L1: Target selection; Lead Identification Flashcards
Describe the 4 stages of Drug development process
- Recombinant systems: protein-drug interaction
- Cell systems: interaction in natural cellular environment
- in vivo: interaction in complex biological system
- clinic: interaction in human system under controlled pathological environment
state the 3 types of NEW drugs
- new drug for NOVEL use [new approach or disease]
- new drug that is a new generation of present drug
- new drug that is another variation of known drug [me-too drug]–> similar to present drugs but different enough to be patented
what are the different approaches to target selection?
- genomic approach
- proteomics approach
- RNAi screens
what is genomic approach in target selection? give one example
analysing entire genetic information of organism in healthy vs disease state –> see how genome correlate to phenotype
eg. chronic myelogenous leukemia (CML): chr translocation that forms fusion gene BCR-Abl-> constitutive activated Abl kinase
what is proteomics approach in target selection? give one example
separation and characterisation of proteins in organism: compare protein expression in healthy vs disease state
problem with using genomic and proteomics approach in target selection?
just bc gene/protein is expressed differently does not mean it cause disease ==> NEED TO VALIDATE using RNAi screeen
how can RNAi screen validate target selection?
specific indiv genes are knocked down to find genes that regulate key disease processes ==> identify potential targets by function
limitations of RNAi screens
limited to studies in vitro [cell lines]
how do you validate your targets?
use in vitro assays and in vivo assays [BOTH REQUIRED]
In vitro: engineer cell lines with gain/loss of function using siRNA or shRNAi –> see ROLE of target
In vivo: usually use transgenic model and conduct loss/gain in function expts
- loss: use shRNA on tumour growing mouse
- gain: over express gene in normal mice
what is a HIT?
a compound that INTERACTS with chosen target at given conc [usually in micromolar range]
what is a LEAD? [3]
A compound with drug-like properties and initial structure-activity relationship and a promising IP position
what is a preclinical development candidate? [3]
a New chemical entity with optimised pharmacological and pharmacokinetic properties and secure IP position
methods of LEAD identification
- rational drug design
- high-throughput screening (HTS): cell-free or cell-based
- Fragment-based screening (FBS)
elab on rational drug design
first identify potential HITS using interaction between drug and target –> require coordination between structural biology and organic chem and design drug based on pharmacophore of endogenous ligand/substrate
elab on high-throughput screening. what it is and methods.
uses either cell-free or cell-based assays. ideally on isolated target molecule aka cell-free. target-specific effects are measured quantitatively by reporter assay eg. fluorescence, luminescence, cell shape
Cell free:
- specific target is bound to antibody on plate + substrate added
- drug added afterwards to see if reaction is inhibited
Cell-based:
- cell+drug and look for reporter gene reaction –> problem: dont know the exact point in pathway that drug is acting on + difficult to do SAR without knowing exact molecular target and mode of drug interaction
give one example of small molecule rational drug design
discovery of drug for chronic myelogenous leukemia. found out that myristoylation of N terminus of c-ABL causes structural change in c-ABL–> autoinhibition of -ABL.
BCR-ABL lacks the N-terminus myristoylation site resulting in constitutive active BCR-ABL
what is robust screening assay? formula?
used to assess quality of HTS assays. measured using z’. z’ ranges between 0-1, the higher the value of z’, the more robust the assay [>0.6 is acceptable].
what does higher z’ score mean?
more robust the assay–> allows for wider range of identifying new drugs
state the pros of rational design [1]
it is a focused analysis of drug candidates
state the cons of the rational drug design [3]
- done on a limited set of candidates –> info gathered on a few drugs only
- not predictive of favourable pharmacological properties-> identified HITS may not be real HITs
- requires extensive knowledge of target
state the pros of high throughput screening [2]
- real data that can identify competitive or allosteric inhibitors from 1 screen [from cell-free assay]
- eliminates compounds that are unstable or cannot access cellular target
state the cons of HTS [2]
- requires screening of many thousands of candidates [more costly and time consuming]
- labour intensive
describe fragment based screening
instead of identifying structures that bind really well to target, we find only those that bind decently –> can collate info on how diff interactions contributes to binding –> use structured based design and interaction to design drug with explored structures
give one example of drug made with fragment based screening
novel stat3 inhibitor.
