous phase. The resulting unimolecular micelles showed a fluorescence quantum yield of 3.9% that is mainly affected by the pendant phenol groups of PTyr side chains and a drug-loading content (DLC) of approximately 15.4% and entrapment efficiency (EE) of 90.6% for DOX, higher than the other micelle analogs, because of the efficient supramolecular interactions of π–π stacking between the PTyr blocks and drug molecules, as well as the moderate hydrophilic chain length. The fluorescence of the PFONPN backbone enables fluorescence resonance energy transfer (FRET) with DOX and visualization of intracellular trafficking of the theranostic micelles. Most importantly, the drug-loaded micelles showed accelerated drug release in the presence of proteinase K because of the enzyme-triggered degradation of PTyr blocks and subsequent deshielding of P(OEGMA-co-SBMA) corona for micelle destruction. Taken together, we developed an efficient approach for the synthesis of enzyme-responsive theranostic zwitterionic conjugated bottlebrush copolymers with a brush-on-brush architecture, and the resulting theranostic micelles with high DLC and tumor microenvironment-specific responsiveness represent a novel nanoplatform for simultaneous cell image and drug delivery.

Polypeptide Composition and Topology Affect Hydrogelation of Star-Shaped Poly(L-lysine)-Based Amphiphilic Copolypeptides

In this research, we studied the effect of polypeptide composition and topology on the hydrogelation of star-shaped block copolypeptides based on hydrophilic, coil poly(L-lysine)20 (s-PLL20) tethered with a hydrophobic, sheet-like polypeptide segment, which is poly(L-phenylalanine) (PPhe), poly(L-leucine) (PLeu), poly(L-valine) (PVal) or poly(L-alanine) (PAla) with a degree of polymerization (DP) about 5. We found that the PPhe, PLeu, and PVal segments are good hydrogelators to promote hydrogelation. The hydrogelation and hydrogel mechanical properties depend on the arm number and hydrophobic polypeptide segment, which are dictated by the amphiphilic balance between polypeptide blocks and the hydrophobic interactions/hydrogen bonding exerted by the hydrophobic polypeptide segment. The star-shaped topology could facilitate their hydrogelation due to the branching chains serving as multiple interacting depots between hydrophobic polypeptide segments. The 6-armed diblock copolypeptides have better hydrogelation ability than 3-armed ones and s-PLL-b-PPhe exhibits better hydrogelation ability than s-PLL-b-PVal and s-PLL-b-PLeu due to the additional cation-π and π-π interactions. This study highlights that polypeptide composition and topology could be additional parameters to manipulate polypeptide hydrogelation.

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.

Star-shaped polypeptides exhibit potent antibacterial activities

Peptide-based biomaterials are a promising class of antimicrobial agents that work by physically damaging bacterial cell membranes rather than targeting intracellular factors, resulting in less susceptibility to drug resistance. Herein we report the synthesis of cationic, star-shaped polypeptides with 3 to 8 arms and their evaluation as antimicrobial agents against different types of bacteria. The effects of the arm number and side chain group on their antimicrobial activities were systematically investigated. Compared to their linear counterparts, these star-shaped polypeptides exhibited potent antibacterial activity (which may involve adhesion and disruption processes). The increase of the arm number can efficiently increase the antibacterial activities up until 8 arms, which did not exhibit further improvement of antibacterial activities. Poly(l-lysine) (PLL) modified with an indole group (PLL-g-indo) exhibited the best antibacterial activity among all grafted copolypeptides and improved cytotoxic selectivity towards pathogens over mammalian cells without compromising their hemolytic activities. In vivo studies showed that the star-shaped PLL-g-indo can effectively suppress Enterohaemorrhagic E. coli (EHEC) infection and attenuate the clinical symptoms in mice, suggesting that they are promising antimicrobial agents.

Zwitterionic polypeptide nanomedicine with dual NIR/reduction-responsivity for synergistic cancer photothermal-chemotherapy

Dual NIR/reduction-responsive and zwitterionic polypeptide nanoparticles of PMC/DOX-ICG were fabricated, which achieved in vivo NIR fluorescence imaging and synergistic cancer PTT-CT treatment, and effectively ablated the HeLa tumors without recurrence for 30 days.

Soluble Zwitterionic Poly(sulfobetaine) Destabilizes Proteins

The widespread interest in neutral, water-soluble polymers such as poly(ethylene glycol) (PEG) and poly(zwitterions) such as poly(sulfobetaine) (pSB) for biomedical applications is due to their widely assumed low protein binding. Here we demonstrate that pSB chains in solution can interact with proteins directly. Moreover, pSB can reduce the thermal stability and increase the protein folding cooperativity relative to proteins in buffer or in PEG solutions. Polymer-dependent changes in the tryptophan fluorescence spectra of three structurally-distinct proteins reveal that soluble, 100 kDa pSB interacts directly with all three proteins and changes both the local polarity near tryptophan residues and the protein conformation. Thermal denaturation studies show that the protein melting temperatures decrease by as much as ∼1.9 °C per weight percent of polymer and that protein folding cooperativity increases by as much as ∼130 J mol^-1 K^-1 per weight percent of polymer. The exact extent of the changes is protein-dependent, as some proteins exhibit increased stability, whereas others experience decreased stability at high soluble pSB concentrations. These results suggest that pSB is not universally protein-repellent and that its efficacy in biotechnological applications will depend on the specific proteins used.