Omeprazole: The First Proton Pump Inhibitor Behnaz Shafii Michigan State University January 23 rd , 2008 Organic Seminar
Omeprazole: The First Proton Pump Inhibitor
Behnaz Shafii
Michigan State University
January 23rd, 2008
Organic Seminar
Outline
- Gastric acid secretion
- Helicobacter pylori, common diseases and treatments
- Proton Pump Inhibitors (PPIs)
- Development of omeprazole
- Mechanism of action
- Pkas and their importance
- Anti-cancer activity and future
- Conclusion
Stomach Cells
Gastric glands
Blood vessels
Stomach
Parietal cell K+
H+
Cytoplasm
Lumen
Mucous cells
� ATP is consumed for ion exchange
http://www.britannica.com/eb/art-68634
Mechanism of Proton Transport
Lys
Asp
Glu
H3 O +
� ATP is consumed for ion exchange
NH3+
COO-
COO-
COO-
Asp
Glu
Glu
Lys
H3O+
NH3+
COO-COO-
COO-
H3O+
K+ K+
H3O+
Glu
Glu
Lys
Ala
ValK+
COO-
COO-
COO-NH3+
Asp
Shin et al, Dig Dis Sci., 51, 2006, 823-833
Lower esophageal
sphincter closed
Lower esophageal
sphincter open
allowing reflux
Esophagus
� Gastroesophageal Reflux Disease (GERD)
Lower esophageal
sphincter closed
Lower esophageal
sphincter open
allowing reflux
� Gastroesophageal Reflux Disease (GERD)
Common Disease Related to Inappropriate Levels of Gastric Acid
Gastric ulcer
� Peptic Ulcer Diseases
Duodenal ulcer
Discovery of Helicobacter pylori (Hp)
Nobel Prize in Medicine 2005- Robin Warren
- Barry Marshall
http://nobelprize.org/nobel_prizes/medicine/laureates/2005/press.html
H. pylori
(NH2)2CO+H2O CO2+2NH3
Urease
Chronic Peptic Ulcer and Cancer
Chronic Ulcer Cancerhttp://nobelprize.org/nobel_prizes/medicine/laureates/2005/press.html
� Once the bacteria have entered stomach, they cause inflammation and
may lead to different diseases.
http://www.worldgastroenterology.org
Helicobacter pylori Infection Globally in 2006
� Helicobacter pylori is common
and infects half of the world’s population.
0
20
40
60
80
100
Per
cen
tag
e
Mexico, Central
and South
America
Africa Asia United States
and Canada
Australia
� Triple therapy:A proton pump inhibitor + two antibiotics
Most Common Helicobacter pylori Treatments
� Quadruple therapyA proton pump inhibitor + two antibiotics + bismuth
Clarithromycin Amoxicillin Bismuth subsalicylate
Proton Pump Inhibition
Histamine
Histamine H2
receptor antagonists
Acetylcholine
Muscarinic antagonists
Gastrin
Parietal Cell Proton pump inhibitors
Olbe, L. et al. Nature reviews, drug discovery, 2003, 2, 132-139
K+
H+
++
Lumen
Cytoplasm
Development of Omeprazole
H 81/75
No effect in humans
H 116/18
Olbe. L, Proton Pump Inhibitors, 1999, 3-20
CMN 131
Severe liver toxicity
H 77/67
Starting point for the X-Y-Z general structures
Development of Omeprazole
H 124/26
Leading compound with
good anti-secretary effect
Olbe. L, Proton Pump Inhibitors, 1999, 3-20
NS
HN
N
H 83/69 (Timoprazole)
Potent anti-secretary but blocking
the uptake of iodine
H 149/94 (Picoprazole)Potent anti-secretary
without thyroid effect
Development of Omeprazole
+2.295-OCH33-CH3, 4-OCH3, 5-CH3
+1.825-OCH34-OCH3, 5-CH3
+1.235-OCH34-CH3, 5-CH3
+0.945-OCH33-CH3, 5-CH3
+0.765-OCH34-CH3
05-OCH3H
∆pKa (Pyridine)R2R1
NH
N
S
O
N
R2 4
5
6
7
3 4
5
6
R1
Olbe. L, Proton Pump Inhibitors, 1999, 3-20
Omeprazole
Development of Omeprazole
H 168/68 (Omeprazole)
Optimal compound
�Prilosec or Losec (Omeprzole) was the world best selling drug by year 2000
( Worldwide sales of US$6.1 b/year)
�Marketed by AstraZeneca
http://www.astrazeneca.com/
Marketed PPIs
Omeprazole Lansoprazole
Pantoprazole Rabeprazole
Tenatoprazole
Mechanism of Action
Shin et al, Cell. Mol. Life Sci., 64, 2007, 1-18
H3CO
NH
N
S
O
N
H3C OCH3
CH3
H
H3CO
NH
N
S
O
N
H3C OCH3
CH3
H
H-
-
-
Omeprazole
Mechanism of Action of Omeprazole
Shin et al, Cell. Mol. Life Sci., 64, 2007, 1-18
S
N
NH
CH3
OCH3
CH3
N
SH K -ATPase
H3CO
H3CO
NH
N
S
O
H
N
CH3
OCH3H3C
N
CH3
OCH3
CH3
N
NH
SOH
H3CO
S
N
N
CH3
OCH3
CH3
NH3CO-H2O
+H2O
Methylation on 6th position
Wallmark, B. et al, J. Med. Chem, 1986, 1327, 1329
� Prevention of formation of the spiro-intermediate by a 6-methyl group
� Strong steric interaction with the imidazole ring
(revealed by molecular modeling)
N
CH3
OCH3
H3C
H3C
SO
N
NH
H3CO
Half-lives of the inhibitory effect
on acid secretion in humans
28 Hours for omeprazole
46 Hours for pantoprazole
Half-lives of PPIs
� De novo synthesis of proton pump protein?
Protein pump half-life 54 Hours
glutathione
�Reduction of disulfide by an endogenous cellular reducing agents
such as glutathione
Shin, J. et al, Gastroenterology, 2002, 123, 1588-1597
Labeling and Inhibition of ATPase by Omeprazole
CPM 0 150 300 450 600 0 150 300 450 600
6
810
Sachs, G. et al, JBC, 1997, 272, 22438-22446
[3H] Omeprazole
10 min 45 min
47% inhibition 83% inhibition KDa
Cys 813
Cys 321
Cys 892
Why PPIs Have Different Half-lives?
Omeprazole
Pantoprazole
Shin, J. et al, Gastroenterology, 2002, 123, 1588-1597
7-8 loop3-4 loop
Cys 892 Cys 321
5-6 loop
Cys 813
Cys 822
28 Hour half-life
46 Hour half-life
34568
Membrane
Protonation:
� Pyridine
� Benzimidazole or imidazopyridine
Rate Limiting Step
Omeprazole
Tenatoprazole
pKa1
pKa2
-
Sachs, G. et al, JACS, 2004, 126, 7800-7811
� Biphasic rate
Co
nv
ers
ion
ra
te c
on
sta
nts
(m
in -1
)
0
0.1
0.2
0.3
0.4
0.5
0.6
-1 0 1 2 3 4 5 6 7 8
pH
Lanzoprazole
Tenatoprazole
Pantoprazole
Omeprazole
Conversion Rates of PPIs at Different pHs
Sachs, G. et al, JACS, 2004, 126, 7800-7811
Protonation of Benzimidazole and Pyridine
[Bz-Py.H+] = [Bz-Py] × 10 (pKa1-pH)
Bz-PyBz-PyH+
BzH+-Py
BzH+-PyH+
-
-
-
[Bz.H+-Py] = [Bz-Py] × 10 (pKa2-pH)
Sachs, G. et al, JACS, 2004, 126, 7800-7811
XH3CO
NH
N
S
O
N
H3C OCH3
CH3
H
XH3CO
NH
N
S
O
N
H3C OCH3
CH3
H
H
H
H
H
H
XH3CO
NH
N
S
O
H
N
CH3
OCH3H3C
XH3CO
NH
N
S
O
N
H3C OCH3
CH3
H
H
1 2
3 4
pKa Measurements by UV Spectroscopy
Sachs, G. et al, JACS, 2004, 126, 7800-7811
H3CO
NH
N
S
CH3
O
H3CO
N
N
S
CH3
O
CH3
F2HCO
NH
N
S
CH3
O
F2HCO
N
N
S
CH3
O
CH3
pKa Measurements by UV Spectroscopy
5 6
Sachs, G. et al, JACS, 2004, 126, 7800-7811
OmeprazolePantoprazole
Tenatoprazole
Rabeprazole
Lansoprazole
Conversion Rates of Methyl-PPIs at Different Medium pH
N1-methyl lanzoprazole
N1-methyl tenatoprazole
N1-methyl pantoprazole
N1-methyl omeprazole
Sachs, G. et al, JACS, 2004, 126, 7800-7811
0
0.02
0.04
0.06
0.08
-0.5 0 0.5 1 1.5 2
Co
nv
ers
ion
ra
te c
on
sta
nts
(m
in -1
)
pH pH
0
0.1
0.2
0.3
0.4
0.5
-1 0 1 2 3 4 5 6 7 8
Lanzoprazole
Tenatoprazole
Pantoprazole
Omeprazole
N1-methyl lanzoprazole
0
0.2
0.4
0.6
0.8
1
230 250 270 290 310 330 350
Ab
sorb
an
ce
Wavelength (nm)
UV Spectra of N1-methyl Lansoprazole in Different pHs
pH 5.60pH 5.02
pH 4.53
pH 1.00
pH 4.03
pH 3.83
pH 1.60
pH 3.24
pH 1.30
pH 2.53
pH 2.30pH 2.00
pH 0.60
pH 0.30
pH 0.00
pH-0.30
Sachs, G. et al, JACS, 2004, 126, 7800-7811
pKa1
pKa2
246 nm
291 nm
pKa Measurements
� N-methylation and protonated pyridinylmethyl sulfinyl effect
pKa2= 0.7
pKa= 1.35
pKa= 1.43
0.7-1.43 = -0.73pyridinylmethylsulfinyl effect
1.43-1.35 = +0.08methylation effect
Sachs, G. et al, JACS, 2004, 126, 7800-7811
Pkas of Proton Pump Inhibitors
pKa1 pKa2
4.06 0.25+_
3.83 0.15+_
3.83 0.24+_
4.53
4.04
0.79
0.62
0.11
0.62
-0.12Actual measurements
Calculated
Omeprazole
Lansoprazole
Pantoprazole
Rabeprazole
Tenatoprazole
Sachs, G. et al, JACS, 2004, 126, 7800-7811
Conversion Rates and Pkas of Proton Pump Inhibitors
pKa1 = 3.83
pKa2 = 0.62
pKa1 = 3.83
pKa2 = 0.11
Lansoprazole Pantoprazole
[Bz-Py.H+] = [Bz-Py] × 10
[Bz.H+-Py] = [Bz-Py] × 10
Sachs, G. et al, JACS, 2004, 126, 7800-7811
(pKa1-pH)
(pKa2-pH)
Bz Py Bz Py
Conversion Rates of Proton Pump Inhibitors
� Substituent effects on the nucleophilicity of pyridine at pKa1 (when pH > 4.0)
� Conversion rates of PPIs are strongly affected by the second protonation
at pKa2 (when pH < 4.0)
First protonation
Second protonation
Sachs, G. et al, JACS, 2004, 126, 7800-7811
Why PPIs Have Different Half-lives?
Omeprazole
Pantoprazole
Shin, J. et al, Gastroenterology, 2002, 123, 1588-1597
7-8 loop3-4 loop
Cys 892 Cys 321
5-6 loop
Cys 813
Cys 822
28 Hour half-life
46 Hour half-life
34568
Membrane
� Drug-drug interaction with other anti-acid drugs
� Since PPIs require stimulation of gastric acid secretion, they are
more effective when administered one hour before breakfast.
� Protecting PPIs from gastric acid prior to absorption (formulated
with an acid-resistant coating)
Acid Related Activity of PPIs
Gastric glands
Blood vessels
Stomach
Enzyme-Inhibitor Complex in Acidic Compartment of the Stomach Cell
S
N
NH
CH3
OCH3
CH3
N
S
H3CO
H+
K+
Parietal cell
Cytoplasm
Mucous cells
NH
NS N
CH3
H3COO
OCH3H3C
H
K+
H+
Lumen
Esophagus
Stomach
Duodenum
Small intestine(jejunum and ileum)
Acid resistance coat
pH < 2
pH 2-5
pH 6.5-7.5
Release of PPIs in the Body
N
H3C
OCH3CH3
S
O
NH
N
OCH3
What other things can PPIs do?
Inappropriate gastric acid levels could be inhibited by PPIs
but:
Other Properties of PPIs
Alternative Uses
Minoxidil tablet
(Hypertension treatment)
(Topical foam)
Inappropriate gastric acid levels could be inhibited by PPIs
but:
Other Properties of PPIs
What is more about PPIs?
Glucose Metabolism in Mammalian Cells
Gateby, R. et al. Nature reviews, Cancer, 2004, 4, 891-899
Effect of Medium Acidity on the Viability of Gastric Cancer Cells
0
20
40
60
80
100
pH 7.5 pH 6.5 pH 5.5
Non-cancer cells
Gastric cancer cells
AGS
SNU-1
SNU-16
SNU-601
MKN-28
MKN-45
KATO IIIRGM
Ce
ll v
iab
ility
(%
)
Yeo, M. et al, Cancer Sci. 2008, 99, 185-192
Reduction of Cell Viability by Treatment with Pantoprazole
0 20 40 60 80 100
AGS
KatoIII
MKN28
MKN45
SNU1
SNU601
Cell viability (%) after PPI treatment
Yeo, M. et al, Cancer Sci. 2008, 99, 185-192
� 0.8 mM PPI for 16 h
Pretreatment of Cancer Cells with Omeprazole
Fais, S. et al, JNCI. 2004, 96, 1702-1713
� Melanoma cell line (MelM6)
0
20
40
60
80
100
0 0.5 5 50%
of
de
ad
ce
lls
[cisplatin] µM
0
20
40
60
80
100
0 0.5 5 50
% o
f d
ea
d c
ell
s
[cisplatin] µM
cisplatinsalineomeprazole (pretreatment)
cisplatinsalineomeprazole + cisplatin
Pretreatment of Cancer Cells with Omeprazole
Fais, S. et al, JNCI. 2004, 96, 1702-1713
� Melanoma cell line (MelM6)
0
20
40
60
80
100
0 0.1 1 10 100 1000
% o
f d
ea
d c
ell
s
0
20
40
60
80
100
0 0.1 1 10 100
% o
f d
ea
d c
ell
s
[5FU] µg/ml [vinblastin] ng/ml
5FU saline
omeprazole (pretreatment)
vinblastinsaline
omeprazole (pretreatment)
Conclusion
� Different conversion rates of proton pump inhibitors in the body
is mostly due to the protonation of benzimidazole ring.
� Inappropriate levels of Gastric acid can be inhibited by proton
pump inhibitors.
�There might be chances of using current FDA approved drugs for
other possible treatments rather than those usages they currently
have.
� PPIs are potentially potent anti-cancer agents (treatment or
pretreatment of cancer cells) which their anti-cancer activity
definitely needs further work.
Clinical Gastroenterology and Hepatology, 2007, 5,5
Acknowledgment
- Dr. Kevin Walker
- Dr. Babak Borhan
- Dr. Daniel Jones
- Dr. Jetze Tepe
- Dr. Ahmad Shafii
- Mark, Washington, Danielle, Yemane, Irosha
Group members:
- Chrysoula, Ramin, Roozbeh,
- Atefeh, Afra, Maryam, Rafida, Behrouz
My friends: