Stimuli-Responsive Biodegradable Hyperbranched Polymer–Gadolinium Conjugates as Efficient and Biocompatible Nanoscale Magnetic Resonance Imaging Contrast Agents

Latest advancements and trends in biomedical polymers for disease prevention, diagnosis, treatment, and clinical application

Biomedical polymers are at the forefront of medical advancements, offering innovative solutions in disease prevention, diagnosis, treatment, and clinical use due to their exceptional physicochemical properties. This review delves into the characteristics, classification, and preparation methods of these polymers, highlighting their diverse applications in drug delivery, medical imaging, tissue engineering, and regenerative medicine. We present a thorough analysis of the recent advancements in biomedical polymer research and their clinical applications, acknowledging the challenges that remain, such as immune response management, controlled degradation rates, and mechanical property optimization. Addressing these issues, we explore future directions, including personalization and the integration of nanotechnology, which hold significant potential for further advancing the field. This comprehensive review aims to provide a deep understanding of biomedical polymers and serve as a valuable resource for the development of innovative polymer materials in both fundamental research and clinical practice.

Recent Advances in Degradable Biomedical Polymers for Prevention, Diagnosis and Treatment of Diseases

Biomedical polymers play a key role in preventing, diagnosing, and treating diseases, showcasing a wide range of applications. Their unique advantages, such as rich source, good biocompatibility, and excellent modifiability, make them ideal biomaterials for drug delivery, biomedical imaging, and tissue engineering. However, conventional biomedical polymers suffer from poor degradation in vivo, increasing the risks of bioaccumulation and potential toxicity. To address these issues, degradable biomedical polymers can serve as an alternative strategy in biomedicine. Degradable biomedical polymers can efficiently relieve bioaccumulation in vivo and effectively reduce patient burden in disease management. This review comprehensively introduces the classification and properties of biomedical polymers and the recent research progress of degradable biomedical polymers in various diseases. Through an in-depth analysis of their classification, properties, and applications, we aim to provide strong guidance for promoting basic research and clinical translation of degradable biomedical polymers.

In Vivo Evaluation of Innovative Gadolinium-Based Contrast Agents Designed for Bioimaging Applications

The aim of this study was the investigation of biochemical and histological changes induced in different tissues, as a result of the subcutaneous administration of Gd nanohydrogels (GdDOTA⸦CS-TPP/HA) in a CD-1 mouse strain. The nanohydrogels were obtained by encapsulating contrast agents (GdDOTA) in a biocompatible polymer matrix composed of chitosan (CS) and hyaluronic acid (HA) through the ionic gelation process. The effects of Gd nanohydrogels on the redox status were evaluated by measuring specific activities of the antioxidant enzymes catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD), as well as oxidative stress markers, such as reduced glutathione (GSH), malondialdehyde (MDA), advanced oxidation protein products (AOPP), and protein-reactive carbonyl groups (PRCG), in the liver, kidney, and heart tissues. The nitrosylated proteins expression were analyzed with Western Blot and the serum biochemical markers were measured with spectrophotometric methods. Also, a histological analysis of CD-1 mouse tissues was investigated. These results indicated that Gd nanohydrogels could potentially be an alternative to current MRI contrast agents thanks to their low toxicity in vivo.

Gadolinium(III) Complex-Backboned Branched Polymers as Imaging Probes for Contrast-Enhanced Magnetic Resonance Angiography

Compared to traditional branched polymers with Gd(III) chelates conjugated on their surface, branched polymers with Gd(III) chelates as the internal skeleton are considered to be a reasonable strategy for preparing efficient magnetic resonance imaging contrast agents. Herein, the Gd(III) ligand DOTA was chosen as the internal skeleton; four different molecular weights (3.5, 5.3, 8.6, and 13.1 kDa) and degrees of branching poly-DOTA branched polymers (P1, P2, P3, and P4) were synthesized by a simple "A₂ + B₄"-type one-pot polymerization. The Gd(III) chelates of these poly-DOTA branched polymers (P1-Gd, P2-Gd, P3-Gd, and P4-Gd) display excellent kinetic stability, which is significantly higher than those of linear Gd-DTPA and cyclic Gd-DOTA-butrol and slightly lower than that of cyclic Gd-DOTA. The T₁ relaxivities of P1-Gd, P2-Gd, P3-Gd, and P4-Gd are 29.4, 38.7, 44.0, and 47.9 Gd mM^-1 s^-1, respectively, at 0.5 T, which are about 6-11 times higher than that of Gd-DOTA (4.4 Gd mM^-1 s^-1). P4-Gd was selected for in vivo magnetic resonance angiography (MRA) because of its high kinetic stability, T₁ relaxivity, and good biosafety. The results showed excellent MRA effect, sensitive detection of vascular stenosis, and prolonged observation window as compared to Gd-DOTA. Overall, Gd(III) chelates of poly-DOTA branched polymers are good candidates of MRI probes, providing a unique design strategy in which Gd chelation can occur at both the interior and surface of the poly-DOTA branched polymers, resulting in excellent relaxivity enhancement. In vivo animal MRA studies of the probe provide possibilities in discovering small vascular pathologies.

Nanocarrier design–function relationship: The prodigious role of properties in regulating biocompatibility for drug delivery applications

The concept of drug delivery systems as a magic bullet for the delivery of bioactive compounds has emerged as a promising approach in the treatment of different diseases with significant advantages over the limitations of traditional methods. While nanocarrier-based drug delivery systems are the main advocates of drug uptake because they offer several advantages including reduced non-specific biodistribution, improved accumulation, and enhanced therapeutic efficiency; their safety and biocompatibility within cellular/tissue systems are therefore important for achieving the desired effect. The underlying power of "design-interplay chemistry" in modulating the properties and biocompatibility at the nanoscale level will direct the interaction with their immediate surrounding. Apart from improving the existing nanoparticle physicochemical properties, the balancing of the hosts' blood components interaction holds the prospect of conferring newer functions altogether. So far, this concept has been remarkable in achieving many fascinating feats in addressing many challenges in nanomedicine such as immune responses, inflammation, biospecific targeting and treatment, and so on. This review, therefore, provides a diverse account of the recent advances in the fabrication of biocompatible nano-drug delivery platforms for chemotherapeutic applications, as well as combination therapy, theragnostic, and other diseases that are of interest to scientists in the pharmaceutical industries. Thus, careful consideration of the "property of choice" would be an ideal way to realize specific functions from a set of delivery platforms. Looking ahead, there is an enormous prospect for nanoparticle properties in regulating biocompatibility.

Polymeric dual-modal imaging nanoprobe with two-photon aggregation-induced emission for fluorescence imaging and gadolinium-chelation for magnetic resonance imaging

Nanoprobes that offer both fluorescence imaging (FI) and magnetic resonance imaging (MRI) can provide supplementary information and hold synergistic advantages. However, synthesis of such dual-modality imaging probes that simultaneously exhibit tunability of functional groups, high stability, great biocompatibility and desired dual-modality imaging results remains challenging. In this study, we used an amphiphilic block polymer from (ethylene glycol) methyl ether methacrylate (OEGMA) and N-(2-hydroxypropyl) methacrylamide (HPMA) derivatives as a carrier to conjugate a MR contrast agent, Gd-DOTA, and a two-photon fluorophore with an aggregation-induced emission (AIE) effect, TPBP, to construct a MR/two-photon fluorescence dual-modality contrast agent, Gd-DOTA-TPBP. Incorporation of gadolinium in the hydrophilic chain segment of the OEGMA-based carrier resulted in a high r₁ value for Gd-DOTA-TPBP, revealing a great MR imaging resolution. The contrast agent specifically accumulated in the tumor region, allowing a long enhancement duration for vascular and tumor contrast-enhanced MR imaging. Meanwhile, coupling TPBP with AIE properties to the hydrophobic chain segment of the carrier not only improved its water solubility and reduced its cytotoxicity, but also significantly enhanced its imaging performance in an aqueous phase. Gd-DOTA-TPBP was also demonstrated to act as an excellent fluorescence probe for two-photon-excited bioimaging with higher resolution and greater sensitivity than MRI. Since high-resolution, complementary MRI/FI dual-modal images were acquired at both cellular and tissue levels in tumor-bearing mice after application of Gd-DOTA-TPBP, it has great potential in the early phase of disease diagnosis.

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A highly stable and biocompatibility MR/two-photon AIE fluorescent dual-modality imaging probe Gd-DOTA-TPBP is prepared.

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Gd-DOTA and TPBP are conjugated to the hydrophilic and hydrophobic chain of the amphiphilic block polymer, respectively.

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The different coupling sites of Gd-DOTA and TPBP promote dual-modality imaging effects of Gd-DOTA-TPBP after self-assembly.

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The dual-modality images with Gd-DOTA-TPBP have obtained complementary information at the cellular and tissue level in vivo.

Recent Advances in Nanotheranostic Agents for Tumor Microenvironment–Responsive Magnetic Resonance Imaging

Nanomaterials integrating a variety of excellent properties (such as controllable/suitable size, surface modifier, and multifunctionality) have attracted increasing attention in the biomedical field and have been considered a new generation of magnetic resonance imaging (MRI) contrast agents (CAs). In recent years, stimuli-responsive nanomaterials with specifically responsive ability have been synthesized as MRI CAs, which can significantly improve the diagnostic sensitivity and accuracy depending on their outstanding performance. Furthermore, the inherent tumor microenvironment (TME) of malignant tumor is considered to possess several unique features, such as low extracellular pH, redox condition, hypoxia, and high interstitial pressure, that are significantly different from healthy tissues. Hence, constructing nanomaterials for TME-responsive MRI as an emerging strategy is expected to overcome the current obstacles to precise diagnosis. This review focuses on recent advances of nanomaterials in their application of TME-responsive MRI that trigger the diagnostic function in response to various endogenous stimulations, including pH, redox, enzyme, and hypoxia. Moreover, the future challenges and trends in the development of nanomaterials serving as TME-responsive MRI CAs are discussed.

Recent development of contrast agents for magnetic resonance and multimodal imaging of glioblastoma

Glioblastoma (GBM) as the most common primary malignant brain tumor exhibits a high incidence and degree of malignancy as well as poor prognosis. Due to the existence of formidable blood–brain barrier (BBB) and the aggressive growth and infiltrating nature of GBM, timely diagnosis and treatment of GBM is still very challenging. Among different imaging modalities, magnetic resonance imaging (MRI) with merits including high soft tissue resolution, non-invasiveness and non-limited penetration depth has become the preferred tool for GBM diagnosis. Furthermore, multimodal imaging with combination of MRI and other imaging modalities would not only synergistically integrate the pros, but also overcome the certain limitation in each imaging modality, offering more accurate morphological and pathophysiological information of brain tumors. Since contrast agents contribute to amplify imaging signal output for unambiguous pin-pointing of tumors, tremendous efforts have been devoted to advances of contrast agents for MRI and multimodal imaging. Herein, we put special focus on summary of the most recent advances of not only MRI contrast agents including iron oxide-, manganese (Mn)-, gadolinium (Gd)-, ¹⁹F- and copper (Cu)-incorporated nanoplatforms for GBM imaging, but also dual-modal or triple-modal nanoprobes. Furthermore, potential obstacles and perspectives for future research and clinical translation of these contrast agents are discussed. We hope this review provides insights for scientists and students with interest in this area.

Cathepsin B-responsive and gadolinium-labeled branched glycopolymer-PTX conjugate-derived nanotheranostics for cancer treatment

Multi-modal therapeutics are emerging for simultaneous diagnosis and treatment of cancer. Polymeric carriers are often employed for loading multiple drugs due to their versatility and controlled release of these drugs in response to a tumor specific microenvironment. A theranostic nanomedicine was designed and prepared by complexing a small gadolinium chelate, conjugating a chemotherapeutic drug PTX through a cathepsin B-responsive linker and covalently bonding a fluorescent probe pheophorbide a (Ppa) with a branched glycopolymer. The branched prodrug-based nanosystem was degradable in the tumor microenvironment with overexpressed cathepsin B, and PTX was simultaneously released to exert its therapeutic effect. The theranostic nanomedicine, branched glycopolymer-PTX-DOTA-Gd, had an extended circulation time, enhanced accumulation in tumors, and excellent biocompatibility with significantly reduced gadolinium ion (Gd³⁺) retention after 96 h post-injection. Enhanced imaging contrast up to 24 h post-injection and excellent antitumor efficacy with a tumor inhibition rate more than 90% were achieved from glycopolymer-PTX-DOTA-Gd without obvious systematic toxicity. This branched polymeric prodrug-based nanomedicine is very promising for safe and effective diagnosis and treatment of cancer.

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A cathepsin B-responsive theranostic nanomedicine (glycopolymer-PTX-DOTA-Gd) based on a branched glycopolymer was prepared.

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Glycopolymer-PTX-DOTA-Gd can be specifically degradated and release drug at tumor enviornment.

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Glycopolymer-PTX-DOTA-Gd enhance the contrast of magnetic resonance imaging (MRI) at tumor sites.

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The nanomedicine have good biocompatibility, excellent tumor targeting and anti-tumor efficacy.

Recent advances in development of dendritic polymer-based nanomedicines for cancer diagnosis

Dendritic polymers have highly branched three-dimensional architectures, the fourth type apart from linear, cross-linked, and branched one. They possess not only a large number of terminal functional units and interior cavities, but also a low viscosity with weak or no entanglement. These features endow them with great potential in various biomedicine applications, including drug delivery, gene therapy, tissue engineering, immunoassay and bioimaging. Most review articles related to bio-related applications of dendritic polymers focus on their drug or gene delivery, while very few of them are devoted to their function as cancer diagnosis agents, which are essential for cancer treatment. In this review, we will provide comprehensive insights into various dendritic polymer-based cancer diagnosis agents. Their classification and preparation are presented for readers to have a precise understanding of dendritic polymers. On account of physical/chemical properties of dendritic polymers and biological properties of cancer, we will suggest a few design strategies for constructing dendritic polymer-based diagnosis agents, such as active or passive targeting strategies, imaging reporters-incorporating strategies, and/or internal stimuli-responsive degradable/enhanced imaging strategies. Their recent applications in in vitro diagnosis of cancer cells or exosomes and in vivo diagnosis of primary and metastasis tumor sites with the aid of single/multiple imaging modalities will be discussed in great detail. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging Diagnostic Tools > in vitro Nanoparticle-Based Sensing.

Application and mechanism of manganese-coated caramelization nanospheres for active targeting in hepatobiliary tumors

Aim: To elucidate the MRI mechanisms of manganese oxide-coated carbohydration nanosphere (Mn@CNS) for active targeting in hepatobiliary tumors. Materials & methods: The cytotoxicity, internalization pathway, metabolism and excretion pathway of Mn@CNS were assessed by several cell types. The MRI of Mn@CNS was verified via rat models bearing hepatobiliary tumors. Results: Mn@CNS showed no obvious cytotoxicity. Mice macrophage and hepatocellular Mn content significantly differed between pre- and post-uptake levels (p < 0.01). The animal experiment revealed fine T1 imaging of hepatobiliary tumors with peak enhancement at 3 h. Mn@CNS was metabolized within the cells and excreted mainly via feces. Conclusion: Mn@CNS is safe, biodegradable, and may serve as a new strategy for active target imaging and treatment applications.

Rhein-based necrosis-avid MRI contrast agents for early evaluation of tumor response to microwave ablation therapy

PURPOSE

Early evaluation of tumor response to thermal ablation therapy can help identify untreated tumor cells and then perform repeated treatment as soon as possible. The purpose of this work was to explore the potential of rhein-based necrosis-avid contrast agents (NACAs) for early evaluation of tumor response to microwave ablation (MWA).

METHODS

3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay was performed to test the cytotoxicity of rhein-based NACAs against HepG2 cells. Rat models of liver MWA were used for investigating the effectiveness of rhein-based NACAs in imaging the MWA lesion, the optimal time period for post-MWA MRI examination, and the metabolic behaviors of ⁶⁸ Ga-labeled rhein-based NACAs. Rat models of orthotopic liver W256 tumor MWA were used for investigating the time window of rhein-based NACAs for imaging the MWA lesion, the effectiveness of these NACAs in distinguishing the residual tumor and the MWA lesion, and their feasibility in early evaluating the tumor response to MWA.

RESULTS

Gadolinium 2,2',2''-(10-(2-((4-(4,5-Dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxamido)butyl)amino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (GdL₂ ) showed low cytotoxicity and high quality in imaging the MWA region. The optimal time period for post-MWA MRI examination using GdL₂ was 2 to 24 h after the treatment. During 2.5 to 3.5 h postinjection, GdL₂ can better visualize the MWA lesion in comparison with gadolinium 2-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl]acetic acid (Gd-DOTA), and the residual tumor would not be enhanced. The tumor response to MWA as evaluated by using GdL₂ -enhanced MRI was consistent with histological examination.

CONCLUSION

GdL₂ appears to be a promising NACA for the tumor response assessment after thermal ablation therapies.

Molybdenum disulfide-based hyaluronic acid-guided multifunctional theranostic nanoplatform for magnetic resonance imaging and synergetic chemo-photothermal therapy

The construction of multifunctional theranostic nanoplatforms to integrate accurate imaging and enhanced therapy to treat tumors is highly attractive but remains a challenge. Here, we developed a molybdenum disulfide (MoS₂)-based hyaluronic acid (HA)-functionalized nanoplatform capable of achieving the targeted co-delivery of the gadolinium (Gd)-based contrast agents (CAs) and the anticancer drug gefitinib (Gef) for magnetic resonance imaging (MRI) and synergetic chemo-photothermal therapy of tumors. Gd³⁺ ions were coupled to HA-grafted MoS₂ nanosheets with diethylenetriaminepentaacetic acid (DTPA) as a linker, followed by the incorporation of Gef. The resulting MoS₂-HA-DTPA-Gd/Gef exhibited enhanced relaxivity, 3.3 times greater than that of the commercial CA DTPA-Gd, which facilitated the MRI in vivo. Moreover, the nanoplatform effectively converted the absorbed near-infrared (NIR) light into heat, which not only induced the photothermal ablation of cancer cells but also triggered the release of Gef from MoS₂-HA-DTPA-Gd/Gef, enabling the synergetic chemo-photothermal therapy. The results of in vitro and in vivo experiments revealed that MoS₂-HA-DTPA-Gd/Gef upon NIR irradiation effectively blocked the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt) signaling pathway and activated apoptosis-related proteins to induce cell apoptosis and suppress cell proliferation, thus inhibiting the tumor growth in lung cancer cell-bearing mice. Taken together, this multifunctional theranostic nanoplatform has significant promise for the diagnosis and treatment of cancer.

Molecular Antioxidant Properties and In Vitro Cell Toxicity of the p-Aminobenzoic Acid (PABA) Functionalized Peptide Dendrimers

BACKGROUND

Exposure to ozone level and ultraviolet (UV) radiation is one of the major concerns in the context of public health. Numerous studies confirmed that abundant free radicals initiate undesired processes, e.g. carcinogenesis, cells degeneration, etc. Therefore, the design of redox-active molecules with novel structures, containing radical quenchers molecules with novel structures, and understanding their chemistry and biology, might be one of the prospective solutions. Methods: We designed a group of peptide dendrimers carrying multiple copies of p-aminobenzoic acid (PABA) and evaluated their molecular antioxidant properties in 1,1'-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) tests. Cytotoxicity against human melanoma and fibroblast cells as well as against primary cerebral granule cells (CGC) alone and challenged by neurotoxic sodium glutamate and production of reactive oxygen species (ROS) in presence of dendrimers were measured. Results: PABA-terminated dendrimers express enhanced radical and radical cation scavenging properties in relation to PABA alone. In cellular tests, the dendrimers at 100 M fully suppress and between 20⁻100 M reduce proliferation of the human melanoma cell line. In concentration 20 M dendrimers generate small amount of the reactive oxygen species (<25%) but even in their presence human fibroblast and mouse cerebellar granule cells remain intact Moreover, dendrimers at 0.2⁻20 µM concentration (except one) increased the percentage of viable fibroblasts and CGC cells treated with 100 M glutamate. Conclusions: Designed PABA-functionalized peptide dendrimers might be a potential source of new antioxidants with cationic and neutral radicals scavenging potency and/or new compounds with marked selectivity against human melanoma cell or glutamate-stressed CGC neurons. The scavenging level of dendrimers depends strongly on the chemical structure of dendrimer and the presence of other groups that may be prompted into radical form. The present studies found different biological properties for dendrimers constructed from the same chemical fragments but the differing structure of the dendrimer tree provides once again evidence that the structure of dendrimer can have a significant impact on drug⁻target interactions.

Water-Mediated Nanostructures for Enhanced MRI: Impact of Water Dynamics on Relaxometric Properties of Gd-DTPA

Recently, rational design of a new class of contrast agents (CAs), based on biopolymers (hydrogels), have received considerable attention in Magnetic Resonance Imaging (MRI) diagnostic field. Several strategies have been adopted to improve relaxivity without chemical modification of the commercial CAs, however, understanding the MRI enhancement mechanism remains a challenge. Methods: A multidisciplinary approach is used to highlight the basic principles ruling biopolymer-CA interactions in the perspective of their influence on the relaxometric properties of the CA. Changes in polymer conformation and thermodynamic interactions of CAs and polymers in aqueous solutions are detected by isothermal titration calorimetric (ITC) measurements and later, these interactions are investigated at the molecular level using NMR to better understand the involved phenomena. Water molecular dynamics of these systems is also studied using Differential Scanning Calorimetry (DSC). To observe relaxometric properties variations, we have monitored the MRI enhancement of the examined structures over all the experiments. The study of polymer-CA solutions reveals that thermodynamic interactions between biopolymers and CAs could be used to improve MRI Gd-based CA efficiency. High-Pressure Homogenization is used to obtain nanoparticles. Results: The effect of the hydration of the hydrogel structure on the relaxometric properties, called Hydrodenticity and its application to the nanomedicine field, is exploited. The explanation of this concept takes place through several key aspects underlying biopolymer-CA's interactions mediated by the water. In addition, Hydrodenticity is applied to develop Gadolinium-based polymer nanovectors with size around 200 nm with improved MRI relaxation time (10-times). Conclusions: The experimental results indicate that the entrapment of metal chelates in hydrogel nanostructures offers a versatile platform for developing different high performing CAs for disease diagnosis.

Linear PVA–DTPA–Gd conjugate for magnetic resonance imaging

In this study, we report the preparation and characterization of the PVA–DTPA–Gd conjugate as a potential MRI contrast agent (CA). The r₁ value and the r₂/r₁ ratio were about 5.6 mM⁻¹ s⁻¹ and 1.31, respectively. In vitro toxicity studies not only demonstrated that the polymeric system possessed good biocompatibility, but also proved that the conjugate could be an attractive candidate for CA.

In this study, we report the preparation and characterization of the PVA–DTPA–Gd conjugate as a potential MRI contrast agent (CA).

Reductive microenvironment responsive gadolinium-based polymers as potential safe MRI contrast agents

A ROX and enzyme-responsive biodegradable gadolinium-based mCA was prepared, demonstrating a short gadolinium retention time and sufficient MRI contrast efficacy in tumors.

PEGylated Multistimuli-Responsive Dendritic Prodrug-Based Nanoscale System for Enhanced Anticancer Activity

A PEGylated multistimuli-responsive dendritic copolymer-doxorubicin (DOX) prodrug-based nanoscale system was developed as a delivery model for hydrophobic drugs. In this system, PEGylation did not only prolong circulation of the nanoscale system in the body (average half-life of 14.6 h, four times longer than that of the free drug), but also allowed the system to aggregate into nanoparticles (NPs) because of interactions between hydrophilic (polyethylene glycol) and hydrophobic (dendritic prodrug) moieties for better uptake through endocytosis (around 150 nm of particle size with a neutrally charged surface for the PEGylated dendritic prodrug with 12.1 wt % of DOX). The dendritic structure was built by bridging poly[ N-(2-hydroxypropyl)methacrylamide] segments with enzyme-responsive GFLG (Gly-Phe-Leu-Gly tetrapeptide) linkers. DOX was released by hydrolyzing the hydrazone bond between DOX and the copolymer framework in the acidic endosomes/lysosomes. In vitro studies on DOX released from the NPs induced mitochondrial dysfunction during apoptosis. By imaging the main organs and tumor tissues from mice treated with the NPs, boosted accumulation of this nanoscale medicine was found in tumor tissues, leading to a decrease in toxicity and side effects to normal tissues and enhancement in drug tolerance. In the 4T1 breast cancer model, these NPs exhibited a superior antitumor efficacy confirmed by inhibiting angiogenesis, proliferation of tumor tissues, and inducing procedural apoptosis of tumor cells. The highest tumor growth inhibition value mediated by the NPs was up to 86.5%. Therefore, this PEGylated multistimuli-responsive dendritic copolymer-DOX prodrug-based nanoscale system may be further explored as an alternative to traditional chemotherapy for breast cancer treatment.

A biocompatible and cathepsin B sensitive nanoscale system of dendritic polyHPMA-gemcitabine prodrug enhances antitumor activity markedly

In an attempt to improve the therapeutic indices of gemcitabine (GEM), a prodrug was designed by conjugating GEM with a stimuli-responsive dendritic polyHPMA copolymer (dendritic polyHPMA-GEM) and synthesized using the one-pot method of RAFT polymerization. The prodrug with dendritic architectures was able to aggregate and form stable nanoscale systems in the order of 46 nm. The high molecular weight (HMW, 168 kDa) dendritic prodrug could biodegrade into segments of low molecular weight (LMW, 29 kDa) for excretion. The prodrug demonstrates enzyme-responsive drug release features; over 95% GEM was released from the carrier in the presence of cathepsin B within 3 h. Investigation of the cellular mechanism underlying the dendritic prodrug suggests that cytotoxicity is associated with cellular uptake and cell apoptosis. The prodrug shows good hemocompatibility and in vivo biosafety. In particular, the dendritic polymer prodrug displays high accumulation within tumors and markedly improved in vivo antitumor activity in the 4T1 murine breast cancer model compared to free GEM. The in vivo antitumor activities are characterized by a marked suppression in tumor volumes indicating much higher tumor growth inhibition (TGI, 83%) than that in GEM treatment (TGI, 36%). In addition, some tumors were eliminated. The tumor xenograft immunohistochemistry study clearly indicates that tumor apoptosis occurs through antiangiogenic effects. These results suggest that the stimuli-responsive dendritic polymer-gemcitabine has great potential as an efficient anticancer agent.

Ultrasmall Hyperbranched Semiconducting Polymer Nanoparticles with Different Radioisotopes Labeling for Cancer Theranostics

Exploiting ultrasmall nanoparticles as multifunctional nanocarriers labeled with different radionuclides for tumor theranostics has attracted great attention in past few years. Herein, we develop multifunctional nanocarriers based on ultrasmall hyperbranched semiconducting polymer (HSP) nanoparticles for different radionuclides including technetium-99m (^99mTc), iodine-131 (¹³¹I), and iodine-125 (¹²⁵I) labeling. SPECT imaging of ^99mTc labeled PEGylated HSP nanoparticles (HSP-PEG) exhibit a prominent accumulation in two-independent tumor models including subcutaneously xenograft and patient derived xenograft model. Impressively, 5,6-dimethylxanthenone-4-acetic acid (DMXAA), as tumor-vascular disrupting agent (VDA), significantly improves the tumor accumulation of ¹³¹I labeled HSP-PEG nanoparticles, further leading to the excellent inhibition of tumor growth after intravenous injection. More importantly, SPECT imaging of ¹²⁵I labeled HSP-PEG indicates that ultrasmall HSP-PEG nanoparticles could be slowly excreted from the body of a mouse through urine and feces in 1 week and cause no obvious toxicity to treated mice from blood analysis and histology examinations. Our finding from the different independent tumor models SPECT imaging shows that HSP-PEG nanoparticles may act as multifunctional nanocarriers to deliver different radionuclides for monitoring the in vivo behaviors of nanoparticles and cancer theranostics, which will provide a strategy for cancer treatment.

Biodegradable Nanoglobular Magnetic Resonance Imaging Contrast Agent Constructed with Host-Guest Self-Assembly for Tumor-Targeted Imaging

Gadolinium-based macromolecular magnetic resonance imaging (MRI) contrast agents (CAs) have attracted increasing interest in tumor diagnosis. However, their practical application is potentially limited because the long-term retention of gadolinium ion in vivo will induce toxicity. Here, a nanoglobular MRI contrast agent (CA) PAMAM-PG- g-s-s-DOTA(Gd) + FA was designed and synthesized on the basis of the facile host-guest interaction between β-cyclodextrin and adamantane, which initiated the self-assembly of poly(glycerol) (PG) separately conjugated with gadolinium chelates by disulfide bonds and folic acid (FA) molecule onto the surface of poly(amidoamine) (PAMAM) dendrimer, finally realizing the biodegradability and targeting specificity. The nanoglobular CA has a higher longitudinal relaxivity ( r₁) than commercial gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA), showing a value of 8.39 mM^-1 s^-1 at 0.5 T, and presents favorable biocompatibility on the observations of cytotoxicity and tissue toxicity. Furthermore, MRI on cells and tumor-bearing mice both demonstrate the obvious targeting specificity, on the basis of which the effective contrast enhancement at tumor location was obtained. In addition, this CA exhibits the ability of cleavage to form free small-molecule gadolinium chelates and can realize minimal gadolinium retention in main organs and tissues after tumor detection. These results suggest that the biodegradable nanoglobular PAMAM-PG- g-s-s-DOTA(Gd) + FA can be a safe and efficient MRI CA for tumor diagnosis.

MRI Contrast Agents Based on Conjugated Polyelectrolytes and Dendritic Polymers

Three complexes of gadolinium-based on dentritic molecules are reported as magnetic resonance imaging (MRI) contrast agents. Their ligands feature four carboxylate groups, which contribute to good water solubility and a strong combination with metal ions. As a new attempt, coupling polymerization is carried out to make a combination of conjugated polyelectrolytes and dendrimers for MRI contrast agents. For comparison, mononuclear and binuclear complexes are also reported. The investigation suggests that the contrast agent with the newly designed macromolecular skeleton provides higher longitudinal relaxivity value (36.2 mm -1 s-1 ) and more visible enhancement in in vivo and in vitro MR images than the small molecular ones. In addition, extremely low cytotoxicity and main clearance via hepatobiliary are confirmed, which reduces the deterioration of chronic kidney disease. All the results indicate that these three complexes are generally applicable as promising clinical contrast agents.

A SERRS/MRI multimodal contrast agent based on naked Au nanoparticles functionalized with a Gd(iii) loaded PEG polymer for tumor imaging and localized hyperthermia

Multimodal contrast agents offer new interesting diagnostic possibilities, summing the benefits of multiple imaging techniques. Magnetic resonance and optical imaging are complementary techniques. The first allows total body screening, even though it suffers from low spatial resolution and needs high loadings, whereas the second shows lower penetration, but bright signals, and a higher spatial resolution and needs lower loadings. We present a plasmonic nanosystem as a MRI (magnetic resonance imaging) and SERRS (surface enhanced resonance Raman scattering) multimodal contrast agent. Naked gold nanoparticles, obtained by laser ablation synthesis in solution, are organized as a highly efficient SERRS substrate with a naphthalocyanine reporter and functionalized with a MRI contrast agent with a newly synthesized 3DOTA-PEG polymer, with a high Gd^III loading. As a proof of concept, in vivo and ex vivo MRI and SERRS experiments are also performed. The plasmonic property of the nanosystem is then exploited to show its usefulness for localized hyperthermia.

Cross-Linked and Biodegradable Polymeric System as a Safe Magnetic Resonance Imaging Contrast Agent

Owing to the low efficacy of clinically used small-molecule gadolinium (Gd)-based magnetic resonance imaging (MRI) agents, we designed and explored biodegradable macromolecular conjugates as MRI contrast agents. The linear polymeric structure and core-cross-linked formulation possessed different characteristics and features, so we prepared and comparatively studied the two kinds of Gd-based N-(2-hydroxypropyl) methacrylamide (HPMA) polymeric systems (the core-cross-linked pHPMA-DOTA-Gd and the linear one) using the clinical agent diethylene-triamine pentaacetic acid-Gd(III) (DTPA-Gd) as a control. This study was aimed to find the optimal polymeric formulation as a biocompatible and efficient MRI contrast agent. The high molecular weight (MW, 181 kDa) and core-cross-linked copolymer was obtained via the cross-linked block linear copolymer and could be degraded to low-MW segments (29 kDa) in the presence of glutathione (GSH) and cleaned from the body. Both core-cross-linked and linear pHPMA-DOTA-Gd copolymers displayed 2-3-fold increased relaxivity (r₁ value) than that of DTPA-Gd. Animal studies demonstrated that two kinds of macromolecular systems led to much longer blood circulation time, higher tumor accumulation, and much higher signal intensity compared with the linear and clinical ones. Finally, in vivo and in vitro toxicity studies indicated that the two macromolecular agents had great biocompatibility. Therefore, we performed preliminary but important studies on the Gd-based HPMA polymeric systems as biocompatible and efficient MRI contrast agents and found that the biodegradable core-cross-linked pHPMA-DOTA-Gd copolymer might have greater benefits for the foreground.

Light- and pH-dually responsive dendrimer-star copolymer containing spiropyran groups: synthesis, self-assembly and controlled drug release

Dendrimer-star copolymer containing spiropyran groups could self-assemble into micelles and presented light- and pH-dually responsive properties.

Poly(HPMA)-DTPA/DOTA-Gd conjugates for magnetic resonance imaging

Poly(HPMA)-DTPA/DOTA-Gd conjugates were fabricated, and the cytotoxicity, hemocompatibility and T₁ relaxivity property were evaluated.

Synthesis of enzyme-responsive phosphoramidate dendrimers for cancer drug delivery

Enzyme-responsive phosphoramidate dendrimers were successfully synthesized and their surfaces were modified with zwitterionic groups for cancer drug delivery.

A tailored nanosheet decorated with a metallized dendrimer for angiography and magnetic resonance imaging-guided combined chemotherapy

Considering the chemical exchange between gadolinium centers and water protons, nanosystems comprising gadolinium conjugated with high specific area nanocarriers might serve as more robust clinical tools for diagnosis and imaging-guided therapy. Herein, a pH-responsive nanosystem containing graphene oxide conjugated with a folic acid- and gadolinium-labeled dendrimer (FA-GCGLD) to boost its T₁ contrast ability was developed, and doxorubicin (DOX) and colchicine (COLC) were efficiently loaded onto this nanosystem (FA-GCGLD-DOX/COLC). This nanosystem showed a prominent T₁ contrast with an ultrahigh relaxivity of up to 11.6 mM^-1 s^-1 and pH-responsive drug release behavior. HepG2 cells treated with FA-GCGLD-DOX/COLC were efficiently inhibited, and the cell contrast was enhanced. In vivo, the tumor accumulation of FA-GCGLD-DOX/COLC significantly increased, thereby facilitating the systemic delivery of particles and exerting tumor growth inhibition and an enhanced tumor contrast effect. Moreover, compared to free drugs, FA-GCGLD-DOX/COLC effectively decreased the drug resistance of the tumor, thereby improving the cancer chemotherapeutic efficacy. In addition, injecting rats with FA-GCGLD afforded excellent magnetic resonance angiography (MRA) images with high-resolution vascular structures because of the long blood circulation time of FA-GCGLD. Thus, this study provides a powerful tool for diverse applications in the biomedical field, including accurate diagnosis and chemotherapy of tumors and the detection of cardiovascular diseases.

CO2-based amphiphilic polycarbonate micelles enable a reliable and efficient platform for tumor imaging

Biodegradable polymeric nanomaterials can be directly broken down by intracellular processes, offering a desirable way to solve toxicity issues for cancer diagnosis and treatment. Among them, aliphatic polycarbonates are approved for application in biological fields by the United States Food and Drug Administration (FDA), however, high hydrophobicity, deficient functionality and improper degradation offer significant room for improvement in these materials.

METHODS

To achieve progress in this direction, herein, we demonstrate that CO2-based amphiphilic polycarbonates (APC) with improved hydrophilicity and processability can be used as a reliable and efficient platform for tumor imaging. To better investigate their potential, we devised a convenient strategy through conjugation of APC with gadolinium (Gd).

RESULTS

The resulting polymeric micelles (APC-DTPA/Gd) exhibit excellent magnetic resonance imaging performance, simultaneously enabling real-time visualization of bioaccumulation and decomposition of polymeric micelles in vivo. Importantly, these micelles can be degraded to renally cleared products within a reasonable timescale without evidence of toxicity.

CONCLUSION

Our findings may help the development of CO2-based amphiphilic polycarbonate for cancer diagnosis and treatment, accompanied by their low-toxicity degradation pathway.

Modulating angiogenesis with integrin-targeted nanomedicines

Targeting angiogenesis-related pathologies, which include tumorigenesis and metastatic processes, has become an attractive strategy for the development of efficient guided nanomedicines. In this respect, integrins are cell-adhesion molecules involved in angiogenesis signaling pathways and are overexpressed in many angiogenic processes. Therefore, they represent specific biomarkers not only to monitor disease progression but also to rationally design targeted nanomedicines. Arginine-glycine-aspartic (RGD) containing peptides that bind to specific integrins have been widely utilized to provide ligand-mediated targeting capabilities to small molecules, peptides, proteins, and antibodies, as well as to drug/imaging agent-containing nanomedicines, with the final aim of maximizing their therapeutic index. Within this review, we aim to cover recent and relevant examples of different integrin-assisted nanosystems including polymeric nanoconstructs, liposomes, and inorganic nanoparticles applied in drug/gene therapy as well as imaging and theranostics. We will also critically address the overall benefits of integrin-targeting.

Gadolinium-Labeled Biodegradable Dendron-Hyaluronic Acid Hybrid and Its Subsequent Application as a Safe and Efficient Magnetic Resonance Imaging Contrast Agent

Novel magnetic resonance imaging (MRI) contrast agents with high sensitivity and good biocompatibility are required for the diagnosis of cancer. Herein, we prepared and characterized the gadolinium [Gd(III)]-labeled peptide dendron-hyaluronic acid (HA) conjugate-based hybrid (dendronized-HA-DOTA-Gd) by combining the advantages of HA and the peptide dendron. The dendronized-HA-DOTA-Gd hybrid with 3.8% Gd(III) as weight percentage showed a negative zeta potential (-35 mV). The in vitro degradation results indicated that the dendronized-HA-DOTA-Gd hybrid degraded into products with low molecular weights in the presence of hyaluronidase. The dendronized-HA-DOTA-Gd hybrid showed a 3-fold increase in longitudinal relaxivity and much higher in vivo signal enhancement in 4T1 breast tumors of mice compared with clinical Magnevist (Gd-DTPA). The dendronized-HA-DOTA-Gd hybrid had a higher accumulation in tumors than Gd-DTPA; it was 2-3-fold after administration. Meanwhile, the polymeric hybrid resulted in low Gd(III) residue in the body compared with that of Gd-DTPA. The systematic biosafety evaluations, including blood compatibility and toxicity assessments, suggested that the dendronized-HA-DOTA-Gd hybrid exhibited good biocompatibility. Thus, the gadolinium-labeled and dendronized HA hybrid shows promise as a safe and efficient macromolecular MRI contrast agent based on high sensitivity, low residue content in the body, and good biosafety.

Enzyme-responsive peptide dendrimer-gemcitabine conjugate as a controlled-release drug delivery vehicle with enhanced antitumor efficacy

Stimuli-responsive peptide dendrimer-drug conjugates have presented significant potential for cancer therapy. To develop an effective nanoscale chemotherapeutic prodrug, we developed a novel enzyme-responsive PEGylated lysine peptide dendrimer-gemcitabine conjugate (Dendrimer-GEM) based nanoparticle via the highly efficient click reaction. Owing to the glycyl phenylalanyl leucyl glycine tetra-peptide (GFLG) as an enzyme-cleavable linker to conjugate gemcitabine (GEM), the prepared nanoparticles were able to release drug significantly faster in the tumor cellular environments, which specifically contains secreted Cathepsin B, quantifiably more than 80% GEM was released with Cathepsin B compared to the condition without Cathepsin B at 24h. This nanoparticle demonstrated enhanced antitumor efficacy in a 4T1 murine breast cancer model without obvious systemic toxicity, resulting in significantly suppressed relative tumor volumes (86.17±38.27%) and a 2-fold higher value of tumor growth inhibition (∼90%) than GEM·HCl treatment. These results suggest that the PEGylated peptide dendrimer-gemcitabine conjugate can be an effective antitumor agent for breast cancer therapy. Statement of Significance We found that the functionalized dendrimer based nanoscale drug delivery vehicles exhibited enhanced therapeutic indexes and reduced toxicity as compared to the free drug gemcitabine. Compared with current nanoparticles, such as dendritic anticancer drug delivery systems, the new design was capable of self-assembling into nanoscale particles with sizes of about 80-110nm, which is suitable as antitumor drug delivery vehicle due to the potential longer intravascular half-life and higher accumulation in tumor tissue via EPR effect. Owing to the optimized architecture, the system was given the enzyme-responsive drug release feature, and showed excellent antitumor activity on the 4T1 breast tumor model due to the evidences from tumor growth curves, immunohistochemical analysis and confocal laser scanning microscopy. Meanwhile, no significant side effect was observed by histological analysis. This study demonstrated that PEGylated peptide dendritic architecture may be used as efficient and safe nanoscale drug delivery vehicle for cancer therapy.

Fusion peptide functionalized hybrid nanoparticles for synergistic drug delivery to reverse cancer drug resistance

A facile self-assembly strategy was developed to decorate polymer/inorganic hybrid nano-sized drug delivery systems with functional peptides. To enhance drug delivery efficacy and overcome tumor drug resistance, a functional fusion peptide containing an RGD sequence for tumor targeting and an R₈ sequence for cell penetration was introduced onto the surface of biotinylated carboxymethyl chitosan/CaCO₃ (BCMC/CaCO₃) hybrid nanoparticles through biotin-avidin interaction to obtain peptide functionalized nanoparticles (PNP). The peptide functionalization results in improved delivery efficiency and effective inhibition for drug resistant tumor cells. Co-delivery of an anti-cancerous drug (doxorubicin hydrochloride, DOX) and a cyclooxygenase-2 inhibitor (celecoxib, CXB) by PNP can further improve the therapeutic efficiency by effectively down-regulating P-gp expression to reduce P-gp mediated drug efflux and increase intracellular drug accumulation.

Stimuli-Sensitive Biodegradable and Amphiphilic Block Copolymer-Gemcitabine Conjugates Self-Assemble into a Nanoscale Vehicle for Cancer Therapy

The availability and the stability of current anticancer agents, particularly water-insoluble drugs, are still far from satisfactory. A widely used anticancer drug, gemcitabine (GEM), is so poorly stable in circulation that some polymeric drug-delivery systems have been under development for some time to improve its therapeutic index. Herein, we designed, prepared, and characterized a biodegradable amphiphilic block N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-GEM conjugate-based nanoscale and stimuli-sensitive drug-delivery vehicle. An enzyme-sensitive oligopeptide sequence glycylphenylalanylleucylglycine (GFLG) was introduced to the main chain with hydrophilic and hydrophobic blocks via the reversible addition-fragmentation chain transfer (RAFT) polymerization. Likewise, GEM was conjugated to the copolymer via the enzyme-sensitive peptide GFLG, producing a high molecular weight (MW) product (90 kDa) that can be degraded into smaller MW segments (<50 kDa), and ensuring potential rapid site-specific release and stability in vivo. The amphiphilic copolymer-GEM conjugate can self-assemble into compact nanoparticles. NIR fluorescent images demonstrated that the conjugate-based nanoparticles could accumulate and be retained within tumors, resulting in significant increased antitumor efficacy compared to free GEM. The conjugate was not toxic to organs of the mice as measured by body weight reductions and histological analysis. In summary, this biodegradable amphiphilic block HPMA copolymer-gemcitabine conjugate has the potential to be a stimuli-sensitive and nanoscale drug-delivery vehicle.

Stimuli-responsive biodegradable and gadolinium-based poly[N-(2-hydroxypropyl) methacrylamide] copolymers: their potential as targeting and safe magnetic resonance imaging probes

Functionalized and biodegradable block pHPMA copolymer–gadolinium conjugates demonstrated good biocompatibility, high T₁ relaxivity, and enhanced tumor signal intensity for MRI.

Hyperbranched poly(glycerol) as a T1 contrast agent for tumor-targeted magnetic resonance imaging in vivo

To explore a convenient and efficient strategy for constructing tumor-targeted T₁ mCAs for MRI, hyperbranched poly(glycerol) prepared in one-pot was used to conjugate gadolinium chelates and folic acid ligands through “click chemistry”.