Why use human tissue and not animals?
Animal models must be used to understand how new drugs will be distributed around the body etc. Indeed animal studies are an essential component of new drug development. However by making more human tissue available for research and the development of in vitro models we may better understand how drugs will be dealt with in the human body prior to clinical trials. In such a way we may anticipate that new drugs will reach the clinic more quickly and that unsuitable drugs will be removed from development at an earlier stage.
A major reason behind differences in animals and humans in addition to nature and size relates to differences in metabolic function. Following the administration of the majority of drugs the drug will be rapidly subjected to some degree of metabolic conversion. Ultimately the drug and its breakdown products will be removed from the body.
In the case of certain drugs this metabolic conversion may be essential to the activity of the drug (Prodrugs) i.e. the drug taken is inactive and requires some form of conversion to have the desired therapeutic effect. Alternatively if the activity of the drug is due to the parent compound then we may desire that the drug be broken down slowly. Otherwise following administration the drug may initially help the condition being treated but such a benefit will quickly disappear corresponding with the breakdown and removal of the active species. If the animal model chosen has different enzymes or different levels of these enzymes then the observation made may not adequately reflect the human scenario. Therefore potentially useful drugs may be lost at the development stage before they ever reach the clinic.