Potential clinical applications of bimodal PET-MRI or SPECT-MRI agents

The use of PET/MRI in radiotherapy

Positron emission tomography/magnetic resonance imaging (PET/MRI) is a hybrid imaging technique that quantitatively combines the metabolic and functional data from positron emission tomography (PET) with anatomical and physiological information from MRI. As PET/MRI technology has advanced, its applications in cancer care have expanded. Recent studies have demonstrated that PET/MRI provides unique advantages in the field of radiotherapy and has become invaluable in guiding precision radiotherapy techniques. This review discusses the rationale and clinical evidence supporting the use of PET/MRI for radiation positioning, target delineation, efficacy evaluation, and patient surveillance.Critical relevance statement This article critically assesses the transformative role of PET/MRI in advancing precision radiotherapy, providing essential insights into improved radiation positioning, target delineation, efficacy evaluation, and patient surveillance in clinical radiology practice.Key points• The emergence of PET/MRI will be a key bridge for precise radiotherapy.• PET/MRI has unique advantages in the whole process of radiotherapy.• New tracers and nanoparticle probes will broaden the use of PET/MRI in radiation.• PET/MRI will be utilized more frequently for radiotherapy.

Microfluidic Fabrication of Gadolinium-Doped Hydroxyapatite for Theragnostic Applications

Among the several possible uses of nanoparticulated systems in biomedicine, their potential as theragnostic agents has received significant interest in recent times. In this work, we have taken advantage of the medical applications of Gadolinium as a contrast agent with the versatility and huge array of possibilities that microfluidics can help to create doped Hydroxyapatite nanoparticles with magnetic properties in an efficient and functional way. First, with the help of Computational Fluid Dynamics (CFD), we performed a complete and precise study of all the elements and phases of our device to guarantee that our microfluidic system worked in the laminar regime and was not affected by the presence of nanoparticles through the flow requisite that is essential to guarantee homogeneous diffusion between the elements or phases in play. Then the obtained biomaterials were physiochemically characterized by means of XRD, FE-SEM, EDX, confocal Raman microscopy, and FT-IR, confirming the successful incorporation of the lanthanide element Gadolinium in part of the Ca (II) binding sites. Finally, the magnetic characterization confirmed the paramagnetic behaviour of the nanoparticles, demonstrating that, with a simple and automatized system, it is possible to obtain advanced nanomaterials that can offer a promising and innovative solution in theragnostic applications.

Nanoparticles and Radioisotopes: A Long Story in a Nutshell

The purpose of this narrative review was to assess the use of nanoparticles (NPs) to deliver radionuclides to targets, focusing on systems that have been tested in pre-clinical and, when available, clinical settings. A literature search was conducted in PubMed and Web of Science databases using the following terms: “radionuclides” AND “liposomes” or “PLGA nanoparticles” or “gold nanoparticles” or “iron oxide nanoparticles” or “silica nanoparticles” or “micelles” or “dendrimers”. No filters were applied, apart from a minimum limit of 10 patients enrolled for clinical studies. Data from some significant studies from pre-clinical and clinical settings were retrieved, and we briefly describe the information available. All the selected seven classes of nanoparticles were highly tested in clinical trials, but they all present many drawbacks. Liposomes are the only ones that have been tested for clinical applications, though they have never been commercialized. In conclusion, the application of NPs for imaging has been the object of much interest over the years, albeit mainly in pre-clinical settings. Thus, we think that, based on the current state, radiolabeled NPs must be investigated longer before finding their place in nuclear medicine.

Synthesis and in vitro proof-of-concept studies on bispecific iron oxide magnetic nanoparticles targeting PSMA and GRP receptors for PET/MR imaging of prostate cancer

Prostate cancer (PCa) is the most common malignancy worldwide in men. This is a proof-of-concept study describing the development of ⁶⁸Ga-magnetic iron oxide nanoparticles (mNP) targeting prostate specific membrane antigen (PSMA) and gastrin releasing peptide (GRPR) receptors as potential tools for diagnosis of PCa with PET/MRI. Two pharmacophores targeting PSMA, 1, and GRPR, 2, were coupled to mNPs carrying -SH (mNP-S1/2) or -NH₂ (mNP-N1/2) groups. The mNP-S1/2 and mNP-N1/2 were characterized for their size, zeta potential, structure, and efficiency of functionalization using dynamic light scattering (DLS), FT-IR and RP-HPLC. A direct ⁶⁸Ga-labelling procedure was followed, where ⁶⁸Ga-mNP-N1/2 proved superior to ⁶⁸Ga-mNP-S1/2 regarding radiolabelling efficiency, and thus were further evaluated in vitro. Toxicity studies in PCa cells (LNCaP, PC-3) showed low toxicity, and minimal hemolysis of red blood cells. In vitro assays in cells expressing PSMA (LNCaP), and GRPR (PC-3), showed specific time-dependent binding (40 min to plateau), high avidity (PC-3: K_d = 28.27 nM, LNCaP: K_d = 11.49 nM) and high internalization rates for ⁶⁸Ga-mNP-N1/2 in both cell lines.

Expanding PET-applications in life sciences with positron-emitters beyond fluorine-18

Positron-emission-tomography (PET) has become an indispensable diagnostic tool in modern nuclear medicine. Its outstanding molecular imaging features allow repetitive studies on one individual and with high sensitivity, though no interference. Rather few positron-emitters with near favourable physical properties, i.e. carbon-11 and fluorine-18, furnished most studies in the beginning, preferably if covalently bound as isotopic label of small molecules. With the advancement of PET-devices the scope of in vivo research in life sciences and especially that of medical applications expanded, and other than "standard" PET-nuclides received increasing significance, like the radiometals copper-64 and gallium-68. Especially during the last decades, positron-emitters of other chemical elements have gotten into the focus of interest, concomitant with the technical advancements in imaging and radionuclide production. With known nuclear imaging properties and main production methods of emerging positron-emitters their usefulness for medical application is promising and even proven for several ones already. Unfortunate decay properties could be corrected for, and β+-emitters, especially with a longer half-life, provided new possibilities for application where slower processes are of importance. Further on, (bio)chemical features of positron-emitters of other elements, among there many metals, not only expanded the field of classical clinical investigations, but also opened up new fields of application. Appropriately labelled peptides, proteins and nanoparticles lend itself as newer probes for PET-imaging, e.g. in theragnostic or PET/MR hybrid imaging. Furthermore, the potential of non-destructive in-vivo imaging with positron-emission-tomography directs the view on further areas of life sciences. Thus, exploiting the excellent methodology for basic research on molecular biochemical functions and processes is increasingly encouraged as well in areas outside of health, such as plant and environmental sciences.

Manganese in PET imaging: Opportunities and challenges

Several radionuclides of the transition metal manganese are known and accessible. Three of them, ⁵¹Mn, ^52mMn, and ^52gMn, are positron emitters that are potentially interesting for positron emission tomography (PET) applications and, thus, have caught the interest of the radiochemical/radiopharmaceutical and nuclear medicine communities. This mini‐review provides an overview of the production routes and physical properties of these radionuclides. For medical imaging, the focus is on the longer‐living ^52gMn and its application for the radiolabelling of molecules and other entities exhibiting long biological half‐lives, the imaging of manganese‐dependent biological processes, and the development of bimodal PET/magnetic resonance imaging (MRI) probes in combination with paramagnetic ^natMn as a contrast agent.

Radiolabeled PET/MRI Nanoparticles for Tumor Imaging

The development of integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners opened a new scenario for cancer diagnosis, treatment, and follow-up. Multimodal imaging combines functional and morphological information from different modalities, which, singularly, cannot provide a comprehensive pathophysiological overview. Molecular imaging exploits multimodal imaging in order to obtain information at a biological and cellular level; in this way, it is possible to track biological pathways and discover many typical tumoral features. In this context, nanoparticle-based contrast agents (CAs) can improve probe biocompatibility and biodistribution, prolonging blood half-life to achieve specific target accumulation and non-toxicity. In addition, CAs can be simultaneously delivered with drugs or, in general, therapeutic agents gathering a dual diagnostic and therapeutic effect in order to perform cancer diagnosis and treatment simultaneous. The way for personalized medicine is not so far. Herein, we report principles, characteristics, applications, and concerns of nanoparticle (NP)-based PET/MRI CAs.

Horizons of nanotechnology applications in female specific cancers

Female-specific cancers are the most common cancers in women worldwide. Early detection methods remain unavailable for most of these cancers, signifying that most of them are diagnosed at later stages. Furthermore, current treatment options for most female-specific cancers are surgery, radiation and chemotherapy. Although important milestones in molecularly targeted approaches have been achieved lately, current therapeutic strategies for female-specific cancers remain limited, ineffective and plagued by the emergence of chemoresistance, which aggravates prognosis. Recently, the application of nanotechnology to the medical field has allowed the development of novel nano-based approaches for the management and treatment of cancers, including female-specific cancers. These approaches promise to improve patient survival rates by reducing side effects, enabling selective delivery of drugs to tumor tissues and enhancing the uptake of therapeutic compounds, thus increasing anti-tumor activity. In this review, we focus on the application of nano-based technologies to the design of novel and innovative diagnostic and therapeutic strategies in the context of female-specific cancers, highlighting their potential uses and limitations.

Use of Molecular Imaging in Clinical Drug Development: a Systematic Review

Background

Molecular imaging such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can provide the crucial pharmacokinetic-pharmacodynamic information of a drug non-invasively at an early stage of clinical drug development. Nevertheless, not much has been known how molecular imaging has been actually used in drug development studies.

Methods

We searched PubMed using such keywords as molecular imaging, PET, SPECT, drug development, and new drug, or any combination of those to select papers in English, published from January 1, 1990, to December 31, 2015. The information about the publication year, therapeutic area of a drug candidate, drug development phase, and imaging modality and utility of imaging were extracted.

Results

Of 10,264 papers initially screened, 208 papers met the eligibility criteria. The more recent the publication year, the bigger the number of papers, particularly since 2010. The two major therapeutic areas using molecular imaging to develop drugs were oncology (47.6%) and the central nervous system (CNS, 36.5%), in which efficacy (63.5%) and proof-of-concept through either receptor occupancy (RO) or other than RO (29.7%), respectively, were the primary utility of molecular imaging. PET was used 4.7 times more frequently than SPECT. Molecular imaging was most frequently used in phase I clinical trials (40.8%), whereas it was employed rarely in phase 0 or exploratory IND studies (1.4%).

Conclusions

The present study confirmed the trend that molecular imaging has been more actively employed in recent clinical drug development studies although its adoption was rather slow and rare in phase 0 studies.

Innovative Magnetic Nanoparticles for PET/MRI Bimodal Imaging

Superparamagnetic iron oxide nanoparticles were developed as positron emission tomography (PET) and magnetic resonance imaging (MRI) bimodal imaging agents. These nanoparticles (NPs), with a specific nanoflower morphology, were first synthesized and simultaneously functionalized with 3,4-dihydroxy-l-phenylalanine (LDOPA) under continuous hydrothermal conditions. The resulting NPs exhibited a low hydrodynamic size of 90 ± 2 nm. The functional groups of LDOPA (-NH₂ and -COOH) were successfully used for the grafting of molecules of interest in a second step. The nanostructures were modified by poly(ethylene glycol) (PEG) and a new macrocyclic chelator MANOTA for further ⁶⁴Cu radiolabeling for PET imaging. The functionalized NPs showed promising bimodal (PET and MRI) imaging capability with high r ₂ and r ₂* (T ₂ and T ₂* relaxivities) values and good stability. They were mainly uptaken from liver and kidneys. No cytotoxicity effect was observed. These NPs appear as a good candidate for bimodal tracers in PET/MRI.

52g/55Mn-Labelled CDTA-based trimeric complexes as novel bimodal PET/MR probes with high relaxivity

Multimeric trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA) derivatives labelled with a mixture of paramagnetic ⁵⁵Mn(ii) and β⁺-emitting ^52gMn(ii) offer the access to bimodal Positron Emission Tomography/Magnetic Resonance (PET/MR) tracers.

PET-MR and SPECT-MR multimodality probes: Development and challenges

Positron emission tomography (PET)-magnetic resonance (MR) or single photon emission computed tomography (SPECT)-MR hybrid imaging is being used in daily clinical practice. Due to its advantages over stand-alone PET, SPECT or MR imaging, in many areas such as oncology, the demand for hybrid imaging techniques is increasing dramatically. The use of multimodal imaging probes or biomarkers in a single molecule or particle to characterize the imaging subjects such as disease tissues certainly provides us with more accurate diagnosis and promotes therapeutic accuracy. A limited number of multimodal imaging probes are being used in preclinical and potential clinical investigations. The further development of multimodal PET-MR and SPECT-MR imaging probes includes several key elements: novel synthetic strategies, high sensitivity for accurate quantification and high anatomic resolution, favourable pharmacokinetic profile and target-specific binding of a new probe. This review thoroughly summarizes all recently available and noteworthy PET-MR and SPECT-MR multimodal imaging probes including small molecule bimodal probes, nano-sized bimodal probes, small molecular trimodal probes and nano-sized trimodal probes. To the best of our knowledge, this is the first comprehensive overview of all PET-MR and SPECT-MR multimodal probes. Since the development of multimodal PET-MR and SPECT-MR imaging probes is an emerging research field, a selection of 139 papers were recognized following the literature review. The challenges for designing multimodal probes have also been addressed in order to offer some future research directions for this novel interdisciplinary research field.

Unsaturated cryptophanes: Toward dual PHIP/hyperpolarised xenon sensors

Cryptophanes, cage-molecules constituted of aromatic bowls, are now well recognised as powerful xenon hosts in ¹²⁹ Xe NMR-based biosensing. In the quest of a dual probe that can be addressed only by NMR, we have studied three cryptophanes bearing a tether with an unsaturated bond. The idea behind this is to build probes that can be detected both via hyperpolarised ¹²⁹ Xe NMR and para-hydrogen induced polarisation ¹ H NMR. Only two of the three cryptophanes experience a sufficiently fast hydrogenation enabling the para-hydrogen induced polarisation effect. Although the in-out xenon exchange properties are maintained after hydrogenation, the chemical shift of xenon encaged in these two cryptophanes is not strikingly modified, which impedes safe discrimination of the native and hydrogenated states via ¹²⁹ Xe NMR. However, a thorough examination of the hyperpolarised ¹ H spectra reveals some interesting features for the catalytic process and gives us clues for the design of doubly smart ¹ H/¹²⁹ Xe NMR-based biosensors.

PET/MRI: a frontier in era of complementary hybrid imaging

With primitive approaches, the diagnosis and therapy were operated at the cellular, molecular, or even at the genetic level. As the diagnostic techniques are more concentrated towards molecular level, multi modal imaging becomes specifically essential. Multi-modal imaging has extensive applications in clinical as well as in pre-clinical studies. Positron Emission Tomography (PET) has flourished in the field of nuclear medicine, which has motivated it to fuse with Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) for PET/CT and PET/MRI respectively. However, the challenges in PET/CT are due to the inability of simultaneous acquisition and reduced soft tissue contrast, which has led to the development of PET/MRI. Also, MRI offers the better soft tissue contrast over CT. Hence, fusion of PET and MRI results in combining structural information with functional image from PET. Yet, it has many technical challenges due to the interference between the modalities. Also, it must be resolved with various approaches for addressing the shortcomings of each system and improvise on the image quantification system. This review elaborates on the various challenges in the present PET/MRI system and the future directions of the hybrid modality. Also, the different data acquisition and analysis techniques of PET/MRI system are discussed with enhanced details on the software tools.

Calcium phosphate-based nanosystems for advanced targeted nanomedicine

Synthetic calcium phosphates (CaPs) are the most widely accepted bioceramics for the repair and reconstruction of bone tissue defects. The recent advancements in materials science have prompted a rapid progress in the preparation of CaPs with nanometric dimensions, tailored surface characteristics, and colloidal stability opening new perspectives in their use for applications not strictly related to bone. In particular, the employment of CaPs nanoparticles as carriers of therapeutic and imaging agents has recently raised great interest in nanomedicine. CaPs nanoparticles, as well as other kinds of nanoparticles, can be engineered to specifically target the site of the disease (cells or organs), thus minimizing their dispersion in the body and undesired organism-nanoparticles interactions. The most promising and efficient approach to improve their specificity is the 'active targeting', where nanoparticles are conjugated with a targeting moiety able to recognize and bind with high efficacy and selectivity to receptors that are highly expressed only in the therapeutic site. The aim of this review is to give an overview on advanced targeted nanomedicine with a focus on the most recent reports on CaP nanoparticles-based systems, specifically designed for the active targeting. The distinctive characteristics of CaP nanoparticles with respect to the other kinds of nanomaterials used in nanomedicine are also discussed.

A cocktail of 165Er(iii) and Gd(iii) complexes for quantitative detection of zinc using SPECT and MRI

Quantitative zinc determination by nuclear and MR imaging using two Ln³⁺ complexes, including purified ¹⁶⁵Er³⁺, indispensable for metal ion quantification.

Fluoride doped γ-Fe2O3nanoparticles with increased MRI relaxivity

Fluoride doping in γ-Fe₂O₃nanoparticles induces large increases in magnetic anisotropy and relaxivities,r₁andr₂.

Optical and nuclear imaging of glioblastoma with phosphatidylserine-targeted nanovesicles

Multimodal tumor imaging with targeted nanoparticles potentially offers both enhanced specificity and sensitivity, leading to more precise cancer diagnosis and monitoring. We describe the synthesis and characterization of phenol-substituted, lipophilic orange and far-red fluorescent dyes and a simple radioiodination procedure to generate a dual (optical and nuclear) imaging probe. MALDI-ToF analyses revealed high iodination efficiency of the lipophilic reporters, achieved by electrophilic aromatic substitution using the chloramide 1,3,4,6-tetrachloro-3α,6α-diphenyl glycoluril (Iodogen) as the oxidizing agent in an organic/aqueous co-solvent mixture. Upon conjugation of iodine-127 or iodine-124-labeled reporters to tumor-targeting SapC-DOPS nanovesicles, optical (fluorescent) and PET imaging was performed in mice bearing intracranial glioblastomas. In addition, tumor vs non-tumor (normal brain) uptake was compared using iodine-125. These data provide proof-of-principle for the potential value of SapC-DOPS for multimodal imaging of glioblastoma, the most aggressive primary brain tumor.

Hybrid core shell nanoparticles entrapping Gd-DTPA and 18F-FDG for simultaneous PET/MRI acquisitions

Aim: Although there has been an improvement in the hardware and software of the PET/MRI system, the development of the nanoprobes exploiting the simultaneous acquisition of the bimodal data is still under investigation. Moreover, few studies on biocompatible and clinically relevant probes are available. This work presents a core-shell polymeric nanocarrier with improved relaxometric properties for simultaneous PET/MRI acquisitions. Materials & methods: Core-shell nanoparticles entrapping the Gd-DTPA and 18F-FDG are obtained by a complex coacervation. Results & discussion: The boosting of r1 of the entrapped Gd-DTPA up to five-times compared with ‘free Gd-DTPA’, is confirmed by the PET/MRI scan. The sorption of 18F-FDG into the nanoparticles is studied and designed to be integrated downstream for the production of the tracer.

Low eddy current RF shielding enclosure designs for 3T MR applications

PURPOSE

Magnetic resonance-compatible medical devices operate within the MR environment while benefitting from the superior anatomic information of MRI. Avoiding electromagnetic interference between such instrumentation and the MR system is crucial. In this work, various shielding configurations for positron emission tomography (PET) detectors were studied and analyzed regarding radiofrequency (RF) shielding effectiveness and gradient-induced eddy current performances. However, the results of this work apply to shielding considerations for any MR-compatible devices.

METHODS

Six shielding enclosure configurations with various thicknesses, patterns, and materials were designed: solid and segmented copper, phosphor bronze mesh (PBM), and carbon fiber composite (CFC). A series of tests was performed on RF shielding effectiveness and the gradient-induced eddy current.

RESULTS

For the shielding effectiveness, the solid copper with various thickness and PBM configurations yield significantly better shielding effectiveness (>15 dB) compared with CFC and segmented configurations. For the gradient-induced eddy current performance, the solid copper shielding configurations with different thicknesses showed significantly worse results, up to a factor of 3.89 dB, compared with the segmented copper, PBM, and the CFC configurations.

CONCLUSIONS

We evaluated the RF shielding effectiveness and the gradient-induced eddy current artifacts of several shielding designs, and only the PBM showed positive outcomes for both aspects. Magn Reson Med 79:1745-1752, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Radiolabelling with isotopic mixtures of (52g/55)Mn(II) as a straight route to stable manganese complexes for bimodal PET/MR imaging

Radiolabelling using isotopic mixtures of (52g/55)Mn(ii) offers fast and easy access to new small molecule PET/MR tracers, composed of chemically identical reporting units. trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) was radiolabelled with carrier-added (52g)Mn(ii) in >99% radiochemical yield, producing the first manganese-based bimodal PET/MR probe. The Mn-CDTA chelate was shown to be very stable to air oxidation and sufficiently inert to decomplexation in blood serum. These data sparked our interest in functionalized CDTA ligands for the design of optimized PET/MR tracers.

Bioengineered Magnetoferritin Nanoprobes for Single-Dose Nuclear-Magnetic Resonance Tumor Imaging

Despite all the advances in multimodal imaging, it remains a significant challenge to acquire both magnetic resonance and nuclear imaging in a single dose because of the enormous difference in sensitivity. Indeed, nuclear imaging is almost 10(6)-fold more sensitive than magnetic resonance imaging (MRI); thus, repeated injections are generally required to obtain sufficient MR signals after nuclear imaging. Here, we show that strategically engineered magnetoferritin nanoprobes can image tumors with high sensitivity and specificity using SPECT and MRI in living mice after a single intravenous injection. The magnetoferritin nanoprobes composed of (125)I radionuclide-conjugated human H-ferritin iron nanocages ((125)I-M-HFn) internalize robustly into cancer cells via a novel tumor-specific HFn-TfR1 pathway. In particular, the endocytic recycling characteristic of TfR1 transporters solves the nuclear signal blocking issue caused by the high dose nanoprobes injected for MRI, thus enabling simultaneous functional and morphological tumor imaging without reliance on multi-injections.

Radioactive Nanomaterials for Multimodality Imaging

Nuclear imaging techniques, including primarily positron emission tomography (PET) and single-photon emission computed tomography (SPECT), can provide quantitative information for a biological event in vivo with ultra-high sensitivity, however, the comparatively low spatial resolution is their major limitation in clinical application. By convergence of nuclear imaging with other imaging modalities like computed tomography (CT), magnetic resonance imaging (MRI) and optical imaging, the hybrid imaging platforms can overcome the limitations from each individual imaging technique. Possessing versatile chemical linking ability and good cargo-loading capacity, radioactive nanomaterials can serve as ideal imaging contrast agents. In this review, we provide a brief overview about current state-of-the-art applications of radioactive nanomaterials in the circumstances of multimodality imaging. We present strategies for incorporation of radioisotope(s) into nanomaterials along with applications of radioactive nanomaterials in multimodal imaging. Advantages and limitations of radioactive nanomaterials for multimodal imaging applications are discussed. Finally, a future perspective of possible radioactive nanomaterial utilization is presented for improving diagnosis and patient management in a variety of diseases.

The Use of Contrast Agents in Clinical and Preclinical PET-MR Imaging

PET-MR imaging is an exciting field of research for imaging chemists that allows for innovative approaches such as the use of cocktails of agents or bimodal contrast. In this review, we provide an overview of some of the work in the in preclinical and clinical PET-MR imaging to date, and discuss limitations in the design and applications of these materials.

89 Zr- and Fe-Labeled Polymeric Micelles for Dual Modality PET and T1 -Weighted MR Imaging

In this study, a new ⁸⁹ Zr- and Fe³⁺ -labeled micelle nanoplatform (⁸⁹ Zr/Fe-DFO-micelles) for dual modality position emission tomography/magnetic resonance (PET/MR) imaging is investigated. The nanoplatform consists of self-assembling amphiphilic diblock copolymers that are functionalized with ⁸⁹ Zr-deferoxamine (⁸⁹ Zr-DFO) and Fe³⁺ -deferoxamine (Fe-DFO) for PET and MR purposes, respectively. ⁸⁹ Zr displays favorable PET imaging characteristics with a 3.3 d half-life suitable for imaging long circulating nanoparticles. The nanoparticles are modified with Fe-DFO as MR T₁ -contrast label instead of commonly used Gd³⁺ -based chelates. As these micelles are cleared by liver and spleen, any long term Gd- related toxicity such as nephrogenic systemic fibrosis is avoided. As a proof of concept, an in vivo PET/MR study in mice is presented showing tumor targeting of ⁸⁹ Zr/Fe-DFO-micelles through the enhanced permeability and retention (EPR) effect of tumors, yielding high tumor-to-blood (10.3 ± 3.6) and tumor-to-muscle (15.3 ± 8.1) ratios at 48 h post injection. In vivo PET images clearly delineate the tumor tissue and show good correspondence with ex vivo biodistribution results. In vivo magnetic resonance imaging (MRI) allows visualization of the intratumoral distribution of the ⁸⁹ Zr/Fe-DFO-micelles at high resolution. In summary, the ⁸⁹ Zr/Fe-DFO-micelle nanoparticulate platform allows EPR-based tumor PET/MRI, and, furthermore, holds great potential for PET/MR image guided drug delivery.

Chelator free gallium-68 radiolabelling of silica coated iron oxide nanorods via surface interactions

The commercial availability of combined magnetic resonance imaging (MRI)/positron emission tomography (PET) scanners for clinical use has increased demand for easily prepared agents which offer signal or contrast in both modalities. Herein we describe a new class of silica coated iron-oxide nanorods (NRs) coated with polyethylene glycol (PEG) and/or a tetraazamacrocyclic chelator (DO3A). Studies of the coated NRs validate their composition and confirm their properties as in vivo T2 MRI contrast agents. Radiolabelling studies with the positron emitting radioisotope gallium-68 (t1/2 = 68 min) demonstrate that, in the presence of the silica coating, the macrocyclic chelator was not required for preparation of highly stable radiometal-NR constructs. In vivo PET-CT and MR imaging studies show the expected high liver uptake of gallium-68 radiolabelled nanorods with no significant release of gallium-68 metal ions, validating our innovation to provide a novel simple method for labelling of iron oxide NRs with a radiometal in the absence of a chelating unit that can be used for high sensitivity liver imaging.

Poly(acrylic acid) Bridged Gadolinium Metal-Organic Framework-Gold Nanoparticle Composites as Contrast Agents for Computed Tomography and Magnetic Resonance Bimodal Imaging

Imaging contrast agents for magnetic resonance imaging (MRI) and computed tomography (CT) have received significant attention in the development of techniques for early stage cancer diagnosis. Gadolinium (Gd)(III), which has seven unpaired electrons and a large magnetic moment, can dramatically influence the water proton relaxation and hence exhibits excellent MRI contrast. On the other hand, gold (Au), which has a high atomic number and high X-ray attenuation coefficient, is an ideal contrast agent candidate for X-ray-based CT imaging. Gd metal-organic framework (MOF) nanoparticles with tunable size, high Gd(III) loading and multivalency can potentially overcome the limitations of clinically utilized Gd chelate contrast agents. In this work, we report for the first time the integration of GdMOF nanoparticles with gold nanoparticles (AuNPs) for the preparation of a MRI/CT bimodal imaging agent. Highly stable hybrid GdMOF/AuNPs composites have been prepared by using poly(acrylic acid) as a bridge between the GdMOF nanoparticles and AuNPs. The hybrid nanocomposites were then evaluated in MRI and CT imaging. The results revealed high longitudinal relaxivity in MRI and excellent CT imaging performance. Therefore, these GdMOF/AuNPs hybrid nanocomposites potentially provide a new platform for the development of multimodal imaging probes.

Final step gallium-68 radiolabelling of silica-coated iron oxide nanorods as potential PET/MR multimodal imaging agents

The investigation of iron oxide-based positron emission tomography/magnetic resonance (PET/MR) multimodal imaging agents is an expanding field in which a variety of nanoparticle sizes, shapes, surface coatings and radioisotopes are open for exploration. This study develops iron oxide nanorods which are coated with various mixtures of poly(ethylene glycol) (PEG) and macrocyclic ligand (DO3A) via the formation of a silica layer on the surface. Gallium-68 radiolabelling of the nanorods was carried out in high radiochemical yields (RCY) and their stability in human serum was demonstrated for all constructs, even in the absence of the macrocyclic chelating unit. Further studies were carried out in an attempt to determine the appropriate amount of PEG coating to give optimal properties for future in vivo studies.

Gadolinium-based nanoparticles for theranostic MRI-radiosensitization

A rapid development of gadolinium-based nanoparticles is observed due to their attractive properties as MRI-positive contrast agents. Indeed, they display high relaxivity, adapted biodistribution and passive uptake in the tumor thanks to enhanced permeability and retention effect. In addition to these imaging properties, it has been recently shown that they can act as effective radiosensitizers under different types of irradiation (radiotherapy, neutron therapy or hadron therapy). These new therapeutic modalities pave the way to therapy guided by imaging and to personalized medicine.

Targeted therapy with MXD3 siRNA, anti-CD22 antibody and nanoparticles for precursor B-cell acute lymphoblastic leukaemia

Conventional chemotherapy for precursor B-cell (preB) acute lymphoblastic leukaemia (ALL) has limitations that could be overcome by targeted therapy. Previously, we discovered a potential therapeutic molecular target, MDX3 (MAX dimerization protein 3), in preB ALL. In this study, we hypothesize that an effective siRNA therapy for preB ALL can be developed using antiCD22 antibody (αCD22 Ab) and nanoparticles. We composed nanocomplexes with super paramagnetic iron oxide nanoparticles (SPIO NPs), αCD22 Abs and MXD3 siRNA molecules based on physical interactions between the molecules. We demonstrated that the MXD3 siRNA-αCD22 Ab-SPIO NP complexes entered leukaemia cells and knocked down MXD3, leading the cells to undergo apoptosis and resulting in decreased live cell counts in the cell line Reh and in primary preB ALL samples in vitro. Furthermore, the cytotoxic effects of the MXD3 siRNA-αCD22 Ab-SPIO NP complexes were significantly enhanced by addition of the chemotherapy drugs vincristine or doxorubicin. We also ruled out potential cytotoxic effects of the MXD3 siRNA-αCD22 Ab-SPIO NP complexes on normal primary haematopoietic cells. Normal B cells were affected while CD34-positive haematopoietic stem cells and non-B cells were not. These data suggest that MXD3 siRNA-αCD22 Ab-SPIO NP complexes have the potential to be a new targeted therapy for preB ALL.