- Email: [email protected]
PET determination of robalzotan occupancy of 5-HT1A receptors in the monkey brain
Sl68
Pl Aflectiue disorders and antidepressants
effect of either drug (F = 1.57, df = 2.60, p = 0.22) compared to control vehicle treated animals. The data presented here suggests that 1 days treatment with venlafaxine and paroxetine has little effect on somatodendritic 5-HTm receptor function in mice, but that after 7 days near maximal attenuation is evident. If an antidepressant action can occur as a result of an attenuation of somatodendritic ~-HT~Areceptor function, as previously suggested (Blier & de Montigny, 1994) then this data supports the view that this may be a mechanism by which venlafaxine acts. Further work is required to examine if there is a difference between venlafaxine and paroxetine in the time course of the development of the attenuation prior to 7 days. Ongoing experiments are attempting to clarify the situation. Acknowledgements: The authors would like to thank Wyeth for tlnancial support for this study.
function between drug concentrations and 5-HTt,., receptor occupancy can be used to predict suitable doses of robalzotan for initial studies in man. References [1] Pike VW, McCarron JA, Lammertsma AA, Osman S, Hume SP, Sargent PA, Bench CJ, Cliffe IA, Fletcher A, Grasby PM. Exquisite delineation of ~-HTIA receptors in human brain with PET and [carbonyl-“CJWAY-100635. Eur J Pharmacol 1996: 301: R5-R7. [2] FardeL, Ito H, SwahnC, Pike vl HalldinC. Quantitativeanalyses of [carbonyl“CIWAY-100635 binding to central 5-HTln-receptors in man. J. Nucl. Med. in press. [3] Karlsson F’,Farde L, Halldin C, Sedvall G, Ynddal L, Sloth-Nielsen M. Oral administration of NNC 756 - a placebo controlled PET study of Dl-dopamine receptor occupancy and phwmacodynamics in man. Psychopharmacology 1995; 119: l-8.
References [1] Blier, P & de Montigny, C. (1994) Current advances in the treatment of depression. Trends in Pharmacological Sciences 15: 220-226. 121 . Derivan. A.. Entsuah. A.R. & Kikta. D. (1995) Venlafaxine: measurinz the onset oi antidepress& action. Psychoph&nacoiogy Bulletin 3 1: 439-447, [3] Martin, K.F., Phillips, I., Hearson, M., Prow, M.R. & Heal, D.J. (1992) Characterisation of S-OH-DPAT-induced hypothermia in mice as a S-HT,,+ autoreceptor response and its evaluation as a model to selectively identify antidepressants. British Journal of Pharmacology 107: 15-21. 1
[p.1.0961
No change in responsiveness of S-HT~A receptors after long-term treatment with the novel 5-HTTA receptor antagonist robalzotan (NAD29g) in rats
D.M. Jackson, C.E. Wallsten’, L.-G. Larsson, L.-M. Lindgren, A. Bengtsson, S.B. Ross. Astra Arcus AB, Preclinical R&D, SISI 85 Siidertiilje, Sweden
(P.1 .o%]
PET-determination of robalzotan occupancy IHTIA receptors in the monkey brain
of
L. Farde, B. And&e*, N. Ginovart, C. Halldin, S.-O. Thorberg’. Department of Clinical Neuroscience, Arcus AB, SGdertiiQe, Sweden
Karolinska Institutet, Stockholm;
‘Astra
Serotonin S-HTt* receptors are currently in focus of research on the pharmacology and pathophysiology of anxiety, depression and schizophrenia. Robalzotan (generic name for NAD-299) is a novel compound developed by Astra Arcus AB, SiidertZlje, Sweden. Robalzotan has been shown to bind with high selectivity and affinity (0.6 nM) to 5-HTtA-receptors in the rodent brain in vitro and in vivo. The aim of the present study was to determine 5-HTm receptor occupancy in the cynomolgus monkey brain in after iv injection of robalzotan. Positron emission tomography (PET) was used to determine the binding of [carbonyl-’’C]WAY-100635 in two Cynomolgus monkeys at baseline conditions, and after pretreatment with robalzotan. [Carbonyl-“C]WAY100635 was the radioligand used for quantitative determination of 5HT~A receptor occupancy (1, 2). The first monkey was given 2 and 20 u&/kg robalzotan iv and the second 10 and 100 p&kg robalzotan iv in separate measurements. Radioactivity in the cerebellum was used as an estimate of free radioligand concentration (F) in brain. Specific binding (B) in the neocortex and the raphe nuclei was defined as the difference between radioactivity in these regions and that in the cerebelhnn. The ratio B/F was calculated for the time interval 20-40 minutes after radioligand injection. Central 5-HT tA receptor occupancy was defined as the percent reduction of B/F as compared with the baseline ratio. The values for 5-HTm receptor occupancy in the raphe and neocortex were plotted versus the concentration of robalzotan in plasma. The curvilinear function for a saturation hyperbola was fitted to the experimental data points (3). In the baseline measurement the ratio B/F was 6-8 for the neocortical regions and about 4 for the raphe nuclei. After pretreatment with robalzotan the radioactivity in the neocortex and the raphe nuclei was reduced in a dose-dependent manner. The highest occupancy (70-80%) was accordingly calculated for the measurement after iv injection of 100 pgikg robalzotan. The relation between plasma drug concentrations and ~-HTIA receptor occupancy could be described by a curvilinear function. The results indicate that 50% of the 5-HTr A-receptors in the raphe nuclei are occupied at a robalzotan plasma concentration of 3.9 nmol/L. The corresponding value for the neocortex was 5.4 nmol/L. It can be concluded that robalzotan binds in a saturable manner to central 5-HTm receptors in the primate brain in vivo. The curvilinear
While it is well documented that 5-HTm receptor agonists induce a functional ~-HT]A receptor desensitisation, little is known about the CffeCtS of ChroniC adminiStdOn of 5-HTm receptor antagonists. The present study has investigated the effects of a 21 day administration with the potent and selective 5-HTm receptor antagonist robalzotan (generic name of NAD-299) (1, see also other abstracts this meeting) or the reference 5.HTt, receptor antagonist WAY-100635on the responsiveness of the 5-HTm receptor. The following in models were used: rate of 5-HT synthesis, 5-HT turnover, the so-called 5-HT syndrome and hypothermia. 5HTm agonists, such as 8-OH-DPAT, decrease 5-HT synthesis and 5HT turnover and induce the 5-HT syndrome and hypothermia. ~-HTIA receptor antagonists block these effects. Sprague-Dawley male rats were treated S.C. twice daily for 21 days with saline, robalzotan (0.03, 0.3 and 3 ymohkg, only the highest dose were given in the 5-HT syndrome and hypothermia experiments) or WAY-100635(0.3 pmolikg, 5-HT synthesis, 5-HT turnover; 0.5 umol/kg, 5-HT-syndrome, hypothermia). The decrease in 5-HTP accumulation (synthesis rate) and 5-HT turnover (ratio 5-HIAA/S-HT) induced by saline or I-OH-DPAT (0,0.03, 0.1 and 0.3 mg/kg s.c.) in rats treated with the decarboxylase inhibitor NSD 1015 (100 m&g s.c.) was determined 2 days after the last injection. The 5-HT syndrome was scored 1, 2 or 7 days after the last injection, in rats challenged with saline or s-OHDPAT (0.125 mg/kg). The temperature response was measured in rats challenged 2 days after the last injection with saline or I-OH-DPAT (0.125 or 0.3 mgikg). Robalzotan-pretreated animals tended to have an elevated rate of 5-HT synthesis which was significant for the two lower doses in hypothalamus and striatum and the lowest dose in frontal cortex. WAY-100635pretreatment did not cause this effect. 5-HT turnover was not significantly changed by the repeated treatment except for the middle dose of robalzotan where a significant elevation of the ratio in striatum was noted. The I-OH-DPAT-induced decrease in 5-HTP accumulation and turnover was the same in all treatment groups. 8-OH-DPAT induced the 5-HT syndrome in all treatment groups. However, no significant differences in response to the I-OH-DPAT-induced 5-HT syndrome were noted between any of the chronic treatment groups. 8-OH-DPAT induced a fall in body temperature in all treatment groups. There was no significant change in the sensitivity of long-term robalzotan treated animals to the hvnothermic effect of 8-OH-DPAT. Animals me-treated with WAY1006% were subsensitive to the effects of the low dose (0.125 mg/kg) but not to the higher dose (0.3 mg/kg) of I-OH-DPAT. Thus, long-term treatment with robalzotan or WAY-100635 did not consistently alter the sensitivity of rats to challenge with 8-OH-DPAT
Pl Aflectiue disorders and antidepressants
effect of either drug (F = 1.57, df = 2.60, p = 0.22) compared to control vehicle treated animals. The data presented here suggests that 1 days treatment with venlafaxine and paroxetine has little effect on somatodendritic 5-HTm receptor function in mice, but that after 7 days near maximal attenuation is evident. If an antidepressant action can occur as a result of an attenuation of somatodendritic ~-HT~Areceptor function, as previously suggested (Blier & de Montigny, 1994) then this data supports the view that this may be a mechanism by which venlafaxine acts. Further work is required to examine if there is a difference between venlafaxine and paroxetine in the time course of the development of the attenuation prior to 7 days. Ongoing experiments are attempting to clarify the situation. Acknowledgements: The authors would like to thank Wyeth for tlnancial support for this study.
function between drug concentrations and 5-HTt,., receptor occupancy can be used to predict suitable doses of robalzotan for initial studies in man. References [1] Pike VW, McCarron JA, Lammertsma AA, Osman S, Hume SP, Sargent PA, Bench CJ, Cliffe IA, Fletcher A, Grasby PM. Exquisite delineation of ~-HTIA receptors in human brain with PET and [carbonyl-“CJWAY-100635. Eur J Pharmacol 1996: 301: R5-R7. [2] FardeL, Ito H, SwahnC, Pike vl HalldinC. Quantitativeanalyses of [carbonyl“CIWAY-100635 binding to central 5-HTln-receptors in man. J. Nucl. Med. in press. [3] Karlsson F’,Farde L, Halldin C, Sedvall G, Ynddal L, Sloth-Nielsen M. Oral administration of NNC 756 - a placebo controlled PET study of Dl-dopamine receptor occupancy and phwmacodynamics in man. Psychopharmacology 1995; 119: l-8.
References [1] Blier, P & de Montigny, C. (1994) Current advances in the treatment of depression. Trends in Pharmacological Sciences 15: 220-226. 121 . Derivan. A.. Entsuah. A.R. & Kikta. D. (1995) Venlafaxine: measurinz the onset oi antidepress& action. Psychoph&nacoiogy Bulletin 3 1: 439-447, [3] Martin, K.F., Phillips, I., Hearson, M., Prow, M.R. & Heal, D.J. (1992) Characterisation of S-OH-DPAT-induced hypothermia in mice as a S-HT,,+ autoreceptor response and its evaluation as a model to selectively identify antidepressants. British Journal of Pharmacology 107: 15-21. 1
[p.1.0961
No change in responsiveness of S-HT~A receptors after long-term treatment with the novel 5-HTTA receptor antagonist robalzotan (NAD29g) in rats
D.M. Jackson, C.E. Wallsten’, L.-G. Larsson, L.-M. Lindgren, A. Bengtsson, S.B. Ross. Astra Arcus AB, Preclinical R&D, SISI 85 Siidertiilje, Sweden
(P.1 .o%]
PET-determination of robalzotan occupancy IHTIA receptors in the monkey brain
of
L. Farde, B. And&e*, N. Ginovart, C. Halldin, S.-O. Thorberg’. Department of Clinical Neuroscience, Arcus AB, SGdertiiQe, Sweden
Karolinska Institutet, Stockholm;
‘Astra
Serotonin S-HTt* receptors are currently in focus of research on the pharmacology and pathophysiology of anxiety, depression and schizophrenia. Robalzotan (generic name for NAD-299) is a novel compound developed by Astra Arcus AB, SiidertZlje, Sweden. Robalzotan has been shown to bind with high selectivity and affinity (0.6 nM) to 5-HTtA-receptors in the rodent brain in vitro and in vivo. The aim of the present study was to determine 5-HTm receptor occupancy in the cynomolgus monkey brain in after iv injection of robalzotan. Positron emission tomography (PET) was used to determine the binding of [carbonyl-’’C]WAY-100635 in two Cynomolgus monkeys at baseline conditions, and after pretreatment with robalzotan. [Carbonyl-“C]WAY100635 was the radioligand used for quantitative determination of 5HT~A receptor occupancy (1, 2). The first monkey was given 2 and 20 u&/kg robalzotan iv and the second 10 and 100 p&kg robalzotan iv in separate measurements. Radioactivity in the cerebellum was used as an estimate of free radioligand concentration (F) in brain. Specific binding (B) in the neocortex and the raphe nuclei was defined as the difference between radioactivity in these regions and that in the cerebelhnn. The ratio B/F was calculated for the time interval 20-40 minutes after radioligand injection. Central 5-HT tA receptor occupancy was defined as the percent reduction of B/F as compared with the baseline ratio. The values for 5-HTm receptor occupancy in the raphe and neocortex were plotted versus the concentration of robalzotan in plasma. The curvilinear function for a saturation hyperbola was fitted to the experimental data points (3). In the baseline measurement the ratio B/F was 6-8 for the neocortical regions and about 4 for the raphe nuclei. After pretreatment with robalzotan the radioactivity in the neocortex and the raphe nuclei was reduced in a dose-dependent manner. The highest occupancy (70-80%) was accordingly calculated for the measurement after iv injection of 100 pgikg robalzotan. The relation between plasma drug concentrations and ~-HTIA receptor occupancy could be described by a curvilinear function. The results indicate that 50% of the 5-HTr A-receptors in the raphe nuclei are occupied at a robalzotan plasma concentration of 3.9 nmol/L. The corresponding value for the neocortex was 5.4 nmol/L. It can be concluded that robalzotan binds in a saturable manner to central 5-HTm receptors in the primate brain in vivo. The curvilinear
While it is well documented that 5-HTm receptor agonists induce a functional ~-HT]A receptor desensitisation, little is known about the CffeCtS of ChroniC adminiStdOn of 5-HTm receptor antagonists. The present study has investigated the effects of a 21 day administration with the potent and selective 5-HTm receptor antagonist robalzotan (generic name of NAD-299) (1, see also other abstracts this meeting) or the reference 5.HTt, receptor antagonist WAY-100635on the responsiveness of the 5-HTm receptor. The following in models were used: rate of 5-HT synthesis, 5-HT turnover, the so-called 5-HT syndrome and hypothermia. 5HTm agonists, such as 8-OH-DPAT, decrease 5-HT synthesis and 5HT turnover and induce the 5-HT syndrome and hypothermia. ~-HTIA receptor antagonists block these effects. Sprague-Dawley male rats were treated S.C. twice daily for 21 days with saline, robalzotan (0.03, 0.3 and 3 ymohkg, only the highest dose were given in the 5-HT syndrome and hypothermia experiments) or WAY-100635(0.3 pmolikg, 5-HT synthesis, 5-HT turnover; 0.5 umol/kg, 5-HT-syndrome, hypothermia). The decrease in 5-HTP accumulation (synthesis rate) and 5-HT turnover (ratio 5-HIAA/S-HT) induced by saline or I-OH-DPAT (0,0.03, 0.1 and 0.3 mg/kg s.c.) in rats treated with the decarboxylase inhibitor NSD 1015 (100 m&g s.c.) was determined 2 days after the last injection. The 5-HT syndrome was scored 1, 2 or 7 days after the last injection, in rats challenged with saline or s-OHDPAT (0.125 mg/kg). The temperature response was measured in rats challenged 2 days after the last injection with saline or I-OH-DPAT (0.125 or 0.3 mgikg). Robalzotan-pretreated animals tended to have an elevated rate of 5-HT synthesis which was significant for the two lower doses in hypothalamus and striatum and the lowest dose in frontal cortex. WAY-100635pretreatment did not cause this effect. 5-HT turnover was not significantly changed by the repeated treatment except for the middle dose of robalzotan where a significant elevation of the ratio in striatum was noted. The I-OH-DPAT-induced decrease in 5-HTP accumulation and turnover was the same in all treatment groups. 8-OH-DPAT induced the 5-HT syndrome in all treatment groups. However, no significant differences in response to the I-OH-DPAT-induced 5-HT syndrome were noted between any of the chronic treatment groups. 8-OH-DPAT induced a fall in body temperature in all treatment groups. There was no significant change in the sensitivity of long-term robalzotan treated animals to the hvnothermic effect of 8-OH-DPAT. Animals me-treated with WAY1006% were subsensitive to the effects of the low dose (0.125 mg/kg) but not to the higher dose (0.3 mg/kg) of I-OH-DPAT. Thus, long-term treatment with robalzotan or WAY-100635 did not consistently alter the sensitivity of rats to challenge with 8-OH-DPAT