Disulfide bonds as a molecular switch of enzyme-activatable anticancer drug precise release for fluorescence imaging and enhancing tumor therapy.

Enzyme-activatable drug delivery systems have been developed for cancer diagnosis and therapy. However, targeted intracellular drug delivery is a challenge for precisely tumor imaging and therapy due to the increased stability of copolymer nanoparticles (NPs) is accompanied by a notable decrease in enzyme degradation. Herein, disulfide bond was designed as an enzyme-activatable molecular switch of SS-P(G2)2/DOX NPs. The copolymer NPs consists of polyvinylpyrrolidone (PVP) with disulfide bonds in the center and enzyme-degradable peptide dendrites (Phe-Lys) to form dendritic-linear-dendritic triblock copolymers (TBCs). The amphiphilic TBCs could be split into two identical amphiphilic diblock copolymers (DBCs) by glutathione (GSH) in cancer cells specifically while maintaining the same hydrophilic-lipophilic equilibrium. This structural transformation significantly reduced the stability of copolymer NPs and enhanced sensitivity of DOX release by cathepsin B-activated. Subsequently, the released DOX acted as an indicator of fluorescence imaging and chemotherapy drug for cancer cells. The polymeric NPs achieved excellent drug-loaded stability and prolonged blood circulation in vivo, and realized fluorescence imaging and specific cancer cell killing capabilities by responding to the overexpression of GSH and cathepsin B in tumor cells. Furthermore, the copolymer NPs demonstrated excellent blood compatibility and biosafety. Therefore, a novel strategy based on one tumor marker acting as the switch for another tumor microenvironment responsive drug delivery system could be designed for tumor intracellular imaging and chemotherapy.

Enzyme and pH dual responsive linear-dendritic block copolymer micelles based on a phenylalanyl-lysine motif and peripherally ketal-functionalized dendron as potential drug carriers.

Stimuli-responsive linear-dendritic block copolymers (LDBCs) have attracted significant research attention as novel drug carriers. We report here three generations of new enzyme and pH dual responsive linear-dendritic block copolymers (LDBCs) with a phenylalanyl-lysine (Phe-Lys) dipeptide linking hydrophilic linear poly(N-vinylpyrrolidone) (PNVP) and a hydrophobic peripherally ketal-functionalized dendron derived from 2,2'-bis(hydroxymethyl)propionic acid (bis-MPA). The LDBCs are synthesized via a combination of interchange of xanthates/reversible addition-fragmentation chain transfer (MADIX/RAFT) polymerization of N-vinylpyrrolidone (NVP) and "chain-first" strategy. Their structures are confirmed by 1H NMR spectra. The gel permeation chromatograph (GPC) analysis revealed that the LDBCs have a narrow molecular weight distribution (PDI ≤ 1.25). The amphiphilic LDBCs can self-assemble into spherical nanomicelles in aqueous solution. The presence of enzyme or/and the change of pH cause disassembly of micelles to release encapsulated cargos. The release rates of the guest molecules are faster in buffer solution at pH 5.0 than those upon the addition of the activating enzyme and can be fine-tuned by changing the generation of bis-MPA dendrons. The combination of enzyme and pH dual stimuli results in significantly accelerated and more complete release of the loaded hydrophobic guests. The cell viability assay confirmed the favorable biocompatibility until the LDBC micelle concentration reached 800 µg mL-1. These results indicate that the LDBCs can be considered as a good candidate for targeting drug delivery.

Photothermal Propelling and Pyroelectric Potential-Promoted Cell Internalization of Janus Nanoparticles and Pyroelectrodynamic Tumor Therapy.

Cancer phototherapy experiences limitations in tissue diffusion and cell internalization of phototherapeutic agents and dose-dependent side effects. Herein, Janus pyroelectric nanoparticles (NPs) are designed to generate self-powered motion and built-in electric fields to overcome the delivery barriers. Polydopamine (PDA) layers are partially coated on tetragonal BaTiO3 (tBT) NPs to prepare Janus tBT@PDA, and Au NPs are deposited on the PDA caps to obtain Janus tBT@PDA-Au NPs. Near-infrared (NIR) illumination of tBT@PDA-Au builds in situ pyroelectric potentials on NPs, which selectively affect the membrane potential of tumor cells rather than normal cells to enhance tumor cell internalization and produce reactive oxygen species (ROS) for pyroelectric dynamic therapy (PEDT). The asymmetric photothermal effect of the Janus NPs creates thermophoretic force to propel NP motion, which enhances tumor diffusion and cellular uptake of NPs and boosts cytotoxicity and intracellular ROS levels. The inoculation of Au NPs increases the photothermal effect, exhibits larger motion velocities, produces higher pyroelectric potentials, and elevates cellular uptake rates, resulting in significant induction of tumor cell apoptosis, suppression of tumor growth, and extension of animal survival. Thus, the concise design of tBT@PDA-Au/NIR treatment has achieved thermophoretic motion-promoted tissue diffusion, built-in electric field-enhanced cell internalization, and photothermal/PEDT-synergized antitumor efficacy.

Pyroelectric Janus nanomotors for synergistic electrodynamic-photothermal-antibiotic therapies of bacterial infections.

Antibacterial electrotherapy is currently activated by external electric field or self-powered generators, but usually needs complicated power management circuits. Herein, near-infrared illumination (NIR) of pyroelectric nanoparticles (NPs) produces a built-in electric field to address the effectiveness and safety concerns in the antibacterial treatment. Janus tBT@PDA NPs were obtained by capping polydopamine (PDA) on tetragonal BaTiO3 (tBT) NPs through defining the polymerization time, followed by ciprofloxacin (CIP) loading on the PDA caps to fabricate Janus tBT@PDA-Cip NPs. NIR illumination of PDA caps creates temperature variations on tBT NPs to generate photothermal and pyroelectric effects. Finite element simulation reveals a pyroelectric potential of over 1 V and sufficient reactive oxygen species (ROS) are produced to exhibit pyroelectric dynamic therapy (PEDT). The elevated temperature on one side of the Janus NPs produces thermophoretic force to drive NP motion, which enhances interactions with bacteria and overcomes limitations in the short action distance and lifespan of ROS. The pyroelectric field accelerates CIP release through weakening the π-π stacking and electrostatic interaction with PDA and also interrupts membrane potentials of bacteria to enhance CIP invasion into bacteria. The synergistic antibacterial effect of pyroelectric tBT@PDA-Cip NPs causes the fully recovery of S. aureus-infected skin wounds and regeneration of intact epidermis, blood vessels and hair follicles, while no obvious pathological change or inflammatory lesion is detected in the major organs. Thus, the pyroelectric Janus nanomotors demonstrate synergistic PEDT/photothermal/antibiotic effects to enhance antibacterial efficacy while avoiding the necessity of excessive heat, ROS and antibiotic doses. STATEMENT OF SIGNIFICANCE: Antibacterial treatment is challenged by antibiotics-derived side effects and the evolution of resistant strains. Phototherapy is commonly associated with excessive heat and oxidative stress, and their combinations with other agents are especially encouraged to strengthen antibacterial efficacy while alleviating the associated side effects. Electric field is another activator to generate antibacterial abilities, but usually requires complicated power management and bulk electrodes, making it inconvenient in a biological setup. To address these challenges, we propose a strategy to generate microelectric field on nanoparticles themselves and achieve synergistic electrodynamic-photothermal-antibiotic therapies. The pyroelectric effect weakens interactions between nanoparticles and antibiotics to accelerate drug release, and the built-in pyroelectric field increases membrane fluidity to enhance bacterial uptake of antibiotics.

Light-triggered theranostic hydrogels for real-time imaging and on-demand photodynamic therapy of skin abscesses.

The management of wound infection remains the major challenges in real-time diagnosis, effective bacterial elimination and rapid wound healing. Herein, we developed injectable theranostic hydrogels to achieve long-term visual imaging of infected wounds and possible infection recurrence and to launch an on-demand bactericidal effect without using any antibiotics. Antimicrobial peptide ε-polylysine (ePL)-derived hydrogels were prepared through the copolymerization of methacrylated ePL (mPL) and the conjugates with tetrakis(4-carboxyphenyl) porphyrin (mPL-TCPP) and phenol red (mPL-Pr). Light illumination of mPL-TCPP produces reactive oxidative species (ROS) to initiate free radical crosslinking into PL@Pr-TCPP hydrogels without using any additional photoinitiators and concurrently exhibits antibacterial photodynamic therapy (PDT). PL@Pr-TCPP hydrogels experience quick color changes from yellow to orange and finally to red when pH values change from 5.0 to 9.0. The actual pH and related bacterial levels in the wounds could be read from G/B signal ratios of hydrogel colors captured by a smart phone. The conjugation of phenol red and TCPP into hydrogels affords a robust bacterial infection diagnosis and persistent bactericidal effect after cycled light illumination. The bacterial capture by ePL hydrogels strengthens PDT effect through alleviating the short lifetime and action distance of ROS. On a Staphylococcus aureus-infected abscess model, light illumination of the pregel solutions achieves in situ formation of hydrogel dressings. The synergistic bactericidal performance significantly relieves inflammatory status, accelerates collagen deposition, and promotes neovascularization, leading to full recovery of the infected wounds with regeneration of skin accessories. PL@Pr-TCPP hydrogels on the wound bed show color changes upon the recurrence of bacterial infection, which could also be totally eliminated after light illumination. Therefore, this study demonstrates a feasible strategy to develop theranostic hydrogel dressings for life-cycle diagnosis and on-demand treatment of wound infections. STATEMENT OF SIGNIFICANCE: Over 30% of skin and soft tissue infections become chronic even after appropriate antibacterial treatment, and recurrent infections are commonly reported after initial infection. Challenges remain in the development of theranostic wound dressings having the capability of point-of-care diagnosis, life-cycle monitoring and on-demand elimination of bacterial infection. Herein, light-triggered gelation is used to develop theranostic hydrogels for reversible naked-eye diagnosis and on-demand photodynamic therapy of wound infections. Light illumination plays a "one-stone-two-birds" role, i.e., photodynamically produced reactive oxidative species enable bactericidal effect without using any antibiotics, and the generated free radicals initiate crosslinking of hydrogels without using any additional photoinitiators. Bacterial infection-activated color changes of hydrogels could be captured with a smart phone for on-site and persistent monitoring of bacterial infection and wound healing process.

Nitric oxide-propelled nanomotors for bacterial biofilm elimination and endotoxin removal to treat infected burn wounds.

Biofilm infection is regarded as a major contributing factor to the failure of burn treatment and a persistent inflammatory state delays healing and leads to the formation of chronic wounds. Herein, self-propelled nanomotors (NMs) are proposed to enhance biofilm infiltration, bacterial destruction, and endotoxin clearance to accelerate the healing of infected burn wounds. Janus nanoparticles (NPs) were prepared through partially coating Fe3O4 NPs with polydopamine (PDA) layers, and then polymyxin B (PMB) and thiolated nitric oxide (SNO) donors were separately grafted onto the Janus NPs to obtain IO@PMB-SNO NMs. In response to elevated glutathione (GSH) levels in biofilms, NO generation from one side of the Janus NPs leads to self-propelled motion and deep infiltration into biofilms. The local release of NO could destroy bacteria inside the biofilm, which provides a non-antibiotic antibiofilm approach without the development of drug resistance. In addition to intrinsic antibacterial effects, the PMB grafts preferentially bind with bacteria and the active motion enhances lipopolysaccharide (LPS) clearance and then significantly attenuates the production of inflammatory cytokines and reactive oxide species by macrophages. Partial-thickness burn wounds were established on mice and infected with P. aeruginosa, and NM treatment almost fully destroyed the bacteria in the wounds. IO@PMB-SNO NMs absorb LPS and remove it from the wounds under a magnetic field, which downregulates the interleukin-6 and tumor necrosis factor-α levels in tissues. The infected wounds were completely healed with the deposition and arrangement of collagen fibers and the generation of skin features similar to those of normal skin. Thus, IO@PMB-SNO NMs achieved multiple-mode effects, including GSH-triggered NO release and self-propelled motion, the NO-induced non-antibiotic elimination of biofilms and bacteria, and PMB-induced endotoxin removal. This study offers a feasible strategy, with integrated antibiofilm and anti-inflammatory effects, for accelerating the healing of infected burn wounds.

Photoactivated Release of Nitric Oxide and Antimicrobial Peptide Derivatives for Synergistic Therapy of Bacterial Skin Abscesses.

It is of paramount importance to develop novel approaches for combating bacterial resistance and the integration of different antibacterial mechanisms is essential to achieve synergistic bactericidal efficiency while reducing the associated side effects. Herein, amphiphilic antimicrobial copolymers derived from poly-l-lysine (PLL), black phosphorus quantum dots (BPQDs) as near-infrared (NIR) sensitizer, and S-nitrosocysteamine (SNO) as nitric oxide (NO) donor, are assembled into PELI@BPQD-SNO nanoparticles through electrostatic interactions. Amphiphilic copolymers with isopentanyl grafts on PLL at a ratio of 50% achieve an optimal balance between antibacterial activity and hemolysis rate. Photothermal effect of BPQDs leads to NIR-responsive release of NO and the combination with amphiphilic copolymers mutually enhances long-term inhibition of bacterial growth. In an S. aureus-infected subcutaneous abscess model, the bactericidal rate of PELI@BPQD-SNO/NIR treatment reaches nearly 99.6%, which is significantly higher than those without NO release (38%) or amphiphilic copolymers (24%) or NIR irradiation (17%). PELI@BPQD-SNO/NIR treatment shows full recovery of infected wounds, efficient retardation of inflammatory cells, and reconstruction of blood vessels similar to those of healthy skin. Therefore, the electrostatic assembly demonstrates a promising strategy to deliver charged therapeutic agents and the photoactivated release of NO and amphiphilic copolymers achieves synergistic antibacterial efficacy without using any antibiotics.

Self-Assembly and Enzyme Responsiveness of Amphiphilic Linear-Dendritic Block Copolymers Based on Poly(N-vinylpyrrolidone) and Dendritic Phenylalanyl-lysine Dipeptides.

In this study, we present the synthesis, self-assembly, and enzyme responsive nature of a unique class of well-defined amphiphilic linear-dendritic block copolymers (PNVP-b-dendr(Phe-Lys)n, n = 1-3) based on linear poly(N-vinylpyrrolidone) (PNVP) and dendritic phenylalanyl-lysine (Phe-Lys) dipeptides. The copolymers were prepared via a combination ofreversible addition-fragmentation chain transfer (RAFT) /xanthates (MADIX) polymerization of N-vinylpyrrolidone and stepwise peptide chemistry. The results of fluorescence spectroscopy, 1H NMR analyses, transmission electron microscopy (TEM), and particle size analysis demonstrated that the copolymers self-assemble in aqueous solution into micellar nanocontainers that can disassemble and release encapsulated anticancer drug doxorubicin or hydrophobic dye Nile red by trigger of a serine protease trypsin under physiological conditions. The disassembly of the formed micelles and release rates of the drug or dye can be adjusted by changing the generation of dendrons in PNVP-b-dendr(Phe-Lys)n. Furthermore, the cytocompatibility of the copolymers have been confirmed using human lung epithelial cells (BEAS-2B) and human liver cancer cells (SMMC-7721). Due to the fact of their enzyme responsive properties and good biocompatibility, the copolymers may have potential applicability in smart controlled release systems capable of site-specific response.