Part of an organism targeted by a ligand or drug to affect behavior
A biological target is anything within a living organism to which some other entity (like an endogenous
ligand or a
drug) is directed and/or binds, resulting in a change in its behavior or function. Examples of common classes of biological targets are
proteins and
nucleic acids. The definition is context-dependent, and can refer to the biological target of a
pharmacologically activedrugcompound, the receptor target of a
hormone (like
insulin), or some other target of an external stimulus. Biological targets are most commonly proteins such as
enzymes,
ion channels, and
receptors.
Mechanism
The external stimulus (i.e., the drug or ligand) physically binds to ("hits") the biological target.[1][2] The interaction between the substance and the target may be:
noncovalent – A relatively weak interaction between the stimulus and the target where no chemical bond is formed between the two interacting partners and hence the interaction is completely reversible.[citation needed]
reversible
covalent – A chemical reaction occurs between the stimulus and target in which the stimulus becomes chemically bonded to the target, but the reverse reaction also readily occurs in which the bond can be broken.[citation needed]
irreversible covalent – The stimulus is permanently bound to the target through irreversible chemical bond formation.[citation needed]
Depending on the nature of the stimulus, the following can occur:[3]
There is no direct change in the biological target, but the binding of the substance prevents other
endogenous substances (such as activating hormones) from binding to the target. Depending on the nature of the target, this effect is referred as
receptor antagonism,
enzyme inhibition, or
ion channel blockade.
A
conformational change in the target is induced by the stimulus which results in a change in target function. This change in function can mimic the effect of the endogenous substance in which case the effect is referred to as
receptor agonism (or channel or
enzyme activation) or be the opposite of the endogenous substance which in the case of receptors is referred to as
inverse agonism.
Drug targets
The term "biological target" is frequently used in
pharmaceutical research to describe the native protein in the body whose activity is modified by a drug resulting in a specific effect, which may be a desirable
therapeutic effect or an unwanted
adverse effect. In this context, the biological target is often referred to as a drug target. The most common drug targets of currently marketed drugs include:[4][5][6]
Identifying the biological origin of a disease, and the potential targets for intervention, is the first step in the discovery of a medicine using the
reverse pharmacology approach. Potential drug targets are not necessarily disease causing but must by definition be disease modifying.[8] An alternative means of identifying new drug targets is
forward pharmacology based on phenotypic screening to identify "orphan" ligands[9] whose targets are subsequently identified through target deconvolution.[10][11][12]
These biological targets are conserved across species, making pharmaceutical pollution of the environment a danger to species who possess the same targets.[13] For example, the synthetic
estrogen in human
contraceptives,
17-R-ethinylestradiol, has been shown to increase the
feminization of fish downstream from sewage treatment plants, thereby unbalancing reproduction and creating an additional
selective pressure on fish survival.[14] Pharmaceuticals are usually found at ng/L to low-μg/L concentrations in the aquatic environment.[15] Adverse effects may occur in non-target species as a consequence of specific drug target interactions.[16] Therefore,
evolutionarily well-conserved drug targets are likely to be associated with an increased risk for non-targeted pharmacological effects.[13]
^Rang HP, Dale MM, Ritter JM, Flower RJ, Henderson G (2012). "Chapter 3: How drugs act: molecular aspects". Rang and Dale's Pharmacology. Edinburgh; New York: Elsevier/Churchill Livingstone. pp. 20–48.
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^Overington JP, Al-Lazikani B, Hopkins AL (December 2006). "How many drug targets are there?". Nature Reviews. Drug Discovery. 5 (12): 993–6.
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10.1038/nrd2199.
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^Lundstrom K (2009). "An overview on GPCRs and drug discovery: structure-based drug design and structural biology on GPCRs". G Protein-Coupled Receptors in Drug Discovery. Methods in Molecular Biology. Vol. 552. pp. 51–66.
doi:
10.1007/978-1-60327-317-6_4.
ISBN978-1-60327-316-9.
PMC7122359.
PMID19513641.
^Moffat JG, Vincent F, Lee JA, Eder J, Prunotto M (2017).
"Opportunities and challenges in phenotypic drug discovery: an industry perspective". Nature Reviews. Drug Discovery. 16 (8): 531–543.
doi:10.1038/nrd.2017.111.
PMID28685762.
S2CID6180139. Novelty of target and MoA [Mechanism of Action] is the second major potential advantage of PDD [Phenotypic Drug Discovery]. In addition to identifying novel targets, PDD can contribute to improvements over existing therapies by identifying novel physiology for a known target, exploring 'undrugged' targets that belong to well known drug target classes or discovering novel MoAs, including new ways of interfering with difficult-to-drug targets.
^Lee H, Lee JW (2016). "Target identification for biologically active small molecules using chemical biology approaches". Archives of Pharmacal Research. 39 (9): 1193–201.
doi:
10.1007/s12272-016-0791-z.
PMID27387321.
S2CID13577563.
^Jung HJ, Kwon HJ (2015). "Target deconvolution of bioactive small molecules: the heart of chemical biology and drug discovery". Archives of Pharmacal Research. 38 (9): 1627–41.
doi:
10.1007/s12272-015-0618-3.
PMID26040984.
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^
abGunnarsson L, Jauhiainen A, Kristiansson E, Nerman O, Larsson DG (August 2008). "Evolutionary conservation of human drug targets in organisms used for environmental risk assessments". Environmental Science & Technology. 42 (15): 5807–5813.
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2008EnST...42.5807G.
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PMID18754513.
^Larsson DG, Adolfsson-Erici M, Parkkonen J, Pettersson M, Berg AM, Olsson PE, Förlin L (April 1999). "Ethinyloestradiol — an undesired fish contraceptive?". Aquatic Toxicology. 45 (2–3): 91–97.
doi:
10.1016/S0166-445X(98)00112-X.