Advances in Mineral Processing, Waste Recycling and Extractive Metallurgy.

The constant growth of the world economy and industry stimulates an increasing production of ferrous and non-ferrous metals, while the depletion of natural resources leads to demands for the development of new technologies for the processing of low-grade ores and the deep recycling of metallurgical and other anthropogenic wastes [...].

The Discrepancy between Coal Ash from Muffle, Circulating Fluidized Bed (CFB), and Pulverized Coal (PC) Furnaces, with a Focus on the Recovery of Iron and Rare Earth Elements.

Coal ash (CA) is not only one of the most solid wastes from combustion, easily resulting in a series of concerns, but it is also an artificial deposit with considerable metals, such as iron and rare earth. The variation in the coal ash characteristics due to the origins, combustion process, and even storage environment has been hindering the metal utilization from coal ash. In this study, three ash sample from lab muffle, circulating fluidized bed (CFB), and pulverized coal (PC) furnace was derived for the discrepancy study from the combustion furnace, including properties, iron, and rare earth recovery. The origins of the coal feed samples have more of an effect on their properties than combustion furnaces. Magnetic separation is suitable for coal ash from PC because of the magnetite product, and the iron content is 58% in the Mag-1 fraction, with a yield of 3%. The particles in CA from CFB appear irregular and fragmental, while those from PC appear spherical with a smooth surface. The results of sequential chemical extraction and observation both indicated that the aluminosilicate phase plays an essential role in rare earth occurrences. Rare earth in CA from muffling and CFB is facilely leached, with a recovery of approximately 50%, which is higher than that from PC ash. This paper aims to offer a reference to easily understand the difference in metal recovery from coal ash.

Rare-Earth Elements Extraction from Low-Alkali Desilicated Coal Fly Ash by (NH4)2SO4 + H2SO4.

Coal fly ash (CFA) obtained from pulverized coal furnaces is a highly refractory waste that can be used for alumina and rare-earth elements (REEs) extraction. The REEs in this type of CFA are associated with a mullite and amorphous glassy mass that forms a core-shell structure. In this research, it was shown that complete dissolution of amorphous aluminosilicates from the mullite surface with the formation of the low-alkali mullite concentrate prior to sulfuric acid leaching with the addition of (NH4)2SO4 helps to accelerate the extraction of REEs. The extraction degree of Sc and other REEs reaches 70-80% after 5 h of leaching at 110 °C and acid concentration of 5 M versus less than 20% for the raw CFA at the same conditions. To study the leaching kinetics of the process, the effects of temperature (90-110 °C), liquid-to-solid ratio (5-10), and leaching time (15-120 min) on the degrees of Al and rare-earth elements (REEs) extraction were evaluated. After 120 min of leaching at 110 °C and L/S ratio = 10, the extraction of Al was found to be lower than 30%. At the same time, total REEs (TREE) and Fe extraction were greater than 60%, which indicates that a part of the TREE was transferred into the acid soluble phase. After leaching, the residues were studied by laser diffraction (LD), X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM-EDS) to evaluate the leaching mechanism and the solubility of Al- and Fe-containing minerals, such as mullite, hematite, and amorphous aluminosilicate.

Angiotensin II type 1 receptor blocker telmisartan inhibits the development of transient hypoxia and improves tumour response to radiation.

Hypoxic tumour cells are radiation-resistant and are associated with poor therapeutic outcome. A poorly understood source of tumour hypoxia is unstable perfusion, which exposes tumour cells to varying oxygen tensions over time creating "transiently" hypoxic cells. Evidence suggests that angiotensin II type 1 receptor blockers (ARBs) can improve tumour perfusion by reducing collagen deposition from cancer associated fibroblasts (CAFs). However, the influence of ARBs on transient hypoxia and tumour radiation response is unknown. We tested how the ARBs losartan and telmisartan affected the solid tumour microenvironment, using fluorescent perfusion dyes and positron emission tomography to quantify tumour perfusion, and a combination of hypoxia markers and the hemorheological agent pentoxifylline to assess transient tumour hypoxia. We found CAF-containing tumours have reduced collagen I levels in response to telmisartan, but not losartan. Telmisartan significantly increased tumour blood flow, stabilized microregional tumour perfusion, and decreased tumour hypoxia by reducing the development of transient hypoxia. Telmisartan-treated tumours were more responsive to radiation, indicating that telmisartan reduces a therapeutically important population of transiently hypoxic tumour cells. Our findings indicate telmisartan is capable of modifying the tumour microenvironment to stabilize tumour perfusion, reduce transient hypoxia, and improve tumour radiation response.

Pharmacokinetics, radiation dosimetry, acute toxicity and automated synthesis of [18F]AmBF3-TATE.

INTRODUCTION: [18F]AmBF3-TATE is a somatostatin agonist that selectively binds to somatostatin receptor subtype 2 (SSTR2). For clinical translation, pharmacokinetics, radiation dosimetry, and acute toxicity of [18F]AmBF3-TATE were assessed with good laboratory practice (GLP) standards. METHODS: ICR mice were intravenously administered 0.8-2.0 MBq of [18F]AmBF3-TATE, with one group pre-injected with 100 µg of [19F]AmBF3-TATE 30 min before radiopharmaceutical administration to assess uptake specificity. The mice were euthanized at 0.5, 1, 2, or 4 h post-injection (p.i.). Blood and tissues were collected, weighed, and counted on a gamma counter to determine percentage injected dose per gram (%ID/g). Dosimetry was calculated based on biodistribution data using the mouse and human phantoms included in OLINDA. Acute toxicity was assessed in Sprague-Dawley rats at the dose of 0.742 mg/kg [19F]AmBF3-TATE, with a 14-day observation/recovery period. Blood chemistry parameters, gross, and histopathology were evaluated. Body weight change and food consumption were monitored. The production of [18F]AmBF3-TATE was automated on a Trasis AllinOne synthesis module. RESULTS: [18F]AmBF3-TATE was cleared through the renal and hepatobiliary pathway. At 1 h p.i., the pancreas (F, 15.7 ± 3.72 and M 14.3 ± 1.61 %ID/g), stomach (F, 15.3 ± 3.63 and M, 19.0 ± 3.49 %ID/g), and lungs (F, 9.26 ± 2.24 and M, 6.17 ± 6.04 %ID/g) were the organs with the highest specific uptake. Pre-injection with [19F]AmBF3-TATE significantly reduced pancreatic uptake (F, 0.13 ± 0.03 and M, 0.18 ± 0.09 %ID/g) at 1 h p.i. For dosimetry extrapolated to the average adult human, the bladder (0.027-0.030 mGy/MBq), pancreas (0.018-0.028 mGy/MBq), and lungs (0.006-0.013 mGy/MBq) are expected to receive the highest doses. No test-item related effects were observed upon evaluation of clinical observations, body weights, food consumption, clinical pathology, gross pathology, and histopathology for acute toxicity. [18F]AmBF3-TATE was produced at activity yields of 15.6 ± 4.59 GBq, average molar activity of 435 ± 162 GBq/µmol, and radiochemical purity of 98.0 ± 1.73% with the automated synthesizer. CONCLUSION: [18F]AmBF3-TATE binds specifically to SSTR2. At 1000× clinical dose, [19F]AmBF3-TATE was well tolerated with no treatment-related adverse effects.

H2CHXhox: Rigid Cyclohexane-Reinforced Nonmacrocyclic Chelating Ligand for [nat/67/68Ga]Ga3.

A rigid chiral acyclic chelator H2CHXhox was synthesized and evaluated for Ga3+-based radiopharmaceutical applications; it was compared to the previously reported hexadentate H2hox to determine the effect of a backbone reinforced from adding a chiral 1S,2S-trans-cyclohexane on metal complex stability, kinetic inertness, and in vivo pharmacokinetics. NMR spectroscopy and theoretical calculation revealed that [Ga(CHXhox)]+ showed a very similar coordination geometry to that of [Ga(hox)]+, and only one isomer in solution was observed by NMR spectroscopy. Solution studies showed that the modification results in a significant improvement in the exceptionally high thermodynamic stability of [Ga(hox)]+ with a 1.56 log unit increase in stability constant (logKML = 35.91(1)). More importantly, H2CHXhox showed very fast Ga3+ complexation at physiological pH 7.4, and acid-assisted Ga3+ complex dissociation kinetic studies (pH 1) in comparison with H2hox revealed a 50-fold increase of the dissociation half-life time from 73 min to 58 h. Fluorescence microscopy imaging study confirmed its cellular uptake and accumulation in endoplasmic reticulum and mitochondria. MTT studies indicated a quite low cytotoxicity of [Ga(CHXhox)]+ over a large concentration range. Dynamic PET imaging studies showed no accumulation in muscle, lungs, bone, and brain, suggesting no release of free Ga3+ ions. [68Ga][Ga(CHXhox)]+ is cleared from the mouse via hepatobiliary and renal pathways. Compared to [68Ga][Ga(hox)]+, the increased lipophilicity of [68Ga][Ga(CHXhox)]+ enhanced heart and liver uptake and decreased kidney clearance. [67Ga][Ga(CHXhox)]+ SPECT/CT imaging and biodistribution study revealed good clearance from liver to gallbladder after 90 min and finally into feces after 5 h. No decomposition or transchelation was observed over the 5 h study. These results confirmed H2CHXhox to be an obvious improvement over H2hox and an excellent candidate in this new "ox" family for the development of radiopharmaceutical compounds.

Recovery of rare earth elements from coal fly ash by integrated physical separation and acid leaching.

Coal fly ash (CFA) is one of the most promising secondary sources of rare earth elements and yttrium (REY). This research first studied the modes of occurrence of REY in CFA collected from a China's power generation plant which utilizes a coal feedstock with an elevated REY content. The fact that rare earth minerals remain in CFA and REY associate with metal oxides was proved by emission-scanning electron microscope with an energy-dispersive X-ray spectrometer. The technical feasibility of recovery of REY from CFA was then studied through conducting various physical separation methods followed by acid leaching. It was found that REY are concentrated in fine particle size, non-magnetic and middle density fractions. Using combined physical separation processes, the REY of CFA was enriched from 782 µg·g-1to 1025 µg g-1. The acid leaching process was optimized for various parameters via the Taguchi three-level experimental design. Upon optimization, the physical separation product was leached at the optimum condition and 79.85% leaching efficiency was obtained. Based on the obtained results, a conceptual process flowsheet was developed for recovery of REY from CFA. Such recovery maximizes REY resources utilization and enhances sustainability of CFA disposal.

One-Step 18F-Labeling and Preclinical Evaluation of Prostate-Specific Membrane Antigen Trifluoroborate Probes for Cancer Imaging.

After the identification of the high-affinity glutamate-ureido scaffold, the design of several potent 18F- and 68Ga-labeled tracers has allowed spectacular progress in imaging recurrent prostate cancer by targeting the prostate-specific membrane antigen (PSMA). We evaluated a series of PSMA-targeting probes that are 18F-labeled in a single step for PET imaging of prostate cancer. Methods: We prepared 8 trifluoroborate constructs for prostate cancer imaging, to study the influence of the linker and the trifluoroborate prosthetic on pharmacokinetics and image quality. After 1-step labeling by 19F-18F isotopic exchange, the radiotracers were injected in mice bearing LNCaP xenografts, with or without blocking controls, to assess specific uptake. PET/CT images and biodistribution data were acquired at 1 h after injection and compared with 18F-DCFPyL on the same mouse strain and tumor model. Results: All tracers exhibited nanomolar affinities, were labeled in good radiochemical yields at high molar activities, and exhibited high tumor uptake in LNCaP xenografts with clearance from nontarget organs. Most derivatives with a naphthylalanine linker showed significant gastrointestinal excretion. A radiotracer incorporating this linker with a dual trifluoroborate-glutamate labeling moiety showed high tumor uptake, low background activity, and no liver or gastrointestinal track accumulation. Conclusion: PSMA-targeting probes with trifluoroborate prosthetic groups represent promising candidates for prostate cancer imaging because of facile labeling while affording high tumor uptake values and contrast ratios that are similar to those obtained with 18F-DCFPyL.

H2hox: Dual-Channel Oxine-Derived Acyclic Chelating Ligand for 68Ga Radiopharmaceuticals.

An acyclic hexadentate oxine-derived chelating ligand, H2hox, was investigated as an alternative to current chelators for 68Ga. The straightforward preparation of H2hox, involving only one or two steps, obviates the synthetic challenges associated with many reported 68Ga chelators; it forms a Ga3+ complex of great stability (log K = 34.4) with a remarkably high gallium scavenging ability (pGa3+ = -log[Ga3+free] = 28.3, ([Ga3+] = 1 µM; [L x-] = 10 µM; pH 7.4, and 25 °C)). Moreover, H2hox coordinates 68Ga quantitatively in 5 min at room temperature in ligand concentrations as low as 1 × 10-7 M, achieving an unprecedented high molar activity of 11 ± 1 mCi/nmol (407 ± 3.7 MBq/nmol) without purification, suggesting prospective kit-based convenience. [68Ga(hox)]+ showed no decomposition in a plasma challenge. Good in vivo stability and fast renal and hepatic clearance of the [68Ga(hox)]+ complex were demonstrated using dynamic positron emission tomography/computed tomography imaging. The intrinsic fluorescence of [Ga(hox)]+ allowed for direct fluorescence imaging of cellular uptake and distribution, demonstrating the dual-channel detectability and intracellular stability of the metal complex.

Effects of Linker Modification on Tumor-to-Kidney Contrast of 68Ga-Labeled PSMA-Targeted Imaging Probes.

68Ga-PSMA-11 is currently the most popular prostate-specific membrane antigen (PSMA) radioligand used in the clinic to detect prostate cancer and metastases. However, the high uptake of 68Ga-PSMA-11 in kidneys can create halo-artifacts resulting in lower detection sensitivity for lesions adjacent to the kidneys. In this study, we developed two 68Ga-labeled PSMA-targeted tracers, 68Ga-HTK01166 and 68Ga-HTK01167, based on 68Ga-PSMA-617 with the goal of improving tumor-to-kidney ratio compared to 68Ga-PSMA-11. The 2-naphthylalanine (2-Nal) in PSMA-617 was replaced with 2-indanylglycine (Igl) or 3,3-diphenylalanine (Dip) to synthesize HTK01166 and HTK01167, respectively. Binding affinities ( Ki) of Ga-PSMA-11, Ga-PSMA-617, Ga-HTK01166, and Ga-HTK01167 to PSMA were 3.13 ± 0.40, 1.23 ± 0.08, 5.74 ± 2.48, and 25.7 ± 9.84 nM, respectively, as determined by in vitro competition binding assays. 68Ga labeling was performed in HEPES buffer with microwave heating, and 68Ga-labeled PSMA-11, PSMA-617, HTK01166, and HTK01167 were obtained in 46-69% average decay-corrected radiochemical yield with >99% radiochemical purity and 62.9-152 GBq/µmol average specific activity. PET imaging and biodistribution studies were performed in mice bearing PSMA-expressing LNCap prostate cancer xenografts. All tracers enabled clear visualization of tumors in PET images with excellent tumor-to-background contrast. The uptake values (%ID/g) for tumor and kidneys at 1 h postinjection were 8.91 ± 0.86 and 204 ± 70.6 for 68Ga-PSMA-11, 16.7 ± 2.30 and 29.2 ± 5.14 for 68Ga-PSMA-617, 14.1 ± 4.40 and 147 ± 59.6 for 68Ga-HTK01166, and 7.79 ± 1.65 and 4.30 ± 1.80 for 68Ga-HTK01167. The tumor-to-kidney ratios for 68Ga-labeled PSMA-11, PSMA-617, HTK01166, and HTK01167 were 0.05 ± 0.02, 0.63 ± 0.10, 0.10 ± 0.02, and 1.98 ± 0.63, respectively. Compared with 68Ga-PSMA-617, 68Ga-HTK01166 showed comparable tumor uptake and almost 5-fold higher kidney uptake, whereas 68Ga-HTK01167 exhibited lower tumor and kidney uptake. Compared with 68Ga-PSMA-11, 68Ga-HTK01167 had similar tumor uptake and tumor-to-blood contrast ratio (23.8 ± 6.71 vs 20.4 ± 4.98) but higher tumor-to-background contrast ratios for other background organs especially for kidneys. Our data indicate that substitution of 2-Nal in PSMA-617 with other lipophilic amino acid can modulate PSMA binding affinity and their pharmacokinetics in vivo.

Preclinical Melanoma Imaging with 68Ga-Labeled α-Melanocyte-Stimulating Hormone Derivatives Using PET.

It is estimated that melanoma accounted for 76,380 new cases and 10,130 deaths in the United States in 2016. The melanocortin 1 receptor (MC1R) is highly expressed in the vast majority of melanomas, which makes it an attractive target for molecular imaging and radionuclide therapy. Lactam bridge-cyclized α-melanocyte-stimulating hormone (Ac-Nle4-cyclo[Asp5-His-D-Phe7-Arg-Trp-Lys10]-NH2, or Nle-CycMSHhex) analogues have been successfully developed and studied for MC1R-targeted imaging, predominantly with single-photon emission computed tomography (SPECT). The goal of this study was to design and evaluate novel peptides for melanoma imaging with positron emission tomography (PET). We designed and synthesized three peptides, DOTA-PEG2-Nle-CycMSHhex (CCZ01047), DOTA-4-amino-(1-carboxymethyl) piperidine (Pip)-Nle-CycMSHhex (CCZ01048), and DOTA-Pip-Pip-Nle-CycMSHhex (CCZ01056). All three peptides exhibited high binding affinity to MC1R with sub-nanomolar Ki values, rapid internalization into B16F10 melanoma cells and high in vivo stability with more than 93% remaining intact at 15 min post-injection (p.i.) in blood plasma. All three 68Ga-labeled tracers produced high contrast PET images in C57BL/6J mice bearing B16F10 tumors, and their respective tumor uptakes were 8.0 ± 3.0, 12.3 ± 3.3, and 6.5 ± 1.4 %ID/g at 1 h p.i. Minimal normal organ activity was observed at 1 h p.i., except for kidneys (5.1 ± 1.4, 4.7 ± 0.5, and 6.2 ± 2.0 %ID/g, respectively), and thyroid (4.1 ± 0.6 %ID/g for CCZ01047 and 2.4 ± 0.6 %ID/g for CCZ01048). Due to high accumulation at tumor sites and rapid background clearance of 68Ga-CCZ01048, we further evaluated it at 2 h p.i., and a tumor uptake of 21.9 ± 4.6 %ID/g was observed, with background activity further decreased. Exceptional image contrast was also achieved, i.e. tumor-to-blood, tumor-to-muscle, tumor-to-bone and tumor-to-kidney ratios were 96.4 ± 13.9, 210.9 ± 20.9, 39.6 ± 11.9 and 4.0 ± 0.9, respectively. A blocking study was also performed by co-injection of excess amount of non-radioactive Ga-coupled of CCZ01048, which confirmed that the tumor uptake was MC1R mediated. In conclusion, the introduction of a cationic Pip linker to Nle-CycMSHhex, CCZ01048, not only improved tumor uptake, but also generated high tumor-to-normal tissue contrast with PET imaging in a preclinical melanoma model. Therefore, CCZ01048 is a promising candidate for PET imaging of melanoma, and potentially as a theranostic agent for radionuclide therapy of melanoma when labeled with α or ß emitters.

2-18F-Fluoroethanol Is a PET Reporter of Solid Tumor Perfusion.

Solid tumor perfusion is a proven variable of interest for predicting cancer aggression and response to therapy. Current methods for noninvasively imaging tumor perfusion with PET are limited by restricted accessibility and short half-lives of perfusion radiotracers. This study presents 2-18F-fluoroethanol (2-18F-FEtOH) as a perfusion reporter that can distinguish between tumors of varying perfusion levels and can be applied to screening drugs that modify tumor perfusion. Methods: Uptake of 2-18F-FEtOH in 4T1 and 67NR murine mammary carcinoma tumors grown in mice was measured using ex vivo radiography as well as static and dynamic PET imaging. 2-18F-FEtOH uptake was directly compared with the 14C-iodoantipyrine perfusion reporter, and the perfusion-modifying drugs nicotinamide, pentoxifylline, and hydralazine were used to manipulate tumor perfusion before 2-18F-FEtOH quantification. Results: Uptake of 2-18F-FEtOH in 4T1 and 67NR tumors was consistent with known perfusion differences within and between these tumors. 2-18F-FEtOH uptake corresponded well with 14C-iodoantipyrine and reflected the tumor perfusion-modifying effects of each drug. Conclusion: 2-18F-FEtOH is a novel 18F-based radiotracer for investigating tumor perfusion with PET imaging. Quantification of 2-18F-FEtOH uptake can be used to distinguish between tumors of varying perfusion and to screen the efficacy of blood flow-modifying drugs for use as adjuvants to existing cancer therapies.

Radiolabeled R954 Derivatives for Imaging Bradykinin B1 Receptor Expression with Positron Emission Tomography.

Peptide receptors have emerged as promising targets for diagnosis and therapy. The aberrant overexpression of these receptors in different cancer subtypes allows for the adoption of new treatment strategies that complement conventional chemotherapies. Bradykinin B1 receptor (B1R) is a G protein-coupled receptor that is overexpressed in many cancers, with limited expression in healthy tissues. Previously, we developed 68Ga- and 18F-labeled derivatives of B1R antagonist peptides B9858 and B9958, and successfully targeted B1R-expressing tumor xenografts in vivo. R954 (Ac-Orn-Arg-Oic-Pro-Gly-αMePhe-Ser-d-2-Nal-Ile), a potent B1R antagonist, is reportedly more stable than B9858 against peptidase degradation. We evaluated two radiolabeled derivatives of R954 (68Ga-HTK01083 and 18F-HTK01146) for B1R PET imaging. Peptides were synthesized via solid phase strategy. Nonradioactive standards were obtain by reacting GaCl3 with DOTA-dPEG2-R954 and by clicking N-propargyl-N,N-dimethylammoniomethyl-trifluoroborate with azidoacetyl-dPEG2-R954. Binding affinity for B1R was determined by an in vitro competition binding assay. 68Ga-HTK01083 was obtained by incubating DOTA-dPEG2-R954 with 68GaCl3 under acidic conditions, while 18F-HTK01146 was prepared via an 18F-19F isotope exchange reaction. Biodistribution and imaging studies were conducted at 1 h postinjection (p.i.) in mice inoculated with B1R-expressing (B1R+) and B1R-nonexpressing (B1R-) cells. HTK01083 and HTK01146 bound B1R with good affinity (Ki = 30.5 and 24.8 nM, respectively). 68Ga/18F-labeled R954 were obtained on average in ≥10% decay-corrected radiochemical yield with >99% radiochemical purity and ≥52 GBq/µmol specific activity. For both tracers, clearance was predominantly renal with minimal involvement of the hepatobiliary system. For PET images, B1R+ tumors, kidneys, and bladder were visible. At 1 h p.i., uptake in B1R+ tumor was comparable between 68Ga-HTK01083 (8.46 ± 1.44%ID/g) and 18F-HTK01146 (9.25 ± 0.69%ID/g). B1R+ tumor-to-blood and B1R+ tumor-to-muscle ratios were 6.32 ± 1.44 and 20.7 ± 3.58 for 68Ga-HTK01083, and 7.24 ± 2.56 and 19.5 ± 4.29 for 18F-HTK01146. Our results indicate R954 is a good lead sequence for optimization of B1R tracers for cancer imaging.

Synthesis and evaluation of a 68Ga-labeled bradykinin B1 receptor agonist for imaging with positron emission tomography.

A novel 68Ga-labeled bradykinin B1 receptor (B1R) agonist, 68Ga-Z01115, was synthesized and evaluated for imaging with positron emission tomography (PET). Z01115 exhibited good binding affinity (Ki=25.4±5.1nM) to hB1R. 68Ga-Z01115 was prepared in 74±5 decay-corrected radiochemical yield with >99% radiochemical purity and 155±89GBq/µmol (4.2±2.4Ci/µmol) specific activity. 68Ga-Z01115 was stable in vitro in mouse plasma (93% remaining intact after 60min incubation), and relatively stable in vivo (51±5% remaining intact at 5min post-injection). PET imaging and biodistribution studies in mice showed that 68Ga-Z01115 cleared rapidly from nontarget tissues/organs, and generated high target-to-nontarget contrast images. The uptake of 68Ga-Z01115 in B1R-positive (B1R+) tumor was 5.65±0.59%ID/g at 1h post-injection. Average contrast ratios of B1R+ tumor-to-B1R- tumor, -to-blood and -to-muscle were 24.3, 24.4 and 82.9, respectively. Uptake of 68Ga-Z01115 in B1R+ tumors was reduced by ∼90% with co-injection of cold standard, confirming it was mediated by B1R. Our data suggest that 68Ga-Z01115 is a promising tracer for imaging the expression of B1R that is overexpressed in a variety of cancers.

Targeting the Neuropeptide Y1 Receptor for Cancer Imaging by Positron Emission Tomography Using Novel Truncated Peptides.

The neuropeptide Y1 receptor (Y1R) is overexpressed in many human cancers, particularly breast cancer. Due to stability issues, limited success has been achieved for Y1R imaging agents, including full length and truncated neuropeptide Y (NPY) analogues. The goal of this study was to evaluate the possibility of using radiolabeled truncated NPY analogues to visualize Y1R expression in a preclinical model of Y1R-positive tumor. Four truncated NPY analogues were synthesized based on the sequence of [Pro30, Tyr32, Leu34]NPY(28-36), also known as BVD15. We substituted Tyr5 and Arg6 with unnatural amino acids aiming to enhance plasma stability while maintaining good receptor binding affinity to Y1R. In addition, we substituted Leu4 to Lys4 in order to conjugate via an optional linker the DOTA chelator for 68Ga labeling. Receptor binding affinity and plasma stability of these compounds were evaluated. Positron emission tomography/computed tomography (PET/CT) imaging and biodistribution studies were performed using immune-compromised mice bearing HEK293T::WT and HEK293T::hY1R tumors. [Lys(Ga-DOTA)4, Bip5]BVD15 (CCZ01035), [Lys(Ahx-Ga-DOTA)4, Bip5]BVD15 (CCZ01053), and [Lys(Pip-Ga-DOTA)4, Bip5]BVD15 (CCZ01055) demonstrated good binding affinity to Y1R (Ki = 23.4-32.3 nM), while [Lys(Ga-DOTA)4, Har6]BVD15 (P05067) showed poor binding affinity (Ki > 1000 nM). In addition, CCZ01055 exhibited low binding affinity (Ki > 1000 nM) to Y2R and Y4R, demonstrating its selectivity to Y1R. The former three peptides showed improved in vitro plasma stability of 7-16% remaining intact after 1 h incubation. PET/CT imaging and biodistribution studies for 68Ga-labeled CCZ01053, CCZ01035, and CCZ01055 showed that radioactivity was mainly cleared by the renal pathway, and HEK293T::hY1R tumors were clearly visualized with minimal background activity with the latter two. Of these two tracers, [68Ga]CCZ01055 provided lower kidney accumulation and higher contrast, i.e., average uptake ratios of Y1R tumor to wild type tumor, blood, and muscle are 3.87 ± 0.83, 4.12 ± 1.14, and 17.6 ± 4.64, respectively. Furthermore, Y1R tumor uptake with [68Ga]CCZ01055 was significantly reduced with coinjection of 100 µg of peptide YY, confirming the specificity of tumor accumulation was receptor mediated. We successfully developed the first Y1R-targeting truncated NPY analogues for PET imaging in a preclinical model, and [68Ga]CCZ01055 is a critical template for designing improved imaging agents to detect Y1R expressing cancers.

An imaging agent to detect androgen receptor and its active splice variants in prostate cancer.

Constitutively active splice variants of androgen receptor (AR-Vs) lacking ligand-binding domain (LBD) are a mechanism of resistance to androgen receptor LBD-targeted (AR LBD-targeted) therapies for metastatic castration-resistant prostate cancer (CRPC). There is a strong unmet clinical need to identify prostate cancer patients with AR-V-positive lesions to determine whether they will benefit from further AR LBD-targeting therapies or should receive taxanes or investigational drugs like EPI-506 or galeterone. Both EPI-506 (NCT02606123) and galeterone (NCT02438007) are in clinical trials and are proposed to have efficacy against lesions that are positive for AR-Vs. AR activation function-1 (AF-1) is common to the N-terminal domains of full-length AR and AR-Vs. Here, we provide proof of concept for developing imaging compounds that directly bind AR AF-1 to detect both AR-Vs and full-length AR. 123I-EPI-002 had specific binding to AR AF-1, which enabled direct visualization of CRPC xenografts that express full-length AR and AR-Vs. Our findings highlight the potential of 123I-EPI-002 as an imaging agent for the detection of full-length AR and AR-Vs in CRPC.

Radiolabeled B9958 Derivatives for Imaging Bradykinin B1 Receptor Expression with Positron Emission Tomography: Effect of the Radiolabel-Chelator Complex on Biodistribution and Tumor Uptake.

Bradykinin B1 receptor (B1R), which is upregulated in a variety of malignancies, is an attractive cancer imaging biomarker. In this study we optimized the selection of radiolabel-chelator complex to improve tumor uptake and tumor-to-background contrast of radiolabeled analogues of B9958 (Lys-Lys-Arg-Pro-Hyp-Gly-Cpg-Ser-d-Tic-Cpg), a potent B1R antagonist. Peptide sequences were assembled on solid phase. Cold standards were prepared by incubating DOTA-/NODA-conjugated peptides with GaCl3, and by incubating AlOH-NODA-conjugated peptide with NaF. Binding affinities were measured via in vitro competition binding assays. (68)Ga and (18)F labeling experiments were performed in acidic buffer and purified by HPLC. Imaging/biodistribution studies were performed in mice bearing both B1R-positive (B1R+) HEK293T::hB1R and B1R-negative (B1R-) HEK293T tumors. Z02176 (Ga-DOTA-Pip-B9958; Pip: 4-amino-(1-carboxymethyl)piperidine), Z02137 (Ga-NODA-Mpaa-Pip-B9958; Mpaa: 4-methylphenylacetic acid), and Z04139 (AlF-NODA-Mpaa-Pip-B9958) bound hB1R with high affinity (Ki = 1.4-2.5 nM). (68)Ga-/(18)F-labeled peptides were obtained on average in ≥32% decay-corrected radiochemical yield with >99% radiochemical purity and 100-261 GBq/µmol specific activity. Biodistribution/imaging studies at 1 h postinjection showed that all tracers cleared rapidly from background tissues (except kidneys) and were excreted predominantly via the renal pathway. Only kidneys, bladders, and B1R+ tumors were clearly visualized in PET images. Uptake in B1R+ tumor was higher by using (68)Ga-Z02176 (28.9 ± 6.21 %ID/g) and (18)F-Z04139 (22.6 ± 3.41 %ID/g) than (68)Ga-Z02137 (14.0 ± 4.86 %ID/g). The B1R+ tumor-to-blood and B1R+ tumor-to-muscle contrast ratios were also higher for (68)Ga-Z02176 (56.1 ± 17.3 and 167 ± 57.6) and (18)F-Z04139 (58.0 ± 20.9 and 173 ± 42.9) than (68)Ga-Z02137 (34.3 ± 15.2 and 103 ± 30.2). With improved target-to-background contrast (68)Ga-Z02176 and (18)F-Z04139 are promising for imaging B1R expression in cancers with PET.

Trimeric Radiofluorinated Sulfonamide Derivatives to Achieve In Vivo Selectivity for Carbonic Anhydrase IX-Targeted PET Imaging.

UNLABELLED: Carbonic anhydrase IX (CA-IX), a transmembrane enzyme, mediates cell survival under hypoxic conditions and is overexpressed in solid malignancies. In this study, we synthesized four (18)F sulfonamide derivatives and evaluated their potential for imaging CA-IX expression with PET. METHODS: Azide derivatives of 2 carbonic anhydrase inhibitors, 4-(2-aminoethyl)benzenesulfonamide (AEBS) and 4-aminobenzensulfonamide (ABS), were coupled to radiosynthons with either 1 or 3 alkynes and a pendent ammoniomethyltrifluoroborate (AmBF3) to generate monovalent or trivalent enzyme inhibitors. Binding affinity to CA-IX and other CA isoforms was determined via a stopped-flow, CA-catalyzed CO2 hydration assay. Tracers were radiolabeled via (18)F-(19)F isotope exchange reactions. Imaging/biodistribution studies were performed using HT-29 tumor-bearing immunocompromised mice. RESULTS: Monomeric AmBF3-AEBS and AmBF3-ABS were obtained in 41% and 40% yields, whereas trimeric AmBF3-(AEBS)3 and AmBF3-(ABS)3 were obtained in 47% and 55% yields, respectively. Derivatives bound CA-I, -II, -IX, and -XII with good affinity (0.49-100.3 nM). (18)F-labeled sulfonamides were obtained in 16.3%-36.8% non-decay-corrected radiochemical yields, with 40-207 GBq/µmol specific activity and greater than 95% radiochemical purity. Biodistribution/imaging studies showed that the tracers were excreted through both renal and hepatobiliary pathways. At 1 h after injection, HT-29 tumor xenografts were clearly visualized in PET images with modest contrast for all 4 tracers. Tumor uptake was 2-fold higher for monovalent tracers (∼0.60 percentage injected dose per gram [%ID/g]) than for trivalent tracers (∼0.30 %ID/g); however, tumor-to-background ratios were significantly better for (18)F-AmBF3-(ABS)3. Preblocking with acetazolamide reduced more than 80% uptake of (18)F-AmBF3-(ABS)3 in HT-29 tumors. CONCLUSION: Our data suggest that trimerization of an otherwise nonspecific CA inhibitor greatly enhances the selectivity for CA-IX in vivo and represents a promising strategy for creating multivalent enzyme inhibitors for selectively imaging extracellular enzyme activity by PET.

Imaging Bradykinin B1 Receptor with 68Ga-Labeled [des-Arg10]Kallidin Derivatives: Effect of the Linker on Biodistribution and Tumor Uptake.

Bradykinin B1 receptor (B1R) that is overexpressed in cancers but minimally expressed in normal healthy tissues represents an attractive biomarker for the development of cancer imaging agents. The goal of this study was to evaluate the effect of different linkers on the pharmacokinetics and tumor uptake of a B1R-targeting radio-peptide sequence, 68Ga-DOTA-linker-Lys-Arg-Pro-Hyp-Gly-Cha-Ser-Pro-Leu. Four peptides, SH01078, P03034, P04115, and P04168, with 6-aminohexanoic acid, 9-amino-4,7-dioxanonanoic acid, Gly-Gly, and 4-amino-(1-carboxymethyl)piperidine, respectively, as the linker were synthesized and evaluated. In vitro competition binding assays showed that the Ki values of SH01078, P03034, P04115, and P04168 were 27.8±4.9, 16.0±1.9, 11.4±2.5, and 3.6±0.2 nM, respectively. Imaging and biodistribution studies were performed in mice bearing both B1R-positive HEK293T::hB1R and B1R-negative HEK293T tumors. All tracers showed mainly renal excretion with excellent tumor visualization and minimal background activity except for kidneys and bladder. The average uptake of 68Ga-labeled SH01078, P03034, and P04115 in HEK293T::hB1R tumor was similar (1.96-2.17%ID/g) at 1 h postinjection. 68Ga-P04168 generated higher HEK293T::hB1R tumor uptake (4.15±1.13%ID/g) and lower background activity, leading to a >2-fold improvement in HEK293T::hB1R tumor-to-background (HEK293T tumor, blood, muscle, and liver) contrasts over those of 68Ga-labeled SH01078, P03034, and P04115. Our results indicate that the choice of linker affects binding affinity, pharmacokinetics, and tumor targeting. The use of the cationic 4-amino-(1-carboxymethyl)piperidine linker improved tumor visualization, and the resulting 68Ga-P04168 might be promising for clinical application for imaging B1R-expressing tumors with positron emission tomography.

Nitroimidazole-Containing H2dedpa and H2CHXdedpa Derivatives as Potential PET Imaging Agents of Hypoxia with (68)Ga.

(68)Ga is an attractive radiometal for use in positron emission tomography (PET) imaging. The success of (68)Ga-based agents is dependent on a chelator that exhibits rapid radiometal incorporation, and strong kinetic inertness to prevent transchelation of (68)Ga in vivo. The linear chelating agents H2dedpa (1,2-[[6-carboxypyridin-2-yl]methylamino]ethane) and H2CHXdedpa (CHX = cyclohexyl/cyclohexane) (N4O2) have recently been developed that bind Ga(3+) quickly and under mild conditions, ideal properties to be incorporated into a (68)Ga PET imaging agent. Herein, nitroimidazole (NI) derivatives of H2dedpa and H2CHXdedpa to investigate specific targeting of hypoxic tumor cells are investigated, given that NI can be reduced and retained exclusively in hypoxic cells. Nine N,N'-bis-alkylated derivatives of H2dedpa and H2CHXdedpa have been synthesized; they have been screened for their ability to bind gallium, and cyclic voltammetry of nonradioactive complexes was performed to probe the redox cycling mechanism of NI. The compounds were radiolabeled with (67)Ga and (68)Ga and show promising radiolabeling efficiencies (>99%) when labeled at 10(-5) M for 10 min at room temperature. Moreover, stability studies (via apo-transferrin challenge, 37 °C) show that the (67)Ga complexes exhibit exceptional stability (86-99% intact) after 2 h. In vitro uptake studies under hypoxic (0.5% O2) and normoxic (21% O2) conditions in three cancerous cell lines [HT-29 (colon), LCC6(HER-2) (breast), and CHO (Chinese hamster ovarian)] were performed. Of the four H2dedpa or H2CHXdedpa NI derivatives tested, all showed preferential uptake in hypoxic cells compared to normoxic cells with hypoxic/normoxic ratios as high as 7.9 ± 2.7 after 120 min. The results suggest that these novel bis-alkylated NI-containing H2dedpa and H2CHXdedpa ligands would be ideal candidates for further testing in vivo for PET imaging of hypoxia with (68)Ga.