Drug targets

Question 1

what is a target

Answer 1

any system that can potentially be modulated by a molecule to produce a beneficial effect
- biological macromolecule or molecular complex that is critical for the disease

Question 2

what is meant by target validation

Answer 2

• form of risk assessment where the better the validation, the lower the risk in advancing the project
• mitigates selection of wrong target and wrong patient population

Question 3

what factors need to be considered in target identification/validation

Answer 3

1. is the target critically involved in disease
2. is the target critically involved in normal biology
3. location of the target
4. does manipulation lead to desired effect
5. can the target be effectively studied
6. is the target amendable to high throughput screening

Question 4

what are the different types of target

Answer 4

1. enzyme inhibitors (competitive or non competitive) or activators
2. receptors- agonist or antagonist
3. ion channels- blockers or activators
4. transporters- inhibit or stimulate
5. viral surface proteins- blocking entry to cell
6. DNA intercalating agents, minor groove binders, anti sense drugs
7. cells- vaccines

Question 5

name the major components of target identification

Answer 5

1. tissue expression
2. genetics
3. clinical experience

Question 6

how is tissue expression involved in target identification

Answer 6

• target protein is expressed or active in the desired organ
• target mRNA expression is altered in the desired disease tissue
• target protein expression is altered in disease tissue

Question 7

how are genetics involved in target identification

Answer 7

• genetic association of a variant with a disease
• genetic polymorphisms linked to a disease state

Question 8

how is clinical experience involved in target identification

Answer 8

• known ligand affecting target pathway or protein has shown efficacy in the disease

Question 9

what methods can be used to identify novel targets

Answer 9

1. DNA microassays
2. proteomics
   - post translational modifications
   - protein isoforms
3. RNA knockdown
   - gene knockouts
   - antisense technology

Question 10

what is needed for a validated target

Answer 10

1. literature survey and competitor information
2. identification of a pathophysiologically relevant molecule target (enzyme, receptor)
3. analysis of molecular signalling pathways
4. molecular pharmacology of variants
5. determination of DNA and the protein structure
6. elucidation of the function and mechanism of the protein
7. proof of therapeutic concept in animals

Question 11

what is the pharmacology behind target validation

Answer 11

1. pharmacological tool modulates disease associated pathway in vitro
2. ligand with intended mode of action modulates disease associated pathways ex vivo or in native tissue
3. ligands with intended mode of action modulate disease associated pathway in vivo with target engagement activity relationship established

Question 12

describe the antisense technology

Answer 12

• sRNA blocks synthesis of the targeted protein
• eg. blockage of the P2X3 receptor was able to lower pain sensitivity

Question 13

what is the advantage of antisense technology

Answer 13

• reversible model, so can be sure that it is the target that is responsible for the effect

Question 14

what is meant by transgenic animals

Answer 14

specific protein expression inhibited in every cell

Question 15

what is an advantage of transgenic animals

Answer 15

can identify the role of the protein not just in disease but also in normal biology

Question 16

what is a disadvantage of transgenic animals

Answer 16

tissue restricted/inducible knockouts are more desirable with the advancements of drug delivery

Question 17

what is meant by ligand pharmacology

Answer 17

determining whether a specific ligand against the identified target have a pharmacological effect in the disease state

Question 18

why are animal models used

Answer 18

essential to bridge the translational gap between preclinical and clinical research
- is there a suitable animal model of the disease you want to treat
- how close is it to the human condition

Question 19

give examples of animal models

Answer 19

1. colitis- DSS model
2. arthritis
3. haemorrhagic shock- blood removal and replacement
4. septic shock
5. adult respiratory distress syndrome
6. myocardial infarction

Question 20

what are the 3 main type 1 diabetes animal models

Answer 20

1. multiple low dose streptozoticin model- chemically induced
   - fast results (data after 21 days)
2. non obese diabetic mouse- genetic
   - incidence increases after 5 weeks
   - 80% of female mice develop diabetes, compared to only 20% of male mice
   - experiments run to 30 weeks
3. virally induced- establish role of viruses in development of diabetes

Question 21

what are the 3 main type 2 diabetes animal models

Answer 21

1. genetically obese models- ZDF rats or OB/OB mice
   - treatments to improve insulin resistance or improve beta cell function
2. induced obesity- high fat feeding mice or rats
3. non obese models- GK rat

Question 22

what are the disadvantages of animal models

Answer 22

can fail to identify effective treatments

Question 23

why can animal studies fail

Answer 23

1. disease model doesn’t truly reflect disease- model is quantitatively wrong with species differences in capacity, sensitivity
2. incorrect translation of the intervention to the patient so target is relevant but not appropriately engaged pharmacologically
   - incorrect dosing regimen because of species differences in pharmacokinetics
3. clinical endpoints differ in animal models
   - quality of life is endpoint used in clinical trials, measured by questionnaire which can’t be done with animals
4. clinical trial design not appropriate to test the intervention under investigation

Question 24

what is the standard drug development approach

Answer 24

1. identify target
2. develop assay for high throughput molecular screen
3. mass screening and directed synthesis programme
4. select one or more lead structures