15/16 - Anticancer Drugs against signalling pathways - Williamson Flashcards
What properties do good drugs need to have?
a) specific against a particular target (nM - tight binding)
b) doesn’t bind to other targets - no side effects
c) need to get to target, preferably by mouth therefore small, hydrophilic
d) suitable pharmacokinetics; good bioavailability, delivered to target, low metabolism and excretion
e) non toxic; metabolites not toxic
what types of drugs need to be created so that it will SPECIFICALLY BIND to its target? (and no where else) (alb)
these drugs need to look v much like the natural substrate for accurate binding
give an example of a drug that SPECIFICALLY BINDS to its target. state how this drug was adapted so that it worked better.
HIV protease inhibitor;
- initially created as Invirase. looked v much like the natural substrate; Asn - Tyr // Pro - Ile but instead of the middle peptide bond, replaced with an OH and an extra C
- however was still easily metabolised
- slightly changed structure again so it looked as ‘un-peptide’ as possible - nelfinavir
what structure do drugs that normally inhibit enzymes mimic?
normally is a transtition state analogue
enzymes work by stabilising the ___ ___ and/or by destabilising the ____
transition state
reactants
what can happen if we design a drug to target a kinase by interfering with ATP binding?
then we interfere with ATP binding to other kinases, or any other enzymes that make or use ATP eg glycolysis, TCA cycle - not specific
what is the therapeutic index? give an example of a drug with a low TI and state its function
TI; ratio between toxic dose and the therapeutic dose. should be as large as possible. many drugs it is often 10 or less
eg Warfarin TI = 2, used to thin blood therefore used in heart attacks to prevent clotting. however if we prevent clotting and clotting doesnt occur as it should -> bleed to death and internal bleeding
why is Gleevec such a good drug in terms of specificity?
- although it is an ATP analogue, binds to the unusual and highly specific conformation of the ATP binding site of abl kinase
- autoinhibited form of Abl kinase does not bind well to ATP but binds well to Gleevec
what needs to happen once a suitable drug has been found that binds to a particular target?
can test to see if it binds anywhere else in the body;
- this may be a good thing eg Viagra. can strike lucky
- or bad. may bind to an additional target -> side effects
what is Lipinski’s rule of 5?
critical that an orally active drug does not violate more than one of…
- not more than 5 H bond donors
- not more than 10 H bond acceptors
- MW < 500 Da
- partition coefficient log(P) < 5 - ie not too hydrophobic
why can a drug not be too hydrophobic?
will sit in the membrane and get metabolised. causes toxicity
what is the trend in the MW of the drug and the stages of the clinical trials it reaches
as the stages progress, the MW tends to decrease and drugs that actually make it to market tend to have v low MWs (around 300 Da)
what is the ligand efficency and overall, what does this tell us about the size of the desired drug?
- binding free energy / no. heavy (nonhydrogen) atoms
- want this to be as large as possible. need strong binding energy and low no. heavy atoms
- tells us that our desired drugs should have small size
what is a major problem with having drugs that are too large?
bigger molecules = more molecules can bind to it and mark it for excretion therefore more ways for it to be toxic when it is degraded. big toxicity problems with big molecules
what are the specific factors of ‘good pharmacokinetics’?
- bioavailability; drug gets into the body
- once in the body, gets where it is needed (once in bloodstream, goes to the liver where the drug can be metabolised - these products of metabolism need to be non toxic)
- drug needs to be cleared relatively slowly (slow metabolism, slow excretion)
- any metabolites and non toxic and inactive (ideally)
give the OVERALL route of developing drugs by companies ie what product is initially designed?
initial design = ‘tool compound’ that meets a-c (specific binding, doesnt bind to anything else, small and hydrophilic)
then modifies this compound so it meets all other requirements - this is where it becomes expensive
what are the PRECLINICAL stages of drug testing? ie what Is the process of drug testing in organisms?
- pure proteins
- cell system
- mice
- larger animals eg cats, rabbits
- monkeys
(this stage should filter out anything that will fail)
give the best case scenario drug development pipeline. state what happens when the drug starts to go wrong during development
PRECLINICAL;
- target discovery - 1yr
- target validation - 1yr
- lead discovery - 2yr
- developed - 2yr (chemistry, pharmacology, animals)
CLINICAL;
- phase I - human volunteers (dosage testing)
- P II - around 100 sick volunteers (does it still behave the same way in sick people)
- P III - around 1000 sick humans
this all takes around 6 years
- when starts to go wrong, eg metabolism, delivery, toxicity then chemists start adding extra bits and changing the structure - almost always means that a-c get worse
what is the conventional approach to drug design?
- pick a target
- screen large no. small molecules to come up with lead compound
- compounds then put through increasingly difficult tests to test their sutability
- companies will start working on the successors in the meantime
what are the 2 things of major concern to develop new drugs?
- v expensive, companies need to make > $1bn off blockbuster drugs to continue to develop new drugs
- patents; only last for 20 years. development processes are long meaning that the drugs have < 10 yrs to make money
why are kinases considered “draggable” targets ?
- inhibitors often ATP analogues
- usually small, polar and follow all of Lipinski’s rules except b - specificity
what should the IC50 no. of a good drug be?
v low number
what are the largest current drug development targets?
kinase inhibitors
what is the most important drug development target?
GPCRs targets
how specific are kinase inhibitors? give examples of kinase inhibitors that are v specific and not so specific
because most kinases are competitive inhibitors of ATP binding would suggest that all kinases would be affected. but the real situation is not too bad.
eg Staurosporine - great kinase inhibitor but has too many kinase targets (eg low TI)
eg Imatinib - not such a good kinase inhibitor but has specific targets
give the 2 targets for RTK - based drugs and expand on each target
1) extracellular domain.
- mAb
- soluble R
- monomeric L
2) Target of catalytic domain
- interfere with ATP binding
- interfere with Substrate phosphorylation
give the name of 2 blockbuster drugs and describe their targets and the diseases they are effective against
- Gleevec/imatinib; inhibits Abl kinase and targets chronic myelogenous leukaemia (CML)
- Herceptin; mAb against HER2 RTK which binds EGF or dimerises with another R
what is Herceptin? and why is it difficult/expensive to produce?
a monoclonal ab
- difficult to maintain consistency; because producing in mammalian cell lines need everything to be constant because need to ensure we do not have impure product that isn’t contaminated
what is the biggest +ve of using mAbs? how is this seen in the numbers of drugs that are mAbs?
- biggest +ve is that they are v specific to their target (although can be so specific that the drug binds to the correct target but we get signalling effects we didn’t think about)
- in 2016, 6/10 top selling drugs were biologics
how does Herceptin stop cell signalling and proliferation seen in breast cancers?
normal activation of HER2/ErbB2 by dimerising with additional receptor (HER1,3,4/EGFR) leads to cell proliferation. MAb to HER2 stops this partner binding, stops activation and therefore stops the cell in G1 phase
apart from just binding to HER2 R and preventing further binding and signalling what else does Herceptin do?
in addition to stopping signal, may also down regulate expression of the R and prevent proteolytic cleavage of extracellular domain of the R (which would otherwise lead to metastasis). may also induce immune response to the cell
what are the problems of Herceptin?
- 70% patients (with high HER2 expression) don’t respond. to do with epigenetics meaning that cells behave differently
- drug resistance; v expensive (around £80,000 per year per patient). because cancer cells mutate v quickly (hallmarks) some may stop responding to Herceptin because they no longer bind the drug. drug companies now know about this and can also use Herceptin in conjunction with other drugs used to to target the mutated cells
- around 10% patients develop heart disease.
how can cancer cells become drug resistant? name the specific mechanisms
- induction of exporters
- mutations to reduce sensitivity (Gleevec)
- overexpresion of targets - eg increase expression of receptors. need a higher dose of drugs for treatment - too toxic
describe the monomeric ligand developed by Asterion. describe its structure, advantages, what it can be used to treat etc
STRUCTURE; growth hormone covalently attached to monomeric domains.
ADVANTAGES; good pharmacokinetics, slower clearance, less immune problems, fewer side effects. this is because part of the drug is shielded by the receptor complex
- less frequent administration however still needs to be injected
343 - 15 word
- actually exists as a long-lived agonist. prolongs the signal. can this be used as a drug to treat dwarfism type diseases ? because it can promote proliferation
what is Gleevec used to treat? describe this disease in more detail - ie how it arises
- chronic myelogenous leukemia (CML)
- CML arises from chromosomal rearrangement that fuses Abl kinase with bar leading to constitutively active Abl kinase
- Gleevec inhibits this Abl kinase
give some positives of Gleevec
- very bioavailable. (98% of Gleevec taken in will end up in body)
- half life in body around 18hrs therefore can be administered daily and conc remains high
- approved for several other diseases ( good patent position)
resistance to Gleevec occurs following mutations. how can this be overcome? are there any problems with this?
- develop drug cocktails - mixture of > 1 drug targeting 2 different cancer areas. problems; do these 2 drugs interact? does 1 cause toxicity which the other one doesnt - develop inhibitors against mutant kinases produced by cancer cells
