Drug design is the approach of finding drugs by design, based on their biological targets. Typically a drug target is a key molecule involved in a particular metabolic or signalling pathway that is specific to a disease condition or pathology, or to the infectivity or survival of a microbial pathogen. Oral medication A medication is a licenced drug taken to cure or reduce symptoms of an illness or medical condition. ... A biological target is an enzyme, receptor or other protein that can be modified by an external stimulus. ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... Santorio Santorio (1561-1636) in his steelyard balance, from Ars de statica medecina, first published 1614 Metabolism (from μεταβολισμος(metavallo), the Greek word for change), in the most general sense, is the ingestion and breakdown of complex compounds, coupled with the liberation of energy, and the consequent generation of waste... The word path has a variety of meanings: a path is a route between two points. ... Pathology (from Greek pathos, feeling, pain, suffering; and logos, study of; see also -ology) is the study of the processes underlying disease and other forms of illness, harmful abnormality, or dysfunction. ... In Epidemiology, Infectivity refers to the ability of a ability of a pathogen to establish an infection. ... E. coli magnified 10,000 times. ... A pathogen or infectious agent is a biological agent that causes disease or illness to its host. ...

Some approaches attempt to stop the functioning of the pathway in the diseased state by causing a key molecule to stop functioning. Drugs may be designed that bind to the active region and inhibit this key molecule. However these drugs would also have to be designed in such a way as not to affect any other important molecules that may be similar in appearance to the key molecules. Sequence homologies are often used to identify such risks. Two or more structures are said to be homologous if they are alike because of shared ancestry, such as two chromosomes that contain the same genes. ...

Other approaches may be to enhance the normal pathway by promoting specific molecules in the normal pathways that may have been affected in the diseased state.

The structure of the drug molecule that can specifically interact with the biomolecules can be modeled using computational tools. These tools can allow a drug molecule to be constructed within the biomolecule using knowledge of its structure and the nature of its active site. Construction of the drug molecule can be made inside out or outside in depending on whether the core or the R-groups are chosen first. However many of these approaches are plagued by the practical problems of chemical synthesis. Computational chemistry is a branch of chemistry that uses the results of theoretical chemistry incorporated into efficient computer programs to calculate the structures and properties of molecules and solids, applying these programs to real chemical problems. ... The term Side chain can have different meanings depending on the context: In chemistry and biochemistry a side chain is a part of a molecule attached to a core structure. ... In chemistry, the phrase chemical synthesis appears to have one of two meanings. ...

Newer approaches have also suggested the use of drug molecules that are large and proteinaceous in nature rather than as small molecules. There have also been suggestions to make these using mRNA. Gene silencing may also have therapeutical applications. The interaction of mRNA in a eukaryote cell. ... Gene silencing is a general term describing epigenetic processes of gene regulation. ...

Rational drug design

Unlike the historical method of drug discovery, by trial-and-error testing of chemical substances on animals, and matching the apparent effects to treatments, rational drug design begins with a knowledge of specific chemical responses in the body or target organism, and tailoring combinations of these to fit a treatment profile. In medicine, biotechnology and pharmacology, drug discovery is the process by which drugs are discovered and/or designed. ... Trial and error is a method for obtaining knowledge, both propositional knowledge and know-how. ... Phyla Subregnum Parazoa Porifera (sponges) Subregnum Agnotozoa Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ...

An important case study in rational drug design is imatinib, a tyrosine kinase inhibitor designed specifically for the bcr-abl fusion protein that is characteristic for Philadelphia chromosome-positive leukemias (chronic myelogenous leukemia and occasionally acute lymphocytic leukemia). Imatinib is substantially different from previous drugs for cancer, as most agents of chemotherapy simply target rapidly dividing cells, not differentiating between cancer cells and other tissues. Imatinib is a drug used to treat certain types of cancer. ... Tyrosine kinases are a subclass of protein kinase, see there for the principles of protein phosphorylation A tyrosine kinase (EC 2. ... Philadelphia chromosome or Philadelphia translocation is a specific genetic, chromosomal abnormality that is associated with chronic myelogenous leukemia (CML) and involves an exchange of material between chromosomes 9 and 22. ... Leukemia or leukaemia (see spelling differences) is a cancer of the blood or bone marrow characterized by an abnormal proliferation of blood cells, usually white blood cells (leukocytes). ... Chronic myelogenous leukemia or Chronic myeloid leukaemia (CML) is a form of chronic leukemia characterized by increased production of myeloid cells in the bone marrow. ... Acute lymphocytic leukaemia (ALL), also known as acute lymphoblastic leukaemia is a cancer of the white blood cells, characterised by the overproduction and continuous multiplication of malignant and immature white blood cells (referred to as lymphoblasts) in the bone marrow. ... When normal cells are damaged beyond repair, they are eliminated by apoptosis. ... Chemotherapy is the use of chemical substances to treat disease. ...

Examples of designed drugs

• Selective COX-2 inhibitor NSAIDs
• SSRIs (selective serotonin reuptake inhibitors), a class of antidepressants
• Zanamivir, an antiviral drug

Non-steroidal anti-inflammatory drugs, usually abbreviated to NSAIDs, are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation. ... Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressants for treating depression, anxiety disorders and some personality disorders. ... An antidepressant is a medication designed to treat or alleviate the symptoms of clinical depression. ... Zanamivir is a neuraminidase inhibitor used in the treatment of and prophylaxis of both influenza A and influenza B. Zanamivir was the first neuraminidase inhibitor commercially developed. ... Antiviral drugs are a class of medication used specifically for treating viral infections. ...

See also

• Drug discovery
• Designer drug
• Enzyme inhibitors
• Bioinformatics
• Cheminformatics
• Biomedical informatics