Usually, scientists are directed to research new targets in specific therapeutic areas based on unmet clinical needs. Once a need is identified and a particular therapeutic area chosen, the biological research begins. It is during this first stage of drug discovery that anecdotal clinical observations, empirical outcomes, and 'data' collected from folk medicine are often employed—if only as direction-finding tools.
Once a direction is chosen, it must be validated scientifically, within a defined biological system. Because human disease or pathology is usually multifactorial, the first task of the researcher is to narrow down the search to better defined mechanisms, preferably a small number of pathophysiolo-gically observable processes, e.g. pinpointing one or two types of cells which can be considered causes of the pathology. From the cellular stage, the researcher next defines specific molecular targets, such as receptors or cellular enzymes that comprise the destructive phenotype.
Researchers will target systems which are affected by, or may be directly involved with, a particular disease. The treatments arising from these types of approaches can be palliative, or may find a market or need as disease-modifying drugs. Prime examples of palliative therapies are drugs designed to alleviate side effects of treatment with toxic chemotherapeutic drugs, such as nausea and wasting. In these cases, drug discovery scientists search for drugs which alleviate each symptom as if it were an isolated pathology.
Disease-modifying drugs are those which directly affect the primary disease. Examples of DMDs are the chemotherapeutic agents themselves, which destroy tumors by preventing their growth.
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