role of drug metabolism+ DMPK and toxicity in lead optimisation

how to increase solubility

add ionisable groups like COOH

add polar groups like OH

add H-bonding carbonyl

reduce LogP

Mw< 500

prefer amorphous over crystalline

reduce particle size

make salts

what is high and low solubility

low<10 microg/ml high>60 microg/ml

how to increase solubility

add ionisable groups like COOH

add polar groups like OH

add H-bonding carbonyl

reduce LogP

Mw< 500

prefer amorphous over crystalline

reduce particle size

make salts

what is high and low solubility

low<10 microg/ml high>60 microg/ml

what are the negative effects of poor solubility

poor absorption and bioavailability, restricted volume for IV dosing, low activity in bioassays, erratic assay results as the material precipitates out, expensive formulation and development times, frequent high-dose admin

Describe kinetic solubility method and when is it used

- Compound dissolved first in an organic solvent (e.g. DMSO, 10 μM stock solution), then aqueous buffer added to solution until precipitation occurs, monitoring with ChemiLuminescent Nitrogen Detection (CLND)

Equilibrium not reached, so not an absolute method, but good enough for trends at lead optimisation stage

Describe thermodynamic solubility and when it's used

Aqueous solvent added to solid directly and mixed for over 24 h to achieve equilibrium , Solubility value varies with form of the solid (amorphous, crystalline, polymorph, hydrate, solvate) , Used when a candidate is identified for development to define melting point and crystalline form

Describe transcellular diffusion and what are the drug properties necessary

Drug molecules cross enterocytes by penetrating apical membrane, diffusing through cytoplasm, and exiting through basolateral membrane into portal blood

MW > 300, logP > 0, are unionised and soluble. HBA < 10 and HBD < 5.

Describe paracellular diffusion, the drug properties and give an example

Drug molecules cross enterocytes through water-filled pores between cells aka tight junctions

MW < 250, logP < 0, positively charged

Example: cimetidine

What is active transport influx, give examples

transporter in small intestinal mucosa

peptide transporters PEPT1, PEPT2- Cephalexin

monocarboxylic acid transporter- Pravastatin

organic anion OATP1, OAT1, OAT3- Fexofenadine

organic cation OCT 1- L-cartinine

What is active transport efflux, give examples

transport of drugs from inside the cell back into the luminal space in brain (protection), liver (removed metabolites to bile for elimination) and kidney( secretion to the proximal tubule)

e.g. p-glycoprotein, breast cancer resistance protein BCRP

Describe Permeability in vitro assays

Permeability is the velocity of compound passage through a membrane barrier such as Caco-2 human colon epithelial cell line or MDCK cell line

Papp: cm/s x 10-6 correlates to human absorption and oral bioavailability

Automated incubations with LC-MS/MS analysis

How to improve permeability

switch to un-ionisable group like OH

increase LogP- add methyl group

replace polar groups with isostere- acid with tetrazole

reduce H-bonding and polarity

make a prodrug- add ester group that is hydrolysed

What is class 1

high solubility and high permeability

what is class 2, and how to resolve it

low solubility, high permeability- make it more soluble with formulation strategies

what is class 3, and how to resolve it

high solubility, low permeability, make a prodrug

what is class 4

low solubility, low permeability, very risky and costly to develop