Lecture #3 Flashcards
where is the NMDA receptor found?
in the brain
what is the role of the NMDA receptor?
a glutamate receptor - a gat3ed ion channel activated by the specific recognition of ligands → particularly glutamate
what is the full name for NMDA?
N-methyl-D-Aspartate
how is glutamate related to the NMDA receptor?
it is a natural agonist of the NMDA receptor that is associated to the ion channel permeable to calcium
what is the NMDA receptor fundamental in?
development of the CNS in learning, memory, and neuroplasicity
what must occur for an NMDA receptor to be activated?
it is fundamental to have the recognition by the glutamate and glycine, two co-agonists → glycine site cross-talks with the glutamate acting as a positive modulator, enabling glutamate to better recognize its own binding site
glycine and glutamate are able to copy their binding site at the same time in order to activate the receptor
under resting conditions what blocks the NMDA channel?
magnesium
receptor has double activation → Glycine/Glu but also magnesium
in pathological conditions how can exicitotoxicity occur?
in pathological conditions there can be an over-activation of the receptors by glutamate causing a massive amount of calcium within the neurons causing neurotoxic activity once a certain concentration is reached
how does the over-activity of the NMDA receptors work?
glutamate is released at a pre-synaptic level and can interact post-synaptically with the other receptor
explain the equilibrium of NMDA receptors:
the excitory amino acids are released and are able to activate mainly AMPA and Kainate receptors getting appropriate levels of depolarization at the post-synaptic level → within a few minutes the equilibrium is rescued and the receptors are “silent”
what does the long term potentiation of the NMDA receptor cause?
responsible for the sprouting of neurities or creating novel synaptic connections
describe what happens to NMDA receptors under long term potentiation:
the increased amount of glutamate is able to depolarize more strongly (than under normal conditions) causing a massive depolarization and therefore release of magnesium
under potentiated conditions, what does the depolarization come through?
the AMPA → as soon as a certain level of depolarization is reached magnesium is detached from its site and the depolarization is amplified by the massive influx of calcium passing through the NMDA receptor
what physiological condition is this potentiation associated with?
the creation of memory
under what pathological conditions can this potentiation occur under?
oxygen deprivation and nutrients in tissues
what compound is obtained from the animal model for middle cerebral artery occlusion model (MCAo)?
GV150526
how is MCAo obtained in a mouse?
the middle cerebellar artery is cauterized causing progressive damage in brain tissue reaching the maximum volume of damage after several hours
what is the dynamic range of intervention for a MCAo model before the surrounding tissue becomes necrotic?
6 hours
what happens when Gavestinesl or other glycine antagonist is administered to MCAo mice?
it is able to block completely the progression of the damage
what happened to Gavestinesl in phase III trials?
trials were stopped because it showed little activity when they expected it to have a strong effect based on what they saw in animal models
what issue did they find with Gavestinesl after the failed clinical trial?
it was unable to cross the BBB and therefore unable to occupy the CNS
why did they think the results were different from MCAo the mouse model to the human clinical trial?
it was an occlusive model, not a hemorrhagic stroke - the results were most likely associated to the fact that the BBB had an altered physiological structure enabling the molecule to penetrate and reach the site of action
what is combinatorial chemistry?
the possibility to get an increased number of molecules instead or characterizing and synthesizing molecules one by one
when does model C of drug discovery begin from?
1990 to the present
what is Model C of drug discovery characterized by?
a target-centric approach
what is a Hit compound?
a chemically traceable entity exhibiting promising signs of in vitro affinity to the selected biological targets
what one characteristic must a hit compound have?
it must be tractable
what does tractable mean in regards to hit compounds?
it means that the chemical structure of the molecule should be adequate for modifications, so it must be easily modified to optimize it
what comes from a molecule being tractable?
the molecule is modifiable and there is the possibility to develop a significant number of analogues
what is a lead compound?
a molecule with a superior level of profile in respect to the hit
what is the drug candidate?
the ideal type of compound possessing the ideal profile for progression → obtained from the lead optimization phase minimizing and eliminating the liabilities and undesired properties
nowadays, what does the drug discovery pathway begin with?
the identification of a novel hypothesis
where does the true validation of a project occur?
during the clinical trials, particularly in phase II
what is the hit identification phase?
the initial phase in which chemistry is involved → all the activities are put into place to identify chemical entities able to recognize the biological target and modulate it
what is typically run in this phase?
high-capacity screening and is fundamental to generalize the assays to enable this type of screening
what happens after the hit identification phase?
a specific selection of the molecule obtained - families of molecules are made and managed to select the the most promising ones for further investigation
what can the process of HIT identification be compared to?
a funnel - start from a large number of compounds and we reduce the number of compounds and improve the quality
what phase is fundamental in getting the molecule with the maximization of quality?
lead optimization (LOP)
what is required in the pre-clinical phase in order to get approval for the “first time in human” phase?
several GLP (good laboratory practices studies) imposed by authorieis
what is one of the major experiments required to be done in the GLP studies?
the “toxological characterization” in two species - rodents and non-rodents
what is the purpose of GLP studies in animals?
to help understand the level of risk in progressing a project from the early development to first time in human
what is phase II?
first time in human
what happens at the begging of phase II?
reduced clinical studies to gather signs of the efficacy of the compounds in humans
roughly how long does target validation take?
a few months to a year
roughly how long does HIT identification take?
about a year
roughly how long does lead identification take?
for the transformation of the molecule showing signs of activity in something more robust it can take a year
roughly how long does LOP take?
core of drug discovery → typically 18-24 months
roughly how long does the early development stage take?
between 12-18 months depending on the complexity of the compound
roughly how long do the first time in human studies last?
up to a year
roughly how long do phase II clinical studies take?
a few years
roughly how long does phase III take?
2-4 years
when is pharmacology involved in the drug discovery process?
involved from time 0 till candidate selection for the identification of the hypothesis validation as well as for running all the screening and assays fundamental for the characterization of the compounds
what four things is pharmacology fundamental for?
- target identification studies
- validation to clarify the relevance of the target selected
- to explore potential approaches for clinical validation
- provides biological data during the characterization phase both in vitro and in vivo
what is fundamental to find during PD studies?
the relationship between the exposure and the PD readout in the animal model → tendency is to associate the PD readout with the exposure obtained in tissues expressing the biological target
what is in-vitro selectivity?
the expansion of the analysis of off-target activities and typically runs between 80-120 different types of biological targets
besides studies in rats, what is fundamental for the drug to be scaled up to human use?
obtaining pk info in dogs or monkeys as well
besides pk and pd information, what else is crucial to consider?
metabolism → how many metabolites are obtained, the structural metabolites, and how to manage , understand whether metabolites could have a genotoxic activity, and a reduced toxicological size
