Agents of renin/angiotensin system - Stevens

Question 1

What is the order of conversion of the angiotensin hormone?

Answer 1

Angiotensinogen
Angiotensin I
Angiotensin II
Angiotensin III

Question 2

What do ACE inhibitors do, and why are they such an attractive therapeutic target?

Answer 2

• catalyzes transformation of angiotensin I to angiotensin II
• catalyzes the degradation of bradykinin

Question 3

ACE inhibitor development: how was it developed?

Answer 3

• peptide isolated from snake venom, but typical peptide drug problems (such as not orally available, short t 1/2 when given IV, and antigenic (can cause allergic reaction)).
• non-peptide analogs: ACE active site knowledge (ACE is a dipeptidyl carboxypeptidase that requires zinc)
• ACE is similar to carboxypeptidase A (which only removes one residue at a time from the C-terminus compared to ACE, which removes two aa’s at a time)

Question 4

Carboxypeptidase A active site description:

Answer 4

• Has S1, zinc, and S’1
• carbonyl of peptide bonds to the zinc
• benzilic ring of peptide bonds to S’1
• hydrolysis product (R)-2-benzylsuccinate

Question 5

What is a potent inhibitor of carboxypeptidase A?

Answer 5

• Needs carbonyl to bind to a positively charged residue in the active site
• Need a carbonyl to coordinate with the zinc
• Need an alkyl group to mimic hydrophobic interaction of the amino acid side chain

Question 6

What does the proposed ACE active site (modeled after carboxypeptidase) look like?

Answer 6

• Has S, S’1, S’2
• Angiotensin has two rings that fit into S and S’, and isobutane chain that fits into S’2.
• Carbonyl of angiotensin interacts with zinc, and carboxylic acid interacts with positively charged area of active site.

Question 7

Based on the hypothetical active site model of ACE and peptide inhibitor SAR, what are the SAR needs of a non-peptide ACE inhibitor?

Answer 7

• A terminal carboxyl group to coordinate with a positive charge in the active site
• A carbonyl able to act as a hydrogen bond acceptor
• A functional group able to coordinate with a zinc ion.

Question 8

What converts Angiotensinogen into Angiotensin I?

Answer 8

Renin

Question 9

What converts Angiotensin I into Angiotensin II?

Answer 9

ACE

Question 10

What converts Angiotensin II into Angiotensin III?

Answer 10

Aminopeptidase

Question 11

On which enzymes do ACE I’s act?

Answer 11

They inhibit ACE’s conversion of angiotensin I into angiotensin II.

Question 12

On what do ARBs act?

Answer 12

They are angiotensin II receptors antagonists . They block the angiotensin II that is produced through escape pathways (such as chymase, t-PA, cathepsin-G pathways)

Question 13

Why is angiotensin II not a good substrate for ACE?

Answer 13

Because of the proline residue in the penultimate position (the position second to last). The proline is known as a stopper.

Question 14

What enzyme cleaves between Leu and Val?

Answer 14

Renin

Question 15

What enzymes cleaves between Asp and Arg?

Answer 15

aminopeptidase

Question 16

What enzyme cleaves between Phe and His?

Answer 16

ACE

Question 17

What is a good feature for an inhibitor of carboxypeptidase A?

Answer 17

Collect products approach, which is focused on carbon-carbon bonds that are difficult to break.

Question 18

What was the simplest compound that met the minimum SAR requirements as a peptidomimetic inhibitor of ACE?

Answer 18

N-succinyl-L-proline. It had a IC50 value of 330 uM (not very potent inhibitor)

Question 19

What kinds of structural improvements were made to N-succinyl-L-proline to change the binding affinity to ACE?

Answer 19

Addition of a methyl group to bind to the S’1 position, lengthening and shortening the chain by adding or subtracting another CH2, and substituting an -SH group for the COOH group.

Question 20

What combination of additions resulted in captopril?

Answer 20

A terminal -SH group, two CH2 groups with a methyl, a carbonyl group, and an N-ring with a terminal carboxyl group.

Question 21

What side effect were associated with the terminal -SH group?

Answer 21

• Metallic taste
• Loss of taste
• Skin rash

Question 22

What changes were made between captopril and enalapril?

Answer 22

• SH group was replaced with -COOH group, which decreased the potency by 1,000, but also took away unwanted SE’s
• Benzene ring was added to increase binding affinity to S1 lipophilic pocket, but the bioavailability was still low. (Enalaprilate) Needed prodrug.
• Ethyl ester (to make prodrug) increased bioavailability. This is enalapril.

Question 23

What does enalapril use to bioactivate? What is the t 1/2?

Answer 23

Ester hydrolysis. 11 hours = t 1/2

Question 24

What pocket does enalaprilat not bind well in?

Answer 24

The S’2 pocket has lots of space to bind in.

Question 25

What aa’s are in the S’1 pocket of ACE?

Answer 25

Three TRPs and Glu

Question 26

What aa’s are in the Zn pocket of the enzyme?

Answer 26

Two His and Glu

Question 27

Which ACE I is not a prodrug?

Answer 27

Lisinopril. It is a de-zwitter ion that is neutral, and therefore has reasonable bioavailability. The lysine on the side chain has a positive charge that balances with the terminal COOH.
Captopril is also not a prodrug.

Question 28

Which ACE I has a spiral moiety?

Answer 28

Spirapril

Question 29

Which ACE I has two methoxy groups?

Answer 29

Moexipril

Question 30

What improvement does fosinopril have over the other ACE I’s?

Answer 30

Fosinopril has a different way of being a prodrug. Heme-Acetal is formed through hydrolysis, which spontaneously falls apart into phosphinic acid. This binds the zinc in the enzyme in the same way as a carboxylic acid.

Question 31

What is ANF?

Answer 31

Atrial natriuretic factor/peptide is the same as ANP. They are endogenous peptides with potent diuretic and vasodilatory actions. They are endogenous antagonists of RAAS. Administering ANF is an effective means of controlling BP.

Question 32

What degrades ANF and other natriuretic factors such as BNP (brain natriuretic peptide) to inactive peptide fragments?

Answer 32

NET (neutral endopeptidase)

Question 33

What can stop NET from degrading ANP?

Answer 33

NET inhibitors

Question 34

What is Nesiritide?

Answer 34

A human recombinant 32 aa BNP (expressed in E. coli) that is normally produced by the ventricular myocardium (ANP is produced by the atrial tissue).

Question 35

Omapatrilat

Answer 35

• Vasopeptidase inhibitor
• First antihypertensive to receive priority review status
• Has features needed for ACE inhibition
• Concerns over angioedema caused it to have application withdrawn

Question 36

What are some vasopeptidase inhibitors that are in clinical trials?

Answer 36

Sampatrilat

Gempatrilat

Question 37

Sacubitril/valsartan

Answer 37

• vasopeptidase inhibitor in combination with ARB
• for treatment of heart failure
• prodrug ethyl ester (needs to be converted through hydrolysis to active drug: carboxyl group
• Active features of ACE I’s not present/effects are minimal.
• T 1/2 = 1.4 hours
• Active metabolite is sacubitrilate, t 1/2 = 12 hours for 2x daily dosing