Dual pH-Responsive Polymer Nanogels with a Core-Shell Structure for Improved Cell Association

Nanomedicine Strategies in Conquering and Utilizing the Cancer Hypoxia Environment

Cancer with a complex pathological process is a major disease to human welfare. Due to the imbalance between oxygen (O2) supply and consumption, hypoxia is a natural characteristic of most solid tumors and an important obstacle for cancer therapy, which is closely related to tumor proliferation, metastasis, and invasion. Various strategies to exploit the feature of tumor hypoxia have been developed in the past decade, which can be used to alleviate tumor hypoxia, or utilize the hypoxia for targeted delivery and diagnostic imaging. The strategies to alleviate tumor hypoxia include delivering O2, in situ O2 generation, reprogramming the tumor vascular system, decreasing O2 consumption, and inhibiting HIF-1 related pathways. On the other side, hypoxia can also be utilized for hypoxia-responsive chemical construction and hypoxia-active prodrug-based strategies. Taking advantage of hypoxia in the tumor region, a number of methods have been applied to identify and keep track of changes in tumor hypoxia. Herein, we thoroughly review the recent progress of nanomedicine strategies in both conquering and utilizing hypoxia to combat cancer and put forward the prospect of emerging nanomaterials for future clinical transformation, which hopes to provide perspectives in nanomaterials design.

Multiple strategies to control the hydrophilic-hydrophobic balance of P(DMA-co-DMAEMA-co-QDMAEMA) coatings

The regulation of the hydrophilic-hydrophobic balance of polymers has an important influence not only on their aggregation behavior in aqueous solution, but also on their adhesion properties on the surface of substrates and the applications of the modified surfaces. Based on this, a random copolymer poly(dopamine methacrylamide-co-2-(dimethylamino)ethyl methacrylate) (P(DMA-co-DMAEMA)) was synthesized as a starting polymer to generate P(DMA-co-DMAEMA-co-QDMAEMA) (PDDQ) derivatives by a programmable quaternization of the DMAEMA precursor. By adjusting the pH or temperature, both the aggregation behavior in aqueous solutions and the surface adhesive behavior on the substrate surfaces of PDDQ copolymers were regulated due to the hydrophilic-hydrophobic balance. Specifically, the surface adsorption of PDDQ copolymers on surfaces was enhanced by the increased hydrophobicity of PDDQ. Stainless steel meshes (SSM) modified with the PDDQ0 copolymer without quaternization showed a superoleophobicity in acidic aqueous media, which endowed it with improved oil-water separation performance. In addition, the hydrophilic-hydrophobic balance of PDDQs and their coatings could also be tuned by changing the ratio of DMAEMA to QDMAEMA in the copolymer. From PDDQ0 to PDDQ100, by increasing the hydrophilic QDMAEMA component of PDDQ copolymers, anti-protein properties and oil/water separation efficiency of the modified surfaces were also enhanced gradually. The results provided a reference for designing P(DMA-co-DMAEMA-co-QDMAEMA) coatings in different application environments.

Dual-reactive nanogels for orthogonal functionalization of hydrophilic shell and amphiphilic network

Amphiphilic nanogels (NGs) combine a soft, water-swollen hydrogel matrix with internal hydrophobic domains. While these domains can encapsulate hydrophobic cargoes, the amphiphilic particle surface can reduce colloidal stability and/or limit biological half-life. Therefore, a functional hydrophilic shell is needed to shield the amphiphilic network and tune interactions with biological systems. To adjust core and shell properties independently, we developed a synthetic strategy that uses preformed dual-reactive nanogels. In a first step, emulsion copolymerization of pentafluorophenyl methacrylate (PFPMA) and a reduction-cleavable crosslinker produced precursor particles for subsequent network modification. Orthogonal shell reactivity was installed by using an amphiphilic block copolymer (BCP) surfactant during this particle preparation step. Here, the hydrophilic block poly(polyethylene glycol methyl ether methacrylate) (PPEGMA) contains a reactive alkyne end group for successive functionalization. The hydrophobic block (P(PFPMA-co-MAPMA) contains random methacryl-amido propyl methacrylamide (MAPMA) units to covalently attach the surfactant to the growing PPFPMA network. In the second step, orthogonal modification of the core and shell was demonstrated. Network functionalization with combinations of hydrophilic (acidic, neutral, or basic) and hydrophobic (cholesterol) groups gave a library of pH- and redox-sensitive amphiphilic NGs. Stimuli-responsive properties were demonstrated by pH-dependent swelling and reduction-induced degradation via dynamic light scattering. Subsequently, copper-catalyzed azide-alkyne cycloaddition was used to attach azide-modified rhodamine as model compound to the shell (followed by UV-Vis). Overall, this strategy provides a versatile platform to develop multi-functional amphiphilic nanogels as carriers for hydrophobic cargoes.

MoO3-x nanosheets-based platform for single NIR laser induced efficient PDT/PTT of cancer

Traditional combination therapy of photodynamic therapy (PDT) and photothermal therapy (PTT) is limited in the field of clinical cancer therapy due to activation by light with separate wavelengths, insufficient O₂ supply, antioxidant ability of glutathione (GSH) in tumor cell, and low penetration depth of light. Here, a multifunctional nanoplatform composed of MoO_3-x nanosheets, Ag nanocubes, and MnO₂ nanoparticles was developed to overcome these drawbacks. For this nanoplatform, hyperthermia and reactive oxygen species (ROS) were simultaneously generated under single 808 nm near-infrared (NIR) light irradiation. Once this nanoplatform accumulated in the tumor region, GSH was depleted by MnO₂ and intracellular H₂O₂ was catalyzed by MnO₂ to produce O₂ to relieve hypoxia. Ultrasound (US) imaging confirmed in-situ O₂ generation. Magnetic resonance (MR) imaging, photoacoustic (PA) imaging, and fluorescence imaging were used to monitor in vivo biodistribution of nanomaterials. This provides a paradigm to rationally design a single NIR laser induced multimodal imaging-guided efficient PDT/PTT cancer strategy.

Correlation of Secondary Particle Number with the Debye-Hückel Parameter for Thickening Mesoporous Silica Shells Formed on Spherical Cores

Mesoporous silica shells were formed on nonporous spherical silica cores during the sol-gel reaction to elucidate the mechanism for the generation of secondary particles that disturb the efficient growth of mesoporous shells on the cores. Sodium bromide (NaBr) was used as a typical electrolyte for the sol-gel reaction to increase the ionic strength of the reactant solution, which effectively suppressed the generation of secondary particles during the reaction wherein a uniform mesoporous shell was formed on the spherical core. The number of secondary particles (N _2nd) generated at an ethanol/water weight ratio of 0.53 was plotted against the Debye-Hückel parameter κ to quantitatively understand the Debye screening effect on secondary particle generation. Parameter κa, where a is the average radius of the secondary particles finally obtained in the silica coating, expresses the trend in N _2nd at different concentrations of ammonia and NaBr. N _2nd was much lower than that expected theoretically from the variation of secondary particle sizes at a constant Debye-Hückel parameter. A similar correlation with κa was observed at the high and low ethanol/water weight ratios of 0.63 and 0.53, respectively, with different hydrolysis rate constants. The good correlation between N _2nd and κa revealed that controlling the ionic strength of the silica coating is an effective approach to suppress the generation of secondary particles for designing mesoporous shells with thicknesses appropriate for their application as high-performance liquid chromatography column packing materials.

Amphiphilic Triblock Copolymer Prodrug for Tumor-Specific pH/Reduction Dual-Triggered Drug Delivery: Effect of Self-Assembly Behaviors

Diblock copolymer-based prodrugs have been widely designed for tumor treatment after self-assembly; however, premature drug leakage could not be ignored because their hydrophobic prodrug cores were directly exposed to the media. Here, an amphiphilic triblock copolymer prodrug with a hydrophilic PEG block, a pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) block, and a hydrophobic reduction-cleavable prodrug block was synthesized for tumor-specific pH/reduction dual-triggered drug delivery, via the successive RAFT polymerization of DPA and a DOX-based monomer (MAL-DOX) with a PEG-based macro-CTA. The core-shell and core-shell-corona nanoparticles could be obtained by one-step and two-step self-assembly. With the pH-sensitive gatekeeper formed by the PDPA block, the core-shell-corona nanoparticles possessed a smaller diameter with narrow distribution and better drug release with lower drug leakage. MTT assays demonstrated the selective cytotoxicity of the core-shell-corona nanoparticles to the cancer cells was dose-dependent because of the reduction-cleavable prodrug. The negligible drug leakage and selective cytotoxicity to cancer cells endow the proposed core-shell-corona prodrug nanoparticles with promising potential for tumor treatment without toxic side effects on the normal cells.

Polypeptide Nanoparticles with pH-Sheddable PEGylation for Improved Drug Delivery

The variation of tumor microenvironments provides a tool for the construction of stimulus-responsive nanomedicines to enhance drug delivery efficacy. Herein, the assembly of drug-loaded polypeptide nanoparticles (NPs) with pH-sheddable modification of poly(ethylene glycol) (PEG) is prepared to enhance therapeutic efficiency. Poly(l-lysine) and poly(l-glutamic acid) were self-assembled to fabricate polypeptide NPs by electrostatic interactions, followed by PEGylation based on amidation reaction. The NP sizes can be controlled by tuning the molecular weight or the ratio of polypeptides. The PEG coating is cleavable at the tumor acid microenvironment to reverse the surface charge and reduce the NP size, which effectively enhances cell uptake. In addition, the presence of reducing reagent (e.g., glutathione) in cancer cells induces the drug (i.e., cisplatin) release from the polypeptide NPs and subsequently results in the cell toxicity. This reported method highlights the engineering of transformable polypeptide drug carriers, which provides a promising way for enhanced drug delivery efficacy.

Protonation-Activity Relationship of Bioinspired Ionizable Glycomimetics for the Growth Inhibition of Bacteria

Variations in physiological parameters (i.e., pH, redox potential, and ions) for distinct types of diseases make them attractive targets. Ionizable groups capable of pH-dependent charge conversion impart pH-switchable materials under acid condition through the protonation effect, which stimulates the emergence of various pH-inspired materials. However, it is confusing to distinguish preferable groups for high-efficiency drug-delivery vehicles attributing to the lack of perceiving the relationship between protonation and activity. Herein, we developed a series of bioinspired ionizable glycomimetics responses to the ambient variation from physiological environment (pH 7.4) to bacterial infectious acidic microenvironment (pH 6.0) to explore the protonation-activity relationship of various ionizable groups. The nanoparticles are coated with bacterial adhesion molecules galactose and fucose to target Pseudomonas aeruginosa. Moreover, the particle cores were composed of ionizable polymers responding to acidic microenvironment changes and entrapped antibiotic payload. Ionizable glyconanoparticles targeted bacteria and local cues as triggers to transfer payloads in on-demand patterns for the inhibition of bacteria-related infection. Significantly, we find that the nanoparticles with the pH-sensitive block of ionizable poly(2-(diisopropylamino)ethyl methacrylate) (pDPA) exhibit predominant bacterial adhesion and killing and growth inhibition of biofilm in acid environment (pH 6.0) due to the ionizable polymer protonation effect with more positive charge cooperated with the lectin-targeted effect of polysaccharide causing a huge bacterial aggregation and a highly favorable germicidal effect. The nanoparticles with poly(2-(hexamethyleneimino)ethyl methacrylate) (pHMEMA) have suboptimal antibacterial activity but advanced protonation at pH 6.3 compared to pDPA at 6.1, suggesting its selection as an applicable pH-switchable group for a slightly higher acid microenvironment like tumor (pH 6.9-6.5) because of the efficient performance after protonation than at deprotonation. On the other hand, the glycomimetic containing poly(2-(dibutylamino)ethyl methacrylate) (pDBA) as a pH-sensitive moiety displayed weak antimicrobial activity and superior stability before protonation (pH 4.7), which make it possible to prevent premature drug leakage, suggesting that pDBA is a good candidate to be applied to construct pH-sensitive drug-delivery carriers for the treatment of bacteria-related infection with a low acidic microenvironment. Overall, the structure-activity relationship of ionizable glycomimetics for the inhibition of bacteria signifies not only the development of a drug-delivery system but also the mechanism-dependent treatment of nanomedicine for infectious diseases.