Smart pH/Redox Dual-Responsive Nanogels for On-Demand Intracellular Anticancer Drug Release

Recent advances in photodynamic therapy combined with chemotherapy for cervical cancer: a systematic review

INTRODUCTION

Despite the evidence that photodynamic therapy (PDT) associated with chemotherapy presents great potential to overcome the limitations of monotherapy, little is known about the current status of this combination against cervical cancer. This systematic review aimed to address the currently available advances in combining PDT and chemotherapy in different research models and clinical trials of cervical cancer.

METHODS

We conducted a systematic review based on PRISMA Statement and Open Science Framework review protocol using PubMed, Web of Science, Embase, Scopus, LILACS, and Cochrane databases. We selected original articles focusing on 'Uterine Cervical Neoplasms' and 'Photochemotherapy and Chemotherapy' published in the last 10 years. The risk of bias in the studies was assessed using the CONSORT and SYRCLE tools.

RESULTS

Twenty-three original articles were included, focusing on HeLa cells, derived from endocervical adenocarcinoma and on combinations of several chemotherapeutics. Most of the combinations used modern drug delivery systems for improved simultaneous delivery and presented promising results with increased cytotoxicity compared to monotherapy.

CONCLUSION

Despite the scarcity of animal studies and the absence of clinical studies, the combination of chemotherapy with PDT presents a potential option for cervical cancer therapy requiring additional studies.

OSF REGISTRATION

https://doi.org/10.17605/OSF.IO/WPHN5 [Figure: see text].

Impact of Protein Corona Formation on the Thermoresponsive Behavior of Acrylamide-Based Nanogels

The ability to fine-tune the volume phase transition temperature (VPTT) of thermoresponsive nanoparticles is essential to their successful application in drug delivery. The rational design of these materials is limited by our understanding of the impact that nanoparticle-protein interactions have on their thermoresponsive behavior. In this work, we demonstrate how the formation of protein corona impacts the transition temperature values of acrylamide-based nanogels and their reversibility characteristics, in the presence of lysozyme, given its relevance for the ocular and intranasal administration route. Nanogels were synthesized with N-isopropylacrylamide or N-n-propylacrylamide as backbone monomers, methylenebis(acrylamide) (2.5-20 molar %) as a cross-linker, and functionalized with negatively charged monomers 2-acrylamido-2-methylpropanesulfonic acid, N-acryloyl-l-proline, or acrylic acid; characterization showed comparable particle diameter (c.a.10 nm), but formulation-dependent thermoresponsive properties, in the range 28-54 °C. Lysozyme was shown to form a complex with the negatively charged nanogels, lowering their VPTT values; the hydrophilic nature of the charged comonomer controlled the drop in VPTT upon complex formation, while matrix rigidity only had a small, yet significant effect. The cross-linker content was found to play a major role in determining the reversibility of the temperature-dependent transition of the complexes, with only 20 molar % cross-linked-nanogels displaying a fully reversible transition. These results demonstrate the importance of evaluating protein corona formation in the development of drug delivery systems based on thermoresponsive nanoparticles.

Nanogel enhances the efficacy of MLN8237 in treating hepatocellular carcinoma

MLN8237, a specific inhibitor of Aurora-A kinase, is proved to be a potential treatment strategy for hepatocellular carcinoma (HCC). Nanogels improve the efficacy of doxorubicin. Therefore, this study aims to investigate the increase in the effect of nanogels on MLN8237 in inhibiting HCC. Doxorubicin or MLN8237 was used as an anti-tumor drug models which were packaged by organic solvent volatilization method to obtain the doxorubicin-loaded nanogel and the MLN8237-loaded nanogel. Subsequently, CCK8 assay, cell cycle assay, apoptosis assay, real-time PCR, western blotting assay and animal experiments were used to detect the effects of MLN8237 nanogel on the proliferation, cell cycle, apoptosis, tumor growth, mRNA and protein levels of aurora-A and PUMA, and AKT phosphorylation levels in HCC cell lines. The results show that the nanogels can realize pH-regulated hydrophobicity reversal, have certain stability, and can realize lysosomal escape. Moreover, the MLN8237-loaded nanogel has a stronger ability to inhibit HCC cell proliferation, block cell cycle, promote apoptosis and inhibit tumor growth than free MLN8237 by suppressing aurora-A and AKT phosphorylation. In short, nanogel can enhance the efficacy of MLN8237.

Metal-organic-framework-based pyroptosis nanotuner with long blood circulation for augmented chemotherapy

Pyroptosis is a proinflammatory form of cell death mediated by members of the gasdermin family, and is a powerful tool against cancer. Herein, a pH-responsive doxorubicin (DOX)-encapsulating zeolitic imidazolate framework-8 (ZIF-8) nanoparticle coated with a carboxybetaine-based zwitterionic polymer (DOX@ZIF-8@PCBMA) was prepared. Furthermore, decitabine (DAC) was loaded to obtain a pyroptosis nanotuner (DOX@ZIF-8@PCBMA-DAC). This nanotuner displayed extended blood circulation and enhanced tumor accumulation. In addition, the ZIF-8 structure and disulfide-crosslinked PCBMA coating endowed DOX@ZIF-8@PCBMA-DAC with acidic-pH- and glutathione-responsive degradation. The nanotuner could robustly activate caspase-3 to induce gasdermin E (GSDME)-dependent pyroptosis via the sustained release of DAC and DOX, contributing to excellent tumor suppression with negligible side effects, which may provide novel insights into traditional chemotherapy.

Understanding the Degradation of Core-Shell Nanogels Using Asymmetrical Flow Field Flow Fractionation

Nanogels are candidates for biomedical applications, and core-shell nanogels offer the potential to tune thermoresponsive behaviour with the capacity for extensive degradation. These properties were achieved by the combination of a core of poly(N-isopropylmethacrylamide) and a shell of poly(N-isopropylacrylamide), both crosslinked with the degradable crosslinker N,N'-bis(acryloyl)cystamine. In this work, the degradation behaviour of these nanogels was characterised using asymmetric flow field flow fractionation coupled with multi-angle and dynamic light scattering. By monitoring the degradation products of the nanogels in real-time, it was possible to identify three distinct stages of degradation: nanogel swelling, nanogel fragmentation, and nanogel fragment degradation. The results indicate that the core-shell nanogels degrade slower than their non-core-shell counterparts, possibly due to a higher degree of self-crosslinking reactions occurring in the shell. The majority of the degradation products had molecule weights below 10 kDa, which suggests that they may be cleared through the kidneys. This study provides important insights into the design and characterisation of degradable nanogels for biomedical applications, highlighting the need for accurate characterisation techniques to measure the potential biological impact of nanogel degradation products.

In Situ Encapsulation of Camptothecin by Self-Assembly of Poly(acrylic acid)-b-Poly(N-Isopropylacrylamide) and Chitosan for Controlled Drug Delivery

Camptothecin (CPT) has been shown to exhibit anticancer activity against several cancers. Nevertheless, CPT is very hydrophobic with poor stability, and thus its medical application is limited. Therefore, various drug carriers have been exploited for effectively delivering CPT to the targeted cancer site. In this study, a dual pH/thermo-responsive block copolymer of poly(acrylic acid-b-N-isopropylacrylamide) (PAA-b-PNP) was synthesized and applied to encapsulate CPT. At temperatures above its cloud point, the block copolymer self-assembled to form nanoparticles (NPs) and in situ encapsulate CPT, owing to their hydrophobic interaction as evidenced by fluorescence spectrometry. Chitosan (CS) was further applied on the surface through the formation of a polyelectrolyte complex with PAA for improving biocompatibility. The average particle size and zeta potential of the developed PAA-b-PNP/CPT/CS NPs in a buffer solution were 168 nm and -30.6 mV, respectively. These NPs were still stable at least for 1 month. The PAA-b-PNP/CS NPs exhibited good biocompatibility toward NIH 3T3 cells. Moreover, they could protect the CPT at pH 2.0 with a very slow-release rate. At pH 6.0, these NPs could be internalized by Caco-2 cells, followed by intracellular release of the CPT. They became highly swollen at pH 7.4, and the released CPT was able to diffuse into the cells at higher intensity. Among several cancer cell lines, the highest cytotoxicity was observed for H460 cells. As a result, these environmentally-responsive NPs have the potential to be applied in oral administration.

ROS-Triggered Self-Assembled Nanoparticles Based on a Chemo-Sonodynamic Combinational Therapy Strategy for the Noninvasive Elimination of Hypoxic Tumors

The hypopermeability and hypoxia in the tumor milieu are important factors that limit multiple treatments. Herein, the reactive oxygen species (ROS)-triggered self-assembled nanoparticles (RP-NPs) was constructed. The natural small molecule Rhein (Rh) was encapsulated into RP-NPs as a sonosensitizer highly accumulated at the tumor site. Then highly tissue-permeable ultrasound (US) irradiation induced apoptosis of tumor cells through the excitation of Rh and acoustic cavitation, which prompted the rapid production of large amounts of ROS in the hypoxic tumor microenvironment. In addition, the thioketal bond structures in the innovatively designed prodrug LA-GEM were triggered and broken by ROS to achieve rapid targeted release of the gemcitabine (GEM). Sonodynamic therapy (SDT) increased the tissue permeability of solid tumors and actively disrupted redox homeostasis via mitochondrial pathways to kill hypoxic tumor cells, and the triggered response mechanism to GEM synergistically amplified the effect of chemotherapy. The chemo-sonodynamic combinational treatment approach is highly effective and noninvasive, with promising applications for hypoxic tumor elimination, such as in cervical cancer (CCa) patients who want to maintain their reproductive function.

Mechano-boosting nanomedicine antitumour efficacy by blocking the reticuloendothelial system with stiff nanogels

Nanomedicine has been developed for cancer therapy over several decades, while rapid clearance from blood circulation by reticuloendothelial system (RES) severely limits nanomedicine antitumour efficacy. We design a series of nanogels with distinctive stiffness and investigate how nanogel mechanical properties could be leveraged to overcome RES. Stiff nanogels are injected preferentially to abrogate uptake capacity of macrophages and temporarily block RES, relying on inhibition of clathrin and prolonged liver retention. Afterwards, soft nanogels deliver doxorubicin (DOX) with excellent efficiency, reflected in high tumour accumulation, deep tumour penetration and outstanding antitumour efficacy. In this work, we combine the advantage of stiff nanogels in RES-blockade with the superiority of soft nanogels in drug delivery leads to the optimum tumour inhibition effect, which is defined as mechano-boosting antitumour strategy. Clinical implications of stiffness-dependent RES-blockade are also confirmed by promoting antitumour efficacy of commercialized nanomedicines, such as Doxil and Abraxane.

Rational polyelectrolyte nanoparticles endow preosteoclast-targeted siRNA transfection for anabolic therapy of osteoporosis

Targeted transfection of siRNA to preosteoclasts features the potential of anti-osteoporosis, yet challenge arises from the development of satisfied delivery vehicles. Here, we design a rational core-shell nanoparticle (NP) composed of cationic and responsive core for controlled load and release of small interfering RNA (siRNA) and compatible polyethylene glycol shell modified with alendronate for enhanced circulation and bone-targeted delivery of siRNA. The designed NPs perform well on transfection of an active siRNA (siDcstamp) that interferes Dcstamp mRNA expression, leading to impeded preosteoclast fusion and bone resorption, as well as promoted osteogenesis. In vivo results corroborate the abundant siDcstamp accumulation on bone surfaces and the enhanced trabecular bone mass volume and microstructure in treating osteoporotic OVX mice by rebalancing bone resorption, formation, and vascularization. Our study validates the hypothesis that satisfied transfection of siRNA enables preserved preosteoclasts that regulate bone resorption and formation simultaneously as potential anabolic treatment for osteoporosis.

Biomedicine Innovations and Its Nanohydrogel Classifications

As one of the most cutting-edge and promising polymer crosslinked network nanoparticle systems. Polymer nano-sized hydrogels (nanogels) have been a hot topic in the biomedical field over the last few decades. Due to their unique characteristics, which include their relatively high drug encapsulation efficiency, ease of preparation, high tunability, low toxicity, high stability in serum and responsive behavior to a range of stimuli to facilitate drug release. Nanogels are thought to be the next generation of drug delivery systems that can completely change the way that drug delivery systems have an impact on patients' lives. Nanogels have demonstrated significant potential in a variety of fields, including chemotherapy, diagnosis, organ targeting, and delivery of bioactive molecules of different dimensions. However, the lack of substantial clinical data from nanogels becomes one of the major barriers to translating the nanogel concept into a practical therapeutic application for many disease conditions. In addition, nanogel safety profiles have been the major concern that hinders it advancement to the clinical trial phase. This review aims to emphasize the unique properties of nanogels as delivery systems for a variety of bioactive molecules over other nano-delivery systems. Also, this review attempts to give insight into the recent progress in nanogels as a carrier in the field of nanomedicine to overcome complex biological barriers. Relevant scientific data and clinical rationale for the development and the potential use of nanogel as a carrier for targeted therapeutic interventions are discussed. Finally, the concluding points of this review highlight the importance of understanding the long-term toxicity profile of nanogel within the biological system to fully understand their biocompatibility.

Extracellular vesicles for improved tumor accumulation and penetration

Extracellular vesicles (EVs), including microparticles and exosomes, have emerged as potential tools for tumor targeting delivery during the past years. Recently, mass of strategies are applied to assist EVs to accumulate and penetrate into deep tumor sites. In this review, EVs from different cells with unique innate characters and engineered approaches (e.g. chemical engineering, genetical engineering and biomimetic engineering) as drug delivery systems to enhance tumor accumulation and penetration are summarized. Meanwhile, efficient biological function modulation (e.g. extracellular matrix degradation, mechanical property regulation and transcytosis) is introduced to facilitate tumor accumulation and penetration of EVs. Finally, the prospects and challenges on further clinical applications of EVs are discussed.

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

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

Rational Design of Nanotherapeutics Based on the Five Features Principle for Potent Elimination of Cancer Stem Cells

Cancer stem cells (CSCs), also known as tumor initiating cells or tumor repopulating cells, which comprise only a small fraction of tumor, have received tremendous attention during the past two decades, as they are considered as the ringleader for initiation and progression of tumors, therapy resistance, metastasis, and recurrence in the clinic. Hence, eradicating CSCs is critical for successful cancer treatment. To that end, various CSC-targeting therapeutic agents have been pursued. However, these CSC-specific drugs are ineffective toward bulk cancer cells. Furthermore, these anti-CSC drugs not only eradicate CSCs but also affect conventional stem cells in normal organs or tissues. By virtue of the enhanced permeability and retention (EPR) effect, nanomaterial drug delivery systems (NDDSs) passively accumulate in tumor tissues, thereby alleviating severe side effects toward normal viscera. NDDSs can be further functionalized with CSC-specific binding molecules to promote targeted drug delivery toward CSCs. Moreover, NDDSs have unique advantages in encapsulating CSC-specific drugs and cytotoxic agents, realizing synchronized killing of CSCs and bulk cancer cells both temporally and spatially. For these reasons, leveraging nanotherapeutic strategies to target CSCs has gained tremendous attention recently.Some ten years ago, we summarized five basic features of efficient nanotherapeutics (the five features principle), which consist of long circulation, tumor accumulation, deep penetration, cellular internalization, and drug release. Based on this design rationale, we constructed several NDDSs, including nanogels with adaptive hydrophobicity, CSC-derived microparticles with tailored softness, and tumor exosome sheathed porous silicon biomimetic nanoparticles, for targeted drug delivery to tumor. To our astonishment, these NDDSs that possess the five basic features achieve decent drug delivery efficiency toward not only bulk tumor cells but more importantly CSCs. Consequently, such nanotherapeutics as-designed based on the five features principle are potent in eradicating CSCs, even with only cytotoxic drugs, for instance, doxorubicin. Furthermore, commercialized nanomedicines, such as Doxil and Abraxane, can be endowed with these five basic features by hyperbaric oxygen therapy and therefore achieve outstanding drug delivery efficiency, potent CSC elimination, and efficient cancer therapy. These studies suggest that intractable CSCs can be tackled with a material-based approach, highlight the critical role of the five features principle in designing effective nanotherapeutics, and pinpoint the significance of drug delivery efficiency in eliminating CSCs and bulk cancer cells.

Nanocatalyst doped bacterial cellulose-based thermosensitive nanogel with biocatalytic function for antibacterial application

Reactive oxygen species (ROS) for treating bacterial infection is an alternative strategy to overcome the drawbacks such as bacterial resistance of commonly used antibiotics. Nanocatalysts have been proved highly effective in regulating intracellular ROS level due to their intrinsic enzymes-mimicking ability. Herein, we prepared a carbon-based nanozyme doped with copper atoms with peroxidase mimetic activity to catalyze the decomposition of bio-safety dosage of H₂O₂ to highly reactive OH radicals for antibacterial treatment. Furthermore, we designed the thermo-responsive nanogels consisting of bacterial cellulose nanowhiskers as the carrier of the nanozyme. The obtained nanogels displayed remarkable intelligent response to temperature change with sol-gel transition temperature of ~33 °C and in situ gel forming ability. Moreover, the nanogels exhibited excellent biocompatibility in vitro, along with remarkable antibacterial efficacy which could inactivate 6.36 log of S. aureus and 6.01 log of E. coli in 3 h, respectively. The findings provide a novel strategy for advancing the development of nanocatalysts-based responsive biomaterials for treating bacterial infections.

Dual-responsive degradable core-shell nanogels with tuneable aggregation behaviour

We report the synthesis of core–shell nanogels by sequential addition of thermoresponsive monomers; N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM). The aggregation behaviour of aqueous dispersions of these particles in the presence of salt can be tuned by varying the monomer ratio. The inclusion of degradable cross-linker bis(acryloyl)cystamine (BAC) allows the nanogels to degrade in the presence of reducing agent, with nanogels composed of a copolymer of the two monomers not showing the same high levels of degradation as the comparable core–shell particles. These levels of degradation were also seen with physiologically relevant reducing agent concentration at pH 7. Therefore, it is hoped that the aggregation of these nanogels will have applications in nanomedicine and beyond.

Core–shell nanogels with a poly(N-isopropylmethacrylamide) core and poly(N-isopropylacrylamide) shell display tuneable thermoresponsive behaviour and high degradability.

Targeted pH/redox dual-responsive nanoparticles for cancer chemotherapy combined with photodynamic/photothermal therapy

The application of intelligent responsive nanoparticles in combination therapy has become an emerging issue for cancer therapeutics. In this work, we have constructed a targeted nanoparticle that is capable of...

Construction multifunctional nanozyme for synergistic catalytic therapy and phototherapy based on controllable performance

Advances in nanozyme involve an efficient catalytic process, which has demonstrated great potential in tumor therapy. The key to improving catalytic therapy is to solve the limitation of the tumor microenvironment on Fenton reaction. In this work, Prussian blue nanoparticles doped with different rare earth ions (Yb³⁺, Gd³⁺, Tm³⁺) were screened to perform synergistic of photothermalandcatalytictumortherapy. The optimized catalytic performance can be further enhanced through photothermal effect to maximize the Fenton reaction to solve the limitation of the tumor microenvironment. Yb-PB, with the optimal photothermal and catalytic performance, was screened out. In order to avoid the scavenging effect of glutathione (GSH) on ·OH in tumor cells and the reaction with a bit H₂O₂ in normal cells, GSH targeted polydopamine (PDA) was wrapped on the surface of Yb-PB to obtain Yb-PB@PDA. It was found that enough hydroxyl radicals (·OH) can be generated even if at high GSH concentration and the NIR irradiation can help produce more ·OH. Cell fluorescence imaging (FOI) and in vivo magnetic resonance imaging (MRI) experiments showed the potential application in FOI/MRI dual-mode imaging guided therapy. In vivo anti-tumor experiments showed that Yb-PB@PDA has a satisfactory anti-cancer effect through the combined effect of catalytic/photothermal therapy. Thus, a multifunctional nanozyme for tumor therapy is constructed.

Strategic Design of Intelligent-Responsive Nanogel Carriers for Cancer Therapy

Owing to the distinctive constituents of tumor tissue from those healthy organs, nanomedicine strategies show significant potentials in smart drug delivery. Nowadays, stimuli-responsive nanogels are playing increasingly important roles in the application of cancer therapy because of their sensitivity to various internal or external physicochemical stimuli, which exhibit site-specific and markedly enhanced drug release. Besides, nanogels are promising as drug carriers because of their porous structures, good biocompatibility, large surface area, and excellent capability with drugs. Taking advantage of multiresponsiveness, recent years have witnessed the rapid evolution of stimulus-responsive nanogels from monoresponsive to multiresponsive systems; however, there lacks a comprehensive review summarizing these reports. In this Review, we discuss the properties, synthesis, and characterization of nanogels. Moreover, tumor microenvironment and corresponding designing strategies for stimuli-response nanogels, both exogenous (temperature, magnetic field, light) and endogenous (pH, biomolecular, redox, ROS, pressure, hypoxia) are summarized on the basis of the recent advances in multistimuli-responsive nanogel systems. Nanogel and two-dimensional material composites show excellent performance in the field of constructing multistimulus-responsive nanoparticles and precise intelligent drug release integrated system for multimodal cancer diagnosis and therapy. Finally, potential progresses and suggestions are provided for the further design of hybrid nanogels based on emerging two-dimensional materials.

Aliphatic Quaternary Ammonium Functionalized Nanogels for Gene Delivery

Gene therapy is a promising treatment for hereditary diseases, as well as acquired genetic diseases, including cancer. Facing the complicated physiological and pathological environment in vivo, developing efficient non-viral gene vectors is needed for their clinical application. Here, poly(N-isopropylacrylamide) (p(NIPAM)) nanogels are presented with either protonatable tertiary amine groups or permanently charged quaternized ammonium groups to achieve DNA complexation ability. In addition, a quaternary ammonium-functionalized nanogel was further provided with an aliphatic moiety using 1-bromododecane to add a membrane-interacting structure to ultimately facilitate intracellular release of the genetic material. The ability of the tertiary amine-, quaternized ammonium-, and aliphatic quaternized ammonium-functionalized p(NIPAM) nanogels (i.e., NGs, NGs-MI, and NGs-BDD, respectively) to mediate gene transfection was evaluated by fluorescence microscopy and flow cytometry. It is observed that NGs-BDD/pDNA complexes exhibit efficient gene loading, gene protection ability, and intracellular uptake similar to that of NGs-MI/pDNA complexes. However, only the NGs-BDD/pDNA complexes show a notable gene transfer efficiency, which can be ascribed to their ability to mediate DNA escape from endosomes. We conclude that NGs-BDD displays a cationic lipid-like behavior that facilitates endosomal escape by perturbing the endosomal/lysosomal membrane. These findings demonstrate that the presence of aliphatic chains within the nanogel is instrumental in accomplishing gene delivery, which provides a rationale for the further development of nanogel-based gene delivery systems.

Design and Applications of Tumor Microenvironment-Responsive Nanogels as Drug Carriers

In recent years, the exploration of tumor microenvironment has provided a new approach for tumor treatment. More and more researches are devoted to designing tumor microenvironment-responsive nanogels loaded with therapeutic drugs. Compared with other drug carriers, nanogel has shown great potential in improving the effect of chemotherapy, which is attributed to its stable size, superior hydrophilicity, excellent biocompatibility, and responsiveness to specific environment. This review primarily summarizes the common preparation techniques of nanogels (such as free radical polymerization, covalent cross-linking, and physical self-assembly) and loading ways of drug in nanogels (including physical encapsulation and chemical coupling) as well as the controlled drug release behaviors. Furthermore, the difficulties and prospects of nanogels as drug carriers are also briefly described.

Guiding cell adhesion and motility by modulating cross-linking and topographic properties of microgel arrays

Biomaterial-driven modulation of cell adhesion and migration is a challenging aspect of tissue engineering. Here, we investigated the impact of surface-bound microgel arrays with variable geometry and adjustable cross-linking properties on cell adhesion and migration. We show that cell migration is inversely correlated with microgel array spacing, whereas directionality increases as array spacing increases. Focal adhesion dynamics is also modulated by microgel topography resulting in less dynamic focal adhesions on surface-bound microgels. Microgels also modulate the motility and adhesion of Sertoli cells used as a model for cell migration and adhesion. Both focal adhesion dynamics and speed are reduced on microgels. Interestingly, Gas2L1, a component of the cytoskeleton that mediates the interaction between microtubules and microfilaments, is dispensable for the regulation of cell adhesion and migration on microgels. Finally, increasing microgel cross-linking causes a clear reduction of focal adhesion turnover in Sertoli cells. These findings not only show that spacing and rigidity of surface-grafted microgels arrays can be effectively used to modulate cell adhesion and motility of diverse cellular systems, but they also form the basis for future developments in the fields of medicine and tissue engineering.

Electromagnetic Field-Programmed Magnetic Vortex Nanodelivery System for Efficacious Cancer Therapy

Effective delivery of anticancer drugs into the nucleus for pharmacological action is impeded by a series of intratumoral transport barriers. Despite the significant potential of magnetic nanovehicles in electromagnetic field (EF)-activated drug delivery, modularizing a tandem magnetoresponsive activity in a one-nanoparticle system to meet different requirements at both tissue and cellular levels remain highly challenging. Herein, a strategy is described by employing sequential EF frequencies in inducing a succession of magnetoresponses in the magnetic nanovehicles that aims to realize cascaded tissue penetration and nuclear accumulation. This nanovehicle features ferrimagnetic vortex-domain iron oxide nanorings coated with a thermo-responsive polyethylenimine copolymer (PI/FVIOs). It is shown that the programmed cascading of low frequency (Lf)-EF-induced magnetophoresis and medium frequency (Mf)-EF-stimulated magneto-thermia can steer the Doxorubicin (DOX)-PI/FVIOs to the deep tissue and subsequently trigger intracellular burst release of DOX for successful nuclear entry. By programming the order of different EF frequencies, it is demonstrated that first-stage Lf-EF and subsequent Mf-EF operation enables DOX-PI/FVIOs to effectively deliver 86.2% drug into the nucleus in vivo. This nanodelivery system empowers potent antitumoral activity in various models of intractable tumors, including DOX-resistant MCF-7 breast cancer cells, triple-negative MDA-MB-231 breast cancer cells, and BxPC-3 pancreatic cancer cells with poor permeability.

Effect of TEOA on the Process of Photopolymerization at 532 nm and Properties of Nanogels

Nanogel is an important kind of biomaterials applied for wound dressings, drug delivery, medical diagnostics and biosensors. The properties of nanogels closely depend on the density of the crosslinking network. In this study, the role of triethanolamine (TEOA) in the effect on the crosslinking degree of nanogels based on poly(ethylene glycol) diacrylate (PEGDA) was investigated and illustrated. The effect of TEOA on the process of photopolymerization at 532 nm and properties of the nanogels was systematically investigated by using UV-vis spectroscopy, FT-IR spectroscopy, ¹ H NMR, DLS, SEM, AFM and DSC. In brief, the double bond conversion of photopolymerization and the crosslinking degree of nanogels can be effectively regulated by TEOA.

Novel Multifunctional Stimuli-Responsive Nanoparticles for Synergetic Chemo-Photothermal Therapy of Tumors

In this study, a novel class of multifunctional responsive nanoparticles is designed and fabricated as drug nanocarriers for synergetic chemo-photothermal therapy of tumors. The proposed nanoparticles are composed of a thermo-/pH-responsive poly(N-isopropylacrylamide-co-acrylic acid) (PNA) nanogel core, a polydopamine (PDA) layer for photothermal conversion, and an outer folic acid (FA) layer as a targeting agent for the folate receptors on tumor cells. The fabricated nanoparticles show good biocompatibility and outstanding photothermal conversion efficiency. The proposed nanoparticles loaded with doxorubicin (DOX) drug molecules are stable under physiological conditions with low leakage of drugs, while rapidly release drugs in environments with low pH conditions and at high temperature. The experimental results show that the drug release process is mainly governed by Fickian diffusion. In vitro cell experimental results demonstrate that the PNA-DOX@PDA-FA nanoparticles can be phagocytized by 4T1 tumor cells and release drugs in tumor cell acidic environments, and confirm that the combined chemo and photothermal therapeutic efficacy of PNA-DOX@PDA-FA nanoparticles is higher than the photothermal therapeutic efficacy or the chemotherapeutic efficacy alone. The proposed multifunctional responsive nanoparticles in this study provide a novel class of drug nanocarriers as a promising tool for synergetic chemo-photothermal therapy of tumors.

Tumor-mediated shape-transformable nanogels with pH/redox/enzymatic-sensitivity for anticancer therapy

Lack of sufficient tumor penetration of the current nanomedicines is a major reason limiting their clinical success in cancer therapy. In this work, we aimed at the development of a novel biodegradable nanoplatform for the selective and controlled delivery of anticancer agents, with improved tumor permeability and the ability to release ultrasmall nanovesicles in the tumor microenvironment. To this end, positively charged nanogels were obtained through the double-crosslinking of chitosan with an ionic physical gelator and a disulfide-containing chemical crosslinker. After conjugation to an anionic oligomer, the cationic nanogels were transformed into negatively charged nanocarriers (CTCP), enabling effective encapsulation of the cationic anticancer agent doxorubicin (DOX) to generate a biodegradable nanomedicine (DOX@CTCP). DOX@CTCP could maintain sustained DOX release and decreased DOX toxicity. Upon arrival at the tumor tissue, the reductive and lysozyme-high microenvironment drives the cleavage of the nanomedicine to release DOX-carrying nanoblocks of smaller size, which together with their acidic-protonable feature achieves an effective therapeutic delivery into cancer cells. The nanomedicine described here showed excellent biocompatibility/biosafety and enhanced in vivo antitumor efficacy.

Synthesis and Characterization of Folate-Modified Cell Membrane Mimetic Copolymer Micelles for Effective Tumor Cell Internalization

The inefficient targeting and phagocytic clearance of nanodrug delivery systems are two major obstacles in cancer therapy. Here, inspired by the special properties of zwitterionic polymers and folic acid (FA), a partly biodegradable copolymer of FA-modified poly(ε-caprolactone) block poly(2-methacryloxoethyl phosphorylcholine), PCL-b-PMPC-FA, was synthesized via atom transfer radical polymerization (ATRP) and click reaction. Non-FA-modified copolymer PCL-b-PMPC was also synthesized as a control. The hydrodynamic diameter of the PCL-b-PMPC-FA micelles is 158 nm (PDI 0.261), slightly larger than that of the PCL-b-PMPC micelles (139 nm, PDI 0.242). The drug doxorubicin (DOX) could be entrapped in the micelles, and as the pH decreased from 7.4 to 5.0, DOX release (in vitro) was accelerated. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay indicated that both the PCL-b-PMPC and the PCL-b-PMPC-FA micelles showed low toxicity to L929, HeLa, and MCF-7 cells. In addition, the DOX-loaded micelles, PCL-b-PMPC/DOX and PCL-b-PMPC-FA/DOX micelles, exhibited low toxicity to L929 cells but high toxicity to HeLa and MCF-7 cells, especially the PCL-b-PMPC-FA/DOX micelles. HeLa and MCF-7 cell uptakes of the PCL-b-PMPC-FA/DOX micelles were 4.8 and 4.5 times higher than that of the PCL-b-PMPC/DOX micelles, respectively. Therefore, PCL-b-PMPC-FA micelles have great potential for developing drug delivery systems with extended circulation times and tumor-targeting properties.

Design and fabrication of dual responsive lignin-based nanogel via "grafting from" atom transfer radical polymerization for curcumin loading and release

The story of human dreams about curing all diseases, disorders and lesions is as old as human history. In the frontier of medical science, nanomedicine is trying to solve the problem. In this study, inspired by nanotechnology and using "grafting from" approach, a novel lignin-based nanogel was synthesized using atom transfer radical polymerization (ATRP) method. N-isopropylacrylamide (NIPAM) and N,N-dimethylaminoethylmethacrylate (DMAEMA) comonomers were graft copolymerized from fully brominated lignin as ATRP macroinitiator to synthesize lignin-g-P(NIPAM-co-DMAEMA) nanogel (LNDNG). By controlling the initial comonomer compositions and ATRP conditions, four LNDNG systems with different lower critical solution temperatures (LCSTs) of 32, 34, 37 and 42 °C were prepared. The LNDNGs were evaluated by GPC, FT-IR, 1H NMR, UV-Vis, DLS, SEM and TEM analyses. The prepared nanogels exhibited an average diameter of 150 nm with dual temperature and pH responsiveness. Curcumin (CUR) loading capacity and encapsulation efficiency of the LNDNGs were 49.69% and 92.62% on average, respectively. The cumulative release amount of loaded CUR was observed to be 65.36% after 72 h. The new lignin-based NGs proposed in the present work seems to be a promising, safe and comparable system in a near future.

Tumor acidity-responsive carrier-free nanodrugs based on targeting activation via ICG-templated assembly for NIR-II imaging-guided photothermal–chemotherapy

Novel tumor microenvironment-driven self-targeting supramolecular nanodrugs via ICG-templated small-molecule self-assembly for NIR-II imaging-guided synergistic photothermal–chemotherapy.

Antimicrobial Nanogels with Nanoinjection Capabilities for Delivery of the Hydrophobic Antibacterial Agent Triclosan

With the ever-growing problem of antibiotic resistance, developing antimicrobial strategies is urgently needed. Herein, a hydrophobic drug delivery nanocarrier is developed for combating planktonic bacteria that enhances the efficiency of the hydrophobic antimicrobial agent, Triclosan, up to a 1000 times. The poly(N-isopropylacrylamide-co-N-[3-(dimethylamino)propyl]methacrylamide), p(NIPAM-co-DMAPMA), based nanogel is prepared via a one-pot precipitation polymerization, followed by quaternization with 1-bromododecane to form hydrophobic domains inside the nanogel network through intraparticle self-assembly of the aliphatic chains (C12). Triclosan, as the model hydrophobic antimicrobial drug, is loaded within the hydrophobic domains inside the nanogel. The nanogel can adhere to the bacterial cell wall via electrostatic interactions and induce membrane destruction via the insertion of the aliphatic chains into the cell membrane. The hydrophobic antimicrobial Triclosan can be actively injected into the cell through the destroyed membrane. This approach dramatically increases the effective concentration of Triclosan at the bacterial site. Both the minimal inhibitory concentration and minimal bactericidal concentration against the Gram-positive bacteria S. aureus and S. epidermidis decreased 3 orders of magnitude, compared to free Triclosan. The synergy of physical destruction and active nanoinjection significantly enhances the antimicrobial efficacy, and the designed nanoinjection delivery system holds great promise for combating antimicrobial resistance as well as the applications of hydrophobic drugs delivery for many other possible applications.

Self-Distinguishing and Stimulus-Responsive Carrier-Free Theranostic Nanoagents for Imaging-Guided Chemo-Photothermal Therapy in Small-Cell Lung Cancer

Lack of tumor targeting and low drug payload severely impedes various nanoagents further employed in small-cell lung cancer (SCLC). Therefore, how to develop a new targeting ligand and enhance drug payload has been an urgent need for SCLC therapy. Herein, we first sift and verify that capreomycin (Cm) has a high affinity toward CD56 receptors overexpressed on SCLC cells. Motivated by the concept of self-targeted drug delivery, Cm is selected as the specific targeting ligand toward CD56 receptors and chemodrug doxorubicin (Dox) is adopted to be covalently linked via the redox-responsive disulfide linkage. The synthesized self-distinguishing prodrug (Dox-ss-Cm) and FDA-approved photosensitizer indocyanine green (ICG) as structural motifs can be self-assembled into theranostic nanoagents (ICG@Dox-ss-Cm NPs) within an aqueous solution. Such carrier-free nanoagents with high drug payload can exert targeted on-demand drug release under multiple stimuli of intracellular lysosomal acidity, glutathione (GSH), and an external near-infrared (NIR) laser. Besides, our nanoagents can be specifically self-targeted to SCLC sites in vivo and self-distinguishing via SCLC cells in vitro; thus, they decrease the undesirable effects on normal tissues and organs. Further in vitro and in vivo studies uniformly confirm that such nanoagents show highly synergistic effects for SCLC chemo-photothermal therapy (PTT) under the precise guidance of NIR fluorescence (NIRF)/photoacoustic (PA) imaging. Taken together, our work can provide a novel and promising strategy for the targeted treatment of SCLC.

Revealing the NIR-triggered chemotherapy therapeutic window of magnetic and thermoresponsive nanogels

The combination of magnetic nanoparticles and thermoresponsive nanogels represents an appealing strategy for the development of theranostic probes. These hybrid nanocarriers present several advantages such as outstanding properties for guided therapy, magnetic resonance imaging, and triggered release of encapsulated cargoes. Most magnetic thermoresponsive nanogels are built with strategies that comprise a physical interaction of particles with the polymeric network or the covalent attachment of a single particle to the linear polymer. Herein, we report a facile synthetic approach for the synthesis of magnetic and thermoresponsive nanogels that allows the controlled incorporation of multiple superparamagnetic inorganic cores as covalent cross-linkers. An ultrasonication-assisted precipitation-polymerization afforded nanogels with sizes in the nanometric range and similar magnetization and light transduction properties compared to the discrete magnetic nanoparticles. The theranostic capability of these nanocarriers was further investigated both in vitro and in vivo. In vivo experiments demonstrated the capacity of these materials as nanocarriers for near-infrared (NIR) triggered chemotherapy and highlighted the relevance of the correct concentration/dose in this antitumoral modality to achieve a superior therapeutic efficacy.

PH and redox dual-responsive polymeric micelles with charge conversion for paclitaxel delivery

Here we demonstrate a type of pH and redox dual-responsive micelles, which were self-assembled in aqueous solution by an amphiphilic polymer, methoxypoly(ethylene glycol)-cystamine-poly(L-glutamic acid)-imidazole (mPEG-SS-PGA-IM). Considering tumor cells or tissues exhibiting low pH values and high glutathione (GSH) concentration, mPEG-SS-PGA-IM micelles possessed the charge conversion at pH of tumor tissues, which can facilitate cellular uptake of tumor cells. Furthermore, mPEG-SS-PGA-IM micelles can escape from endo/lysosomes based on the proton sponge effect, following degraded by higher concentration of GSH in cytoplasm. CLSM images of HCT116 cells indicated that mPEG-SS-PGA-IM micelles can escape from endo/lysosomes and enter cytoplasm. MTT assay showed that (paclitaxel) PTX-loaded mPEG-SS-PGA-IM micelles had higher cytotoxicity against HCT116 cells compared with PTX-loaded mPEG-PBLG and mPEG-SS-PBLG micelles. These results indicated that these mPEG-SS-PGA-IM micelles, as novel and effective pH- and redox-responsive nanocarriers, have great potential to both improve drug targeting efficiency while also enhancing the antitumor efficacy of PTX.

Tunable nanogels by host-guest interaction with carboxylate pillar[5]arene for controlled encapsulation and release of doxorubicin

Nanogels have become one of the most attractive systems for application as delivery vectors or for theragnostic approaches in nanomedicine, which is mainly related to the ease of their synthesis by precipitation polymerization. However, only a few suitable monomers have been reported so far and stabilization of the nanogels requires the incorporation of rather defined amounts of in most cases charged co-monomers, such as acrylic acid, which limits the flexibility in their design. Here, we present an alternative approach using a pyridinium based monomer, which not only provides stability due to the positive charge, but also allows the attachment of functional carboxylate-pillar[5]arene by the formation of a host-guest complex. This approach is tested on pH-sensitive nanogels based on the monomer N-[(2,2-dimethyl-1,3-dioxolane)methyl]acrylamide (DMDOMA) featuring an acetal group, which is hydrolysed under acidic conditions. As carboxylates are known to catalyze this hydrolysis, we tested different amounts of carboxylate-pillar[5]arenes to tune the hydrolysis rate of the acetal group and found a direct correlation. Additional encapsulation studies with doxorubicin (DOX) revealed that surface potential and charge density represent additional key factors not only for the loading capacity, but also for the release profile of the nanogels. The option to tune such properties simply by the addition of a co-factor, in this case, the carboxylate-pillar[5]arenes provides a powerful tool to optimize characteristics of functional nanogels for drug delivery or other applications.

Cell Type-Dependent Specificity and Anti-Inflammatory Effects of Charge-Reversible MSNs-COS-CMC for Targeted Drug Delivery in Cervical Carcinoma

The surface charge of nanocarriers inevitably affects drug delivery efficiency; however, the cancer cell specificity, anti-inflammatory effects, and charge-reversal points remain to be further addressed in biomedical applications. The aim of this study was to comprehensively assess the cancer cell specificity of DOX-loaded mesoporous silica-chitosan oligosaccharide-carboxymethyl chitosan nanoparticles (DOX@MSNs-COS-CMC) in MCF-7 and HeLa cells, inhibit the production of inflammatory cytokines, and improve the drug accumulation in the tumor site. Intracellular results reveal that the retention time prolonged to 48 h in both HeLa and MCF-7 cells at pH 7.4. However, DOX@MSNs-COS-CMC exhibited a cell type-dependent cytotoxicity and enhanced intracellular uptake in HeLa cells at pH 6.5, due to the clathrin-mediated endocytosis and macropinocytosis in HeLa cells in comparison with the vesicular transport in MCF-7 cells. Moreover, Pearson's correlation coefficient value significantly decreased to 0.25 after 8 h, prompting endosomal escape and drug delivery into the HeLa nucleus. After the treatment of MSNs-COS-CMC at 200 μg/mL, the inflammatory cytokines IL-6 and TNF-α level decreased by 70% and 80%, respectively. Tumor inhibition of DOX@MSNs-COS-CMC was 0.4 times higher than free DOX, alleviating cardiotoxicity and inflammation in the HeLa xenograft tumor model. Charge-reversible DOX@MSNs-COS-CMC could be a possible candidate for clinical therapy of cervical carcinoma.

Reduction-responsive molecularly imprinted nanogels for drug delivery applications

Degradable molecularly imprinted polymers (MIPs) with affinity for S-propranolol were prepared by the copolymerization of methacrylic acid as functional monomer and a disulfide-containing cross-linker, bis(2-methacryloyloxyethyl)disulfide (DSDMA), using bulk polymerization or high dilution polymerization for nanogels synthesis. The specificity and the selectivity of DSDMA-based molecularly imprinted polymers toward S-propranolol were studied in batch binding experiments, and their binding properties were compared to a traditional ethylene glycol dimethacrylate (EDMA)-based MIP. Nanosized MIPs prepared with DSDMA as crosslinker could be degraded into lower molecular weight linear polymers by cleaving the disulfide bonds and thus reversing cross-linking using different reducing agents (NaBH4, DTT, GSH). Turbidity, viscosity, polymer size and IR-spectra were measured to study the polymer degradation. The loss of specific recognition and binding capacity of S-propranolol was also observed after MIP degradation. This phenomenon was applied to modulate the release properties of the MIP. In presence of GSH at its intracellular concentration, the S-propranolol release was higher, showing that these materials could potentially be applied as intracellular controlled drug delivery system.

Gd-metallofullerenol drug delivery system mediated macrophage polarization enhances the efficiency of chemotherapy

Treatment of solid tumors by chemotherapy is usually failed in clinical because of its low effectiveness and side effects. Stimulation of immune system in vivo to fight cancer has been proved to be a pleasant complementary to systemic chemotherapy. Herein, we have developed a combination cancer therapy strategy by using polymer nanoparticles to deliver Gd-metallofullerenol and doxorubicin simultaneously. The Gd-metallofullerenol provoked the Th1 immune response by regulating the M1 macrophage polarization and the doxorubicin realized direct tumor cells killing by its cytotoxic effect. Also, the Gd-metallofullerenol as part of component in delivery system enhances the encapsulation efficiency of doxorubicin in polymer cargo for potential passive tumor target. The biocompatible and reliable method by combining nanoparticle-induced immune modulation and chemotherapy triggers systemic antitumor immune responses for the synergistic inhibition of tumor growth in vivo. The integration of Gd-metallofullerenol and doxorubicin with potentially complementary functions in one nanoplatform may provide new opportunities to improve cancer treatments.

A glance over doxorubicin based-nanotherapeutics: From proof-of-concept studies to solutions in the market

Cancer is one of the leading causes of death worldwide and, as such, efforts are being done to find new chemotherapeutic drugs or, alternatively, novel approaches for the delivery of old ones. In this scope, when used as vehicles for drugs, nanomaterials may potentially maximize the efficacy of the treatment and reduce its side effects, for example by a change in drug's pharmacokinetics, cell targeting and/or specific stimuli-responsiveness. This is the case of doxorubicin (DOX) that presents a broad spectrum of activity and is one of the most widely used chemotherapeutic drugs as first-line treatment. Indeed, DOX is a very interesting example of a drug for which several nanosized delivery systems have been developed over the years. While it is true that some of these systems are already in the market, it is also true that research on this subject remains very active and that there is a continuing search for new solutions. In this sense, this review takes the example of doxorubicin, not so much with the focus on the drug itself, but rather as a case study around which very diverse and imaginative nanotechnology approaches have emerged.

Polyphotosensitizer nanogels for GSH-responsive histone deacetylase inhibitors delivery and enhanced cancer photodynamic therapy

Photodynamic therapy (PDT) is one of the non-invasive and selective treatment methodologies for cancer. However, many highly efficient photosensitizers (PSs) are usually low physiological solubility, limited bioavailability and tending aggregation, impeding the effectiveness of PDT, as well as cancer resistance of PDT further reduce its therapeutic effect. Though some smart delivery systems have been developed, the problem of photosensitizer leakage/release has not been completely solved. Herein, we developed a smart therapeutic nanoplatform based on polyphotosensitizer nanogel as novel nanophotosensitizers and drug carriers. Moreover, by loading of histone deacetylase inhibitors (SAHA), it allows for enhanced synergistic therapy strategy of prostate cancer via inhibiting HIF-1α and VEGF pathways of cancer cells involved in PDT resistance. Our study presents the well-designed nanoplatform of nanogel-Ce6, which could serve as a photodynamic agent without Ce6 molecules release in the responsive environment, offering the potential to encapsulate diverse functional components for smart drug release and imaging-guided combination therapy in vitro and in vivo.

Antifouling and pH-Responsive Poly(Carboxybetaine)-Based Nanoparticles for Tumor Cell Targeting

Nanocarriers with responsibility and surface functionality of targeting molecules have been widely used to improve therapeutic efficiency. Hence, we report the assembly of pH-responsive and targeted polymer nanoparticles (NPs) composed of poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) as the core and poly(carboxybetaine methacrylate) (PCBMA) as the shell, functionalized with cyclic peptides containing Arginine-Glycine-Aspartic acid-D-Phenylalanine-Lysine (RGD). The resulting polymer NPs (PDPA@PCBMA-RGD NPs) can maintain the pH-responsivity of PDPA (pKa ~6.5) and low-fouling property of PCBMA that significantly resist non-specific interactions with RAW 264.7 and HeLa cells. Meanwhile, PDPA@PCBMA-RGD NPs could specifically target αvβ3 integrin-expressed human glioblastoma (U87) cells. The pH-responsiveness and low-fouling properties of PDPA@PCBMA NPs are comparable to PDPA@poly(ethylene glycol) (PDPA@PEG) NPs, which indicates that PCBMA is an alternative to PEG for low-fouling coatings. The advantage of PDPA@PCBMA NPs lies in the presence of carboxyl groups on their surfaces for further modification (e.g., RGD functionalization for cell targeting). The reported polymer NPs represent a new carrier that have the potential for targeted therapeutic delivery.

Smart Nanotherapeutic Targeting of Tumor Vasculature

The past decades have witnessed the development of a field dedicated to targeting tumor vasculature for cancer therapy. In contrast to conventional chemotherapeutics that need to penetrate into tumor tissues for killing tumor cells, the agents targeting tumor vascular system have two major advantages: direct contact with vascular endothelial cells or the blood and less possibility to induce drug resistance because of high gene stability of endothelial cells. More specifically, various angiogenesis inhibitors (AIs) and vascular disrupting agents (VDAs) that block tumor blood supply to inhibit tumor progression, some of which have been applied clinically, have been described. However, off-target effects and high effective doses limit the utility of these formulations in cancer patients. Thus, new strategies with improved therapeutic efficacy and safety are needed for tumor vessel targeting therapy. With the burgeoning developments in nanotechnology, smart nanotherapeutics now offer unprecedented potential for targeting tumor vasculature. Based on specific structural and functional features of the tumor vasculature, a number of different nanoscale delivery systems have been proposed for cancer therapy. In this Account, we summarize several distinct strategies to modulate tumor vasculature with various smart nanotherapeutics for safe and effective tumor therapy developed by our research programs. Inspired by the blood coagulation cascade, we generated nanoparticle-mediated tumor vessel infarction strategies that selectively block tumor blood supply to starve the tumor to death. By specifically delivering thrombin loaded DNA nanorobots (Nanorobot-Th) into tumor vessels, an intratumoral thrombosis is triggered to induce vascular infarction and, ultimately, tumor necrosis. Mimicking the coagulation cascade, a smart polymeric nanogel achieves permanent and peripheral embolization of liver tumors. Considering the critical role of platelets in maintaining tumor vessel integrity, a hybrid (PLP-D-R) nanoparticle selectively depleting tumor-associated platelets (TAP) to boost tumor vessel permeability was developed for enhancing intratumoral drug accumulation. In addition, benefiting from a better understanding of the molecular and cellular underpinnings of vascular normalization, several tumor acidity responsive nanotherapeutics, encapsulating therapeutic peptides, and small interfering RNA were developed to correct the abnormal features of the tumor vasculature. This made the tumor vessels more efficient for drug delivery. While we are still exploring the mechanisms of action of these novel nanoformulations, we expect that the strategies summarized here will offer a promising platform to design effective next-generation nanotherapeutics against cancer and facilitate the clinical translation of smart nanotherapeutics that target tumor vasculature.

Understanding the Phase and Morphological Behavior of Dispersions of Synergistic Dual-Stimuli-Responsive Poly(N-isopropylacrylamide) Nanogels

This work represents a detailed investigation into the phase and morphological behavior of synergistic dual-stimuli-responsive poly(N-isopropylacrylamide) nanogels, a material that is of considerable interest as a matrix for in situ forming implants. Nanogels were synthesized with four different diameters (65, 160, 310, and 450 nm) as monodispersed particles. These different samples were then prepared and characterized as both dilute (0.1 wt %) and concentrated dispersions (2-22 wt %). In the dilute form, all of the nanogels had the same response to the triggers of the physiological temperature and ionic strength. In water, the nanogels would deswell when heated above 32 °C, while they would aggregate if heated above this temperature at the physiological ionic strength. In the concentrated form, the nanogels exhibited a wide range of morphological changes, with liquid, swollen gel, shrunken gel, and aggregate structures all possible. The occurrence of these structures was dependent on many factors such as the temperature, ionic strength of the solvent, size and ζ-potential of the nanogel, and dispersion concentration. We explored these factors in detail with techniques such as visual studies, rheology, effective volume fraction, and shape factor measurement. The different-sized nanogels displayed differing phase and morphological behavior, but generally higher concentrations of the nanogels (>7 wt %) yielded gels in water with the transitions depending on the temperature. The smallest nanogel (65 nm diameter) exhibited the most unique behavior; it did not form a swollen gel at any concentration tested. Shape factor measurement for the nanogel samples showed that two of the larger three samples (160 and 310 nm) had core-shell structures with denser core cross-linking, while the smallest nanogel sample displayed a homogeneous cross-linked structure. We hypothesize that the smallest nanogels are able to undergo more extensive interpenetration compared to the larger nanogels, which meant that the smallest nanogel was not able to form a swollen gel. In the presence of salt at 12 wt %, all of the nanogels formed aggregates when heated above 35 °C due to the screening of the electrostatic stabilization by the salt. This work revealed unique behavior of the smallest nanogel with a homogeneous cross-linked structure; its phase and morphological behavior were unlike a particle dispersion, rather these were more similar to those of a branched polymer solution. In total, these findings can be used to provide information about the design of poly(N-isopropylacrylamide) nanogel dispersions for different applications where highly specific spatiotemporal control of morphology is required, for example, in the formation of in situ forming implants or for pore blocking behavior.