Quantitative Mapping of the Spatial Distribution of Nanoparticles in Endo-Lysosomes by Local pH

Recent Advances in Self-Assembling Peptide-Based Nanomaterials for Enhanced Photodynamic Therapy

Self-assembling peptide-based materials with ordered nanostructures possess advantages such as good biocompatibility and biodegradability, superior controllability, and ease of chemical modification. Through covalent conjugation or non-covalent encapsulation, photosensitizers (PSs) can be carried by self-assembling peptide-based nanomaterials for targeted delivery towards tumor tissues. This improves the stability, solubility, and tumor accumulation of PSs, as well as reduces their dark toxicity. More importantly, these nanomaterials can be tailored with responsiveness to tumor microenvironment, which enables smart release of PSs for precise and enhanced photodynamic therapy (PDT). In this review, the self-assembly of peptide from the perspective of driving forces is first described, and various self-assembling peptide materials with zero to 3D nanostructures are subsequently highlighted for PDT of cancers in recent years. Finally, an outlook in this field is provided to motivate fabrication of advanced PDT nanomaterials.

Nanoparticle-Mediated Delivery of Deferasirox: A Promising Strategy Against Invasive Aspergillosis

BACKGROUND

Invasive aspergillosis (IA) is a deadly fungal lung infection. Antifungal resistance and treatment side effects are major concerns. Iron chelators are vital for IA management, but systemic use can cause side effects. We developed nanoparticles (NPs) to selectively deliver the iron chelator deferasirox (DFX) for IA treatment.

METHODS

DFX was encapsulated in poly(lactic-co-glycolic acid) (PLGA) NPs using a single emulsion solvent evaporation method. The NPs were characterized by light scattering and electron microscopy. DFX loading efficiency and release were assessed spectrophotometrically. Toxicity was evaluated using SRB, luciferase, and XTT assays. Therapeutic efficacy was tested in an IA mouse model, assessing fungal burden by qPCR and biodistribution via imaging.

RESULTS

DFX-NPs had a size of ~50 nm and a charge of ~-30 mV, with a loading efficiency of ~80%. Release kinetics showed DFX release via diffusion and bioerosion. The EC50 of DFX-NPs was significantly lower (p < 0.001) than the free drug, and they were significantly less toxic (p < 0.0001) in mammalian cell cultures. In vivo, NP treatment significantly reduced Af burden (p < 0.05).

CONCLUSION

The designed DFX-NPs effectively target and kill Af with minimal toxicity to mammalian cells. The significant in vivo therapeutic efficacy suggests these NPs could be a safe and effective treatment for IA.

ECM-Mimicking Strontium-Doped Nanofibrous Microspheres for Periodontal Tissue Regeneration in Osteoporosis

Regenerating periodontal defects in osteoporosis patients presents a significant clinical challenge. Unlike the relatively straightforward regeneration of homogeneous bone tissue, periodontal regeneration requires the intricate reconstruction of the cementum-periodontal ligament-alveolar bone interface. Strontium (Sr)-doped biomaterials have been extensively utilized in bone tissue engineering due to their remarkable pro-osteogenic attributes. However, their application in periodontal tissue regeneration has been scarcely explored. In this study, we synthesized an innovative injectable Sr-BGN/GNM scaffold by integrating Sr-doped bioactive glass nanospheres (Sr-BGNs) into the nanofiber architecture of gelatin nanofiber microspheres (GNMs). This design, mimicking the natural bone extracellular matrix (ECM), enhanced the scaffold's mechanical properties and effectively controlled the sustained release of Sr ions (Sr2+), thereby promoting the proliferation, osteogenic differentiation, and ECM secretion of PDLSCs and BMSCs, as well as enhancing vascularization in endothelial cells. In vivo experiments further indicated that the Sr-BGNs/GNMs significantly promoted osteogenesis and angiogenesis. Moreover, the scaffold's tunable degradation kinetics optimized the prolonged release and pro-regenerative effects of Sr2+ in vivo, matching the pace of periodontal regeneration and thereby facilitating the regeneration of functional periodontal tissues under osteoporotic conditions. Therefore, Sr-BGNs/GNMs emerge as a promising candidate for advancing periodontal regeneration strategies.

Pulmonary Surfactant Homeostasis Dysfunction Mediates Multiwalled Carbon Nanotubes Induced Lung Fibrosis via Elevating Surface Tension

Multiwalled carbon nanotubes (MWCNTs) have been widely used in many disciplines and raised great concerns about their negative health impacts, especially environmental and occupational exposure. MWCNTs have been reported to induce fibrotic responses; however, the underlying mechanisms remain largely veiled. Here, we reported that MWCNTs inhalation induced lung fibrosis together with decreased lung compliance, increased elastance in the mice model, and elevated surface tension in vitro. Specifically, MWCNTs increased surface tension by impairing the function of the pulmonary surfactant. Mechanistically, MWCNTs induced lamellar body (LB) dysfunction through autophagy dysfunction, which then leads to surface tension elevated by pulmonary surfactant dysfunction in the context of lung fibrosis. This is a study to investigate the molecular mechanism of MWCNTs-induced lung fibrosis and focus on surface tension. A direct mechanistic link among impaired LBs, surface tension, and fibrosis has been established. This finding elucidates the detailed molecular mechanisms of lung fibrosis induced by MWCNTs. It also highlights that pulmonary surfactants are expected to be potential therapeutic targets for the prevention and treatment of lung fibrosis induced by MWCNTs.

Hyperbranched Polymers: Recent Advances in Photodynamic Therapy against Cancer

Hyperbranched polymers are a class of three-dimensional dendritic polymers with highly branched architectures. Their unique structural features endow them with promising physical and chemical properties, such as abundant surface functional groups, intramolecular cavities, and low viscosity. Therefore, hyperbranched-polymer-constructed cargo delivery carriers have drawn increasing interest and are being utilized in many biomedical applications. When applied for photodynamic therapy, photosensitizers are encapsulated in or covalently incorporated into hyperbranched polymers to improve their solubility, stability, and targeting efficiency and promote the therapeutic efficacy. This review will focus on the state-of-the-art studies concerning recent progress in hyperbranched-polymer-fabricated phototherapeutic nanomaterials with emphases on the building-block structures, synthetic strategies, and their combination with the codelivered diagnostics and synergistic therapeutics. We expect to bring our demonstration to the field to increase the understanding of the structure-property relationships and promote the further development of advanced photodynamic-therapy nanosystems.

Transferrin receptor-mediated internalization and intracellular fate of conjugates of a DNA aptamer

Aptamers have excellent specificity and affinity in targeting cell surface receptors, showing great potential in targeted delivery of drugs, siRNA, mRNA, and various nanomaterials with therapeutic function. A better insight of the receptor-mediated internalization process of aptameric conjugates could facilitate the design of new targeted drugs. In this paper, human transferrin receptor-targeted DNA aptamer (termed HG1-9)-fluorophore conjugates were synthesized to visualize the internalization, intracellular transport, and nano-environmental pH of aptameric conjugates. Unlike transferrin that showed high recycling rate and short duration time in cells, the synthetic aptameric conjugates continuously accumulated within cells at a relatively slower rate, besides recycling back to cell surface. After long incubation (≥2 h), only very small amounts of HG1-9 conjugates (approximately 5%) entered late endosomes or lysosomes, and more than 90% of internalized HG1-9 was retained in cellular vesicles (pH 6.0–6.8), escaping from degradation. And among the internalized HG1-9 conjugates, approximately 20% was dissociated from transferrin receptor. The lower recycling ratios of HG1-9 conjugates and their dissociation from receptors promote the accurate and efficient release of their loaded drugs. These results suggest that aptamer HG1-9 could be provided as a versatile tool for specific and effective delivery of diverse therapeutic payloads.

Emerging strategies in developing multifunctional nanomaterials for cancer nanotheranostics

Cancer involves a collection of diseases with a common trait - dysregulation in cell proliferation. At present, traditional therapeutic strategies against cancer have limitations in tackling various tumors in clinical settings. These include chemotherapeutic resistance and the inability to overcome intrinsic physiological barriers to drug delivery. Nanomaterials have presented promising strategies for tumor treatment in recent years. Nanotheranostics combine therapeutic and bioimaging functionalities at the single nanoparticle level and have experienced tremendous growth over the past few years. This review highlights recent developments of advanced nanomaterials and nanotheranostics in three main directions: stimulus-responsive nanomaterials, nanocarriers targeting the tumor microenvironment, and emerging nanomaterials that integrate with phototherapies and immunotherapies. We also discuss the cytotoxicity and outlook of next-generation nanomaterials towards clinical implementation.

A Dual pH-Responsive DOX-Encapsulated Liposome Combined with Glucose Administration Enhanced Therapeutic Efficacy of Chemotherapy for Cancer

BACKGROUND

The acidic microenvironment of cancer can promote tumor metastasis and drug resistance. Acidic tumor microenvironment-targeted therapy is currently an important means for treating tumors, inhibiting metastasis, and overcoming drug resistance. In this study, a dual pH-responsive DOX-encapsulated liposome (DOPE-DVar7-lip@DOX) was designed and fabricated for targeting the acidic tumor microenvironment. On the one hand, the response of acid-sensitive peptide (DVar7) to the acidic tumor microenvironment increased the uptake of liposomes in tumors and prolonged the retention time; on the other hand, the response of acid-sensitive phospholipid (DOPE) to the acidic tumor microenvironment improved the controlled release of DOX in tumors.

METHODS

The acid-sensitive peptide DVar7 modified liposomes can be obtained by simple incubation of DSPE-DVar7 with DOX-loaded DOPE liposomes (DOPE-lip@DOX). The tumor targeting of the dual pH-responsive liposome was investigated in vitro and in vivo by near-infrared fluorescence imaging. The tumor therapeutic efficacy of DOPE-DVar7-lip@DOX was evaluated in breast cancer mouse model using the traditional liposome as a control. Moreover, we regulated the tumor microenvironment acidity by injecting glucose to further enhance the therapeutic efficacy of cancer.

RESULTS

DVar7 can allosterically insert into the tumor cell membrane in the acidic tumor microenvironment to enhance the tumor uptake of liposomes and prolong the retention time of liposomes in tumor. In addition, the therapeutic efficacy of pH-responsive liposomes can be further enhanced by glucose injection regulating the acidity of tumor microenvironment.

DISCUSSION

DVar7 modified acid-sensitive nanocarriers combined with acidity regulation have great potential to improve drug resistance in clinical practice, thus improving the response rate and therapeutic effect of chemotherapy.

Smart Nanotheranostics Responsive to Pathological Stimuli

The development of nanotheranostics represents one of the most dynamic technological frontiers in the treatment of different pathological conditions. With the goal in mind to generate nanocarriers with both therapeutic and diagnostic properties, current research aims at implementing these technologies with multiple functions, including targeting, multimodal imaging, and synergistic therapies. The working mechanism of some nanotheranostics relies on physical, chemical, and biological triggers allowing for the activation of the therapeutic and/or the diagnostic properties only at the diseased site. In this review, we explored new advances in the development of smart nanotheranostics responsive to pathological stimuli, including altered pH, oxidative stress, enzymatic expression, and reactive biological molecules with a deep focus on the material used in the field to generate the particles in the context of the analyzed disease.

Triggered Release Enhances the Cytotoxicity of Stable Colloidal Drug Aggregates

Chemotherapeutics that self-assemble into colloids have limited efficacy above their critical aggregation concentration due to their inability to penetrate intact plasma membranes. Even when colloid uptake is promoted, issues with colloid escape from the endolysosomal pathway persist. By stabilizing acid-responsive lapatinib colloids through coaggregation with fulvestrant, and inclusion of transferrin, we demonstrate colloid internalization by cancer cells, where subsequent lapatinib ionization leads to endosomal leakage and increased cytotoxicity. These results demonstrate a strategy for triggered drug release from stable colloidal aggregates.

In Vivo High-resolution Ratiometric Fluorescence Imaging of Inflammation Using NIR-II Nanoprobes with 1550 nm Emission

Quantitatively imaging the spatiotemporal distribution of biological events in living organisms is essential to understand fundamental biological processes. Self-calibrating ratiometric fluorescent probes enable accurate and reliable imaging and sensing, but conventional probes using wavelength of 400-900 nm suffer from extremely low resolution for in vivo application due to the disastrous photon scattering and tissue autofluorescence background. Here, we develop a NIR-IIb (1500-1700 nm) emissive nanoprobe for high-resolution ratiometric fluorescence imaging in vivo. The obtained nanoprobe shows fast ratiometric response to hypochlorous acid (HOCl) with a detection limit down to 500 nM, through an absorption competition-induced emission (ACIE) bioimaging system between lanthanide-based downconversion nanoparticles and Cy7.5 fluorophores. Additionally, we demonstrate the superior spatial resolution of 1550 nm to a penetration depth of 3.5 mm in a scattering tissue phantom, which is 7.1-fold and 2.1-fold higher than that of 1064 and 1344 nm, respectively. With this nanoprobe, clear anatomical structures of lymphatic inflammation in ratiometric channel are observed with a precise resolution of ∼477 μm. This study will motivate the further research on the development of NIR-II probes for high-resolution biosensing in vivo.

pH-Responsive polyelectrolyte coated gadolinium oxide-doped mesoporous silica nanoparticles (Gd2O3@MSNs) for synergistic drug delivery and magnetic resonance imaging enhancement

Theranostic platforms that combine therapeutic and imaging modalities have received increasing interest.

Quantitation of Lysosomal Trapping of Basic Lipophilic Compounds Using In Vitro Assays and In Silico Predictions Based on the Determination of the Full pH Profile of the Endo-/Lysosomal System in Rat Hepatocytes

Lysosomal sequestration may affect the pharmacokinetics, efficacy, and safety of new basic lipophilic drug candidates potentially impacting their intracellular concentrations and tissue distribution. It may also be involved in drug-drug interactions, drug resistance, and phospholipidosis. However, currently there are no assays to evaluate the lysosomotropic behavior of compounds in a setting fully meeting the needs of drug discovery. We have, therefore, integrated a set of methods to reliably rank order, quantify, and calculate the extent of lysosomal sequestration in rat hepatocytes. An indirect fluorescence-based assay monitors the displacement of the fluorescence probe LysoTracker Red by test compounds. Using a lysosomal-specific evaluation algorithm allows one to generate IC50 values at lower than previously reported concentrations. The concentration range directly agrees with the concentration dependency of the lysosomal drug content itself directly quantified by liquid chromatography-tandem mass spectrometry and thus permits a quantitative link between the indirect and the direct trapping assay. Furthermore, we have determined the full pH profile and corresponding volume fractions of the endo-/lysosomal system in plated rat hepatocytes, enabling a more accurate in silico prediction of the extent of lysosomal trapping based only on pK a values as input, allowing early predictions even prior to chemical synthesis. The concentration dependency-i.e., the saturability of the trapping-can then be determined by the IC50 values generated in vitro. Thereby, a more quantitative assessment of the susceptibility of basic lipophilic compounds for lysosomal trapping is possible.

Genetically Encoding Albumin Binding into Chemotherapeutic-loaded Polypeptide Nanoparticles Enhances Their Antitumor Efficacy

We report the development of drug-encapsulating nanoparticles that bind endogenous albumin upon intravenous injection and evaluate their in vivo performance in a murine as well as canine animal model. The gene encoding a protein-G derived albumin binding domain (ABD) was fused to that of a chimeric polypeptide (CP), and the ABD-CP fusion was recombinantly synthesized by bacterial expression of the gene. Doxorubicin (DOX) was conjugated to the C-terminus of the ABD-CP fusion, and conjugation of multiple copies of the drug to one end of the ABD-CP triggered its self-assembly into ∼100 nm diameter spherical micelles. ABD-decorated micelles exhibited submicromolar binding affinity for albumin and also preserved their spherical morphology in the presence of albumin. In a murine model, albumin-binding micelles exhibited dose-independent pharmacokinetics, whereas naked micelles exhibited dose-dependent pharmacokinetics. In addition, in a canine model, albumin binding micelles resulted in a 3-fold increase in plasma half-life and 6-fold increase in plasma exposure as defined by the area under the curve (AUC) of the drug, compared with naked micelles. Furthermore, in a murine colon carcinoma model, albumin-binding nanoparticles demonstrated lower uptake by the reticuloendothelial system (RES) system organs, the liver and spleen, that are the main target organs of toxicity for nanoparticulate delivery systems and higher uptake by the tumor than naked micelles. The increased uptake by s.c. C26 colon carcinoma tumors in mice translated to a wider therapeutic window of doses ranging from 20 to 60 mg equivalent of DOX per kg body weight (mg DOX equiv·kg-1 BW) for albumin-binding ABD-CP-DOX micelles, as compared to naked micelles that were only effective at their maximum tolerated dose of 40 mg DOX equiv·kg-1 BW.

Solid lipid nanoparticles release DNA upon endosomal acidification in human embryonic kidney cells

Nanotechnology can produce materials with unique features compared to their bulk counterparts, which can be useful for medical applications (i.e. nanomedicine). Among the therapeutic agents used in nanomedicine, small molecules or biomacromolecules, such as proteins or genetic materials, can be designed for disease diagnostics and treatment. To transport these biomacromolecules to the target cells, nanomedicine requires nanocarriers. Solid lipid nanoparticles (SLNs) are among the promising nanocarriers available, because they can be made from biocompatible materials and present high stability (over one year). In addition, upon the binding genetic material, SLNs form SLNplexes. However, little is yet known about how cells process these SLNplexes-in particular, how internalization and endosome acidification affects the transfection mediated by SLNplexes. Therefore, we aim to investigate how these processes affect SLNplex transfection in HEK293T cells. We find that the SLNplex is mainly internalized by clathrin-mediated endocytosis, which is a fast and reliable pathway to transfection, leading to approximately 60% transfection efficiency. Interestingly, upon acidification (below pH 5.0), the SLN seems to release its DNA content, which can be an essential step for SLNplex transfection. The underlying mechanisms described in this work may help improve SLNplex formulations and transfection efficiency. Moreover, these advances can improve the field of nanomedical research and bring new ways to cure diseases.

Exocytosis of gold nanoparticle and photosensitizer from cancer cells and their effects on photodynamic and photothermal processes

We first illustrate the faster decrease of the photothermal (PT) effect with the delay time of laser treatment, in which the illumination of a 1064 nm laser effectively excites the localized surface plasmon (LSP) resonance of cell-up-taken gold nanoring (NRI) linked with a photosensitizer (PS), when compared with the photodynamic (PD) effect produced by the illumination of a 660 nm laser for effective PS excitation. The measurement results of the metal contents of Au NRI and PS based on inductively coupled plasma mass spectroscopy and the PS fluorescence intensity based on flow cytometry show that the linkage of NRI and PS is rapidly broken for releasing PS through the effect of glutathione in lysosome after cell uptake. Meanwhile, NRI escapes from a cell with a high rate such that the PT effect decays fast while the released PS can stay inside a cell longer for producing a prolonged PD effect. The effective delivery of PS through the linkage with Au NRI for cell uptake and the advantageous effect of LSP resonance at a PS absorption wavelength on the PD process are also demonstrated.

Ratiometric optical nanoprobes enable accurate molecular detection and imaging

Exploring and understanding biological and pathological changes are of great significance for early diagnosis and therapy of diseases. Optical sensing and imaging approaches have experienced major progress in this field. Particularly, an emergence of various functional optical nanoprobes has provided enhanced sensitivity, specificity, targeting ability, as well as multiplexing and multimodal capabilities due to improvements in their intrinsic physicochemical and optical properties. However, one of the biggest challenges of conventional optical nanoprobes is their absolute intensity-dependent signal readout, which causes inaccurate sensing and imaging results due to the presence of various analyte-independent factors that can cause fluctuations in their absolute signal intensity. Ratiometric measurements provide built-in self-calibration for signal correction, enabling more sensitive and reliable detection. Optimizing nanoprobe designs with ratiometric strategies can surmount many of the limitations encountered by traditional optical nanoprobes. This review first elaborates upon existing optical nanoprobes that exploit ratiometric measurements for improved sensing and imaging, including fluorescence, surface enhanced Raman scattering (SERS), and photoacoustic nanoprobes. Next, a thorough discussion is provided on design strategies for these nanoprobes, and their potential biomedical applications for targeting specific biomolecule populations (e.g. cancer biomarkers and small molecules with physiological relevance), for imaging the tumor microenvironment (e.g. pH, reactive oxygen species, hypoxia, enzyme and metal ions), as well as for intraoperative image guidance of tumor-resection procedures.

Sensitive detection of intracellular microRNA based on a flowerlike vector with catalytic hairpin assembly

A flowerlike nanovector with horn-shaped tips is developed for in situ detection of intracellular microRNA with multiple signal outputs.

The Weak Link: Optimization of the Ligand-Nanoparticle Interface To Enhance Cancer Cell Targeting by Polymer Micelles

Many promising targeting ligands are hydrophobic peptides, and these ligands often show limited accessibility to receptors, resulting in suboptimal targeting. A systematic study to elucidate the rules for the design of linkers that optimize their presentation on nanoparticles has not been carried out to date. In this study, we recombinantly synthesized an elastin-like polypeptide diblock copolymer (ELP_BC) that self-assembles into monodisperse micelles. AHNP and EC1, two hydrophobic ErbB2-targeted peptide ligands, were incorporated at the C-terminus of the ELP_BC with an intervening peptide linker. We tested more than 20 designs of peptide linkers, where the linker could be precisely engineered at the gene level to systematically investigate the molecular parameters-sequence, length, and charge-of the peptide linker that optimally assist ligands in targeting the ErbB2 receptor on cancer cells. We found that peptide linkers with a minimal length of 12 hydrophilic amino acids and an overall cationic charge-and that impart a zeta potential of the micelle that is close to neutral-were necessary to enhance the uptake of peptide-modified ELP_BC micelles by cancer cells that overexpress the ErbB2 receptor. This work advances our understanding of the optimal presentation of hydrophobic ligands by nanoparticles and suggests design rules for peptide linkers for targeted delivery by polymer micelles, an emerging class of nanoparticle carriers for drugs and imaging agents.

A quantitative study of the intracellular fate of pH-responsive doxorubicin-polypeptide nanoparticles

Nanoscale carriers with an acid-labile linker between the carrier and drug are commonly used for drug delivery. However, their efficacy is potentially limited by inefficient linker cleavage, and lysosomal entrapment of drugs. To address these critical issues, we developed a new imaging method that spatially overlays the location of a nanoparticle and the released drug from the nanoparticle, on a map of the local intracellular pH that delineates individual endosomes and lysosomes, and the therapeutic intracellular target of the drug-the nucleus. We used this method to quantitatively map the intracellular fate of micelles of a recombinant polypeptide conjugated with doxorubicin via an acid-labile hydrazone linker as a function of local pH and time within live cells. We found that hydrolysis of the acid-labile linker is incomplete because the pH range of 4-7 in the endosomes and lysosomes does not provide complete cleavage of the drug from the nanoparticle, but that once cleaved, the drug escapes the acidic endo-lysosomal compartment into the cytosol and traffics to its therapeutic destination-the nucleus. This study also demonstrated that unlike free drug, which enters the cytosol directly through the cell membrane and then traffics into the nucleus, the nanoparticle-loaded drug almost exclusively traffics into endosomes and lysosomes upon intracellular uptake, and only reaches the nucleus after acid-triggered drug release in the endo-lysosomes. This methodology provides a better and more quantitative understanding of the intracellular behavior of drug-loaded nanoparticles, and provides insights for the design of the next-generation of nanoscale drug delivery systems.