Hit to Lead and Lead to drug part 2

Question 1

Medchem strategies: Subtype selectivity

Answer 1

Modification of Subtype Selectivity: Occurs early in assay cascade as likely to be relevant to all hits and leads

Increae potency: the greater the potency the more likely to identify selective compounds/ SAR

Structure guided approaches: may identify differences which can be exploited

Increase fraction SP3

Question 2

Medchem strategies: Off target/cytoxicity

Answer 2

• Done later in assay cascade because likely different in each compound
• Reduce LogP(CYP inhibition)
• Develop target/off target/cytotox SAR

Question 3

Structural alerts

Answer 3

Typically reactive compounds which form covealent bonds with proteins

Two classes:

• Inherently reactive (electrophiles and nucleophiles)
  i. e. Aldehydes, aß unsaturated ketones
• Bioactivated: converted to reactive species upon metabolism in vivo

Question 4

Example structual alerts for bioactivation

Answer 4

Aromatics with two hydroxyl groups is the main one

Others: analines and nitrobenzene, goes to arylnitroso compounds which are mitochonrial toxic

Question 5

Measuring level of bioactivation, radiolabelling

Answer 5

• Radiolabel compound and measure level of uptake into cellular compartments
• Add radiolabelled compound to human liver microsomes
• washout free drug and measure level of radiation to quantitate drug incorporation
• <50 pmol equivalent/ mg

Pros: Most direct measure of protein drug binding

Cons: complicated/exoensive for early stage medchem

Question 6

Measuring levels of bioactivation, GSH incorporation

Answer 6

Pros: This can be easily achieved by adding GSH to human liver microsomes and measuing incorporation to the drug by LC/MS

Cons: indirect measure of protein activation, incorporation of the active media

Question 7

Strategies for overcoming bioactivation

Answer 7

• avoid incorporation of structural alerts
• avoid redox reactive groups (aromatic groups, thiols, thiocarbonyls, sulfides)
• use biosteric replacements
• add electron withdrawing groups to aromatics to reduce their rate of oxidation (no nitro groups)
• add stericaly hindiring groups to block site of activation
• redirect metabolism to give a non reactive metabolite

Question 8

Generic remidies for preventing aromatic hydroxylation and formation of reactive intermediates

Answer 8

• Add F groups, electron withdrawing so prevent electron abstraction which is required for aromatic oxidation
• CH3 to CF3 of CF2R
• OMe to OCF3
• Use sparingly as very hydrophobic

Question 9

Other things to consider

Answer 9

Ampiphiles:

• Can insert into lipi bilayers and disrupt protein function
• avoid adding a polar headgroup to otherwise non-polar molecules

Polyfused aromatics:

• Piestacking, planar which may result in them targeting DNA

Metal binding groups: (picture)