medchem exam 2 ADMET 2

march 30th class, 10, all done

dose formula

f(time (of exposure), []); think about how stable it is when exposed - repeated doses, or one dose and then wait, depends on ADME

risk assessment

This discipline bridges the intricate relationship between a drug's physical and chemical properties, its formulation, delivery, and the biological systems it interacts with. By focusing on the absorption, distribution, metabolism, and excretion (ADME) processes, biopharmaceutic risk assessment provides critical insights that guide the optimization of drug bioavailability and therapeutic effectiveness, while mitigating safety concerns.

transporters role in excretion

specialized transporters - diff kidney cells look different, diff face that is in direction of urine, diff to blood

blood and drugs

plasma cells - contain proteins that can bind drugs; free drug amount - unbound; the more protein binding - the less efficient effective drug concentration at the target site; drug unbound to protein: plasma [] == effective []

how to see if a drug is viable in terms of blood []

use serum which also has proteins - can see effective [] then

St Johns Wort descr

• herbal compound, inhibits drug availability, induce P-glycoprotein and intestinal and liver CYP3A4

• High metabolism, lower drug availability

point of toxicology

to find what else a drug can do- side effects, how it can be harmful

how to find MEC

usually tested in animals and then approximated to humans, does not work 100% though; different again with children

phase I clinical studies how

do not take the min effective dose, go slowly and build it up, ONLY CARE ABOUT dose finding/safety, PK/PD, not effectiveness yet!! 20-100 healthy volunteers

animal timelines

Acute: 14 days, chronic: 90 days, carcinogenicity: 2 yrs, reproductive/developmental

LD50 test

lethal dose 50%, test to determine the single dose of chemicals that would kill half of the animals exposed to it

comparative toxicity index

allows to compare relative toxicity of compounds for the first time - a lot of appeal to government regulators

phase II clinical trial

100-300 patients, efficacy, safety

phase III clinical trials

300-3000 patients, efficacy, safety, more people

clonal cell models

each represents a unique patient/animal/tissue; cell models + metabolism/transporters = nuclear receptors, signal transduction, stress response pathways, immune system, etc

genetic variation and drug action (3)

drug transporters (eg P glycoprotein, variability in drug absorption/distribution/elimination)
drug metabolizing enzymes (eg P450s, variability in drug metabolism, side effects/toxicity)
drug targets (eg receptors, variability in drug effects)

SNPs in drug discovery (3)

SNP variant causes of disease (eg LH receptor), SNP variant less/not sensitive to drug, SNP variant modulates drug response indirectly

how to adjust drug [] based on patients metabolism

if poor metabolizer - lower drug []
if higher metabolizer - higher drug []

Multi drug resistance gene

MDR-1: P glycoprotein (PGP), in cancer cells/intestine/BBB; pumps substance out of the cell - protects against toxic metabolites; many drugs are PGP substrates (eg cancer resistance, limits oral availability, limits brain penetration)

what else do you need to consider for side effects

metabolites - eg from an active drug can have an inactive metabolite, an active metabolite and a reactive intermediate that leads to an inactive metabolite but also through reaction w/ cellular macromolecules can be bioactivated into toxicity

genetic variations of P450 enzymes and the results

deletion in gene - no enzyme - no metabolism
SNPs in gene - ““ , unstable enzyme - reduced metabolism; normal enzyme - normal metabolism; altered substrate specificity - other metabolites possibly formed
duplicate or multiple copies of gene - higher enzyme levels - increased metabolism

multicopy P450-2D6 genes effect on plasma kinetics

extensive metabolizers

look at diagram

what can lead to activation or inactivation of genes after diff types of DNA damage

DNA base modifications → mutation
DNA-breaks → chromosome breaks, translocation, aneuploidy

how to end up w/ intact DNA after diff DNA damage

DNA base modifications - DNA repair
DNA-breaks → DNA repair
intact DNA through elecrophiles, radicals or phase I metabolism can lead to DNA damage again

AMES test descr

genetically engineered Salmonella (bacteria), site-directed mutation or frameshift-mutation in gene for protein involved in histidine-biosynthesis, unable to grow in histidine-free medium (bc histidine is an essential aa), after exposure to mutagen MUTATION to functional gene: growth in histidine-free medium

what is this

ames test

test systems (3 catergories and many types (7:1:)

animals: apes, dogs, rat, mice, fish, flies, worms
bacteria
in vitro cell systems: cell lines, primary cells from donors, iPS cells from donors, complex cell systems (eg organs on a chip)

pros/cons of whole animal models (3, 4)

pros: complete physiological system, generational studies possible, genetic manipulation possible (KO animals)
cons: adverse drug rxns often diff than huamns (30-50% of false negatives, also false positives), valid ethical concerns, expensive, not well suited to molecular investigations at cellular level

pros/cons of human based in vitro systems (2: 8)

cons: incomplete/reductionist physiological system, easy to do bad experiments
pros: human derived (although cancer cells can be very different from normal), no animal suffering, potentially cheaper and quicker, applicable to high through-put, ideally suited to molecular investigations - much deeper mechanistic info, genetic manipulation easier than in whole animals, can capture human population variation, can study human genetic diseases directly

IC50 descr

50% inhibition of activity (amount of enzyme activity needed for)

gold standard for tests

primary human cells - eg liver cells from liver biopsy

primary human cells pros/cons (3:5)

pros: already differentiated, mortal - therefore “normal” cell cycle, epigenetic imprint of the donor prevails
cons: dedifferentiated during culturing, limited donor data, limited expansion possibilities, limited availability, unique source

human cell lines pros/cons (3:)

pros: unlimited lifespan, easier to standardise, high reproducibility
cons: may have gained/lost characteristics, may be altered due to immortalisation, genetically less stable

what is needed for iPSCs

transfect adult somatic cells with Yamanaka factors

iPS cells pros/cons (4:4)

pros: mortal, represents specific indivs, multiple target cells possible, genetic background usually known
cons: elaborate differentiation protocols, need for characterisation every differentiation, not as good (yet) as primary target cells, loss of epigenetic imprint likely

iPSCs; continous cell lines from (living) donors (5)

relatively simple to generate (also from non invasive sources like urine), large biobanks available, genetic background of donor maintained (unlike cancer cells), cells mortal w/ normal cell cycle characteristics, can perform coculture w/ autologous cells

3 egs of human in vitro models

liver, intestine, lung

can protein damage, DNA damage and reactive chemicals/metals lead to?

sensor proteins → effector proteins → stress responses

3 lines of defense after stress/drug/metabolite/ROS

1st line: drug metabolism - basal expression of genes co-ordinating cell defense, phase II enzymes, antioxidant proteins
2nd line: antioxidant response, induction of genes co-ordinating cell defense: phase II enzymes, antioxidant proteins, Nrf2 response
3rd line: apoptosis - suicide of the cell
finally - necrosis

oxidative stress response

oxygen radicals/reactive metabolites → (in cytosol) Keap1 (sensor) and Nrf2 (effector) → stress response → (in nucleus) Nrf2, upregulation of protective enzymes

what is Nrf2

transcription factor

HERG channel - Torsade de Pointes decsr

most common cause of withdrawl/restriction of drugs, prolongation of QT-interval via interaction w/ HERG K+ channel - irregular heart beats, acute cardiac arrest → sudden death; need to test for it to get approval for your drug

2 important transporters

BSEP and MRP

MPR2 descr

export of conjugates of lipophilic substances w/ sulphate, etc.

when is pharmacogenomics relevant

at all stages of drug discovery: absorption (P-glycoprotein), metabolism (cytochrome P4502D6), pharmacology (receptors), etc

pros/cons personalized medicine

select right patients for clinical trials, give patient right drug → better response of drug treatment → better compliance, BUT with smaller patient populations will huge costs of development be covered

DDI long

drug drug interactions

important note about PH

large interindividual differences in pharmacokinetics

take home messages toxicology (3)

new opportunities for human-based cell models (replacing animal studies), in silico models keep improving (also PK/PD), animals still only real-life physiology model available w/ all vital organs and immune system