Is relaxation of human detrusor by sildenafil relying on PDE5 inhibition ?

EAU Congress, Stockholm,

March 19, 2009

Introduction

� PDE5 inhibitors: first-line therapy in erectile dysfunction (ED).

� ED is often associated with lower urinary tract symptoms (LUTS),independently of age and cardiovascular comorbidies

PDE5

sildenafiltadalafilvardenafil

Corpus cavernosumsmooth muscle cell

PDE5 inhibitors for LUTS/BPH :Clinical trials

• Sildenafil

• Tadalafil

• Vardenafil

McVary KT, et al, J Urol2007;177:1401-1407

McVary KT, et al J Urol2007;177:1071-1077

Stief CG, et al Eur Urol

2008;53:1236-1244.

Patients with LUTS associated with BPH

Roehrborn et al., J Urol

2008; Oct;180(4):1228-34 *

Randomized placebo-controlled trials

*double-blinded

+++

irritative symptoms

+++

obstructive symptoms

Mechanism of action ?

+++ irritative symptoms

+++ obstructive symptoms

PDE5 inhibitors

NO-cGMP pathway

?

+++ irritative symptoms

PDE5 inhibitors

?

Objectives

� Assess the ability of sildenafil to relax human detrusor smooth muscle

� Investigate the signaling pathways that could be involved in sildenafil-mediated relaxation

Experimental design

� Human bladder samples

� Bladder samples were obtained

from 20 patients (65±2.1 years)

undergoing cystoprostatectomy for

infiltrating bladder cancer with no history of bladder dysfunction

according to their medical chart.

� Strips are excised from the tissue samples and connected to force transducers for isometric tension recording

�Evaluation of the smooth muscle contractile reactivity with isolated organ baths

� Organ baths are filled with Krebs buffer maintained at 37°C and bubbled with 95%O2 and 5%CO2, pH 7.4

Effect of sildenafil on carbachol-precontracted human detrusor strips

By which mechanism of action does sildenafil relax human bladder tissue ?

-8 -7 -6 -5 -4

-75

-50

-25

0 vehicle (n=20)

sildenafil (n=20)###

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***

***

log [compound], M

% in

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-8 -7 -6 -5 -4

-60

-50

-40

-30

-20

-10

0

vehicle

SNAP 10 µMns

two-way Anova

Pre-treatment

log [sildenafil], M

% o

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-8 -7 -6 -5 -4

-60

-50

-40

-30

-20

-10

0

ODQ 10 µM

vehicle###

**

***

p<0.001, two-wayAnova

Pre-treatment

log [sildenafil], M

% o

f in

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sNO/cGMP-dependent mechanism of action?

Effect of a NO donorEffect of guanylate cyclase inhibition

� Relaxation of carbachol-precontracted human bladder by sildenafil involves a cGMP-independent mechanism pathway;

Indeed, a NO donor does not enhance sildenafil effect

?

cAMP-dependent mechanism of action?

Effect of adenylate cyclase inhibition

�Sildenafil inhibits carbachol-induced human bladder contractions via a cAMP-dependent mechanism pathway

-8 -7 -6 -5 -4

-60

-50

-40

-30

-20

-10

0

MDL-12,330A 10 µM

vehicle###

&&&

&&&

&

p<0.001, two-wayAnova

Pre-treatment

log [sildenafil], M

% o

f in

hib

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Other mechanisms of action ?

-8 -7 -6 -5 -4

-60

-50

-40

-30

-20

-10

0

MDL-12,330A

ODQ

vehicle

MDL-12,330A +ODQ

nsns

******

log [sildenafil], M

% o

f in

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Effect of guanylate and adenylate cyclases inhibition

�Sildenafil also exerts its inhibitory effect by an other pathway, independent of cGMP or cAMP signaling pathways, since some relaxing

activity remains in presence of both MDL 123,330A and ODQ

?

K+ channel-dependent mechanism of action ?

Effect of SKCa channels blockingEffect of BKCa channels blocking

Effect of KATP channels blocking

�KATP, BKCa, and SKCa channels are involved in the relaxation elicited by sildenafil on human detrusor tissue

-8 -7 -6 -5 -4

-60

-45

-30

-15

0

glibenclamide 10 µM

vehicle

§

###

p<0.001,two-way Anova

Pre-treatment

log [sildenafil], M

% o

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hib

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s-8 -7 -6 -5 -4

-60

-45

-30

-15

0

iberiotoxin 30 nM

vehicle**

p<0.01,two-way Anova

Pre-treatment

log [sildenafil], M

% o

f in

hib

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fcarb

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-8 -7 -6 -5 -4

-60

-45

-30

-15

0

vehicle

apamin 100 nM***

p<0.001,two-way Anova

Pre-treatment

log [sildenafil], M

% o

f in

hib

itio

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fc

arb

ac

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§

�The relaxant effect of sildenafil on carbachol-induced human detrusor contraction involves cAMP-dependent signaling pathway and K+ channels dependent mechanism of action

�The contribution of the NO-cGMP signaling pathway in sildenafil-induced relaxation appears to be minor

�Sildenafil in part improves urinary symptoms in men with LUTS associated with BPH via direct relaxation of

the detrusor

Conclusions