Synthesis and ring-opening (co)polymerization ofL-lysineN-carboxyanhydrides containing labile side-chain protective groups

GLUT-Targeting Phototherapeutic Nanoparticles for Synergistic Triple Combination Cancer Therapy

The combination of multimodal therapies into one nanocarrier system is promising for its potential to enhance treatment performance by overcoming the efficacy problems encountered in conventional monomodal therapy. In this study, targeted and multimodal therapeutic hybrid nanocarriers are fabricated for breast cancer treatments. In this context, the synthesized gold nanorods (AuNRd), photothermal therapy (PTT) agent, are coated with doxorubicin (DOX) conjugated, targeted, and biocompatible tetrablock glycopeptide (P(DMAEMA-b-HMBAMA-b-FrucMA)-b-P(Lys)/DOX, P-DOX) polymer. Here, fructose-based (Fruc) glycopeptide polymer enhances cellular uptake into breast cancer through GLUT5. A photosensitizer molecule, indocyanine green (ICG), was loaded into the particles to provide photodynamic therapy (PDT) upon NIR light at 808 nm. In the final step of the fabrication, the polymer-coated nanoparticles are integrated with antisense ISIS5132 oligonucleotides to prevent apoptotic resistance of cells against drug molecules. The biocompatibility and therapeutic efficacy of the nanoparticles are evaluated on both human normal skin fibroblast cell (CCD-1079Sk) and human breast cancer cell (MCF7) lines. These multimodal therapeutic AuNRd@P-DOX/ICG/ISIS5132 nanoparticles demonstrate an efficient triple synergistic effect of chemo-/PTT/PDT, which is desired for breast cancer treatment. We believe that this promising multimodal therapeutic nanoparticle system can promote the further clinical application in the treatment of breast cancer and can also be adapted to other types of cancer.

Synthesis and Characterization of the Novel Nε-9-Fluorenylmethoxycarbonyl-l-Lysine N-Carboxy Anhydride. Synthesis of Well-Defined Linear and Branched Polypeptides

The synthesis of well-defined polypeptides exhibiting complex macromolecular architectures requires the use of monomers that can be orthogonally deprotected, containing primary amines that will be used as the initiator for the Ring Opening Polymerization (ROP) of N-carboxy anhydrides. The synthesis and characterization of the novel monomer N^ε-9-Fluorenylmethoxycarbonyl-l-Lysine N-carboxy anhydride (N^ε-Fmoc-l-Lysine NCA), as well as the novel linear Poly(N^ε-Fmoc-l-Lys)_n homopolypeptide and Poly(l-Lysine)₇₈-block-[Poly(l-Lysine)₁₀-graft-Poly(l-Histidine)₁₅] block-graft copolypeptide, are presented. The synthesis of the graft copolypeptide was conducted via ROP of the N^ε-Boc-l-Lysine NCA while using n-hexylamine as the initiator, followed by the polymerization of N^ε-Fmoc-l-Lysine NCA. The last block was selectively deprotected under basic conditions, and the resulting ε-amines were used as the initiating species for the ROP of N^im-Trityl-l-Histidine NCA. Finally, the Boc- and Trt- groups were deprotected by TFA. High Vacuum Techniques were applied to achieve the conditions that are required for the synthesis of well-defined polypeptides. The molecular characterization indicated that the polypeptides exhibited high degree of molecular and compositional homogeneity. Finally, Dynamic Light Scattering, ζ-potential, and Circular Dichroism measurements were used in order to investigate the ability of the polypeptide to self-assemble in different conditions. This monomer opens avenues for the synthesis of polypeptides with complex macromolecular architectures that can define the aggregation behavior, and, therefore, can lead to the synthesis of "smart" stimuli-responsive nanocarriers for controlled drug delivery applications.

Injectable polypeptide hydrogels via methionine modification for neural stem cell delivery

Injectable hydrogels with tunable physiochemical and biological properties are potential tools for improving neural stem/progenitor cell (NSPC) transplantation to treat central nervous system (CNS) injury and disease. Here, we developed injectable diblock copolypeptide hydrogels (DCH) for NSPC transplantation that contain hydrophilic segments of modified l-methionine (Met). Multiple Met-based DCH were fabricated by post-polymerization modification of Met to various functional derivatives, and incorporation of different amino acid comonomers into hydrophilic segments. Met-based DCH assembled into self-healing hydrogels with concentration and composition dependent mechanical properties. Mechanical properties of non-ionic Met-sulfoxide formulations (DCHMO) were stable across diverse aqueous media while cationic formulations showed salt ion dependent stiffness reduction. Murine NSPC survival in DCHMO was equivalent to that of standard culture conditions, and sulfoxide functionality imparted cell non-fouling character. Within serum rich environments in vitro, DCHMO was superior at preserving NSPC stemness and multipotency compared to cell adhesive materials. NSPC in DCHMO injected into uninjured forebrain remained local and, after 4 weeks, exhibited an immature astroglial phenotype that integrated with host neural tissue and acted as cellular substrates that supported growth of host-derived axons. These findings demonstrate that Met-based DCH are suitable vehicles for further study of NSPC transplantation in CNS injury and disease models.

Biodegradable copolypeptide hydrogel prodrug accelerates dermal wound regeneration by enhanced angiogenesis and epithelialization

Hydrogels are one of the most promising wound dressings. However, their effectiveness on wound healing is still largely limited due to either the non-degradability or the release of non-therapeutic degradable products. Herein, a biodegradable copolypeptide hydrogel based on the glutamic acid and lysine was synthesized and applied as both wound dressing and therapeutic prodrug. The hydrogel can degrade in the existence of elevated degradative enzymes in a wound environment, which will release therapeutic amino acids to enhance the wound healing. In vivo results found that the hydrogel could effectively promote wound regeneration in both macroscopic and microscopic scales. Further investigation revealed that the wound healing effect of the hydrogel was highly attributed to its enhanced impact on angiogenesis, cell proliferation and re-epithelialization of the wound. All in all, the present study proves that the degradable copolypeptide hydrogel can efficiently improve wound healing and indicates its potent clinical application for wound regeneration.

Biodegradable hydrogel as a wound dressing and therapeutic prodrug promoting wound regeneration through enhanced angiogenesis and epithelialization.

Oxadiazabicyclooctenone as a versatile monomer for the construction of pH sensitive functional polymers via ROMP

Herein, oxadiazabicyclooctenone is successfully developed as a versatile monomer for the construction of new pH-sensitive polymers by ROMP.

Nanoparticle conjugates of a highly potent toxin enhance safety and circumvent platinum resistance in ovarian cancer

Advanced-stage epithelial ovarian cancers are amongst the most difficult to treat tumors and have proven to be refractory to most cytotoxic, molecularly targeted, or immunotherapeutic approaches. Here, we report that nanoparticle-drug conjugates (NDCs) of monomethyl auristatin E (MMAE) significantly increase loading on a per-vehicle basis as compared to antibody-drug conjugates (ADCs). Their intraperitoneal administration enabled triggered release of the active MMAE toxin to inhibit tumor growth and to extend animal survival to >90 days in a cell-line xenograft model of disseminated ovarian cancer. In a patient-derived xenograft model of advanced-stage and platinum-resistant ovarian cancer, an MMAE-based NDC doubled the duration of tumor growth inhibition as compared to cisplatin. NDCs of highly potent toxins thus introduce a translatable platform that may be exploited to maximize the safety and efficacy of cytotoxic chemotherapies, combining the best features of ADCs with those of nanoparticle-based therapeutics.

Improving the safety and efficacy of chemotherapeutics will help to enhance their effects. Here, the authors show that intraperitoneal delivery of nanoparticle conjugates of a potent toxin prolongs tumor inhibition and survival as compared to cisplatin in advanced-stage and platinum-resistant ovarian cancer mouse models.

Strategies to Fabricate Polypeptide-Based Structures via Ring-Opening Polymerization of N-Carboxyanhydrides

In this review, we provide a general and clear overview about the different alternatives reported to fabricate a myriad of polypeptide architectures based on the ring-opening polymerization of N-carbonyanhydrides (ROP NCAs). First of all, the strategies for the preparation of NCA monomers directly from natural occurring or from modified amino acids are analyzed. The synthetic alternatives to prepare non-functionalized and functionalized NCAs are presented. Protection/deprotection protocols, as well as other functionalization chemistries are discussed in this section. Later on, the mechanisms involved in the ROP NCA polymerization, as well as the strategies developed to reduce the eventually occurring side reactions are presented. Finally, a general overview of the synthetic strategies described in the literature to fabricate different polypeptide architectures is provided. This part of the review is organized depending on the complexity of the macromolecular topology prepared. Therefore, linear homopolypeptides, random and block copolypeptides are described first. The next sections include cyclic and branched polymers such as star polypeptides, polymer brushes and highly branched structures including arborescent or dendrigraft structures.

pH-controllable cell-penetrating polypeptide that exhibits cancer targeting

Helical peptides were naturally-occurring ordered conformations that mediated various biological functions essential for biotechnology. However, it was difficult for natural helical polypeptides to be applied in biomedical fields due to low bioavailability. To avoid these problems, synthetic alpha-helical polypeptides have recently been introduced by further modifying pendants in the side chain. In spite of an attractive biomimetic helical motif, these systems could not be tailored for targeted delivery mainly due to nonspecific binding events. To address these issues, we created a conformation-transformable polypeptide capable of eliciting a pH-activated cell-penetrating property solely at the cancer region. The developed novel polypeptide showed that the bare helical conformation had a function at physiological conditions while the pH-induced helical motif provided an active cell-penetrating characteristic at a tumor extracellular matrix pH. The unusual conformation-transformable system can elicit bioactive properties exclusively at mild acidic pH.

STATEMENT OF SIGNIFICANCE

We developed pH-controllable cell-penetrating polypeptides (PCCPs) undergoing pH-induced conformational transitions. Unlike natural cell-penetrating peptides, PCCPs was capable of penetrating the plasma membranes dominantly at tumor pH, driven by pH-controlled helicity. The conformation of PCCPs at neutral pH showed low helical propensity because of dominant electrostatic attractions within the side chains. However, the helicity of PCCPs was considerably augmented by the balance of electrostatic interactions, thereby inducing selective cellular penetration. Three polypeptides undergoing different conformational transitions were prepared to verify the selective cellular uptake influenced by their structures. The PCCP undergoing low-to-high helical conformation provided the tumor specificity and enhanced uptake efficiency. pH-induced conformation-transformable polypeptide might provide a novel platform for stimuli-triggered targeting systems.

pH-Responsive Peptide Supramolecular Hydrogels with Antibacterial Activity

Smart hydrogels have received increasing attention for many applications. Here, we synthesized a class of cationic peptide amphiphiles that can self-assemble into hydrogels by ring-opening polymerization (ROP) and post-modification strategy. The incorporation of cationic lysine residues suppresses the formation of fibril-like structure and further the gelation ability of the samples. Sodium alginate (SA) is used to enhance the rheology performance of the hydrogels. The hydrogels exhibit pH-dependent self-assembly and the gelation behavior that enables them to be ideal smart hydrogel systems for biomedical applications. Furthermore, the as-prepared hybrid peptide hydrogels show antibacterial activity.

Development of ionic strength/pH/enzyme triple-responsive zwitterionic hydrogel of the mixed l-glutamic acid and l-lysine polypeptide for site-specific drug delivery

Environmentally responsive hydrogels for drug delivery.

Development of polypeptide-based zwitterionic amphiphilic micelles for nanodrug delivery

Protein molecules, which typically have a hydrophobic core and a zwitterionic shell with a polypeptide backbone, could be ideal materials for nanodrug vehicles (NDVs) with low side effects. Here, we synthesized poly(l-aspartic acid(lysine))-b-poly(l-lysine(Z)) (PAsp(Lys)-b-PLys(Z)) (PALLZ), a novel amphiphilic block polypeptide with key structures of protein to investigate the possibility for use as a NDV. This polypeptide can spontaneously self-assemble into micelles in aqueous solution with a zwitterionic brush (the PAsp(Lys) part) to provide the nonfouling shell and a hydrophobic core (the PLys(Z) part) for loading hydrophobic drugs. The doxorubicin (DOX) loaded PALLZ micelles showed excellent resistance to nonspecific protein adsorption in FBS, which leads to very low internalization. Moreover, PALLZ micelles showed no cytotoxicity to MCF7, HeLa and HepG-2 cells up to 500 μg mL^-1. All these results indicated that zwitterionic amphiphilic block polypeptides could be promising materials for NDVs.

Thermoresponsive and Mechanical Properties of Poly(L-proline) Gels

Gelation of the left helical N-substituted homopolypeptide poly(L-proline) (PLP) in water was explored, employing rheological and small-angle scattering studies at different temperatures and concentrations in order to investigate the network structure and its mechanical properties. Stiff gels were obtained at 10 wt % or higher at 5 °C, the first time gelation has been observed for homopolypeptides. The secondary structure and helical rigidity of PLP has large structural similarities to gelatin but as gels the two materials show contrasting trends with temperature. With increasing temperature in D2O, the network stiffens, with broad scattering features of similar correlation length for all concentrations and molar masses of PLP. A thermoresponsive transition was also achieved between 5 and 35 °C, with moduli at 35 °C higher than gelatin at 5 °C. The brittle gels could tolerate strains of 1% before yielding with a frequency-independent modulus over the observed range, similar to natural proline-rich proteins, suggesting the potential for thermoresponsive or biomaterial-based applications.

Synthesis and multimodal responsiveness of poly(α-amino acid)s bearing OEGylated azobenzene side-chains

Photo and thermal dual-responsive poly(α-amino acid)s with radial amphiphilicity were designed and synthesized.

Polyplex Micelles with Double-Protective Compartments of Hydrophilic Shell and Thermoswitchable Palisade of Poly(oxazoline)-Based Block Copolymers for Promoted Gene Transfection

Improving the stability of polyplex micelles under physiological conditions is a critical issue for promoting gene transfection efficiencies. To this end, hydrophobic palisade was installed between the inner core of packaged plasmid DNA (pDNA) and the hydrophilic shell of polyplex micelles using a triblock copolymer consisting of hydrophilic poly(2-ethyl-2-oxazoline), thermoswitchable amphiphilic poly(2-n-propyl-2-oxazoline) (PnPrOx) and cationic poly(L-lysine). The two-step preparation procedure, mixing the triblock copolymer with pDNA below the lower critical solution temperature (LCST) of PnPrOx, followed by incubation above the LCST to form a hydrophobic palisade of the collapsed PnPrOx segment, induced the formation of spatially aligned hydrophilic-hydrophobic double-protected polyplex micelles. The prepared polyplex micelles exhibited significant tolerance against attacks from nuclease and polyanions compared to those without hydrophobic palisades, thereby promoting gene transfection. These results corroborated the utility of amphiphilic poly(oxazoline) as a molecular thermal switch to improve the stability of polyplex gene carriers relevant for physiological applications.

Complexation-Driven Mutarotation in Poly(L-proline) Block Copolypeptides

Novel poly(L-lysine)-block-poly(L-proline) (PLL-b-PLP)-based materials with all PLP helical conformers, i.e., PLP II and the rare PLP I are here reported. Electrostatic supramolecular complexation of the adjacent cationic PLL with anionic molecules bearing DNA analogue H-bonding functionalities, such as deoxyguanosine monophosphate (dGMP), preserves the extended PLP II helix, and the complexed molecule is locked and held in position by orthogonal shape-persistent hydrogen-bonded dGMP ribbons and their extended π-stacking. The branched anionic surfactant dodecylbenzenesulfonic acid (DBSA) on the other hand, introduces periodicity frustration and interlayer plasticization, leading to a reversed mutarotation to the more compact PLP I helix by complexation, without external stimuli, and is here reported for the first time. We foresee that our findings can be used as a platform for novel molecularly adaptive functional materials, and could possibly give insight in many proline-related transmembrane biological functions.

Establishment of a controlled insulin delivery system using a glucose-responsive double-layered nanogel

Glucose-responsive glycol chitosan/sodium alginate-poly(l-glutmate-co-N-3-l-glutamylphenylboronic acid) double-layered nanogel is a promising platform for controlled insulin release systems, achieving glucose-triggered insulin release at diabetic glucose levels in vivo.

A facile glovebox-free strategy to significantly accelerate the syntheses of well-defined polypeptides by N-carboxyanhydride (NCA) ring opening polymerizations

A facile N2 flow-accelerated N-carboxyanhydride ring opening polymerization (NCA ROP) is demonstrated, herein, with rigorous kinetic studies to evaluate the methodology in detail. By using n-hexylamine as initiator and γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) as monomer, the NCA ROP via a normal amine mechanism (NAM) reached 90% conversion in 2 h under N2 flow at room temperature in a fume hood, much shorter than the time required for the same polymerization conducted in a glove box (14 h). The efficient removal of CO2 from the reaction by N2 flow drove the carbamic acid-amine equilibrium toward the formation of active nucleophilic amino termini and promoted polymerization. The detailed kinetic studies of the polymerization with different feed ratios and N2 flow rates were conducted, demonstrating the living feature of the NCA ROP and the tuning of the polymerization rate by simply changing the flow rate of N2. Maintenance of the reactivity of the amino ω-chain terminus and control during a subsequent polymerization were confirmed by performing chain extension reactions. The N2 flow method provides a new straightforward strategy to synthesize well-defined polypeptides with predictable molecular weights and narrow molecular weight distributions (PDI < 1.19).

Development of functional amino acid-based star polymers

Various arm and core functionalized amino acid-based star polymer are prepared. Furthermore, a detailed investigation of reaction parameters affecting star formation is presented.

How controlled and versatile is N-carboxy anhydride (NCA) polymerization at 0 °C? Effect of temperature on homo-, block- and graft (co)polymerization

The polymerization of N-carboxyanhydride (NCA) at low temperatures is controlled and allows the synthesis of a variety of well-defined polypetides.

Formation of reversible shell cross-linked micelles from the biodegradable amphiphilic diblock copolymer poly(L-cysteine)-block-poly(L-lactide)

A novel biodegradable diblock copolymer, poly(L-cysteine)-b-poly(L-lactide) (PLC-b-PLLA), was synthesized by ring-opening polymerization (ROP) of N-carboxyanhydride of beta-benzyloxycarbonyl-L-cysteine (ZLC-NCA) with amino-terminated poly(L-lactide) (NH 2-PLLA) as a macroinitiator in a convenient way. The diblock copolymer and its precursor were characterized by (1)H NMR, Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), and X-ray photoelectron spectroscopy (XPS) measurements. The length of each block polymer could be tailored by molecular design and the ratios of feeding monomers. The cell adhesion and cell spread on the PZLC-b-PLLA and PLC-b-PLLA films were enhanced compared to those on pure PLA film. PLC-b-PLLA can self-assemble to form micelles in aqueous media. A pyrene probe is used to demonstrate the micelle formation of PLC-b-PLLA in aqueous solution. Due to the ease of disulfide exchange with thiols, the obtained micelles are reversible shell cross-linked (SCL) micelles. The morphology and size of the micelles are studied by dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM).

Polypeptides and 100 years of chemistry of alpha-amino acid N-carboxyanhydrides

Syntheses and polymerizations of alpha-amino acid N-carboxyanhydrides (NCAs) were reported for the first time by Hermann Leuchs in 1906. Since that time, these cyclic and highly reactive amino acid derivatives were used for stepwise peptide syntheses but mainly for the formation of polypeptides by ring-opening polymerizations. This review summarizes the literature after 1985 and reports on new aspects of the polymerization processes, such as the formation of cyclic polypeptides or novel organometal catalysts. Polypeptides with various architectures, such as diblock, triblock, and multiblock sequences, and star-shaped or dendritic structures are also mentioned. Furthermore, lyotropic and thermotropic liquid-crystalline polypeptides will be discussed and the role of polypeptides as drugs or drug carriers are reviewed. Finally, the hypothetical role of NCAs in molecular evolution on the prebiotic Earth is discussed.

Amphiphilic amino acid copolymers as stabilizers for the preparation of nanocrystal dispersion

The recent advance of particle size engineering in nanometer ranges has widened the formulation opportunities of relatively water-insoluble drugs. However, the 'nanoformulation' suffers from a lack of systematic understanding about the requirements of polymeric stabilizers. Furthermore, the polymers that can be used for the preparation of nanocrystals are so limited that finding a proper stabilizer for a given formulation is often difficult. In this study, amino acid copolymers whose properties can systematically be tailored are developed, and their morphological and compositional effects are investigated. Copolymers containing lysine (K) as their hydrophilic segments, and phenylalanine (F) or leucine (L) as their hydrophobic segments successfully produce stable nanocrystals (200-300 nm) in water, while copolymers of K and alanine (A) could not generate nanosized particles. Not the morphology but the hydrophobicity of copolymers seems to be a critical parameter in the preparation of drug nanocrystals by wet comminution. The effective stabilization performance of copolymers requires the hydrophobic moiety content to be higher than 15 mol%. Comminution for only 5 min is long enough for nanocrystal preparation, and the crystallinity of drug is found intact after the processing.

Self-assembled nanostructures from peptide-synthetic hybrid block copolymers: complex, stimuli-responsive rod-coil architectures

The synthesis, solution and solid state self-assembly properties of a series of polyisoprene-b-poly(epsilon-benzyloxycarbonyl-L-lysine) PI-b-PZLys and polyisoprene-b-poly(L-lysine) PI-b-PLys block copolymers have been examined. The formation of stimuli-responsive micelles in water has been studied as a function of pH and ionic strength using static and dynamic light scattering, UV-circular dichroism and transmission electron microscopy. The observed change in the micelles dimensions has been directly attributed to the conformational transition in the secondary structure of polypeptide chains. In bulk, these rod-coil copolymers form self-assembled structures that have been characterized using DSC, DMA, WAXS and SAXS techniques. Hexagonal in lamellar (HL) and more interestingly hexagonal in hexagonal (HH) morphologies have been evidenced as a function of the chemical composition.