Gated Mesoporous Silica Nanocarriers for Hypoxia-Responsive Cargo Release

Nitroreductase-responsive gated mesoporous silica nanocarriers for hypoxia-targeted drug delivery

Hypoxia, i.e., low oxygen concentration at the tissue level, is a common feature of most solid tumors, and is responsible for their enhanced aggressiveness and resistance to chemotherapy, radiotherapy and photodynamic therapy. Hypoxic microenvironments are also characterized by the overexpression of various reductase enzymes such as nitroreductases. Herein, we report a hypoxia-responsive hybrid nanomaterial consisting of mesoporous silica nanoparticles, loaded with the chemotherapy drug doxorubicin, and functionalized on their surface with a self-immolative gatekeeper responsive to nitroreductases, for the controlled release of the cargo. Thus, under bioreductive conditions, elicited by the presence of nitroreductase and NADH, the reduction of the nitroaromatic containing molecular gate induces a self-immolative elimination leading to the disintegration of the gatekeeper and the delivery of the doxorubicin from inside the pores. The nitroreductase-responsive nanocarrier has been tested in vitro with A549 cells, that are known to express nitroreductase, to demonstrate its effectiveness as drug carrier for doxorubicin release, showing great potential for the treatment of hypoxic tumors.

Hypoxia-responsive micelles deprive cofactor of stearoyl-CoA desaturase-1 and sensitize ferroptotic ovarian cancer therapy

Ferroptosis has been recognized as a promising therapeutic strategy for cancer due to its unique mechanism of action. However, the upregulation of stearoyl-CoA desaturase 1 (SCD1) in ovarian cancer leads to resistance to ferroptotic therapy. Zinc ion (Zn2+) serves as the cofactor of SCD1. It was hypothesized that selective deprivation of Zn2+ from SCD1 could sensitize ferroptotic ovarian cancer therapy. Here, we report a hypoxia-responsive polymer micelle for enhanced ferroptosis of ovarian cancer cells. A SCD1 inhibitor, PluriSIn 1 (Plu), and a ferroptosis inducer, Auranofin (Aur), were co-encapsulated in nitroimidazole-bearing micelles. Under the hypoxic tumor microenvironment, the conversion of nitroimidazole to aminoimidazole triggered the cargo release and induced the depletion of antioxidant molecules (e.g., glutathione, thioredoxin, and NADPH). Meanwhile, because of the strong coordination between aminoimidazole and Zn2+ compared to that of histidine and Zn2+, such conversion can deprive the metal cofactor of SCD1, hence sensitizing the action of Plu and Aur. The proof-of-concept was demonstrated in cell and animal models with minimal systemic toxicity. The current work integrates ferroptosis induction with SCD1 inhibition in a hypoxia-responsive vehicle, offering a promising strategy for addressing the ferroptosis resistance and opening novel avenues for managing the difficult-to-treat ovarian cancer.

Navigating the future: Microfluidics charting new routes in drug delivery

Microfluidics has emerged as a transformative force in the field of drug delivery, offering innovative avenues to produce a diverse range of nano drug delivery systems. Thanks to its precise manipulation of small fluid volumes and its exceptional command over the physicochemical characteristics of nanoparticles, this technology is notably able to enhance the pharmacokinetics of drugs. It has initiated a revolutionary phase in the domain of drug delivery, presenting a multitude of compelling advantages when it comes to developing nanocarriers tailored for the delivery of poorly soluble medications. These advantages represent a substantial departure from conventional drug delivery methodologies, marking a paradigm shift in pharmaceutical research and development. Furthermore, microfluidic platformsmay be strategically devised to facilitate targeted drug delivery with the objective of enhancing the localized bioavailability of pharmaceutical substances. In this paper, we have comprehensively investigated a range of significant microfluidic techniques used in the production of nanoscale drug delivery systems. This comprehensive review can serve as a valuable reference and offer insightful guidance for the development and optimization of numerous microfluidics-fabricated nanocarriers.

Strengthening the Combinational Immunotherapy from Modulating the Tumor Inflammatory Environment via Hypoxia-Responsive Nanogels

Despite the success of immuno-oncology in clinical settings, the therapeutic efficacy is lower than the expectation due to the immunosuppressive inflammatory tumor microenvironment (TME) and the lack of functional lymphocytes caused by exhaustion. To enhance the efficacy of immuno-oncotherapy, a synergistic strategy should be used that can effectively improve the inflammatory TME and increase the tumor infiltration of cytotoxic T lymphocytes (CTLs). Herein, a TME hypoxia-responsive nanogel (NG) is developed to enhance the delivery and penetration of diacerein and (-)-epigallocatechin gallate (EGCG) in tumors. After systemic administration, diacerein effectively improves the tumor immunosuppressive condition through a reduction of MDSCs and Tregs in TME, and induces tumor cell apoptosis via the inhibition of IL-6/STAT3 signal pathway, realizing a strong antitumor effect. Additionally, EGCG can effectively inhibit the expression of PD-L1, restoring the tumor-killing function of CTLs. The infiltration of CTLs increases at the tumor site with activation of systemic immunity after the combination of TIM3 blockade therapy, ultimately resulting in a strong antitumor immune response. This study provides valuable insights for future research on eliciting effective antitumor immunity by suppressing adverse tumor inflammation. The feasible strategy proposed in this work may solve the urgent clinical concerns of the dissatisfactory checkpoint-based immuno-oncotherapy.

Hypoxia and Singlet Oxygen Dual-Responsive Micelles for Photodynamic and Chemotherapy Therapy Featured with Enhanced Cellular Uptake and Triggered Cargo Delivery

Introduction

Combination therapy provides better outcomes than a single therapy and becomes an efficient strategy for cancer treatment. In this study, we designed a hypoxia- and singlet oxygen-responsive polymeric micelles which contain azo and nitroimidazole groups for enhanced cellular uptake, repaid cargo release, and codelivery of photosensitizer Ce6 and hypoxia-activated prodrug tirapazamine TPZ (DHM-Ce6@TPZ), which could be used for combining Ce6-mediated photodynamic therapy (PDT) and PDT-activated chemotherapy to enhance the therapy effect of cancer.

Methods

The hypoxia- and singlet oxygen-responsive polymeric micelles DHM-Ce6@TPZ were prepared by film hydration method. The morphology, physicochemical properties, stimuli responsiveness, in vitro singlet oxygen production, cellular uptake, and cell viability were evaluated. In addition, the in vivo therapeutic effects of the micelles were verified using a tumor xenograft mice model.

Results

The resulting dual-responsive micelles not only increased the concentration of intracellular photosensitizer and TPZ, but also facilitated photosensitizer and TPZ release for enhanced integration of photodynamic and chemotherapy therapy. As a photosensitizer, Ce6 induced PDT by generating toxic singlet reactive oxygen species (ROS), resulting in a hypoxic tumor environment to activate the prodrug TPZ to achieve efficient chemotherapy, thereby evoking a synergistic photodynamic and chemotherapy therapeutic effect. The cascade synergistic therapeutic effect of DHM-Ce6@TPZ was effectively evaluated both in vitro and in vivo to inhibit tumor growth in a breast cancer mice model.

Conclusion

The designed multifunctional micellar nano platform could be a convenient and powerful vehicle for the efficient co-delivery of photosensitizers and chemical drugs for enhanced synergistic photodynamic and chemotherapy therapeutic effect of cancer.

Azo Reductase Activated Magnetic Resonance Tuning Probe with "Switch-On" Property for Specific and Sensitive Tumor Imaging in Vivo

Cancer remains a threat to human health. However, if tumors can be detected in the early stage, then the effectiveness of cancer treatment could be significantly improved. Therefore, it is worthwhile to develop more sensitive and accurate cancer diagnostic methods. Herein, we demonstrated an azo reductase (AzoR)-activated magnetic resonance tuning (MRET) probe with a "switch-on" property for specific and sensitive tumor imaging in vivo. Specifically, Gd-labeled DNA1 (DNA1-Gd) and cyclodextrin-coated magnetic nanoparticles (MNP-CD) were employed as enhancer and quencher of MRET, respectively, while DNA2, an azobenzene (Azo) group-modified aptamer (AS1411), served as a linker between enhancer and quencher to construct the MRET probe of MNP@DNA(1-2)-Gd. In tumor tissues with high-level AzoR, the T1-weighted magnetic resonance signal of the MRET probe could be restored by intelligently regulating the switch from "OFF" to "ON" after activation with AzoR, thus accurately indicating the location of the tumor accurately. Moreover, the tumor with a 4 times smaller size than that of the normal tumor model could be imaged based on the proposed MRET probe. The as-proposed MRET-based magnetic resonance imaging strategy not only achieves tumor imaging accurately but also shows promise for early diagnosis of tumors, which might improve patients' survival rates and provide an opportunity for image-guided biomedical applications in the future.

Metal-Organic Framework for Hypoxia/ROS/pH Triple-Responsive Cargo Release

Nanoparticulate antitumor photodynamic therapy (PDT) is suffering from a very short lifetime, limited diffusion distance of reactive oxygen species (ROS). Herein, a hypoxia/ROS/pH triple-responsive metal-organic framework (MOF) is designed to facilitate the on-demand release of photosensitizers and hence enhanced PDT efficacy. Tailored azo-containing imidazole ligand is coordinated with zinc to form MOF where photosensitizer (Chlorin e6/Ce6) is encapsulated. Azo can be reduced by overexpressed azoreductase in hypoxic tumor cells, resulting in depletion of glutathione (GSH) and thioredoxin (Trx) which are major antioxidants against ROS oxidative damage in PDT, resulting in rapid cargo release and additional efficacy amplification. The imidazole ionization causes a proton sponge effect to ensure the disintegration of the nanocarriers in acidic organelles, allowing the rapid release of Ce6 through lysosome escape. Under light irradiation, ROS produced by Ce6 may oxidize imidazole to urea, resulting in rapid cargo release. All of the triggers are expected to show interactive synergism. The pH- and hypoxia-responsiveness can improve the release rate of Ce6 for enhanced PDT therapy, whereas the consumption of oxygen by PDT may induce elevated hypoxia and hence in turn enhanced cargo release. This work highlights the role of triple-responsive nanocarriers for triggered photosensitizer release and improved antitumor PDT efficacy.

Engineering CAR-NK cell derived exosome disguised nano-bombs for enhanced HER2 positive breast cancer brain metastasis therapy

HER2-positive breast cancer brain metastasis (HER2+ BCBM) is a refractory malignancy with a high recurrence rate and poor prognosis. The efficacies of conventional treatments, including radiation and the FDA-approved drug trastuzumab, are compromised due to their significant obstacles, such as limited penetration through the blood-brain barrier (BBB), off-target effects on HER2+ tumor cells, and systemic adverse reactions, ultimately resulting in suboptimal therapeutic outcomes. In order to address these challenges, a novel biomimetic nanoplatform was created, which consisted of a combination of chimeric antigen receptor-natural killer (CAR-NK) cell-derived exosomes (ExoCAR), and a nanobomb (referred to as Micelle). This nanoplatform, known as ExoCAR/T7@Micelle, was designed to enhance the effectiveness of antitumor treatment by disrupting ferroptosis defense mechanisms. Due to the transferrin receptor binding peptide (T7) modification and CAR expression on the exosome surface, the nanoplatform successfully traversed the blood-brain barrier and selectively targeted HER2+ breast cancer cells. Moreover, integration of the reactive oxygen species (ROS) -amplified and photodynamic therapy (PDT)-based nanobomb facilitated the spatiotemporal release of the cargos at specific sites. Upon systemic administration of ExoCAR/T7@Micelle, mice with orthotopic HER2+ BCBM demonstrated a robust antitumor response in vivo, leading to a significant extension in survival time. Furthermore, histological analyses and blood index studies revealed no discernible side effects. Collectively, this study is the first to indicate the possibility of HER2+ BCBM therapy with a CAR-NK cell-derived biomimetic drug delivery system.

Mesoporous Silica Nanoparticles-Based Nanoplatforms: Basic Construction, Current State, and Emerging Applications in Anticancer Therapeutics

In recent years, researchers are developing novel nanoparticles for diagnostic applications using imaging techniques and for therapeutic purposes through drug delivery techniques. The unique physical and chemical properties of mesoporous silica nanoparticles (MSNs) make it possible to integrate a variety of commonly used therapeutic and imaging agents to construct a multimodal synergistic anticancer drug delivery system. Herein, recent advances in MSNs synthesis for drug delivery and smart response applications are reviewed. First, synthetic strategies for the fabrication of ordered MSNs, hollow MSNs, core-shell structured MSNs, dendritic MSNs, and biodegradable MSNs are outlined. Then, the recent research progress in designing functional MSN materials with various controlled release mechanisms in anticancer therapy is discussed, and new properties are introduced to suggest the latest design requirements as drug delivery materials. The review also highlights significant achievements in bioimaging using MSNs and their multifunctional counterparts as delivery vehicles. Finally, personal views on key directions for future work in this area are presented.

Mesoporous Silica and Oligo (Ethylene Glycol) Methacrylates-Based Dual-Responsive Hybrid Nanogels

Polymeric-inorganic hybrid nanomaterials have emerged as novel multifunctional platforms because they combine the intrinsic characteristics of both materials with unexpected properties that arise from synergistic effects. In this work, hybrid nanogels based on mesoporous silica nanoparticles, oligo (ethylene glycol) methacrylates, and acidic moieties were developed employing ultrasound-assisted free radical precipitation/dispersion polymerization. Chemical structure was characterized by infrared spectroscopy and nuclear magnetic resonance. Hydrodynamic diameters at different temperatures were determined by dynamic light scattering, and cloud point temperatures were determined by turbidimetry. Cell viability in fibroblast (NIH 3T3) and human prostate cancer (LNCaP) cell lines were studied by a standard colorimetric assay. The synthetic approach allows covalent bonding between the organic and inorganic components. The composition of the polymeric structure of hybrid nanogels was optimized to incorporate high percentages of acidic co-monomer, maintaining homogeneous nanosized distribution, achieving appropriate volume phase transition temperature values for biomedical applications, and remarkable pH response. The cytotoxicity assays show that cell viability was above 80% even at the highest nanogel concentration. Finally, we demonstrated the successful cell inhibition when they were treated with camptothecin-loaded hybrid nanogels.

Hypoxia-responsive nanocarriers for chemotherapy sensitization via dual-mode inhibition of hypoxia-inducible factor-1 alpha

The overexpression of hypoxia-inducible factor-1 alpha (HIF-1α) in solid tumor compromises the potency of chemotherapy under hypoxia. The high level of HIF-1α arises from the stabilization effect of reduced nicotinamideadeninedinucleotide(phosphate) NAD(P)H: quinone oxidoreductase 1 (NQO1). It was postulated that the inhibition of NQO1 could degrade HIF-1α and sensitize hypoxic cancer cells to antineoplastic agents. In the current work, we report hypoxia-responsive polymer micelles, i.e. methoxyl poly(ethylene glycol)-co-poly(aspartate-nitroimidazole) orchestrate with a NQO1 inhibitor (dicoumarol) to sensitize the ovarian cancer cell line (SKOV3) to a model anticancer agent (sorafenib) at low oxygen conditions. Both cargos were physically encapsulated in the nanoscale micelles. The placebo micelles transiently induced the depletion of reduced nicotinamideadeninedinucleotidephosphate (NADPH) as well as glutathione and thioredoxin under hypoxia, which further inactivated NQO1 because NADPH was the cofactor of NQO1. As a consequence, the expression of HIF-1α was repressed due to the dual action of dicoumarol and polymer. The degradation of HIF-1α significantly increased the vulnerability of SKOV3 cells to sorafenib-induced apoptosis, as indicated by the enhancement of cytotoxicity, and increase of caspase 3 and cytochrome C. The current work opens new avenues of addressing hypoxia-induced drug resistance in chemotherapy.

A Lesion Microenvironment-Responsive Fungicide Nanoplatform for Crop Disease Prevention and Control

Controlled fungicide delivery in response to the specific microenvironment produced by fungal pathogens is an advisable strategy to improve the efficacy of fungicides. Herein, the authors construct a smart fungicide nanoplatform, using mesoporous silica nanoparticles (MSNs) as nanocarriers loaded with eugenol (EU) and Ag⁺ coordinated polydopamine (Ag⁺ -PDA) as a coating to form Ag⁺ -PDA@MSNs-EU NPs for Botrytis cinerea (B. cinerea) control. As a botanical fungicide, EU offers an eco-friendly alternative to synthetic fungicides and can upregulate several defense-related genes in the tomato plant. The Ag⁺ -PDA coating can lock the EU inside the nanocarriers and respond to the oxalic acid produced by B. cinerea to corelease the loaded EU and Ag⁺ . The results demonstrate that Ag⁺ -PDA@MSNs-EU NPs can effectively inhibit the mycelial growth of B. cinerea on detached and potted tomato leaves. The construction of such a smart fungicide nanoplatform provides new guidance to design controlled fungicides release systems, which can respond to the microenvironment associated with plant pathogen to realize fungus control.

Triggered azobenzene-based prodrugs and drug delivery systems

Azobenzene-based molecules show unique trans-cis isomerization upon ultraviolet light irradiation, which induce the change of polarity, crystallinity, stability, and binding affinity with pharmacological target. Moreover, azobenzene is the substrate of azoreductase that is often overexpressed in many pathological sites, e.g. hypoxic solid tumor. Therefore, azobenzene can be a multifunctional molecule in material science, pharmaceutical science and biomedicine because of its sensitivity to light, hypoxia and certain enzymes, hence showing potential application in site-specific smart therapy. Herein we focus on the employment of azobenzene and its derivatives for engineering triggered prodrug and drug delivery systems, and provide an overview of photoswitchable azo-based prodrugs, the associated problems regarding ultraviolet light and reversible isomerization, as well as the potential solutions. We also present the advance of azo-bearing delivery vehicles wherein azobenzene act as the linker, capping agent, and building block, and discuss the corresponding mechanisms for controlled cargo release, endocytosis enhancement and sensitization of free radical cancer therapy.

Exploring the role of mesoporous silica nanoparticle in the development of novel drug delivery systems

The biocompatible nature of mesoporous silica nanoparticles (MSN) attracted researchers' attention to deliver therapeutic agents in the treatment of various diseases, where their porous nature, high drug loading efficiency, and suitability to functionalize with a specific ligand of MSN helped to obtain the desired outcome. The application of MSN has been extended to deliver small chemicals to large-sized peptides or proteins to fight against complex diseases. Recently, formulation researches with MSN have been progressed for various non-conventional drug delivery systems, including liposome, microsphere, oro-dispersible film, 3D-printed formulation, and microneedle. Low bulk density, retaining mesoporous structure during downstream processing, and lack of sufficient in vivo studies are some of the important issues towards the success of mesoporous silica-based advanced drug delivery systems. The present review has aimed to evaluate the application of MSN in advanced drug delivery systems to critically analyze the role of MSN in the respective formulation over other functionalized polymers. Finally, an outlook on the future direction of MSN-based advanced drug delivery systems has been drawn against the existing challenges with this platform.

Advances in the therapeutic delivery and applications of functionalized Pluronics: A critical review

Pluronic (PEO-PPO-PEO) block copolymers can form nano-sized micelles with a structure composed of a hydrophobic PPO core and hydrophilic PEO shell layer. Pluronics are U.S. Food and Drug Administration approved polymers, which are widely used for solubilization of drugs and their delivery, gene/therapeutic delivery, diagnostics, and tissue engineering applications due to their non-ionic properties, non-toxicity, micelle forming ability, excellent biocompatibility and biodegradability. Although Pluronics have been employed as drug carrier systems for several decades, numerous issues such as rapid dissolution, shorter residence time in biological media, fast clearance and weak mechanical strength have hindered their efficacy. Pluronics have been functionalized with pH-sensitive, biological-responsive moieties, antibodies, aptamers, folic acid, drugs, different nanoparticles, and photo/thermo-responsive hydrogels. These functionalization strategies enable Pluronics to act as stimuli responsive and targeted drug delivery vehicles. Moreover, Pluronics have emerged in nano-emulsion formulations and have been utilized to improve the properties of cubosomes, dendrimers and nano-sheets, including their biocompatibility and aqueous solubility. Functionalization of Pluronics results in the significant improvement of target specificity, loading capacity, biocompatibility of nanoparticles and stimuli responsive hydrogels for the promising delivery of a range of drugs. Therefore, this review presents an overview of all advancements (from the last 15 years) in functionalized Pluronics, providing a valuable tool for industry and academia in order to optimize their use in drug or therapeutic delivery, in addition to several other biomedical applications.

Pathogen infection-responsive nanoplatform targeting macrophage endoplasmic reticulum for treating life-threatening systemic infection

Systemic infections caused by life-threatening pathogens represent one of the main factors leading to clinical death. In this study, we developed a pathogen infection-responsive and macrophage endoplasmic reticulum-targeting nanoplatform to alleviate systemic infections. The nanoplatform is composed of large-pore mesoporous silica nanoparticles (MSNs) grafted by an endoplasmic reticulum-targeting peptide, and a pathogen infection-responsive cap containing the reactive oxygen species-cleavable boronobenzyl acid linker and bovine serum albumin. The capped MSNs exhibited the capacity to high-efficiently load the antimicrobial peptide melittin, and to rapidly release the cargo triggered by H₂O₂ or the pathogen-macrophage interaction system, but had no obvious toxicity to macrophages. During the interaction with pathogenic Candida albicans cells and macrophages, the melittin-loading nanoplatform MSNE+MEL+TPB strongly inhibited pathogen growth, survived macrophages, and suppressed endoplasmic reticulum stress together with pro-inflammatory cytokine secretion. In a systemic infection model, the nanoplatform efficiently prevented kidney dysfunction, alleviated inflammatory symptoms, and protected the mice from death. This study developed a macrophage organelle-targeting nanoplatform for treatment of life-threatening systemic infections.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (N₂ adsorption curves of the initial synthesized MSNs, FT-IR spectra of MSN, and MSNE, MEL release from the FITC-MEL-loading MSNE + TPB induced by different concentration of H₂O₂, viability of NIH3T3 cells, and DC2.4 cells after treatment of free MEL or the used nanoparticles, effect of MEL on C. albicans growth and macrophage death during the interaction between C. albicans and macrophages, effect of MEL and the nanoparticles on S. aureus growth and macrophage death during the interaction between S. aureus and macrophages, quantification of GRP78 (a) and activated Caspase-3, flow cytometry analysis of kidney non-macrophages with the Alexa Fluor 594 signal, survival curve of the infected mice treated by MEL or MSNE + MEL, kidney burden, blood urea levels and serum TNF-α levels in the infected mice) is available in the online version of this article at 10.1007/s12274-022-4211-z.

Hypoxia responsive nano-drug delivery system based on angelica polysaccharide for liver cancer therapy

Based on the tumor hypoxic microenvironment and the new programmed cell death mode of combined ferroptosis, an angelica polysaccharide-based nanocarrier material was synthesized. The polymer contains hydrophilic angelica polysaccharide (ASP) that is linked by azobenzene (AZO) linker with ferrocene (Fc), and then the side chain was covalently modified with arachidonic acid (AA). It was postulated that the polymer micelles could work as an instinctive liver targeting drug delivery carrier, owing to the existence of ASP with liver targeting. Moreover, the aim was to engineer hypoxia-responsive polymer micelles which was modified by AA, for selective enhancement of ferroptosis in solid tumor, via diminishing glutathione (GSH) under hypoxia. Finally, we synthesized the amphiphilic polymer micelles AA/ASP-AZO-Fc (AAAF) by self-assembling. The structure of AAAF was confirmed by ¹H-NMR and FT-IR. Then, we exemplified the hydrophobic medication curcumin into polymer micelles AAAF@Cur, which has smooth and regular spheres. In vitro release test affirmed that AAAF@Cur can achieve hypoxia response to drug release. In addition, a series of cell experiments confirmed that hypoxia could enhance cell uptake and effectively improve the proliferation inhibitory activity of HepG2 cells. In conclusion, AAAF, as an effective cell carrier, is expected to develop in sensitizing ferroptosis and anti-tumor.

Hyaluronic Acid Derived Hypoxia-Sensitive Nanocarrier for Tumor Targeted Drug Delivery

Hyaluronic acid (HA) is conjugated with BHQ3 moiety with azo bonds to prepare hypoxia-responsive polymer conjugate. Because of the amphiphilic nature, the polymer conjugate self-assembles to HA-BHQ3 nanoparticles (NPs). The anticancer drug doxorubicin (DOX) is loaded into the NPs. In the physiological environment, DOX is released slowly. In contrast, under hypoxic conditions, the azo bond in BHQ3 is cleaved, thus significantly enhancing the DOX release rate. For instance, after 24 h, 25% of DOX is released under normal conditions, while 74% of DOX is released under hypoxic conditions. In vitro cytotoxicity demonstrates higher toxicity in the hypoxic conditions. DOX@HA-BHQ3 NPs exhibit greater toxicity levels against 4T1 cells in hypoxic conditions. The fluorescent microscope images confirm the oxygen-dependent intracellular DOX release from the NPs. The in vivo biodistribution results suggest the tumor targetability of HA-BHQ3 NPs in 4T1 tumor-bearing mice.

FRET Ratiometric Nanoprobes for Nanoparticle Monitoring

Fluorescence labelling is often used for tracking nanoparticles, providing a convenient assay for monitoring nanoparticle drug delivery. However, it is difficult to be quantitative, as many factors affect the fluorescence intensity. Förster resonance energy transfer (FRET), taking advantage of the energy transfer from a donor fluorophore to an acceptor fluorophore, provides a distance ruler to probe NP drug delivery. This article provides a review of different FRET approaches for the ratiometric monitoring of the self-assembly and formation of nanoparticles, their in vivo fate, integrity and drug release. We anticipate that the fundamental understanding gained from these ratiometric studies will offer new insights into the design of new nanoparticles with improved and better-controlled properties.

Super-Assembled Periodic Mesoporous Organosilica Frameworks for Real-Time Hypoxia-Triggered Drug Release and Monitoring

Hypoxia, induced by inadequate oxygen supply, is a key indication of various major illnesses, which necessitates the need to develop new nanoprobes capable of sensing hypoxia environments for the targeted system monitoring and drug delivery. Herein, we report a hypoxia-responsive, periodic mesoporous organosilica (PMO) nanocarrier for repairing hypoxia damage. β-cyclodextrin (β-CD) capped azobenzene functionalization on the PMO surface could be effectively cleaved by azoreductase under a hypoxia environment. Moreover, the nanosystem is equipped with fluorescence resonance energy transfer (FRET) pair (tetrastyrene derivative (TPE) covalently attached to the PMO framework as the donor and Rhodamine B (RhB) in the mesopores as the receptor) for intracellular visualization and tracking of drug release in real-time. The design of intelligent nanocarriers capable of simultaneous reporting and treating of hypoxia conditions highlights a great potential in the biomedical domain.

Recent advances in active targeting of nanomaterials for anticancer drug delivery

One of the challenges in cancer chemotherapy is the low target to non-target ratio of therapeutic agents which incur severe adverse effect on the healthy tissues. In this regard, nanomaterials have tremendous potential for impacting cancer therapy by altering the toxicity profile of the drug. Some of the striking advantages provided by the nanocarriers mediated targeted drug delivery are relatively high build-up of drug concentration at the tumor site, improved drug content in the formulation and enhanced colloidal stability. Further, nanocarriers with tumor-specific moieties can be targeted to the cancer cell through cell surface receptors, tumor antigens and tumor vasculatures with high affinity and accuracy. Moreover, it overcomes the bottleneck of aimless drug biodistribution, undesired toxicity and heavy dosage of administration. This review discusses the recent developments in active targeting of nanomaterials for anticancer drug delivery through cancer cell surface targeting, organelle specific targeting and tumor microenvironment targeting strategies. Special emphasis has been given towards cancer cell surface and organelle specific targeting as delivery of anticancer drugs through these routes have made paradigm change in cancer management. Further, the current challenges and future prospects of nanocarriers mediated active drug targeting are also demonstrated.

Smart Nanoparticles for Chemo-Based Combinational Therapy

Cancer is a heterogeneous and complex disease. Traditional cancer therapy is associated with low therapeutic index, acquired resistance, and various adverse effects. With the increasing understanding of cancer biology and technology advancements, more strategies have been exploited to optimize the therapeutic outcomes. The rapid development and application of nanomedicine have motivated this progress. Combinational regimen, for instance, has become an indispensable approach for effective cancer treatment, including the combination of chemotherapeutic agents, chemo-energy, chemo-gene, chemo-small molecules, and chemo-immunology. Additionally, smart nanoplatforms that respond to external stimuli (such as light, temperature, ultrasound, and magnetic field), and/or to internal stimuli (such as changes in pH, enzymes, hypoxia, and redox) have been extensively investigated to improve precision therapy. Smart nanoplatforms for combinational therapy have demonstrated the potential to be the next generation cancer treatment regimen. This review aims to highlight the recent advances in smart combinational therapy.

Enhanced efficacy and drug delivery with lipid coated mesoporous silica nanoparticles in cancer therapy

The exposure of cancer cells to subtherapeutic drug concentrations results in multidrug resistance (MDR). The uniqueness of mesoporous silica nanoparticles (MSNPs) with larger surface area for higher drug loading can solve the issue by delivering higher amounts of chemotherapeutics to the cancer cells. However, premature drug release and lower biocompatibility remain challenging. Lipid coating of MSNPs at the same time, can enhance the stability and biocompatibility of nanocarriers. Furthermore, the lipid coating can reduce the systemic drug release and deliver higher amounts to the tumor site. Herein, lipid coated MSNPs were prepared by utilizing cationic liposomes and further investigations were made. Our studies have shown the higher entrapment of doxorubicin (Dox) to MSNPs due to availability of porous structure. Lipid coating could provide a barrier to sustain the release of drug along with reduced premature leakage. In addition, the biocompatibility and enhanced interaction of cationic liposomes to cell membranes resulted in better cellular uptake. Lipid coated silica nanoparticles have shown higher cellular toxicity as compared to non-lipid coated particles. The increase in cytotoxicity with time supports the hypothesis of sustained release of drug from lipid coated MSNPs. We propose the Lip-Dox-MSNPs as an effective approach to treat cancer by delivering and maintaining effective concentration of drugs to the tumor site without systemic side effects.

The pH-triggered drug release and simultaneous carrier decomposition of effervescent SiO2-drug-Na2CO3 composite nanoparticles: to improve the antitumor activity of hydrophobic drugs

To achieve a better release effect of hydrophobic drugs and spontaneous nanocarrier disintegration by dissolution as well as the CO₂ production of Na₂CO₃ further, improving the therapeutic effect of hydrophobic drugs, and thereby avoiding the accumulation of the nanocarrier in vivo to produce organ toxicity, effervescent SiO₂–drug–Na₂CO₃ composite nanoparticles (ESNs) were prepared in this study using a tetraethyl orthosilicate hydrolysis method. Sodium carbonate was used as the effervescent disintegrant to respond to the acidic microenvironment of the tumor. The properties of ESNs were assessed and TEM images were taken to verify the self-disintegration characteristics of nanocarrier materials. The in vitro anticancer efficacy of ESNs was evaluated in human breast cancer MCF-7 cells. ESNs loaded with hydrophobic drugs were successfully constructed, and showed high entrapment efficiency and drug loading. The nanocarrier successfully achieved self-disintegration in a PBS environment of pH value at 5.0, and showed excellent antitumor effect in vitro. ESNs can effectively load hydrophobic drugs and achieve self-disintegration, while avoiding toxicity from the accumulation of the nanocarrier. These results suggest that ESNs are a promising drug delivery system capable of maximizing the anticancer therapeutic efficacy and minimizing the systemic toxicity.

Effervescent SiO₂–drug–Na₂CO₃ composite nanoparticles were prepared in this study using a tetraethyl orthosilicate hydrolysis method to achieve a better release effect of hydrophobic drugs and spontaneous nanocarrier disintegration by dissolution.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

Electron-Accepting Micelles Deplete Reduced Nicotinamide Adenine Dinucleotide Phosphate and Impair Two Antioxidant Cascades for Ferroptosis-Induced Tumor Eradication

Ferroptotic antitumor therapy has been compromised by various intracellular antioxidants, particularly glutathione and thioredoxin. Both are cofactors of glutathione peroxide 4 (GPX4) that act against oxidative stress via catalyzing the reduction of lipid peroxides. It was postulated that tailored polymer micelles could enhance ferroptotic antitumor efficacy via diminishing glutathione and thioredoxin under hypoxia. The aim was to engineer hypoxia-responsive micelles for selective enhancement of ferroptotic cell death in solid tumor. The polymer contains hydrophilic poly(ethylene glycol) (PEG) that is linked by azobenzene linker with nitroimidazole-conjugated polypeptide. The tailored polymer could self-assemble into nanoscale micelles to encapsulate RAS-selective lethal small molecule 3, a covalent GPX4 inhibitor. Under hypoxia, the azobenzene moiety enabled PEG shedding and enhanced micelles uptake in 4T1 cells. Likewise, the nitroimidazole moiety was reduced by the overexpressed nitroreductase with reduced nicotinamide adenine dinucleotide phosphate (NADPH) as the cofactor, resulting in transient depletion of NADPH. This impaired both the glutathione and thioredoxin redox cycle, leading to diminished intracellular glutathione and thioredoxin. The selective potency of ferroptotic micelles in depleting NADPH, glutathione and thioredoxin was further verified in vivo in the 4T1 tumor xenograft mice model. This work highlights the role of hypoxia-responsive polymers in enhancing the potency of ferroptotic inducers against solid tumors without additional side effects to healthy organs.

Endocytic recycling as cellular trafficking fate of simvastatin-loaded discoidal reconstituted high-density lipoprotein to coordinate cholesterol efflux and drug influx

Reconstituted high-density lipoproteins (rHDLs) hold promise as nanocarriers for atherosclerosis-targeted delivery, with biofunctions typified by mediating cholesterol efflux. The paradox is how rHDL offloads the delivered drugs into atherosclerotic foam cells, while simultaneously transferring cholesterol out of cells. Herein, simvastatin-loaded discoidal rHDL (ST-d-rHDL), constructed based on established paradigms, was employed to investigate its basic trafficking mechanism in foam cells. As proved, ST-d-rHDL was resecreted via lysosomal and Golgi apparatus-recycling endosome-mediated pathways following clathrin-mediated endocytosis. And the resecretion ratio reached 60% within 6-h chase with excessive ST-d-rHDLs. During the rHDL resecretion, 39% of cellular cholesterol efflux was detected, accompanied by 85% of the encapsulated cargo released intracellularly. Furthermore, the recycling rate was demonstrated to be promoted by smaller rHDL size and higher cellular lipid contents. Collectively, endocytic recycling confers the synergism in ST-d-rHDL to coordinate cholesterol efflux and intracellular drug release, providing new insights into design of biofunctional rHDL.

Emerging Strategies in Anticancer Combination Therapy Employing Silica-Based Nanosystems

Combination therapy has emerged as one of the most promising approaches for cancer treatment. However, beyond remotely-triggered therapies that require advanced infrastructures and optimization, new combination therapies based on internally triggered cell-killing effects have also demonstrated promising therapeutic profiles. In this revision, the focus is on self-triggered strategies able to improve the therapeutic effect of drug delivery nanosystems. As reviewed, ferroptosis, hypoxia, and immunotherapy show potency enough to treat satisfactorily tumors in vivo. However, the interest of combining those with chemotherapeutics, especially with carriers based on mesoporous silica, has provided a new generation of therapeutic nanomedicines with potential enough to achieve complete tumor remission in murine models.

Azo-inserted responsive hybrid liposomes for hypoxia-specific drug delivery

Stimuli-responsive drug delivery systems using endogenous stimuli from tumor microenvironments such as acidic pH, over-expressed enzyme, and high redox potential as triggers have shown tremendous promise in cancer therapy. However, their clinical application is severely limited because of tumor heterogeneity. Hypoxia, a physiological feature observed in almost all solid tumors and even in nodules with very small size, has currently emerged as a more general but efficient stimulus to trigger release. Herein, we developed hypoxia-responsive hybrid liposomes (HR-HLPs), composed of azo-inserted organokoxysilane-based lipid analogue as a responsive component and commercial phospholipid for reducing the rigidity of liposomal membrane caused by azo, for drug delivery targeting tumor hypoxia. HR-HLPs had the advantages of high structural stability to avoid premature drug leakage when circulating in the blood and high sensitivity in responding to hypoxia once reaching tumor sites. HR-HLPs exhibit deep tumor penetration capability, enabling effective delivery to hypoxic regions distant from tumor vessels. Moreover, HR-HLPs could selectively release their payload, co-localizing with over-expressed hypoxia inducible factor 1α (HIF-1α) in vitro and in vivo. As a result, HR-HLPs showed improved therapeutic outcome accompanied by reduced adverse effects. The results highlighted the potential application of azo-inserted responsive hybrid liposomes for hypoxia-targeted drug delivery. STATEMENT OF SIGNIFICANCE.

Orally administered mesoporous silica capped with the cucurbit[8]uril complex to combat colitis and improve intestinal homeostasis by targeting the gut microbiota

RATIONALE

Inflammatory bowel diseases (IBDs) are still awaiting innovative treatments that can maximize the efficiency of site-specific drug release in the colon while enhancing intestinal homeostasis.

METHODS

Herein, we present multilayer-coated mesoporous silica (MSs) which release payload drugs specifically in the colon tract in the presence of azoreductase produced by the gut microbiota, and simultaneously rejuvenate the tryptophan metabolism of the microbiome to induce activation of the aryl hydrocarbon receptor (AHR) for increased anti-inflammatory effects. The MSs were prepared by using cucurbit[8]uril (CB[8]) as a supramolecular "handcuff" to assemble chitosan/hyaluronic acid multilayers on the periphery of a mesoporous silica core.

RESULTS

Strikingly, although MSs remained fairly stable in both acidic and neutral pH, they exhibited excellent responsiveness towards dithionite, an azo-reducing agent employed as a substitute to mimic the specific azoreductase environment in vitro. In comparison with the drug in its free form, hydrocortisone-loaded MSs showed optimized accumulation of therapeutics in the colonic mucosa with minimized premature release in the upper gastrointestinal tract in in vivo imaging and biodistribution studies. The enhanced therapeutic effects of MSs were confirmed in dextran sodium sulfate-induced colitis in mice with promoted colonic epithelial barrier integrity, elevated level of AHR agonists and modulated production of inflammatory cytokines. Furthermore, 16S rRNA analysis showed that the disrupted gut homeostasis of colitic mice was partly corrected by MSs.

CONCLUSION

This novel drug delivery system using self-assembly of tryptophan-functionalized chitosan, which was precomplexed with CB[8], and azobenzene-functionalized hyaluronic acid on the surface of mesoporous silica nanoparticles provides a synergistic gut microbiota-targeting approach for IBD therapy.

Stimuli-Responsive Polymeric Nanocarriers for Drug Delivery, Imaging, and Theragnosis

In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers could be further modified as stimuli-responsive systems based on the mechanism of triggered release, i.e., response to a specific stimulus, either endogenous (pH, enzymes, temperature, redox values, hypoxia, glucose levels) or exogenous (light, magnetism, ultrasound, electrical pulses) for the effective biodistribution and controlled release of drugs or genes at specific sites. Various nanoparticles (NPs) have been functionalized and used as templates for imaging systems in the form of metallic NPs, dendrimers, polymeric NPs, quantum dots, and liposomes. The use of polymeric nanocarriers for imaging and to deliver active compounds has attracted considerable interest in various cancer therapy fields. So-called smart nanopolymer systems are built to respond to certain stimuli such as temperature, pH, light intensity and wavelength, and electrical, magnetic and ultrasonic fields. Many imaging techniques have been explored including optical imaging, magnetic resonance imaging (MRI), nuclear imaging, ultrasound, photoacoustic imaging (PAI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). This review reports on the most recent developments in imaging methods by analyzing examples of smart nanopolymers that can be imaged using one or more imaging techniques. Unique features, including nontoxicity, water solubility, biocompatibility, and the presence of multiple functional groups, designate polymeric nanocues as attractive nanomedicine candidates. In this context, we summarize various classes of multifunctional, polymeric, nano-sized formulations such as liposomes, micelles, nanogels, and dendrimers.

Oxygen-Self-Supplying and HIF-1α-Inhibiting Core-Shell Nanosystem for Hypoxia-Resistant Photodynamic Therapy

Extreme hypoxia together with the expression of hypoxia-inducible factor-1α (HIF-1α) represents a significant barrier against the effective photodynamic therapy (PDT) of tumor. To mitigate these issues, we created a core-shell nanosystem that can simultaneously alleviate tumor hypoxia and suppress the expression of HIF-1α to combat tumor resistance against PDT. Specifically, a carrier-free, dual-drug nanocore was formed by the self-assembly of hydrophobic photosensitizer (chlorin e6, Ce6) and rapamycin (RAP), and then the surface was coated by a layer of metal-organic frameworks (MOFs) to load catalase, reaching an overall drug loading of ∼60%. In such system, catalase acted as oxygen-self-supplier to catalyze the decomposition of tumor-abundant H₂O₂ into O₂, and the sustained release of RAP downregulated HIF-1α, which collectively potentiated the PDT efficacy against tumor. The nanosystem could passively accumulate into tumor, realize in situ oxygen generation and HIF-1α inhibition in tumor tissue, and thus exhibit strong PDT effect toward highly hypoxia tumor. This work provides a highly promising nanoplatform to reverse hypoxia-mediated tumor resistance and overcome the restriction of PDT treatment.