pH-Responsive Polypeptide-Based Smart Nano-Carriers for Theranostic Applications

Recent Progress of pH-Responsive Peptides, Polypeptides, and Their Supramolecular Assemblies for Biomedical Applications

Peptides and polypeptides feature a variety of active functional groups on their side chains (including carboxylic acid, hydroxyl, amino, and thiol groups), enabling diverse chemical modifications. This versatility makes them highly valuable in stimuli-responsive systems. Notably, pH-responsive peptides and polypeptides, due to their ability to respond to pH changes, hold significant promise for applications in cellular pathology and tumor targeting. Extensive researches have highlighted the potentials of low pH insertion peptides (pHLIPs), peptide-drug conjugates (PDCs), and antibody-drug conjugates (ADCs) in biomedicine. Peptide self-assemblies, with their structural stability, ease of regulation, excellent biocompatibility, and biodegradability, offer immense potentials in the development of novel materials and biomedical applications. We also explore specific examples of their applications in drug delivery, tumor targeting, and tissue engineering, while discussing future challenges and potential advancements in the field of pH-responsive self-assembling peptide-based biomaterials.

Advances in peptide-based drug delivery systems

Drug delivery systems (DDSs) are designed to deliver drugs to their specific targets to minimize their toxic effects and improve their susceptibility to clearance during targeted transport. Peptides have high affinity, low immunogenicity, simple amino acid composition, and adjustable molecular size; therefore, most peptides can be coupled to drugs via linkers to form peptide-drug conjugates (PDCs) and act as active pro-drugs. PDCs are widely thought to be promising DDSs, given their ability to improve drug bio-compatibility and physiological stability. Peptide-based DDSs are often used to deliver therapeutic substances such as anti-cancer drugs and nucleic acid-based drugs, which not only slow the degradation rate of drugs in vivo but also ensure the drug concentration at the targeted site and prolong the half-life of drugs in vivo. This article provides an profile of the advancements and future development in functional peptide-based DDSs both domestically and internationally in recent years, in the expectation of achieving targeted drug delivery incorporating functional peptides and taking full advantage of synergistic effects.

Tumor Microenvironment-Responsive Drug Delivery Based on Polymeric Micelles for Precision Cancer Therapy: Strategies and Prospects

In clinical practice, drug therapy for cancer is still limited by its inefficiency and high toxicity. For precision therapy, various drug delivery systems, including polymeric micelles self-assembled from amphiphilic polymeric materials, have been developed to achieve tumor-targeting drug delivery. Considering the characteristics of the pathophysiological environment at the drug target site, the design, synthesis, or modification of environmentally responsive polymeric materials has become a crucial strategy for drug-targeted delivery. In comparison to the normal physiological environment, tumors possess a unique microenvironment, characterized by a low pH, high reactive oxygen species concentration, hypoxia, and distinct enzyme systems, providing various stimuli for the environmentally responsive design of polymeric micelles. Polymeric micelles with tumor microenvironment (TME)-responsive characteristics have shown significant improvement in precision therapy for cancer treatment. This review mainly outlines the most promising strategies available for exploiting the tumor microenvironment to construct internal stimulus-responsive drug delivery micelles that target tumors and achieve enhanced antitumor efficacy. In addition, the prospects of TME-responsive polymeric micelles for gene therapy and immunotherapy, the most popular current cancer treatments, are also discussed. TME-responsive drug delivery via polymeric micelles will be an efficient and robust approach for developing clinical cancer therapies in the future.

Activatable Probes for Ratiometric Imaging of Endogenous Biomarkers In Vivo

Dynamic variations in the concentration and abnormal distribution of endogenous biomarkers are strongly associated with multiple physiological and pathological states. Therefore, it is crucial to design imaging systems capable of real-time detection of dynamic changes in biomarkers for the accurate diagnosis and effective treatment of diseases. Recently, ratiometric imaging has emerged as a widely used technique for sensing and imaging of biomarkers due to its advantage of circumventing the limitations inherent to conventional intensity-dependent signal readout methods while also providing built-in self-calibration for signal correction. Here, the recent progress of ratiometric probes and their applications in sensing and imaging of biomarkers are outlined. Ratiometric probes are classified according to their imaging mechanisms, and ratiometric photoacoustic imaging, ratiometric optical imaging including photoluminescence imaging and self-luminescence imaging, ratiometric magnetic resonance imaging, and dual-modal ratiometric imaging are discussed. The applications of ratiometric probes in the sensing and imaging of biomarkers such as pH, reactive oxygen species (ROS), reactive nitrogen species (RNS), glutathione (GSH), gas molecules, enzymes, metal ions, and hypoxia are discussed in detail. Additionally, this Review presents an overview of challenges faced in this field along with future research directions.

Knockdown of BACE1 by a multistage brain-targeting polyion complex improved memory and learning behaviors in APP/PS1 transgenic mouse model

Cleavage of Amyloid precursor protein (APP) by the β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the rate-limiting step in the production of amyloid-β (Aβ) synaptotoxins. The siRNA-mediated silencing to attenuate the expression of BACE1 to ameliorate cognitive dysfunction in mice had been investigated. To improve therapeutic gene delivery to the central nervous system, cationic copolymer poly(ethylene glycol)-b-poly[N-(N'-{N''-[N'''-(2-aminoethyl)-2-aminoethyl]-2-aminoethyl}-2-aminoethyl)aspartamide]-cholesterol was synthesized, then RVG29 and Tet1 peptides were exploited as ligands to construct a dual-targeting brain gene delivery polyion complex (Tet1/RVG29-PIC). The cell uptake of a coculture cell model showed that the Tet1/RVG29-PIC exhibited notable transport characteristics and possessed affinity towards nerve cells. In vivo transfection, Tet1/RVG29-PIC possessed the highest expression of luciferase in brain compared with that of RVG29-PIC or Tet1-PIC, which were 1.25 and 1.22 times respectively. Silence BACE1 expression using siRNA-expressing plasmid loaded Tet1/RVG29-PIC that improved behavioral deficits in the APP/PS1 mouse model, demonstrating the favorable brain delivery properties of Tet1/RVG29-PIC by synergistical engagement of GT1B and nicotinic acetylcholine receptors. Our results suggested that the nanoformulation has the potential to be exploited as a multistage-targeting gene vector for the CNS disease therapy.

Molecular Complementarity of Proteomimetic Materials for Target-Specific Recognition and Recognition-Mediated Complex Functions

As biomolecules essential for sustaining life, proteins are generated from long chains of 20 different α-amino acids that are folded into unique 3D structures. In particular, many proteins have molecular recognition functions owing to their binding pockets, which have complementary shapes, charges, and polarities for specific targets, making these biopolymers unique and highly valuable for biomedical and biocatalytic applications. Based on the understanding of protein structures and microenvironments, molecular complementarity can be exhibited by synthesizable and modifiable materials. This has prompted researchers to explore the proteomimetic potentials of a diverse range of materials, including biologically available peptides and oligonucleotides, synthetic supramolecules, inorganic molecules, and related coordination networks. To fully resemble a protein, proteomimetic materials perform the molecular recognition to mediate complex molecular functions, such as allosteric regulation, signal transduction, enzymatic reactions, and stimuli-responsive motions; this can also expand the landscape of their potential bio-applications. This review focuses on the recognitive aspects of proteomimetic designs derived for individual materials and their conformations. Recent progress provides insights to help guide the development of advanced protein mimicry with material heterogeneity, design modularity, and tailored functionality. The perspectives and challenges of current proteomimetic designs and tools are also discussed in relation to future applications.

Development and characterization of Factor Xa-responsive materials for applications in cell culture and biologics delivery

Stimuli-responsive biomaterials may be used to better control the release of bioactive molecules or cells for applications involving drug delivery and controlled cell release. In this study, we developed a Factor Xa (FXa)-responsive biomaterial capable of controlled release of pharmaceutical agents and cells from in vitro culture. FXa-cleavable substrates were formed as hydrogels that degraded in response to FXa enzyme over several hours. Hydrogels were shown to release both heparin and a model protein in response to FXa. Additionally, RGD-functionalized FXa-degradable hydrogels were used to culture mesenchymal stromal cells (MSCs), enabling FXa-mediated cell dissociation from hydrogels in a manner that preserved multicellular structures. Harvesting MSCs using FXa-mediated dissociation did not influence their differentiation capacity or indoleamine 2,3-dioxygenase (IDO) activity (a measure of immunomodulatory capacity). In all, this FXa-degradable hydrogel is a novel responsive biomaterial system that may be used for on-demand drug delivery, as well as for improving processes for in vitro culture of therapeutic cells.

Pancreatic tumor microenvironmental acidosis and hypoxia transform gold nanorods into cell-penetrant particles for potent radiosensitization

Coating nanoparticles with stealth epilayers increases circulation time by evading opsonization, macrophage phagocytosis, and reticuloendothelial sequestration. However, this also reduces internalization by cancer cells upon reaching the tumor. We designed gold nanorods (GNRs) with an epilayer that retains stealth properties in circulation but transforms spontaneously in the acidotic tumor microenvironment to a cell-penetrating particle. We used a customized stoichiometric ratio of l-glutamic acid and l-lysine within an amphiphilic polymer of poly(l-glutamic acid-co-l-lysine), or P(Glu-co-Lys), to effect this transformation in acidotic environments. P(Glu-co-Lys)-GNRs were internalized by cancer cells to facilitate potent in vitro radiosensitization. When administered intravenously in mice, they accumulate in the periphery and core of tumors without any signs of serum biochemical or hematological alterations, normal organ histopathological abnormalities, or overt deterioration in animal health. Furthermore, P(Glu-co-Lys)-GNRs penetrated the tumor microenvironment to accumulate in the hypoxic cores of tumors to potently radiosensitize heterotopic and orthotopic pancreatic cancers in vivo.

Mitochondria-targeting folic acid-modified nanoplatform based on mesoporous carbon and a bioactive peptide for improved colorectal cancer treatment

Oral colon-targeted drug delivery systems (OCDDs) are designed to deliver the therapeutic agents to colonic disease sites to improve the effectiveness of drug treatment, increase bioavailability, and reduce systemic side effects and are beneficial for the treatment of colorectal cancer (CRC) and inflammatory bowel disease (IBD). However, concerns about the biosafety of OCDDs are increasing, and changes in the physiological environment of the gastrointestinal tract can affect the therapeutic efficacy of the drug. Herein, we report about an orally administered colon-accumulating mitochondria-targeted drug delivery nanoplatform (M27-39@FA-MCNs), which was synthesized using the small peptide, M27-39, and folic acid (FA)-modified mesoporous carbon nanoparticles (FA-MCNs). The phenolic resin polymerized with phloroglucinol and formaldehyde (PF) was used for fabricating MCNs using a one-step soft-template method. Folic acid (FA) can be covalently combined with chitosan-modified MCNs to obtain FA-MCNs. The M27-39@FA-MCNs were stable with a spherical morphology and an average diameter of 129 nm. The cumulative release rate of M27-39@FA-MCNs in the artificial gastric fluid (pH = 1.2) and intestinal fluid (pH = 6.8) for 6 h was 87.77%. This nanoplatform maintains the advantages of both FA and MCNs to improve the bioactivity of M27-39 with high drug accumulation in colorectal tumor tissues and the ease of excretion, thus ameliorating its biosafety and targetability. Furthermore, M27-39@FA-MCNs induced tumor-cell apoptosis and inhibited tumor growth by disrupting mitochondrial energy metabolism and regulating the mitochondrial apoptosis signaling pathway and immune inflammatory response. Thus, such a mitochondria-targeting FA-modified nanoplatform based on mesoporous carbon and a bioactive peptide may provide a precise strategy for CRC treatment. STATEMENT OF SIGNIFICANCE: In this study, we constructed an orally administered colon-accumulating mitochondria-targeted drug delivery nanoplatform (M27-39@FA-MCNs), which was synthesized using the small peptide (M27-39) and folic acid-modified mesoporous carbon nanoparticles (FA-MCNs). M27-39@FA-MCNs increased the targeting ability of M27-39 toward mitochondria and colon based on the properties of FA-MCNs; they also increased M27-39 accumulation and residence time in colon tumors. Oral administration of M27-39@FA-MCNs remarkably alleviated colorectal cancer (CRC) by targeting tumor cell mitochondria and interfering with the mitochondrial energy metabolism process, and inducing apoptosis related P53/Caspase-3 mitochondrial pathway activation. Therefore, M27-39@FA-MCNs may provide a safe and precise therapeutic strategy for CRC.

Synthesis of doxorubicin-loaded peptosomes hybridized with gold nanorod for targeted drug delivery and CT imaging of metastatic breast cancer

BACKGROUND

Cancer nanomedicines based on synthetic polypeptides have attracted much attention due to their superior biocompatibility and biodegradability, stimuli responsive capability through secondary conformation change, adjustable functionalities for various cargos such as peptides, proteins, nucleic acids and small therapeutic molecules. Recently, a few nanoformulations based on polypeptides comprising NK105, NC6004, NK911, CT2103, have entered phase I-III clinical trials for advanced solid tumors therapy. In the current study, we prepared polypeptide-based vesicles called peptosome via self-assembly of amphiphilic polypeptide-based PEG-PBLG diblock copolymer.

RESULTS

In this regard, poly(γ-benzyl L-glutamate (PBLG) was synthesized via ring opening polymerization (ROP) of γ-benzyl L-glutamate-N-carboxyanhydride (BLG-NCA) using N-hexylamine as initiator. Then amine-terminated PBLG was covalently conjugated to heterofuctional maleimide PEG-carboxylic acid or methyl-PEG-carboxylic acid. The PEG-PBLG peptosomes were prepared through double emulsion method for the co-delivery of doxorubicin.HCl and gold nanorods as hydrophilic and hydrophobic agents in interior compartment and membrane of peptosomes, respectively (Pep@MUA.GNR-DOX) that DOX encapsulation efficiency and loading capacity were determined 42 ± 3.6 and 1.68 ± 3.6. Then, theranostic peptosomes were decorated with thiol-functionalized EpCAM aptamer throught thiol-maleimide reaction producing Apt-Pep@MUA.GNR-DOX for targeted delivery. The non-targeted and targeted peptosomes showed 165.5 ± 1.1 and 185 ± 4.7 nm diameters, respectively while providing sustained, controlled release of DOX. Furthermore, non-targeted and targeted peptosomes showed considerable serum stability. In vitro study on MCF-7 and 4T1 cells showed significantly higher cytotoxicity for Apt-Pep@MUA.GNR-DOX in comparison with Pep@MUA.GNR-DOX while both system did not show any difference in cytotoxicity against CHO cell line. Furthermore, Apt-Pep@MUA.GNR-DOX illustrated higher cellular uptake toward EpCAM-overexpressing 4T1 cells compared to Pep@MUA.GNR-DOX. In preclinical stage, therapeutic and diagnostic capability of the prepared Pep@MUA.GNR-DOX and Apt-Pep@MUA.GNR-DOX were investigated implementing subcutaneous 4T1 tumor model in BALB/c mice. The obtained data indicated highest therapeutic index for Apt-Pep@MUA.GNR-DOX compared to Pep@MUA.GNR-DOX and free DOX. Moreover, the prepared system showed capability of CT imaging of tumor tissue in 4T1 tumorized mice through tumor accumulation even 24 h post-administration.

CONCLUSION

In this regard, the synthesized theranostic peptosomes offer innovative hybrid multipurpose platform for fighting against breast cancer.

Glucose Metabolism Intervention-Facilitated Nanomedicine Therapy

Ordinarily, cancer cells possess features of abnormally increased nutrient intake and metabolic pathways. The disorder of glucose metabolism is the most important among them. Therefore, starvation therapy targeting glucose metabolism specifically, which results in metabolic disorders, restricted synthesis, and inhibition of tumor growth, has been developed for cancer therapy. However, issues such as inadequate targeting effectiveness and drug tolerance impede their clinical transformation. In recent years, nanomaterial-assisted starvation treatment has made significant progress in addressing these challenges, whether as a monotherapy or in combination with other medications. Herein, representative researches on the construction of nanosystems conducting starvation therapy are introduced. Elaborate designs and interactions between different treatment mechanisms are meticulously mentioned. Not only are traditional treatments based on glucose oxidase involved, but also newly sprung small molecule agents targeting glucose metabolism. The obstacles and potential for advancing these anticancer therapies were also highlighted in this review.

Self-assembling, pH-responsive nanoflowers for inhibiting PAD4 and neutrophil extracellular trap formation and improving the tumor immune microenvironment

Self-assembling carrier-free nanodrugs are attractive agents because they accumulate at tumor by an enhanced permeability and retention (EPR) effect without introduction of inactive substances, and some nanodrugs can alter the immune environment. We synthesized a peptidyl arginine deiminase 4 (PAD4) molecular inhibitor, ZD-E-1M. It could self-assembled into nanodrug ZD-E-1. Using confocal laser scanning microscopy, we observed its cellular colocalization, PAD4 activity and neutrophil extracellular traps (NETs) formation. The populations of immune cells and expression of immune-related proteins were determined by single-cell mass cytometry. ZD-E-1 formed nanoflowers in an acidic environment, whereas it formed nanospheres at pH 7.4. Accumulation of ZD-E-1 at tumor was pH-responsive because of its pH-dependent differences in the size and shape. It could enter the nucleus and bind to PAD4 to prolong the intracellular retention time. In mice, ZD-E-1 inhibited tumor growth and metastasis by inhibiting PAD4 activity and NETs formation. Besides, ZD-E-1 could regulate the ratio of immune cells in LLC tumor-bearing mice. Immunosuppressive proteins like LAG3 were suppressed, while IFN-γ and TNF-α as stimulators of tumor immune response were upregulated. Overall, ZD-E-1 is a self-assembling carrier-free nanodrug that responds to pH, inhibits PAD4 activity, blocks neutrophil extracellular traps formation, and improves the tumor immune microenvironment.

A "Double-Locked" and Enzyme/pH-Activated Theranostic Agent for Accurate Tumor Imaging and Therapy

Theranostic agents for concurrent cancer therapy and diagnosis have begun attracting attention as a promising modality. However, accurate imaging and identification remains a great challenge for theranostic agents. Here, we designed and synthesized a novel theranostic agent H6M based on the "double-locked" strategy by introducing an electron-withdrawing nitro group into 1-position of a pH-responsive 3-amino-β-carboline and further covalently linking the hydroxamic acid group, a zinc-binding group (ZBG), to the 3-position of β-carboline to obtain histone deacetylase (HDAC) inhibitory effect for combined HDAC-targeted therapy. We found that H6M can be specifically reduced under overexpressed nitroreductase (NTR) to produce H6AQ, which emits bright fluorescence at low pH. Notably, H6M demonstrated a selective fluorescence imaging via successive reactions with NTR (first "key") and pH (second "key"), and precisely identified tumor margins with a high S/N ratio to guide tumor resection. Finally, H6M exerted robust HDAC1/cancer cell inhibitory activities compared with a known HDAC inhibitor SAHA. Therefore, the NTR/pH-activated theranostic agent provided a novel tool for precise diagnosis and efficient tumor therapy.

GSH/ROS Dual-Responsive Supramolecular Nanoparticles Based on Pillar[6]arene and Betulinic Acid Prodrug for Chemo-Chemodynamic Combination Therapy

Chemodynamic therapy (CDT) based on intracellular Fenton reactions is attracting increasing interest in cancer treatment. A simple and novel method to regulate the tumor microenvironment for improved CDT with satisfactory effectiveness is urgently needed. Therefore, glutathione (GSH)/ROS (reactive oxygen species) dual-responsive supramolecular nanoparticles (GOx@BNPs) for chemo–chemodynamic combination therapy were constructed via host–guest complexation between water-soluble pillar[6]arene and the ferrocene-modified natural anticancer product betulinic acid (BA) prodrug, followed by encapsulation of glucose oxidase (GOx) in the nanoparticles. The novel supramolecular nanoparticles could be activated by the overexpressed GSH and ROS in the tumor microenvironment (TME), not only accelerating the dissociation of nanoparticles—and, thus, improving the BA recovery and release capability in tumors—but also showing the high-efficiency conversion of glucose into hydroxyl radicals (·OH) in succession through intracellular Fenton reactions. Investigation of antitumor activity and mechanisms revealed that the dramatic suppression of cancer cell growth induced by GOx@BNPs was derived from the elevation of ROS, decrease in ATP and mitochondrial transmembrane potential (MTP) and, finally, cell apoptosis. This work presents a novel method for the regulation of the tumor microenvironment for improved CDT, and the preparation of novel GSH/ROS dual-responsive supramolecular nanoparticles, which could exert significant cytotoxicity against cancer cells through the synergistic interaction of chemodynamic therapy, starvation therapy, and chemotherapy (CDT/ST/CT).

Smart magnetic resonance imaging-based theranostics for cancer

Smart theranostics are dynamic platforms that integrate multiple functions, including at least imaging, therapy, and responsiveness, in a single agent. This review showcases a variety of responsive theranostic agents developed specifically for magnetic resonance imaging (MRI), due to the privileged position this non-invasive, non-ionising imaging modality continues to hold within the clinical imaging field. Different MRI smart theranostic designs have been devised in the search for more efficient cancer therapy, and improved diagnostic efficiency, through the increase of the local concentration of therapeutic effectors and MRI signal intensity in pathological tissues. This review explores novel small-molecule and nanosized MRI theranostic agents for cancer that exhibit responsiveness to endogenous (change in pH, redox environment, or enzymes) or exogenous (temperature, ultrasound, or light) stimuli. The challenges and obstacles in the design and in vivo application of responsive theranostics are also discussed to guide future research in this interdisciplinary field towards more controllable, efficient, and diagnostically relevant smart theranostics agents.

Smart Stimuli-Responsive and Mitochondria Targeting Delivery in Cancer Therapy

Dysfunction in the mitochondria (Mc) contributes to tumor progression. It is a major challenge to deliver therapeutic agents specifically to the Mc for precise treatment. Smart drug delivery systems are based on stimuli-responsiveness and active targeting. Here, we give a whole list of documented pathways to achieve smart stimuli-responsive (St-) and Mc-targeted DDSs (St-Mc-DDSs) by combining St and Mc targeting strategies. We present the formulations, targeting characteristics of St-Mc-DDSs and clarify their anti-cancer mechanisms as well as improvement in efficacy and safety. St-Mc-DDSs usually not only have Mc-targeting groups, molecules (lipophilic cations, peptides, and aptamers) or materials but also sense the surrounding environment and correspondingly respond to internal biostimulators such as pH, redox changes, enzyme and glucose, and/or externally applied triggers such as light, magnet, temperature and ultrasound. St-Mc-DDSs exquisitely control the action site, increase therapeutic efficacy and decrease side effects of the drug. We summarize the clinical research progress and propose suggestions for follow-up research. St-Mc-DDSs may be an innovative and sensitive precision medicine for cancer treatment.

Multi-Smart and Scalable Bioligands-Free Nanomedical Platform for Intratumorally Targeted Tambjamine Delivery, a Difficult to Administrate Highly Cytotoxic Drug

Cancer is one of the leading causes of mortality worldwide due, in part, to limited success of some current therapeutic approaches. The clinical potential of many promising drugs is restricted by their systemic toxicity and lack of selectivity towards cancer cells, leading to insufficient drug concentration at the tumor site. To overcome these hurdles, we developed a novel drug delivery system based on polyurea/polyurethane nanocapsules (NCs) showing pH-synchronized amphoteric properties that facilitate their accumulation and selectivity into acidic tissues, such as tumor microenvironment. We have demonstrated that the anticancer drug used in this study, a hydrophobic anionophore named T21, increases its cytotoxic activity in acidic conditions when nanoencapsulated, which correlates with a more efficient cellular internalization. A biodistribution assay performed in mice has shown that the NCs are able to reach the tumor and the observed systemic toxicity of the free drug is significantly reduced in vivo when nanoencapsulated. Additionally, T21 antitumor activity is preserved, accompanied by tumor mass reduction compared to control mice. Altogether, this work shows these NCs as a potential drug delivery system able to reach the tumor microenvironment, reducing the undesired systemic toxic effects. Moreover, these nanosystems are prepared under scalable methodologies and straightforward process, and provide tumor selectivity through a smart mechanism independent of targeting ligands.

Stimuli-Responsive Iron Oxide Nanotheranostics: A Versatile and Powerful Approach for Cancer Therapy

Recent advancements in unravelling elements of cancer biology involved in disease progression and treatment resistance have highlighted the need for a holistic approach to effectively tackle cancer. Stimuli-responsive nanotheranostics based on iron oxide nanoparticles are an emerging class of versatile nanomedicines with powerful capabilities to "seek, sense, and attack" multiple components of solid tumors. In this work, the rationale for using iron oxide nanoparticles and the basic physical principles that impact their function in biomedical applications are reviewed. Subsequently, recent advances in the integration of iron oxide nanoparticles with various stimulus mechanisms to facilitate the development of stimuli-responsive nanotheranostics for application in cancer therapy are summarized. The integration of an iron oxide core with various surface coating mechanisms results in the generation of hybrid nanoconstructs with capabilities to codeliver a wide variety of highly potent anticancer therapeutics and immune modulators. Finally, emerging future directions and considerations for their clinical translation are touched upon.

Advances in Multiple Stimuli-Responsive Drug-Delivery Systems for Cancer Therapy

Nanomedicines afford unique advantages in therapeutic intervention against tumors. However, conventional nanomedicines have failed to achieve the desired effect against cancers because of the presence of complicated physiological fluids and the tumor microenvironment. Stimuli-responsive drug-delivery systems have emerged as potential tools for advanced treatment of cancers. Versatile nano-carriers co-triggered by multiple stimuli in different levels of organisms (eg, extracorporeal, tumor tissue, cell, subcellular organelles) have aroused widespread interest because they can overcome sequential physiological and pathological barriers to deliver diverse therapeutic “payloads” to the desired targets. Furthermore, multiple stimuli-responsive drug-delivery systems (MSR-DDSs) offer a good platform for co-delivery of agents and reversing multidrug resistance. This review affords a comprehensive overview on the “landscape” of MSR-DDSs against tumors, highlights the design strategies of MSR-DDSs in recent years, discusses the putative advantage of oncotherapy or the obstacles that so far have hindered the clinical translation of MSR-DDSs.

Microglia-targeting nanotherapeutics for neurodegenerative diseases

Advances in nanotechnology have enabled the design of nanotherapeutic platforms that could address the challenges of targeted delivery of active therapeutic agents to the central nervous system (CNS). While the majority of previous research studies on CNS nanotherapeutics have focused on neurons and endothelial cells, the predominant resident immune cells of the CNS, microglia, are also emerging as a promising cellular target for neurodegeneration considering their prominent role in neuroinflammation. Under normal physiological conditions, microglia protect neurons by removing pathological agents. However, long-term exposure of microglia to stimulants will cause sustained activation and lead to neuronal damage due to the release of pro-inflammatory agents, resulting in neuroinflammation and neurodegeneration. This Perspective highlights criteria to be considered when designing microglia-targeting nanotherapeutics for the treatment of neurodegenerative disorders. These criteria include conjugating specific microglial receptor-targeting ligands or peptides to the nanoparticle surface to achieve targeted delivery, leveraging microglial phagocytic properties, and utilizing biocompatible and biodegradable nanomaterials with low immune reactivity and neurotoxicity. In addition, certain therapeutic agents for the controlled inhibition of toxic protein aggregation and for modulation of microglial activation pathways can also be incorporated within the nanoparticle structure without compromising stability. Overall, considering the multifaceted disease mechanisms of neurodegeneration, microglia-targeted nanodrugs and nanotherapeutic particles may have the potential to resolve multiple pathological determinants of the disease and to guide a shift in the microglial phenotype spectrum toward a more neuroprotective state.

A Cyclodextrin-Based Controlled Release System in the Simulation of In Vitro Small Intestine

A novel cyclodextrin (CD)-based controlled release system was developed in the small intestine to control the rate of drug release, on the premise of enteric-coated tablets. The system was designed based on the enzymes exogenous β-cyclodextrin glycosyltransferase (β-CGTase) and endogenous maltase-glucoamylase (MG), wherein MG is secreted in the small intestine and substituted by a congenerous amyloglucosidase (AG). The vanillin-/curcumin-β-CD complexes were prepared and detected by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), and host CD degradation was measured based on the glucose yield. The combination of β-CGTase and AG was also functional in the CD complex system. The variations in the concentrations of added β-CGTase, with AG constantly in excess, could effectively alter the rate of host CD degradation and guest release by monitoring glucose production and color disappearance, thus, demonstrating that guest release in the CD complex system could be precisely controlled by changing the amount of β-CGTase used. Thus, the in vitro simulation of the system indicated that a novel controlled release system, based on endogenous MG, could be established in the small intestine. The CD-based controlled release system can be potentially applied in drug delivery and absorption in the small intestine.

Nanomedicine Fight against Antibacterial Resistance: An Overview of the Recent Pharmaceutical Innovations

Based on the recent reports of World Health Organization, increased antibiotic resistance prevalence among bacteria represents the greatest challenge to human health. In addition, the poor solubility, stability, and side effects that lead to inefficiency of the current antibacterial therapy prompted the researchers to explore new innovative strategies to overcome such resilient microbes. Hence, novel antibiotic delivery systems are in high demand. Nanotechnology has attracted considerable interest due to their favored physicochemical properties, drug targeting efficiency, enhanced uptake, and biodistribution. The present review focuses on the recent applications of organic (liposomes, lipid-based nanoparticles, polymeric micelles, and polymeric nanoparticles), and inorganic (silver, silica, magnetic, zinc oxide (ZnO), cobalt, selenium, and cadmium) nanosystems in the domain of antibacterial delivery. We provide a concise description of the characteristics of each system that render it suitable as an antibacterial delivery agent. We also highlight the recent promising innovations used to overcome antibacterial resistance, including the use of lipid polymer nanoparticles, nonlamellar liquid crystalline nanoparticles, anti-microbial oligonucleotides, smart responsive materials, cationic peptides, and natural compounds. We further discuss the applications of antimicrobial photodynamic therapy, combination drug therapy, nano antibiotic strategy, and phage therapy, and their impact on evading antibacterial resistance. Finally, we report on the formulations that made their way towards clinical application.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.