Rational Design and Pharmacomodulation of 18F-Labeled Biotin/FAPI-Conjugated Heterodimers.

Due to the complex heterogeneity in different cancer types, the heterodimeric strategy has been intensively practiced to improve the effectiveness of tumor diagnostics. In this study, we developed a series of novel 18F-labeled biotin/FAPI-conjugated heterobivalent radioligands ([18F]AlF-NSFB, [18F]AlF-NSFBP2, and [18F]AlF-NSFBP4), synergistically targeting both fibroblast activation protein (FAP) and biotin receptor (BR), to enhance specific tumor uptake and retention. The in vitro and in vivo biological properties of these dual-targeting tracers were evaluated, with a particular focus on positron emission tomography imaging in A549 and HT1080-FAP tumor-bearing mice. Notably, in comparison to the corresponding FAP-targeted monomer [18F]AlF-NSF, biotin/FAPI-conjugated heterodimers exhibited a high uptake in tumor and prolong retention. In conclusion, as a proof-of-concept study, the findings validated the superiority of biotin/FAPI-conjugated heterodimers and the positive influence of biotin and linker on pharmacokinetics of radioligands. Within them, the bispecific [18F]AlF-NSFBP4 holds significant promise as a candidate for further clinical translational studies.

Synthesis and preliminary evaluation of benzylaminoimidazoline derivatives as novel norepinephrine transporter ligands.

A series of benzylaminoimidazoline derivatives was synthesized and evaluated for norepinephrine transporter (NET) targeting. Among them, N-(3-iodobenzyl)-4,5-dihydro-1H-imidazol-2-amine (Compound 9) displayed the highest affinity for NET (IC50 = 5.65 ± 0.97 µM). The corresponding radiotracer [125 I]9 was further prepared by copper-mediated radioiodination and evaluated both in vitro and in vivo. The cellular uptake results suggested that [125 I]9 was specifically taken up by the NET-expressing SK-N-SH cell line. Biodistribution studies showed that [125 I]9 accumulated in the heart (5.54 ± 1.24 %ID/g at 5 min p.i. and 0.79 ± 0.08 %ID/g at 2 h p.i.) and adrenal gland (14.83 ± 3.47 %ID/g at 5 min p.i. and 3.87 ± 0.24 %ID/g at 2 h p.i.). The uptake in the heart and adrenal gland could be significantly inhibited by preinjection of desipramine (DMI). These results indicated that the benzylaminoimidazoline derivatives retained affinity for NET, which could provide structure-activity relationship data for further studies.

A new method for identifying industrial clustering using the standard deviational ellipse.

Industrial agglomeration has attracted extensive attention from economists and geographers, yet it is still a challenge to identify the multi-agglomeration spatial structure and degree of industrial agglomeration in continuous space-there is still a lack of a more targeted industrial clustering method. The clustering method and the standard deviational ellipse (simply, ellipse) model have advantages in identifying the spatial structure and representing spatial information respectively. On this basis, we propose an ellipse-based approach to identifying industrial clusters. Our ellipse-based approach rests upon group nearest neighbor using the group-based nearest neighbor (GNN) ordering and spatial compactness matrix, where a number of point sequences with varying lengths, generated under the GNN ordering, are characterized by an ellipse and the elliptical parameters of these point sequences formulate the values and structure of the compactness matrix. Clustering is reformulated to identify ellipses with a specified parameter among a number of potential candidate ellipses, with significant changes (especially in the area) used as the cutoff criterion for determining the clusters' border point. Our approach is illustrated in the location pattern of firms in Shanghai City, China in comparison with four well-known clustering methods. With the combination of elliptical parameters and spatial compactness, our approach may bring a new analytical ground for future industrial clustering research.

68Ga-FAPI PET/CT for molecular assessment of fibroblast activation in right heart in pulmonary arterial hypertension: a single-center, pilot study.

BACKGROUND: Positron emission tomography (PET) imaging with radiolabeled fibroblasts activation protein inhibitor (FAPI) provides the opportunity to directly visualize fibrosis. This study aimed to investigate the feasibility of 68Ga-FAPI PET imaging in assessing right ventricular (RV) fibrotic remodeling and the relationship between FAPI uptake with parameters of pulmonary hemodynamics and cardiac function in pulmonary arterial hypertension (PAH) patients. METHODS: In this pilot study, sixteen PAH patients were enrolled to participate in cardiac 68Ga-FAPI PET/CT imaging. All patients underwent right heart catheterization and echocardiography for assessment of pulmonary hemodynamics and cardiac function within seven days. Cardiac FAPI uptake was visually assessed and quantified as maximum standardized uptake value (SUVmax). RESULTS: Twelve PAH patients exhibited FAPI uptake in RV free wall and insertion point. The overall activity of FAPI accumulated in the RV free wall (SUVmax: 2.5 ± 1.8, P < 0.001) and insertion point (SUVmax:2.5 ± 1.7, P < 0.001) was significantly upregulated compared to left ventricle (SUVmax:1.5 ± 0.5). Patients with tricuspid annular plane systolic excursion (TAPSE) < 17 mm presented significantly higher uptake than those with TAPSE ≥ 17 mm in both RV free wall (SUVmax: 3.4 ± 1.9 vs 1.7 ± 1.1, P = 0.010) and insertion point (SUVmax: 3.4 ± 1.9 vs 1.6 ± 0.7, P = 0.028), indicating RV uptake of FAPI was associated with RV dysfunction. There was significant positive correlation between cardiac FAPI uptake and total pulmonary resistance and the level of N-terminal pro b-type natriuretic peptide. CONCLUSIONS: 68Ga-FAPI PET/CT imaging is feasible to directly visualize fibrotic remodeling of RV in patients with PAH.

Rational Design and Pharmacomodulation of Protein-Binding Theranostic Radioligands for Targeting the Fibroblast Activation Protein.

The fibroblast activation protein (FAP), overexpressed on cancer-associated fibroblasts (CAFs), has become a valuable target for tumor diagnosis and therapy. However, most FAP-based radioligands show insufficient tumor uptake and retention. In this study, three novel albumin-binding FAP ligands (denoted as FSDD0I, FSDD1I, and FSDD3I) were labeled with 68Ga and 177Lu to overcome these limitations. Cell-based studies and molecular docking assays were performed to identify the specificity and protein-binding properties for FAP. Positron emission tomography (PET) scans in human hepatocellular carcinoma patient-derived xenografts (HCC-PDXs) animal models revealed longer blood retention of 68Ga-FSDD0I than 68Ga-FAPI-04, 68Ga-FSDD1I, and 68Ga-FSDD3I. Remarkably, 68Ga-FSDD3I had prominent tumor-to-nontarget (T/NT) ratios. The prominent tumor retention properties of 177Lu-FSDD0I in single photon emission computed tomography (SPECT) imaging and biodistribution studies were demonstrated. In summary, this study reports a proof-of-concept study of albumin-binding radioligands for FAP-targeted imaging and targeted radionuclide therapy (TRT).

Novel [18F]-Labeled Meta-Bromobenzylguanidine Derivatives: Potential Positron Emission Tomography Imaging Probes for the Norepinephrine Transporter.

To develop novel norepinephrine transporter (NET)-targeting positron emission tomography (PET) probes with optimal pharmacokinetic properties, a series of meta-bromobenzylguanidine derivatives was synthesized. 4-Fluorodiethoxyethane-3-bromobenzylguanidine (compound 12) showed relatively good affinity for the NET (IC50 = 1.00 ± 0.04 µM). The corresponding radiotracer 18F-12 was prepared in high radiochemical purity (>98%) via a three-step method. The in vitro cellular uptake results demonstrated that 18F-12 was specifically taken up by NET-expressing SK-N-SH cells by the uptake-1 mechanism. Biodistribution studies in mice showed that 18F-12 exhibited high cardiac uptake (10.45 ± 0.66 %ID/g at 5 min p.i. and 6.44 ± 0.40 %ID/g at 120 min p.i.), faster liver clearance, and a lower dose of absorbed radiation than [123I]-labeled meta-iodobenzylguanidine ([123I]MIBG). Small animal PET imaging confirmed the high heart-to-background ratio of 18F-12 and the uptake-1 mechanism specific for the NET in rats, indicating its potential as a promising PET radiotracer for cardiac sympathetic nerve imaging.

99mTc-3SPboroxime: A neutral 99mTc(III) radiotracer with high heart uptake and long myocardial retention.

BACKGROUND: 99mTc-3SPboroxime is a 99mTc(III) complex with high initial heart uptake comparable to that of 99mTc-Teboroxime, but with significantly longer myocardial retention in Sprague-Dawley rats. This study was performed to demonstrate its feasibility on myocardial perfusion imaging and myocardial blood flow quantification in swine models. METHODS: Dynamic single-photon emission computed tomography (SPECT) studies with 99mTc-3SPboroxime were performed in normal (with/without dipyridamole, n = 9) and acute myocardial infarction (AMI) swine (n = 3) in comparison with 99mTc-Teboroxime and 99mTc-Sestamibi. List-mode acquisitions were immediately started after injection and continued for 15 minutes. Regions of interest were drawn on heart (infarct and remote areas of AMI swine) and liver to generate time activity curves. Heart/liver and infarct/remote radioactivity ratios were calculated. One-tissue compartment model was implemented to obtain K1 and K2 values. RESULTS: The initial heart uptake of 99mTc-3SPboroxime was close to that of 99mTc-Teboroxime, but higher than that of 99mTc-Sestamibi. 99mTc-3SPboroxime had a myocardial retention longer than that of 99mTc-Teboroxime. The heart/liver ratio of 99mTc-3SPboroxime was higher than that of 99mTc-Teboroxime at later stage (13-15 minutes post-injection). The K1 value of 99mTc-3SPboroxime was much higher than that of 99mTc-Sestamibi, and the K2 value was significantly lower than that of 99mTc-Teboroxime both at rest and dipyridamole stress (rest K1: 0.63 ± 0.11 vs 0.40 ± 0.04 mL·min-1·g-1, P = 0.027; stress K1: 0.89 ± 0.05 vs 0.54 ± 0.08 mL·min-1·g-1, P = 0.031; rest K2: 0.22 ± 0.04 vs 0.33 ± 0.11 mL·min-1·g-1, P = 0.003; stress K2: 0.31 ± 0.03 vs 0.60 ± 0.30 mL·min-1·g-1, P = 0.047). High quality SPECT images could be obtained in any of the 5 minutes windows over the first 15 minutes after injection of 99mTc-3SPboroxime in normal and AMI swine models. Apical and anterior perfusion defects were clearly visualized in AMI swine. CONCLUSION: 99mTc-3SPboroxime is a promising radiotracer for future clinical translation considering its heart uptake, heart/liver ratio and SPECT image quality, as well as the advantage over 99mTc-Sestamibi in the definition of stress flow.

Runx2 (Runt-Related Transcription Factor 2)-Mediated Microcalcification Is a Novel Pathological Characteristic and Potential Mediator of Abdominal Aortic Aneurysm.

OBJECTIVE: Abdominal aortic aneurysms (AAAs) are highly lethal diseases without effective clinical predictors and therapeutic targets. Vascular microcalcification, as detected by fluorine-18-sodium fluoride, has recently been recognized as a valuable indicator in predicting atherosclerotic plaque rupture and AAA expansion. However, whether vascular microcalcification involved in the pathogenesis of AAA remains elusive. Approach and Results: Microcalcification was analyzed in human aneurysmal aortas histologically and in AngII (angiotensin II)-infused ApoE-/- mouse aortas by fluorine-18-sodium fluoride positron emission tomography and X-ray computed tomography scanning in chronological order in live animals. AAA patients' aortic tissue showed markedly enhanced microcalcification in the aortic media within the area proximal to elastic fiber degradation, compared with non-AAA patients. Enhanced fluorine-18-sodium fluoride uptake preceded significant aortic expansion in mice. Microcalcification-positive mice on day 7 of AngII infusion showed dramatic aortic expansion on subsequent days 14 to 28, whereas microcalcification-negative AngII-infused mice and saline-induced mice did not develop AAA. The application of hydroxyapatite, the main component of microcalcification, aggravated AngII-induced AAA formation in vivo. RNA-sequencing analysis of the suprarenal aortas of 4-day-AngII-infused ApoE-/- mice and bioinformatics analysis with ChIP-Atlas database identified the potential involvement of the osteogenic transcriptional factor Runx2 (runt-related transcription factor 2) in AAA. Consistently, vascular smooth muscle cell-specific Runx2 deficiency markedly repressed AngII-induced AAA formation in the ApoE-/- mice compared with the control littermates. CONCLUSIONS: Our studies have revealed microcalcification as a novel pathological characteristic and potential mediator of AAA, and targeting microcalcification may represent a promising strategy for AAA prevention and treatment.

68Ga-labeled dimeric and trimeric cyclic RGD peptides as potential PET radiotracers for imaging gliomas.

68Ga-labeled cyclic RGD dimers and trimer were evaluated as PET radiotracers. It was found that the linker group had little impact on αvß3 binding affinity of RGD dimers, which share similar αvß3 binding affinity with the RGD trimer despite of their different multiplicity. Biodistribution properties of 68Ga radiotracers depend on RGD peptides and radiometal chelates. Among the 68Ga radiotracers evaluated, 68Ga-I2P-RGD2 has the best tumor uptake with good tumor-to-background ratios, and is a good PET radiotracer for imaging gliomas.

Sulfonyl-Containing Boronate Caps for Optimization of Biological Properties of 99mTc(III) Radiotracers [99mTcCl(CDO)(CDOH)2B-R] (CDOH2 = Cyclohexanedione Dioxime).

In this study, different boronate caps were used to optimize biodistribution properties of radiotracers [99mTcCl(CDO)(CDOH)2B-R] (1, R = 3S; 2, R = 3SP; 3, R = 3MS; 4, R = 3DMS; 5, R = 3MSB; 6, R = 3MMS; 7, R = 3MSA; 8, R = 3DMSA; 9, R = 4S; 10, R = 4MS; 11, R = 4MSB). Among the 11 new 99mTc radiotracers, 2 shows the most promising characteristics of an optimal heart imaging agent. Its initial heart uptake is close to that of 99mTc-Teboroxime, but its heart retention time is significantly longer. Its heart/liver, heart/lung, and heart/muscle ratios are also better than those of 99mTc-Teboroxime. The SPECT image quality with 2 in SD rats is better than that with 99mTc-Teboroxime. The high initial heart uptake, long heart retention, and high heart/background ratios make 2 an excellent SPECT radiotracer for MPI.

Novel Approach for 99mTc-Labeling of Red Blood Cells: Evaluation of 99mTc-4SAboroxime as a Blood Pool Imaging Agent.

Angiography with radiolabeled red blood cells (RBCs) plays an important role in diagnosis and prognosis in vascular diseases. Both in vitro and in vivo methods have been developed for 99mTc-labeling of RBCs. However, these methods are complicated and lack reproducibility. Therefore, it is highly desirable to develop an alternative method for routine 99mTc-labeling of RBCs. In this report, we present a novel approach for 99mTc-labeling of RBCs. We prepared a new 99mTc(III) radiotracer [99mTcCl(CDO)(CDOH)2B-4AS] (99mTc-4ASboroxime: 4AS-B(OH)2 = 4-aminosulfonylphenyl)boronic acid, and CDOH2 = cyclohexanedione dioxime) in >95% radiochemical purity. Imaging and biodistribution studies were performed in Sprague-Dawley (SD) rats. It was found that the blood radioactivity was ∼6.0%ID/g (∼90% injected dose for 200-225 g SD rats) for 99mTc-4ASboroxime with low uptake in the myocardium, kidneys, liver, lungs, and muscle, most likely due to lack of leakage of 99mTc-labeled RBCs from the intravascular space. The blood radioactivity was almost unchanged over the 2 h period, suggesting that the binding of 99mTc-4ASboroxime to blood components (cells, proteins, and plasma) is stable. The results from γ-counting of the isolated blood components showed that 99mTc-4ASboroxime had >95% of blood radioactivity binding to RBCs, ∼1% to albumin, and ∼3% remaining free in blood plasma, demonstrating its RBC-specificity. The results from imaging studies in SD rats indicated that 99mTc-4ASboroxime is predominantly distributed in the blood pool. Main blood vessels were well delineated in the head/neck and abdominal regions. This statement was further substantiated by the results from imaging studies in pigs. 99mTc-4ASboroxime is an excellent blood pool agent with the potential for diagnosis and prognosis of vascular diseases.

Effect of methoxy group position on biological properties of 18F-labeled benzyl triphenylphosphonium cations.

INTRODUCTION: 18F-labeled phosphonium cations targeting mitochondrial membrane potential would be promising for positron emission tomography (PET) myocardial perfusion imaging (MPI). The purpose of this study was to examine the influence of additional methoxy group and its different positions on myocardium uptake and pharmacokinetics properties of 18F-labeled benzyl triphenylphosphonium cations. METHOD: In this study, three novel 18F-labeled phosphonium cations, [18F]4-(fluoromethyl)benzyltris(4-methoxyphenyl) phosphonium cation (1b), [18F]4-(fluoromethyl)benzyltris(2-methoxyphenyl) phosphonium cation (2b) and [18F]4-(fluoromethyl)benzyltris(3-methoxyphenyl) phosphonium cation (3b), were efficiently prepared by a One-Pot method starting from the substitution of non-carried-added fluoride-18. Radiotracers were purified by HPLC. Physicochemical properties, in vitro cell uptake assay, in vivo mice biodistribution and rat micro-PET imaging were investigated. RESULTS: Results suggested that the position of methoxy group exhibited significant effect on the biological properties of 18F-labeled benzyl triphenylphosphonium cations. The addition of methoxy group on orth- or meta-position of the radiotracers accelerated the radioactivity clearance from liver. The para-radiotracer had the highest uptake in the heart and other non-targeting organs. According to the biodistribution data, 2b (ortho-) displayed the fastest liver clearance and highest heart-to-background ratios. And its rat micro-PET images at 60min post-injection revealed a good visualization of heart and favorable heart-to-background contrast. Nevertheless, 2b exhibited a lower initial liver uptake and quicker liver clearance compared with 99mTc-sestamibi. CONCLUSION: The ortho- compound (2b) displayed the most favorable biological properties as a potential MPI agent to acquire high contrast images early after injection.

Iminodiacetic acid as bifunctional linker for dimerization of cyclic RGD peptides.

INTRODUCTION: In this study, I2P-RGD2 was used as the example to illustrate a novel approach for dimerization of cyclic RGD peptides. The main objective of this study was to explore the impact of bifunctional linkers (glutamic acid vs. iminodiacetic acid) on tumor-targeting capability and excretion kinetics of the 99mTc-labeled dimeric cyclic RGD peptides. METHODS: HYNIC-I2P-RGD2 was prepared by reacting I2P-RGD2 with HYNIC-OSu in the presence of diisopropylethylamine, and was evaluated for its αvß3 binding affinity against 125I-echistatin bound to U87MG glioma cells. 99mTc-I2P-RGD2 was prepared with high specific activity (~185GBq/µmol). The athymic nude mice bearing U87MG glioma xenografts were used to evaluate its biodistribution properties and image quality in comparison with those of 99mTc-3P-RGD2. RESULTS: The IC50 value for HYNIC-I2P-RGD2 was determined to be 39±6nM, which was very close to that (IC50=33±5nM) of HYNIC-3P-RGD2. Replacing glutamic acid with iminodiacetic acid had little impact on αvß3 binding affinity of cyclic RGD peptides. 99mTc-I2P-RGD2 and 99mTc-3P-RGD2 shared similar tumor uptake values over the 2h period, and its αvß3-specificity was demonstrated by a blocking experiment. The uptake of 99mTc-I2P-RGD2 was significantly lower than 99mTc-3P-RGD2 in the liver and kidneys. The U87MG glioma tumors were visualized by SPECT with excellent contrast using both 99mTc-I2P-RGD2 and 99mTc-3P-RGD2. CONCLUSION: Iminodiacetic acid is an excellent bifunctional linker for dimerization of cyclic RGD peptides. Bifunctional linkers have significant impact on the excretion kinetics of 99mTc radiotracers. Because of its lower liver uptake and better tumor/liver ratios, 99mTc-I2P-RGD2 may have advantages over 99mTc-3P-RGD2 for diagnosis of tumors in chest region.

Synthesis and Evaluation of (18)F-labeled Pyridaben Analogues for Myocardial Perfusion Imaging in Mice, Rats and Chinese mini-swine.

This study reports three novel (18)F-labeled pyridaben analogues for potential myocardial perfusion imaging (MPI). Three precursors and the corresponding nonradioactive compounds were synthesized and characterized. The radiolabeled tracers were obtained by substituting tosyl with (18)F. The total radiosynthesis time of these tracers was 70-90 min. Typical decay-corrected radiochemical yields were 47-58%, with high radiochemical purities (>98%). Tracers were evaluated as MPI agents in vitro, ex vivo and in vivo. In the mouse biodistribution study, all three radiotracers showed high initial heart uptake (34-54% ID/g at 2 min after injection) and fast liver clearance. In the microPET imaging study, [(18)F]Fmpp2 produced heart images with good quality in both mice and rats. In the whole-body PET/CT images of mini-swine, [(18)F]Fmpp2 showed excellent initial heart standardized uptake value (SUV) (7.12 at 5 min p.i.) and good retention (5.75 at 120 min p.i.). The heart/liver SUV ratios were 4.12, 5.42 and 5.99 at 30, 60 and 120 min after injection, respectively. The favorable biological properties of [(18)F]Fmpp2 suggest that it is worth further investigation as a potential MPI agent.

Comparison of biological properties of 99mTc-labeled cyclic RGD Peptide trimer and dimer useful as SPECT radiotracers for tumor imaging.

INTRODUCTION: This study sought to evaluate a 99mTc-labeled trimeric cyclic RGD peptide (99mTc-4P-RGD3) as the new radiotracer for tumor imaging. The objective was to compare its biological properties with those of 99mTc-3P-RGD2 in the same animal model. METHODS: HYNIC-4P-RGD3 was prepared by reacting 4P-RGD3 with excess HYNIC-OSu in the presence of diisopropylethylamine. 99mTc-4P-RGD3 was prepared using a kit formulation, and evaluated for its tumor-targeting capability and biodistribution properties in the BALB/c nude mice with U87MG human glioma xenografts. Planar and SPECT imaging studies were performed in athymic nude mice with U87MG glioma xenografts. For comparison purpose, 99mTc-3P-RGD2 (a αvß3-targeted radiotracer currently under clinical evaluation for tumor imaging in cancer patients) was also evaluated in the same animal models. Blocking experiments were used to demonstrate the αvß3 specificity of 99mTc-4P-RGD3. RESULTS: 99mTc-4P-RGD3 was prepared with >95% RCP and high specific activity (~200GBq/µmol). 99mTc-4P-RGD3 and 99mTc-3P-RGD2 shared almost identical tumor uptake and similar biodistribution properties. 99mTc-4P-RGD3 had higher uptake than 99mTc-3P-RGD2 in the intestines and kidneys; but it showed better metabolic stability. The U87MG tumors were clearly visualized by SPECT with excellent contrast with 99mTc-4P-RGD3 and 99mTc-3P-RGD2. CONCLUSION: Increasing peptide multiplicity from 3P-RGD2 to 4P-RGD3 offers no advantages with respect to the tumor-targeting capability. 99mTc-4P-RGD3 is as good a SPECT radiotracer as 99mTc-3P-RGD2 for imaging αvß3-positive tumors.

Synthesis and bioevaluation of 4-chloro-2-tert-butyl-5-[2-[[1-[2-[(18) F]fluroethyl]-1H-1,2,3-triazol-4-yl]methyl]phenylmethoxy]-3(2H)-pyridazinone as potential myocardial perfusion imaging agent with PET.

This study reports the synthesis and characterization of 4-chloro-2-tert-butyl-5-[2-[[1-[2-[(18) F]fluroethyl]-1H-1,2,3-triazol-4-yl]methyl]phenylmethoxy]-3(2H)-pyridazinone ([(18) F]Fmp2) for myocardial perfusion imaging (MPI). The tosylate precursor and non-radioactive compound [(19) F]Fmp2 were synthesized and characterized by infrared, (1) H-NMR, (13) C-NMR, and mass spectra (MS). The radiotracer [(18) F]Fmp2 was obtained by one-step nucleophilic substitution of tosyl with (18) F, and evaluated as an MPI agent in vitro and in vivo. Starting from [(18) F]KF/K222 solution, the typical decay-corrected radiochemical yield (RCY) was 38 ± 8.8% with high radiochemical purity (>98%). The specific activity was calculated as 10 GBq/µmol at the end of synthesis determined by HPLC analysis. In the mice biodistribution, [(18) F]Fmp2 showed very high initial heart uptake (53.35 ± 5.47 %ID/g at 2 min after injection) and remarkable retention. The heart/liver, heart/lung, and heart/blood ratios were 7.98, 8.20, and 53.13, respectively at 2 min post-injection. In the Positron Emission Tomography (PET) imaging study of Chinese mini-swine, the standardized uptake value of the liver decreased modestly during the 2 h post-injection, while the heart uptake and heart/liver ratios continued to increase with time. [(18) F]Fmp2 exhibited good stability, high heart uptake and low lung uptake in mice and Chinese mini-swine. It may be worthy of further modification to improve liver clearance for MPI in the future.

Synthesis and Bio-Evaluation of New (18) F-Labeled Pyridaben Analogs with Improved Stability for Myocardial Perfusion Imaging in Mice.

To improve the stability of (18) F-labeled pyridaben analogs for myocardial perfusion imaging, three new analogs of pyridaben ([(18) F]FPTP2, [(18) F]FPTP-P2, and [(18) F]FPTP-P3) were synthesized with 'side chain' modifications. The radiolabeled tracers and corresponding non-radioactive compounds were obtained by substituting tosyl group with (18/19) F. The effect of structure modification on myocardial targeting and physicochemical properties of new tracers were evaluated in vitro and in vivo. The total radiosynthesis time of these tracers was approximately 70-90 min with high decay-corrected radiochemical yields (36-65%) and good radiochemical purity (> 98%). These lipophilic tracers exhibited obvious improved stability in water. Studies of their biodistribution in normal Kunming mice demonstrated that [(18) F]FPTP2 exhibited very high initial heart uptake (39.70 ± 2.81 %ID/g at 2 min after injection) and low background in the liver, blood, and soft tissues. The heart-to-liver, heart-to-lung, and heart-to-blood ratios were 3.59, 19.34, and 67.34 at 15 min postinjection, respectively. Favorable myocardial targeting property and remarkable improvement of stability of [(18) F]FPTP2 suggest that the substitution of the phenyl 'sidechain' with other non-phenyl rings has no effect on the myocardial targeting property of (18) F-labeled pyridaben analogs.

Synthesis and preliminary evaluation of novel (99m)Tc-labeled folate derivative via click reaction for SPECT imaging.

The folate receptor is over expressed in a wide variety of human tumors. In this study, a novel (99m)Tc-labeled folate derivative ((99m)Tc-HYNIC-T-FA) was synthesized as a potential FR-targeting imaging probe and its efficiency was evaluated. This (99m)Tc-complex could be obtained through practical manner and showed improved in vivo characteristics compared with other radiofolates. Thus, this novel (99m)Tc-HYNIC-T-FA compound could serve as a potential imaging agent for folate receptor positive tumors.

Highly efficient one-pot labeling of new phosphonium cations with fluorine-18 as potential PET agents for myocardial perfusion imaging.

Lipophilic cations such as phosphonium salts can accumulate in mitochondria of heart in response to the negative inner-transmembrane potentials. Two phosphonium salts [(18)F]FMBTP and [(18)F]mFMBTP were prepared and evaluated as potential myocardial perfusion imaging (MPI) agents in this study. The cations were radiolabeled via a simplified one-pot method starting from [(18)F]fluoride and followed by physicochemical property tests, in vitro cellular uptake assay, ex vivo mouse biodistribution, and in vivo rat microPET imaging. The total radiosynthesis time was less than 60 min including HPLC purification. The [(18)F] labeled compounds were obtained in high radiolabeling yield (∼50%) and good radiochemical purity (>99%). Both compounds were electropositive, and their log P values at pH 7.4 were 1.16 ± 0.003 (n = 3) and 1.05 ± 0.01 (n = 3), respectively. Both [(18)F]FMBTP and [(18)F]mFMBTP had high heart uptake (25.24 ± 2.97% ID/g and 31.02 ± 0.33% ID/g at 5 min postinjection (p.i.)) in mice with good retention (28.99 ± 3.54% ID/g and 26.82 ± 3.46% ID/g at 120 min p.i.). From the PET images in rats, the cations exhibited high myocardium uptake and fast clearance from liver and small intestine to give high-contrast images across all time points. These phosphonium cations were radiosynthesized via a highly efficient one-pot procedure for potential MPI offering high heart accumulation and rapid nontarget clearance.