Targeted Contrast Agents Research Articles

Intraoperative molecular imaging can identify lung adenocarcinomas during pulmonary resection

BackgroundMore than 80,000 people undergo resection of a pulmonary tumor each year, and the only method to determine if the tumor is malignant is histologic analysis. We propose that a targeted molecular contrast agent could bind lung adenocarcinomas, which could be identified using real-time optical imaging at the time of surgery. MethodsFifty patients with a biopsy-proven lung adenocarcinoma were enrolled. Before surgery, patients were systemically administered 0.1 mg/kg of a fluorescent folate receptor alpha (FRα)–targeted molecular contrast agent by intravenous infusion. During surgery, tumors were imaged in situ and ex vivo, after the lung parenchyma was dissected to directly expose the tumor to the imaging system. ResultsTumors ranged from 0.3 to 7.5 cm (mean: 2.6 cm), and 46 of 50 (92%) lung adenocarcinomas were fluorescent. No false uptake occurred, and in 2 cases, intraoperative imaging revealed tumor metastases (3 mm and 6 mm) that were not recognized preoperatively. Four adenocarcinomas were not fluorescent, and immunohistochemistry showed that these adenocarcinomas did not express FRα. Tumor fluorescence was independent of nodule size, uptake of 2-deoxy-2-(18F)fluoro-D-glucose, histology, and tumor differentiation. Molecular imaging could identify only 7 of the 50 adenocarcinomas in situ in the patient without bisection. The most important predictor of the success of molecular imaging in locating the tumor in situ was the distance of the nodule from the pleural surface. ConclusionsIntraoperative molecular imaging with a targeted contrast agent can identify lung adenocarcinomas, and this technology is currently useful in patients with subpleural tumors, irrespective of size. With further refinements, this tool may prove useful in locating adenocarcinomas that are deeper in the lung parenchyma, in lymph nodes, and at pleural and resection margins.

Monoclonal antibody-conjugated superparamagnetic iron oxide nanoparticles for imaging of epidermal growth factor receptor-targeted cells and gliomas.

The objective of this study was to successfully synthesize epidermal growth factor receptor monoclonal antibody-conjugated superparamagnetic iron oxide nanoparticles (EGFRmAb-SPIONs) and explore their biocompatibility and potential applications as a targeted magnetic resonance imaging (MRI) contrast agent for the EGFR-specific detection of brain glioma in vivo. After conjugation of EGFRmAb with SPIONs, the magnetic characteristics of EGFRmAb-SPIONs were investigated. Thereafter, the targeting abilities of EGFRmAb-SPIONs with MRI were qualitatively and quantitatively assessed in EGFR-positive C6 glioma cells in vitro and in a Wistar rat model bearing C6 glioma in vivo. Furthermore, the preliminary biocompatibility and toxicity of EGFRmAb-SPIONs were evaluated in normal rats through hematology assays and histopathologic analyses. Statistical analysis was performed using one-way analysis of variance and Student t-test, with a significance level of p < .05. From the results of EGFRmAb-SPION characterizations, the average particle size was 10.21 nm and the hydrodynamic diameter was 161.5 ± 2.12 nm. The saturation magnetization was 55 emu/g·Fe, and T2 relaxivity was 92.73 s-1mM-1 in distilled water. The preferential accumulation of the EGFRmAb-SPIONs within glioma and subsequent MRI contrast enhancement were demonstrated both in vitro in C6 cells and in vivo in rats bearing C6 glioma. After intravenous administration of EGFRmAb-SPIONs, T2-weighted MRI of the rat model with brain glioma exhibited an apparent hypointense region within glioma from 2 to 48 hours. The maximal image contrast was reached at 24 hours, where the signal intensity decreased and the R2 value increased by 30% compared to baseline. However, T2-weighted imaging of the rat model administered with SPIONs showed no visible signal changes within the tumor over the same time period. Moreover, no evident toxicities in vitro and in vivo with EGFRmAb-SPIONs were clearly identified based on the laboratory examinations. EGFRmAb-SPIONs could potentially be employed as a targeted contrast agent in the molecule-specific diagnosis of brain glioma in MRI.

A multifactorial analysis of complex pharmaceutical platforms: an application of design of experiments to targetable polyacrylamide and ultrasound contrast agents

To improve visualization of malignant regions in the colon epithelium during diagnostic procedures, we have recently suggested a multimodal system comprising the water‐soluble cationized polyacrylamide, tagged with the near infrared dye derivative IR‐783‐S‐Ph‐COOH [fluorescent‐cationized polyacrylamide (Flu‐CPAA)] and conjugated to the recognition peptide VRPMPLQ to form Flu‐CPAA‐Pep. The fluorescent‐cationized polyacrylamide‐peptide conjugate (Flu‐CPAA‐Pep) is then incorporated into echogenic microbubbles (MBs) made of polylactic acid (PLA) to protect it from pre‐mature interactions with plasma proteins upon intravenous administration. It is expected that under directed ultrasound interrogation the Flu‐CPAA‐Pep cargo would be released in the region of interest, as a result of the MBs rupture into submicron PLA fragments (SPF). Due to their nanoscale dimension, the SPF will escape from the vasculature and allow a specific binding of the Flu‐CPAA‐Pep to the suspected malignant tissue.The complex nature of the system requires a multifaceted statistically based experimental design. Here we apply a design of experiment methodology to enable effective screening of key parameters in our experimental setup. It enables the assessment of the role of the different formulation parameters by identifying statistically significant interactions as observed in vitro (cell lines) and in vivo (colon cancer‐induced rat model). Particularly important was the identification of the interaction between the fraction (mol%) of the cationic monomer in the Flu‐CPAA and (a) the presence of recognition peptide as assessed in the in vitro experiments and (b) the use of a presenting platform (whether MBs or SPF) as assessed in the in vivo experiments. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Experimental system to detect a labeled cell monolayer in a microfluidic environment.

To investigate the feasibility of detecting a living cell monolayer labeled with gadoterate (Gd-DOTA) in a microfluidic environment, by micromagnetic resonance imaging (MRI) in a 2.35T small-animal system. The development of new targeted contrast agents (CAs) requires proof-of-concept studies in order to establish the detectability of the CA and to predict the role of biodistribution in its uptake mechanisms. A promising approach is to carefully mimic the in vivo pharmacokinetic context with reduced experimental complexity compared to in vivo situations. A dedicated experimental system was built by combining a microfluidic slide and a radiofrequency probe based on a 6 mm diameter multiturn transmission-line resonator. Adherent KB cells were incubated with different concentrations of Gd. MRI data were acquired at 2.35T with a 3D gradient echo and a resolution of 12.4 μm perpendicular to the cell layer. The longitudinal relaxation rate, R1 , was measured as a function of the amount of Gd internalized by the cells. R1 measurements for different Gd concentrations per cell were performed using data with an signal-to-noise ratio (SNR) of 100. Relaxation-rate variations ΔR1 of 0.035 s(-1) were measured. A quenching effect was observed at Gd concentrations above 20 fmol/cell. Our results suggest that this dedicated experimental system is suitable for specifically assessing new high-relaxivity targeted CAs under real-time uptake conditions.

Molecular imaging with ultrasound: Steps toward clinical translation

Molecular imaging provides the ability to non-invasively assess expression levels of molecules by measuring imaging signals generated with the help of molecularly targeted contrast agents. These contrast agents can be directed to bind various molecular targets, thereby visualizing and quantifying disease processes at the molecular level in vivo. In recent years, the field of molecular imaging has been rapidly expanding and involves multiple imaging modalities. Among those, ultrasound imaging is a widely available, relatively inexpensive, and real-time imaging technique without exposing patients to radiation. It is already the first-line radiological imaging modality for many organs and disease processes in patients. By combining the these advantages of ultrasound with the ability to image molecular signatures using novel molecularly targeted ultrasound contrast agents, molecular ultrasound imaging is a quickly evolving imaging strategy that has great potential as a highly accurate and quantitative method ...

Targeted nanodiamonds as phenotype-specific photoacoustic contrast agents for breast cancer.

The aim is to develop irradiated nanodiamonds (INDs) as a molecularly targeted contrast agent for high-resolution and phenotype-specific detection of breast cancer with photoacoustic (PA) imaging. The surface of acid treated radiation-damaged nanodiamonds was grafted with PEG to improve its stability and circulation time in blood, followed by conjugation to an anti-HER2 peptide with a final nanoparticle size of approximately 92 nm. Immunocompetent mice bearing orthotopic HER2-positive or negative tumors were administered INDs and PA imaged using an 820-nm near-infrared laser. PA images demonstrated that INDs accumulate in tumors and completely delineated the entire tumor within 10 h. HER2 targeting significantly enhanced imaging of HER2-positive tumors. Pathological examination demonstrated INDs are nontoxic. PA technology is adaptable to low-cost bedside medicine, and with new contrast agents described herein, PA can achieve high-resolution (sub-mm) and phenotype-specific monitoring of cancer growth.

Spatially Resolved Quantification of Gadolinium(III)‐Based Magnetic Resonance Agents in Tissue by MALDI Imaging Mass Spectrometry after In Vivo MRI

AbstractGadolinium(III)‐based contrast agents improve the sensitivity and specificity of magnetic resonance imaging (MRI), especially when targeted contrast agents are applied. Because of nonlinear correlation between the contrast agent concentration in tissue and the MRI signal obtained in vivo, quantification of certain biological or pathophysiological processes by MRI remains a challenge. Up to now, no technology has been able to provide a spatially resolved quantification of MRI agents directly within the tissue, which would allow a more precise verification of in vivo imaging results. MALDI imaging mass spectrometry for spatially resolved in situ quantification of gadolinium(III) agents, in correlation to in vivo MRI, were evaluated. Enhanced kinetics of Gadofluorine M were determined dynamically over time in a mouse model of myocardial infarction. MALDI imaging was able to corroborate the in vivo imaging MRI signals and enabled in situ quantification of the gadolinium probe with high spatial resolution.

Spatially resolved quantification of gadolinium(III)-based magnetic resonance agents in tissue by MALDI imaging mass spectrometry after in vivo MRI.

Gadolinium(III)-based contrast agents improve the sensitivity and specificity of magnetic resonance imaging (MRI), especially when targeted contrast agents are applied. Because of nonlinear correlation between the contrast agent concentration in tissue and the MRI signal obtained in vivo, quantification of certain biological or pathophysiological processes by MRI remains a challenge. Up to now, no technology has been able to provide a spatially resolved quantification of MRI agents directly within the tissue, which would allow a more precise verification of in vivo imaging results. MALDI imaging mass spectrometry for spatially resolved in situ quantification of gadolinium(III) agents, in correlation to in vivo MRI, were evaluated. Enhanced kinetics of Gadofluorine M were determined dynamically over time in a mouse model of myocardial infarction. MALDI imaging was able to corroborate the in vivo imaging MRI signals and enabled in situ quantification of the gadolinium probe with high spatial resolution.

Dendrimers in Medicine: Therapeutic Concepts and Pharmaceutical Challenges.

Dendrimers are three-dimensional macromolecular structures originating from a central core molecule and surrounded by successive addition of branching layers (generation). These structures exhibit a high degree of molecular uniformity, narrow molecular weight distribution, tunable size and shape characteristics, as well as multivalency. Collectively, these physicochemical characteristics together with advancements in design of biodegradable backbones have conferred many applications to dendrimers in formulation science and nanopharmaceutical developments. These have included the use of dendrimers as pro-drugs and vehicles for solubilization, encapsulation, complexation, delivery, and site-specific targeting of small-molecule drugs, biopharmaceuticals, and contrast agents. We briefly review these advances, paying particular attention to attributes that make dendrimers versatile for drug formulation as well as challenging issues surrounding the future development of dendrimer-based medicines.

Nanoparticles functionalised with an anti-platelet human antibody for in vivo detection of atherosclerotic plaque by magnetic resonance imaging

Atherosclerosis is an inflammatory disease associated with the formation of atheroma plaques likely to rupture in which platelets are involved both in atherogenesis and atherothrombosis. The rupture is linked to the molecular composition of vulnerable plaques, causing acute cardiovascular events. In this study we propose an original targeted contrast agent for molecular imaging of atherosclerosis. Versatile USPIO (VUSPIO) nanoparticles, enhancing contrast in MR imaging, were functionalised with a recombinant human IgG4 antibody, rIgG4 TEG4, targeting human activated platelets. The maintenance of immunoreactivity of the targeted VUSPIO against platelets was confirmed in vitro by flow cytometry, transmission electronic and optical microscopy. In the atherosclerotic ApoE−/− mouse model, high-resolution ex vivo MRI demonstrated the selective binding of TEG4-VUSPIO on atheroma plaques. It is noteworthy that the rationale for targeting platelets within atherosclerotic lesions is highlighted by our targeted contrast agent using a human anti-αIIbβ3 antibody as a targeting moiety. From the Clinical EditorCurrent clinical assessment of atherosclerotic plagues is suboptimal. The authors in the article designed functionalized superparamagnetic iron oxide nanoparticles with TEG4, a recombinant human antibody, to target activated platelets. By using MRI, these nanoparticles can be utilized to study the process of atheroma pathogenesis.

Synthesis and characterization of Bombesin-superparamagnetic iron oxide nanoparticles as a targeted contrast agent for imaging of breast cancer using MRI

The targeted delivery of superparamagnetic iron oxide nanoparticles (SPIONs) as a contrast agent may facilitate their accumulation in cancer cells and enhance the sensitivity of MR imaging. In this study, SPIONs coated with dextran (DSPIONs) were conjugated with bombesin (BBN) to produce a targeting contrast agent for detection of breast cancer using MRI. X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer analyses indicated the formation of dextran-coated superparamagnetic iron oxide nanoparticles with an average size of 6.0 ± 0.5 nm. Fourier transform infrared spectroscopy confirmed the conjugation of the BBN with the DSPIONs. A stability study proved the high optical stability of DSPION–BBN in human blood serum. DSPION–BBN biocompatibility was confirmed by cytotoxicity evaluation. A binding study showed the targeting ability of DSPION–BBN to bind to T47D breast cancer cells overexpressing gastrin-releasing peptide (GRP) receptors. T2-weighted and T2*-weighted color map MR images were acquired. The MRI study indicated that the DSPION–BBN possessed good diagnostic ability as a GRP-specific contrast agent, with appropriate signal reduction in T2*-weighted color map MR images in mice with breast tumors.

Folate-bovine serum albumin functionalized polymeric micelles loaded with superparamagnetic iron oxide nanoparticles for tumor targeting and magnetic resonance imaging

Polymeric micelles functionalized with folate conjugated bovine serum albumin (FA-BSA) and loaded with superparamagnetic iron oxide nanoparticles (SPIONs) are investigated as a specific contrast agent for tumor targeting and magnetic resonance imaging (MRI) in vitro and in vivo. The SPIONs-loaded polymeric micelles are produced by self-assembly of amphiphilic poly(HFMA-co-MOTAC)-g-PEGMA copolymers and oleic acid modified Fe3O4 nanoparticles and functionalized with FA-BSA by electrostatic interaction. The FA-BSA modified magnetic micelles have a hydrodynamic diameter of 196.1nm, saturation magnetization of 5.5emu/g, and transverse relaxivity of 167.0mM−1S−1. In vitro MR imaging, Prussian blue staining, and intracellular iron determination studies demonstrate that the folate-functionalized magnetic micelles have larger cellular uptake against the folate-receptor positive hepatoma cells Bel-7402 than the unmodified magnetic micelles. In vivo MR imaging conducted on nude mice bearing the Bel-7402 xenografts after bolus intravenous administration reveals excellent tumor targeting and MR imaging capabilities, especially at 24h post-injection. These findings suggest the potential of FA-BSA modified magnetic micelles as targeting MRI probe in tumor detection.

Structure-inherent targeting of near-infrared fluorophores for parathyroid and thyroid gland imaging.

The typical method for creating targeted contrast agents requires covalent conjugation of separate targeting and fluorophore domains. In this study, we demonstrate that it is possible create tissue-specific near-infrared fluorophores using the inherent chemical structure. Thus, a single compact molecule performs both targeting and imaging. We use this strategy to solve a major problem in head/neck surgery, the identification and preservation of parathyroid and thyroid glands. We synthesized 700-nm and 800-nm halogenated fluorophores that show high uptake in the specific glands after a single intravenous injection of only 0.06 mg kg−1 in a pig. Using a dual-channel near-infrared imaging system, we demonstrate the real-time, high-sensitivity, unambiguous identification of parathyroid and thyroid glands simultaneously in the context of blood and surrounding soft tissue. This novel technology lays the foundation for head/neck surgery performed with increased precision and efficiency, and potentially lowers morbidity, and a general strategy for targeted near-infrared fluorophore development.

Synthesis and stability test of radiogadolinium(III)-DOTA-PAMAM G3.0-trastuzumab as SPECT-MRI molecular imaging agent for diagnosis of HER-2 positive breast cancer

Nonivasive diagnosis of cancer can be provided by molecular imaging using hybrid modality to obtain better sensitivity, specificity and depiction localization of the disease. In this study, we developed a new molecular imaging agent, radiogadolinium(III)-DOTA-PAMAM G3.0-trastuzumab in the form of 147Gd-DOTA-PAMAM G3.0-trastuzumab, that can be both target-specific radiopharmaceutical in SPECT as well as targeted contrast agent in MRI for the purpose of diagnosis of HER-2 positive breast cancer. 147Gd radionuclide emits γ-rays that can be used in SPECT modality, but because of technical constraint, 147Gd radionuclide was simulated by its radioisotope, 153Gd. Gd-DOTA complex has also been known as good MRI contrast agent. PAMAM G3.0 is useful to concentrate Gd-DOTA compelexes in large quantities, thus minimizing the number of trastuzumab molecules used. Trastuzumab is human monoclonal antibody that can spesifically interact with HER-2. Synthesis of radiogadolinium(III)-DOTA-PAMAM G3.0-trastuzumab was initiated by conjugating DOTA NHS ester ligand with PAMAM G3.0 dendrimer. The DOTA-PAMAM G3.0 produced was conjugated to trastuzumab molecule and labeled with 153Gd. Characterization DOTA-PAMAM G3.0-trastuzumab immunoconjugate was performed using HPLC system equipped with SEC. The formation of immunoconjugate was indicated by the shorter retention time (6.82 min) compared to that of trastuzumab (7.06 min). Radiochemical purity of radiogadolinium(III)-DOTA-PAMAM G3.0-trastuzumab was >99% after purification process by PD-10 desalting column. Radiogadolinium(III)-DOTA-PAMAM G3.0-trastuzumab compound was stable at room temperature and at 2–8 0C as indicated by its radiochemical purity 97.6 ± 0.5%–99.1 ± 0.5% after 144 h storage.

Synthesis and Characterization of a Biotinylated Multivalent Targeted Contrast Agent.

A new bimodal and multivalent dendritic contrast agent (CA) that targets the protein avidin was prepared and characterized. The tripartite lysine core was used to link the ligand biotin, the fluorescent dye, and the dendron carrying GdDOTA (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) chelates for amplification of the magnetic resonance imaging (MRI) signal. The longitudinal relaxivity of this dendrimeric CA was greater than those of its GdDOTA chelate and most of the common commercial agents at the investigated high magnetic field (7 T). The capacity of the dendrimeric CA to bind to the target protein was confirmed by fluorescence measurements upon its treatment with NeutrAvidin-agarose gel or NeutrAvidin-coated microspheres and the results were compared with those of its monomeric analogue. The fluorescence intensity of monomer-treated targets was found to be greater than that from those treated with dendrimeric CA; however, a several-fold increase in the MRI signal was observed on the same samples treated with the dendrimeric CA. The inductively coupled plasma mass spectrometry analysis of the digested samples indicated somewhat higher Gd3+ content and hence slightly better binding of monomeric versus dendrimeric CA. This bimodal and multivalent targeted probe opens an avenue for the preparation of new nanosized CAs that allow high-resolution MRI of various targets, such as cellular receptors or specific cellular populations.

NI-08 * OPTIMIZATION OF MOLECULAR MR IMAGING OF GLIOMA

BACKGROUND: MRI has been widely recognized as a diagnostic tool for early cancer detection, treatment monitoring and image guided surgery. Of particular interest is imaging of high-grade gliomas due to their rapid growth and very poor prognosis with a median survival rate of only 9 months. Standard contrast enhanced MRI, not provide sufficiently high specificity for tumor diagnosis and thus require targeted contrast agents which can be applied to provide information on tumor status. Therefore we applied targeted contrast agents based on iron oxide, that shorten mostly T2 relaxation time. The aim of this study was to optimize contrast-to-noise ratio (CNR) using spin-echo (SE), gradient echo (GE) and GE with flow compensation (GEFC) pulse sequences in T2 contrast-enhanced molecular MRI of glioma. METHODS: A mouse model of glioma and 9.4T MRI were used. MR imaging was performed. The CNR was measured prior, 20 min, 2 hrs and 24 hrs post intravenous tail administration of the glioma targeted paramagnetic nanoparticles (NPs) using spin-echo (SE), gradeint-ech (GE), gradient-echo flow compensation (GEFC) pulse sequences. Susceptibility weighted images (SWI) based on GEFC were also obtained for comparison. RESULTS: The results showed significant differences in CNR among all pulse sequences prior injection. GEFC provided higher CNR post contrast agent injection when compared to GE and SE. Post injection CNR was the highest with SWI and significantly different from any other pulse sequence. The optimum CNR was found to be TE = 7 ms for GE and GEFC pulse sequences and TE = 60 ms for SE. CONCLUSION: The study showed, that molecular MR imaging using targeted contrast agents can enhance the detection of glioma cells at 9.4T if the optimal pulse sequence is used. Hence, the use of flow compensated pulse sequences, beside SWI, should to be considered in the molecular imaging studies.

Entropy based detection of molecularly targeted nanoparticle ultrasound contrast agents in tumors

In this study, we demonstrate the use of “joint entropy” of two random variables (X,Y) can be applied to markedly improve tumor conspicuity (where X = f(t) =backscattered waveform and Y = g(t) = a reference waveform; both differentiable functions). Previous studies have shown that a good initial choice of reference is a reflection of the original insonifying pulse taken from a stainless-steel reflector. Using this choice, joint entropy analysis is more sensitive to accumulation of targeted contrast agents than conventional gray-scale or signal energy analysis by roughly a factor of 2[Hughes, M. S., et al., J. Acoust. Soc. Am., 133(1), p 283, 2013]. We now derive an improved reference that is applied to three groups of (MDA-435, breast tumor) flank tumor-implanted athymic nude mice to identify tumor vasculature after binding perfluorocarbon nanoparticles (~250 nm) to neovascular avb3 integrins. Five mice received i.v.avb3-targeted nanoparticles, five received nontargeted nanoparticles, and five received saline at a dose of 1 ml/kg, which was allowed to circulate for up to two hours prior to imaging. Three analogous groups of nonimplanted mice were imaged in the same region following the same imaging protocol. Our results indicate an improvement in contrast by a factor of 2.5 over previously published results. Thus, judicious selection of the reference waveform is critical to improving contrast-to-noise in tumor environments when attempting to detect targeted nanostructures for molecular imaging of sparse features.

Phosphonated near-infrared fluorophores for biomedical imaging of bone.

The conventional method for creating targeted contrast agents is to conjugate separate targeting and fluorophore domains. A new strategy is based on the incorporation of targeting moieties into the non-delocalized structure of pentamethine and heptamethine indocyanines. Using the known affinity of phosphonates for bone minerals in a model system, two families of bifunctional molecules that target bone without requiring a traditional bisphosphonate are synthesized. With peak fluorescence emissions at approximately 700 or 800 nm, these molecules can be used for fluorescence-assisted resection and exploration (FLARE) dual-channel imaging. Longitudinal FLARE studies in mice demonstrate that phosphonated near-infrared fluorophores remain stable in bone for over five weeks, and histological analysis confirms their incorporation into the bone matrix. Taken together, a new strategy for creating ultra-compact, targeted near-infrared fluorophores for various bioimaging applications is described.

Phosphonated Near‐Infrared Fluorophores for Biomedical Imaging of Bone

AbstractThe conventional method for creating targeted contrast agents is to conjugate separate targeting and fluorophore domains. A new strategy is based on the incorporation of targeting moieties into the non‐delocalized structure of pentamethine and heptamethine indocyanines. Using the known affinity of phosphonates for bone minerals in a model system, two families of bifunctional molecules that target bone without requiring a traditional bisphosphonate are synthesized. With peak fluorescence emissions at approximately 700 or 800 nm, these molecules can be used for fluorescence‐assisted resection and exploration (FLARE) dual‐channel imaging. Longitudinal FLARE studies in mice demonstrate that phosphonated near‐infrared fluorophores remain stable in bone for over five weeks, and histological analysis confirms their incorporation into the bone matrix. Taken together, a new strategy for creating ultra‐compact, targeted near‐infrared fluorophores for various bioimaging applications is described.

Progesterone-targeted magnetic resonance imaging probes.

Determination of progesterone receptor (PR) status in hormone-dependent diseases is essential in ascertaining disease prognosis and monitoring treatment response. The development of a noninvasive means of monitoring these processes would have significant impact on early detection, cost, repeated measurements, and personalized treatment options. Magnetic resonance imaging (MRI) is widely recognized as a technique that can produce longitudinal studies, and PR-targeted MR probes may address a clinical problem by providing contrast enhancement that reports on PR status without biopsy. Commercially available MR contrast agents are typically delivered via intravenous injection, whereas steroids are administered subcutaneously. Whether the route of delivery is important for tissue accumulation of steroid-modified MRI contrast agents to PR-rich tissues is not known. To address this question, modification of the chemistry linking progesterone with the gadolinium chelate led to MR probes with increased water solubility and lower cellular toxicity and enabled administration through the blood. This attribute came at a cost through lower affinity for PR and decreased ability to cross the cell membrane, and ultimately it did not improve delivery of the PR-targeted MR probe to PR-rich tissues or tumors in vivo. Overall, these studies are important, as they demonstrate that targeted contrast agents require optimization of delivery and receptor binding of the steroid and the gadolinium chelate for optimal translation in vivo.