Exploring the radiosynthesis and in vitro characteristics of [68Ga]Ga‐DOTA‐Siglec‐9

Vascular adhesion protein 1 is a leukocyte homing‐associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283–297 of sialic acid‐binding IgG‐like lectin 9 (Siglec‐9) “CARLSLSWRGLTLCPSK” bind to vascular adhesion protein 1 and hence makes the radioactive analogues of this compound ([⁶⁸Ga]Ga‐DOTA‐Siglec‐9) interesting as a noninvasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 are presented and compared with previously published methods. A simple, robust radiosynthesis of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 with a yield of 62% (non decay‐corrected) was identified, and it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 were analyzed in vitro in mouse, rat, rabbit, pig, and human plasma and compared with in vivo pig results. The plasma in vitro protein binding of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 was the lowest in the pig followed by rabbit, human, rat, and mouse. It was considerably higher in the in vivo pig experiments. The in vivo stability in pigs was lower than the in vitro stability. Despite considerable species differences, the observed characteristics of [⁶⁸Ga]Ga‐DOTA‐Siglec‐9 are suitable as a positron emission tomography tracer.     

Automated production of [68Ga]Ga‐DOTANOC and [68Ga]Ga‐PSMA‐11 using a TRACERlab FXFN synthesis module

The interest in gallium‐68 labelled positron‐emission tomography probes continues to increase around the world. However, one of the barriers for routine clinical use is the cost of the automated synthesis units for relatively simple labelling procedures. Herein, we describe the adaptation of a TRACERlab FX_FN synthesis module for the automated production of gallium‐68 radiopharmaceuticals using a cation‐exchange cartridge for postprocessing of the ⁶⁸Ge/⁶⁸Ga generator eluate. The recovery of activity from the cartridge was 95.6% to 98.9% using solutions of acidified sodium chloride (5 M with pH = 1‐3). The radiosyntheses of [⁶⁸Ga]Ga‐DOTANOC and [⁶⁸Ga]Ga‐PSMA‐11 were performed using acetate sodium buffer or 4‐(2‐hydroxyethyl)piperazine‐1‐ethanesulfonic acid, with a total duration of 21 and 23 minutes, respectively, including generator elution and radiopharmaceutical dispensing. Activity yields were 77% ± 2% for [⁶⁸Ga]Ga‐PSMA‐11 and 68% ± 3% for [⁶⁸Ga]Ga‐DOTANOC (n > 100). The labelled peptides had a radiochemical purity exceeding 97%, and all quality control parameters were in conformity with the limits prescribed by the European Pharmacopoeia.     

Synthesis and characterization of scVEGF‐PEG‐[68Ga]NOTA and scVEGF‐PEG‐[68Ga]DOTA PET tracers

Vascular endothelial growth factor (VEGF) signaling via vascular endothelial growth factor receptor 2 (VEGFR‐2) on tumor endothelial cells is a critical driver of tumor angiogenesis. Novel anti‐angiogenic drugs target VEGF/VEGFR‐2 signaling and induce changes in VEGFR‐2 prevalence. To monitor VEGFR‐2 prevalence in the course of treatment, we are evaluating ⁶⁸Ga positron emission tomography imaging agents based on macrocyclic chelators, site‐specifically conjugated via polyethylene glycol (PEG) linkers to engineered VEGFR‐2 ligand, single‐chain (sc) VEGF. The ⁶⁸Ga‐labeling was performed at room temperature with NOTA (2,2′,2′′‐(1,4,7‐triazonane‐1,4,7‐triyl) triacetic acid) conjugates or at 90 °C by using either conventional or microwave heating with NOTA and DOTA (2,2′,2′′,2′′′‐(1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrayl) tetraacetic acid) conjugates. The fastest (~2 min) and the highest incorporation (>90%) of ⁶⁸Ga into conjugate that resulted in the highest specific radioactivity (~400 MBq/nmol) was obtained with microwave heating of the conjugates. The bioactivity of the NOTA‐ and DOTA‐containing tracers was validated in 3‐D tissue culture model of 293/KDR cells engineered to express high levels of VEGFR‐2. The NOTA‐containing tracer also displayed a rapid accumulation (~ 20 s after intravenous injection) to steady‐state level in xenograft tumor models. A combination of high specific radioactivity and maintenance of functional activity suggests that scVEGF‐PEG‐[⁶⁸ Ga]NOTA and scVEGF‐PEG‐[⁶⁸ Ga]DOTA might be promising tracers for monitoring VEGFR‐2 prevalence and should be further explored. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and biological evaluation of 68Ga‐labeled Pteroyl‐Lys conjugates for folate receptor‐targeted tumor imaging

In order to develop novel ⁶⁸Ga‐labeled PET tracers for folate receptor imaging, two DOTA‐conjugated Pteroyl‐Lys derivatives, Pteroyl‐Lys‐DOTA and Pteroyl‐Lys‐DAV‐DOTA, were designed, synthesized and radiolabeled with ⁶⁸Ga. Biological evaluations of the two radiotracers were performed with FR‐positive KB cell line and athymic nude mice bearing KB tumors. Both ⁶⁸Ga‐DOTA‐Lys‐Pteroyl and ⁶⁸Ga‐DOTA‐DAV‐Lys‐Pteroyl exhibited receptor specific binding in KB cells in vitro. The tumor uptake values of ⁶⁸Ga‐DOTA‐Lys‐Pteroyl and ⁶⁸Ga‐DOTA‐DAV‐Lys‐Pteroy were 10.06 ± 0.59%ID/g and 11.05 ± 0.60%ID/g at 2 h post‐injection, respectively. Flank KB tumor was clearly visualized with ⁶⁸Ga‐DOTA‐DAV‐Lys‐Pteroyl by Micro‐PET imaging at 2 h post‐injection, suggesting the feasibility of using ⁶⁸Ga‐labeled Pteroyl‐Lys conjugates as a novel class of FR targeted probes.     

A new 68Ga anionic concentration and purification method for automated synthesis of [68Ga]‐DOTA or NODAGA conjugated peptides in high radiochemical purity

The ⁶⁸Ge/⁶⁸Ga generator is of increasing interest for clinical PET. For successful labelling, the eluate has to be purified. The aim of our approach is to improve the existing anionic methods which have a number of advantages compared to other methods but which use high concentrated HCl, and require an additional anionizing step. A new ⁶⁸Ga‐eluate anionic purification method that enables rapid and high efficiency labelling of DOTA and NODAGA conjugated peptides in high radiochemical purity is described. The new method uses NaCl as an alternative Cl^? source to the corrosive HCl and combines the three standard steps in a single step. The recovery yield was ≥90%, and the ⁶⁸Ge breakthrough was in conformity with the European Pharmacopeia limit. An automated labelling of DOTA and NODAGA‐conjugated peptides was performed with the new method, using acetate sodium buffer, with a total duration of 13 min and a radiochemical yield >85%. The labelled peptides have a radiochemical purity exceeding 99% and can be used directly without any further purification step and without the quality control by gas chromatography. Furthermore, the new method has an economic advantage: it offers the possibility to use generator until 20 months after the calibration date.     

Preclinical assessment of 68Ga‐PSMA‐617 entrapped in a microemulsion delivery system for applications in prostate cancer PET/CT imaging

It has in recent years been reported that microemulsion (ME) delivery systems provide an opportunity to improve the efficacy of a therapeutic agent whilst minimising side effects and also offer the advantage of favourable treatment regimens. The prostate‐specific membrane antigen (PSMA) targeting agents PSMA‐11 and PSMA‐617, which accumulate in prostate tumours, allow for [⁶⁸Ga]Ga³⁺‐radiolabelling and positron emission tomography/computed tomography (PET) imaging of PSMA expression in vivo. We herein report the formulation of [⁶⁸Ga]Ga‐PSMA‐617 into a ME ≤40 nm including its evaluation for improved cellular toxicity and in vivo biodistribution. The [⁶⁸Ga]Ga‐PSMA‐617‐ME was tested in vitro for its cytotoxicity to HEK293 and PC3 cells. [⁶⁸Ga]Ga‐PSMA‐617‐ME was administered intravenously in BALB/c mice followed by microPET/computed tomography (CT) imaging and ex vivo biodistribution determination. [⁶⁸Ga]Ga‐PSMA‐617‐ME indicated negligible cellular toxicity at different concentrations. A statistically higher tolerance towards the [⁶⁸Ga]Ga‐PSMA‐617‐ME occurred at 0.125 mg/mL by HEK293 cells compared with PC3 cells. The biodistribution in wild‐type BALB/C mice showed the highest amounts of radioactivity (%ID/g) presented in the kidneys (31%) followed by the small intestine (10%) and stomach (9%); the lowest uptake was seen in the brain (0.5%). The incorporation of [⁶⁸Ga]Ga‐PSMA‐617 into ME was successfully demonstrated and resulted in a stable nontoxic formulation as evaluated by in vitro and in vivo means.     

Development of 68Ga‐labeled fatty acids for their potential use in cardiac metabolic imaging

While [¹¹C]palmitate continues to be a promising tracer for cardiovascular Positron Emission Tomography (PET) imaging, unfavourable logistics due to the short half‐life of ¹¹C (20 min) and cumbersome labeling methodologies are the major impediments that limit its widespread use. In order to circumvent such limitations, an attempt has been made to explore the potential of ⁶⁸Ga‐labeled fatty acid analogs for metabolic imaging owing to the availability of ⁶⁸Ga through a ⁶⁸Ge/⁶⁸Ga generator on an on‐demand basis. In this study, two fatty acid conjugates were synthesized by conjugation of p‐SCN‐benzyl NOTA with the ω‐amino group of 11‐amino undecanoic acid and 12‐amino dodecanoic acid, respectively, under alkaline conditions. Both derivatives were radiolabeled in high yields with ⁶⁸Ga obtained from an in‐house ⁶⁸Ge/⁶⁸Ga generator. Biodistribution studies in Swiss mice showed reasonable myocardial uptake at 2 min for both derivatives (7.4 ± 2.8% ID/g for 11‐carbon fatty acid‐NOTA conjugate and 6.4 ± 2.1% ID/g for 12‐carbon fatty acid‐NOTA conjugate), which cleared rapidly over 30 min. However, significant activity was found in blood for both tracers, with heart/blood ratios observed to be below 0.5 at all time points, diminishing the potential of the synthesized complexes for cardiac imaging. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and evaluation of 68Ga‐HBED‐CC‐EDBE‐folate for positron‐emission tomography imaging of overexpressed folate receptors on CT26 tumor cells

The ⁶⁸Ga is a positron‐emitting radionuclide that can be combined with bifunctional chelating agents and bioactive substances for use as positron‐emission tomography (PET) diagnostic agents. The HBED‐CC is an acyclic chelating agent that is rapidly labeled with ⁶⁸Ga under mild conditions. To target cancer cells, bioactive substances can be conjugated to the carboxyl terminus of HBED‐CC. Because folic acid strongly binds to folate receptors that are overexpressed on the surfaces of many types of cancer cells, it was coupled with HBED‐CC through a small polyethylene glycol‐based linker (EDBE) to generate an active, receptor‐selective targeting system. The HBED‐CC‐EDBE‐folate (HCEF) precursor was readily labeled with ⁶⁸Ga in 5 minutes at room temperature (98% radiochemical yield; 99% radiochemical purity after isolation). In cellular uptake tests, higher uptakes of ⁶⁸Ga‐HCEF were observed for the CT26 and KB cell lines (which express folate receptors) than for the A549 cell line (which does not). Finally, in vivo micro‐PET measurements over 2 hours of binding in BALB/c mice into which CT26 tumors had been transplanted showed the selective accumulation of ⁶⁸Ga‐HCEF in the folate receptor‐expressing CT26 tumors. These results confirmed the potential of ⁶⁸Ga‐HCEF as a PET diagnostic agent for tumors that express folate receptors.     

Preparation of 68Ga‐Mg‐Ca‐phytate colloid and its evaluation as a liver imaging agent

The objective of this study was to investigate the radiosynthesis of ⁶⁸Ga‐Mg‐Ca‐phytate colloid and then characterise the formulation for radiochemical purity (RCP), radioactive particle size distribution, and biodistribution in normal rats. This radiocolloid was prepared by mixing an aqueous solution of phytic acid, ⁶⁸Ga³⁺ ions, a dispersant, Mg²⁺ and Ca²⁺ ions, and then heating the contents at 100°C for 5 minutes. After cooling the vial to 5°C, the solution was basified to pH 5 and stored in the cold. The resulting product contained 92±3% RCP ⁶⁸Ga‐colloidal particles and a low level (8±3%) of soluble ⁶⁸Ga‐Mg‐Ca‐phytate. Particle size experiments defined the radioactive particle population was 6±4% <20 nm, 90±6% 20 to 200 nm, and 4% were >200 nm in diameter. Intravenous injection of the ⁶⁸Ga‐colloid dispersion to rats resulted in 93% uptake by the liver plus spleen, 1% lungs, 1% total blood, and 6% in the carcass after 20 minutes. This optimal formulation remained stable at 5°C for 1½ hours in vitro, and it resulted in the same biodistribution as the formulation prepared at t  = 0 hours. The preclinical data so far indicate that ⁶⁸Ga‐Mg‐Ca‐colloid has excellent potential as a liver imaging agent.     

Synthesis and in vivo evaluation of gallium‐68‐labeled glycine and hippurate conjugates for positron emission tomography renography

The objective of this study was to evaluate four new ⁶⁸Ga‐labeled 1,4,7,10‐cyclododeca‐1,4,7,10‐tetraacetic acid (DOTA)/1,4,7‐triazacyclononane‐1,4,7‐triacetic acid derived (NODAGA)‐glycine/hippurate conjugates and select a lead candidate for potential application in positron emission tomography (PET) renography. The non‐metallated conjugates were synthesized by a solid phase peptide synthesis method. The ⁶⁸Ga labeling was achieved by reacting an excess of the non‐metallated conjugate with ⁶⁸GaCl₄^? at pH ?4.5 and 10‐min incubation either at room temperature for NODAGA or 90 °C for DOTA. Radiochemical purity of all ⁶⁸Ga conjugates was found to be >98%. ⁶⁸Ga‐NODAGA‐glycine displayed the lowest serum protein binding (0.4%) in vitro among the four ⁶⁸Ga conjugates. Biodistribution of ⁶⁸Ga conjugates in healthy Sprague Dawley rats at 1‐h post‐injection revealed an efficient clearance from circulation primarily through the renal–urinary pathway with <0.2% of injected dose per gram remaining in the blood. The kidney/blood and kidney/muscle ratios of ⁶⁸Ga‐NODAGA‐glycine were significantly higher than other ⁶⁸Ga conjugates. On the basis of these results, ⁶⁸Ga‐NODAGA‐glycine was selected as the lead candidate. ⁶⁸Ga‐NODAGA‐glycine PET renograms obtained in healthy rats suggest ⁶⁸Ga‐NODAGA‐glycine as a PET alternate of ^99mTc‐Diethylenetriaminepentaacetic acid (DTPA).     

Syntheses and evaluation of 68Ga‐ and 153Sm‐labeled DOTA‐conjugated bisphosphonate ligand for potential use in detection of skeletal metastases and management of pain arising from skeletal metastases

This article reports the syntheses and evaluation of ⁶⁸Ga‐ and ¹⁵³Sm‐complexes of a new DOTA (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid)‐conjugated geminal bisphosphonate, DOTA‐Bn‐SCN‐BP, for their potential uses in the early detection of skeletal metastases by imaging and palliation of pain arising from skeletal metastases, respectively. The conjugate was synthesized in high purity following an easily adaptable three‐step reaction scheme. Gallium‐68‐ and ¹⁵³Sm‐complexes were prepared in high yield (>98%) and showed excellent in vitro stability in phosphate‐buffered saline (PBS) and human serum. Both the complexes showed high affinity for hydroxyapatite particles in in vitro binding study. In biodistribution studies carried out in normal Wistar rats, both the complexes exhibited rapid skeletal accumulation with almost no retention in any other major organ. The newly synthesized molecule DOTA‐Bn‐SCN‐BP would therefore be a promising targeting ligand for the development of radiopharmaceuticals for both imaging skeletal metastases and palliation of pain arising out of it in patients with cancer when radiolabeled with ⁶⁸Ga and ¹⁵³Sm, respectively. A systematic comparative evaluation, however, showed that there was no significant improvement of skeletal accumulation of the ¹⁵³Sm‐DOTA‐Bn‐SCN‐BP complex over ¹⁵³Sm‐DOTMP (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetramethylenephosphonic acid) as the later itself demonstrated optimal properties required for an agent for bone pain palliation.     

Comparative evaluation of 68Ga‐labeled NODAGA,DOTAGA, and HBED‐CC‐conjugated cNGR peptide chelates as tumor‐targeted molecular imaging probes

The biological behavior of ⁶⁸Ga‐based radiopharmaceuticals can be significantly affected by the chelators’ attributes (size, charge, lipophilicity). Thus, this study aimed at examining the influence of three different chelators, DOTAGA, NODAGA, and HBED‐CC on the distribution pattern of ⁶⁸Ga‐labeled NGR peptides targeting CD13 receptors. ⁶⁸Ga‐DOTAGA‐c(NGR), ⁶⁸Ga‐NODAGA‐c(NGR), and ⁶⁸Ga‐HBED‐CC‐c(NGR) were observed to be hydrophilic with respective log p values being −3.5 ± 0.2, −3.3 ± 0.08, and −2.8 ± 0.14. The three radiotracers exhibited nearly similar uptake in human fibrosarcoma HT‐1080 tumor cells with 86%, 63%, and 33% reduction during blocking studies with unlabeled cNGR peptide for ⁶⁸Ga‐DOTAGA‐c(NGR), ⁶⁸Ga‐NODAGA‐c(NGR), and ⁶⁸Ga‐HBED‐CC‐c(NGR), respectively, indicating higher receptor specificity of the first two radiotracers. The neutral radiotracer ⁶⁸Ga‐NODAGA‐c(NGR) demonstrated better target‐to‐non‐target ratios during in vivo studies compared to its negatively charged counterparts, ⁶⁸Ga‐DOTAGA‐c(NGR) and ⁶⁸Ga‐HBED‐CC‐c(NGR). The three radiotracers had similar HT‐1080 tumor uptake and being hydrophilic exhibited renal excretion with minimal uptake in non‐target organs. Significant reduction (p < .005) in HT‐1080 tumor uptake of the radiotracers was observed during blocking studies. It may be inferred from these studies that the three radiotracers are promising probes for in vivo imaging of CD13 receptor expressing cancer sites; however, ⁶⁸Ga‐NODAGA‐c(NGR) is a better candidate.     

Synthesis,radiofluorination, and preliminary evaluation of the potential 5‐HT2A receptor agonists [18F]Cimbi‐92 and [18F]Cimbi‐150

An agonist PET tracer is of key interest for the imaging of the 5‐HT_2A receptor, as exemplified by the previously reported success of [¹¹C]Cimbi‐36. Fluorine‐18 holds several advantages over carbon‐11, making it the radionuclide of choice for clinical purposes. In this respect, an ¹⁸F‐labelled agonist 5‐HT_2A receptor (5‐HT_2AR) tracer is highly sought after. Herein, we report a 2‐step, 1‐pot labelling methodology of 2 tracer candidates. Both ligands display high in vitro affinities for the 5‐HT_2AR. The compounds were synthesised from easily accessible labelling precursors, and radiolabelled in acceptable radiochemical yields, sufficient for in vivo studies in domestic pigs. PET images partially conformed to the expected brain distribution of the 5‐HT_2AR; a notable exception however being significant uptake in the striatum and thalamus. Additionally, a within‐scan displacement challenge with a 5‐HT_2AR antagonist was unsuccessful, indicating that the tracers cannot be considered optimal for neuroimaging of the 5‐HT_2AR.     

Development of novel PET probes, [18F]BCPP‐EF, [18F]BCPP‐BF,and [11C]BCPP‐EM for mitochondrial complex 1 imaging in the living brain

We developed three novel positron‐emission tomography (PET) probes, 2‐tert‐butyl‐4‐chloro‐5‐{6‐[2‐(2[¹⁸F]fluoroethoxy)‐ethoxy]‐pyridin‐3‐ylmethoxy}‐2H‐pyridazin‐3‐one ([¹⁸F]BCPP‐EF), 2‐tert‐butyl‐4‐chloro‐5‐[6‐(4‐[¹⁸F]fluorobutoxy)‐pyridin‐3‐ylmethoxy]‐2H‐pyridazin‐3‐one ([¹⁸F]BCPP‐BF), and 2‐tert‐butyl‐4‐chloro‐5‐{6‐[2‐(2‐[¹¹C]methoxy‐ethoxy)‐ethoxy]‐pyridin‐3‐ylmethoxy}‐2H‐pyridazin‐3‐one ([¹¹C]BCPP‐EM), for quantitative imaging of mitochondrial complex 1 (MC‐1) activity in vivo. These three PET probes were successfully labeled by nucleophilic [¹⁸F]fluorination or by [¹¹C]methylation of their corresponding precursor with sufficient radioactivity yield, good radiochemical purity, and sufficiently high specific radioactivity for PET measurement. The specificity of these probes for binding to MC‐1 was assessed with rotenone, a specific MC‐1 inhibitor, by a rat brain slice imaging method in vitro. Rat whole‐body imaging by small‐animal PET demonstrated that all probes showed high uptake levels in the brain as well as in the heart sufficient to image them clearly. The rank order of uptake levels in the brain and the heart just after injection was as follows: high in [¹⁸F]BCPP‐BF, intermediate in [¹¹C]BCPP‐EM, and low in [¹⁸F]BCPP‐EF. The kinetics of [¹⁸F]BCPP‐EF and [¹¹C]BCPP‐EM provided a reversible binding pattern, whereas [¹⁸F]BCPP‐BF showed nonreversible accumulation‐type kinetics in the brain and heart. Metabolite analyses indicated that these three compounds were rapidly metabolized in the plasma but relatively stable in the rat brain up to 60 min post‐injection. The present study demonstrated that [¹⁸F]BCPP‐EF could be a useful PET probe for quantitative imaging of MC‐1 activity in the living brain by PET.     

Synthesis,labelling and first evaluation of [18F]R91150 as a serotonin 5‐HT2A receptor antagonist for PET

In psychiatric disorders such as anxiety, depression and schizophrenia, 5‐HT_2A receptors play an important role. In order to investigate them in vivo there is an increasing interest in selective and high‐affinity radioligands for receptor binding studies using positron emission tomography (PET). Since available radioligands have disadvantages, R91150, which is a selective and high‐affinity ligand for 5‐HT_2A receptors, was labelled with fluorine‐18. This was accomplished in six steps via 4‐[¹⁸F]fluorophenol and 1‐(3‐bromopropoxy)‐4‐[¹⁸F]fluorobenzene within 190 min starting from no‐carrier‐added [¹⁸F]fluoride. The overall radiochemical yield was 3.8±2% and the specific activity was at least 335 GBq/µmol at the end of the synthesis. First ex vivo studies in mice proved the uptake of [¹⁸F]R91150 in the brain. Radiometabolite studies revealed no radiometabolites in the brain, whereas in the plasma at least two could be detected 30 min p.i. Further preclinical studies are encouraged to evaluate the potential of this new 5‐HT_2A ligand as a radiotracer for PET. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 68Ga‐labeled NOTA‐RGD‐GE11 heterodimeric peptide for dual integrin and epidermal growth factor receptor‐targeted tumor imaging

Radiolabeled Arg‐Gly‐Asp (RGD) peptide analogs have been extensively studied for α_vβ₃ integrin‐targeted angiogenesis imaging. According to recently presented evidence, the dodecapeptide GE11 has high affinity to the epidermal growth factor receptor (EGFR), which is overexpressed in many types of cancer. Dual‐receptor molecular imaging probes with two different heterodimeric peptides exhibit improved cancer targeting efficacy. In the present study, the design and synthesis of a new RGD‐GE11 peptide heterodimer for dual α_vβ₃ integrin/EGFR‐targeted cancer imaging are described. The RGD‐GE11 heterodimer was linked with 6‐aminohexanoic acid (6‐Ahx) and cysteine and conjugated with 1,4,7‐triazacyclononane‐N,N′,N″‐triacetic acid (NOTA) to form NOTA‐RGD‐cys‐6‐Ahx‐GE11. The monomeric peptides, NOTA‐cys‐6‐Ahx‐GE11 and c(RGDyK), were formed by a peptide synthesizer. The peptide heterodimer NOTA‐RGD‐GE11 was obtained by NOTA‐cys‐6‐Ahx‐GE11 and maleimidopropyl‐c(RGDyK) conjugation with a thioether linkage. The NOTA peptide conjugate was labeled with freshly eluted ⁶⁸Ga and purified using reversed‐phase high‐performance liquid chromatography. The ⁶⁸Ga‐NOTA‐RGD‐cys‐6‐Ahx‐GE11 was successfully prepared, in this study, with a radiochemical yield of 85% and a radiochemical purity of >98%. These results warrant further investigation of this heterodimeric peptide's binding affinity to the receptors.     

Synthesis of C‐14 and C‐13, H‐2‐labeled IKK inhibitor: [14C] and [13C4,D3]‐N‐(6‐chloro‐7‐methoxy‐9H‐pyrido[3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide

[¹⁴C]‐N‐(6‐Chloro‐7‐methoxy‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide (5B ), an IKK inhibitor, was synthesized from [¹⁴C]‐barium carbonate in two steps in an overall radiochemical yield of 41%. The intermediate, [carboxyl‐¹⁴C]‐2‐methylnicotinic acid, was prepared by the lithiation and carbonation of 3‐bromo‐2‐methylpyridine. [¹³C₄,D₃]‐N‐(6‐chloro‐7‐methoxy‐9H‐pyrido [3,4‐b]indol‐8‐yl)‐2‐methyl‐3‐pyridinecarboxamide (5C ) was synthesized from [1,2,3,4‐¹³C₄]‐ethyl acetoacetate and [D₄]‐methanol in six steps in an overall yield of 2%. [¹³C₄]‐2‐methylnicotic acid, was prepared by condensation of [¹³C₄]‐ethyl 3‐aminocrotonate and acrolein, followed by hydrolysis with lithium hydroxide. Copyright © 2006 John Wiley & Sons, Ltd.