Pharmacological Glossary

AgonistA drug that binds to and activates a receptor. Can be full, partial or inverse. A full agonist has high efficacy, producing a full response while occupying a relatively low proportion of receptors. A partial agonist has lower efficacy than a full agonist. It produces sub-maximal activation even when occupying the total receptor population, therefore cannot produce the maximal response, irrespective of the concentration applied. An inverse agonist produces an effect opposite to that of an agonist, yet binds to the same receptor binding-site as an agonist.
Allosteric ModulatorA drug that binds to a receptor at a site distinct from the active site. Induces a conformational change in the receptor, which alters the affinity of the receptor for the endogenous ligand. Positive allosteric modulators increase the affinity, whilst negative allosteric modulators decrease the affinity.
AntagonistA drug that attenuates the effect of an agonist. Can be competitive or non-competitive, each of which can be reversible or irreversible. A competitive antagonist binds to the same site as the agonist but does not activate it, thus blocks the agonist's action. A non-competitive antagonist binds to an allosteric (non-agonist) site on the receptor to prevent activation of the receptor. A reversible antagonist binds non-covalently to the receptor, therefore can be "washed out". An irreversible antagonist binds covalently to the receptor and cannot be displaced by either competing ligands or washing.
BmaxThe maximum amount of drug or radioligand, usually expressed as picomoles (pM) per mg protein, which can bind specifically to the receptors in a membrane preparation. Can be used to measure the density of the receptor site in a particular preparation.
DesensitisationA reduction in response to an agonist while it is continuously present at the receptor, or progressive decrease in response upon repeated exposure to an agonist.
EC50The molar concentration of an agonist that produces 50% of the maximum possible response for that agonist.
ED50In vitro or in vivo dose of drug that produces 50% of its maximum response or effect.
EfficacyDescribes the way that agonists vary in the response they produce when they occupy the same number of receptors. High efficacy agonists produce their maximal response while occupying a relatively low proportion of the total receptor population. Lower efficacy agonists do not activate receptors to the same degree and may not be able to produce the maximal response
Ex vivoTaking place outside a living organism.
Half-lifeHalf-life (t½) is an important pharmacokinetic measurement. The metabolic half-life of a drug in vivo is the time taken for its concentration in plasma to decline to half its original level. Half-life refers to the duration of action of a drug and depends upon how quickly the drug is eliminated from the plasma. The clearance and distribution of a drug from the plasma are therefore important parameters for the determination of its half-life.
i.a.Intra-arterial route of drug administration
IC50In a functional assay, the molar concentration of an agonist or antagonist which produces 50% of its maximum possible inhibition. In a radioligand binding assay, the molar concentration of competing ligand which reduces the specific binding of a radioligand by 50%.
i.c.Intracerebral route of drug administration
i.c.v.Intracerebroventricular route of drug administration
ID50In vitro or in vivo dose of a drug that causes 50% of the maximum possible inhibition for that drug.
i.d.Intradermal route of drug administration
i.g.Intragastric route of administration
i.m.Intramuscular route of drug administration
In vitroTaking place in a test-tube, culture dish or elsewhere outside a living organism.
In vivoTaking place in a living organism.
i.p.Intraperitoneal route of drug administration
i.t.Intrathecal route of drug administration
Inverse AgonistInverse agonist is an agent that binds to the same receptor as an agonist but induces a pharmacological response opposite to that agonist. A neutral antagonist has no activity in the absence of an agonist or inverse agonist but can block the activity of either.
Competitive AntagonistCompetitive antagonists bind to receptors at the same binding site (active site) as the endogenous ligand or agonist, but without activating the receptor.
Irreversible AntagonistIrreversible antagonist is a type of antagonist that binds permanently to a receptor, either by forming a covalent bond to the active site, or alternatively just by binding so tightly that the rate of dissociation is effectively zero at relevant time scales.
i.v.Intravenous route of drug administration
KBThe equilibrium dissociation constant for a competitive antagonist: the molar concentration that would occupy 50% of the receptors at equilibrium.
KdThe dissociation constant for a radiolabeled drug determined by saturation analysis. It is the molar concentration of radioligand which, at equilibrium, occupies 50% of the receptors.
KiThe inhibition constant for a ligand, which denotes the affinity of the ligand for a receptor. Measured using a radioligand competition binding assay, it is the molar concentration of the competing ligand that would occupy 50% of the receptors if no radioligand was present. It is calculated from the IC50 value using the Cheng-Prusoff equation.
Neutral AntagonistNeutral antagonist binds equally to both active and inactive states of a G‐protein‐coupled receptor, regardless of activation state, and therefore blocks the actions of agonists and inverse agonists alike.
Non-Specific BindingThe proportion of radioligand that is not displaced by other competitive ligands specific for the receptor. It can be binding to other receptors or proteins, partitioning into lipids or other things.
pA2Measure of the potency of an antagonist. It is the negative logarithm of the molar concentration of an antagonist that would produce a 2-fold shift in the concentration response curve for an agonist.
pD2The negative logarithm of the EC50 or IC50 value.
pEC50The negative logarithm of the EC50 value.
pIC50The negative logarithm of the IC50 value.
pKBThe negative logarithm of the KB value.
pKdThe negative logarithm of the Kd value.
pKiThe negative logarithm of the Ki value.
p.o.Oral (by mouth) route of drug administration
PotencyA measure of the concentrations of a drug at which it is effective.
s.c.Subcutaneous route of drug administration
Specific BindingThe proportion of radioligand that can be displaced by competitive ligands specific for the receptor.
Silent AntagonistA drug that attenuates the effects of agonists or inverse agonists, producing a functional reduction in signal transduction. Affects only ligand-dependent receptor activation and displays no intrinsic activity itself. Also known as a neutral antagonist.
SystemicIn the periphery of the body (not in the central nervous system
Biological half-life
AbsorbanceAbsorbance is used for assays such as ELISA assays, protein and nucleic acid quantification or enzyme activity assays (i.e. in the MTT assay for cell viability). A light source illuminates the sample using a specific wavelength (selected by an optical filter, or a monochromator), and a light detector located on the other side of the well measures how much of the initial (100 %) light is transmitted through the sample: the amount of transmitted light will typically be related to the concentration of the molecule of interest.
ADMEAn acronym in pharmacokinetics and pharmacology for absorption, distribution, metabolism, and excretion, and describes the disposition of a pharmaceutical compound within an organism.
AUCThe area under the plasma (serum, or blood) concentration versus time curve.It is used in toxicology, biopharmaceutics and pharmacokinetics.
BALB/cAn albino strain of laboratory mouse from which a number of common substrains are derived. BALB/c substrains are "particularly well known for the production of plasmacytomas on injection with mineral oil," an important process for the production of monoclonal antibodies. They are also reported as having a "low mammary tumour incidence, but do develop other types of cancers in later life, most commonly reticular neoplasms, lung tumours, and renal tumours.
C57BL/6C57BL/6 often referred to as "C57 black 6" or just "black 6" is a common inbred strain of lab mouse. Dark brown, nearly black, coat. Easily irritable temperament. They have a tendency to bite. The immune response of mice from the C57BL/6 strain distinguish it from other inbred strains like BALB/c.
CYPThe cytochrome P450 superfamily. The function of most CYP enzymes is to catalyze the oxidation of organic substances. The most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction. RH (organic substrate) + O2 + 2H+ + 2e- → ROH + H2O. CYP families in humans divided among 18 families of cytochrome P450 genes and 43 subfamilies.
DMPK(1) Drug Metabolism and Pharmacokinetics; (2) Dystrophia Myotonica Protein Kinase.
ELISAEnzyme-linked immunosorbent assay, also known as an enzyme immunoassay (EIA), is a biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample.
FluorescenceA first optical system (excitation system) illuminates the sample using a specific wavelength (selected by an optical filter, or a monochromator). As a result of the illumination, the sample emits light (it fluoresces) and a second optical system (emission system) collects the emitted light, separates it from the excitation light (using a filter or monochromator system), and measures the signal using a light detector such as a photomultiplier tube (PMT). The advantages of fluorescence detection over absorbance detection are sensitivity, as well as application range, given the wide selection of fluorescent labels available today.
Fluorescence polarizationThe samples in the microplate are excited using polarized light (instead of non-polarized light in FI and TRF modes). Depending on the mobility of the fluorescent molecules found in the wells, the light emitted will either be polarized or not.
HitA chemical compound that produces a result in a preliminary biochemical test indicating that the compound merits further study as part of a drug discovery project.
LC-MSLiquid chromatography-mass spectrometry. an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography (or HPLC) with the mass analysis capabilities of mass spectrometry. There are a lot of mass analyzers that can be used in LC/MS. Single Quadrupole, Triple Quadrupole, Ion Trap, TOF (time of Flight) and Quadrupole-time of flight (Q-TOF).
Lead compound(1) a compound that has been selected from a group of hit compounds based on qualities such as the intensity of the biochemical effect that occurs when the compound is present (efficacy), or the absence of coincidental effects (specificity);(2) a chemical compound that has pharmacological or biological activity and whose chemical structure is used as a starting point for chemical modifications in order to improve potency, selectivity, or pharmacokinetic parameters.
LuminescenceThe difference with fluorescence is that the light emitted by the samples is the result of a chemical or biochemical reaction (instead of being the result of excitation by light). Luminescence plate readers are simpler optically than fluorescence readers, as they don't require a light source, just a light detector. Typically, the optical system consists in a light-tight reading chamber, and PMT detector measuring the light emitted by the samples during the reaction. Common applications include luciferase-based gene expression assays, as well as cell viability and cytotoxicity assays based on the luminescent detection of ATP.
Nude mouseA laboratory mouse from a strain with a genetic mutation that causes a deteriorated or absent thymus, resulting in an inhibited immune system due to a greatly reduced number of T cells. The genetic basis of the nude mouse mutation is a disruption of the FOXN1 gene. Most strains of nude mice are slightly "leaky" and do have a few T cells, especially as they age.
Time-of-flight mass spectrometry (TOFMS)Time-of-flight mass spectrometry (TOFMS) is a method of mass spectrometry in which ions are accelerated by an electric field of known strength. This acceleration results in an ion having the same kinetic energy as any other ion that has the same charge. The velocity of the ion depends on the mass-to-charge ratio. The time that it subsequently takes for the particle to reach a detector at a known distance is measured. This time will depend on the mass-to-charge ratio of the particle (heavier particles reach lower speeds). From this time and the known experimental parameters one can find the mass-to-charge ratio of the ion.
Time-resolved fluorescence (TRF)Relies on the use of very specific fluorescent molecules, called lanthanides, that have the unusual property of emitting over long periods of time (measured is milliseconds) after excitation, when most standard fluorescent dyes (e.g. fluorescein) emit within a few nanoseconds of being excited. As a result, it is possible to excite lanthanides using a pulsed light source (Xenon flash lamp or pulsed laser for example), and measure after the excitation pulse. This results in lower measurement backgrounds than in standard FI assays.
Triple quadrupole mass spectrometerA tandem mass spectrometer consisting of two quadrupole mass spectrometers in series, with a (non mass-resolving) radio frequency (RF) only quadrupole between them to act as a collision cell for collision-induced dissociation. The first (Q1) and third (Q3) quadrupoles serve as mass filters, whereas the middle (q2) quadrupole serves as a collision cell. This collision cell is an RF only quadrupole (non-mass filtering) using an inert gas such as Ar, He or N2 gas to provide collision-induced dissociation of a selected precursor ion that is selected in Q1. Subsequent fragments are passed through to Q3 where they may be filtered or scanned.
XTT(sodium 3´-[1-(phenylaminocarbonyl)- 3,4-tetrazolium]-bis (4-methoxy-6-nitro) benzene sulfonic acid hydrate).Colorimetric assay for the non-radioactive quantification of cell proliferation and viability. The assay is based on the cleavage of the yellow tetrazolium salt XTT to form an orange formazan dye by metabolic active cells.