Preclinical evaluation of potential infection‐imaging probe [68Ga]Ga‐DOTA‐K‐A9 in sterile and infectious inflammation

The development of bacteria‐specific infection radiotracers is of considerable interest to improve diagnostic accuracy and enabling therapy monitoring. The aim of this study was to determine if the previously reported radiolabelled 1,4,7,10‐tetraazacyclododecane‐N,N′,N″,N?‐tetraacetic acid (DOTA) conjugated peptide [⁶⁸Ga]Ga‐DOTA‐K‐A9 could detect a staphylococcal infection in vivo and distinguish it from aseptic inflammation. An optimized [⁶⁸Ga]Ga‐DOTA‐K‐A9 synthesis omitting the use of acetone was developed, yielding 93 ± 0.9% radiochemical purity. The in vivo infection binding specificity of [⁶⁸Ga]Ga‐DOTA‐K‐A9 was evaluated by micro positron emission tomography/magnetic resonance imaging of 15 mice with either subcutaneous Staphylococcus aureus infection or turpentine‐induced inflammation and compared with 2‐deoxy‐2‐[¹⁸F]fluoro‐D‐glucose ([¹⁸F]FDG). The scans showed that [⁶⁸Ga]Ga‐DOTA‐K‐A9 accumulated in all the infected mice at injected doses ≥3.6 MBq. However, the tracer was not found to be selective towards infection, since the [⁶⁸Ga]Ga‐DOTA‐K‐A9 also accumulated in mice with inflammation. In a concurrent in vitro binding evaluation performed with a 5‐carboxytetramethylrhodamine (TAMRA) fluorescence analogue of the peptide, TAMRA‐K‐A9, the microscopy results suggested that TAMRA‐K‐A9 bound to an intracellular epitope and therefore preferentially targeted dead bacteria. Thus, the [⁶⁸Ga]Ga‐DOTA‐K‐A9 uptake observed in vivo is presumably a combination of local hyperemia, vascular leakiness and/or binding to an epitope present in dead bacteria.     

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.     

Efficient gallium‐68 radiolabeling reaction of DOTA derivatives using a resonant‐type microwave reactor

Gallium‐68 (⁶⁸Ga, t_1/2 = 68 min) can be easily obtained from a ⁶⁸Ge/⁶⁸Ga generator, and several such systems are commercially available. The use of positron emission tomography (PET) imaging using ⁶⁸Ga‐labeled radiopharmaceuticals is expected to increase in both preclinical and clinical settings. However, the chelation between a ⁶⁸Ga cation and the bifunctional macrocyclic chelates that are used for labeling bioactive substances, such as 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA), requires a relatively long reaction time and high temperature to achieve a high radiochemical yield. Previously, we reported on a novel resonant‐type microwave reactor that can be used for radiosynthesis and the usefulness of this reactor in the PET radiosynthesis of ¹⁸F. In the present study, the usefulness of this resonant‐type microwave reactor was evaluated for the radiolabeling of model macrocyclic chelates with ⁶⁸Ga. As a result, microwave heating of resonant‐type microwave reactor notably improved the rate of the ⁶⁸Ga labeling chelate reaction in a short time period of 2 minutes, compared with the use of a conventional heating method. Additionally, it was found that the use of this reactor made it possible to decrease the amount of precursors required in the reaction and to improve the molar activity of the labeled compounds.     

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.     

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.     

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.     

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.     

An improved assay for 68Ga‐hydroxide in 68Ga‐DOTATATE formulations intended for neuroendocrine tumour imaging

The objective of this study was to identify a more rapid assay for ⁶⁸Ga(OH)₃ impurity in ⁶⁸Ga‐DOTATATE formulations. Three methods were used to prepare ⁶⁸Ga(OH)₃ reference material (pharmacopoeial, bench titration and automated radiosynthesis), and four quality control methods for its assessment (thin layer chromatography, membrane filtration, HPLC and solid phase extraction). The optimal method of preparing ⁶⁸Ga(OH)₃ was by titrating ⁶⁸Ga³⁺ with buffered sodium hydroxide solutions to pH 5.6 ± 0.2. The precipitate was quantitatively isolated by membrane filtration (0.02 µm)/hydrochloric acid (HCl; pH 5.6) solvent, and also it remained 100% at the origin on instant thin layer chromatography with silica gel paper/HCl (pH 5.6) solvent. For ⁶⁸Ga‐DOTATATE samples, the thin layer chromatography technique was used with a single paper strip developed separately on two occasions, once in HCl (pH 5.6) and next in methanol solvent. This so‐called double‐developed (DD) method separated ⁶⁸Ga(OH)₃ impurity located at the origin, from ⁶⁸Ga‐DOTATATE plus ⁶⁸Ga³⁺ at ~R_f 0.4, and it was superior to the other methods. It assayed for the impurity similarly to the pharmacopoeial method. The advantages of the DD method were that it required inexpensive test materials and it reproducibly determined % ⁶⁸Ga(OH)₃ in ⁶⁸Ga‐DOTATATE in 12 min, 13 min earlier than the pharmacopoeial method. This time efficiency resulted in a surplus of 12% ⁶⁸Ga‐DOTATATE counts in the product vial, and this provided a contingency of radioactivity or time for the injection/imaging processes in the Nuclear Medicine Department.     

Fusarinine C,a novel siderophore‐based bifunctional chelator for radiolabeling with Gallium‐68

Fusarinine C (FSC), a siderophore‐based chelator coupled with the model peptide c(RGDfK) (FSC(succ‐RGD)₃), revealed excellent targeting properties in vivo using positron emission tomography (PET). Here, we report the details of radiolabeling conditions and specific activity as well as selectivity for ⁶⁸Ga. ⁶⁸Ga labeling of FSC(succ‐RGD)₃ was optimized regarding peptide concentration, pH, temperature, reaction time, and buffer system. Specific activity (SA) of [⁶⁸Ga]FSC(succ‐RGD)₃ was compared with ⁶⁸Ga‐1,4,7‐triazacyclononane, 1‐glutaric acid‐4,7 acetic acid RGD ([⁶⁸Ga]NODAGA‐RGD). Stability was evaluated in 1000‐fold ethylenediaminetetraacetic acid (EDTA) solution (pH 7) and phosphate‐buffered saline (PBS). Metal competition tests (Fe, Cu, Zn, Al, and Ni) were carried out using [⁶⁸Ga]‐triacetylfusarinine C. High radiochemical yield was achieved within 5 min at room temperature, in particular allowing labeling with ⁶⁸Ga up to pH 8 with excellent stability in 1000‐fold EDTA solution and PBS. The 10‐fold to 20‐fold lower concentrations of FSC(succ‐RGD)₃ led to the same radiochemical yield compared with [⁶⁸Ga]NODAGA‐RGD with SA up to 1.8 TBq/µmol. Metal competition tests showed high selective binding of ⁶⁸Ga to FSC. FSC is a multivalent siderophore‐based bifunctional chelator allowing fast and highly selective labeling with ⁶⁸Ga in a wide pH range and results in stable complexes with high SA. Thus it is exceptionally well suited for the development of new ⁶⁸Ga‐tracers for in vivo molecular imaging with PET.     

Synthesis,radiolabeling, and evaluation of gastrin releasing peptide receptor antagonist 68Ga‐HBED‐CC‐RM26

The acyclic chelator HBED‐CC has attained huge clinical significance owing to high thermodynamic and kinetic stability of ⁶⁸Ga‐HBED‐CC chelate. It provides an excellent platform for quick preparation of ⁶⁸Ga‐based radiotracers in high yield. Thus, the present study aimed at conjugation of gastrin releasing peptide receptor (GRPr) antagonist, RM26, with HBED‐CC chelator for ⁶⁸Ga‐labeling. In vitro and vivo behavior of the peptide tracer, ⁶⁸Ga‐HBED‐CC‐PEG₂‐RM26, was assessed and compared with ⁶⁸Ga‐NODAGA‐PEG₂‐RM26. The peptide tracers, ⁶⁸Ga‐HBED‐CC‐PEG₂‐RM26 and ⁶⁸Ga‐NODAGA‐PEG₂‐RM26, prepared either by wet chemistry or formulated using freeze‐dried kits exhibited excellent radiochemical yield and in vitro stability. The two peptide tracers cleared rapidly from the blood. Biodistribution studies in normal mice demonstrated slightly higher or comparable uptake of ⁶⁸Ga‐HBED‐CC‐PEG₂‐RM26 in GRPr‐expressing organs pancreas, stomach, and intestine. The preliminary studies suggest high potential of ⁶⁸Ga‐HBED‐CC‐PEG₂‐RM26 for further investigation as a GRPr imaging agent and the wide scope of HBED‐CC chelator in development of ⁶⁸Ga‐based peptide tracers.     

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).     

68Ga‐labeled Ciprofloxacin Conjugates as Radiotracers for Targeting Bacterial Infection

With an aim of developing a bacteria‐specific molecular imaging agent, ciprofloxacin has been modified with a propylamine spacer and linked to two common bifunctional chelators, p‐SCN‐Bz‐DOTA and p‐SCN‐Bz‐NOTA. The two ciprofloxacin conjugates, CP‐PA‐SCN‐Bz‐DOTA ( 1 ) and CP‐PA‐SCN‐Bz‐NOTA ( 2 ), were radiolabeled with ⁶⁸Ga in >90% radiochemical yield and were moderately stable in vitro for 4 h. The efficacy of ⁶⁸Ga‐ 1 and ⁶⁸Ga‐ 2 has been investigated in vitro in Staphylococcus aureus cells where bacterial binding of the radiotracers (0.9–1.0% for ⁶⁸Ga‐ 1 and 1.6–2.3% for ⁶⁸Ga‐ 2 ) could not be blocked in the presence of excess amount of unlabeled ciprofloxacin. However, uptake of radiotracers in live bacterial cells was significantly higher (p < 0.01) than that in non‐viable bacterial cells. Bacterial infection targeting efficacy of ⁶⁸Ga‐ 1 and ⁶⁸Ga‐ 2 was tested in vivo in rats where the infected muscle‐to‐inflamed muscle (⁶⁸Ga‐ 1 : 2 ± 0.2, ⁶⁸Ga‐ 2 : 3 ± 0.5) and infected muscle‐to‐normal muscle ratios (⁶⁸Ga‐ 1 : 3 ± 0.4, ⁶⁸Ga‐ 2 : 6.6 ± 0.8) were found to improve at 120 min p.i. Fast blood clearance and renal excretion was observed for both the radiotracers. The two ⁶⁸Ga‐labeled infection targeting radiotracers could discriminate between bacterial infection and inflammation in vivo and are worthy of further detailed investigation as infection imaging agents at the clinical level.     

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 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.     

Radiolabeling of a high potency cannabinoid subtype‐1 receptor ligand,N‐(4‐fluoro‐benzyl)‐4‐(3‐(piperidin‐1‐yl)‐indole‐1‐sulfonyl)benzamide (PipISB), with carbon‐11 or fluorine‐18

PipISB [N‐(4‐fluoro‐benzyl)‐4‐(3‐(piperidin‐1‐yl)‐indole‐1‐sulfonyl)benzamide, 9] was identified as a selective high potency CB₁ receptor ligand. Here we describe the labeling of 9 with positron‐emitters to provide candidate radioligands for imaging brain CB₁ receptors with positron emission tomography (PET). The radiolabeling of 9 was achieved by two methods, method A with carbon‐11 and method B with fluorine‐18. In method A, [¹¹C]9 was prepared in one step from [¹¹C]carbon monoxide, itself prepared from cyclotron‐produced [¹¹C]carbon dioxide. In method B, [¹⁸F]9 was prepared from cyclotron‐produced [¹⁸F]fluoride ion in a two‐stage, four‐step synthesis with [¹⁸F]4‐fluoro‐benzyl bromide as a labeling agent. The radiosynthesis time for method A was 44 min; decay‐corrected radiochemical yields (RCYs) from [¹¹C]carbon monoxide ranged from 3.1 to 11.6% and specific radioactivities ranged from 21 to 67 GBq/µmol. The radiosynthesis time for method B was 115 min; RCYs from [¹⁸F]fluoride ion ranged from 1.5 to 5.6% and specific radioactivities ranged from 200 to 348 GBq/µmol. With these methods, [¹¹C]9 and [¹⁸F]9 may be prepared in adequate activity and quality for future evaluation as PET radioligands. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and preliminary bioevaluation studies of 68Ga‐NOTA‐rituximab fragments as radioimmunoscintigraphic agents for non‐Hodgkin lymphoma

Rituximab is used for the treatment of non‐Hodgkin lymphoma (NHL). This study focuses on development of ⁶⁸Ga‐labeled rituximab fragments, (⁶⁸Ga‐NOTA‐F (ab′)‐rituximab and ⁶⁸Ga‐NOTA‐F (ab′)₂‐rituximab, as PET‐imaging agents for NHL. Rituximab was digested with immobilized pepsin and papain to yield F (ab′)₂ and Fab fragments respectively that were characterized by size exclusion HPLC (SE‐HPLC) and SDS‐PAGE. They were conjugated with p‐SCN‐Bn‐NOTA, labeled with ⁶⁸Ga and characterized by SE‐HPLC. Intact rituximab was labeled with gallium‐68 for comparison. Specificity of ⁶⁸Ga‐labeled immunoconjugates was ascertained by immunoreactivity and cell binding studies in Raji cells, while biodistribution studies were performed in normal Swiss mice. Gradient SDS‐PAGE under nonreducing condition showed molecular weights of F (ab′)₂‐rituximab and F (ab′)‐rituximab as approximately 100 and 40 Kd, respectively. Radiochemical purity (RCP) of ⁶⁸Ga‐NOTA‐F (ab′)₂‐rituximab and ⁶⁸Ga‐NOTA‐F (ab′)‐rituximab were 98.2 ± 0.5% and 98.8 ± 0.2% respectively with retention times of 17.1 ± 0.1 min and 19.3 ± 0.1 min in SE‐HPLC. ⁶⁸Ga‐labeled rituximab fragments were stable in saline and serum up to 2‐hour post preparation and exhibited specificity to CD20 antigen. Immunoreactivity of ⁶⁸Ga‐labeled immunoconjugates was greater than 80%. Clearance of the fragmented radioimmunoconjugates was predominantly through renal route. Preliminary results from this study demonstrate the potential of ⁶⁸Ga‐ NOTA‐F (ab′)₂‐rituximab and ⁶⁸Ga‐NOTA‐F (ab′)‐rituximab as PET imaging agents for NHL.     

Fine‐tuning of the automated [18F]PSMA‐1007 radiosynthesis

Radiolabeled prostate‐specific membrane antigen (PSMA) targeting PET‐tracers have become desirable radiopharmaceuticals for the imaging of prostate cancer (PC). Recently, the PET radiotracer [¹⁸F]PSMA‐1007 was introduced as an alternative to [⁶⁸Ga]Ga‐PSMA‐11, for staging and diagnosing biochemically recurrent PC. We incorporated a one‐step procedure for [¹⁸F]PSMA‐1007 radiosynthesis, using both Synthra RNplus and GE TRACERlab FxFN automated modules, in accordance with the recently described radiolabeling procedure. Although the adapted [¹⁸F]PSMA‐1007 synthesis resulted in repeatable radiochemical yields (55 ± 5%, NDC), suboptimal radiochemical purities of 87 ± 8% were obtained using both modules. As described here, modifications made to the radiolabeling and the solid‐phase extraction purification steps reduced synthesis time to 32 minutes and improved radiochemical purity to 96.10%, using both modules, without shearing the radiochemical yield.     

Detailed evaluation of different 68Ge/68Ga generators: an attempt toward achieving efficient 68Ga radiopharmacy

The present study is aimed at carrying out a comparative performance evaluation of different types of ⁶⁸Ge/⁶⁸Ga generators to identify the best choice for use in ⁶⁸Ga‐radiopharmacy. Over the 1 year period of evaluation, the elution yields from the CeO₂‐based and SiO₂‐based ⁶⁸Ge/⁶⁸Ga generators remained almost consistent, in contrast to the sharp decrease observed in the elution yields from TiO₂ and SnO₂‐based generators. The level of ⁶⁸Ge impurity in ⁶⁸Ga eluates from the CeO₂ and SiO₂‐based ⁶⁸Ge/⁶⁸Ga generator was always <10^?3%, while this level increased from 10^?3% to 10^?1% in case of TiO₂ and SnO₂‐based generators. The level of chemical impurities in ⁶⁸Ga eluates from CeO₂ and SiO₂‐based ⁶⁸Ge/⁶⁸Ga generators was negligibly low (<0.1 ppm) in contrast to the significantly higher level (1–20 ppm) of such impurities in eluates from other two generators. As demonstrated by radiolabeling studies carried out using DOTA‐coupled dimeric cyclic RGD peptide derivative (DOTA‐RGD₂), CeO₂‐PAN and SiO₂‐based generators are directly amenable for radiopharmaceutical preparation, whereas the other generators can be only used after post‐elution purification of ⁶⁸Ga eluates. Clinically relevant dose of ⁶⁸Ga‐DOTA‐RGD₂ was prepared in a hospital radiopharmacy for non‐invasive visualization of tumors in breast cancer patients using positron emission tomography.     

A simple method for preparation of pure 68Ga‐acetate precursor for formulation of radiopharmaceuticals: Physicochemical characteristics of the 68Ga eluate of the SnO2 based‐68Ge/68Ga column generator

Gallium‐68 radioisotope is an excellent source in clinical positron emission tomography application due to its ease of availability from germanium‐68 (⁶⁸Ge)/gallium‐68 (⁶⁸Ga) generator having a shelf life of 1 year. In this paper, a modified method for purification of the primary eluate of ⁶⁸Ge‐⁶⁸Ga generator by using a small cation exchange resin (Dowex‐50) column has been described. The breakthrough of ⁶⁸Ge before and after purification of ⁶⁸Ga eluate was 0.014% and 0.00027%, respectively. The average recovery yield of ⁶⁸Ga after purification was 84% ± 8.6% (SD, n  = 335). The results of the physiochemical studies confirmed that the ⁶⁸Ga‐acetate obtained is suitable for labeling of radiopharmaceuticals.