7 research outputs found
Direct Plasma Metabolite Analysis of Positron Emission Tomography Radioligands by Micellar Liquid Chromatography with Radiometric Detection
Determination of radio-metabolites in plasma samples
taken during a positron emission tomography (PET) study is an important
component in the pharmacokinetic evaluation of PET radioligands. We
have developed and validated a new analytical procedure for the plasma
metabolite analysis of PET radioligands based on micellar liquid chromatography
using an anionic surfactant mobile phase. Chromatographic separation
was performed on an octadecyl semipreparative column (10 mm I.D. ×
160 mm, 10 μm) using 100 mM sodium dodecyl sulfate (SDS) and
1-butanol in 10 mM sodium-phosphate (pH 7.2) at a flow rate of 5 mL/min.
The samples taken from monkey or human plasma during PET measurements
were directly injected into a liquid chromatographic (LC) system coupled
to an online radiometric detector under micellar conditions using
1–2% (v/v) 1-butanol mobile phase to remove plasma proteins
and concentrate the analytes at the column head. At 2 min, mobile
phase was changed to elute and separate PET radioligand and its radiometabolites
with high peak capacity under high submicellar conditions (10–25%
1-butanol). This procedure allowed direct plasma injection (up to
2 mL) into the LC column without any pretreatment with a short analysis-time
of 8–10 min. Satisfactory reproducibility, linearity, sensitivity,
accuracy and recovery were obtained in the validation study. The developed
method was successfully applied to study the metabolism for diverse
groups of PET radioligands and provided reliable determination of
PET radioligands in human and monkey plasma. This method is advantageous
in terms of simplifying and shortening the processes required to analyze
short-lived radioligands as well as in providing a more accurate estimation
of the metabolite corrected input function, especially for the radioligands
with lower recoveries or degradation potential during the deproteination
process in a conventional procedure
Direct Plasma Metabolite Analysis of Positron Emission Tomography Radioligands by Micellar Liquid Chromatography with Radiometric Detection
Determination of radio-metabolites in plasma samples
taken during a positron emission tomography (PET) study is an important
component in the pharmacokinetic evaluation of PET radioligands. We
have developed and validated a new analytical procedure for the plasma
metabolite analysis of PET radioligands based on micellar liquid chromatography
using an anionic surfactant mobile phase. Chromatographic separation
was performed on an octadecyl semipreparative column (10 mm I.D. ×
160 mm, 10 μm) using 100 mM sodium dodecyl sulfate (SDS) and
1-butanol in 10 mM sodium-phosphate (pH 7.2) at a flow rate of 5 mL/min.
The samples taken from monkey or human plasma during PET measurements
were directly injected into a liquid chromatographic (LC) system coupled
to an online radiometric detector under micellar conditions using
1–2% (v/v) 1-butanol mobile phase to remove plasma proteins
and concentrate the analytes at the column head. At 2 min, mobile
phase was changed to elute and separate PET radioligand and its radiometabolites
with high peak capacity under high submicellar conditions (10–25%
1-butanol). This procedure allowed direct plasma injection (up to
2 mL) into the LC column without any pretreatment with a short analysis-time
of 8–10 min. Satisfactory reproducibility, linearity, sensitivity,
accuracy and recovery were obtained in the validation study. The developed
method was successfully applied to study the metabolism for diverse
groups of PET radioligands and provided reliable determination of
PET radioligands in human and monkey plasma. This method is advantageous
in terms of simplifying and shortening the processes required to analyze
short-lived radioligands as well as in providing a more accurate estimation
of the metabolite corrected input function, especially for the radioligands
with lower recoveries or degradation potential during the deproteination
process in a conventional procedure
Direct Plasma Metabolite Analysis of Positron Emission Tomography Radioligands by Micellar Liquid Chromatography with Radiometric Detection
Determination of radio-metabolites in plasma samples
taken during a positron emission tomography (PET) study is an important
component in the pharmacokinetic evaluation of PET radioligands. We
have developed and validated a new analytical procedure for the plasma
metabolite analysis of PET radioligands based on micellar liquid chromatography
using an anionic surfactant mobile phase. Chromatographic separation
was performed on an octadecyl semipreparative column (10 mm I.D. ×
160 mm, 10 μm) using 100 mM sodium dodecyl sulfate (SDS) and
1-butanol in 10 mM sodium-phosphate (pH 7.2) at a flow rate of 5 mL/min.
The samples taken from monkey or human plasma during PET measurements
were directly injected into a liquid chromatographic (LC) system coupled
to an online radiometric detector under micellar conditions using
1–2% (v/v) 1-butanol mobile phase to remove plasma proteins
and concentrate the analytes at the column head. At 2 min, mobile
phase was changed to elute and separate PET radioligand and its radiometabolites
with high peak capacity under high submicellar conditions (10–25%
1-butanol). This procedure allowed direct plasma injection (up to
2 mL) into the LC column without any pretreatment with a short analysis-time
of 8–10 min. Satisfactory reproducibility, linearity, sensitivity,
accuracy and recovery were obtained in the validation study. The developed
method was successfully applied to study the metabolism for diverse
groups of PET radioligands and provided reliable determination of
PET radioligands in human and monkey plasma. This method is advantageous
in terms of simplifying and shortening the processes required to analyze
short-lived radioligands as well as in providing a more accurate estimation
of the metabolite corrected input function, especially for the radioligands
with lower recoveries or degradation potential during the deproteination
process in a conventional procedure
Development of [<i>Carbonyl</i>-<sup>11</sup>C]AZ13198083, a Novel Histamine Type‑3 Receptor Radioligand with Favorable Kinetics
The
histamine subtype-3 receptor (H<sub>3</sub>R) is implicated
in a range of central nervous system disorders, and several radioligands
have been developed for H<sub>3</sub>R positron emission tomography
imaging. However, a limitation of currently used PET radioligands
for H<sub>3</sub>R is the slow binding kinetics in high density brain
regions. To address this, we herein report the development of three
novel candidate H<sub>3</sub>R radioligands, namely, [<i>carbonyl</i>-<sup>11</sup>C]AZ13153556 ([<i>carbonyl</i>-<sup>11</sup>C]<b>4</b>), [<i>carbonyl</i>-<sup>11</sup>C]AZD5213([<i>carbonyl</i>-<sup>11</sup>C]<b>5</b>), and [<i>carbonyl</i>-<sup>11</sup>C]AZ13198083 ([<i>carbonyl</i>-<sup>11</sup>C]<b>6</b>), and their subsequent preclinical evaluation in
nonhuman primates (NHP). Radioligands [<i>carbonyl</i>-<sup>11</sup>C]<b>4</b>–<b>6</b> were produced and
isolated in high radioactivity (>1000 MBq), radiochemical purity
(>99%),
and moderate molar activity (19–28 GBq/μmol at time of
injection) using a palladium-mediated <sup>11</sup>C-aminocarbonylation
protocol. All three radioligands showed high brain permeability as
well as a regional brain radioactivity distribution in accordance
with H<sub>3</sub>R expression (striatum > cortex > cerebellum).
[<i>Carbonyl</i>-<sup>11</sup>C]<b>6</b> displayed
the most
favorable in vivo kinetics and brain uptake, with an early peak in
the striatal time–activity curve followed by a progressive
washout from the brain. The specificity and on-target kinetics of
[<i>carbonyl</i>-<sup>11</sup>C]<b>6</b> were next
investigated in pretreatment and displacement studies. After pretreatment
or displacement with <b>5</b> (0.1 mg/kg), a uniformly low distribution
of radioactivity across the NHP brain was observed. Collectively,
this work demonstrates that [<i>carbonyl</i>-<sup>11</sup>C]<b>6</b> is a promising candidate for H<sub>3</sub>R imaging
in human subjects
Development of [<i>Carbonyl</i>-<sup>11</sup>C]AZ13198083, a Novel Histamine Type‑3 Receptor Radioligand with Favorable Kinetics
The
histamine subtype-3 receptor (H<sub>3</sub>R) is implicated
in a range of central nervous system disorders, and several radioligands
have been developed for H<sub>3</sub>R positron emission tomography
imaging. However, a limitation of currently used PET radioligands
for H<sub>3</sub>R is the slow binding kinetics in high density brain
regions. To address this, we herein report the development of three
novel candidate H<sub>3</sub>R radioligands, namely, [<i>carbonyl</i>-<sup>11</sup>C]AZ13153556 ([<i>carbonyl</i>-<sup>11</sup>C]<b>4</b>), [<i>carbonyl</i>-<sup>11</sup>C]AZD5213([<i>carbonyl</i>-<sup>11</sup>C]<b>5</b>), and [<i>carbonyl</i>-<sup>11</sup>C]AZ13198083 ([<i>carbonyl</i>-<sup>11</sup>C]<b>6</b>), and their subsequent preclinical evaluation in
nonhuman primates (NHP). Radioligands [<i>carbonyl</i>-<sup>11</sup>C]<b>4</b>–<b>6</b> were produced and
isolated in high radioactivity (>1000 MBq), radiochemical purity
(>99%),
and moderate molar activity (19–28 GBq/μmol at time of
injection) using a palladium-mediated <sup>11</sup>C-aminocarbonylation
protocol. All three radioligands showed high brain permeability as
well as a regional brain radioactivity distribution in accordance
with H<sub>3</sub>R expression (striatum > cortex > cerebellum).
[<i>Carbonyl</i>-<sup>11</sup>C]<b>6</b> displayed
the most
favorable in vivo kinetics and brain uptake, with an early peak in
the striatal time–activity curve followed by a progressive
washout from the brain. The specificity and on-target kinetics of
[<i>carbonyl</i>-<sup>11</sup>C]<b>6</b> were next
investigated in pretreatment and displacement studies. After pretreatment
or displacement with <b>5</b> (0.1 mg/kg), a uniformly low distribution
of radioactivity across the NHP brain was observed. Collectively,
this work demonstrates that [<i>carbonyl</i>-<sup>11</sup>C]<b>6</b> is a promising candidate for H<sub>3</sub>R imaging
in human subjects
Synthesis of Three Novel Fluorine-18 Labeled Analogues of l-Deprenyl for Positron Emission Tomography (PET) studies of Monoamine Oxidase B (MAO-B)
The aim in this project was to synthesize and to study fluorine-18 labeled analogues of l-deprenyl which bind selectively to the enzyme monoamine oxidase B (MAO-B). Three fluorinated l-deprenyl analogues have been generated in multistep organic syntheses. The most promising fluorine-18 compound <i>N</i>-[(2<i>S</i>)-1-[<sup>18</sup>F]fluoro-3-phenylpropan-2-yl]-<i>N</i>-methylprop-2-yn-1-amine (<b>4c</b>) was synthesized by a one-step fluorine-18 nucleophilic substitution reaction. Autoradiography on human brain tissue sections demonstrated specific binding for compound <b>4c</b> to brain regions known to have a high content of MAO-B. In addition, the corresponding nonradioactive fluorine-19 compound (<b>13</b>) inhibited recombinant human MAO-B with an IC<sub>50</sub> of 170.5 ± 29 nM but did not inhibit recombinant human MAO-A (IC<sub>50</sub> > 2000 nM), demonstrating its specificity. Biodistribution of <b>4c</b> in mice showed high initial brain uptake leveling at 5.2 ± 0.04%ID/g after 2 min post injection. In conclusion, compound <b>4c</b> is a specific inhibitor of MAO-B with high initial brain uptake in mice and is, therefore, a candidate for further investigation in PET
Discovery and Preclinical Validation of [<sup>11</sup>C]AZ13153556, a Novel Probe for the Histamine Type 3 Receptor
The histamine type 3 receptor (H<sub>3</sub>) is a G protein-coupled
receptor implicated in several disorders of the central nervous system.
Herein, we describe the radiolabeling and preclinical evaluation of
a candidate radioligand for the H<sub>3</sub> receptor, 4-(1<i>S</i>,2<i>S</i>)-2-(4-cyclobutylpiperazine-1-carbonyl)cyclopropyl]-<i>N</i>-methyl-benzamide (<b>5</b>), and its comparison
with one of the frontrunner radioligands for H<sub>3</sub> imaging,
namely, GSK189254 (<b>1</b>). Compounds <b>1</b> and <b>5</b> were radiolabeled with tritium and carbon-11 for in vitro
and in vivo imaging experiments. The in vitro binding of [<sup>3</sup>H]<b>1</b> and [<sup>3</sup>H]<b>5</b> was examined by
(i) saturation binding to rat and nonhuman primate brain tissue homogenate
and (ii) in vitro autoradiography on tissue sections from rat, guinea
pig, and human brain. The in vivo binding of [<sup>11</sup>C]<b>1</b> and [<sup>11</sup>C]<b>5</b> was examined by PET imaging
in mice and nonhuman primates. <i>B</i><sub>max</sub> values
obtained from Scatchard analysis of [<sup>3</sup>H]<b>1</b> and
[<sup>3</sup>H]<b>5</b> binding were in good agreement. Autoradiography
with [<sup>3</sup>H]<b>5</b> on rat, guinea pig, and human brain
slices showed specific binding in regions known to be enhanced in
H<sub>3</sub> receptors, a high degree of colocalization with [<sup>3</sup>H]<b>1</b>, and virtually negligible nonspecific binding
in tissue. PET measurements in mice and nonhuman primates demonstrated
that [<sup>11</sup>C]<b>5</b> binds specifically and reversibly
to H<sub>3</sub> receptors in vivo with low nonspecific binding in
brain tissue. Whereas [<sup>11</sup>C]<b>1</b> showed similar
binding characteristics in vivo, the binding kinetics appeared faster
for [<sup>11</sup>C]<b>5</b> than for [<sup>11</sup>C]<b>1</b>. Conclusions: [<sup>11</sup>C]<b>5</b> has suitable
properties for quantification of H<sub>3</sub> receptors in nonhuman
primate brain and has the potential to offer improved binding kinetics
in man compared to [<sup>11</sup>C]<b>1</b>