CMOA 1CMOA 15

5-HT4 Receptor Physiology and Pharmacodynamic Effects of

Tegaserod

5-HT4 Receptor Physiology and Pharmacodynamic Effects of

Tegaserod

Michael Camilleri, MD

Gastroenterology Research UnitMayo Clinic Foundation

Michael Camilleri, MD

Gastroenterology Research UnitMayo Clinic Foundation

CMOA 2CMOA 25

5-HT4 Receptor Physiology and Pharmacodynamic Effects of Tegaserod

5-HT4 Receptor Physiology and Pharmacodynamic Effects of Tegaserod

Physiologic role of serotonin (5-HT) and its type-4 receptors (5-HT4) in GI functions

Tegaserod, a partial 5-HT4 receptor agonist,

and its pharmacodynamic effects on the GI tract

Physiologic role of serotonin (5-HT) and its type-4 receptors (5-HT4) in GI functions

Tegaserod, a partial 5-HT4 receptor agonist,

and its pharmacodynamic effects on the GI tract

CMOA 3CMOA 3

Physiologic Distribution of Serotonin(5-Hydroxytryptamine, 5-HT)

Physiologic Distribution of Serotonin(5-Hydroxytryptamine, 5-HT)

5% CNS5% CNS

95% GI tract

90% EC s 10% Neurons

95% GI tract

90% EC s 10% Neurons

5-Hydroxytryptamine5-Hydroxytryptamine

NH2

OH

NH

5

CMOA 4CMOA 45

Role of 5-HT in the GI TractRole of 5-HT in the GI Tract

Four main 5-HT receptor subtypes identified in the human GI tract : 5-HT1, 5-HT2, 5-HT3, and 5-HT4

– Diverse effects due to different receptor subtypes

5-HT3 and 5-HT4 receptors involved in multiple GI functions: motor, sensory, secretory

Location of 5-HT4 receptors: neurons, EC cells, enterocytes, smooth muscle cells

Four main 5-HT receptor subtypes identified in the human GI tract : 5-HT1, 5-HT2, 5-HT3, and 5-HT4

– Diverse effects due to different receptor subtypes

5-HT3 and 5-HT4 receptors involved in multiple GI functions: motor, sensory, secretory

Location of 5-HT4 receptors: neurons, EC cells, enterocytes, smooth muscle cells

Inhibition

5

SerosaLongitudinal muscleSerosaLongitudinal muscle

Myenteric plexusMyenteric plexus

Submucosal plexusSubmucosal plexus

Muscularis mucosaeLamina propriaEpithelium

Muscularis mucosaeLamina propriaEpithelium

Circular muscleCircular muscle

Dorsal Root Ganglion

Intrinsic Signaling PathwaysIntrinsic Signaling PathwaysMOA 5MOA 5

Intrinsic primaryafferent neuronsIntrinsic primaryafferent neurons

EnterocytesEnterocytes ECsECs

Extrinsic primaryafferent neurons

ECs

CNS

Inhibitorymotor neuron

Excitatorymotor neuron

5-HT

ActivationActivation

ECs: Enterochromaffin cellsECs: Enterochromaffin cells

5-HT4 receptor

5

Intrinsic primaryafferent neurons

SerosaLongitudinal muscleSerosaLongitudinal muscle

Myenteric plexusMyenteric plexus

Submucosal plexusSubmucosal plexus

Muscularis mucosaeLamina propriaEpithelium

Muscularis mucosaeLamina propriaEpithelium

Circular muscleCircular muscle

EnterocytesEnterocytes ECsECs

Inhibitorymotor neuron

Excitatorymotor neuron

Extrinsic Signaling PathwaysExtrinsic Signaling PathwaysMOA 6MOA 6

Extrinsic primaryafferent neuronsExtrinsic primaryafferent neurons

ECsECs

Dorsal Root GanglionDorsal Root Ganglion

CNSCNSInhibitionInhibition

ECs: Enterochromaffin cellsECs: Enterochromaffin cells

5-HT4 receptor

CMOA 7CMOA 75

5-HT4 Receptor Physiology and Pharmacodynamic Effects of Tegaserod

5-HT4 Receptor Physiology and Pharmacodynamic Effects of Tegaserod

Physiologic role of serotonin (5-HT) and its type-4 receptors (5-HT4) in GI functions

Tegaserod, a partial 5-HT4 receptor agonist, and its pharmacodynamic effects

– Effects on motility– Effects on visceral sensitivity

Physiologic role of serotonin (5-HT) and its type-4 receptors (5-HT4) in GI functions

Tegaserod, a partial 5-HT4 receptor agonist, and its pharmacodynamic effects

– Effects on motility– Effects on visceral sensitivity

CMOA 8CMOA 8

SerotoninSerotonin

5

NH2

OH

NH

N

O

NH

NH

NHNH

TegaserodTegaserod

TegaserodTegaserod

A representative of a new chemical class of compounds, aminoguanidine indoles, designed to act specifically at 5 HT4 receptors in the GI tract:

A representative of a new chemical class of compounds, aminoguanidine indoles, designed to act specifically at 5 HT4 receptors in the GI tract:

CMOA 9CMOA 95

Pharmacologic Profile of TegaserodPharmacologic Profile of Tegaserod

Tegaserod, a partial agonist, displays high affinity for human 5-HT4 receptors (KB = 18 nM)

Tegaserod mimics action of 5-HT and potently stimulates intrinsic sensory neurons triggering the peristaltic reflex (EC50 5 nM)

Tegaserod has negligible affinity for 5-HT3

receptors (KB = 7,200 nM); therefore, it is devoid

of relevant 5-HT3 receptor antagonism

Tegaserod, a partial agonist, displays high affinity for human 5-HT4 receptors (KB = 18 nM)

Tegaserod mimics action of 5-HT and potently stimulates intrinsic sensory neurons triggering the peristaltic reflex (EC50 5 nM)

Tegaserod has negligible affinity for 5-HT3

receptors (KB = 7,200 nM); therefore, it is devoid

of relevant 5-HT3 receptor antagonism

CMOA 10CMOA 10

Tegaserod Triggers the Peristaltic ReflexTegaserod Triggers the Peristaltic Reflex

5

EnterocytesEnterocytes ECsECs

5-HT5-HT

ACh,Substance P

ACh,Substance P

VIP,PACAP, NOVIP,PACAP, NO

TegaserodTegaserod

CMOA 11CMOA 115

Neurotransmitter Release Induced by Tegaserod is Inhibited by Selective 5-HT4 Antagonist

Neurotransmitter Release Induced by Tegaserod is Inhibited by Selective 5-HT4 Antagonist

Means ± SE (n = 3 - 8)Grider et al. Gastroenterology 1998; 115: 370-380

f

mo

l /

10

0 m

g ·

min

Humanjejunum

Guinea pigcolon

Ratcolon

8

7

6

5

4

3

2

1

0

Substance PSubstance P

f

mo

l /

10

0 m

g ·

min

7

6

5

4

3

2

1

0Humanjejunum

Guinea pigcolon

Ratcolon

VIPVIP

8

Tegaserod alone

+ 5-HT3 antagonist

+ 5-HT4 antagonist

CMOA 12CMOA 12

1 10 100 1,0000

80

100

120

140

160

180

200

% o

f c

on

tro

l

Tegaserod concentration (nM)

Jin et al. Jin et al. J. Pharmacol. Exp. Ther.J. Pharmacol. Exp. Ther. 1999; 288: 93- 1999; 288: 93-9797

5

Tegaserod-Induced Propulsion in Guinea Pig Colon

Tegaserod-Induced Propulsion in Guinea Pig Colon

Means ± SEM (n = 3 - 4)

Velocity of propulsionVelocity of propulsion

CMOA 13CMOA 13

50 mm Hg50 mm HgColonColon

JejunumJejunum

IleumIleum

0 90

TegaserodTegaserod

MinutesMinutes

Nguyen et al. JPET. 1997;280:1270-1276.

5

Tegaserod Stimulates Canine Small Bowel and Colonic Motility After IV Tegaserod

Tegaserod Stimulates Canine Small Bowel and Colonic Motility After IV Tegaserod

CMOA 14CMOA 14

Distribution of colonic isotope at 30 minutes following IV administration of tegaserodDistribution of colonic isotope at 30 minutes following IV administration of tegaserod

Saline Vehicle 0.03 0.1 0.30

20

40

60

80

100

Nguyen et al. J. Pharmacol. Exp. Ther. 1997; 280: 1270-1276

5

RectosigmoidProximal Distal

Tegaserod dose (mg/kg)

Co

lon

ic c

on

ten

ts i

n r

eg

ion

, %

Tegaserod Stimulates CanineColonic Motility and Transit

Tegaserod Stimulates CanineColonic Motility and Transit

Means ± SEM (n = 6)

CMOA 15CMOA 15

Effect of Tegaserod on Gastrointestinal Transit in Healthy Subjects

Effect of Tegaserod on Gastrointestinal Transit in Healthy Subjects

Means ± SEM (n = 12)

*P < .05 vs placebo, †P < .005 vs placebo

Perc

en

t of

Con

trol

-60

-40

-20

0

20

40

60

Gastricemptying

rate

Small boweltransit

time

**

†† Tegaserod 0.6 mg IV

Tegaserod 6 mg PO

Degen et al. Gastroenterology 2000; AGA Meeting, abstract

CMOA 16CMOA 16

Baseline 1 week0

20

40

60

80

100

Baseline 1 weekTegaserod Placebo

Col

onic

fil

ing,

%

Prather, et al. Gastroenterology. 2000.

Colonic Filling at 6 HoursEffect of Tegaserod in C-IBS

Colonic Filling at 6 HoursEffect of Tegaserod in C-IBS

CMOA 17CMOA 17

0

1

2

3

4

Baseline Week 1 Baseline Week 1

Geo

met

ric

Cen

ter

(48

ho

urs

)

Effect of Tegaserod on Colonic Transit in C-IBSEffect of Tegaserod on Colonic Transit in C-IBS

PlaceboPlacebo Tegaserod (2 mg b.i.d.)

Tegaserod (2 mg b.i.d.)

00

11

22

33

44

55StoolStool

Prather et al. Gastroenterology 2000; 118: 463-468

5

*

Means ± S.E.M. (n = 12)*P < .05 vs baseline

Colonic localization of radiotracer

CMOA 18CMOA 185

Summary : Motor Effects of Tegaserod

Summary : Motor Effects of Tegaserod

Tegaserod mimics the physiologic response to serotonin released from enterochromaffin cells, triggering the peristaltic reflex

Tegaserod promotes motility throughout theGI tract in animals and humans

Tegaserod mimics the physiologic response to serotonin released from enterochromaffin cells, triggering the peristaltic reflex

Tegaserod promotes motility throughout theGI tract in animals and humans

CMOA 19CMOA 195

5-HT4 Receptor Physiology and Pharmacodynamic Effects of Tegaserod

5-HT4 Receptor Physiology and Pharmacodynamic Effects of Tegaserod

Physiologic role of serotonin (5-HT) and its type-4 receptors (5-HT4) in GI functions

Tegaserod, a partial 5-HT4 receptor agonist, and its pharmacodynamic effects

– Effects on motility– Effects on visceral sensitivity

Physiologic role of serotonin (5-HT) and its type-4 receptors (5-HT4) in GI functions

Tegaserod, a partial 5-HT4 receptor agonist, and its pharmacodynamic effects

– Effects on motility– Effects on visceral sensitivity

CMOA 20CMOA 20

Visceral Sensitivity End-Points for Preclinical Studies in Small AnimalsVisceral Sensitivity End-Points for

Preclinical Studies in Small Animals

Single afferent fiber recordings

Pseudo-affective measurements:

– Animal behavior, eg, withdrawal, writhing

– Abdominal contractions

– Drop in arterial BP (under anesthesia)

Single afferent fiber recordings

Pseudo-affective measurements:

– Animal behavior, eg, withdrawal, writhing

– Abdominal contractions

– Drop in arterial BP (under anesthesia)

CMOA 21CMOA 21

Static stimulus-response curve

(single afferent unit in dorsal

root S2 )

Submaximal firing rates at 50 mm Hg

Static stimulus-response curve

(single afferent unit in dorsal

root S2 )

Submaximal firing rates at 50 mm Hg

Ruehl et al. Ruehl et al. Neurogastroenterol. MotNeurogastroenterol. Mot. 1998; 10: 219-222. 1998; 10: 219-222

Effect of Tegaserod on Visceral Sensitivity in Cats

Effect of Tegaserod on Visceral Sensitivity in Cats

5

1 ms

CMOA 22CMOA 22

Schikowski et al. Gastroenterology 1999; 116: A643

5

Dose-Dependent Inhibition by Tegaserod of Afferent Nerve Activity to Rectal Distension in Cats

Dose-Dependent Inhibition by Tegaserod of Afferent Nerve Activity to Rectal Distension in Cats

100

80

60

40

20

0 0 0.3 0.6 0.9 1.2 1.5

Tegaserod dose (mg/kg IV)

EC50 = 0.7 mg/kg

Effect inhibited by 5-HT4 antagonistEffect inhibited by 5-HT4 antagonist

**

*

* *

Means ± SD (n = 9)*P < .05

% o

f ve

hic

le c

on

tro

l

Firing rate at 50 mm Hg distensionFiring rate at 50 mm Hg distension

CMOA 23CMOA 23

Tegaserod Inhibits Abdominal Contractions in Response to Colorectal Distension in Awake Rats

Tegaserod Inhibits Abdominal Contractions in Response to Colorectal Distension in Awake Rats

*

*

5

0

10

20

30

40

50

0 15 30 45 60Balloon pressure, mm Hg

Ab

do

min

al c

on

tra

cti

on

s/5

min

ute

s Control

Vehicle

Tegaserod 1 mg/kg IP

Mean ± SEM (n = 7)

*P < .05 versus vehicle

Coelho, et al. Gastroenterology. 2000;118:A835.

CMOA 24CMOA 24

Summary : Sensory Effects of Tegaserod

Summary : Sensory Effects of Tegaserod

During colorectal distension:

Tegaserod reduces visceral afferent firingin cats via stimulation of 5-HT4 receptors

Tegaserod inhibits visceral discomfort / pain in rats

During colorectal distension:

Tegaserod reduces visceral afferent firingin cats via stimulation of 5-HT4 receptors

Tegaserod inhibits visceral discomfort / pain in rats

CMOA 25CMOA 25

SummarySummary

Serotonin and its 5-HT4 receptors are involved

in motor, secretory, and sensory processes in the GI tract

Tegaserod, a partial 5-HT4 receptor agonist,

stimulates GI motor functions, and inhibits visceral sensitivity

Tegaserod may influence the sensorimotor dysfunctions and symptoms of constipation-predominant IBS

Serotonin and its 5-HT4 receptors are involved

in motor, secretory, and sensory processes in the GI tract

Tegaserod, a partial 5-HT4 receptor agonist,

stimulates GI motor functions, and inhibits visceral sensitivity

Tegaserod may influence the sensorimotor dysfunctions and symptoms of constipation-predominant IBS