Non-covalent interactions in controlling pH-responsive behaviors of self-assembled nanosystems

Which Lipid Nanoparticle (LNP) Designs Work? A Simple Kinetic Model Linking LNP Chemical Structure to In Vivo Delivery Performance

Although lipid nanoparticles (LNPs) are the predominant nanocarriers for short-interfering RNA (siRNA) delivery, most therapies use nearly identical formulations that have taken 30 years to design but lack the diverse property ranges necessary for versatile application. This dearth in variety and the extended timeline for implementation are attributed to a limited understanding of how LNP properties facilitate overcoming biological barriers. Herein, a simple kinetic model was developed by using major rate-limiting steps for siRNA delivery, and this model enabled the identification of a critical parameter to predict LNP efficacy without extensive experimental testing. A volume-averaged log D, the "solubility" of charged molecules as a function of pH weighted by component volume fractions, resulted in a good correlation between LNP composition and siRNA delivery. Both the effects of modifying the structures of ionizable lipids and LNP composition on gene silencing were easily captured in the model predictions. Thus, this approach provides a robust LNP structure-activity relationship to dramatically accelerate the realization of effective LNP formulations.

In Situ Interfacial Polymerized Arginine-Doped Polydopamine Thin-Film Nanocomposite Membranes for High-Separation and Antifouling Reverse Osmosis

In this work, we synthesized polydopamine nanoparticles (PDNPs-M, M = I, II, III, and IV) with uniform particle sizes but varying l-arginine (Arg) contents (0%, 0.53%, 3.73%, and 6.62%) through a one-pot synthesis approach. Thin-film nanocomposite (TFN) membranes were fabricated via in situ interfacial polymerization (IP). The effects of the PDNPs-M chemical structure on the IP process and the consequent impacts on the structure and properties of the polyamide (PA) selective layer were investigated. The hydrophilicity and dispersibility of PDNPs-M exhibited an upward trend with the Arg content. Furthermore, Arg doping contributes to a denser and smoother PA layer. Among the TFC and TFN membranes, TFN-PDNPs-IV exhibited a water permeability of 3.89 L·m-2·h-1·bar-1 (55.1% higher than that of TFC-0) with a NaCl rejection rate of 98.8%, signifying superior water/salt selectivity. Additionally, TFN-PDNPs-IV exhibited regular pressure stability, commendable acid/alkali stability, and enhanced antifouling properties. These findings highlight the significant impact of nanoparticle hydrophilic functional groups on the structural and functional attributes of TFN membranes, offering a promising approach for developing advanced reverse osmosis membranes.

Elucidation of Protonation Cooperativity of a STING-Activating Polymer

Stimuli-responsive nanomaterials have the potential to improve the performance and overcome existing barriers of conventional nanotherapeutics. Molecular cooperativity design in stimuli-responsive nanomedicine can amplify physiological signals, enabling a cooperative response for improved diagnostic and therapeutic precision. Previously, this work reported an ultra-pH-sensitive polymer, PEG-b-PC7A, that possesses innate immune activating properties by binding to the stimulator of interferon genes (STING) through polyvalent phase condensation. This interaction enhances STING activation and synergizes with the endogenous STING ligand for robust cancer immunotherapy. Despite its successes in innate immune activation, the fundamental physicochemical and pH-responsive properties of PC7A require further investigation. Here, this study elucidates the protonation cooperativity driven by the phase transition of PC7A copolymer. The highly cooperative system displays an "all-or-nothing" proton distribution between highly charged unimer (all) and neutral micelle (nothing) states without gradually protonated intermediates. The binary protonation behavior is further illustrated in pH-precision-controlled release of a representative anticancer drug, β-lapachone, by PC7A micelles over a noncooperative PE5A polymer. Furthermore, the bimodal distribution of protons is represented by a high Hill coefficient (nH  > 9), featuring strong positive cooperativity. This study highlights the nanoscale pH cooperativity of an immune activating polymer, providing insights into the physicochemical characterization and design parameters for future nanotherapeutics development.

Charge Regulation of Poly(acrylic acid) in Solutions of Non-Charged Polymer and Colloids

Weak polyelectrolytes (WPEs) are responsive materials used as active charge regulators in a variety of applications, including controlled release and drug delivery in crowded bio-related and synthetic environments. In these environments, high concentrations of solvated molecules, nanostructures, and molecular assemblies are ubiquitous. Here, we investigated the effect of high concentrations of non-adsorbing, short chains of poly(vinyl alcohol), PVA, and colloids dispersed by the very same polymers on charge regulation (CR) of poly(acrylic acid), PAA. PVA does not interact with PAA (throughout the full pH range) and thus can be used to examine the role of non-specific (entropic) interactions in polymer-rich environments. Titration experiments of PAA (mainly 100 kDa in dilute solutions, no added salt) were carried out in high concentrations of PVA (13-23 kDa, 5-15 wt%) and dispersions of carbon black (CB) decorated by the same PVA (CB-PVA, 0.2-1 wt%). The calculated equilibrium constant (and pKa) was up-shifted in PVA solutions by up to ~0.9 units and down-shifted in CB-PVA dispersions by ~0.4 units. Thus, while solvated PVA chains increase the charging of the PAA chains, as compared to PAA in water, CB-PVA particles reduce PAA charging. To investigate the origins of the effect, we analyzed the mixtures using small-angle X-ray scattering (SAXS) and cryo-TEM imaging. The scattering experiments revealed re-organization of the PAA chains in the presence of the solvated PVA but not in the CB-PVA dispersions. These observations clearly indicate that the acid-base equilibrium and the degree of ionization of PAA in crowded liquid environments is affected by the concentration, size, and geometry of seemingly non-interacting additives, probably due to depletion and excluded volume interactions. Thus, entropic effects that do not depend on specific interactions should be taken into consideration when designing functional materials in complex fluid environments.

Cooperative transitions involving hydrophobic polyelectrolytes

Hydrophobic polyelectrolytes (HPEs) can solubilize bilayer membranes, form micelles, or can reversibly aggregate as a function of pH. The transitions are often remarkably sharp. We show that these cooperative transitions occur by a competition between two or more conformational states and can be explained within the framework of Monod-Wymann-Changeux (MWC) theory that was originally formulated for allosteric interactions. Here, we focus on the pH-dependent destabilization and permeation of bilayer membranes by HPEs. We formulate the general conditions that lead to sharp conformational transitions involving simple macromolecules mediated by concentration variations of molecular ligands. That opens up potential applications ranging from medicine to the development of switchable materials.

Effects of Non-Ionic Micelles on the Acid-Base Equilibria of a Weak Polyelectrolyte

Weak polyelectrolytes (WPEs) are widely used as pH-responsive materials, pH modulators and charge regulators in biomedical and technological applications that involve multi-component fluid environments. In these complex fluids, coupling between (often weak) interactions induced by micelles, nanoparticles and molecular aggregates modify the pKa as compared to that measured in single component solutions. Here we investigated the effect of coupling between hydrogen bonding and excluded volume interactions on the titration curves and pKa of polyacrylic acid (PAA) in solutions comprising PEO-based micelles (Pluronics and Brij-S20) of different size and volume fraction. Titration experiments of dilute, salt-free solutions of PAA (5 kDa, 30 kDa and 100 kDa) at low degree of polymer ionization (α < 0.25) drive spatial re-organization of the system, reduce the degree of ionization and consequentially increase the pKa by up to ~0.7 units. These findings indicate that the actual degree of ionization of WPEs measured in complex fluids is significantly lower (at a given pH) than that measured in single-component solutions.

Phase Separation of Aqueous Poly(diisopropylaminoethyl methacrylate) upon Heating

Poly(diisopropylaminoethyl methacrylate) (PDPA) is a pH- and thermally responsive water-soluble polymer. This study deepens the understanding of its phase separation behavior upon heating. Phase separation upon heating was investigated in salt solutions of varying pH and ionic strength. The effect of the counterion on the phase transition upon heating is clearly demonstrated for chloride-, phosphate-, and citrate-anions. Phase separation did not occur in pure water. The buffer solutions exhibited similar cloud points, but phase separation occurred in different pH ranges and with different mechanisms. The solution behavior of a block copolymer comprising poly(dimethylaminoethyl methacrylate) (PDMAEMA) and PDPA was investigated. Since the PDMAEMA and PDPA blocks phase separate within different pH- and temperature ranges, the block copolymer forms micelle-like structures at high temperature or pH.

Reversible photonic hydrogel sensors via holographic interference lithography

Continuous monitoring of physiological conditions and biomarkers via optical holographic sensors is an area of growing interest to facilitate the expansion of personalised medicine. Here, a facile laser-induced dual polymerization method is developed to fabricate holographic hydrogel sensors for the continuous and reversible colorimetric determination of pH variations over a physiological range in serum (pH 7-9). Readout parameters simulated through a Finite-difference time-domain Yee's algorithm retrieve the spectral response through expansion. Laser lithography of holographic hydrogel sensor fabrication is achieved via a single 355 nm laser pulse to initiate polymerization of ultrafine hydrogel fringes. Eliminating the requirement for complex processing of toxic components and streamlining the synthetic procedure provides a simpler route to mass production. Optimised pH-responsive hydrogels contain amine bearing functional co-monomers demonstrating reversible Bragg wavelength shifts of 172 nm across the entire visible wavelength range with pH variation from 7.0 to 9.0 upon illumination with broadband light. Photolithographic recording of information shows the ability to convey detailed information to users for qualitative identification of pH. Holographic sensor reversibility over 20 cycles showed minimal variation in replay wavelength supporting reliable and consistent readout, with optimised sensors showing rapid response times of <5 min. The developed sensors demonstrate the application to continuous monitoring in biological fluids, withstanding interference from electrolytes, saccharides, and proteins colorimetrically identifying bovine serum pH over a physiological range. The holographic sensors benefit point-of-care pH analysis of biological analytes which could be applied to the identification of blood gas disorders and wound regeneration monitoring through colorimetric readouts.

Modulating Boronic Ester Stability in Block Copolymer Micelles via the Neighbor Effect of Copolymerized Tertiary Amines for Controlled Release of Polyphenolic Drugs

The traceless and pH-sensitive properties of boronic esters are attractive for the synthesis of polymer-drug conjugates, but current platforms suffer from both low stability under physiologically relevant conditions and synthetically demanding optimization to tune drug release profiles. We hypothesized that the high catechol affinity and stability of Wulff-type boronic acids could be mimicked by copolymerization of phenyl boronic acid with a tertiary amine and subsequent micellization. This strategy yielded a versatile platform for the preparation of reversible polymer-drug conjugates, which more than doubled the oxidative stability of encapsulated polyphenolic drug cargo at physiologically relevant pH and enabled simple and incremental tuning of drug release kinetics. Moreover, we validated, with ¹⁹F NMR, that these copolymers exhibit uniquely high catechol affinity that could not be replicated by combinations of similarly functionalized small molecules. Overall, this report demonstrates that copolymerization of boronic acid and tertiary amine monomers is a powerful and modular approach to improving boronic ester chemistry for drug delivery applications.

Carrier-Free Small Molecular Self-Assembly Based on Berberine and Curcumin Incorporated in Submicron Particles for Improving Antimicrobial Activity

Nanocarrier-based pesticide formulations have been severely restricted in agriculture practices due to their high-cost preparation process, poor loading capacity, and toxicity issues. To overcome these issues, carrier-free small molecular self-assembled submicron particles (SMPs) with an improved photoactivated antimicrobial activity based on two natural microbicides berberine hydrochloride (BBR) and curcumin (CM) are constructed by noncovalent interactions through a simple and fast preparation process (solvent exchange method) without using any adjuvant. The results show that the optimized molar ratio of BBR to CM is 2:1 at pH 5 and 25 °C in an aqueous solution for the formation of B-C SMPs. The obtained B-C SMPs exhibit excellent physicochemical properties, such as uniform morphology (407 nm), low polydispersity index (0.283), and strong ζ-potential (+24.4 mV). The antibacterial activities of B-C SMPs against Pseudomonas syringae pv. lachrymans, Clavibater michiganensis subsp. Michiganensis, and Sclerotinia sclerotiorum are 4, 2, and 1.5 times that of B + C MIX, respectively, suggesting a synergistic antimicrobial activity based on BBR and CM incorporation in the submicron particles. The genotoxicity evaluation results show that the self-assembled B-C SMPs are harmless to plant cells. Therefore, due to rational utilization of natural resources (natural microbicides, sunlight, and oxygen), carrier-free small molecular self-assembled B-C SMPs with synergistic photoactivated antimicrobial activity developed by a simple and fast preparation process would have great potential for sustainable plant disease management.

Core Role of Hydrophobic Core of Polymeric Nanomicelle in Endosomal Escape of siRNA

Efficient endosomal escape is the most essential but challenging issue for siRNA drug development. Herein, a series of quaternary ammonium-based amphiphilic triblock polymers harnessing an elaborately tailored pH-sensitive hydrophobic core were synthesized and screened. Upon incubating in an endosomal pH environment (pH 6.5-6.8), mPEG₄₅-P(DPA₅₀-co-DMAEMA₅₆)-PT₅₃ (PDDT, the optimized polymer) nanomicelles (PDDT-Ms) and PDDT-Ms/siRNA polyplexes rapidly disassembled, leading to promoted cytosolic release of internalized siRNA and enhanced silencing activity evident from comprehensive analysis of the colocalization and gene silencing using a lysosomotropic agent (chloroquine) and an endosomal trafficking inhibitor (bafilomycin A1). In addition, PDDT-Ms/siPLK1 dramatically repressed tumor growth in both HepG2-xenograft and highly malignant patient-derived xenograft models. PDDT-Ms-armed siPD-L1 efficiently blocked the interaction of PD-L1 and PD-1 and restored immunological surveillance in CT-26-xenograft murine model. PDDT-Ms/siRNA exhibited ideal safety profiles in these assays. This study provides guidelines for rational design and optimization of block polymers for efficient endosomal escape of internalized siRNA and cancer therapy.

The Importance of Apparent pKa in the Development of Nanoparticles Encapsulating siRNA and mRNA

Polymer and lipid nanoparticles have been extensively used as carriers to address the biological barriers encountered in siRNA and mRNA delivery. We summarize the crucial role of nanoparticle charge and ionizability in complexing RNAs, binding to biological components, escaping from the endosome, and releasing RNAs into the cytoplasm. We highlight the significant impact of the apparent pKa of nanoparticles on their efficacy and toxicity, and the importance of optimizing pKa in the development of lead formulations for RNAs. We also discuss the feasibility of fine-tuning the pKa in nanoparticles and the applications of this approach in the optimization of delivery systems for RNAs.

pH-Sensitive Polycations for siRNA Delivery: Effect of Asymmetric Structures of Tertiary Amine Groups

pH-sensitive polyelectrolytes provide enormous opportunity for siRNA delivery. Especially, their tertiary amine structures can not only bind genes but also act as pH-sensitive hydrophobic structure to control genes release. However, the influence of molecular structures on siRNA delivery still remains elusive, especially for the asymmetric alkyl substituents of the tertiary amine groups. Herein, a library of N-methyl-N-alkyl aminoethyl methacrylate monomers (MsAM) with asymmetric alkyl substituents on the tertiary amine group is synthesized and used to prepare a series of tri-block polycationic copolymers poly(aminoethyl methacrylate)-block-poly (N-methyl-N-alkyl aminoethyl methacrylate)-block-poly(ethylene glycol methacrylate) (PAMA-PMsMA-PEG). And the properties of these polycations and their self-assembled micelles are characterized, including molecular structure, proton buffering capacity, pH-sensitivity, size, and zeta potential. With the length increase of one alkyl substituent, the proton buffering capacity of both monomers and polycations is demonstrated to be narrowed down. The siRNA delivery efficiency and cytotoxicity of these micelles are also evaluated on HepG2 cells. In particular, poly(aminoethyl methacrylate)-block-poly(N-methyl-N-ethyl aminoethyl methacrylate)-block-poly(ethylene glycol methacrylate) (PAMA-PMEMA-PEG) elicited the best luciferase knockdown efficiency and low cytotoxicity. Besides, PAMA-PMEMA-PEG/siRRM2 also induced significant anti-tumor activity in vitro. These results indicated PAMA-PMEMA-PEG has potential for further use in the design of gene vehicles with the improved efficiency of siRNA delivery.

Thermoresponsive polysaccharides with tunable thermoresponsive properties via functionalisation with alkylamide groups

Polysaccharides have been used widely in many industries, from food technology and mining to cosmetics and biomedical applications. Over recent years there has been growing interest in the development of responsive polysaccharides with unique and switchable properties, particularly systems that display lower-critical solution temperatures (LCSTs). Therefore, in this study we aimed to investigate a novel strategy that would allow the conversion of non-responsive polysaccharides into thermoresponsive polysaccharides with tuneable LCSTs. Through the functionalisation of dextran with alkylamide groups (isopropyl amide, diethyl amide, piperidinyl and diisobutyl amide) using a carbodiimide coupling approach in conjunction with amic acid derivatives, we prepared a library of novel dextrans with various degrees of substitution (DS), which were characterised via nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The alkylamide-functionalised dextrans were found to have good solubility in aqueous solutions, with the exception of those having a high DS of large hydrophobic substituents. Determination of the thermoresponsive characteristics of the polymer solutions via UV-vis spectroscopy revealed that the LCST of the alkylamide-functionalised dextrans was highly dependent on the type of alkylamide group and the DS and could be tuned over a large range (5-35 °C). Above the LCST, all of the thermoresponsive alkylamide-functionalised dextrans formed colloidal dispersions with particles sizes ranging from 400 -600 nm, as determined by dynamic light scattering (DLS). In addition, the polymers were found to exhibit a fast and reversible phase transition in solution with narrow hysteresis (∼ 1-5 °C). Finally, the injectability and biocompatibility of the novel thermoresponsive dextrans was confirmed in vivo via subcutaneous and intracranial ventricle injections, with no local or systemic toxicity noted over a 14 d period. Overall, the alkylamide-functionalised dextrans display interesting thermoresponsive properties and trends that may make them useful in biomedical applications, such as drug-delivery.

Polycarbonate-based ultra-pH sensitive nanoparticles improve therapeutic window

Stimuli-sensitive nanomaterials with cooperative response are capable of converting subtle and gradual biological variations into robust outputs to improve the precision of diagnostic or therapeutic outcomes. In this study, we report the design, synthesis and characterization of a series of degradable ultra-pH sensitive (dUPS) polymers that amplify small acidic pH changes to efficacious therapeutic outputs. A hydrolytically active polycarbonate backbone is used to construct the polymer with pH-dependent degradation kinetics. One dUPS polymer, PSC7A, can achieve activation of the stimulator of interferon genes and antigen delivery upon endosomal pH activation, leading to T cell-mediated antitumor immunity. While a non-degradable UPS polymer induces granulomatous inflammation that persists over months at the injection site, degradable PSC7A primes a transient acute inflammatory response followed by polymer degradation and complete tissue healing. The improved therapeutic window of the dUPS polymers opens up opportunities in pH-targeted drug and protein therapy.

Liposomal delivery of antibiotic loaded nucleic acid nanogels with enhanced drug loading and synergistic anti-inflammatory activity against S. aureus intracellular infections

The persistence of Staphylococcus aureus has been accredited to its ability to escape immune response via host cell invasion. Despite the efficacy of many antibiotics against S. aureus, the high extracellular concentrations of conventional antibiotics required for bactericidal activity is limited by their low cellular accumulation and poor intracellular retention. While nanocarriers have received tremendous attention for antibiotic delivery against persistent pathogens, they suffer daunting challenges such as low drug loading, poor retention and untimely release of hydrophilic cargos. Here, a hybrid system (Van_DNL) is fabricated wherein nucleic acid nanogels are caged within a liposomal vesicle for antibiotic delivery. The central principle of this approach relies on exploiting non-covalent electrostatic interactions between cationic cargos and polyanionic DNA to immobilize antibiotics and enable precise temporal release against intracellular S. aureus. In vitro characterization of Van_DNL revealed a stable homogenous formulation with circular morphology and enhanced vancomycin loading efficiency. The hybrid system significantly sustained the release of vancomycin over 24 h compared to liposomal or nanogel controls. Under enzymatic conditions relevant to S. aureus infections, lipase triggered release of vancomycin was observed from the hybrid. While using Van_DNL to treat S. aureus infected macrophages, a dose dependent reduction in intracellular bacterial load was observed over 24 h and exposure to Van_DNL for 48 h caused negligible cellular toxicity. Pre-treatment of macrophages with the antimicrobial hybrid resulted in a strong anti-inflammatory activity in synergy with vancomycin following endotoxin stimulation. Conceptually, these findings highlight these hybrids as a unique and universal platform for synergistic antimicrobial and anti-inflammatory therapy against persistent infections.

Indole-based high-performance polymeric materials with enhanced mechanical and thermal properties via cation-π interaction

The preparation of high-performance polymeric materials with both excellent overall mechanical properties and heat resistance remains a considerable challenge. Inspired by the delicate self-assembly processes in nature, a facile strategy is reported for the preparation of high-performance polymeric materials with enhanced mechanical strength and improved thermal stability. In this instance, we successfully constructed a cation- π cross-linked polyimide (Na-poly(aryl indole) imide (Na-PINI)) film with enhanced mechanical performance and heat resistance (∼490°C). This work presents an innovative design strategy for realizing robust polymeric materials with integrated strength and thermal stability; the cation- π interaction is demonstrated to be a new method that may achieve many useful properties for high-performance polymers.

Modular Fabrication of Intelligent Material-Tissue Interfaces for Bioinspired and Biomimetic Devices

One of the goals of biomaterials science is to reverse engineer aspects of human and nonhuman physiology. Similar to the body's regulatory mechanisms, such devices must transduce changes in the physiological environment or the presence of an external stimulus into a detectable or therapeutic response. This review is a comprehensive evaluation and critical analysis of the design and fabrication of environmentally responsive cell-material constructs for bioinspired machinery and biomimetic devices. In a bottom-up analysis, we begin by reviewing fundamental principles that explain materials' responses to chemical gradients, biomarkers, electromagnetic fields, light, and temperature. Strategies for fabricating highly ordered assemblies of material components at the nano to macro-scales via directed assembly, lithography, 3D printing and 4D printing are also presented. We conclude with an account of contemporary material-tissue interfaces within bioinspired and biomimetic devices for peptide delivery, cancer theranostics, biomonitoring, neuroprosthetics, soft robotics, and biological machines.

Transistor-like Ultra-pH-Sensitive Polymeric Nanoparticles

Electronic transistors have revolutionized the fields of microelectronics, computers, and mobile devices. Their ability to digitize electronic signals allows high fidelity data transfer as well as formation of logic gates. Inspired by electronic transistors, transistor-like organic materials have been under intensive investigation to amplify biological signals in a broad range of applications such as biosensing, diagnostic imaging, and therapeutic delivery. This Account highlights the inception and implementation of a "proton transistor" nanoparticle that can digitize acidotic pH signals in biological systems. Similar to electronic transistors, the ultra-pH-sensitive (UPS) nanoparticles derive their binary threshold response from phase separation phenomena. Hydrophobic micellization drives nanophase separation from unimers to aggregated polymeric micelles, which is responsible for the all-or-nothing proton distribution between the micelle and unimer states. Depending on the assembly status, conjugated fluorophores are quenched (micelle state) or freely fluoresce (solution unimer state) allowing robust detection of the phase transition behavior across a narrow pH range. Based on this mechanistic insight, we created a UPS nanoparticle library encompassing a broad physiological pH range from 4.0 to 7.4. For biological applications, we engineered a barcode-like nanosensor capable of digitizing multiple pH signals at a single organelle resolution in live cells. The barcode system allowed easy identification of mutant Kirsten rat sarcoma viral oncogene (KRAS), a common mutation involved in tumorigenesis, which leads to rapid cellular proliferation, as the protein driver for accelerated organelle acidification and lysosome catabolism in a broad set of isogenic as well as heterogeneous cancer cell lines. Adoption of the technology to an ON-OFF/Always-ON design allowed the quantification of proton flux across the membranes of endocytic organelles. For medical applications, we demonstrate the ability to achieve binary detection of solid cancers with clear tumor margin delineation by near-infrared fluorescence imaging. Image-guided resection of head/neck and breast tumors resulted in significantly improved long-term survival over white light or tumor debulking surgeries in tumor-bearing mice, catapulting the clinical evaluation of the UPS nanosensor in cancer patients. This Account serves as the first comprehensive summary of the molecular mechanism and biological applications of the digital pH threshold sensors. Building on the concept of cooperative phase transition behavior, we hope this Account will promote the rational design and development of additional transistor-like chemical sensors to digitize analog biological signals.

Peripheral Modifications of meso-Hydroxyporphyrins: Formation of π-Electronic Anions and Ion-Pairing Assemblies

Phenyl groups were introduced at the β-positions proximal to the meso-hydroxy moiety in hydroxyporphyrin Ni^II complexes by oxidized BINAP Pd^II complexes. Ion-pairing assemblies of deprotonated π-electronic anions, anionic site of which was stabilized by the introduced phenyl moieties with a bulky cation, were formed. They showed charge-by-charge assemblies, assembly modes of which were modulated by the anionic building units.

Targeting the Oncogene KRAS Mutant Pancreatic Cancer by Synergistic Blocking of Lysosomal Acidification and Rapid Drug Release

Survival of KRAS mutant pancreatic cancer is critically dependent on reprogrammed metabolism including elevated macropinocytosis, autophagy, and lysosomal degradation of proteins. Lysosomal acidification is indispensable to protein catabolism, which makes it an exploitable metabolic target for KRAS mutant pancreatic cancer. Herein we investigated ultra-pH-sensitive micelles (UPSM) with pH-specific buffering of organelle pH and rapid drug release as a promising therapy against pancreatic cancer. UPSM undergo micelle-unimer phase transition at their apparent p K_a, with dramatically increased buffer capacity in a narrow pH range (<0.3 pH). Cell studies including amino acid profiling showed that UPSM inhibited lysosomal catabolism more efficiently than conventional lysosomotropic agents ( e. g., chloroquine) and induced cell apoptosis under starved condition. Moreover, pH-triggered rapid drug release from triptolide prodrug-loaded UPSM (T-UPSM) significantly enhanced cytotoxicity over non-pH-sensitive micelles (T-NPSM). Importantly, T-UPSM demonstrated superior safety and antitumor efficacy over triptolide and T-NPSM in KRAS mutant pancreatic cancer mouse models. Our findings suggest that the ultra-pH-sensitive nanoparticles are a promising therapeutic platform to treat KRAS mutant pancreatic cancer through simultaneous lysosomal pH buffering and rapid drug release.

Enhancing the In Vitro and In Vivo Stabilities of Polymeric Nucleic Acid Delivery Nanosystems

Gene therapy holds great promise for various medical and biomedical applications. Nonviral gene delivery systems formed by cationic polymer and nucleic acids (e.g., polyplexes) have been extensively investigated for targeted gene therapy; however, their in vitro and in vivo stability is affected by both their intrinsic properties such as chemical compositions (e.g., polymer molecular weight and structure, and N/P ratio) and a number of environmental factors (e.g., shear stress during circulation in the bloodstream, interaction with the serum proteins, and physiological ionic strength). In this review, we surveyed the effects of a number of important intrinsic and environmental factors on the stability of polymeric gene delivery systems, and discussed various strategies to enhance the stability of polymeric gene delivery systems, thereby enabling efficient gene delivery into target cells. Future opportunities and challenges of polymeric nucleic acid delivery nanosystems were also briefly discussed.

Recent Development of pH-Responsive Polymers for Cancer Nanomedicine

Cancer remains a leading cause of death worldwide with more than 10 million new cases every year. Tumor-targeted nanomedicines have shown substantial improvements of the therapeutic index of anticancer agents, addressing the deficiencies of conventional chemotherapy, and have had a tremendous growth over past several decades. Due to the pathophysiological characteristics that almost all tumor tissues have lower pH in comparison to normal healthy tissues, among various tumor-targeted nanomaterials, pH-responsive polymeric materials have been one of the most prevalent approaches for cancer diagnosis and treatment. In this review, we summarized the types of pH-responsive polymers, describing their chemical structures and pH-response mechanisms; we illustrated the structure-property relationships of pH-responsive polymers and introduced the approaches to regulating their pH-responsive behaviors; we also highlighted the most representative applications of pH-responsive polymers in cancer imaging and therapy. This review article aims to provide general guidelines for the rational design of more effective pH-responsive nanomaterials for cancer diagnosis and treatment.

pH-sensitive polymer micelles provide selective and potentiated lytic capacity to venom peptides for effective intracellular delivery

Endocytosed biomacromolecule delivery systems must escape the endosomal trafficking pathway in order for their cargo to exert effects in other cellular compartments. Although endosomal release is well-recognized as one of the greatest barriers to efficacy of biologic drugs with intracellular targets, most drug carriers have relied on cationic materials that passively induce endosomal swelling and membrane rupture with low efficiency. To address the endosome release challenge, our lab has developed a diblock copolymer system for nucleic acid delivery that selectively displays a potent membrane-lytic peptide (melittin) in response to the pH drop during the endosomal maturation. To further optimize this system, we evaluated a panel of peptides with reported lytic activity in comparison to melittin. Nineteen different lytic peptides were synthesized and their membrane-lytic properties at both neutral and acidic pH characterized using a red blood cell hemolysis assay. The top five performing peptides were then conjugated to our pH-sensitive diblock copolymer via disulfide linkers and used to deliver a variety of nucleic acids to cultured mammalian cells as well as in vivo to the mouse brain. We demonstrate that the sharp pH-transition of VIPER compensates for potential advantages from pH-sensitive peptides, such that polymer-peptide conjugates with poorly selective but highly lytic peptides achieve safe and effective transfection both in vitro and in vivo. In addition, peptides that require release from polymer backbones for lysis were less effective in the VIPER system, likely due to limited endosomal reducing power of target cells. Finally, we show that certain peptides are potentiated in lytic ability by polymer conjugation and that these peptide-polymer constructs are most effective in vivo.

Endogenous pH-responsive nanoparticles with programmable size changes for targeted tumor therapy and imaging applications

Nanotechnology-based antitumor drug delivery systems, known as nanocarriers, have demonstrated their efficacy in recent years. Typically, the size of the nanocarriers is around 100 nm. It is imperative to achieve an optimum size of these nanocarriers which must be designed uniquely for each type of delivery process. For pH-responsive nanocarriers with programmable size, changes in pH (~6.5 for tumor tissue, ~5.5 for endosomes, and ~5.0 for lysosomes) may serve as an endogenous stimulus improving the safety and therapeutic efficacy of antitumor drugs. This review focuses on current advanced pH-responsive nanocarriers with programmable size changes for anticancer drug delivery. In particular, pH-responsive mechanisms for nanocarrier retention at tumor sites, size reduction for penetrating into tumor parenchyma, escaping from endo/lysosomes, and swelling or disassembly for drug release will be highlighted. Additional trends and challenges of employing these nanocarriers in future clinical applications are also addressed.

Cooperativity Principles in Self-Assembled Nanomedicine

Nanomedicine is a discipline that applies nanoscience and nanotechnology principles to the prevention, diagnosis, and treatment of human diseases. Self-assembly of molecular components is becoming a common strategy in the design and syntheses of nanomaterials for biomedical applications. In both natural and synthetic self-assembled nanostructures, molecular cooperativity is emerging as an important hallmark. In many cases, interplay of many types of noncovalent interactions leads to dynamic nanosystems with emergent properties where the whole is bigger than the sum of the parts. In this review, we provide a comprehensive analysis of the cooperativity principles in multiple self-assembled nanostructures. We discuss the molecular origin and quantitative modeling of cooperative behaviors. In selected systems, we describe the examples on how to leverage molecular cooperativity to design nanomedicine with improved diagnostic precision and therapeutic efficacy in medicine.

Facile synthesis of recyclable Zn(ii)-metallosupramolecular polymers and the visual detection of tensile strength and glass transition temperature

A series of recyclable crosslinked Zn(ii)-metallosupramolecular coordination polymers are successfully achieved, of which tensile strength and T_g could be visually detected.

Investigation of endosome and lysosome biology by ultra pH-sensitive nanoprobes

Endosomes and lysosomes play a critical role in various aspects of cell physiology such as nutrient sensing, receptor recycling, protein/lipid catabolism, and cell death. In drug delivery, endosomal release of therapeutic payloads from nanocarriers is also important in achieving efficient delivery of drugs to reach their intracellular targets. Recently, we invented a library of ultra pH-sensitive (UPS) nanoprobes with exquisite fluorescence response to subtle pH changes. The UPS nanoprobes also displayed strong pH-specific buffer effect over small molecular bases with broad pH responses (e.g., chloroquine and NH4Cl). Tunable pH transitions from 7.4 to 4.0 of UPS nanoprobes cover the entire physiological pH of endocytic organelles (e.g., early and late endosomes) and lysosomes. These unique physico-chemical properties of UPS nanoprobes allowed a 'detection and perturbation' strategy for the investigation of luminal pH in cell signaling and metabolism, which introduces a nanotechnology-enabled paradigm for the biological studies of endosomes and lysosomes.

Post-synthetic modification of polyvinyl alcohol with a series of N-alkyl-substituted carbamates towards thermo and CO2-responsive polymers

Intensive efforts have been devoted to the synthesis of thermoresponsive polymers with terminal N-alkyl-substituted groups.