week 2 Flashcards
What is the current drug discovery process?
arduous and costly
What does majority of drug candidate entering clinical trial fail to make?
to the marketplace
What does microengineering and microfluidics provide?
- microeenginering provide precise control over cellular microenvironment
- Microfluidics provide ability to perfuse the constructs on a chip and to connect individual sections with each other
What does the organ-on-a-chip platform be utilized for?
Developing disease model as well as conducting for drug testing studies
Why is there such a low success rate ?
Inability to predict the toxicity and efficacy of drugs before expensive human clinical trials
What does microfabrication and microfluidic technologies create?
small structures for a variety of applications in biotechnology
In drug discovery, what can micro-scale platform allow?
precise delivery of fluids with reduced reagent volumes and can be utilised for high-throughput screening
What can Microengineering technologised be used for?
Fabricating tissue-like structures that mimic the natural complexity of tissues
What may these microscale tissue platform be useful in?
Recreating the intricacies of the in-vivo environment with microscale precision and provide mechanical chemical or electrical cues representative of living environment
What can microscale perfusion bioreactors be generated for
Manipulation of biological materials such as proteins, cells or tissues
What can be used to stimulate signals from brain slices?
the fabrication of
metal electrodes on ultra thin stretchable substrates
what is being developed to
monitor tissue viability and functionality in real-time
on-chip sensors
What can ‘organs-on-a-chip’ provide?
opportunities to probe the
cellular behavior against a plethora of stimuli
What can organ-on-chip create?
- disease models
2. perfused to create dynamic culture environments
What did Aubin et al study?
three-dimensional functionality of cardiac tissue using microscale hydrogels
What did Aubin et el do?
- cardiomyctes were encapsulated inside hydrogels with different micropatterns and align and form fiber-like structures
What did the results of Aubin et al study indicate?
Microscale scaffolds could be engineered to mimic the size and shape of individual cardiac fibers in vivo
What did Giridharan et al culture?
embryonic cardiac cells inside a microscale cylindrical bioreactor and exposed them to pulsatile flow and varying strains to mimic cardiac cycle in left heart ventricle
What can devices like merging, electrical, chemical and mechanical impulses with a tissue culture reactor be utilized for?
Studies of human stem-cell derived cardiac cells
- predict toxicity of drugs and environmental agents on the human heart
- enable development of more efficient treatment for common diseases such as arrythmia
- lead to personalized medicine - allow drug testing on patients own cells to maximise success of treatment
Define medical translation
The practice of translating various documents
- training materials
- medical bulletins
- drug data sheets
for health care
What is important in the medical field for translation?
Avoid all errors in comprehension, change or suppression of information
What does not often translate effectively to human conditions?
drug efficacy in experimental disease model
what can overreliance on animal studies lead to?
inappropriate conclusion
How do we translate?
pop into cell (GPCR)
talk to evoke a response in cell
messengers may be different to therapeutic target
important to have allosteric mediators to help
What should we consider when doing translation?
- native tissue
- intact neurocircuitry
- species-specific paths/receptors
- therapeutic relevance
- access to disease
Why is host cell coupling mis-leading?
popping loads of receptors into the cell so that an agonist starts to look like an antagonist
What happens as you pop GPCR?
- couples
- secondary messengers
- amplify a response when you start measuring
What is important for drug discovery and for basic biology?
Accurate measurements of affinity and efficacy
what underpins analyses of ligand/receptor interaction in both SAR and mutagenesis analysis
The receptor structure and function
What remains largely unknown?
The molecular basis for morphological, physiological, biochemical and behavioural variation in laboratory mice
What enabled our ability to relate sequence to function?
decoding the complete genome of one strain C57BL/6J (the mouse reference genome)
What accelerated the discovery of mouse sequence diversity?
Creating a complete set of null alleles for all genes
Genome sequence of 17 inbred strains of laboratory mice
Identify almost ten times more variants than previously known
What was used to explore phylogenetic history of laboratory mouse
genome sequence of inbred strains
- examine functional consequence of allele-specific variation on transcript abundance
What does 12% of transcripts show?
Significant tissue-specific expression bias
What was the total count in 17 strains?
56.6M unique sites
What are other types of sequence polymorphism that have previously been difficult to assess on a genome- wide scale?
Indels at 8.8M unqiue sites and 0.28M structural variants
How often are mouse models proven to be relevant to human disease?
- Humans have a different receptor identification
- It is not a simple cell - intact neurocircuitry
- Mice and humans have evolved in and became adapted to different environment
- Mice often respond to experimental intervention in ways that differ strikingly from humans
- mouse strains have phenotypes that differ from human counterparts
A phase III trial
90% of total drug development cost (>1 billon)
What is the GI hormone motilin?
A substance released from the duodenum to increase gastric emptying
In human, where is motilin released from?
Fasting and after eating
What is motilin?
highly conserved across species
22 amino acid peptide hormone expressed throughout GI of humans and other species
What does motilin affect?
Gastric motility by stimulating interdigestive antrum and dudodenal contractions
What does motilin receptor activation affect?
brain function in rats and mice
What was increased by low concentration of motilin?
electrically-evoked, cholinergically mediated contractions of humans and rabbit isolated stomach
What does the major therapeutic activity of motilin receptor agonist relies on?
Faciliatation of cholinergic activity
Where was the motilin gene found to be absent in?
Rodents where the receptors are pseudogenes
What shares common ancestry with motilin?
Ghrelin
What is the specific absence of functional motilin associated with?
Specialised digestive physiology, including:
- loss of ability to vomit
What is motilin conserved to regulate?
caecotrophy
specialised digestive strategy
What is motilin receptor agonist being under development as?
gastroprokinetic drugs
What are gastroprokinetic drugs?
medications that help control acid flux
What do human and rodent kappa opioid receptors share?
~94% AA sequence homolgy
what was the opioid receptor gene, in humans rats and mouse ORPK aligned using?
ClustalX
What was evaluated for potential impact on G-protein coupling?
Amino acid in the third intracellular loop
C terminus of OPRK
in the 3rd intracellular loop and C terminal region
What is found in the 3rd intracellular region?
Ala308Val (neutral substitution in rat)
What is found in C terminal region in rat and mouse?
- Leu348IIE
2. Ser358Asn
what was ICI204448 and asimadoline found to be?
approximately equi-effective and equi-potent inhibitors of response to EFS
What had a slower onset of action?
Asimadoline
What acts as a kappa receptor agonist?
ICI204448 and asimadoline
What reduced contractions of the distal colon ?
ICI204448 and asimadoline
What did low concentration of asimadoline reduce?
the activity of ICI204448
What is an issue of translation with host cells and tissues?
one compound may have 100% efficacy and other compound 50% efficacy
Define pharmacokinetics
How the body affects a specific chemical after administration
Define oral bioavailability
The fraction of an oral administered drug that reaches systemic circulation
What happens after intravenous administration?
A drug is directly and fully available in the bloodstream
can be distributed via systemic circulation to a point where a pharmacological effect takes place
What happens if a drug is administered orally?
has to cross further barriers to reach systemic circulation
can significantly reduce the final extent of a drug in bloodstream
what can high oral bioavailability reduce?
The amount of administered drug necessary to achieve a desired pharmacological effect
reduce the risk of side-effects and toxicity
What can a low oral bioavailibility result in?
- low efficacy
- higher inter-individual variability
- give unpredictable response to a drug
What happens when a drug survives gut?
Go to small intestine
Features of small intestine
Area of high degree of absroption
- foldings - villi - protrusions like microvilli
- lined with capillaries - absorbed into the portal vein which drains the intestine to liver
Define first pass metabolism
Concentration of the drug is greatly reduced before it reaches the systemic circulation
What does the liver do?
Detoxifies and metabolises substances and drugs by oxidation
What are the features of blood brain barrier?
- mostly endothelial - plenty of gaps b/w epithelia
- tight junctions between epithelial
protect from fluctuations
- carrier proteins within epithelial to kick stuff out
Define pharmacodynamics
How a specific chemical affects function of the body after administration
Where does efficacy of molecules exist in?
In-vivo
exert activity at the receptor in native environment
What has corticotropin-releasing factor type 1 (CRF1) been implicated in?
increased emotionality accompanying exposure to environmental stressors
What is function of agonist CRF?
- produce anxiogenic-like behaviour
2. potentiate the effects of stressor exposure
What does limbic and brain stem region promote?
Arousal and fear-like behaviours
enriched with CRF1 receptors
What does CRF1 receptor knock down produce?
Calming , anti-stress effects
what is a stressor that activates the hypothalamo-pituitary-adrenal axis and produces an anxiogenic-like behavioral response ?
Swim Stressor forced swimming at ambient water temperature
What was Swim stressor forced swimming at ambient water temperatures?
- Rats exposed to water (21-23C) in a pool for 90S
2. The animal was placed in the pool and allowed to swim or float with no means of climbing out
What is a validated testing model of anxiety?
The elevated plus-maze
four-arms constructed
2 of arms were enclosed with walls and two arms had no walls
subjects placed individually onto centre of maze facing of the closed arms and allowed free access to all four arms for 5 mins
time spent on each arm was recorded
What is selectivity of action?
ability of a drug to act against a range of other receptors, channels and enzymes
What may selectivity of action be associated with?
Unwanted side effects
What does selective toxicity refer to?
The ability of drug to target sites that are relative specific to microogranism responsible for infection
What do patients do?
- Take bigger doses
- Take multiple drugs
- Never read labels
- Never take advice
Define Therapeutic window
Difference between effective dose and toxic doses
What is TD 50?
Dose toxic for 50% of population
What is ED 50?
minimum effective dose for 50% of population
what is TI?
TD50/ED5-
What is ADR?
- Adverse drug reactions
2. receptor variations that could cause a serious side effects
Drug-Drug interactions
Within medicine you do not know hypothesis will work until it is tested and followed for a long time
highly unpredictable
What is the 5th most common cause of hospital death?
ADR
What can pharmacovigilance reduce?
death and suffering caused by adverse reactions
what happened in 2000 on ADR?
has been on the market for 7 years and started to be associated with cardiac arrythmia
What does ADR hit?
delayed rectifier potassium cycle- delaying the cardiac cycle
What is hERG?
φ φ hERG is a gene that codes for a protein known as Kv11.1, the alpha subunit of a potassium ion channel.
What is hERG best known for?
This ion channel is best known for its contribution to the electrical activity of the heart: the hERG channel mediates the repolarizing IKr current in the cardiac action potential, which helps coordinate the heart’s beating.
What can hERG lead to?
a potentially fatal disorder called long QT syndrome.
What may not be translated to humans?
- Pain
- Anxiety
- Irritable bowel syndrome
How do you convince boss about efficacy, kinetics, selectivity, properties- but then unsure if it cures the disease as there is no animal model available that you trust ?
φ Can measure surrogate effect and mechanistic pathways
φ Cannot do anything at all and take a novel candidate to human and test it on- if the clinical need is high enough go straight to human
Other factors to consider before selection
- Save enough to invest further
- Early elimination of obviously toxic compounds
- have conducted at least some safety evaluations (‘toxicology’)
