Gadolinium-Loaded Poly(N-vinylcaprolactam) Nanogels: Synthesis, Characterization, and Application for Enhanced Tumor MR Imaging

Nanogel-based nitric oxide-driven nanomotor for deep tissue penetration and enhanced tumor therapy

Antitumor agents often lack effective penetration and accumulation to achieve high therapeutic efficacy in treating solid tumors. Nanomotor-based nanomaterials offer a potential solution to address this obstacle. Among them, nitric oxide (NO) based nanomotors have garnered attention for their potential applications in nanomedicine. However, there widespread clinical adoption has been hindered by their complex preparation processes. To address this limitation, we have developed a NO-driven nanomotor utilizing a convenient and scalable nanogel preparation procedure. These nanomotors, loaded with the fluorescent probe / sonosensitizer chlorin e6 (Ce6), were specifically engineered for sonodynamic therapy. Through comprehensive in vitro investigations using both 2D and 3D cell models, as well as in vivo analysis of Ce6 fluorescent signal distribution in solid tumor models, we observed that the self-propulsion of these nanomotors significantly enhances cellular uptake and tumor penetration, particularly in solid tumors. This phenomenon enables efficient access to challenging tumor regions and, in some cases, results in complete tumor coverage. Notably, our nanomotors have demonstrated long-term in vivo biosafety. This study presents an effective approach to enhancing drug penetration and improving therapeutic efficacy in tumor treatment, with potential clinical relevance for future applications.

Multifunctional Low-Generation Dendrimer Nanogels as an Emerging Probe for Tumor-Specific CT/MR Dual-Modal Imaging

The development of nanoprobes that have amplified enhanced permeability and retention (EPR) effect is crucial for their precise cancer diagnosis performance. Here, we present the development of functional dendrimer-based nanogels (DNGs) with the generation three primary amine-terminated poly(amidoamine) (PAMAM) dendrimers (G3·NH₂) cross-linked by N,N'-bis(acryloyl) cystamine (BAC). The DNGs were prepared through a Michael addition reaction between G3·NH₂ dendrimers and BAC via an inverse microemulsion method and entrapped with gold nanoparticles (Au NPs) to form Au-DNGs. The Au-DNGs were sequentially modified with diethylenetriamine penta-acetic acid (DTPA)-gadolinium (Gd) complex, poly(ethylene glycol) (PEG)-linked arginine-glycine-aspartic (RGD) peptide, and 1,3-propanesultone (1,3-PS). The formed multifunctional RGD-Gd@Au-DNGs-PS (R-G@ADP) possessing an average diameter of 122 nm are colloidally stable and display a high X-ray attenuation coefficient, excellent r₁ relaxivity (9.13 mM^-1 s^-1), desired protein resistance rendered by the zwitterionic modification, and cytocompatibility. With the targeting specificity mediated by RGD and the much better tumor penetration capability than the counterpart material of single dendrimer-entrapped Au NPs, the developed multifunctional R-G@ADP enable targeted and enhanced computed tomography (CT)/magnetic resonance (MR) dual-modal imaging of a pancreatic tumor model in vivo. The current work demonstrates a unique design of targeted and zwitterionic DNGs with prolonged blood circulation time as an emerging nanoprobe for specific tumor CT/MR imaging through amplified passive EPR effect.

Multifunctional stimuli-responsive hybrid nanogels for cancer therapy: Current status and challenges

With cancer research shifting focus to achieving multifunctionality in cancer treatment strategies, hybrid nanogels are making a rapid rise to the spotlight as novel, multifunctional, stimuli-responsive, and biocompatible cancer therapeutic strategies. They can possess cancer cell-specific cytotoxic effects themselves, carry drugs or enzymes that can produce cytotoxic effects, improve imaging modalities, and target tumor cells over normal cells. Hybrid nanogels bring together a wide range of desirable properties for cancer treatment such as stimuli-responsiveness, efficient loading and protection of molecules such as drugs or enzymes, and effective crossing of cellular barriers among other properties. Despite their promising abilities, hybrid nanogels are still far from being used in the clinic, and their available data remains relatively limited. However, many studies can be done to facilitate this clinical transition. This review is critically summarizing and analyzing the recent information and progress on the use of hybrid nanogels particularly inorganic nanoparticle-based and organic nanoparticle-based hybrid nanogels in the field of oncology and future directions to aid in transferring those results to the clinic. This work concludes that the future of hybrid nanogels is greatly impacted by therapeutic and non-therapeutic factors. Therapeutic factors include the lack of hemocompatibility studies, acute and chronic toxicological studies, and information on agglomeration capability and extent, tumor heterogeneity, interaction with proteins in physiological fluids, endocytosis-exocytosis, and toxicity of the nanogels' breakdown products. Non-therapeutic factors include the lack of clear regulatory guidelines and standardized assays, limitations of animal models, and difficulties associated with good manufacture practices (GMP).

One stone, many birds: Recent advances in functional nanogels for cancer nanotheranostics

Inspired by the development of nanomedicine and nanotechnology, more and more possibilities in cancer theranostic have been provided in the last few years. Emerging therapeutic modalities like starvation therapy, chemodynamic therapy, and tumor oxygenation have been integrated with diagnosis, giving a plethora of theranostic nanoagents. Among all of them, nanogels (NGs) show superiority benefiting from their unique attributes: high stability, high water-absorption, large specific surface area, mechanical strength, controlled responsiveness, and high encapsulation capacity. There have been a vast number of investigations supporting various NGs combining drug delivery and multiple bioimaging techniques, encompassing photothermal imaging, photoacoustic imaging, fluorescent imaging, ultrasound imaging, magnetic resonance imaging, and computed tomography. This review summarizes recent advances in functional NGs for theranostic nanomedicine and discusses the challenges and future perspectives of this fast-growing field. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Polysaccharide-Based Theranostic Systems for Combined Imaging and Cancer Therapy: Recent Advances and Challenges

Designing novel systems for efficient cancer treatment and improving the quality of life for patients is a prime requirement in the healthcare sector. In this regard, theranostics have recently emerged as a unique platform, which combines the benefits of both diagnosis and therapeutics delivery. Theranostics have the desired contrast agent and the drugs combined in a single carrier, thus providing the opportunity for real-time imaging to monitor the therapy results. This helps in reducing the hazards related to treatment overdose or underdose and gives the possibility of personalized therapy. Polysaccharides, as natural biomolecules, have been widely explored to develop theranostics, as they act as a matrix for simultaneously loading both contrast agents and drugs for their utility in drug delivery and imaging. Additionally, their remarkable physicochemical attributes (biodegradability, satisfactory safety profile, abundance, and diversity in functionality and charge) can be tuned via postmodification, which offers numerous possibilities to develop theranostics with desired characteristics. Hence, we provide an overview of recent advances in polysaccharide matrix-based theranostics for drug delivery combined with magnetic resonance imaging, computed tomography, positron emission tomography, single photon emission computed tomography, and ultrasound imaging. Herein, we also summarize the toxicity assessment of polysaccharides, associated contrast agents, and nanotoxicity along with the challenges and future research directions.

NVCL-Based Hydrogels and Composites for Biomedical Applications: Progress in the Last Ten Years

Hydrogels consist of three-dimensionally crosslinked polymeric chains, are hydrophilic, have the ability to absorb other molecules in their structure and are relatively easy to obtain. However, in order to improve some of their properties, usually mechanical, or to provide them with some physical, chemical or biological characteristics, hydrogels have been synthesized combined with other synthetic or natural polymers, filled with inorganic nanoparticles, metals, and even polymeric nanoparticles, giving rise to composite hydrogels. In general, different types of hydrogels have been synthesized; however, in this review, we refer to those obtained from the thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL) and we focus on the definition, properties, synthesis techniques, nanomaterials used as fillers in composites and mainly applications of PNVCL-based hydrogels in the biomedical area. This type of material has great potential in biomedical applications such as drug delivery systems, tissue engineering, as antimicrobials and in diagnostic and bioimaging.

Boosting Chemodynamic Therapy via a Synergy of Hypothermal Ablation and Oxidation Resistance Reduction

Chemodynamic therapy (CDT), deemed as a cutting-edge antineoplastic therapeutic tactics, efficaciously suppresses tumors via catalytically yielding hydroxyl radicals (^•OH) in tumor regions. Nevertheless, its biomedical applications are often restricted by the limited hydrogen peroxide (H₂O₂) level and upregulated antioxidant defense. Herein, a versatile nanoreactor is elaborately designed via integrating Cu_2-xS and MnO₂ for T₁-weighted magnetic resonance (MR) imaging-guided CDT, synergistically enhanced through hypothermal ablation and oxidation resistance reduction, thereby displaying splendid antitumor efficiency as well as suppression on pulmonary metastasis. The as-synthesized Cu_2-xS@MnO₂ nanoreactors afford acid-dependent Cu-based and glutathione (GSH)-activated Mn-based catalytic properties for bimodal CDT. Owing to excellent absorbance at the second near-infrared (NIR-II) window, the Cu_2-xS furnishes hypo-photo-thermal therapy (PTT) against tumor growth and ameliorates the catalytic performance for thermal-enhanced CDT. Additionally, MnO₂ significantly downregulates GSH and glutathione peroxidase 4, which synergistically boosts CDT via promoting oxidative stress, simultaneously generating Mn²⁺ for MR contrast improvement and activatable tumor imaging. Therefore, this study proffers a new attempt centered on the collaborative strategy integrating NIR-II hypothermal PTT and synergistically enhanced CDT for tumor eradication.

Multilobular morphology: the key for biphase multifunctional nanogels

Nanogels play a leading role in controlled release systems because they possess high water retention capacity resulting in high loading capabilities, stability in biological fluids and biocompatibility. In this scenario, every tool that allows extending the nanogel properties and expanding their potential applications is of high interest in the field of biomedicine. This article aims to contribute to the development of multifunctional nanogels, based on the combination of two polymer phases in a multilobular morphology. The synthesized multilobed nanogels (mLNGs) presented a core of crosslinked poly(N-vinylcaprolactam) (PVCL) and a shell formed by 3-D distributed lobes of a low T_g copolymer. This particular multilobular morphology is able to exploit the synergetic contribution of both phases. While the PVCL-based core conferred its characteristic thermal response and the ability to load and release a cargo molecule, the low T_g lobes incorporated the capability of film formation. Moreover, the multilobular arrangement of NGs allows films to undergo unrestricted mass transfer. The development of mLNG morphology and the effect of synthesis parameters were deeply studied with the help of a previously developed mathematical model for the dynamic evolution of particle morphology. Finally, this study presents, for the first time, the synthesis of two-phase nanogels with multilobular morphology and underlines their potential as a candidate for controlled delivery platforms.

Dendrimer-decorated nanogels: Efficient nanocarriers for biodistribution in vivo and chemotherapy of ovarian carcinoma

Nanomedicine has revolutionized disease theranostics by the accurate diagnosis and efficient therapy. Here, the PAMAM dendrimer decorated PVCL-GMA nanogels (NGs) were developed for favorable biodistribution in vivo and enhanced antitumor efficacy of ovarian carcinoma. By an ingenious design, the NGs with a unique structure that GMA-rich domains were localized on the surface were synthesized via precipitation polymerization. After G2 dendrimer decoration, the overall charge is changed from neutral to positive, and the NGs-G2 display the whole charge nature of positively charged corona and neutral core. Importantly, the unique architecture and charge conversion of NGs-G2 have a profound impact on the biodistribution and drug delivery in vivo. As a consequence of this alteration, the NGs-G2 as nanocarriers emerge the highly sought biodistribution of reduced liver accumulation, enhanced tumor uptake, and promoted drug release, resulting in the significantly augmented antitumor efficacy with low side effects. Remarkably, this finding is contrary to some reported work that the nanocarriers with positive charge have preferential liver uptake. Moreover, the NGs-G2 also displayed thermal/pH dual-responsive behaviors, excellent biocompatibility, improved cellular uptake, and stimuli-responsive drug release. Encouragingly, this work demonstrates a novel insight into the strategy for optimizing design, improving biodistribution and enhancing theranostic efficacy of nanocarriers.

Intelligent Design of Ultrasmall Iron Oxide Nanoparticle-Based Theranostics

Rapid advances in nanotechnology have opened up innovative trails to break through the current limitation in clinical treatments of cancer and other critical diseases that plague human beings. Ultrasmall iron oxide nanoparticles (USIO NPs) with sizes smaller than 5 nm have been emerging as a novel category of nanomaterials with increasing interest in the biomedical domains. To overcome their intrinsic shortcomings, naked USIO NPs can be functionalized, clustered, assembled, or incorporated with other nanomaterials to generate various kinds of intelligent nanoplatforms for single-mode or dynamic magnetic resonance (MR) imaging, multimode imaging, as well as imaging-guided precision therapy. In this spotlight on applications, first, we propose the principal aspects in the design and application of USIO NPs for biomedical uses. Second, we cover the recent design strategies of USIO NP-based nanoplatforms mainly developed by our group, describe the rationale on the combination of other functional materials with USIO NPs, and review their resultant applications in theranostics. In addition, we provide herein a perspective on the possible future directions toward USIO NP-based nanoplatforms as smart nanomedicines.

Simple Host-Guest Assembly for High-Resolution Magnetic Resonance Imaging of Microvasculature

Magnetic resonance angiography (MRA) is an important imaging technique that can be used to identify and characterize various types of vascular diseases. However, currently used molecular contrast agents are unsuitable for MRA due to the short intravascular retention time, the whole-body distribution, and the relatively low contrast effect. In this study, we developed a vascular analysis contrast agent (i.e., VasCA) for MRA, which is a simple and biocompatible 1:1 host-guest assembly of PEGylated β-cyclodextrin and gadolinium chelate with renal clearable size and high relaxivity (r1 = 9.27 mM-1 s-1). Its biocompatibility was confirmed by in vivo animal studies as well as in vitro 3D cell culture. In a tumor-bearing rat model, VasCA circulated in the blood vessels much longer (4.3-fold increase) than gadoterate meglumine (Dotarem) and was mainly excreted by the renal system after intravenous injection. This feature of VasCA allows characterization of tumor microvasculature (e.g., feeding and draining vessels) as well as visualization of small vessels in the brain and body organs. Furthermore, after treatment with an angiogenesis inhibitor (i.e., sorafenib), VasCA revealed the vessel normalization process and allowed the assessment of viable and necrotic tumor regions. Our study provides a useful tool for diverse MRA applications, including tumor characterization, early-stage evaluation of drug efficacy, and treatment planning, as well as diagnosis of cardiovascular diseases.

Core-Shell Tecto Dendrimers Enable Enhanced Tumor MR Imaging through an Amplified EPR Effect

Development of nanoplatforms that can amplify the passive tumor targeting effect based on enhanced permeability and retention (EPR) effect is crucial for precision cancer nanomedicine applications. Herein, we present the development of core-shell tecto dendrimers (CSTDs) as a platform for enhanced tumor magnetic resonance (MR) imaging through an amplified EPR effect. In this work, poly(amidoamine) (PAMAM) dendrimers of generation 5 (G5) were decorated with β-cyclodextrin (CD) and then assembled with G3 PAMAM dendrimers premodified with adamantane (Ad) via supramolecular recognition of CD and Ad. The formed G5-CD/Ad-G3 CSTDs were conjugated with tetraazacyclododecane tetraacetic acid (DOTA)-Gd(III) chelators and further acetylated to neutralize the remaining CSTD periphery amines. We reveal that the formed CSTD.NHAc-DOTA(Gd) (CSTD-D-Gd) complexes have a narrow size distribution and satisfactory colloidal stability, and are cytocompatible within the concentration range studied. Compared to the single dendrimer counterpart of G5.NHAc-DOTA(Gd) (G5-D-Gd) complexes, the CSTD-D-Gd complexes with a higher molecular weight and volume possess a longer rotation correlation time, hence having a longitudinal relaxivity (r₁) of 7.34 mM^-1 s^-1, which is 1.5 times larger than that of G5-D-Gd complexes (4.92 mM^-1 s^-1). More importantly, the CSTD-D-Gd complexes display better permeability in the three-dimensional (3D) cell spheroids in vitro through fluorescence imaging and a more significant EPR effect for improved tumor MR imaging in vivo than the G5-DOTA-Gd complexes. The generated CSTD-D-Gd complexes may be adopted for enhanced tumor MR imaging through an amplified passive EPR effect and also be further extended for different cancer theranostic applications.

Surface-Charge-Switchable Nanoclusters for Magnetic Resonance Imaging-Guided and Glutathione Depletion-Enhanced Photodynamic Therapy

Photodynamic therapy (PDT) is an effective noninvasive therapeutic method that employs photosensitizers (PSs) converting oxygen to highly cytotoxic singlet oxygen (¹O₂) under light irradiation. The conventional PDT efficacy is, however, compromised by the nonspecific delivery of PSs to tumor tissue, the hypoxic tumor microenvironment, and the reduction of generated ¹O₂ by the intracellular antioxidant glutathione (GSH). Herein, an intelligent multifunctional synergistic nanoplatform (CMGCC) for T₁-weighted magnetic resonance (MR) imaging-guided enhanced PDT is presented, which consists of nanoparticles composed of catalase (CAT) and manganese dioxide (MnO₂) that are integrated within chlorin-e6-modified glycol chitosan (GC) polymeric micelles. In this system, (1) GC polymers with pH-sensitive surface charge switchability from neutral to positive could improve the PS accumulation within the tumor region, (2) CAT could effectively reoxygenate the hypoxic tumor via catalyzing endogenous hydrogen peroxide to O₂, and (3) MnO₂ could consume the intracellular GSH while simultaneously producing Mn²⁺ as a contrast agent for T₁-weighted MR imaging. The CMGCC particles possess uniform size distribution, well-defined structure, favorable enzyme activity, and superior ¹O₂ generation ability. Both in vitro and in vivo experiments demonstrate that the CMGCC exhibit significantly enhanced PDT efficacy toward HeLa cells and subcutaneous HeLa tumors. Our study thereby demonstrates this to be a promising synergistic theranostic nanoplatform with highly efficient PDT performance for cancer therapy.

Systematic overview of soft materials as a novel frontier for MRI contrast agents

Magnetic resonance imaging (MRI) is a well-known diagnostic technique used to obtain high quality images in a non-invasive manner. In order to increase the contrast between normal and pathological regions in the human body, positive (T1) or negative (T2) contrast agents (CAs) are commonly intravenously administered. The most efficient class of T1-CAs are based on kinetically stable and thermodynamically inert gadolinium complexes. In the last two decades many novel macro- and supramolecular CAs have been proposed. These approaches have been optimized to increase the performance of the CAs in terms of the relaxivity values and to reduce the administered dose, decreasing the toxicity and giving better safety and pharmacokinetic profiles. The improved performances may also allow further information to be gained on the pathological and physiological state of the human body. The goal of this review is to report a systematic overview of the nanostructurated CAs obtained and developed by manipulating soft materials at the nanometer scale. Specifically, our attention is centered on recent examples of fibers, hydrogels and nanogel formulations, that seem particularly promising for overcoming the problematic issues that have recently pushed the European Medicines Agency (EMA) to withdraw linear CAs from the market.

Gd(iii)-nanostructurated Constrast Agents (CAs) for Magnetic Resonance Imaging (MRI) can be designed and developed by manipulating soft material, including fibers, hydrogels and nanogels, in the nanometer scale.

Polyethylenimine Nanogels Incorporated with Ultrasmall Iron Oxide Nanoparticles and Doxorubicin for MR Imaging-Guided Chemotherapy of Tumors

Development of versatile nanoplatforms for cancer theranostics remains a hot topic in the area of nanomedicine. We report here a general approach to create polyethylenimine (PEI)-based hybrid nanogels (NGs) incorporated with ultrasmall iron oxide (Fe₃O₄) nanoparticles (NPs) and doxorubicin for T₁-weighted MR imaging-guided chemotherapy of tumors. In this study, PEI NGs were first prepared using an inverse emulsion approach along with Michael addition reaction to cross-link the NGs, modified with citric acid-stabilized ultrasmall Fe₃O₄ NPs through 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide hydrochloride (EDC) coupling, and physically loaded with anticancer drug doxorubicin (DOX). The formed hybrid NGs possess good water dispersibility and colloidal stability, excellent DOX loading efficiency (51.4%), pH-dependent release profile of DOX with an accelerated release rate under acidic pH, and much higher r₁ relaxivity (2.29 mM^-1 s^-1) than free ultrasmall Fe₃O₄ NPs (1.15 mM^-1 s^-1). In addition, in contrast to the drug-free NGs that possess good cytocompatibility, the DOX-loaded hybrid NGs display appreciable therapeutic activity and can be taken up by cancer cells in vitro. With these properties, the developed hybrid NGs enabled effective inhibition of tumor growth under the guidance of T₁-weighted MR imaging. The developed hybrid NGs may be applied as a versatile nanoplatform for MR imaging-guided chemotherapy of tumors.

Multifunctional PVCL nanogels with redox-responsiveness enable enhanced MR imaging and ultrasound-promoted tumor chemotherapy

Development of versatile nanoplatforms that simultaneously integrate therapeutic and diagnostic features for stimuli-responsive delivery to tumors remains a great challenge. In this work, we report a novel intelligent redox-responsive hybrid nanosystem composed of MnO₂ nanoparticles (NPs) and doxorubicin (DOX) co-loaded within poly(N-vinylcaprolactam) nanogels (PVCL NGs) for magnetic resonance (MR) imaging-guided and ultrasound-targeted microbubble destruction (UTMD)-promoted tumor chemotherapy. Methods: PVCL NGs were first synthesized via a precipitation polymerization method, decorated with amines using ethylenediamine, and loaded with MnO₂ NPs through oxidation with permanganate and DOX via physical encapsulation and Mn-N coordination bonding. The as-prepared DOX/MnO₂@PVCL NGs were well characterized. UTMD-promoted cellular uptake and therapeutic efficacy of the hybrid NGs were assessed in vitro, and a xenografted tumor model was used to test the NGs for MR imaging and UTMD-promoted tumor therapy in vivo. Results: The as-prepared DOX/MnO₂@PVCL NGs with a size of 106.8 nm display excellent colloidal stability, favorable biocompatibility, and redox-responsiveness to the reductive intracellular environment and tumor tissues having a relatively high glutathione (GSH) concentration that can trigger the synchronous release of Mn²⁺ for enhanced T₁-weighted MR imaging and DOX for enhanced cancer chemotherapy. Moreover, the DOX/MnO₂@PVCL NGs upon the UTMD-promotion exhibit a significantly enhanced tumor growth inhibition effect toward subcutaneous B16 melanoma owing to the UTMD-improved cellular internalization and tumor penetration. Conclusion: Our work thereby proposes a promising theranostic nanoplatform for stimuli-responsive T₁-weighted MR imaging-guided tumor chemotherapy.

Gd-/CuS-Loaded Functional Nanogels for MR/PA Imaging-Guided Tumor-Targeted Photothermal Therapy

The second near-infrared (NIR-II, 1000-1700 nm) light-based diagnosis and therapy have received extensive attention for neoplastic disease treatments because of the fact that light in the NIR-II window possesses less photon scattering along with deeper tissue penetration than that in the NIR-I (700-950 nm) window. Herein, we present a Gd- and copper sulfide (CuS)-integrated nanogel (NG) platform for magnetic resonance (MR)/photoacoustic (PA) imaging-guided tumor-targeted photothermal therapy (PTT). In our approach, we prepared cross-linked polyethylenimine (PEI) NGs via an inverse emulsion method, modified the PEI NGs with Gd chelates, targeting ligand folic acid (FA) through a polyethylene glycol (PEG) spacer and 1,3-propanesultone, and finally loaded CuS nanoparticles (NPs) within the functional NGs. The as-synthesized Gd/CuS@PEI-FA-PS NGs with a mean size of 85 nm exhibit a good water dispersibility and protein resistance property, admirable r₁ relaxivity (11.66 mM^-1 s^-1), excellent NIR-II absorption feature, high photothermal conversion efficiency (26.7%), and FA-mediated targeting specificity to cancer cells overexpressing FA receptor (FAR). With these properties along with the good cytocompatibility, the developed Gd/CuS@PEI-FA-PS NGs enable MR/PA dual-mode imaging-guided targeted PTT of FAR-overexpressing tumors under the irradiation of an NIR-II (1064 nm) laser. The designed Gd/CuS@PEI-FA-PS NGs may be used as a promising theranostic agent for MR/PA dual-mode imaging-guided PTT of other FAR-expressing tumors.

Peptide-Based Soft Hydrogels Modified with Gadolinium Complexes as MRI Contrast Agents

Poly-aromatic peptide sequences are able to self-assemble into a variety of supramolecular aggregates such as fibers, hydrogels, and tree-like multi-branched nanostructures. Due to their biocompatible nature, these peptide nanostructures have been proposed for several applications in biology and nanomedicine (tissue engineering, drug delivery, bioimaging, and fabrication of biosensors). Here we report the synthesis, the structural characterization and the relaxometric behavior of two novel supramolecular diagnostic agents for magnetic resonance imaging (MRI) technique. These diagnostic agents are obtained for self-assembly of DTPA(Gd)-PEG8-(FY)3 or DOTA(Gd)-PEG8-(FY)3 peptide conjugates, in which the Gd-complexes are linked at the N-terminus of the PEG8-(FY)3 polymer peptide. This latter was previously found able to form self-supporting and stable soft hydrogels at a concentration of 1.0% wt. Analogously, also DTPA(Gd)-PEG8-(FY)3 and DOTA(Gd)-PEG8-(FY)3 exhibit the trend to gelificate at the same range of concentration. Moreover, the structural characterization points out that peptide (FY)3 moiety keeps its capability to arrange into β-sheet structures with an antiparallel orientation of the β-strands. The high relaxivity value of these nanostructures (~12 mM⁻¹·s⁻¹ at 20 MHz) and the very low in vitro cytotoxicity suggest their potential application as supramolecular diagnostic agents for MRI.

Nanocomposites of ionic copolymer integrating Gd-containing polyoxometalate as a multiple platform for enhanced MRI and pH-response chemotherapy

Nanocomposites from the co-assemblies of block copolymers and a gadolinium-grafting inorganic cluster were constructed as a multifunctional platform for MRI enhancement, drug loading, and environment-response release at local positions.

Single enzyme loaded nanoparticles for combinational ultrasound-guided focused ultrasound ablation and hypoxia-relieved chemotherapy

Constructing nanosystems that synergistically combine therapeutic and diagnostic features is of great interest to the nanomedicine community but also remains a tremendous challenge. Methods: In this work, we report novel catalytic nanoparticles composed of the enzyme catalase, encapsulated in a polymer shell and surface decorated with pH-sensitive poly(ethylene glycol) (PEGylated nCAT). These nanoparticles were used as a promoter for ultrasound (US)-guided focused ultrasound (FUS) ablation and hypoxia alleviation for application in Doxorubicin-based chemotherapy. Results: The PEGylated nCAT produced highly effectively O2 from endogenous H2O2 to ameliorate the hypoxic and therefore poor-acoustic tumor environment. The generated O2 was utilized as 1) a contrast agent for US imaging; 2) strengthening agent for FUS ablation and 3) normoxia inducer to enhance chemotherapeutic efficacy. The PEGylated nCAT exhibited favorable enzyme activity after long-term storage, and after exposure to proteolytic conditions and elevated temperatures. The pH-responsive PEGylation contributed on the one hand to an extended in vivo circulation time over 48 h and on the other hand enabled PEG cleavage in the vicinity of cancer cells to facilitate cellular uptake. Conclusion: The developed PEGylated nCAT can therefore effectively combine US-guided FUS and chemotherapy and can be regarded as a highly promising theranostic platform.

Influence of size, crosslinking degree and surface structure of poly(N-vinylcaprolactam)-based microgels on their penetration into multicellular tumor spheroids

Current nanomedicine suffers from a big challenge due to the fact that most of the nanocarrier systems lack the desired tumor penetration depth, thereby limiting their clinical translation. Unlike the nanomaterials with a similar size or shape, microgels display excellent softness, fluidity and deformability, as well as stimuli-responsiveness in the tumor microenvironment. Herein, we report the synthesis of temperature-responsive poly(N-vinylcaprolactam)/oligo (ethylene glycol) acrylate/glycidyl methacrylate (PVCL/OEGA/GMA) microgels with different hydrodynamic radii (100-500 nm), crosslinking densities, 2-methoxyethyl acrylate (MEA) contents and OEGA chain lengths using a precipitation polymerization method and the investigation of the microgels in terms of their tumor penetration capability using a multicellular tumor spheroid (MCTS) model. The prepared microgels were well characterized with different techniques. We show that regardless of the size, crosslinking density, MEA content and OEGA chain length, all microgels display the desired cytocompatibility in the given concentration range. In vitro cellular uptake data reveal that similar to 2-dimensional (2-D) adherent cells, microgels with a smaller size display more enhanced cellular uptake than those having a larger size in the 3-D MCTS model. Likewise, 3-D MCTS penetration results indicate that the PVCL/OEGA/GMA microgels with the smallest radius of 100 nm exhibit the deepest penetration length. We then selected the microgels with a radius of 200 nm but with different physicochemical parameters to investigate their cellular uptake and tumor penetration behavior. Our data show that microgels with varying crosslinking densities, MEA contents and OEGA chain lengths do not have any appreciable changes in terms of their cellular uptake and penetration in the 3-D MCTS model. Our study provides new insights for the design of different microgel-based systems for further cancer theranostic applications.

Evaluation of cationic core-shell thermoresponsive poly(N-vinylcaprolactam)-based microgels as potential drug delivery nanocarriers

The present work investigates the potentiality of poly(N-vinyl caprolactam) (PVCL)-based thermoresponsive microgels decorated with cationic polymer brushes as drug delivery carriers. The effect of physico-chemical features of the colloids on cell viability response have to be carefully investigated to establish the range of suitable hydrodynamic diameters, crosslinking densities, lengths and ratios of the cationic polyelectrolyte shell which allow their efficient and effective use for cargo loading, transport and delivery. The colloidal stability of all cationic thermoresponsive microgels is maintained over several days of incubation at 37 °C in biological mimicking medium (Dulbecco's Modified Eagle's Medium supplemented with fetal bovine serum). The thin cationic polymer shell covalently anchored does not hinder the all range of microgels to be biocompatible while the higher cytotoxicity of the doxorubicin-loaded microgels on HeLa cells proves their anti-tumor activity. The core-shell PVCL drug delivery nanocarriers allow a sustained release of doxorubicin with a slightly higher viability of HeLa cells incubated in the presence of DOXO-loaded microgels compared to the free DOXO. The nature of the endocytosis pathway is investigated through a quantification of the extent of the cellular survival rate in the presence of various cellular uptake inhibitors. A clathrin-dependent internalization was observed.

Amylose-Coated Biohybrid Microgels by Phosphorylase-Catalyzed Grafting-From Polymerization

Herein, the synthesis of amylose-coated, temperature-responsive poly(N-vinylcaprolactam) (VCL)-based copolymer microgels by enzyme-catalyzed grafting-from polymerization with phosphorylase b from rabbit muscle is reported. The phosphorylase is able to recognize the oligosaccharide maltoheptaose as primer and attach glucose units from the monomer glucose-1-phosphate to it, thereby forming amylose chains while releasing inorganic phosphate. Therefore, to enable the phosphorylase-catalyzed grafting-from polymerization of glucose-1-phosphate from the PVCL-based microgels, the maltoheptaose primer is covalently attached to the microgel in the first synthesis step. This is realized by adding N-(2-aminoethyl)methacrylamide (AEMAA) as a comonomer to the PVCL microgel to integrate primary amino groups and subsequent coupling of maltoheptaonolactone. Both the PVCL/AEMAA microgel as well as the obtained microgel-maltoheptaose construct are characterized in detail by dynamic light scattering, electrophoretic mobility measurements, IR spectroscopy, and atomic force microscopy. From the microgel-maltoheptaose construct, the grafting-from polymerization of glucose-1-phosphate is performed by the addition of phosphorylase b. Atomic force microscopy images clearly demonstrate the formation of an amylose shell around the microgels. The developed amylose-coated microgels open up promising application possibilities, for example, as colloidal scavengers, since amylose helices can serve as host molecules for inclusion of hydrophobic guest molecules.

Stem cell-mediated delivery of nanogels loaded with ultrasmall iron oxide nanoparticles for enhanced tumor MR imaging

The development of new nanoplatforms with enhanced tumor accumulation for accurate diagnosis still remains a great challenge in current precision nanomedicine. Herein, we report the design of stem cell-mediated delivery of nanogels (NGs) loaded with ultrasmall iron oxide (Fe3O4) nanoparticles (NPs) for enhanced magnetic resonance (MR) imaging of tumors. In this study, sodium citrate-stabilized ultrasmall Fe3O4 NPs with a size of 3.16 ± 1.30 nm were first synthesized using a solvothermal route, coated with polyethyleneimine (PEI), and used as crosslinkers to crosslink alginate (AG) NGs formed via a double emulsion approach, where the AG carboxyl groups were pre-activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The thus prepared Fe3O4 NP-loaded NGs (AG/PEI-Fe3O4 NGs) with a size of 47.68 ± 3.41 nm are water-dispersible, colloidally stable, cytocompatible in a given concentration range, display a relatively high r1 relaxivity (r1 = 1.5 mM-1 s-1), and are able to be taken up by bone mesenchymal stem cells without compromising cell viability and stem cell characteristics. Due to the tumor-chemotaxis or tumor tropism, the BMSCs are able to mediate the enhanced delivery of AG/PEI-Fe3O4 NGs to the tumor site after intravenous injection, thus enabling significantly strengthened MR imaging of tumors when compared to free NGs. These findings suggest that the developed AG/PEI-Fe3O4NGs, once mediated by stem cells may serve as a novel, safe, effective and targeted platform for enhanced MR imaging of tumors.

Merging metal organic framework with hollow organosilica nanoparticles as a versatile nanoplatform for cancer theranostics

With great potential in nanomedicine, the integration of a metal organic framework (MOF) with a nanocarrier for smart and versatile cancer theranostics still seeks to expand. In this study, MOF was successfully merged with hollow mesoporous organosilica nanoparticles (HMONs) with a polydopamine (PDA) interlayer to form molecularly organic/inorganic hybridized nanocomposites (HMONs-PMOF). The well-defined nanostructure and favorable biocompatibility of HMONs-PMOF were demonstrated first. Doxorubicin hydrochloride (DOX) and indocyanine green (ICG) were separately loaded into the interior cavity of HMONs and the outer porous shell of MOF with high loading efficacy, respectively. The obtained dual drug-loaded nanocomposites (DI@HMONs-PMOF) displayed favorable photothermal properties and pH/NIR-triggered DOX release manner. Furthermore, in vitro cell experiments validated that HMONs-PMOF can efficiently deliver DOX into cancer cells. Upon entry into cancer cells, the photothermal effect of DI@HMONs-PMOF can induce the lysosome rupture, thereby facilitating the "lysosome escape" process and accelerating the DOX diffusion in the cytoplasm. Benefiting from the iron ion coordinated on PDA and ICG confined in MOF, magnetic resonance (MR) and photoacoustic (PA) dual-modality imaging were performed to verify the effective accumulation of DI@HMONs-PMOF at the tumor site. Interestingly, the results also suggested that the existence of ICG can cooperatively enhance the MR imaging capability of prepared nanocomposites. In addition, the significantly improved synergistic therapeutic efficacy was confirmed both in vitro and in vivo. Thus, our results indicated that the merged nanostructure of HMONs and MOF is promising for versatile cancer theranostics. STATEMENT OF SIGNIFICANCE: Metal organic framework (MOF) has recently emerged as a class of fascinating nanocarriers. The integration of MOF with other nanostructures can endow the new nanoformulation with collective functionality and synergistic performance that are not accessed from single-component nanostructure. Herein, we reported the successful merging of MOF and hollow mesoporous organosilica nanoparticles (HMONs) to form a hollow nanocontainer with a well-defined nanostructure. The large cavity of HMONs and highly porous network of MOF enable high drug loading efficacy. Moreover, the dual-modality magnetic resonance and photoacoustic imaging can be realized, which is also benefited from the merged nanostructure. Overall, we expected this paradigm could pave way for integrating MOF with other nanocarriers to achieve more diverse applications.

Poly(amidoamine) Dendrimer-Coordinated Copper(II) Complexes as a Theranostic Nanoplatform for the Radiotherapy-Enhanced Magnetic Resonance Imaging and Chemotherapy of Tumors and Tumor Metastasis

The development of a powerful nanoplatform to realize the simultaneous therapy and diagnosis of cancer using a similar element for theranostics remains a critical challenge. Herein, we report such a theranostic nanoplatform based on pyridine (Pyr)-functionalized generation 5 (G5) poly(amidoamine) dendrimers complexed with copper(II) (Cu(II)) for radiotherapy-enhanced T₁-weighted magnetic resonance (MR) imaging and the synergistic radio-chemotherapy of both tumors and tumor metastasis. In this study, amine-terminated G5 dendrimers were covalently linked with 2-pyridinecarboxylic acid, acetylated to neutralize their remaining terminal amines, and complexed with Cu(II) through both the internal tertiary amines and the surface Pyr groups to form the G5.NHAc-Pyr/Cu(II) complexes. We show that the complexes are able to inhibit the proliferation of different cancer cell lines with half-maximal inhibitory concentrations ranging from 4 to 10 μM and induce significant cancer cell apoptosis. Due to the presence of Cu(II), the G5.NHAc-Pyr/Cu(II) complexes display an r₁ relaxivity of 0.7024 mM^-1 s^-1, enabling effective in vivo MR imaging of tumor xenografts and lung metastatic nodules. Further, under radiotherapy (RT) conditions, the tumor MR imaging sensitivity can be significantly enhanced, and the G5.NHAc-Pyr/Cu(II) complexes enable the enhanced chemotherapy of both a xenografted tumor model and a blood-vessel metastasis model. With the demonstrated theranostic potential of the dendrimer-Cu(II) nanocomplexes without additional agents or elements for RT-enhanced MR imaging and chemotherapy of tumor and tumor metastasis, this novel Cu(II)-based nanohybrids may hold great promise for the theranostics of different cancer types and metastases.

Gadolinium-containing polymer microspheres: a dual-functional theranostic agent for magnetic resonance imaging and cancer therapy

Preparation of poly(gadolinium methacrylate-co-methacrylic acid) copolymer microspheres with high MRI contrast efficiency and controlled anti-cancer drug loading and release capability.

In Situ Growth and Size Regulation of Single Gold Nanoparticles in Composite Microgels

Herein, a novel method for the in situ growth of single gold nanoparticles (AuNPs) in microgel (MG) networks is presented. The key feature in this approach is the localization of β-diketone groups capable of both complexation and reduction of aurate ions in the MGs' core, which allows localization of the nucleation and growth of single AuNPs. The MG synthesis is carried out via precipitation polymerization in water with N-vinylcaprolactam as the main monomer and with the two comonomers acetoacetoxyethyl methacrylate (AAEM) and acrylic acid (AAc), where AAEM is mainly located in the MGs' core and AAc in their shell. For the synthesis of AuNPs, a certain amount of chloroauric acid (HAuCl₄ ) is added to the dispersion, followed by fast reduction with sodium borohydride (NaBH₄ ). In situ synthesized AuNPs in MGs possess a spherical shape, with a diameter of 8.1 ± 0.8 nm, being localized in the center of every MG. In addition, these AuNPs embedded into MG networks can be used as seeds that grow in their size after the addition of HAuCl₄ up to 46.0 ± 9.5 nm under mild reaction conditions (room temperature, aqueous dispersion) and without the use of any additional reducing and stabilizing agents.

Functional Microgels: Recent Advances in Their Biomedical Applications

Here, a spotlight is shown on aqueous microgel particles which exhibit a great potential for various biomedical applications such as drug delivery, cell imaging, and tissue engineering. Herein, different synthetic methods to develop microgels with desirable functionality and properties along with degradable strategies to ensure their renal clearance are briefly presented. A special focus is given on the ability of microgels to respond to various stimuli such as temperature, pH, redox potential, magnetic field, light, etc., which helps not only to adjust their physical and chemical properties, and degradability on demand, but also the release of encapsulated bioactive molecules and thus making them suitable for drug delivery. Furthermore, recent developments in using the functional microgels for cell imaging and tissue regeneration are reviewed. The results reviewed here encourage the development of a new class of microgels which are able to intelligently perform in a complex biological environment. Finally, various challenges and possibilities are discussed in order to achieve their successful clinical use in future.

2D transition metal dichalcogenide nanosheets for photo/thermo-based tumor imaging and therapy

Two-dimensional (2D) graphene-like nanomaterials show wide applications in the fields of nanodevices, sensors, energy materials, catalysis, drug delivery, bioimaging, and tissue engineering. Recently, many studies have been focused on the synthesis and application of 2D transition metal dichalcogenide (TMD) nanosheets for various biomedical applications. In particular, 2D TMD nanosheets exhibit great advantages for tumor imaging and therapy compared to some traditional nanomaterials due to their high specific surface area, good biocompatibility, easy modification, and ultrahigh light and heat conversion efficiency. In this review, we summarize the recent advances in the synthesis, modification, and photo/thermo-based tumor imaging and therapy of 2D TMD nanosheets. The important studies on tumor bioimaging with TMD nanosheets, such as X-ray computed tomography, magnetic resonance imaging, and photoacoustic imaging, are demonstrated and discussed. In another section, the physical photothermal and photodynamic therapies as well as the pharmacological therapy of tumors with TMD nanosheet-based nanohybrids are introduced. It is expected that this work will be valuable for readers to understand the synthesis and modification of TMD nanosheets to design novel 2D functional nanomaterials for photo/thermo-based tumor imaging and therapy in one aspect, and in another aspect will extend the applications of TMD-based nanomaterials in materials science, analytical science, electrocatalysis, tissue engineering, and others.

Construction of Hybrid Alginate Nanogels Loaded with Manganese Oxide Nanoparticles for Enhanced Tumor Magnetic Resonance Imaging

Development of sensitive contrast agents for positive magnetic resonance (MR) imaging of biosystems still remains a great challenge. Herein, we report a facile process to construct hybrid alginate (AG) nanogels (NGs) loaded with manganese oxide (Mn₃O₄) nanoparticles (NPs) for enhanced tumor MR imaging. The obtained AG/PEI-Mn₃O₄ NGs with a mean size of 141.6 nm display excellent colloidal stability in aqueous solution and good cytocompatibility in the studied concentration range. Moreover, the hybrid NGs have a high r₁ relaxivity of 26.12 mM^-1 s^-1, which is about 19.5 times higher than that of PEI-Mn₃O₄ NPs with PEI surface amine acetylated (PEI.Ac-Mn₃O₄ NPs). Furthermore, the AG/PEI-Mn₃O₄ NGs presented longer blood circulation time and better tumor MR imaging performances in vivo than PEI.Ac-Mn₃O₄ NPs. With the good biosafety confirmed by histological examinations, the developed AG/PEI-Mn₃O₄ NGs may be potentially used as an efficient contrast agent for enhanced MR imaging of different biosystems.

Structural, luminescence, thermodynamic and theoretical studies on mononuclear complexes of Eu(III) with pyridine monocarboxylate-N-oxides in aqueous solution

The mononuclear complexes formed by Eu(III) with three isomeric pyridine monocarboxylate-N-oxides namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO) in aqueous solutions were studied by potentiometry, luminescence spectroscopy and isothermal titration calorimetry (ITC) to determine the speciation, coordination, luminescence properties and thermodynamic parameters of the complexes formed during the course of the reaction. More stable six membered chelate complexes with stoichiometry (ML_i, i=1-4) are formed by Eu(III) with PANO while non chelating ML and ML₂ complexes are formed by NANO and IANO. The stability of Eu(III) complexes follow the order PANO>IANO>NANO. The ITC studies inferred an endothermic and innersphere complex formation of Eu(III)-PANO and Eu(III)-IANO whereas an exothermic and outer-sphere complex formation for Eu(III)-NANO. The luminescence life time data further supported the ITC results. Density functional theoretical calculations were carried out to optimize geometries of the complexes and to estimate the energies, structural parameters (bond distances, bond angles) and charges on individual atoms of the same. Theoretical approximations are found to be in good agreement with the experimental observations.

Gadolinium-conjugated star-block copolymer polylysine-modified polyethylenimine as high-performance T 1 MR imaging blood pool contrast agents

Core-shell copolymers have received widespread attention because of their unique properties, such as suitable for surface modification and increasing the functionality. Thus, they have been increasingly used in many fields including biomedical, pharmaceutical, electronics and optics. Here, a new core-shell copolymer system was developed to synthesize potential blood pool contrast agent (CA) for magnetic resonance imaging (MRI). The novel CA with high T ₁ relaxivity was synthesized by conjugating gadolinium (Gd) chelators onto star-block copolymer polyethylenimine-grafted poly(l-lysine) (PEI-PLL) nanoparticles (NPs). The T ₁ relaxivity of PEI-PLL-DTPA-Gd NPs measured on a 7.0 T small animal MRI scanner was 8.289 mM^-1 s^-1, higher than that of T ₁ contrast agents widely used in the clinic, such as Gd-DTPA (also known as Magnevist, r ₁ = 4.273 mM^-1 s^-1). These results show that PEI-PLL-DTPA-Gd exhibits more efficient T ₁ MR contrast enhancement compared to Gd-DTPA. More importantly, the PEI-PLL-DTPA-Gd core-shell NPs exhibited extremely low toxicity when measured against the HepG2 cell line over a similar concentration rang of Magnevist. In in vivo experiments, PEI-PLL-DTPA-Gd not only displayed good T ₁ contrast enhancement for the abdominal aorta, but also showed prolonged blood circulation time compared with Gd-DTPA, which should enable longer acquisition time, for MR and MR angiographic images, with high resolution in clinical practice. PEI-PLL-DTPA-Gd NPs have potential to serve as high T ₁ relaxivity blood pool MRI CA in the clinic.

A unique nanogel-based platform for enhanced dual mode tumor MR/CT imaging

Alginate nanogels loaded with gold nanoparticles and gadolinium can be synthesized via a nanoparticle-crosslinking approach for enhanced tumor MR/CT imaging.

Europium complexes: choice of efficient synthetic routes from RM1 thermodynamic quantities as figures of merit

Faced with many different plausible synthetic pathways for the preparation of europium complexes, the synthetic chemist can now easily compute RM1 thermodynamic quantities for all of them and likely arrive at the most effective synthetic strategies.

Geometrical confinement directed albumin-based nanoprobes as enhanced T1 contrast agents for tumor imaging

We report a facile strategy to assemble geometrically confined albumin-based nanoparticles as T₁ contrast agents for sensitive tumor imaging.