About drug design

What is drug design?

The field of medicine that deals with designing new molecules and improving their performance to make them likely candidates for becoming new drugs. First, a promising candidate molecule is identified, called the lead. Identifying a lead molecule is like getting the outline of a sketch right.  Adding details to the hasty outline makes the picture look more and more complete. Similarly, the tweaking the chemical structure of the molecule to change its physical, physico-chemical and biological properties as desired is called lead optimization. Designing new drug molecules is followed by synthesis,  laboratory testing and formulation. After preclinical studies, the drug enters clinical trials, the stage which evaluates the effect that these designed drugs have on  appropriate human volunteers. If the molecule fails to work or to impress in any of these stages, further optimization of the designed molecule is needed. This involves chemical modifications to the molecule’s structure. Sometimes, entire redesigning might be necessary.

What is the need for drug design?

The introduction of an identified lead as a drug into the market is a billion dollar industry. With careful study, one can reduce effort and money involved. For example, early elimination of molecules based on traits that “characterize failure” or reducing the number of steps leading to clinical trials reduce the cost of advancing a lead. Now, one might wonder why this is a demanding and growing field. In other words, once a few new drugs have been discovered for a particular disease conditions,  and a few of its derivatives have been explored, why would there be a continued need for drug design? Several factors motivate the search for a new drug. Patentability is one strong reason; one can patent a molecule, the chemical space around it, the formulation, its application, etc. Another factor that drives drug discovery and design is drug resistance. This is common among problem among antimicrobial drugs (drugs that kill or inhibit disease causing microorganisms). Microbes find ways to become resistant in a few years or so to drugs that have been considered  most effective when introduced. For example penicillin was a savior drug during the world war II, but today it is almost useless; about 80% of the Staphylococcus aureus bacteria are resistant to it. A better option is the cephalosporin class of drugs which are related to penicillin, and are chemically modified from the 7-aminocephalosporanic acid obtained from natural source. A third reason is to minimize side-effects. For example, even with a large number of muscle relaxants such as D-tubocurarine, gallamine, atracurium, etc. pancuronium was synthesized and became most popular. This is because it caused least cardiovascular side effects. Further, Vecuronium was synthesized. This was similar to pancuronium in the lack of side effects, but, going one step further, did not have the noradrenaline re-uptake blocking effects of the latter.

What subjects make up the field?

Drug design as a multidisciplinary field is still evolving and expanding its frontiers. One can imagine the field to consist of a core of chemistry and biochemistry, and a secondary layer of some physics, computer science, pharmaceutical sciences, statistics, biology, etc. However, on reading accounts of how the application of graph theory, polymer physics, combinatorics, quantum physics, etc., advance our understanding of the functioning of DNA, RNA, proteins and a host of biochemical processes, it becomes difficult to restrict the frontiers of the field to a few basic sciences.

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