Lecture8.2

Question 1

What are some approaches to improve permeability of lead compounds?

Answer 1

1. adding nonpolar side chains to increase lipophilicity
2. Decrease H-bonds
3. make prodrugs

Question 2

Name a drug that was made more permeable by decreasing H-bonds

Answer 2

Razaxaban, an anti-clotting agent

Question 3

How to increase CNS permeability of drugs?

Answer 3

1. decreasing number of H-bonds
2. increase in lipophilicity

Question 4

Rank the BBB permeability of the following compounds.

Codeine, Morphine, Heroin

Answer 4

Morphine < Codeine < Heroin

*Codeine: hydroxyl groups of Morphine replaced with methoxyl group
*Heroin: hydroxyl groups of Morphine replaced with acetate

Question 5

Compare the polarity of the following groups

Methoxyl, hydroxyl, acetate

Answer 5

hydroxyl&raquo_space; methoxyl&raquo_space; acetate

Question 6

What are the molecular properties that govern solubility and permeability?

Answer 6

◼ H-bonding capacity
◼ Size/MW
◼ Lipophilicity
◼ Ionization/charge

All these properties are inter related and changing one can affect several others

Question 7

How will increase in H-bonding capacity and ionization affect solubility and permeability?

Answer 7

increase solubility
decrease permeability

Question 8

How will increasing lipophilicity and size affect solubility and permeability?

Answer 8

increase permeability to some extent
decrease solubility

Question 9

How to improve metabolic stability of lead compounds?

Answer 9

structure modifications

–> phenolic hydroxyl can be changed to an isostere (e.g., cyclic urea and thiourea) or a prodrug to reduce glucuronidation

Question 10

How to reduce glucuronidation in Phase II reactions?

Answer 10

phenolic hydroxyl can be changed to an isostere (e.g., cyclic urea and thiourea)

Question 11

How is compound decomposition carried out in plasma?

Answer 11

by hydrolytic enzymes

Question 12

How to improve plasma stability of a lead/drug?

Answer 12

1. increasing steric hindrance near a hydrolyzable group
2. replacing hydrolyzable group with less reactive group
   —> amides more stable than esters against plasma hydrolysis

Question 13

Which is more stable against plasma hydrolysis? amides or esters?

Answer 13

amides

Question 14

Is bio-activation one of the major causes of drug toxicity?

Answer 14

Yes

Question 15

Give some examples of substructures that will produce reactive metabolites resulting in toxicity.

Answer 15

-Aromatic amine
-carboxylic acid
-phenol
-polycyclic aromatic
-vinyl

Question 16

What are some strategies to improve safety of lead compounds/drugs?

Answer 16

• avoid substances that can induce toxic response
• increase metabolic stability to reduce metabolic bio-activation

Question 17

What is meant by hydrolysis of drug in plamsa?

Answer 17

enzymatic breakdown of a drug molecule in the bloodstream through the addition of water (H₂O)

typically occurs to ester or amide groups

Question 18

What Happens During Hydrolysis?

Answer 18

Example of Ester Hydrolysis:
Drug (ester) + H₂O → Alcohol + Acid

Example of Amide Hydrolysis:
Drug (amide) + H₂O → Amine + Acid

Question 19

What is the system that regulates blood pressure?

Answer 19

Renin-Angiotensin-Aldosterone System

Question 20

What is the role of renin in Renin-Angiotensin-Aldosterone System? When is it released? Where is it produced?

Answer 20

-produced and stored in kidney
- released when Na+ conc or blood pressure fails
- converts angiotensinogen to angiotensin I

Question 21

What is ACE? What is it for?

Answer 21

Angiotensin-converting enzyme

-Converts angiotensin I to angiotensin II, which triggers formation of aldosterone

Question 22

What is the role of aldosterone in Renin-Angiotensin-Aldosterone System?

Answer 22

–> causes the kidneys to retain salt (sodium) and excrete potassium
–>The sodium causes water to be
retained

thus increasing blood volume and blood pressure.

Question 23

What is the role of angiotensin II in Renin-Angiotensin-Aldosterone System?

Answer 23

-triggers formation of aldosterone
-causes the muscular walls of small arteries (arterioles) to constrict,
increasing blood pressure

Question 24

Describe the cascade of Renin-Angiotensin-Aldosterone System that results in an increase in blood pressure.

Answer 24

1. Renin convert angiotensinogen to angiotensin I
2. ACE converts angiotensin I to angiotensin II
   3a angiotensin II triggers formation of Aldosterone
   3b angiotensin II causes the muscular walls of small arteries to constrict –> increase bp
3. Aldosterone causes kidneys to retain salt (sodium) and
   excrete potassium –> water retained –> increase blood vol & bp increases

Question 25

What is peptidomimetics?

Answer 25

altered, unnatural analogs of peptides to make them more resistant to digestion before absorption from GI tract

Question 26

Name 2 ligands of zinc atom. Which is stronger?

Answer 26

1. carboxyl group 2. sulfhydryl group sulfhydryl group is stronger

Question 27

What are the three main 'compartments' of the initial drug (Captopril) designed to bind to ACE (a zinc protease)?

Answer 27

-benzyl moiety to bind to lipophilic pocket -carboxyl group to interact with basic part (amine) of enzyme -sulfhydryl group to interact with zinc to inactivate enzyme

Question 28

What was the problem with 'captopril' when it was used for high bp in market?

Answer 28

sulfhydryl group caused loss of taste and rashses

Question 29

Having 2 carboxyl groups for a drug might make it less effective. Why? How could the problem be overcome?

Answer 29

too ionizable for oral activity --> replace carboxyl group with ethyl ester -->or alter isoelectric point such as by introducing amino group to balance acidity of carboxyl groups

Question 30

On what parameters are potent and selective leads evaluated?

Answer 30

1. metabolic stability 2. plasma-protein binding 3. permeability 4. cLogP 5. solubility

Question 31

An experimental drug lead needs to be tested in a test tube or in animals prior to being used on humans. The preclinical animal and laboratory studies must be done and documented according to the current good laboratory practices (cGLPs). True or false

Answer 31

True

Question 32

What disciplines work in parallel during preclinical characterisation of the lead?

Answer 32

◼ Efficacy Pharmacology/PKPD ◼ Safety/Pharmacology/Toxicology/ Pathology ◼ Bio-analytical Research

Question 33

During Preclinical Characterization of the Lead, what are toxicity tests of leads carried out on?

Answer 33

tissue samples, organ cultures, and animals

Question 34

What information does 'pharmacological evaluation' of a drug entail in preclinical characterisation of the lead?

Answer 34

1. info concerning ADME and PD properties 2. drug’s potential interaction with other drugs/OTC medicines --> could also be investigated further in human trials

Question 35

What information does toxicity studies of a drug entail in preclinical characterisation of the lead?

Answer 35

1. info on drug's damage to organs 2. relationship of damage to dose 3. relationship of damage to duration the drug remains in body 3. whether damage is reversible

Question 36

How is 'absorption' (and permeability) evaluated in preclinical studies?

Answer 36

1. intestinal transport study --> Caco-2 cell model 2. BBB transport study --> mdr1-MDCK cell model

Question 37

How is distribution evaluated in preclinical studies?

Answer 37

Plasma protein binding assay --> equilibrium dialysis

Question 38

How is metabolism evaluated in preclinical studies?

Answer 38

1.metabolite profiling and identification --> hepatic microsomes incubation 2. metabolic stability screening --> hepatic microsomes incubation

Question 39

What are the physicochemical studies evaluated in preclinical studies?

Answer 39

stability and lipophilicity

Question 39

How is permeability measured in absorption studies using Caco-2 or MDR1-MDCK cell cultures?

Answer 39

based on the appearance of test drug in the basolateral side after 1h incubation

Question 40

What equipment is used to meaure plasma protein binding in preclinical studies?

Answer 40

Equilibrium Dialyzer Each unit has 1. dosing compartment (drug+plasma) 2. semi-micro membrane 3. buffer compartment (phosphate buffer)

Question 41

How is protein binding (%) calculated using equilibrium dialyzer in plasma protein binding studies during preclinical studies?

Answer 41

{[C(dosing comp) - C(buffer comp)] / C(dosing) comp} * 100%

Question 42

In preclinical studies, what is used to study drug metabolism?

Answer 42

hepatic microsomes containing cytochrome CYP450 - test compound incubated with rat liver microsomes at 37C for 30mins - mixture analysed by HPLC or LCMS for metabolite profiling

Question 43

What are hepatic microsomes? How are they prepared?

Answer 43

subcellular fractions derived from the endoplasmic reticulum (ER) of liver cells ---> breaking open liver cells, the smooth ER (where drug-metabolizing enzymes are located) fragments into small vesicles, which can be isolated as hepatic microsomes.

Question 44

What animal is used as a model in pharmacokinetic studies?

Answer 44

albino rat

Question 45

What kind of samples are collected during pharmacokinetic studies involving animal models in preclinical studies?

Answer 45

- blood samples routinely collected -excreta for metabolite profiling and ID -bile - tissues and organs for determining distribution of drug

Question 46

How is blood collected from a rat?

Answer 46

from the tail vein and abdominal aorta, or by cardiac puncture