Neurochem. Int. Vol.20, Suppl.,pp. 329S-333S,1992 Printed in GreatBritain.All fightsreserved
0197-0186/92$5.00+0.00 Copyright© 1992PergamonPressplc
IMAGING OF D O P A M I N E RECEPTORS USING PET A N D SPECT H]~KAN HALL,~ LARS FARDE,~ CHRISTERHALLDIN,l THOMASHOGBERG,3 STIG LARSSON2 and Cr~RANSEDVALL! ~Department of Psychiatryand Psychology,and 2Department of Radiation Physics, Karolinska Hospital, 10401 Stockholm, Sweden; and 3CNS2 Research and Development, Astra Research Centre AB, 15185 S6dertiije, Sweden
The development of new brain imaging tecniques such as PET (positron emission tomography) and SPECT (Single Photon Emission Computed Tomograpy) has provided potential tools for the study of dopamine receptors in the living human brain (Sedvall et al. 1986). To visualize dopamine Dmreceptors with PET, ["C]SCH 23390 has been prepared and used both in monkey (I-Ialldin et al. 1986) and in humans (Farde et aL 1987). For the examination of dopamine D2 receptors spiperone derivatives have been used (Wagner et al. 1983), ligands known to have affinity also for 5HT2 receptors (Leysen et al. 1978). More selective ligands for the dopamine D2 receptors are found among the substituted benzamides, of which raclopride, and its analogue eticlopride, have both been labelled with the positron emitting isotope "C and have been used extensively in monkey and human brain studies (Farde et al. 1985, 1986, Halldin et al. 1990a).
with ~SFin the ethyl group results in a compound with a lower affinity, and this analogue has been shown to be unsuitable for use in PET (Halldin et al. 1989). SPECT may, due to general availability and comparatively low costs, be used for the examination of a large population of patients (Maurer 1988). For SPECT studies, the ligand should preferably be labelled with a gamma emitting isotope, and ~23I, an isotope with a half-life of 13.3 hours, is suitable for these studies. Another gamma emitting isotope, m25I, has a longer half-life (60 days), but with a photon energy that is too low for SPECT. However, m25Ilabelled ligands may be used for receptor binding studies /n vitro and in vivo as well as for autoradiographic studies. For the development of'~I-labelled radioligands for SPECT, the use of the ~25I-labelled ligand provides essential information about the binding properties of the ligand in vitro and in rive in animals. OH
O
CI ~
N
-
-
I 1CH3
C2H5
CI
[HC]SCH 23390
[11C]Raclopride
The useful properties of ['~C]raclopride for PET studies has encouraged us to search for other substituted benzamides suitable as ligands for the examination of dope.mine D2 receptors both with PET and SPECT. Of particular interest has been to find a compound that could be labelled with the positron emitting isotope ~SF, which has a half-life of 110 minutes (T~/2of"C is 20 minutes), allowing PET studies covering a time span of hours. Labelling raclopride
In this presentation, we report on some recent studies with ["qraclopride, and present two new substituted benzamides useful for/n rive visualization of dopamine D2 receptor using PET and SPECT. PET STUDIESIN HUMANSUSING["C]IIACLOPRID[
We have examined dopamine D2 receptors in drug naive schizophrenic patients with ["qraclopride. The
329S
330S
Dopamine 90 Table 1. Dopamine D 2 ([~C]raclopride binding) and dopamine D~ ([J~C]SCH 2339~! binding) receptor occupancy in patients treated with psychoactive drugs Drug
Daily dosage (rag)
Phenotiazines Chlorpromazine
2 ~ 100 2 ~ 100 2 × 5 2 × 4 2 × 8
80 75 80 79 0
2 x 5 40 weekly
74
Thioridazine Trifluoperazine
Perphenazine Perphenazine Thioxantenes Flupentixol Flupentixol Zuclopentixot Butyrophenones
Receptor occupancy (%) ........................................................... Dopamine D, Dopamine D,
29 0
36 11
200 weekly
Haloperidol
2 2 2 2
× 6 x 3 x 3 x 2 3 × 100
86 85 89 81 70
2 × 4
77
2 x 300 2 × 150
65 40
Raclopride
2 x 400 2 x 400 2 × 400 2 × 4 2 x ~
82 73 68 72 65
Tricyclie antidepressant Nortriptyline
2 × 25
-3
Haloperidol Haloperidot Haloperidol Melperone
Diphenylbutyls Pimozide
Dibenzodiazepines Clozapine Clozapine Substituted benzamides Sulpiride Sulpiride Sulpiride Raclopride
42 -7
The receptor occupancies were calculated in relation to uptake of radioligand in healthy subjects.
density of dopamine D, receptors was shown to be similar in the schizophrenic patients and in matched controls (Farde et al. 1990). In patients on treatment with neuroleptic drugs 60-80% of the dopamine D, receptors in the basal ganglia are occupied by the neuroleptic, as measured with ["C]raclopride and PET (Table 1, Farde et al. 1988, 1989). Treatment with the atypical neuroleptic clozapine, however, blocks a lower amount of['~C]raclopride binding. Compared to classical neuroleptics, clozapine also blocks a high proportion of [IzC]SCH 23390 binding in the basal ganglia (Table 1, Farde et al. 1990). PET STUDIES IN A MONKEY USING[~SFINCQi 15 In order to be able to perform longer PET studies we have looked for compounds suitable for labelling with tSF. Of the substituted benzamides with a fluorine in the structure was chosen NCQ 115 ((R)-5-bromo-N[(l-(4-fluorobenzyl)-2-pyrrolidinyl) methyl]-2.3-dimethoxybenzamide), a compound which in initial in vitro binding studies has been shown to be potent inhibitor of the dopamine Dz receptors (Hogberg et al. 1991, Hall et al. 1991a). NCQ 115 was developed from a
O
CH30
18F fiSF1NCO
115
series of substituted benzamides with varying substituents on the nitrogen in the pyrrolidine ring. Substitution of the N-ethyl group to an N-benzyl g r o u p , or as in NCQ l l 5 , to a n N-4-fluorobenzyl group, results in a reversed stereoselectivity, i.e. the affinity is confined to the R-enantiomer, which contrasts to the corresponding l-ethyl derivatives like FLB 457, raclopride and sulpiride, where the pharmacological activity is found in the (S)enantiomer. [~SF]NCQ 115 was prepared and examined in a PET study on a Cynomolgus monkey (Haltdin et aL 1990b). There was a marked uptake of [~SF]NCQ l l5 in the basal ganglia (Figs l and 2) indicating that this 'SF-
Dopamine 90
331S
OH
0
CH2
z
1 Ctt3
(A)
. . . .
l:
Fig. 1. PET imase showing the distribution of radioactivity in a horizontal brain section of a Cynomolgus monkey after the IV injection of 45 MBq [~SF]NCQ115.
,so~
_ ~3 ~
--'T0V
0,o
o
$o
60 Time
90 (mln)
12o
ISO
t
.... W
~
o Time'(hours)' '
•
iv.
Fig. 2. Time course of radioactivity in striatum (squares)and cerebellum (open circles) in a Cynomolgus monkey after administration of 45 MBq [~SF]NCQ 115. Shown is also specific binding, defined as radioactivity in the striatum minus that in the cerebellum (triangles) and ratio of radioactivity striatum/cerebellum (filledcircles). labelled ligand is suitable for PET-studies for the examination of binding during a couple of hours.
~
a
loo
Oo
1
~2
s
4
8
•
11me ('-noem) Fig. 3. Time course of a~eumulation of radioa~'vity in the striatum and cerebellum of two ~ 1 1 ~ monkeys after the IV injection [mI]NCQ 298 (90 MBq and 145 MBq, respectively). Radioactivity (corrected for recovery) vs time in two brain resiom (striauma and cmebelh~) ~ binding in striatum (as defined from the r•dilw~vity of striatum minus that in cerebellum)vs time. Two l m l ~ mad 15 minutes after injection, 12 nag raclopride was injected IV to one of the monkeys.
SPECTSTUDIESIN MONKEYSUSING[t=IINCQ296 For the use in SPECT, NCQ 298 ((S)-3-iodo-N-[(1ethyl-2-pyrrolidinyl)methyl]-5,6-dimehtoxysalicylamide) was prepared (Hogberg et al. 1990) (Table 2). The binding characteristics of [~25I]NCQ 298 was determined in vitro and/n vivo, as well as its anatomical distribution in brain using in vitro autoradiography (Hall et al. 1991b). The in vivo binding of[125I]NCQ 298 was saturated at very low concentrations, both in striatal and cortical tissue homogenates. The Bmax was rather low in the rat striatum (11.3 fmol/mg tissue, Table 3) as compared to that of [3H]raclopride
Table2 Name Raelopride Etielopride IBZM NCQ 298
Y
2
C! C2H5 I I
Ci CI H OCH3
(Bmax=23.5 fmol/mg tissue, Kohler et aL 1985). Binding could also be determined in tissue prepared from the rat cortex (Bmax = 0.26 fmol/mg, Table 3). The distribution in the brain of [mI]NCQ 298 was
332S
I)opamine 90 Table 3. Density
0197-0186/92$5.00+0.00 Copyright© 1992PergamonPressplc
IMAGING OF D O P A M I N E RECEPTORS USING PET A N D SPECT H]~KAN HALL,~ LARS FARDE,~ CHRISTERHALLDIN,l THOMASHOGBERG,3 STIG LARSSON2 and Cr~RANSEDVALL! ~Department of Psychiatryand Psychology,and 2Department of Radiation Physics, Karolinska Hospital, 10401 Stockholm, Sweden; and 3CNS2 Research and Development, Astra Research Centre AB, 15185 S6dertiije, Sweden
The development of new brain imaging tecniques such as PET (positron emission tomography) and SPECT (Single Photon Emission Computed Tomograpy) has provided potential tools for the study of dopamine receptors in the living human brain (Sedvall et al. 1986). To visualize dopamine Dmreceptors with PET, ["C]SCH 23390 has been prepared and used both in monkey (I-Ialldin et al. 1986) and in humans (Farde et aL 1987). For the examination of dopamine D2 receptors spiperone derivatives have been used (Wagner et al. 1983), ligands known to have affinity also for 5HT2 receptors (Leysen et al. 1978). More selective ligands for the dopamine D2 receptors are found among the substituted benzamides, of which raclopride, and its analogue eticlopride, have both been labelled with the positron emitting isotope "C and have been used extensively in monkey and human brain studies (Farde et al. 1985, 1986, Halldin et al. 1990a).
with ~SFin the ethyl group results in a compound with a lower affinity, and this analogue has been shown to be unsuitable for use in PET (Halldin et al. 1989). SPECT may, due to general availability and comparatively low costs, be used for the examination of a large population of patients (Maurer 1988). For SPECT studies, the ligand should preferably be labelled with a gamma emitting isotope, and ~23I, an isotope with a half-life of 13.3 hours, is suitable for these studies. Another gamma emitting isotope, m25I, has a longer half-life (60 days), but with a photon energy that is too low for SPECT. However, m25Ilabelled ligands may be used for receptor binding studies /n vitro and in vivo as well as for autoradiographic studies. For the development of'~I-labelled radioligands for SPECT, the use of the ~25I-labelled ligand provides essential information about the binding properties of the ligand in vitro and in rive in animals. OH
O
CI ~
N
-
-
I 1CH3
C2H5
CI
[HC]SCH 23390
[11C]Raclopride
The useful properties of ['~C]raclopride for PET studies has encouraged us to search for other substituted benzamides suitable as ligands for the examination of dope.mine D2 receptors both with PET and SPECT. Of particular interest has been to find a compound that could be labelled with the positron emitting isotope ~SF, which has a half-life of 110 minutes (T~/2of"C is 20 minutes), allowing PET studies covering a time span of hours. Labelling raclopride
In this presentation, we report on some recent studies with ["qraclopride, and present two new substituted benzamides useful for/n rive visualization of dopamine D2 receptor using PET and SPECT. PET STUDIESIN HUMANSUSING["C]IIACLOPRID[
We have examined dopamine D2 receptors in drug naive schizophrenic patients with ["qraclopride. The
329S
330S
Dopamine 90 Table 1. Dopamine D 2 ([~C]raclopride binding) and dopamine D~ ([J~C]SCH 2339~! binding) receptor occupancy in patients treated with psychoactive drugs Drug
Daily dosage (rag)
Phenotiazines Chlorpromazine
2 ~ 100 2 ~ 100 2 × 5 2 × 4 2 × 8
80 75 80 79 0
2 x 5 40 weekly
74
Thioridazine Trifluoperazine
Perphenazine Perphenazine Thioxantenes Flupentixol Flupentixol Zuclopentixot Butyrophenones
Receptor occupancy (%) ........................................................... Dopamine D, Dopamine D,
29 0
36 11
200 weekly
Haloperidol
2 2 2 2
× 6 x 3 x 3 x 2 3 × 100
86 85 89 81 70
2 × 4
77
2 x 300 2 × 150
65 40
Raclopride
2 x 400 2 x 400 2 × 400 2 × 4 2 x ~
82 73 68 72 65
Tricyclie antidepressant Nortriptyline
2 × 25
-3
Haloperidol Haloperidot Haloperidol Melperone
Diphenylbutyls Pimozide
Dibenzodiazepines Clozapine Clozapine Substituted benzamides Sulpiride Sulpiride Sulpiride Raclopride
42 -7
The receptor occupancies were calculated in relation to uptake of radioligand in healthy subjects.
density of dopamine D, receptors was shown to be similar in the schizophrenic patients and in matched controls (Farde et al. 1990). In patients on treatment with neuroleptic drugs 60-80% of the dopamine D, receptors in the basal ganglia are occupied by the neuroleptic, as measured with ["C]raclopride and PET (Table 1, Farde et al. 1988, 1989). Treatment with the atypical neuroleptic clozapine, however, blocks a lower amount of['~C]raclopride binding. Compared to classical neuroleptics, clozapine also blocks a high proportion of [IzC]SCH 23390 binding in the basal ganglia (Table 1, Farde et al. 1990). PET STUDIES IN A MONKEY USING[~SFINCQi 15 In order to be able to perform longer PET studies we have looked for compounds suitable for labelling with tSF. Of the substituted benzamides with a fluorine in the structure was chosen NCQ 115 ((R)-5-bromo-N[(l-(4-fluorobenzyl)-2-pyrrolidinyl) methyl]-2.3-dimethoxybenzamide), a compound which in initial in vitro binding studies has been shown to be potent inhibitor of the dopamine Dz receptors (Hogberg et al. 1991, Hall et al. 1991a). NCQ 115 was developed from a
O
CH30
18F fiSF1NCO
115
series of substituted benzamides with varying substituents on the nitrogen in the pyrrolidine ring. Substitution of the N-ethyl group to an N-benzyl g r o u p , or as in NCQ l l 5 , to a n N-4-fluorobenzyl group, results in a reversed stereoselectivity, i.e. the affinity is confined to the R-enantiomer, which contrasts to the corresponding l-ethyl derivatives like FLB 457, raclopride and sulpiride, where the pharmacological activity is found in the (S)enantiomer. [~SF]NCQ 115 was prepared and examined in a PET study on a Cynomolgus monkey (Haltdin et aL 1990b). There was a marked uptake of [~SF]NCQ l l5 in the basal ganglia (Figs l and 2) indicating that this 'SF-
Dopamine 90
331S
OH
0
CH2
z
1 Ctt3
(A)
. . . .
l:
Fig. 1. PET imase showing the distribution of radioactivity in a horizontal brain section of a Cynomolgus monkey after the IV injection of 45 MBq [~SF]NCQ115.
,so~
_ ~3 ~
--'T0V
0,o
o
$o
60 Time
90 (mln)
12o
ISO
t
.... W
~
o Time'(hours)' '
•
iv.
Fig. 2. Time course of radioactivity in striatum (squares)and cerebellum (open circles) in a Cynomolgus monkey after administration of 45 MBq [~SF]NCQ 115. Shown is also specific binding, defined as radioactivity in the striatum minus that in the cerebellum (triangles) and ratio of radioactivity striatum/cerebellum (filledcircles). labelled ligand is suitable for PET-studies for the examination of binding during a couple of hours.
~
a
loo
Oo
1
~2
s
4
8
•
11me ('-noem) Fig. 3. Time course of a~eumulation of radioa~'vity in the striatum and cerebellum of two ~ 1 1 ~ monkeys after the IV injection [mI]NCQ 298 (90 MBq and 145 MBq, respectively). Radioactivity (corrected for recovery) vs time in two brain resiom (striauma and cmebelh~) ~ binding in striatum (as defined from the r•dilw~vity of striatum minus that in cerebellum)vs time. Two l m l ~ mad 15 minutes after injection, 12 nag raclopride was injected IV to one of the monkeys.
SPECTSTUDIESIN MONKEYSUSING[t=IINCQ296 For the use in SPECT, NCQ 298 ((S)-3-iodo-N-[(1ethyl-2-pyrrolidinyl)methyl]-5,6-dimehtoxysalicylamide) was prepared (Hogberg et al. 1990) (Table 2). The binding characteristics of [~25I]NCQ 298 was determined in vitro and/n vivo, as well as its anatomical distribution in brain using in vitro autoradiography (Hall et al. 1991b). The in vivo binding of[125I]NCQ 298 was saturated at very low concentrations, both in striatal and cortical tissue homogenates. The Bmax was rather low in the rat striatum (11.3 fmol/mg tissue, Table 3) as compared to that of [3H]raclopride
Table2 Name Raelopride Etielopride IBZM NCQ 298
Y
2
C! C2H5 I I
Ci CI H OCH3
(Bmax=23.5 fmol/mg tissue, Kohler et aL 1985). Binding could also be determined in tissue prepared from the rat cortex (Bmax = 0.26 fmol/mg, Table 3). The distribution in the brain of [mI]NCQ 298 was
332S
I)opamine 90 Table 3. Density
