Gd-DTPA-loaded polymer-metal complex micelles with high relaxivity for MR cancer imaging

Nanocarriers address intracellular barriers for efficient drug delivery, overcoming drug resistance, subcellular targeting and controlled release

The cellular barriers are major bottlenecks for bioactive compounds entering into cells to accomplish their biological functions, which limits their biomedical applications. Nanocarriers have demonstrated high potential and benefits for encapsulating bioactive compounds and efficiently delivering them into target cells by overcoming a cascade of intracellular barriers to achieve desirable therapeutic and diagnostic effects. In this review, we introduce the cellular barriers ahead of drug delivery and nanocarriers, as well as summarize recent advances and strategies of nanocarriers for increasing internalization with cells, promoting intracellular trafficking, overcoming drug resistance, targeting subcellular locations and controlled drug release. Lastly, the future perspectives of nanocarriers for intracellular drug delivery are discussed, which mainly focus on potential challenges and future directions. Our review presents an overview of intracellular drug delivery by nanocarriers, which may encourage the future development of nanocarriers for efficient and precision drug delivery into a wide range of cells and subcellular targets.

PEGylated Amphiphilic Gd-DOTA Backboned-Bound Branched Polymers as Magnetic Resonance Imaging Contrast Agents

MRI contrast agents with high kinetic stability and relaxivity are the key objectives in the field. We previously reported that Gd-DOTA backboned-bound branched polymers possess high kinetic stability and significantly increased T1 relaxivity than traditional branched polymer contrast agents. In this work, non-PEGylated and PEGylated amphiphilic Gd-DOTA backboned-bound branched polymers [P(GdDOTA-C6), P(GdDOTA-C10), mPEG-P(GdDOTA-C6), and mPEG-P(GdDOTA-C10)] were obtained by sequential introduction of rigid carbon chains (1,6-hexamethylenediamine or 1,10-diaminodecane) and mPEG into the structure of Gd-DOTA backboned-bound branched polymers. It is found that the introduction of both rigid carbon chains, especially the longer one, and mPEG can increase the kinetic stability and T1 relaxivity of Gd-DOTA backboned-bound branched polymers. Among them, mPEG-P(GdDOTA-C10) possesses the highest kinetic stability (significantly higher than those of linear Gd-DTPA and cyclic Gd-DOTA-butrol) and T1 relaxivity (42.9 mM-1 s-1, 1.5 T), 11 times that of Gd-DOTA and 1.4 times that of previously reported Gd-DOTA backboned-bound branched polymers. In addition, mPEG-P(GdDOTA-C10) showed excellent MRA effect in cardiovascular and hepatic vessels at a dose (0.025 or 0.05 mmol Gd/kg BW) far below the clinical range (0.1-0.3 mmol Gd/kg BW). Overall, effective branched-polymer-based contrast agents can be obtained by a strategy in which rigid carbon chains and PEG were introduced into the structure of Gd-DOTA backbone-bound branched polymers, resulting in excellent kinetic stability and enhanced T1 relaxivity.

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.

Metal-Assembled Collagen Peptide Microflorettes as Magnetic Resonance Imaging Agents

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents.

Recent Advances in Imaging Agents Anchored with pH (Low) Insertion Peptides for Cancer Theranostics

The acidic extracellular microenvironment has become an effective target for diagnosing and treating tumors. A pH (low) insertion peptide (pHLIP) is a kind of peptide that can spontaneously fold into a transmembrane helix in an acidic microenvironment, and then insert into and cross the cell membrane for material transfer. The characteristics of the acidic tumor microenvironment provide a new method for pH-targeted molecular imaging and tumor-targeted therapy. As research has increased, the role of pHLIP as an imaging agent carrier in the field of tumor theranostics has become increasingly prominent. In this paper, we describe the current applications of pHLIP-anchored imaging agents for tumor diagnosis and treatment in terms of different molecular imaging methods, including magnetic resonance T1 imaging, magnetic resonance T2 imaging, SPECT/PET, fluorescence imaging, and photoacoustic imaging. Additionally, we discuss relevant challenges and future development prospects.

Assemblies of poly(N-vinyl-2-pyrrolidone)-based double hydrophilic block copolymers triggered by lanthanide ions: characterization and evaluation of their properties as MRI contrast agents

Because of the formation of specific antibodies to poly(ethylene glycol) (PEG) leading to life-threatening side effects, there is an increasing need to develop alternatives to treatments and diagnostic methods based on PEGylated copolymers. Block copolymers comprising a poly(N-vinyl-2-pyrrolidone) (PVP) segment can be used for the design of such vectors without any PEG block. As an example, a poly(acrylic acid)-block-poly(N-vinyl-2-pyrrolidone) (PAA-b-PVP) copolymer with controlled composition and molar mass is synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Mixing this copolymer with lanthanide cations (Gd³⁺, Eu³⁺, Y³⁺) leads to the formation of hybrid polyion complexes with increased stability, preventing the lanthanide cytotoxicity and in vitro cell penetration. These new nanocarriers exhibit enhanced T₁ MRI contrast, when intravenously administered into mice. No leaching of gadolinium ions is detected from such hybrid complexes.

Integration of PEG-conjugated gadolinium complex and superparamagnetic iron oxide nanoparticles as T 1-T 2 dual-mode magnetic resonance imaging probes

The T 1-T 2 dual-mode probes for magnetic resonance imaging (MRI) can non-invasively acquire comprehensive information of different tissues or generate self-complementary information of the same tissue at the same time, making MRI a more flexible imaging modality for complicated applications. In this work, three Gadolinium-diethylene-triaminepentaaceticacid (Gd-DTPA) complex conjugated superparamagnetic iron oxide (SPIO) nanoparticles with different Gd/Fe molar ratio (0.94, 1.28 and 1.67) were prepared as T 1-T 2 dual-mode MRI probes, named as SPIO@PEG-GdDTPA0.94, SPIO@PEG-GdDTPA1.28 and SPIO@PEG-GdDTPA1.67, respectively. All SPIO@PEG-GdDTPA nanocomposites with 8 nm spherical SPIO nanocrystals showed good Gd3+ chelate stability. SPIO@PEG-GdDTPA0.94 nanocomposites with lowest Gd/Fe molar ratio show no cytotoxicity to Raw 264.7 cells as compared to SPIO@PEG-GdDTPA1.28 and SPIO@PEG-GdDTPA1.67. SPIO@PEG-GdDTPA0.94 nanocomposites with r 1 (8.4 mM-1s-1), r 2 (83.2 mM-1s-1) and relatively ideal r 2/r 1 ratio (9.9) were selected for T 1-T 2 dual-mode MRI of blood vessels and liver tissue in vivo. Good contrast images were obtained for both cardiovascular system and liver in animal studies under a clinical 3 T scanner. Importantly, one can get high-quality contrast-enhanced blood vessel images within the first 2 h after contrast agent administration and acquire liver tissue anatomy information up to 24 h. Overall, the strategy of one shot of the dual mode MRI agent could bring numerous benefits not only for patients but also to the radiologists and clinicians, e.g. saving time, lowering side effects and collecting data of different organs sequentially.

Metal-Coordinated Supramolecular Self-Assemblies for Cancer Theranostics

Metal-coordinated supramolecular nanoassemblies have recently attracted extensive attention as materials for cancer theranostics. Owing to their unique physicochemical properties, metal-coordinated supramolecular self-assemblies can bridge the boundary between traditional inorganic and organic materials. By tailoring the structural components of the metal ions and binding ligands, numerous multifunctional theranostic nanomedicines can be constructed. Metal-coordinated supramolecular nanoassemblies can modulate the tumor microenvironment (TME), thus facilitating the development of TME-responsive nanomedicines. More importantly, TME-responsive organic-inorganic hybrid nanomaterials can be constructed in vivo by exploiting the metal-coordinated self-assembly of a variety of functional ligands, which is a promising strategy for enhancing the tumor accumulation of theranostic molecules. In this review, recent advancements in the design and fabrication of metal-coordinated supramolecular nanomedicines for cancer theranostics are highlighted. These supramolecular compounds are classified according to the order in which the coordinated metal ions appear in the periodic table. Furthermore, the prospects and challenges of metal-coordinated supramolecular self-assemblies for both technical advances and clinical translation are discussed. In particular, the superiority of TME-responsive nanomedicines for in vivo coordinated self-assembly is elaborated, with an emphasis on strategies that enhance the accumulation of functional components in tumors for an ideal theranostic outcome.

Versatile gadolinium(III)-phthalocyaninate photoagent for MR/PA imaging-guided parallel photocavitation and photodynamic oxidation at single-laser irradiation

Current light-mediated photodynamic therapy (PDT) is far underutilized in clinical cancer treatment due to its low pharmacological effect. We herein proposed a new gadolinium(III)-phthalocyanine (GdPc)-enabled phototherapeutics, photoacoustic/dynamic therapy (PADT), towards in vivo solid tumors via parallel-produced photocavitation and photodynamic oxidation with excitation by a single pulsed laser. We demonstrated that pulsed irradiation of GdPc could simultaneously produce an intense acoustic effect and a high-level ¹O₂ quantum yield to afford mitochondrial damage and initiate programmed cell death. Under the guidance of magnetic resonance/photoacoustic dual-modal imaging, the mechanical oxygen-independent destruction of acoustic cavitation and the chemical damage of ¹O₂ were validated to afford combinatorial inhibition of tumors under either normal or hypoxic conditions after the agent delivered into the cancer cells by a pH-sensitive nanomicelle. The single-laser initiated PADT using GdPc as a versatile photoagent maximizes the use of light energy to minimize the dose requirement of oxygen and agent towards high therapeutic efficacy, surpassing dramatically over conventional PDT.

Investigating plasma volume expanders as novel macromolecular MRI-CEST contrast agents for tumor contrast-enhanced imaging

PURPOSE

The aim of this study was to investigate two clinically approved plasma volume expanders (dextran 70 and voluven) as macromolecular MRI-chemical exchange saturation transfer (CEST) contrast agents to assess tumor vascular properties.

METHODS

CEST contrast efficiency of both molecules (6% w/v) was measured in vitro at various irradiation saturation powers (1-6 μT for 5 s) and pH values (range, 5.5-7.9) and the exchange rate of hydroxyl protons was calculated. In vivo studies in a murine adenocarcinoma model (n = 4 mice for each contrast agent) upon i.v. injection provided CEST-derived perfusion tumor properties that were compared with those obtained with a gadolinium-based blood-pool agent (Gd-AAZTA-Madec).

RESULTS

In vitro measurements showed a marked CEST contrast dependency to pH, with higher CEST contrast at lower pH values for both molecules. The measured prototropic exchange rates confirmed a base-catalyzed exchange rate that was faster for dextran 70 in comparison to voluven. Both molecules showed a similar CEST contrast increase (ΔST% > 3%) in the tumor tissue up to 30 min postinjection, with heterogeneous accumulation. In tumors receiving both CEST and T₁ -weighted agents, a voxel-by-voxel analysis indicated moderate spatial correlation of perfusion properties between voluven/dextran 70 and Gd-AAZTA-Madec, suggesting different distribution patterns according to their molecular size.

CONCLUSIONS

The obtained results showed that both voluven and dextran 70 can be exploited as MRI-CEST contrast agents for evaluating tumor enhancement properties. Their increased accumulation in tumors and prolonged contrast enhancement promote their use as blood-pool MRI-CEST agents to examine tumor vascularization.

Gadolinium-loaded calcium phosphate nanoparticles for magnetic resonance imaging of orthotopic hepatocarcinoma and primary hepatocellular carcinoma

The development of magnetic resonance imaging (MRI) contrast agents with high sensitivity and good biocompatibility is of great value for the diagnosis of primary hepatocellular carcinoma (HCC). Here, a novel MRI contrast agent based on calcium phosphate (CaP) nanoparticles modified with a liver cancer cell targeting peptide A54 (A54-CaP) was fabricated. The T1-positive contrast agent Gd-DTPA was encapsulated inside the nanoparticles (A54-CaPNPs), with a mean diameter of 30 nm and a high encapsulation efficiency of 92.73%. The A54-CaPNP solution exhibited higher longitudinal relaxivity (6.07 mM-1 s-1) than that of the clinically used MRI contrast agent Gd-DTPA (3.56 mM-1 s-1). A much higher accumulation of the nanoparticles in the liver cells was observed, which was directed by the A54 targeting peptide. Furthermore, the MRI diagnostic efficiency of A54-CaPNPs was systematically investigated in an orthotopic liver cancer model and primary HCC model. In vivo MRI experiments showed that A54-CaPNPs had higher sensitivity in the BEL-7402 orthotopic liver cancer model with a more remarkable contrast enhancement and a longer imaging time compared to those without A54 modification. Moreover, the experiments on primary HCC models suggested that A54-CaPNPs showed greatly enhanced MR imaging performance in comparison with Gd-DTPA. These results suggest that A54-CaPNPs possess great potential to enable the non-invasive early diagnosis of primary HCC for timely surgical resection.

Palladium-based nanomaterials for cancer imaging and therapy

In recent decade, palladium-based (Pd-based) nanomaterials have shown significant potential for biomedical applications because of their unique optical properties, excellent biocompatibility and high stability in physiological environment. Compared with other intensively studied noble nanomaterials, such as gold (Au) and silver (Ag) nanomaterials, research on Pd-based nanomaterials started late, but the distinctive features, such as high photothermal conversion efficiency and high photothermal stability, have made them getting great attention in the field of nanomedicine. The goal of this review is to provide a comprehensive and critical perspective on the recent progress of Pd-based nanomaterials as imaging contrast agents and therapeutic agents. The imaging section focuses on applications in photoacoustic (PA) imaging, single-photon emission computed tomography (SPECT) imaging, computed tomography (CT) imaging and magnetic resonance (MR) imaging. For treatment of cancer, single photothermal therapy (PTT) and PTT combined with other therapeutic modalities will be discussed. Finally, the safety concerns, forthcoming challenges and perspective of Pd-based nanomaterials on biomedical applications will be presented.

Ligand-installed anti-VEGF genomic nanocarriers for effective gene therapy of primary and metastatic tumors

The systemic dosage regimen exhibited low therapeutic efficacy and incurred severe adverse effect, thus, the development of tumor-targeted therapeutics is crucial important for tumor precision therapy. Herein, the active targeted modulation of tumor microenvironments was schemed by developing hyaluronic acid-installed genomic nanocarriers (HA-NPs) for effectively ablation of both primary and metastatic tumors through anti-vascular endothelial growth factor (anti-VEGF) approach. The anti-VEGF genomic payloads were strategically packaged into the well-defined synthetic nanocarriers by layer-by-layer preparation strategy, exhibiting high colloidal stability and much lower cell viability than the cationic gene carriers. Besides, the HA-NPs could specifically and efficiently internalize with cancer cells for efficient intracellular gene delivery, leading to high gene transfection efficacy. Moreover, it further demonstrated efficient extravasation, high accumulation and deep penetration in tumors, which markedly facilitated tumor-targeted expression of anti-VEGF genomic payloads for inhabitation of neo-vasculature, consecutively contributing to potent ablation of solid tumors. In addition, the ligand-installed nanocarriers facilitated systemic treatment of melanoma lung metastasis by the expressed anti-VEGF proteins, which were extensively spread along blood circulation and metastatic niches to diminish the formation of neovasculature for tumorigenesis. Therefore, the proposed anti-VEGF genomic nanocarriers could shed intriguing implication in effectively treatment of primary tumors and metastasis.

Albumin nanocomposites with MnO2/Gd2O3 motifs for precise MR imaging of acute myocardial infarction in rabbit models

The severe mortality and morbidity of myocardial infarction requests appropriate and accurate detection. Considering pathological profile of the acidic myocardial infarction microenvironments, herein, the low pH-sensitive albumin nanocomposites with MnO₂ motifs (MnO₂@BSA) have been engineered for T₁-weighted MR imaging of myocardial infarction, while using non-pH-responsive Gd₂O₃@BSA nanocomposites as control. The nanocomposites were 20-30 nm in diameter with spheroid morphology. Besides, the MnO₂@BSA have exhibited pH-triggered releasing of Mn²⁺, demonstrating approximately 38-fold and 55-fold increased molecular relaxivity at acute myocardial infarction-mimicking pH 6.5 (13.08 mM^-1s^-1) and macrophage intracellular pH 5.0 (18.76 mM^-1s^-1) compared to the extremely low relaxivity (0.34 mM^-1s^-1) at normal physiological conditions (pH 7.4). However, the Gd₂O₃@BSA with molecular relaxivity approximately 10 mM^-1s^-1 were without pH-sensitive properties. Furthermore, the MnO₂@BSA have demonstrated high accumulation in the acute myocardial infarction regions and fast metabolism from the body after systemic injection, accounting high contrast enhancement for accurate MR imaging of acute myocardial infarction in rabbit models, demonstrating better diagnostic performance over the controls.

Calcium phosphate nanocarriers for drug delivery to tumors: imaging, therapy and theranostics

Calcium phosphate (CaP) was engineered as a drug delivery nanocarrier nearly 50 years ago due to its biocompatibility and biodegradability. In recent years, several approaches have been developed for the preparation of size-controllable, stable and multifunctional CaP nanocarriers, and several targeting moieties have also been decorated on the surface of these nanocarriers for active targeting. The CaP nanocarriers have been utilized for loading probes, nucleic acids, anticancer drugs and photosensitizers for cancer imaging, therapy and theranostics. Herein, we reviewed the recent advances in the preparation strategies of CaP nanocarriers and the applications of these nanocarriers in tumor diagnosis, gene delivery, drug delivery and theranostics and finally provided perspectives.

Visual targeted therapy of hepatic cancer using homing peptide modified calcium phosphate nanoparticles loading doxorubicin guided by T1 weighted MRI

Effective treatment and real-time monitoring of hepatic cancer are essential. A multifunctional calcium phosphate nanoparticles loading chemotherapeutic agent doxorubicin and magnetic resonance imaging contrast agent diethylenetriaminepentaacetic acid gadolinium (A54-CaP/Gd-DTPA/DOX) was developed for visual targeted therapy of hepatic cancer via T1-weighted MRI in real-time. A54-CaP/Gd-DTPA/DOX exhibited a higher longitudinal relaxivity (6.02 mM^-1 s^-1) than commercial MR contrast agent Gd-DTPA (3.3765 mM^-1 s^-1). The DOX release from the nanoparticles exhibited a pH dependent behavior. The cellular uptake results showed that the internalization of A54-CaP/Gd-DTPA/DOX into BEL-7402 cells was1.9-fold faster than that of HepG2 cells via A54 binding. In vivo experiments presented that A54-CaP/Gd-DTPA/DOX had higher distribution and longer retention time in tumor tissue than CaP/Gd-DTPA/DOX and free DOX, and also displayed great antitumor efficacy (95.38% tumor inhibition rate) and lower toxicity. Furthermore, the Gd-DTPA entrapped in the nanoparticles could provide T1-weighted MRI for real-time monitoring the progress of tumor treatment.

Structural, Mechanical, Imaging and in Vitro Evaluation of the Combined Effect of Gd3+ and Dy3+ in the ZrO2-SiO2 Binary System

Mechanical strength and biocompatibility are considered the main prerequisites for materials in total hip replacement or joint prosthesis. Noninvasive surgical procedures are necessary to monitor the performance of a medical device in vivo after implantation. To this aim, simultaneous Gd³⁺ and Dy³⁺ additions to the ZrO₂-SiO₂ binary system were investigated. The results demonstrate the effective role of Gd³⁺ and Dy³⁺ to maintain the structural and mechanical stability of cubic zirconia ( c-ZrO₂) up to 1400 °C, through their occupancy of ZrO₂ lattice sites. A gradual tetragonal to cubic zirconia ( t-ZrO₂ → c-ZrO₂) phase transition is also observed that is dependent on the Gd³⁺ and Dy³⁺ content in the ZrO₂-SiO₂. The crystallization of either ZrSiO₄ or SiO₂ at elevated temperatures is delayed by the enhanced thermal energy consumed by the excess inclusion of Gd³⁺ and Dy³⁺ at c-ZrO₂ lattice. The addition of Gd³⁺ and Dy³⁺ leads to an increase in the density, elastic modulus, hardness, and toughness above that of unmodified ZrO₂-SiO₂. The multimodal imaging contrast enhancement of the Gd³⁺ and Dy³⁺ combinations were revealed through magnetic resonance imaging and computed tomography contrast imaging tests. Biocompatibility of the Gd³⁺ and Dy³⁺ dual-doped ZrO₂-SiO₂ systems was verified through in vitro biological studies.

Tumor-penetrating Peptide Conjugated and Doxorubicin Loaded T1-T2 Dual Mode MRI Contrast Agents Nanoparticles for Tumor Theranostics

The conventional chemotherapeutics could not be traced in vivo and provide timely feedback on the clinical effectiveness of drugs.

Methods: In this study, a tumor-penetrating peptide RGERPPR (RGE) modified, Gd-DTPA conjugated, and doxorubicin (DOX) loaded Fe₃O₄@SiO₂@mSiO₂ nanoparticle drug delivery system (Fe₃O₄@SiO₂@mSiO₂/DOX-(Gd-DTPA)-PEG-RGE NPs) was prepared for tumor theranostics.

Results: The Fe₃O₄@SiO₂@mSiO₂/DOX-(Gd-DTPA)-PEG-RGE NPs showed a z-average hydrodynamic diameter of about 90 nm, and a pH-sensitive DOX release profile. The 3 T MRI results confirmed the relaxivity of the NPs (r₁ = 6.13 mM^-1S^-1, r₂ = 36.89 mM^-1S^-1). The in vitro cellular uptake and cytotoxicity assays on U87MG cells confirmed that the conjugation of RGERPPR played a significant role in increasing the cellular uptake and cytotoxicity of the NPs. The near-infrared fluorescence in vivo imaging results showed that the NPs could be significantly accumulated in the U87MG tumor tissue, which should result from the mediation of the tumor-penetrating peptide RGERPPR. The MRI results showed that the NPs offered a T₁-T₂ dual mode contrast imaging effect which would lead to a more precise diagnosis. Compared with unmodified NPs, the RGE-modified NPs showed significantly enhanced MR imaging signal in tumor tissue and antitumor effect, which should also be attributed to the tumor penetrating ability of RGERPPR peptide. Furthermore, the Hematoxylin and Eosin (H&E) staining and TUNEL assay proved that the NPs produced obvious cell apoptosis in tumor tissue.

Conclusions: These results indicated that Fe₃O₄@SiO₂@mSiO₂/DOX-(Gd-DTPA)-PEG-RGE NPs are an effective targeted delivery system for tumor theranostics, and should have a potential value in the personalized treatment of tumor.

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.

Gadolinium Doping in Zirconia-Toughened Alumina Systems and Their Structural, Mechanical, and Aging Behavior Repercussions

A series of Gd³⁺ dopings in zirconia-toughened alumina (ZTA) systems were undertaken to explore the resultant structural, morphological, hydrothermal aging, and mechanical behavior and imaging contrast abilities. The results from the characterization techniques demonstrate the significance of Gd³⁺ in preserving the structural stability of ZTA systems. ZTA undergoes phase degradation with 10 wt % Gd³⁺ at 1400 °C, while the 100 wt % Gd³⁺ yields GdAlO₃ even at 1200 °C. Gd³⁺ doping at the intermediate level preserves the structural stability of ZTA systems until 1400 °C. Gd³⁺ occupies the ZrO₂ lattice, and its gradual accumulation induces tetragonal ZrO₂ (t-ZrO₂) to cubic ZrO₂ (c-ZrO₂) phase transition. α-Al₂O₃ crystallizes at 1200 °C and remains unperturbed except for its reaction with the free Gd³⁺ ions to yield GdAlO₃. Aging studies and mechanical tests signify the impeccable role of Gd³⁺ in ZTA systems to resist phase degradation. Further, the imaging contrast ability of ZTA systems due to Gd³⁺ doping is verified from the in vitro magnetic resonance imaging (MRI) tests.

MRI-guided targeting delivery of doxorubicin with reduction-responsive lipid-polymer hybrid nanoparticles

In recent years, there has been increasing interest in developing a multifunctional nanoscale platform for cancer monitoring and chemotherapy. However, there is still a big challenge for current clinic contrast agents to improve their poor tumor selectivity and response. Herein, we report a new kind of Gd complex and folate-coated redox-sensitive lipid-polymer hybrid nanoparticle (Gd-FLPNP) for tumor-targeted magnetic resonance imaging and therapy. Gd-FLPNPs can simultaneously accomplish diagnostic imaging, and specific targeting and controlled release of doxorubicin (DOX). They exhibit good monodispersity, excellent size stability, and a well-defined core-shell structure. Paramagnetic nanoparticles based on gadolinium-diethylenetriaminepentaacetic acid-bis-cetylamine have paramagnetic properties with an approximately two-fold enhancement in the longitudinal relaxivity compared to clinical used Magnevist. For targeted and reduction-sensitive drug delivery, Gd-FLPNPs released DOX faster and enhanced cell uptake in vitro, and exhibited better antitumor effect both in vitro and in vivo.

Preparation and In Vitro Evaluation of a MRI Contrast Agent Based on Aptamer-Modified Gadolinium-Loaded Liposomes for Tumor Targeting

The aim of this study was to prepare aptamer-modified liposomes loaded with gadolinium (Gd) to enhance the effective diagnosis for tumor by MRI. A modified GBI-10 (GBI-10_m) was used to prepare targeted liposomes (G_mLs). Liposomes with GBI-10 aptamer (GLs) and without aptamer (non-targeted liposomes (NLs)) were also prepared as controls. The particle size and zeta potential of G_mLs, GLs, and NLs were all assayed. A clinical 3.0 T MR scanner was employed to assess the imaging efficiency and measure the longitudinal relaxivity (r ₁) of the above liposomes. Confocal laser scanning microscopy and flow cytometry were used to analyze and compare the targeting effects of G_mLs, GLs, and NLs to MDA-MB-435s cells at 37°C. The particle size of the prepared liposomes was scattered at 100-200 nm, and their values of r ₁ were ∼4 mM^-1 s^-1. The images of confocal laser scanning microscopy showed that G_mLs in the cytoplasm were significantly more than GLs and both G_mLs and GLs were more than NLs. The fluorescence intensity of G_mLs was increased by about two times than that of GLs and three times than that of NLs by flow cytometry. Therefore, the G_mLs in this initial study were suggested to be a potential MRI contrast agent at 37°C for diagnosing tumors with the protein of tenascin-C over-expressed.

A Novel Gd-DTPA-conjugated Poly(L-γ-glutamyl-glutamine)-paclitaxel Polymeric Delivery System for Tumor Theranostics

The conventional chemotherapeutics could not be traced in vivo and provide timely feedback on the clinical effectiveness of drugs. In this study, poly(L-γ-glutamyl-glutamine)-paclitaxel (PGG-PTX), as a model polymer, was chemically conjugated with Gd-DTPA (Gd-diethylenetriaminepentaacetic acid), a T₁-contrast agent of MRI, to prepare a Gd-DTPA-conjugated PGG-PTX (PGG-PTX-DTPA-Gd) delivery system used for tumor theranostics. PGG-PTX-DTPA-Gd can be self-assembled to NPs in water with a z-average hydrodynamic diameter about 35.9 nm. The 3 T MRI results confirmed that the relaxivity of PGG-PTX-DTPA-Gd NPs (r₁ = 18.98 mM⁻¹S⁻¹) was increased nearly 4.9 times compared with that of free Gd-DTPA (r₁ = 3.87 mM⁻¹S⁻¹). The in vivo fluorescence imaging results showed that PGG-PTX-DTPA-Gd NPs could be accumulated in the tumor tissue of NCI-H460 lung cancer animal model by EPR effect, which was similar to PGG-PTX NPs. The MRI results showed that compared with free Gd-DTPA, PGG-PTX-DTPA-Gd NPs showed significantly enhanced and prolonged signal intensity in tumor tissue, which should be attributed to the increased relaxivity and tumor accumulation. PGG-PTX-DTPA-Gd NPs also showed effective antitumor effect in vivo. These results indicated that PGG-PTX-DTPA-Gd NPs are an effective delivery system for tumor theranostics, and should have a potential value in personalized treatment of tumor.

Ultrasmall graphene oxide based T1 MRI contrast agent for in vitro and in vivo labeling of human mesenchymal stem cells

Herein, we report on development of a two-dimensional nanomaterial graphene oxide (GO)-based T₁ magnetic resonance imaging (MRI) contrast agent (CA) for in vitro and in vivo labeling of human mesenchymal stem cells (hMSCs). The CA was synthesized by PEGylation of ultrasmall GO, followed by conjugation with a chelating agent DOTA and then gadolinium(III) to form GO-DOTA-Gd complexes. Thus-prepared GO-DOTA-Gd complexes exhibited significantly improved T₁ relaxivity, and the r₁ value was 14.2 mM^-1s^-1 at 11.7 T, approximately three times higher than Magnevist, a commercially available CA. hMSCs can be effectively labeled by GO-DOTA-Gd, leading to remarkably enhanced cellular MRI effect without obvious adverse effects on proliferation and differentiation of hMSCs. More importantly, in vivo experiment revealed that intracranial detection of 5×10⁵ hMSCs labeled with GO-DOTA-Gd is achieved. The current work demonstrates the feasibility of the GO-based T₁ MRI CA for stem cell labeling, which may find potential applications in regenerative medicine.

Nanoparticles as Theranostic Vehicles in Experimental and Clinical Applications-Focus on Prostate and Breast Cancer

Prostate and breast cancer are the second most and most commonly diagnosed cancer in men and women worldwide, respectively. The American Cancer Society estimates that during 2016 in the USA around 430,000 individuals were diagnosed with one of these two types of cancers, and approximately 15% of them will die from the disease. In Europe, the rate of incidences and deaths are similar to those in the USA. Several different more or less successful diagnostic and therapeutic approaches have been developed and evaluated in order to tackle this issue and thereby decrease the death rates. By using nanoparticles as vehicles carrying both diagnostic and therapeutic molecular entities, individualized targeted theranostic nanomedicine has emerged as a promising option to increase the sensitivity and the specificity during diagnosis, as well as the likelihood of survival or prolonged survival after therapy. This article presents and discusses important and promising different kinds of nanoparticles, as well as imaging and therapy options, suitable for theranostic applications. The presentation of different nanoparticles and theranostic applications is quite general, but there is a special focus on prostate cancer. Some references and aspects regarding breast cancer are however also presented and discussed. Finally, the prostate cancer case is presented in more detail regarding diagnosis, staging, recurrence, metastases, and treatment options available today, followed by possible ways to move forward applying theranostics for both prostate and breast cancer based on promising experiments performed until today.

Gadolinium-based nanoscale MRI contrast agents for tumor imaging

Gadolinium-based nanoscale magnetic resonance imaging (MRI) contrast agents (CAs) have gained significant momentum as a promising nanoplatform for detecting tumor tissue in medical diagnosis, due to their favorable capability of enhancing the longitudinal relaxivity (r₁) of individual gadolinium ions, delivering to the region of interest a large number of gadolinium ions, and incorporating different functionalities. This mini-review highlights the latest developments and applications, and simultaneously gives some perspectives for their future development.

Development of Gd3N@C80 encapsulated redox nanoparticles for high-performance magnetic resonance imaging

As novel magnetic resonance imaging (MRI) contrast agent, gadofullerene encapsulated redox nanoparticles (Gd₃NPs) were prepared by encapsulation of Gd₃N@C₈₀ in the core of core-shell-type polymer micelles composed of original polyamine with a reactive oxygen species (ROS)-scavenging ability. Because Gd₃NPs possess biocompatible PEG shell with a smaller size (ca. 50 nm), they had high colloidal stability in a physiological environment, and showed low cytotoxicity. Specific accumulation of Gd₃NPs in a tumor was confirmed in tumor-bearing mice after systemic administration. The tumor/muscle (T/M) ratio of the Gd ion reached five at 7.5 h after the administration. T₁-weighted MRI signal enhancement of the T/M ratio increased by 8% at 6 h postinjection of Gd₃NPs (Gd dose:14.35 μmol/kg). Although Gd₃NPs showed a tendency for extended blood circulation, they did not have severe adverse effects, probably due to the confinement of Gd in a hydrophobic fullerene in addition to the ROS-scavenging capacity of these nanoparticles. In sharp contrast, systemic administration of Gd-chelate nanoparticles (GdCNPs) to mice disrupts liver function, increases leukocyte counts, and destroys spleen and skin tissues. Leaking of Gd ions from GdCNPs may cause such adverse effects. Based on these results, we expect that Gd₃NPs is high-performance MRI contrast agents for tumor diagnosis.

Bioinspired Coordination Micelles Integrating High Stability, Triggered Cargo Release, and Magnetic Resonance Imaging

Catechol-Fe³⁺ coordinated micelles show the potential for achieving on-demand drug delivery and magnetic resonance imaging in a single nanoplatform. Herein, we developed bioinspired coordination-cross-linked amphiphilic polymeric micelles loaded with a model anticancer agent, doxorubicin (Dox). The nanoscale micelles could tolerate substantial dilution to a condition below the critical micelle concentration (9.4 ± 0.3 μg/mL) without sacrificing the nanocarrier integrity due to the catechol-Fe³⁺ coordinated core cross-linking. Under acidic conditions (pH 5.0), the release rate of Dox was significantly faster compared to that at pH 7.4 as a consequence of coordination collapse and particle de-cross-linking. The cell viability study in 4T1 cells showed no toxicity regarding placebo cross-linked micelles. The micelles with improved stability showed a dramatically increased Dox accumulation in tumors and hence the enhanced suppression of tumor growth in a 4T1 tumor-bearing mouse model. The presence of Fe³⁺ endowed the micelles T₁-weighted MRI capability both in vitro and in vivo without the incorporation of traditional toxic paramagnetic contrast agents. The current work presented a simple "three birds with one stone" approach to engineer the robust theranostic nanomedicine platform.

PEGylated chitosan grafted with polyamidoamine-dendron as tumor-targeted magnetic resonance imaging contrast agent

PEGylated chitosan grafted with polyamidoamine-dendron was fabricated as a tumor-targeted mCA and its application was well demonstrated.

pH-responsive magnetic micelles gelatin-g-poly(NIPAAm-co-DMAAm-co-UA)-g-dextran/Fe3O4 as a hydrophilic drug carrier

In the study, pH-selective magnetic targeting micelle, Gelatin-g-poly(NIPAAm-co-DMAAm-co-UA)-g-dextran/Fe₃O₄ (GPDF), has been synthesized for controlled release of a hydrophilic insulin-promoting factor, nicotinamide.

Multi-arm star-branched polymer as an efficient contrast agent for tumor-targeted magnetic resonance imaging

Contrast agents with high efficiency and safety are excellent candidates as magnetic resonance imaging probes.

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”.

Characterization and adsorptive properties of cross-linked poly (1-vinylimidazole)-iron (III) complex synthesized in supercritical carbon dioxide

In this study, poly (1-vinylimidazole)-iron(III) [PVIm-Fe(III)] complex was investigated along with adsorption behavior of bovine serum albumin (BSA). The cross-linked PVIm-Fe(III) was synthesized in supercritical carbon dioxide by using N,N′-methylenebisacrylamide (BIS) as a cross-linker. The obtained products were analyzed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) analysis. The results reveal that iron ion is complexed by coordination with basic (-N) functional groups of 1-vinylimidazole successfully. The effects of the operating pressure, the ratio of iron and cross-linker concentration were investigated. A fine and yellow powder was obtained at high yield and crosslinking degrees at 20 MPa, 70°C. Additionally, the property of PVIm-Fe(III) complexes in terms of BSA adsorption has been studied, and the higher adsorption capacity was 660 mg/g.

Amphiphilic dendritic nanomicelle-mediated co-delivery of 5-fluorouracil and doxorubicin for enhanced therapeutic efficacy

Combination cancer therapy has attracted considerable attention due to its enhanced antitumor efficacy and reduced toxicity granted by synergistic effects over monotherapy. The application of nanotechnology is expected to achieve coencapsulation of multiple anticancer agents with enhanced therapeutic efficacy. Herein, a unique nanomicelle based on amphiphilic dendrimer (AmD) consisting of a hydrophilic polyamidoamine dendritic shell and a hydrophobic polylactide core is developed for effectively loading and shuttling 5-fluorouracil (5-Fu) and doxorubicin (Dox). The yielded drug-encapsulated dendritic nanomicelle (5-Fu/Dox-DNM) has a modest average size of 68.6 ± 3.3 nm and shows pH-sensitive drug release manner. The parallel activity of 5-Fu and Dox show synergistic anticancer efficacy. The IC₅₀ value of 5-Fu/Dox-DNM toward human breast cancer (MDA-MB-231) cells was 0.25 μg/mL, presenting an 11.2-fold and 6.1-fold increase in cytotoxicity compared to Dox-DNM and 5-Fu-DNM, respectively. Furthermore, 5-Fu/Dox-DNM significantly inhibits the progression of tumor growth in the MDA-MB-231 xenograft tumor mice model. In conclusion, we have demonstrated that our AmD-based combination therapeutic system has promising potential to open an avenue for coencapsulation of multiple chemotherapeutic agents to promote superior anticancer effect.