Name: 18F-Labeling of Radiotracers Functionalized with a Silicon Fluoride Acceptor (SiFA) for Positron Emission Tomography (Video) | JoVE Journal
Uploaded: 2020-01-11T16:00:00.000+00:00
Duration: 9 min 57 s
Description: Learn F-18 labeling of radiotracers using silicon fluoride acceptor (SiFA) compounds for PET imaging. This simplified method enables efficient radiopharmaceutical synthesis with milder conditions and reduced precursor requirements.

ai_agent_IP

ai_agent

maintenance

instantTrialDurationMinutes

isBiopharma

enableNewMyJoveSectionDesign

educationFeatures

seoMetaApi

ai_copilot_institution_blacklist

ai_chat_institution_blacklist

freeAccessWindow

ssoRoleCapture

scheduledMaintenanceBanner

joveLabsFeatures

disable_autoplay_for_bots

extended_trial_duration

5 minutes

The authors have no acknowledgements.

CAUTION: One must keep in mind that 18F is a radioactive isotope, and therefore it is necessary to carry out all procedures behind adequate shielding. Lead shielding is appropriate for this type of radiation. Be sure to wear radiation detection badges throughout the entirety of this procedure. Additionally, immediately dispose of gloves before touching anything after the synthesis, as they may be contaminated with radioactive activity. Utilize hand-foot monitors as well as pancake Geiger counters to check for contamination of sleeves, hands, and feet.
1. Azeotropic drying of 18F-anion
NOTE: Figure 2A shows a workflow graph of this procedure, which takes ~10 min.
<ol>
	<li>Precondition a quaternary methyl ammonium (QMA) anion exchange cartridge (Table of Materials) by passing 0.5 M K2CO3 (10 mL) through the cartridge, followed by deionized water (10 mL).</li>
	<li>Pass an aqueous solution of [18F]F-/[18O]H2O (100&#8722;500 MBq) through the preconditioned QMA cartridge in reverse, using a male to male adapter. Discard the [18O]H2O. 
	NOTE: These steps can be performed using an automated synthesis module, or by using additional shielding on the syringe.</li>
	<li>Elute the first four drops of the fixed [18F]fluoride anions from the QMA cartridge into a prepared solution of [2.2.2]cryptand (Table of Materials) (10 mg), 0.2 M K2CO3 (50 &#956;L, 10 &#956;mol), and acetonitrile (1 mL) in a thick-walled v-vial, and seal the vial. 
	NOTE: Only the first four drops are used as the majority of the radioactive [18F]fluoride is eluted off the QMA in these drops. This reduces the amount of base carried forward in the [18F]fluoride stock solution, which is necessary to avoid degradation of the SiFA moiety.</li>
	<li>Seal the vial and place in a 90 &#176;C mineral oil bath positioned on a hot plate. Insert a vent needle and a needle connected to a stream of argon gas into the septum of the vial cap. Wait 5 min to evaporate the solvents under the gentle stream of argon. Remove any remaining traces of water by adding 1 mL of acetonitrile to facilitate azeotropic co-evaporation. Repeat this step 2x to ensure dryness.</li>
	<li>Once the solvent is visibly removed, stop the argon flow, and remove the syringes from the vial cap, and remove the vial from the oil bath.</li>
	<li>Resuspend the dried [18F]fluoride in the reaction solvent of choice. 
	NOTE: In this case, acetonitrile (1 mL) is added to create a stock solution of highly reactive [18F-]F- (100&#8722;500 MBq). This solution can now be used for labeling.</li>
</ol>
2. One-step SiFA-ligand labeling
NOTE: Figure 2B shows a workflow graph of this procedure, which takes ~15 min.
<ol>
	<li>Precondition a C-18 cartridge (Table of Materials) by rinsing it with ethanol (10 mL) and distilled water (10 mL).</li>
	<li>Add the [18F-]fluoride stock solution to a reaction vial containing a SiFA-labeled precursor (100 &#956;L, 20&#8722;100 nmol). Allow the labeling reaction to proceed for 5 min at room temperature without stirring the solution. 
	NOTE: The entire stock solution can be added or an aliquot, depending on how much activity is desired for the reaction.</li>
	<li>Draw up the reaction mixture in a 20 mL syringe containing 0.1 M phosphate buffer (9 mL) and pass the solution through the preconditioned C-18 cartridge to trap the labeled tracer.</li>
	<li>Wash the cartridge with distilled water (5 mL), then elute trapped tracer from the C-18 cartridge with ethanol (300 &#956;L), and dilute with sterile phosphate buffer for injection (3 mL).</li>
	<li>Pass the purified [18F]SiFA-tracer through a sterile filter. 
	NOTE: To obtain a clear PET imagine for small animal imaging, the partitioned patient dose should be between 5&#8722;8 MBq. For human use, the partitioned patient dose should be between 200&#8722;300 MBq.</li>
	<li>Inject a small aliquot (~4 MBq) of the purified [18F]SiFA-tracer onto an HPLC system equipped with a reversed-phase C-18 column to confirm that the radiochemical purity is greater than 95%.</li>
</ol>

<ol><li>Wahl, R. L., Buchanan, J. W. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aWahl%2C+RL+%22Principles+and+practice+of+positron+emission+tomography%22">Principles and practice of positron emission tomography</a>. , Lippincott Williams & Wilkins. Philadelphia, PA. (2002).</li>
<li>Wängler, C., Schirrmacher, R., Bartenstein, P., Wängler, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Click-chemistry+reactions+in+radiopharmaceutical+chemistry%3A+Fast+%26+easy+introduction+of+radiolabels+into+biomolecules+for+in+vivo+imaging%5BTitle%5D)+AND+%22Current+Medical+Chemistry%22%5BJournal%5D)">Click-chemistry reactions in radiopharmaceutical chemistry: Fast & easy introduction of radiolabels into biomolecules for in vivo imaging.</a> Current Medical Chemistry. 17, 1092-1116 (2010).</li>
<li>Schirrmacher, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((18F-labeling+of+peptides+by+means+of+an+organosilicon-based+fluoride+acceptor%5BTitle%5D)+AND+%22Angewandte+Chemie+International+Edition%22%5BJournal%5D)">18F-labeling of peptides by means of an organosilicon-based fluoride acceptor.</a> Angewandte Chemie International Edition. 45, 6047-6050 (2006).</li>
<li>Kostikov, A. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Oxalic+acid+supported+Si-18F-radiofluorination%3A+One-step+radiosynthesis+of+N-succinimidyl+3-%28di-tert-butyl%5B18F%5Dfluorosilyl%29benzoate+%28%5B18F%5DSiFB%29+for+protein+labeling%5BTitle%5D)+AND+%22Bioconjugate+Chemistry%22%5BJournal%5D)">Oxalic acid supported Si-18F-radiofluorination: One-step radiosynthesis of N-succinimidyl 3-(di-tert-butyl[18F]fluorosilyl)benzoate ([18F]SiFB) for protein labeling.</a> Bioconjugate Chemistry. 23 (1), 106-114 (2012).</li>
<li>Cacace, F., Speranza, M., Wolf, A. P., Macgregor, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nucleophilic+aromatic+substitution%3B+kinetics+of+fluorine-18+substitution+reactions+in+polyfluorobenzenes.+Isotopic+exchange+between+18F-+and+polyfluorobenzenes+in+dimethylsulfoxide.+A+kinetic+study%5BTitle%5D)+AND+%22Journal+of+Fluorine+Chemistry%22%5BJournal%5D)">Nucleophilic aromatic substitution; kinetics of fluorine-18 substitution reactions in polyfluorobenzenes. Isotopic exchange between 18F- and polyfluorobenzenes in dimethylsulfoxide. A kinetic study.</a> Journal of Fluorine Chemistry. 21, 145-158 (1982).</li>
<li>Schirrmacher, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Synthesis+of+p-%28di-tert-butyl%5B18F%5Dfluorosilyl%29benzaldehyde+%28%5B18F%5DSiFA-A%29+with+high+specific+activity+by+isotopic+exchange%3A+A+convenient+labeling+synthon+for+the+18F-labeling+of+N-amino-oxy+derivatized+peptides%5BTitle%5D)+AND+%22Bioconjugate+Chemistry%22%5BJournal%5D)">Synthesis of p-(di-tert-butyl[18F]fluorosilyl)benzaldehyde ([18F]SiFA-A) with high specific activity by isotopic exchange: A convenient labeling synthon for the 18F-labeling of N-amino-oxy derivatized peptides.</a> Bioconjugate Chemistry. 18, 2085-2089 (2007).</li>
<li>Kostikov, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((N-%284-%28di-tert-butyl%5B18F%5Dfluorosilyl%29benzyl%29-2-hydroxy-N%2CN-dimethylethylammonium+bromide+%28%5B18F%5DSiFAN%2BBr-%29%3A+A+novel+lead+compound+for+the+development+of+hydrophilic+SiFA-based+prosthetic+groups+for+18F-labeling%5BTitle%5D)+AND+%22Journal+of+Fluorine+Chemistry%22%5BJournal%5D)">N-(4-(di-tert-butyl[18F]fluorosilyl)benzyl)-2-hydroxy-N,N-dimethylethylammonium bromide ([18F]SiFAN+Br-): A novel lead compound for the development of hydrophilic SiFA-based prosthetic groups for 18F-labeling.</a> Journal of Fluorine Chemistry. 132, 27-34 (2011).</li>
<li>Wängler, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Kit-like+18F-labeling+of+proteins%3A+Synthesis+of+4-%28di-tert-butyl%5B18F%5Dfluorosilyl%29benzenethiol+%28Si%5B18F%5DFA-SH%29+labeled+rat+serum+albumin+for+blood+pool+imaging+with+PET%5BTitle%5D)+AND+%22Bioconjugate+Chemistry%22%5BJournal%5D)">Kit-like 18F-labeling of proteins: Synthesis of 4-(di-tert-butyl[18F]fluorosilyl)benzenethiol (Si[18F]FA-SH) labeled rat serum albumin for blood pool imaging with PET.</a> Bioconjugate Chemistry. 20, 317-321 (2009).</li>
<li>Iovkova, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((para-Functionalized+aryl-di-tert-butylfluorosilanes+as+potential+labeling+synthons+for+18F+radiopharmaceuticals%5BTitle%5D)+AND+%22Chemistry%22%5BJournal%5D)">para-Functionalized aryl-di-tert-butylfluorosilanes as potential labeling synthons for 18F radiopharmaceuticals.</a> Chemistry. 15, 2140-2147 (2009).</li>
<li>Wängler, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((One-step+18F-labeling+of+carbohydrate-conjugated+octreotate-derivatives+containing+a+silicon-fluoride-acceptor+%28SiFA%29%3A+In+vitro+and+in+vivo+evaluation+as+tumor+imaging+agents+for+positron+emission+tomography+%28PET%29%5BTitle%5D)+AND+%22Bioconjugate+Chemistry%22%5BJournal%5D)">One-step 18F-labeling of carbohydrate-conjugated octreotate-derivatives containing a silicon-fluoride-acceptor (SiFA): In vitro and in vivo evaluation as tumor imaging agents for positron emission tomography (PET).</a> Bioconjugate Chemistry. 21, 2289-2296 (2010).</li>
<li>Ilhan, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((First-in-human+18F-SiFAlin-TATE+PET%2FCT+for+NET+imaging+and+theranostics%5BTitle%5D)+AND+%22European+Journal+of+Nuclear+Medicine+and+Molecular+Imaging%22%5BJournal%5D)">First-in-human 18F-SiFAlin-TATE PET/CT for NET imaging and theranostics.</a> European Journal of Nuclear Medicine and Molecular Imaging. 46, 2400-2401 (2019).</li>
</ol>

The authors have nothing to disclose.

SiFA labeling chemistry represents one of the first 18F-labeling methods employing an extraordinarily efficient isotopic exchange reaction that can be performed at room temperature. A typical radiochemical reaction relies on the formation of a carbon-fluorine bond via reaction of [18F]fluoride with a fluoride-reactive functionality through an elimination or substitution pathway. These reaction conditions are often harsh, performed at extreme pH or high temperature, and are laden with byproducts or r...

Fluorine-18 (109-minute half-life, 97% positron emission) is among the most important radionuclides for positron emission tomography (PET), a noninvasive imaging method that visualizes and quantifies the bio-distribution of radiolabeled tracers for various diseases1. Peptides and proteins are especially difficult to label with [18F]fluoride because they require building blocks formed by multi-step syntheses2. To reduce the complexity of 18F-radiolabeling, silicon-fluoride acceptor (SiFA) was recently introduced as reliable tools3. The SiFA group consists of a central silicon atom connected to two tertiary butyl groups, a derivatized phenyl moiety, and a non-radioactive fluorine atom. The tertiary butyl groups impart hydrolytic stability to the silicon-fluoride bond, which is a critical feature for in vivo applications of SiFA conjugates as imaging agents.
When attached to a small molecule or biomolecule, the SiFA building blocks bind radioactive [18F]fluoride anions by exchanging fluorine-19 for fluorine-18 at nanomolar concentrations without forming significant amounts of radioactive side products4. Moreover, a high radiochemical yield is quickly achieved by labeling the SiFA moiety in dipolar aprotic solvents at low temperatures. This is in stark contrast to classical isotopic exchange reactions, which produce radiotracers of low specific activity5. In these cases, large amounts of precursor (in the range of milligrams) must be used to obtain reasonable incorporation of [18F]fluoride. Isotopic exchange reactions using SiFAs are far more efficient, as confirmed by kinetic studies and density functional theory calculations6,7. Labeled SiFAs are easily purified by solid-phase extraction since both the labeled and unlabeled SiFA compounds are chemically identical. This differs from traditional radiolabeled tracers, where the precursor molecule and the labeled product are two different chemical species and must be separated after radiolabeling by high-performance liquid chromatography (HPLC). Using SiFA building blocks, small-molecules, proteins, and peptides can be successfully labeled with [18F]fluoride by one- and two-step labeling protocols devoid of complicated purification procedures (Figure 1)4,8,9. Moreover, some SiFA-labeled compounds are reliable in vivo imaging agents for blood flow and tumors10. The simplicity of SiFA chemistry enables even untrained investigators to use [18F]fluoride for radiotracer synthesis and development.

<table><tbody><tr><td>[&lt;sup&gt;18&lt;/sup&gt;F]F&lt;sup&gt;-&lt;/sup&gt;/H&lt;sub&gt;2&lt;/sub&gt;[&lt;sup&gt;18&lt;/sup&gt;O]O</td><td>(Cyclotron produced)</td><td>-</td><td>-</td></tr><tr><td>[2.2.2]Cryptand</td><td>Aldrich</td><td>291110</td><td>Kryptofix 2.2.2</td></tr><tr><td>Acetonitrile anhydrous</td><td>Aldrich</td><td>271004</td><td>-</td></tr><tr><td>Deionized water</td><td>Baxter</td><td>JF7623</td><td>-</td></tr><tr><td>Ethanol, anhydrous</td><td>Commercial Alcohols</td><td></td><td>-</td></tr><tr><td>Potassium carbonate</td><td>Aldrich</td><td>209619</td><td>-</td></tr><tr><td>QMA cartridge</td><td>Waters</td><td>186004540</td><td>QMA SepPak Light (46 mg) cartridge</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>C-18 cartridge</td><td>Waters</td><td>WAT023501</td><td>C-18 SepPak Light cartridge</td></tr><tr><td>C18 column</td><td>Phenomenex</td><td>00G-4041-N0</td><td>HPLC Luna C18 250 x 10 mm, 5 &amp;micro;m</td></tr><tr><td>HPLC</td><td>Agilent Technologies</td><td>-</td><td>HPLC 1200 series</td></tr><tr><td>micro-PET Scanner</td><td>Siemens</td><td>-</td><td>micro-PET R4 Scanner</td></tr><tr><td>Radio-TLC plate reader</td><td>Raytest</td><td>-</td><td>Radio-TLC Mini Gita</td></tr><tr><td>Sterile filter 0.22&amp;micro;m</td><td>Millipore</td><td>SLGP033RS</td><td>-</td></tr></tbody></table>

18f-labeling of radiotracers functionalized with a silicon fluoride acceptor (sifa) for positron emission tomography

18F-Labeling of Radiotracers Functionalized with a Silicon Fluoride Acceptor (SiFA) for Positron Emission Tomography

The para-substituted di-tert-butylfluorosilylbenzene structural motif known as the silicon-fluoride acceptor (SiFA) is a useful tag in the radiochemist&#39;s toolkit for incorporating radioactive [18F]fluoride into tracers for use in positron emission tomography. In comparison to conventional radiolabeling strategies, isotopic exchange of fluorine-19 from SiFA with [18F]fluoride is carried out at room temperature and requires minimal reaction participants. The formation of by-products is thus negligible, and purification is greatly simplified. However, while the precursor molecule used for labeling and the final radiolabeled product are isotopically discrete, they are chemically identical and are thus inseparable during purification procedures. The SiFA tag is also susceptible to degradation under the basic conditions arising from the processing and drying of [18F]fluoride. The &#39;4 drop method&#39;, wherein only the first 4 drops of eluted [18F]fluoride are used from the solid-phase extraction, reduces the amount of base in the reaction, facilitates lower molar amounts of precursor, and reduces degradation.

The simplistic SiFA isotopic exchange can achieve high a degree of radiochemical incorporation of [18F]fluoride (60−90%) with a minimum amount of synthetic complexity (Figure 1). Most molecules can be radiolabeled with [18F]fluoride in one step without involving HPLC for purification (Figure 2). Radio-HPLC can be used for quality control purposes, wherein the ultraviolet (UV) absorbance peak of the final product should coincide with its rad...

The synthesis of fluorine-18 (18F) labeled radiopharmaceuticals for positron emission tomography typically requires months of experience. When incorporated into a radiotracer, the silicon-fluoride acceptor (SiFA) motif enables a simple 18F-labeling protocol that is independent of costly equipment and preparatory training, while reducing precursor quantity needed and utilizing milder reaction conditions.

The para-substituted di-tert-butylfluorosilylbenzene structural motif known as the silicon-fluoride acceptor (SiFA) is a useful tag in the ...

18f-labeling-radiotracers-functionalized-with-silicon-fluoride

Research

JoVE Journal

Chemistry

A facile, one-pot synthesis of N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) was developed based on a non-aqueous, three-step radiochemical process. Using microwave heating, the entire procedure can be completed in less than 30 min, or 60 min with further purification by preparative HPLC. The decay-corrected radiochemical yields (RCYs) were 35-5% (n &gt; 30).

Microwave-assisted One-pot Synthesis of N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB)

Due to its multi-day radioactive half-life and favorable decay properties, the positron-emitting radiometal 89Zr is extremely well-suited for use in antibody-based radiopharmaceuticals for PET imaging. In this protocol, the bioconjugation, radiosynthesis, and preclinical application of 89Zr-labeled antibodies will be described.

The Bioconjugation and Radiosynthesis of 89Zr-DFO-labeled Antibodies

We demonstrate the semi-automated radiochemical synthesis of [18F]3F4AP and quality control procedures.

Automated Radiochemical Synthesis of [18F]3F4AP: A Novel PET Tracer for Imaging Demyelinating Diseases

We describe a protocol for preclinical in vivo tracking of cancer metastasis. It is based on a radionuclide-fluorescence reporter combining the sodium iodide symporter, detected by non-invasive [18F]tetrafluoroborate-PET, and a fluorescent protein for streamlined ex vivo confirmation. The method is applicable for preclinical in vivo cell tracking beyond tumor biology.

Radionuclide-fluorescence Reporter Gene Imaging to Track Tumor Progression in Rodent Tumor Models

Positron-emission tomography (PET) imaging sites that are involved in multiple early clinical research trials need robust and versatile radiotracer manufacturing capabilities. Using the radiotracer [18F]Clofarabine as an example, we illustrate how to automate the synthesis of a radiotracer using a flexible, cassette-based radiosynthesizer and validate the synthesis for clinical use.

Automation of a Positron-emission Tomography (PET) Radiotracer Synthesis Protocol for Clinical Production

[18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography is useful for studying glucose metabolism related to brain function. Here, we present a protocol for an [18F]FDG tracer set-up and semiquantitative assessment of the region-of-interest analysis for targeted brain areas associated with clinical manifestations in patients with severe traumatic brain injury.

Semi-quantitative Assessment Using [18F]FDG Tracer in Patients with Severe Brain Injury

We report an efficient carbon-11 radiolabeling technique to produce clinically relevant tracers for Positron Emission Tomography (PET) using solid phase extraction cartridges. 11C-methylating agent is passed through a cartridge preloaded with precursor and successive elution with aqueous ethanol provides chemically and radiochemically pure PET tracers in high radiochemical yields.

Solid Phase 11C-Methylation, Purification and Formulation for the Production of PET Tracers

Here, we describe the radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-tryptophan, a positron emission tomography imaging agent for studying tryptophan metabolism, using a one-pot, two-step strategy in a radiochemistry synthesis system with good radiochemical yields, high enantiomeric excess, and high reliability.

Radiosynthesis of 1-(2-[18F]Fluoroethyl)-L-Tryptophan using a One-pot, Two-step Protocol

This work describes the automated production of up to 1.7 GBq of [68Ga]Ga-FAPI-46 on the iPHASE MultiSyn synthesizer for PET imaging of fibroblast activation protein.

An Automated Radiosynthesis of [68Ga]Ga-FAPI-46 for Routine Clinical Use

This paper describes the radiosynthesis, formulation, quality control of a new radiolabeled probe (i.e., 68Ga-labeled nanobody NM-02), and its use for small animal PET/CT imaging in a xenograft model.

Radiosynthesis, Quality Control, and Small Animal Positron Emission Tomography Imaging of 68Ga-Labelled Nano Molecules

This research describes the automated process for [68Ga]Ga-3BP-3940 production with the GAIA V2 synthesizer, for PET imaging of fibroblast activation protein. The results of quality control tests performed on three test batches are also presented.

Automated Preparation of [68Ga]Ga-3BP-3940 on a Synthesis Module for PET Imaging of the Tumor Microenvironment

Learn F-18 labeling of radiotracers using silicon fluoride acceptor (SiFA) compounds for PET imaging. This simplified method enables efficient radiopharmaceutical synthesis with milder conditions and reduced precursor requirements.

¹⁸F-Labeling of Radiotracers Functionalized with a Silicon Fluoride Acceptor (SiFA) for Positron Emission Tomography

Explore More Videos