Synthesis of a new fluorine-18 glycosylated 'click' cyanoquinoline for the imaging of epidermal growth factor receptor

Article abstract of DOI:10.1002/jlcr.3170

This study reports the radiosynthesis of a new fluorine-18 glycosylated 'click' cyanoquinoline [¹⁸F]5 for positron emission tomography imaging of epidermal growth factor receptor (EGFR). The tracer was obtained in 47.7 ± 7.5% (n = 3) decay-corr

Full text of DOI:10.1002/jlcr.3170

Research Article
Received 29 August 2013,
Revised 31 October 2013,
Accepted 1 November 2013
Published online 5 December 2013 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.3170
Synthesis of a new fluorine-18 glycosylated
‘click’ cyanoquinoline for the imaging of
epidermal growth factor receptor
a
a
a,b
Federica Pisaneschi,a,b Rozanna L. Slade, Lisa Iddon, Guillaume P. C. George,
*
Quang-Dé Nguyen,a Alan C. Spivey,b and Eric O. Aboagyea
This study reports the radiosynthesis of a new fluorine-18 glycosylated ‘click’ cyanoquinoline [18F]5 for positron emission
tomography imaging of epidermal growth factor receptor (EGFR). The tracer was obtained in 47.7 7.5% (n = 3) decay-
corrected radiochemical yield from 2-[18F]fluoro-2-deoxy-β-D-glucopyranosyl azide, and the overall nondecay-corrected
radiochemical yield from aqueous fluoride was 8.6 2.3% (n = 3). An in vitro preliminary cellular uptake study showed
selectivity of the tracer for EGFR-positive A431 cell lines versus EGFR-negative MCF-7 cell lines. [18F]5 tracer uptake in
A431 cells was significantly reduced by addition of the cold isotope analogue compound 5.
Keywords: EGFR; PET imaging; TKI; click chemistry; radiolabelling
In this context, we recently reported a fluorine-18-labelled
Introduction
cyanoquinoline irreversible imaging agent, [18F]1 (Figure 1),
Epidermal growth factor receptor (EGFR) is a transmembrane
protein belonging to the ErbB receptor kinase family that is
involved in cell proliferation, apoptosis, migration and
which was radiolabelled using a ‘click’ reaction with the
prosthetic group 2-[18F]fluoroethylazide ([18F]FEA).6 Compound
[18F]1 displayed fourfold higher in vivo tumour uptake, relative
angiogenesis. Over-expression of EGFR is frequently detected
to muscle, in EGFR over-expressing A431 tumour bearing mice
in a wide range of human cancers.1 EGFR-targeted therapies
and low tracer retention in other organs including bone, brain
including monoclonal antibodies, for example, cetuximab, and
and heart. The tracer appeared to be metabolically stable as the
small molecule tyrosine kinase inhibitors (TKIs), for example
parent compound was found to be the major radioactive species
in liver and plasma at 60 min post-injection. The gallbladder and
gefitinib and erlotinib, are used clinically.2 TKIs have proven to
be beneficial in some patients with tumours expressing wild type
the urine presented the highest tissue radioactivity levels,
EGFR. Moreover, patients with nonsmall cell lung cancer
suggesting tracer elimination via both the hepatobiliary and the
expressing L858R- or 746_750del-activated mutant EGFR
renal routes. Finally, the detection of high levels of radioactivity
showed significantly higher response to TKI treatment relative
in the intestine was a concern and led us to reevaluate the
to wild type.3 In terms of diagnostics, however, a noninvasive
pharmacokinetic properties of the tracer. Compound [18F]1 has
technique to image EGFR expression in vivo in a clinical setting
a calculated logarithm of distribution coefficient (logDpH 7.4) of
has yet to emerge. As positron emission tomography (PET)
3.97,7 which is deemed too high for a PET oncology imaging
imaging has the potential to give valuable insights into EGFR
agent directed at somatic lesions; an optimal logDpH 7.4 would
probably be in the 0–3 range.8 The high lipophilicity of [18F]1
biology, a number of PET tracers have been published in recent
years with mixed results.4 Reversible tracers, which do not bind
could account at least in part for the suboptimal excretion profile
of the tracer.
to the enzyme active site via covalent bonds, are mainly based
on the quinazoline structure of gefitinib and erlotinib. These
tracers, although displaying promising properties in vitro, were
found to be generally unsuitable for in vivo imaging with only
a recent clinical study by Bahce et al.5 showing promising results
for the detection of mutant EGFR with [11C]erlotinib. The aFaculty of Medicine, Comprehensive Cancer Imaging Centre, Imperial College
London, Hammersmith Hospital Campus, Du Cane Road, London W12
0NN, UK
underlying reason for such inadequacy for in vivo imaging with
reversible TKIs has been attributed to competition between high
bDepartment of Chemistry, Imperial College London, South Kensington Campus,
levels of intracellular ATP and reversible inhibitors for tyrosine
kinase domain occupancy. Therefore, inhibitors bearing a London SW7 2AZ, UK
Michael acceptor, which binds covalently and therefore
*Correspondence to: Federica Pisaneschi, Comprehensive Cancer Imaging Centre,
Imperial College London, Faculty of Medicine, Hammersmith Hospital Campus,
Du Cane Road, London W12 0NN, UK.
irreversibly to cysteine-773 of the EGFR tyrosine kinase, are
expected to attenuate washout by intracellular ATP and to be
more promising for in vivo imaging.
E-mail: f.pisaneschi@imperial.ac.uk
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Copyright © 2013 John Wiley & Sons, Ltd.

F. Pisaneschi et al.
Figure 1. Epidermal growth factor receptor irreversible positron emission tomography imaging agents.
by an in-house developed automated system consisting of an eight two-
In order to circumvent this suboptimal pharmacokinetic
profile, introduction of polar group, such as short
way valve tower system, a mass flow controller, an oven and a six-port/
a
a
two-way HPLC valve. 18O-enriched water, >98% 18O atom, was
polyethylene glycol (PEG) linker or a carbohydrate unit, was
considered an attractive strategy by which to increase the
hydrophilicity of our imaging agent. In the field of EGFR PET
tracers, radiolabelled PEG-anilinoquinazoline derivatives have
been reported by Mishani, Biasco et al.9 (2a–c) and Gelovani
et al.10 (3) (Figure 1). Compounds 2a–c were studied in vitro
and in vivo in mice bearing xenografts derived from human
glioblastoma cell lines U-138 MG (EGFR negative) and U-87 MG.
wtEGFR (EGFR positive). The in vivo imaging protocol showed
only a small increase in uptake in some tumours and no
significant difference between the two model cell lines. The
authors concluded that the lack of specific tumour uptake could
be due to nonselective binding and fast metabolism. Compound
3, [18F]F-PEG6-IPQA, was reported to show high uptake in
activated L858R mutant tumour, whereas low-to-moderate
uptake was observed in wild type EGFR and resistant T790M
mutant tumours. However, despite these promising properties,
the tracer also displayed undesirable rapid metabolism. The
observed rapid metabolism could be partially due to the
presence of the PEG linker. This assumption prompted us to test
the carbohydrate moiety strategy and to couple it to our lead
cyanoquinoline compound by using a triazole linker, which is
known to be highly metabolically stable.
purchased from Rotem.
Siemens Eclipse HP cyclotrons. Semi-preparative HPLC used to isolate
18F]5 was carried out on a Gilson 121 model and quality control (QC)
[
18F]Fluoride was produced using 11 MeV
[
HPLC on a QC Agilent 1100 series (quaternary pump with diode array
UV detector).
Chemistry
Compounds 6, 7 and 10 were synthesised following literature procedures.6,11
Synthesis of compound 5
Sugar 6 (80 mg, 0.38 mmol) and alkyne 7 (44 mg, 0.08 mmol) were
dissolved in CH3CN (1 mL) and water (1.5 mL), and CuSO4.5H2O
(16 mg, 0.06 mmol) and Na ascorbate (16 mg, 0.08 mmol) were added.
The mixture was stirred at room temperature overnight. The mixture
was concentrated, and the resulting Boc-protected compound Boc-5
was purified by flash chromatography on silica gel (AcOEt then
AcOEt/MeOH = 10,1). Boc-protected compound Boc-5 (47 mg, 75%)
was deprotected by adding dioxane (1 mL) and concentrated HCl
(0.1 mL) at room temperature for 10 min. Compound 5.HCl (yellow
salt, 40 mg, 69%) was precipitated with MeOH and dried under
vacuum.
Experimental
tert-Butyl N-[(2E)-3-({4-[(3-chloro-4-fluorophenyl)amino]-3-cyano-7-
ethoxyquinolin-6-yl}carbamoyl)prop-2-en-1-yl]-N-({1-[3-fluoro-4,5-
dihydroxy-6-(hydroxymethyl)oxan-2-yl]-1H-1,2,3-triazol-4-yl}methyl)
carbamate (Boc-5)
General
All reagents and solvents were purchased from Sigma-Aldrich or Fluka
and used without further purification. Flash column chromatography
was carried out on silica gel (Fluka 230–400 mesh, for flash Rf: 0.34 (AcOEt/MeOH = 10,1); 1H NMR (400 MHz, MeOD) δ 8.94 (s, 1H),
chromatography). Thin layer chromatography was performed on 8.54 (br s, 1H), 8.20 (s, 1H), 7.40 (dd, J = 6.5, 1.9, 1H), 7.37–7.30 (m, 1H),
aluminium plates precoated with silica (200 μm, 60 F254), which were 7.28–7.19 (m, 2H), 6.93–6.78 (m, 1H), 6.48–6.33 (m, 1H), 5.92 (d, J = 9.3,
visualised either by quenching of ultraviolet fluorescence (λmax = 254 nm) 1H), 4.81 (dt, JHF = 48.9, JHH = 9.1, 1H), 4.65–4.53 (m, 2H), 4.33 (q, J = 7.0,
or by charring with a KMnO4 dip. 1H and 13C spectra were obtained at 2H), 4.21–4.06 (m, 2H), 3.89–3.77 (m, 2H), 3.71–3.59 (m, 2H), 3.58–3.51
300 K on Bruker AV-400, DRX-400 or AV-500 instruments. Chemical shifts (m, 1H), 1.56 (t, J = 6.8, 3H), 1.47 (s, 9H); 13C NMR (101 MHz, CDCl3) δ
(δ) are given in parts per million (ppm) as referenced to the appropriate 173.0 (s), 166.0 (s), 158.8 (s), 156.4 (s), 154.8 (s), 154.7 [s, (d, JCF = 432.2)],
residual solvent peaks. 13C chemical shifts are assigned as s, d, t and q for
C, CH, CH2 and CH3, respectively. Coupling constant (J) are given in Hertz 125.9, 125.5 (d), 124.3, 123.8 (d), 122.23 [s, (d, JCF = 19.3)], 118.1 [d, (d, JCF
153.5 (s), 142.6 (d), 138.1 (s), 129.5 (s), 128.0 (d), 126.2 [d, (d, JCF = 7.6)],
=
(Hz). Mass spectra were obtained in positive electrospray ionisation
mode on a Micromass LCT Premier equipped with a Waters Atlantis
C18 3 μ column 2.1 × 30 mm. Mobile phase (A) water (0.1% formic acid),
(B) acetonitrile. HR-MS values are valid up to 5 ppm. Synthesis of [18F]
5 was carried out with the help of an Advion Nanotek platform followed
22.6)], 117.8 (s), 114.6 (d), 108.8 (s), 92.1 [d, (d, JCF = 188.0)], 86.5 [d, (d,
JCF = 24.5)], 82.2 (s), 81.2 (d), 76.4 [d, (d, JCF = 16.7)], 70.1 [d, (d, JCF = 7.7)],
66.3 (t), 62.2 (t), 49.8 (t), 43.4, 42.8 (t), 28.6 (q, 3C), 14.7 (q); HR-MS (ESI)
calcd for C36H40ClF2N8O8: 785.2626, found 785.2641 (Δ 1.9 ppm); MS
(ESI): m/z (%) 785 [MH+] (100).
J. Label Compd. Radiopharm 2014, 57 92–96
Copyright © 2013 John Wiley & Sons, Ltd.
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F. Pisaneschi et al.
a pipette. The gamma-counting tubes were placed in a gamma counter
and analysed for 1 min each.
(2E)-N-{4-[(3-Chloro-4-fluorophenyl)amino]-3-cyano-7-ethoxyquinolin-
6-yl}-4-[({1-[3-fluoro-4,5-dihydroxy-6-(hydroxymethyl)oxan-2-yl]-1H-1,2,
3-triazol-4-yl}methyl)amino]but-2-enamide (5)
1H NMR (500 MHz, D2O) δ 8.88 (s, 1H), 8.64 (s, 1H), 8.41 (s, 1H), 7.56 (dd,
J = 2.2, 6.4, 1H), 7.38–7.31 (m, 2H), 7.25 (s, 1H), 6.85 (dt, J = 6.7, 15.3, 1H),
6.58 (d, J = 15.5, 1H), 6.06 (dd, J = 2.6, 9.0, 1H), 4.87 (dt, J = 50.6, 9.0, 1H),
4.47 (s, 2H), 4.33 (q, J = 7.0, 2H), 4.03–3.94 (m, 3H), 3.85 (d, J = 10.5, 1H),
3.77–3.64 (m, 2H), 3.60 (t, J = 9.4, 1H), 1.47 (t, J = 7.0, 3H); 13C NMR
(126 MHz, D2O) δ 164.7 (s), 160.5 [s, (d, JCF = 352.5),] 155.6 (s), 154.5 (s),
151.3 (s), 148.2 (d), 138.3 (s), 137.6 (s), 134.2 (d), 133.1 (s), 129.7 (d),
In vitro cell uptake
A431 and MCF7 cells were seeded 48 h prior to the experiment in
complete Dulbecco’s modified Eagle’s medium in triplicate wells of six-
well plates at densities of 4 × 105 and 3 × 105 cells per well, respectively.
On the day of the experiment, cells were incubated with 0.55 MBq
(15 μCi) of [18F]5 for 60 min at 37 °C. After incubation, the excess
radioactivity was washed from the cells twice with PBS. Cells were
trypsinised and transferred into a counting tube. Following centrifugation
at 5000 rpm for 2 min at 4 °C, the obtained cell pellet was resuspended in
lysis buffer, and counts were measured on a gamma counter. The decay-
corrected counts per minute acquired were normalised to the protein
levels by carrying out a bicinchoninic acid assay.
129.5 (d), 128.6 (s), 127.7 [d, (d, JCF = 8.1)], 126.0 (d), 117.5 [d, (d, JCF
22.8)], 114.2 (d), 111.4 (s), 101.5 (d), 90.4 [d, (d, JCF = 187.5)], 85.6 (s),
84.7 [d, (d, JCF = 24.1)], 79.0 (s), 74.1 [d, (d, JCF = 16.5)], 68.5 [d, (d, JCF
=
=
8.0)], 66.6 (t), 66.5 (d), 60.1 (t), 46.9 (t), 40.9 (t), 13.4 (q); HR-MS (ESI) calcd
for C31H32ClF2N8O6: 685.2101, found 685.2109 (Δ 1.2 ppm); MS (ESI): m/z
(%) 685 [MH+] (20).
Results and discussion
Radiochemistry
In order to improve the pharmacokinetic properties of our
cyanoquinoline tracer while retaining high metabolic stability, we
synthesised a glycosylated triazole cyanoquinoline [18F]5, which
was designed to be radiolabelled by ‘click’ chemistry with the
prosthetic group 2-[18F]fluoro-2-deoxy-β-D-glucopyranosyl azide
([18F]6) (Figure 2).[11a] Not only have 2-[18F]fluoro-2-deoxy-β-D-
glucopyranosyl triazoles been found to be metabolically stable,
but also, incorporation of these moieties have been reported
previously to improve the in vivo properties of PET radiotracers,
such as [18F]fluorodeoxyglucose folate.12 Furthermore, the
calculated distribution coefficient of cyanoquinoline 5 (logDpH
7.4 = 2.40)7 appeared to be more favourable for PET imaging of
somatic lesions.
Unlabelled reference compound 5 was obtained by Cu(I)-
catalysed Huisgen cycloaddition (the ‘click’ reaction) between
2-fluoro-2-deoxy-β-D-glucopyranosyl azide 6 and the N-Boc-
protected alkynylcyanoquinoline 7 (Scheme 1) followed by
deprotection with concentrated HCl–dioxane in 69% overall
yield. Building blocks 6 and 7 were synthesised following
literature procedures.6,11
Synthesis of [18F]6
Aqueous [18F]fluoride (2 mL) was trapped on a QMA cartridge and eluted
with a mixture of Kryptofix-2.2.2 (400μL of a 12 mg/mL stock solution in
water), K2CO3 (100 μL of an 18 mg/mL stock solution in water) and KH2PO4
(100μL of a 18 mg/mL stock solution in water). [18F]Fluoride was dried at
105°C under a stream of nitrogen. MeCN (0.5 mL) was added and
distillation continued. After cooling at room temperature, triflate precursor
8 (3 mg) in acetonitrile (300 μL) was added. This procedure was performed
automatically on the Advion Nanotek platform. The mixture was delivered
into an external heating block and heated at 80 °C for 5 min. The mixture
was then diluted in water (8 mL), and the activity was trapped on a Sep-
Pak light tC18 cartridge (Waters), which was then washed with water
(5 mL). Activity as eluted in a vial with MeCN (2 mL) and concentrated at
80 °C under a stream of He (flow rate 20 mL/min) in ~10 min. NaOH
(60 mM, 250 μL) was added and the mixture heated at 80 °C for 10 min
then neutralised with HCl (60 mM, 250 μL).
Synthesis of [18F]5
A mixture of CuSO4.5H2O (50 μL of a 34.8 mg/mL stock solution in water),
sodium ascorbate (50 μL of a 174 mg/mL stock solution in phosphate-
buffered saline (PBS)), bathophenanthroline disulfonic acid disodium salt
(BPDS) (2.5 mg in 20 μL of PBS) and alkyne 10 (1 mg in 25 μL of water and
25 μL of MeCN) was added to [18F]6, and the mixture was left at room
temperature for 5 min. [18F]5 was isolated by semi-preparative HPLC
[Phenomenex Luna C18 150 × 10 mm HPLC column, isocratic mobile
phase of 20% MeCN/water (5 mM H3PO4), flow rate 3 mL/min]. The HPLC
solution was diluted with water (5 mL) and the activity trapped on a Sep-
Pak light C18 cartridge (Waters, preconditioned with 5 mL of EtOH and
10 mL of PBS). The cartridge was washed with water (5 mL) and the
activity eluted in EtOH/PBS: 1,1.
Figure 2. Epidermal growth factor receptor glycosylated ‘click’ cyanoquinoline
[
18F]5.
Epidermal growth factor receptor tyrosine kinase enzyme inhibition
assay
Epidermal growth factor receptor tyrosine kinase enzyme inhibition
assay was performed as reported in the literature.6
LogD determination
To 50 μL of
[
18F]5 formulated in 10% EtOH in PBS, 450 μL of
preequilibrated PBS and 500 μL of preequilibrated n-octanol were added.
The mixture was vortexed for 20 s before centrifugation at 15 krpm for
3 min. To each of five Eppendorf tubes, 75 μL from the upper n-octanol
layer, 175 μL of preequilibrated n-octanol and 250 μL of preequilibrated
PBS were added. The Eppendorf tubes were vortexed and centrifuged
as earlier. From the upper n-octanol layer, 100 μL was transferred to a
gamma-counting tube with a pipette. The lower PBS layer was first
transferred with a syringe fitted on a thin needle to a second Eppendorf
tube from which 100 μL was transferred to a gamma-counting tube with
Scheme 1. Synthesis of reference compound 5. Reagents and conditions: a)
CuSO4.5H2O, Na ascorbate, water, CH3CN, r.t., 12 h. b) 10% concentrated HCl in
dioxane, r.t., 10 min (69% overall yield).
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F. Pisaneschi et al.
We have previously shown6 that modification of the terminus the solution of azide [18F]6. The cycloaddition was complete in
of the Michael acceptor does not have a significant detrimental 5 min at room temperature, at which point [18F]5 was purified
effect on the ability of this class of inhibitors to irreversibly bind by semi-preparative HPLC and reformulated by solid phase
to EGFR. Receptor binding efficiency of cyanoquinoline 5 was extraction by using a Waters Sep-Pak light C18 cartridge. The
assessed using a cell-free kinase activity inhibition assay (Perkin tracer was obtained in 47.7 7.5% (n = 3) decay-corrected
Elmer, UK). The inhibitor displayed an IC50 value—half maximal radiochemical yield from [18F]6 and >99% radiochemical purity.
inhibitory concentration—of 4.5 0.7 nM, comparable with that The identity of [18F]5 was confirmed by co-elution with the
of cyanoquinoline 1 (1.8 0.2 nM), which demonstrates that it nonradioactive compound 5. Overall nondecay-corrected
retains high EGFR binding property and prompted the radiochemical yield from aqueous fluoride was 8.6 2.3%
subsequent in vitro evaluation (Figure 3).
(n = 3). The radiosynthesis took ~90 min and yielded the tracer
The radiolabelled congener of compound 5, [18F]5, was ready for injection with specific activity of 7.3 GBq/μmol. The
synthesised semi-manually with the help of an Advion Nanotek radioimaging agent [18F]5 was stable for at least 4 h after
automated system. Alkyne-containing cyanoquinoline 10 was formulation in PBS. The distribution coefficient of the tracer [18F]
obtained from the corresponding N-Boc-protected compound 5 was then evaluated by measuring the distribution of radioactivity
7 by treatment with concentrated HCl in 1,4-dioxane in between preequilibrated n-octanol and PBS (pH 7.4) using the
quantitative yield.6 Prosthetic group [18F]6 was synthesised as ‘shake flask’ method.14 The logarithm of the ratio was found to
reported by Maschauer et al.[11a] from the β-mannosyl azide be logDpH 7.4 = 2.51 0.02 (n = 5). This value is similar to the
precursor 8[11a] using [18F]KF/Kryptofix-2.2.2 at 80 °C for 5 min. calculated value (logDpH 7.4 = 2.40)7 and should allow reasonable
In the process of forming the [18F]KF/cryptand complex, KH2PO4 cell penetration and subsequent localisation to the tyrosine kinase
was added in order to buffer the basicity of K2CO3 and reduce domain of EGFR. Moreover, as this logD falls within the desired 0–3
degradation of the precursor. The Advion Nanotek was used to range, this derivative is expected to display a more favourable
dry the fluoride and to add precursor 8, whereas the pharmacokinetic profile.
radiolabelling reaction to form the intermediate [18F]9 was
Compound [18F]5 was tested in vitro in a cellular uptake
performed in an external heating block. Intermediate [18F]9 experiment. A431 cells, harbouring high EGFR expression, were
was purified from any unreacted [18F]fluoride by solid phase compared with low EGFR expressing MCF7 cells, as shown in
extraction on a Waters Sep-Pak light tC18 cartridge and released Figure 4. The uptake of [18F]5 was twofold higher in the A431
with acetonitrile. Acetonitrile was removed at 80 °C under a cells than in the MCF7 cells. Moreover, the uptake of [18F]5 in
stream of nitrogen and 60-mM aqueous NaOH was added to the A431 cells was significantly reduced when cells were
remove the acetate protecting groups. The reaction was pretreated with cold 5 prior to incubation with [18F]5. On the
complete after 10 min at 80 °C, as assessed by radio-HPLC. The other hand, pretreatment with cold 5 had no effect on tracer
reaction mixture was then neutralised by addition of 60-mM uptake in MCF7 cells. This set of experiments strongly suggest
aqueous HCl and used in the ‘click’ reaction without further that tracer [18F]5 exhibits selectivity for EGFR.
purification (Scheme 2).
The ‘click’ reaction was performed in a CuSO4/Na ascorbate
solution containing BPDS (Scheme 3). BPDS is a Cu(I)-stabilising
bidentate ligand, which has been shown previously to enhance
greatly the rate of the ‘click’ reaction.13 Precursor 10 was added
to this solution, and the resulting mixture was then added to
Scheme 3. Reagents and conditions: a) CuSO4, Na ascorbate, bathophenanthroline
disulfonic acid disodium salt, water, MeCN, PBS, rt, 5 min.
Figure 3. In vitro cell-free inhibition of epidermal growth factor receptor kinase
activity by compound 5.
Figure 4. A. Cellular uptake of [18F]5 in A431 and MCF7 cells. Data show mean
standard error of the mean from triplicate of three independent experiments. B.
Western blot analysis of epidermal growth factor receptor (EGFR) expression in
Scheme 2. Reagents and conditions: a) [18F]KF/K222, 80 °C, 5 min. b) NaOH(aq)
A431 and MCF7 cells indicates significantly higher EGFR levels in A431 cells as
(60 mM), 80 °C, 10 min then HCl(aq) (60 mM).
compared with MCF7 cells.
J. Label Compd. Radiopharm 2014, 57 92–96
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www.jlcr.org

F. Pisaneschi et al.
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Conclusion
In conclusion, a new EGFR-specific tracer [18F]5 has been
synthesised by ‘click’ chemistry with 2-[18F]fluoro-2-deoxy-β-D-
glucopyranosyl azide ([18F]6). The tracer was obtained in
47.7 7.5% (n = 3) decay-corrected radiochemical yield from
[18F]6, and the overall nondecay-corrected radiochemical yield
from aqueous [18F]fluoride was 8.6 2.3% (n = 3). An in vitro
preliminary study showed selectivity of the tracer for EGFR and
encourages further evaluation.
Acknowledgements
This work was funded by Cancer Research UK–Engineering and
Physical Sciences Research Council grant (in association with
the Medical Research Council and Department of Health
(England)) grant C2536/A10337. E. O. A.’s laboratory receives core
funding from the UK Medical Research Council
(MC_A652_5PY80). F. P. thanks Imanova Ltd for providing the
radiolabelling facilities.
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Conflict of Interest
The authors did not report any conflict of interest.
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Supporting information
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J. Label Compd. Radiopharm 2014, 57 92–96