Potential Imaging Agent Research Articles

Synthesis, 18F-radiolabeling and apoptosis inducing studies of novel 4, 7-disubstituted coumarins.

In present study, a new series of 4, 7-disubstituted coumarin derivatives (7a-y) have been synthesized as galectin-1 targeting apoptosis inducing agents and evaluated for their in vitro cytotoxic potentials against a panel of selected human cancer cell lines namely, Brest (MCF7), Ovarian (SKOV3), Prostate (PC-3 & DU145) and normal embryonic kidney (HEK293T) cells, using MTT assay. Most of the compounds exhibited potent growth inhibitory action against the treated cancer cell lines with an IC50 range of 10-30µM. Compound 7q exhibited a significant growth inhibition against prostate cancer (PC-3 & DU145) cell lines with an IC50 value of 7.45±0.03µM, 8.95±0.17µM respectively. Further, the target compound 7q was radiolabeled with fluorine-18 [18F] to be used as a novel PET radiotracer for imaging of tumors via targeting galectin-1, using appropriate reaction conditions in the GE Tracer-lab FX2N synthesis module. The purification of the [18F] radiolabeled compound [18F]-7q was successfully achieved with 60% ethanol. The radiochemical purity was>85% and residual solvent limits of DMF was 65±3ppm as analysed by HPLC, TLC & GC analytical methods. The apoptosis studies confirm the inhibition of cell proliferation with morphological changes like cell shrinkage, blebbing and cell wall deformation, increasing the ROS levels, and loss of mitochondrial membrane potential by Acridine orange/Ethidium bromide staining, Hoechst-33342 staining, H2DCFDA staining, annexin V-FITC/PI, and JC-1 staining methods. In flow cytometric analysis, 7q selectively arrested the sub-G1 phase of the cell cycle in a dose-dependent manner. In Gal-1 ELISA studies, compound 7q efficiently reduced the levels of Gal-1 protein in dose-dependent manner with an IC50 value of 100µM. The binding constant (Ka) of 7q with Gal-1 was observed as 1.3×104 M-1 by fluorescence spectroscopy. The molecular docking studies clearly showed possible interactions and the pharmacokinetic (ADMET) properties of compound 7q with Gal-1. Hence, the novel 4, 7-disubstituted coumarins could be a potential cytotoxic and PET imaging agents via Gal-1.

Synthesis and evaluation of 2-(2'-((dimethylamino)methyl)-4'-(2-fluoroethoxy-substituted)phenylthio)benzenamine derivatives as potential positron emission tomography imaging agents for serotonin transporters.

A series of diphenylsulfide derivatives with various substitutions at the 4-position on phenyl ring A and different lengths of the 2-fluoroethoxy-substituted side-chain at the 4'-position on ring B were synthesized and evaluated as potential positron emission tomography (PET) imaging agents for serotonin transporters (SERT). These ligands exhibited high SERT binding affinities (Ki=0.11-1.3nM) and the 4-methyl-substituted (4-Me) compounds 7a and 8a displayed excellent selectivity for SERT versus norepinephrine transporters (NET) (392- and 700-fold, respectively). In the parallel artificial membrane permeability assay (PAMPA), these ligands demonstrated moderate to high brain penetration, and the 4-Me analogs showed higher BBB permeability than the corresponding 4-F analogs. The 2-fluoroethoxy-substituted ligands showed higher metabolic stability and lower lipophilicity than 4-F-ADAM. [18F]7a-c were readily prepared using an automatic synthesizer and exhibited significant uptake and slow washout in rat brains. At 120min after iv injection, [18F]7a exhibited the highest uptake in the midbrain, whereas [18F]7b exhibited the highest uptake in the hypothalamus and midbrain. After treatment with citalopram, a SERT-selective ligand, the uptake of [18F]7a in the hypothalamus and striatum was significantly decreased. The potent and highly selective SERT binding and the selective and reversible accumulation in SERT-rich brain regions suggested that [18F]7a is a promising lead for the further development of novel [18F]-labeled PET imaging agents for SERT binding sites in the brain.

The Radiolabeling of a Gly-Sar Dipeptide Derivative with Flourine-18 and Its Use as a Potential Peptide Transporter PET Imaging Agent.

We have developed a novel fluorine-18 radiotracer, dipeptide 1, radiolabeled in two steps from mesylate 3. The initial radiolabeling is achieved in a short reaction time (10 min) and purified through solid-phase extraction (SPE) with modest radiochemical yields (rcy = 10 ± 2%, n = 5) in excellent radiochemical purity (rcp > 99%, n = 5). The de-protection of the tert-butyloxycarbonyl (Boc) and trityl group was achieved with mild heating under acidic conditions to provide 18F-tagged dipeptide 1. Preliminary analysis of 18F-dipeptide 1 was performed to confirm uptake by peptide transporters (PepTs) in human pancreatic carcinoma cell lines Panc1, BxPC3, and ASpc1, which are reported to express the peptide transporter 1 (PepT1). Furthermore, we confirmed in vivo uptake of 18F-dipeptide tracer 1 using microPET/CT in mice harboring subcutaneous flank Panc1, BxPC3, and Aspc1 tumors. In conclusion, we have established the radiolabeling of dipeptide 1 with fluoride-18, and demonstrated its potential as an imaging agent which may have clinical applications for the diagnosis of pancreatic carcinomas.

Iodinated Metallacrowns: Toward Combined Bimodal Near-Infrared and X-Ray Contrast Imaging Agents.

Multimodal probes capable of combining imaging modalities within a single molecule are in high demand today as they can provide information at both molecular and anatomical levels. Herein, a study was conducted on a series of gallium(III)/lanthanide(III) bis(12-MC-4) metallacrowns (MCs) with the general composition {Ln[12-MCGa III N(shi) -4]}2 (iph)4 (Ln-Ix , x=0, 4, 8, 12), where shi and iph are salicylhydroximate and isophthalate ligands, respectively, or their iodinated derivatives. For Yb-Ix , the attenuation in X-ray computed tomography (XCT) imaging and near-infrared (NIR) luminescence properties can be finely tuned by controlled structural modifications based on iodo groups. Solutions of Yb-Ix appear to be 22-40 times more efficient as XCT agents in comparison to the commercially available iobitridol, while providing an intense emission signal in the NIR range with total quantum yields up to 8.6 %, which are among the highest values reported so far. Therefore, these molecules are promising potential bimodal agents for combined NIR luminescence and XCT imaging.

Mediated Imaging and Improved Targeting of Farnesylthiosalicylic Acid Delivery for Pancreatic Cancer via Conjugation with Near-Infrared Fluorescence Heptamethine Carbocyanine Dye.

S-trans-trans-Farnesylthiosalicylic acid (FTS) is a Ras inhibitor that exhibits desirable anticancer property and currently undergoing clinical trials for pancreatic cancer (PC). However, its poor water solubility and low bioavailability have severely hampered clinical applications. A strategy to improve FTS bioavailability is to develop a suitable drug delivery method. Here, we use a near-infrared fluorescence (NIRF) heptamethine carbocyanine (HC) dye conjugated with FTS (to produce FTS-148) as a drug delivery system to enhance FTS bioavailability. We further investigate its tumor-targeting functions. FTS-148 displayed better bioavailability and photophysical property and selective recognition of cancer cells. FTS-148 significantly reduced PC cell proliferation, and more effective than FTS in restricting tumor growth both in a cell-derived xenograft (CDX) model and a patient-derived tumor xenograft (PDX) model. FTS-148 can specifically recognize PC cells in mice subcutaneous models or rabbit orthotopic models and allows real-time monitoring of the therapeutic effects by NIRF optical imaging. FTS-148 treatment significantly reduced Ras expression in PC cells and increased tumor tissue apoptosis. In short, FTS conjugated with HC dye had enhanced bioavailability and tumor-targeting property. It provides a potential agent for imaging and therapy of PC.

Evaluation of [18F]-N-Methyl lansoprazole as a Tau PET Imaging Agent in First-in-Human Studies

Development of positron emission tomography (PET) imaging agents capable of quantifying tau aggregates in neurodegenerative disorders such as Alzheimer's disease (AD) is of enormous importance in the field of dementia research. The aim of the present study was to conduct first-in-man imaging studies with the potential novel tau imaging agent [18F]N-methyl lansoprazole ([18F]NML). Herein we report validation of the synthesis of [18F]NML for clinical use by labeling the trifluoromethyl group via radiofluorination of the corresponding gem-difluoro enol ether precursor. This is the first use of this method for clinical production of PET radiotracers and confirmed that it can be readily implemented at multiple production facilities to provide [18F]NML in good noncorrected radiochemical yield (3.4 ± 1.5 GBq, 4.6% ± 2.6%) and molar activity (120.1 ± 186.3 GBq/μmol), excellent radiochemical purity (>97%), and suitable for human use (n = 15). With [18F]NML in hand, we conducted rodent biodistribution, estimates of human dosimetry, and preliminary evaluation of [18F]NML in human subjects at two imaging sites. Healthy controls (n = 4) and mildly cognitively impaired (MCI) AD patients (n = 6) received [18F]NML (tau), [18F]AV1451 (tau), and [18F]florbetaben or [18F]florbetapir (amyloid) PET scans. A single progressive supranuclear palsy (PSP) patient also received [18F]NML and [18F]AV1451 PET scans. [18F]NML showed good brain uptake, reasonable pharmacokinetics, and appropriate imaging characteristics in healthy controls. The mean ± SD of the administered mass of [18F/19F]NML was 2.01 ± 2.17 μg (range, 0.16-8.27 μg) and the mean administered activity was 350 ± 62 MBq (range, 199-403 MBq). There were no adverse or clinically detectable pharmacologic effects in any of the 11 subjects, and no significant changes in vital signs were observed. However, despite high affinity for tau in vitro, brain retention in MCI/AD and PSP patients was low, and there was no evidence of specific signals in vivo that corresponded to tau. Although it is still unclear why clinical translation of the radiotracer was unsuccessful, we nevertheless conclude that further development of [18F]NML as a tau PET imaging agent is not warranted at this time.

Synthesis and preliminary evaluation of a 99mTc labelled deoxyglucose complex {[99mTc]DTPA-bis(DG)} as a potential SPECT based probe for tumor imaging

[99mTc]DTPA-bis(DG): a potent tumor imaging probe.

Biodistribution of 68Ga-DTPMP as a potential bone-seeking imaging agent in normal rats and rats with experimental model of bone callus

Bone metastases are common in advanced stages of various cancers. Positron emission tomography (PET) with radiotracers based on phosphonates and gallium-68 is a promising method of bone metastases detection. In this work a new complex based on diethylene triamine pentamethylene phosphonate (DTPMP) labeled with 68Ga was developed and its biodistribution in normal Wistar rats and rats with experimental model of bone callus was studied. The biodistribution studies in normal rats revealed high skeletal uptake of 68Ga-DTPMP (up to 1.45 %ID/g in femur) with rapid blood clearance and minimal uptake in any other major organs, except kidneys. In rats with experimental model of bone callus the accumulation of activity in bones and soft organs and tissues was slightly lower as compared with normal rats. The amount of 68Ga-DTPMP in femur with bone callus was higher than in non-lesion bones and reached 1.90 %ID/g at 2 h p.i. Therefore, 68Ga-DTPMP could be a promising radiotracer for bone tumors imaging and could be a valuable alternative to 18F-FDG and 18F-NaF for PET centers without an onsite cyclotron.

To Sandwich Technetium: Highly Functionalized Bis‐Arene Complexes [99mTc(η6‐arene)2]+ Directly from Water and [99mTcO4]−

AbstractThe labeling of (bio)molecules with metallic radionuclides such as 99mTc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis‐arene sandwich complexes are generally prepared by the Fischer–Hafner reaction. In extension of this, we show that [99mTc(η6‐C6R6)2]+‐type complexes are directly accessible from water and [99mTcO4]−, even using arenes incompatible with Fischer–Hafner conditions. To unambiguously confirm the nature of these unprecedented 99mTc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η6‐C10H8)2]+ with the corresponding phenyl groups. The ease with which highly stable [99mTc(η6‐C6R6)2]+ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures.

To Sandwich Technetium: Highly Functionalized Bis-Arene Complexes [99m Tc(η6 -arene)2 ]+ Directly from Water and [99m TcO4

The labeling of (bio)molecules with metallic radionuclides such as 99m Tc demands conjugated, multidentate chelators. However, this is not always necessary since phenyl rings can directly serve as integrated, organometallic ligands. Bis-arene sandwich complexes are generally prepared by the Fischer-Hafner reaction. In extension of this, we show that [99m Tc(η6 -C6 R6 )2 ]+ -type complexes are directly accessible from water and [99m TcO4 ]- , even using arenes incompatible with Fischer-Hafner conditions. To unambiguously confirm the nature of these unprecedented 99m Tc complexes, their rhenium homologous have been prepared by substituting naphthalene ligands in [Re(η6 -C10 H8 )2 ]+ with the corresponding phenyl groups. The ease with which highly stable [99m Tc(η6 -C6 R6 )2 ]+ complexes are formed under standard labeling conditions enables a multitude of new potential imaging agents based on commercial pharmaceuticals or lead structures.

Assessment of Gd2O3 nanoparticles as exogenous imaging contrast agent for swept source optical coherence tomography

Optical coherence tomography (OCT) is a non-invasive and non-contact imaging technique that uses the reflection of light waves for tissue imaging. Compared to all other OCT variants, the swept-source OCT (SS-OCT) configuration offers higher imaging speed, better signal-to-noise ratio, and more resolution. Despite its numerous advantages, SS-OCT greatly suffers from limited contrast and reduced penetration ability. Over the years, several nanoparticles (NPs) like AgNP, TiO2, ZnO, etc have been exploited extensively as exogenous contrast agents to enhance the image contrast. Subsequently, herein, we have presented gadolinium oxide (Gd2O3) as a potential exogenous contrast agent for 3D non-invasive depth-resolved imaging of animal (chicken breast) tissue using an in-house developed SS-OCT system with centre wavelength of 1060 nm. In this work, OCT imaging of agar filled capillary tubes (phantoms) and chicken breast tissue (in vitro) was performed both with and without the application of Gd2O3 NPs. Scattering coefficient and contrast-to-noise ratio (CNR) calculations were done to study the effect of Gd2O3 NPs on the tissue sample at different time exposures. Post analysing the OCT images, a significant increase, in contrast, observed with time, where both the scattering coefficient (0.4879 mm−1 to 1.3782 mm−1) and the CNR of OCT B-scans (12.42 dB to 42.21 dB) increased substantially.

New 55Co-labeled Albumin-Binding Folate Derivatives as Potential PET Agents for Folate Receptor Imaging.

Overexpression of folate receptors (FRs) on different tumor types (e.g., ovarian, lung) make FRs attractive in vivo targets for directed diagnostic/therapeutic agents. Currently, no diagnostic agent suitable for positron emission tomography (PET) has been adopted for clinical FR imaging. In this work, two 55Co-labeled albumin-binding folate derivatives-[55Co]Co-cm10 and [55Co]Co-rf42-with characteristics suitable for PET imaging have been developed and evaluated. High radiochemical yields (≥95%) and in vitro stabilities (≥93%) were achieved for both compounds, and cell assays demonstrated FR-mediated uptake. Both 55Co-labeled folate conjugates demonstrated high tumor uptake of 17% injected activity per gram of tissue (IA/g) at 4 h in biodistribution studies performed in KB tumor-bearing mice. Renal uptake was similar to other albumin-binding folate derivatives, and liver uptake was lower than that of previously reported [64Cu]Cu-rf42. Small animal PET/CT images confirmed the biodistribution results and showed the clear delineation of FR-expressing tumors.

Synthesis and Preliminary Biological Evaluation of 99mTc Tricarbonyl Ropinirole as a Potential Brain Imaging Agent

Ropinirole, a non-ergoline dopamine agonist, was labeled with 99mTc tricarbonyl {[99mTc(CO)3·(H2O)3]+} with the aim of obtaining a new brain imaging agent. For in vivo use, the radiosynthesis of 99mTc tricarbonyl ropinirole was performed by heating a solution containing ropinirole and the precursor, 99mTc tricarbonyl, on a boiling water bath for 30 min. The influence of the substrate amount and pH on the reaction was studied to optimize the synthesis. The biodistribution and scintigraphic studies demonstrate the suitability of 99mTc tricarbonyl ropinirole as a novel tracer for brain tumor imaging.

Stabilizing gold nanoparticles for use in X-ray computed tomography imaging of soil systems.

This investigation establishes a system of gold nanoparticles that show good colloidal stability as an X-ray computed tomography (XCT) contrast agent under soil conditions. Gold nanoparticles offer numerous beneficial traits for experiments in biology including: comparatively minimal phytotoxicity, X-ray attenuation of the material and the capacity for functionalization. However, soil salinity, acidity and surface charges can induce aggregation and destabilize gold nanoparticles, hence in biomedical applications polymer coatings are commonly applied to gold nanoparticles to enhance stability in the in vivo environment. Here we first demonstrate non-coated nanoparticles aggregate in soil-water solutions. We then show coating with a polyethylene glycol (PEG) layer prevents this aggregation. To demonstrate this, PEG-coated nanoparticles were drawn through flow columns containing soil and were shown to be stable; this is in contrast with control experiments using silica and alumina-packed columns. We further determined that a suspension of coated gold nanoparticles which fully saturated soil maintained stability over at least 5 days. Finally, we used time resolved XCT imaging and image based models to approximate nanoparticle diffusion as similar to that of other typical plant nutrients diffusing in water. Together, these results establish the PEGylated gold nanoparticles as potential contrast agents for XCT imaging in soil.

Understanding the High Longitudinal Relaxivity of Gd(DTPA)-Intercalated (Zn,Al)-Layered Double Hydroxide Nanoparticles.

In this study, biocompatible gadolinium diethylenetriaminepentaacetate (Gd(DTPA))-intercalated (Zn,Al)-layered double hydroxide (LDH) nanoparticles were synthesized, characterized for Gd(DTPA) loading percentage and nanostructure, and the spin-lattice relaxation times (T1) measured to determine their suitability as a potential T1-weighted contrast agent for magnetic resonance imaging (MRI). Compared to the most commonly used contrast agent in clinical MRI (i.e., molecular Gd(DTPA)), significant increases in longitudinal relaxivity (r1) were measured for all Gd(DTPA)-intercalated nanoparticles. For a specific Zn2Al(OH)6(Cl,0.5CO3)0.56Gd(DTPA)0.086·xH2O composition, r1 was found to be 28.38 s-1 mM-1, which is over 6 times the r1 of molecular Gd(DTPA). This dramatic increase in r1 is attributed to (a) the much longer rotational correlation time (τR) of nanoparticles and (b) the inherent water of LDH that forms the second-/outer-sphere in the vicinity of intercalated Gd(DTPA)2-. The latter, with an extensive hydrogen bonding network and insignificant translational motion, results in a longer mean residence lifetime (τM), which makes the contribution of second-/outer-sphere significant. Therefore, when the Gd(DTPA)2- loading percentage increases from 8.6 to 55%, the diminution of the ratio of inherent water to Gd(DTPA)2- concomitantly diminishes the contributions by second-/outer-sphere water to r1. Additionally, the modest increase in r1 with decreasing particle size (∼315-540 nm) is perhaps due to the shortening of τM. Finally, the spin-spin relaxation times (T2) of 17O, determined at various temperatures, show a negligible exchange of water molecules at room temperature. Therefore, the very high r1 of nanoparticles indicate that protons of the bulk water are still accessible to the Gd3+ centers, possibly dominated by prototropic exchange through the hydrogen bonding network.

Searching for diagnostic properties of novel fluorine-18-labeled D-allose.

Two fluorine-18-labeled analogues, 3-deoxy-3-[18F]fluoro-D-allose (3-[18F]FDA) and 6-deoxy-6-[18F]fluoro-D-allose (6-[18F]FDA), were synthesized and their potentials of diagnostic property were characterized. In vitro rat red blood cell (RBC) transport and phosphorylation by yeast hexokinase were evaluated in comparison with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG). The rate of protein binding in pooled human serum was measured by an ultrafiltration method. In vivo metabolite analysis in mice was also performed. Biodistribution, urine excretion, and in vivo renal kinetics in mice were compared with 2-deoxy-2-[18F]fluorosorbitol ([18F]FDS). Rat RBC uptake of 3- and 6-[18F]FDA (7.8 ± 2.5%ID and 10.2 ± 4.8%ID, respectively) was significantly lower than that of [18F]FDG (44.7 ± 8.7%ID). RBC uptake of 3-[18F]FDA was inhibited by D-glucose (30%) and cytochalasin B (40%), indicating the involvement of GLUT1-dependent transport. In contrast, 6-[18F]FDA transport was not inhibited by D-glucose and cytochalasin B. 3- and 6-[18F]FDA were not phosphorylated by yeast hexokinase under the conditions that result in 60% conversion of [18F]FDG into [18F]FDG-6-phosphate within 30min. Serum protein binding of 3- and 6-[18F]FDA was negligible. Metabolic transformation of both tracers was not detected in plasma and urine at 30min after injection. The highest tissue uptake of both tracers was observed in kidneys. Heart and brain uptake of both tracers was below blood levels throughout the biodistribution studies (until 120min after injection). No significant uptake in the bone was observed, indicating the absence of de-fluorination in mice. In vivo PET imaging visualized rapid excretion of the administered 3- and 6-[18F]FDA from the kidneys, with minimal tracer accumulation in other organs. The urine excretion rate of 3-[18F]FDA was much lower than that of 6-[18F]FDA and [18F]FDS. 3- and 6-[18F]FDA might be unsatisfactory for tumor imaging. In contrast, these tracers demonstrated high levels of kidney uptake and excretion, low serum protein binding, and high metabolic stability as preferable properties for renal imaging. Notably, the urine excretion rate and kidney uptake kinetics of 6-[18F]FDA were comparable with those of the potential renal imaging agent [18F]FDS. Further validation studies in animal models are required to confirm the feasibility of 6-[18F]FDA as a functional renal imaging agent.

Development and evaluation of a 99mTc(V)-nitrido complex derived from estradiol for breast cancer imaging

Estrogen receptors are overexpressed in 70% of breast cancer and identification of their presence is important to select the appropriate treatment. This work proposes the preparation and evaluation of an estradiol derived as potential ER imaging agent. Ethinylestradiol was derivatized to introduce a dithiocarbamate function for Tc coordination. Labeling was achieved through the formation of a symmetric Tc(V)-nitrido complex with a radiochemical purity (RCP) > 95%. Physicochemical evaluation, cell uptake, biodistribution in normal animals and in nude mice bearing induced ER + breast tumors showed promising results.

Synthesis and bioevaluation of novel radioiodinated PEG-modified 2-nitroimidazole derivatives for tumor hypoxia imaging

Two novel radioiodinated PEG-modified 2-nitromidazole derivatives were prepared. The two radiotracers demonstrate good stability in vitro. In the cellular uptake experiments, the uptakes in hypoxic condition are higher than those in aerobic condition for two radiotracers. The biodistribution results in mice bearing S180 tumor demonstrate the uptakes of the two radiotracers in tumor show maximum at 1 h. The two radiotracers could be eliminated quickly from normal tissue. In SPECT/CT imaging study, the tumor could be observed clearly in S180 tumor using the two radiotracers. These results suggest they are worth of further study as potential hypoxia imaging agents.

Radiolabeling, Preparation, and Bioevaluation of 99mTc-Azathioprine as a Potential Targeting Agent for Solid Tumor Imaging

Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH, and reaction temperature and time were systematically studied to determine the optimum conditions, under which the 95% radiochemical yield was achieved. Biodistribution studies demonstrate the suitability of 99mTc-azathioprine as a novel tracer for tumor imaging. It shows high selectivity to high-replicating solid tumors.

PP#165 - Novel 4-nitroimidazole isocyanide labelled with 99mTc(I) core and [99mTc(I)(CO)3]+ core as potential tumor hypoxia imaging agents

PP#165 - Novel 4-nitroimidazole isocyanide labelled with 99mTc(I) core and [99mTc(I)(CO)3]+ core as potential tumor hypoxia imaging agents