Limits...
Radiosynthesis and evaluation of an 18F-labeled positron emission tomography (PET) radioligand for metabotropic glutamate receptor subtype 4 (mGlu4).

Kil KE, Poutiainen P, Zhang Z, Zhu A, Choi JK, Jokivarsi K, Brownell AL - J. Med. Chem. (2014)

Bottom Line: Of these compounds, N-(3-chloro-4-(4-fluoro-1,3-dioxoisoindolin-2-yl)phenyl)-2-picolinamide (3, KALB001) exhibited improved binding affinity (IC50 = 5.1 nM) compared with ML128 (1) and was subsequently labeled with (18)F.In vivo imaging studies in a monkey showed that the radiotracer quickly penetrated the brain with the highest accumulation in the brain areas known to express mGlu4.Despite some unfavorable radiotracer properties like fast washout in rodent studies, [(18)F]3 is the first (18)F-labeled mGlu4 radioligand, which can be further modified to improve pharmacokinetics and brain penetrability for future human studies.

View Article: PubMed Central - PubMed

Affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital , Charlestown, Massachusetts 02129, United States.

ABSTRACT
Four 4-phthalimide derivatives of N-(3-chlorophenyl)-2-picolinamide were synthesized as potential ligands for the PET imaging of mGlu4 in the brain. Of these compounds, N-(3-chloro-4-(4-fluoro-1,3-dioxoisoindolin-2-yl)phenyl)-2-picolinamide (3, KALB001) exhibited improved binding affinity (IC50 = 5.1 nM) compared with ML128 (1) and was subsequently labeled with (18)F. When finally formulated in 0.1 M citrate buffer (pH 4) with 10% ethanol, the specific activity of [(18)F]3 at the end of synthesis (EOS) was 233.5 ± 177.8 GBq/μmol (n = 4). The radiochemical yield of [(18)F]3 was 16.4 ± 4.8% (n = 4), and the purity was over 98%. In vivo imaging studies in a monkey showed that the radiotracer quickly penetrated the brain with the highest accumulation in the brain areas known to express mGlu4. Despite some unfavorable radiotracer properties like fast washout in rodent studies, [(18)F]3 is the first (18)F-labeled mGlu4 radioligand, which can be further modified to improve pharmacokinetics and brain penetrability for future human studies.

Show MeSH
Bindingcurves from competitive binding assay (mGlu4).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4230996&req=5

fig2: Bindingcurves from competitive binding assay (mGlu4).

Mentions: Table 1 presents the IC50 valuesof compounds 1–4, 7,and 8 obtained from in vitro competitive binding assayusing [3H]1. The results show that the leadcompounds from N-phenyl-2-picolinamide series 1 and 2 have IC50 values of 12.8 and9.9 nM, respectively. Compound 2 has been used for invivo mGlu4 blocking experiments for [11C]1.17 The phthalimide derivatives, 3 (5.1 nM) and 4 (4.2 nM) gave improved affinitycompared to 1 while compounds 7 (11.8 nM)and 8 (26.3 nM) showed similar or less affinity to mGlu4 compared to 1. This result shows that 3 and 4 have similar affinity while Merck’spatent20 presents that 4 (11nM) has better affinity than 3 (36 nM), which may becaused from using cells expressing different mGlu4 receptors.We used the rat mGlu4, while Merck employed the human mGlu4. The results verified that 3 and 4 are more potent compounds for developing an mGlu4 PETligand. The results also indicate that these phthalimide compoundsinteract with the same allosteric site in mGlu4 where 1 binds because the quantitative specific binding curves ofthese compounds show complete replacement of the radioligand at ahigher concentration (Figure 2). In addition,the selectivities of 3 to mGlu1, mGlu5, and mGlu8 were determined by the functional assays,which showed little activity against to these mGluRs (Supporting Information B).22,23


Radiosynthesis and evaluation of an 18F-labeled positron emission tomography (PET) radioligand for metabotropic glutamate receptor subtype 4 (mGlu4).

Kil KE, Poutiainen P, Zhang Z, Zhu A, Choi JK, Jokivarsi K, Brownell AL - J. Med. Chem. (2014)

Bindingcurves from competitive binding assay (mGlu4).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230996&req=5

fig2: Bindingcurves from competitive binding assay (mGlu4).
Mentions: Table 1 presents the IC50 valuesof compounds 1–4, 7,and 8 obtained from in vitro competitive binding assayusing [3H]1. The results show that the leadcompounds from N-phenyl-2-picolinamide series 1 and 2 have IC50 values of 12.8 and9.9 nM, respectively. Compound 2 has been used for invivo mGlu4 blocking experiments for [11C]1.17 The phthalimide derivatives, 3 (5.1 nM) and 4 (4.2 nM) gave improved affinitycompared to 1 while compounds 7 (11.8 nM)and 8 (26.3 nM) showed similar or less affinity to mGlu4 compared to 1. This result shows that 3 and 4 have similar affinity while Merck’spatent20 presents that 4 (11nM) has better affinity than 3 (36 nM), which may becaused from using cells expressing different mGlu4 receptors.We used the rat mGlu4, while Merck employed the human mGlu4. The results verified that 3 and 4 are more potent compounds for developing an mGlu4 PETligand. The results also indicate that these phthalimide compoundsinteract with the same allosteric site in mGlu4 where 1 binds because the quantitative specific binding curves ofthese compounds show complete replacement of the radioligand at ahigher concentration (Figure 2). In addition,the selectivities of 3 to mGlu1, mGlu5, and mGlu8 were determined by the functional assays,which showed little activity against to these mGluRs (Supporting Information B).22,23

Bottom Line: Of these compounds, N-(3-chloro-4-(4-fluoro-1,3-dioxoisoindolin-2-yl)phenyl)-2-picolinamide (3, KALB001) exhibited improved binding affinity (IC50 = 5.1 nM) compared with ML128 (1) and was subsequently labeled with (18)F.In vivo imaging studies in a monkey showed that the radiotracer quickly penetrated the brain with the highest accumulation in the brain areas known to express mGlu4.Despite some unfavorable radiotracer properties like fast washout in rodent studies, [(18)F]3 is the first (18)F-labeled mGlu4 radioligand, which can be further modified to improve pharmacokinetics and brain penetrability for future human studies.

View Article: PubMed Central - PubMed

Affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital , Charlestown, Massachusetts 02129, United States.

ABSTRACT
Four 4-phthalimide derivatives of N-(3-chlorophenyl)-2-picolinamide were synthesized as potential ligands for the PET imaging of mGlu4 in the brain. Of these compounds, N-(3-chloro-4-(4-fluoro-1,3-dioxoisoindolin-2-yl)phenyl)-2-picolinamide (3, KALB001) exhibited improved binding affinity (IC50 = 5.1 nM) compared with ML128 (1) and was subsequently labeled with (18)F. When finally formulated in 0.1 M citrate buffer (pH 4) with 10% ethanol, the specific activity of [(18)F]3 at the end of synthesis (EOS) was 233.5 ± 177.8 GBq/μmol (n = 4). The radiochemical yield of [(18)F]3 was 16.4 ± 4.8% (n = 4), and the purity was over 98%. In vivo imaging studies in a monkey showed that the radiotracer quickly penetrated the brain with the highest accumulation in the brain areas known to express mGlu4. Despite some unfavorable radiotracer properties like fast washout in rodent studies, [(18)F]3 is the first (18)F-labeled mGlu4 radioligand, which can be further modified to improve pharmacokinetics and brain penetrability for future human studies.

Show MeSH