Dendrimers as high relaxivity MR contrast agents

Impact of inner hydrophobicity of dendrimer nanomicelles on biodistribution: a PET imaging study

Self-assembly is a powerful strategy for building nanosystems for biomedical applications. We have recently developed small amphiphilic dendrimers capable of self-assembling into nanomicelles for tumor imaging. In this context, we studied the impact of increased hydrophobicity of the amphiphilic dendrimer on hydrophilic/hydrophobic balance and consequently on the self-assembly and subsequent biodistribution. Remarkably, despite maintaining the exact same surface chemistry, similar zeta potential, and small size, the altered and enlarged hydrophobic component within the amphiphilic dendrimer led to enhanced stability of the self-assembled nanomicelles, with prolonged circulation time and massive accumulation in the liver. This study reveals that even structural alteration within the interior of nanomicelles can dramatically impact biodistribution profiles. This finding highlights the deeper complexity of rational design for nanomedicine and the need to consider factors other than surface charge and chemistry, as well as size, all of which significantly impact the biodistribution of self-assembling nanosystems.

Nanoparticle-Based Approaches in the Diagnosis and Treatment of Brain Tumors

Glioblastomas are highly invasive brain tumors among perilous diseases. They are characterized by their fast proliferation and delayed detection that render them a significant focal point for medical research endeavors within the realm of cancer. Among glioblastomas, Glioblastoma multiforme (GBM) is the most aggressive and prevalent malignant brain tumor. For this, nanomaterials such as metallic and lipid nanoparticles and quantum dots have been acknowledged as efficient carriers. These nano-materials traverse the blood-brain barrier (BBB) and integrate and reach the necessary regions for neuro-oncology imaging and treatment purposes. This paper provides a thorough analysis on nanoparticles used in the diagnosis and treatment of brain tumors, especially for GBM.

Recent advances in nanomaterial-driven strategies for diagnosis and therapy of vascular anomalies

Nanotechnology has demonstrated immense potential in various fields, especially in biomedical field. Among these domains, the development of nanotechnology for diagnosing and treating vascular anomalies has garnered significant attention. Vascular anomalies refer to structural and functional anomalies within the vascular system, which can result in conditions such as vascular malformations and tumors. These anomalies can significantly impact the quality of life of patients and pose significant health concerns. Nanoscale contrast agents have been developed for targeted imaging of blood vessels, enabling more precise identification and characterization of vascular anomalies. These contrast agents can be designed to bind specifically to abnormal blood vessels, providing healthcare professionals with a clearer view of the affected areas. More importantly, nanotechnology also offers promising solutions for targeted therapeutic interventions. Nanoparticles can be engineered to deliver drugs directly to the site of vascular anomalies, maximizing therapeutic effects while minimizing side effects on healthy tissues. Meanwhile, by incorporating functional components into nanoparticles, such as photosensitizers, nanotechnology enables innovative treatment modalities such as photothermal therapy and photodynamic therapy. This review focuses on the applications and potential of nanotechnology in the imaging and therapy of vascular anomalies, as well as discusses the present challenges and future directions.

Advances in nanoprobes for molecular MRI of Alzheimer's disease

Alzheimer's disease is the most common cause of dementia and a leading cause of mortality in the elderly population. Diagnosis of Alzheimer's disease has traditionally relied on evaluation of clinical symptoms for cognitive impairment with a definitive diagnosis requiring post-mortem demonstration of neuropathology. However, advances in disease pathogenesis have revealed that patients exhibit Alzheimer's disease pathology several decades before the manifestation of clinical symptoms. Magnetic resonance imaging (MRI) plays an important role in the management of patients with Alzheimer's disease. The clinical availability of molecular MRI (mMRI) contrast agents can revolutionize the diagnosis of Alzheimer's disease. In this article, we review advances in nanoparticle contrast agents, also referred to as nanoprobes, for mMRI of Alzheimer's disease. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

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.

Dendrimer: An update on recent developments and future opportunities for the brain tumors diagnosis and treatment

A brain tumor is an uncontrolled cell proliferation, a mass of tissue composed of cells that grow and divide abnormally and appear to be uncontrollable by the processes that normally control normal cells. Approximately 25,690 primary malignant brain tumors are discovered each year, 70% of which originate in glial cells. It has been observed that the blood-brain barrier (BBB) limits the distribution of drugs into the tumour environment, which complicates the oncological therapy of malignant brain tumours. Numerous studies have found that nanocarriers have demonstrated significant therapeutic efficacy in brain diseases. This review, based on a non-systematic search of the existing literature, provides an update on the existing knowledge of the types of dendrimers, synthesis methods, and mechanisms of action in relation to brain tumours. It also discusses the use of dendrimers in the diagnosis and treatment of brain tumours and the future possibilities of dendrimers. Dendrimers are of particular interest in the diagnosis and treatment of brain tumours because they can transport biochemical agents across the BBB to the tumour and into the brain after systemic administration. Dendrimers are being used to develop novel therapeutics such as prolonged release of drugs, immunotherapy, and antineoplastic effects. The use of PAMAM, PPI, PLL and surface engineered dendrimers has proven revolutionary in the effective diagnosis and treatment of brain tumours.

Applications and Limitations of Dendrimers in Biomedicine

Biomedicine represents one of the main study areas for dendrimers, which have proven to be valuable both in diagnostics and therapy, due to their capacity for improving solubility, absorption, bioavailability and targeted distribution. Molecular cytotoxicity constitutes a limiting characteristic, especially for cationic and higher-generation dendrimers. Antineoplastic research of dendrimers has been widely developed, and several types of poly(amidoamine) and poly(propylene imine) dendrimer complexes with doxorubicin, paclitaxel, imatinib, sunitinib, cisplatin, melphalan and methotrexate have shown an improvement in comparison with the drug molecule alone. The anti-inflammatory therapy focused on dendrimer complexes of ibuprofen, indomethacin, piroxicam, ketoprofen and diflunisal. In the context of the development of antibiotic-resistant bacterial strains, dendrimer complexes of fluoroquinolones, macrolides, beta-lactamines and aminoglycosides have shown promising effects. Regarding antiviral therapy, studies have been performed to develop dendrimer conjugates with tenofovir, maraviroc, zidovudine, oseltamivir and acyclovir, among others. Furthermore, cardiovascular therapy has strongly addressed dendrimers. Employed in imaging diagnostics, dendrimers reduce the dosage required to obtain images, thus improving the efficiency of radioisotopes. Dendrimers are macromolecular structures with multiple advantages that can suffer modifications depending on the chemical nature of the drug that has to be transported. The results obtained so far encourage the pursuit of new studies.

Opportunities in Interventional and Diagnostic Imaging by Using High-Performance Low-Field-Strength MRI

Background Commercial low-field-strength MRI systems are generally not equipped with state-of-the-art MRI hardware, and are not suitable for demanding imaging techniques. An MRI system was developed that combines low field strength (0.55 T) with high-performance imaging technology. Purpose To evaluate applications of a high-performance low-field-strength MRI system, specifically MRI-guided cardiovascular catheterizations with metallic devices, diagnostic imaging in high-susceptibility regions, and efficient image acquisition strategies. Materials and Methods A commercial 1.5-T MRI system was modified to operate at 0.55 T while maintaining high-performance hardware, shielded gradients (45 mT/m; 200 T/m/sec), and advanced imaging methods. MRI was performed between January 2018 and April 2019. T1, T2, and T2* were measured at 0.55 T; relaxivity of exogenous contrast agents was measured; and clinical applications advantageous at low field were evaluated. Results There were 83 0.55-T MRI examinations performed in study participants (45 women; mean age, 34 years ± 13). On average, T1 was 32% shorter, T2 was 26% longer, and T2* was 40% longer at 0.55 T compared with 1.5 T. Nine metallic interventional devices were found to be intrinsically safe at 0.55 T (<1°C heating) and MRI-guided right heart catheterization was performed in seven study participants with commercial metallic guidewires. Compared with 1.5 T, reduced image distortion was shown in lungs, upper airway, cranial sinuses, and intestines because of improved field homogeneity. Oxygen inhalation generated lung signal enhancement of 19% ± 11 (standard deviation) at 0.55 T compared with 7.6% ± 6.3 at 1.5 T (P = .02; five participants) because of the increased T1 relaxivity of oxygen (4.7e-4 mmHg-1sec-1). Efficient spiral image acquisitions were amenable to low field strength and generated increased signal-to-noise ratio compared with Cartesian acquisitions (P < .02). Representative imaging of the brain, spine, abdomen, and heart generated good image quality with this system. Conclusion This initial study suggests that high-performance low-field-strength MRI offers advantages for MRI-guided catheterizations with metal devices, MRI in high-susceptibility regions, and efficient imaging. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Grist in this issue.

Cytotoxicity of Dendrimers

Drug delivery systems are molecular platforms in which an active compound is packed into or loaded on a biocompatible nanoparticle. Such a solution improves the activity of the applied drug or decreases its side effects. Dendrimers are promising molecular platforms for drug delivery due to their unique properties. These macromolecules are known for their defined size, shape, and molecular weight, as well as their monodispersity, the presence of the void space, tailorable structure, internalization by cells, selectivity toward cells and intracellular components, protection of guest molecules, and controllable release of the cargo. Dendrimers were tested as carriers of various molecules and, simultaneously, their toxicity was examined using different cell lines. It was discovered that, in general, dendrimer cytotoxicity depended on the generation, the number of surface groups, and the nature of terminal moieties (anionic, neutral, or cationic). Higher cytotoxicity occurred for higher-generation dendrimers and for dendrimers with positive charges on the surface. In order to decrease the cytotoxicity of dendrimers, scientists started to introduce different chemical modifications on the periphery of the nanomolecule. Dendrimers grafted with polyethylene glycol (PEG), acetyl groups, carbohydrates, and other moieties did not affect cell viability, or did so only slightly, while still maintaining other advantageous properties. Dendrimers clearly have great potential for wide utilization as drug and gene carriers. Moreover, some dendrimers have biological properties per se, being anti-fungal, anti-bacterial, or toxic to cancer cells without affecting normal cells. Therefore, intrinsic cytotoxicity is a comprehensive problem and should be considered individually depending on the potential destination of the nanoparticle.

A review of molecular imaging of atherosclerosis and the potential application of dendrimer in imaging of plaque

Despite the fact that technological advancements have been made in diagnosis and treatment, cardiovascular diseases (CVDs) remain the leading cause of mortality and morbidity worldwide. Early detection of atherosclerosis (AS), especially vulnerable plaques, plays a crucial role in the prevention of acute coronary syndrome (ACS). Targeting the critical cytokines and molecules that are upregulated during the biological process of AS by in vivo molecular imaging has been widely used in plaque imaging. With their three-dimensional architecture, composition, and abundant terminal functional groups, dendrimers provide a platform for multitargeting and multimodal imaging. Thus, modified dendrimers with the key molecules upregulated in AS plaques will be an innovative attempt to achieve targeted imaging of AS plaques specifically and efficiently. This review was aimed to address some recent works on imaging of AS plaques using various types of image technology and further discuss the applications of dendrimers, an innovative yet seldom used method in imaging of AS plaques due to some limitations and challenges, and we highlight the bright future of the modified dendrimers in characterizing AS plaques.

Perspectives on dendritic architectures and their biological applications: From core to cell

The challenges of medicine today include the increasing stipulation for sensitive and effective systems that can improve the pathological responses with a simultaneous reduction in accumulation and drug side effects. The demand can be fulfilled through the advancements in nanomedicine that includes nanostructures and nanodevices for diagnosing, treating, and prevention of various diseases. In this respect, the nanoscience provides various novel techniques with carriers such as micelles, dendrimers, particles and vesicles for the transportation of active moieties. Further, an efficient way to improve these systems is through stimuli a responsive system that utilizes supramolecular hyperbranched structures to meet the above criteria. The stimuli-responsive dendritic architectures exhibit spatial, temporal, convenient, effective, safety and controlled drug release in response to specific trigger through electrostatic interactions plus π stacking. The stimuli-responsive systems are capable of sequestering the drug molecules underneath a predefined set of conditions and discharge them in a different environment through either exogenous or endogenous stimulus. The incorporation of photoresponsive moieties at various components of dendrimer such as core, branches or at the peripheral end exaggerates its significance in various allied fields of nanotechnology which includes sensors, photoswitch, electronic widgets and in drug delivery systems. This is due to the light instigated geometrical modifications at the core or at the surface molecules which generates huge conformational changes throughout the hyperbranched structure. Further, numerous synthetic methodologies have been investigated for utilization of dendrimers in therapeutic drug delivery and its applicability towards stimuli responsive systems such as photo-instigated, thermal-instigated, and pH-instigated hyperbranched structures and their advancement in the field of nanomedicine. This paper highlights the fascinating theoretical advances and principal mechanisms of dendrimer synthesis and their ability to capture light that strengthens its applicability from radiant energy to medical photonics.

Expanding the potential of MRI contrast agents through multifunctional polymeric nanocarriers

MRI is a sought-after, noninvasive tool in medical diagnostics, yet the direct application of contrast agents to tissue suffers from several drawbacks. Hosting the contrast agents in polymeric nanocarriers can solve many of these issues while creating additional benefit through exploitation of the intrinsic characteristics of the polymeric carriers. In this report, the versatility is highlighted with recent examples of dendritic and hyperbranched polymers, polymer nanoparticles and micelles, and polymersomes as multifunctional bioresponsive nanocarriers for MRI contrast agents.

Encapsulation of Gadolinium Oxide Nanoparticle (Gd2O3) Contrasting Agents in PAMAM Dendrimer Templates for Enhanced Magnetic Resonance Imaging in Vivo

There has been growing interest in the research of nanomaterials for biomedical applications in recent decades. Herein, a simple approach to synthesize the G4.5-Gd₂O₃-poly(ethylene glycol) (G4.5-Gd₂O₃-PEG) nanoparticles (NPs) that demonstrate potential as dual (T₁ and T₂) contrasting agents in magnetic resonance imaging (MRI) has been reported in this study. Compared to the clinically popular Gd-DTPA contrasting agents, G4.5-Gd₂O₃-PEG NPs exhibited a longer longitudinal relaxation time (T₁) and better biocompatibility when incubated with macrophage cell line RAW264.7 in vitro. Furthermore, the longitudinal relaxivity (r₁) of G4.5-Gd₂O₃-PEG NPs was 53.9 s^-1 mM^-1 at 7T, which is equivalent to 4.8 times greater than to the Gd-DTPA contrasting agents. An in vivo T₁-weighted MRI results revealed that G4.5-Gd₂O₃-PEG NPs significantly enhanced signals in the intestines, kidney, liver, bladder, and spleen. In addition, the T₂-weighted MRI results revealed darker contrast in the kidney, which proves that G4.5-Gd₂O₃-PEG NPs can be exploited as T₁ and T₂ contrasting agents. In summary, these findings suggest that the G4.5-Gd₂O₃-PEG NPs synthesized by an alternative approach can be used as dual MRI contrasting agents.

Dendrimer-Based Responsive MRI Contrast Agents (G1-G4) for Biosensor Imaging of Redundant Deviation in Shifts (BIRDS)

Biosensor imaging of redundant deviation in shifts (BIRDS) is a molecular imaging platform for magnetic resonance that utilizes unique properties of low molecular weight paramagnetic monomers by detecting hyperfine-shifted nonexchangeable protons and transforming the chemical shift information to reflect its microenvironment (e.g., via temperature, pH, etc.). To optimize translational biosensing potential of BIRDS we examined if this detection scheme observed with monomers can be extended onto dendrimers, which are versatile and biocompatible macromolecules with modifiable surface for molecular imaging and drug delivery. Here we report on feasibility of paramagnetic dendrimers for BIRDS. The results show that BIRDS is resilient with paramagnetic dendrimers up to the fourth generation (i.e., G1-G4), where the model dendrimer and chelate were based on poly(amido amine) (PAMAM) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA(4-)) complexed with thulium ion (Tm(3+)). Temperature sensitivities of two prominent signals of Gn-PAMAM-(TmDOTA(-))x (where n = 1-4, x = 6-39) were comparable to that of prominent signals in TmDOTA(-). Transverse relaxation times of the coalesced nonexchangeable protons on Gn-PAMAM-(TmDOTA(-))x were relatively short to provide signal-to-noise ratio that was comparable to or better than that of TmDOTA(-). A fluorescent dye, rhodamine, was conjugated to a G2-PAMAM-(TmDOTA)12 to create a dual-modality nanosized contrast agent. BIRDS properties of the dendrimer were unaltered with rhodamine conjugation. Purposely designed paramagnetic dendrimers for BIRDS in conjunction with novel macromolecular surface modification for functional ligands/drugs could potentially be used for biologically compatible theranostic sensors.

Current progress in nanotechnology applications for diagnosis and treatment of kidney diseases

Significant progress has been made in nanomedicine, primarily in the form of nanoparticles, for theranostic applications to various diseases. A variety of materials, both organic and inorganic, have been used to develop nanoparticles with promise to achieve improved efficacy in medical applications as well as reduced systemic side effects compared to current standard of care medical practices. In particular, this article highlights the recent development and application of nanoparticles for diagnosing and treating nephropathologies.

A neutral polydisulfide containing Gd(III) DOTA monoamide as a redox-sensitive biodegradable macromolecular MRI contrast agent

This work aims to develop safe and effective gadolinium (III)-based biodegradable macromolecular MRI contrast agents for blood pool and cancer imaging. A neutral polydisulfide containing macrocyclic Gd-DOTA monoamide (GOLS) was synthesized and characterized. In addition to studying the in vitro degradation of GOLS, its kinetic stability was also investigated in an in vivo model. The efficacy of GOLS for contrast-enhanced MRI was examined with female BALB/c mice bearing 4T1 breast cancer xenografts. The pharmacokinetics, biodistribution, and metabolism of GOLS were also determined in mice. GOLS has an apparent molecular weight of 23.0 kDa with T1 relaxivities of 7.20 mM(-1) s(-1) per Gd at 1.5 T, and 6.62 mM(-1) s(-1) at 7.0 T. GOLS had high kinetic inertness against transmetallation with Zn(2+) ions, and its polymer backbone was readily cleaved by L-cysteine. The agent showed improved efficacy for blood pool and tumor MR imaging. The structural effect on biodistribution and in vivo chelation stability was assessed by comparing GOLS with Gd(HP-DO3A), a negatively charged polydisulfide containing Gd-DOTA monoamide GODC, and a polydisulfide containing Gd-DTPA-bisamide (GDCC). GOLS showed high in vivo chelation stability and minimal tissue deposition of gadolinium. The biodegradable macromolecular contrast agent GOLS is a promising polymeric contrast agent for clinical MR cardiovascular imaging and cancer imaging.

Developing MR probes for molecular imaging

Molecular imaging plays an important role in the era of personalized medicine, especially with recent advances in magnetic resonance (MR) probes. While the first generation of these probes focused on maximizing contrast enhancement, a second generation of probes has been developed to improve the accumulation within specific tissues or pathologies, and the newest generation of agents is also designed to report on changes in physiological status and has been termed "smart" agents. This represents a paradigm switch from the previously commercialized gadolinium and iron oxide probes to probes with new capabilities, and leads to new challenges as scanner hardware needs to be adapted for detecting these probes. In this chapter, we highlight the unique features for all five different categories of MR probes, including the emerging chemical exchange saturation transfer, (19)F, and hyperpolarized probes, and describe the key physical properties and features motivating their design. As part of this comparison, the strengths and weaknesses of each category are discussed.

Cluster analysis of quantitative parametric maps from DCE-MRI: application in evaluating heterogeneity of tumor response to antiangiogenic treatment

PURPOSE

The objective of this study was to compare a clustering approach to conventional analysis methods for assessing changes in pharmacokinetic parameters obtained from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) during antiangiogenic treatment in a breast cancer model.

MATERIALS AND METHODS

BALB/c mice bearing established transplantable her2+ tumors were treated with a DNA-based antiangiogenic vaccine or with an empty plasmid (untreated group). DCE-MRI was carried out by administering a dose of 0.05 mmol/kg of Gadocoletic acid trisodium salt, a Gd-based blood pool contrast agent (CA) at 1T. Changes in pharmacokinetic estimates (K(trans) and vp) in a nine-day interval were compared between treated and untreated groups on a voxel-by-voxel analysis. The tumor response to therapy was assessed by a clustering approach and compared with conventional summary statistics, with sub-regions analysis and with histogram analysis.

RESULTS

Both the K(trans) and vp estimates, following blood-pool CA injection, showed marked and spatial heterogeneous changes with antiangiogenic treatment. Averaged values for the whole tumor region, as well as from the rim/core sub-regions analysis were unable to assess the antiangiogenic response. Histogram analysis resulted in significant changes only in the vp estimates (p<0.05). The proposed clustering approach depicted marked changes in both the K(trans) and vp estimates, with significant spatial heterogeneity in vp maps in response to treatment (p<0.05), provided that DCE-MRI data are properly clustered in three or four sub-regions.

CONCLUSIONS

This study demonstrated the value of cluster analysis applied to pharmacokinetic DCE-MRI parametric maps for assessing tumor response to antiangiogenic therapy.

Emerging concepts in dendrimer-based nanomedicine: from design principles to clinical applications

Dendrimers are discrete nanostructures/nanoparticles with 'onion skin-like' branched layers. Beginning with a core, these nanostructures grow in concentric layers to produce stepwise increases in size that are similar to the dimensions of many in vivo globular proteins. These branched tree-like concentric layers are referred to as 'generations'. The outer generation of each dendrimer presents a precise number of functional groups that may act as a monodispersed platform for engineering favourable nanoparticle-drug and nanoparticle-tissue interactions. These features have attracted significant attention in medicine as nanocarriers for traditional small drugs, proteins, DNA/RNA and in some instances as intrinsically active nanoscale drugs. Dendrimer-based drugs, as well as diagnostic and imaging agents, are emerging as promising candidates for many nanomedicine applications. First, we will provide a brief survey of recent nanomedicines that are either approved or in the clinical approval process. This will be followed by an introduction to a new 'nanoperiodic' concept which proposes nanoparticle structure control and the engineering of 'critical nanoscale design parameters' (CNDPs) as a strategy for optimizing pharmocokinetics, pharmocodynamics and site-specific targeting of disease. This paradigm has led to the emergence of CNDP-directed nanoperiodic property patterns relating nanoparticle behaviour to critical in vivo clinical translation issues such as cellular uptake, transport, elimination, biodistribution, accumulation and nanotoxicology. With a focus on dendrimers, these CNDP-directed nanoperiodic patterns are used as a strategy for designing and optimizing nanoparticles for a variety of drug delivery and imaging applications, including a recent dendrimer-based theranostic nanodevice for imaging and treating cancer. Several emerging preclinical dendrimer-based nanotherapy concepts related to inflammation, neuro-inflammatory disorders, oncology and infectious and ocular diseases are reviewed. Finally we will consider challenges and opportunities anticipated for future clinical translation, nanotoxicology and the commercialization of nanomedicine.