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LIPOSOMES IN THERAPEUTIC AND PREVENTIVE MEDICINE: THE DEVELOPMENT OF THE DRUG‐CARRIER CONCEPT

Successful application of drugs in medicine is largely dependent on selective action. Since targets (e.g., cells) by and large share a number of similar attributes with normal (nontarget) areas, it is to be expected that unless interaction between drug and target is based on a unique property of the latter (as in antimicrobial therapy), so-called side effects will occur and hamper or even altogether prevent treatment. A good example is our failure in most cases of cancer chemotherapy, in which, because of similarities between malignant and normal cells, cytotoxic drugs cannot discriminate. An additional important problem is the inability of many active drugs to reach diseased areas. This is best illustrated in the treatment of many parasitic diseases in which microorganisms are thriving within cellular organelles inaccessible to a wide range of otherwise effective agents. Likewise, in some metabolic disturbances (e.g., Tay Sachs disease) there is accumulation of substances within cells impermeable to therapeutic agents (e.g., enzymes). Yet in other situations administration of a drug through a particular route, which would have been beneficial to the patient, is impossible because of the drug’s properties. Oral treatment of diabetes with insulin, for instance, is prevented by the hormone’s vulnerability in the gut. Manipulation of the body’s defenses, as with immunization against disease, is another area of medicine that would greatly benefit were vaccines to be made more effective through the use of an adjuvant acceptable to man. A good adjuvant could reduce the amount of antigen needed in immunization programs (resulting in savings, which would be especially relevant to developing countries) and would also render some vaccines (e.g., cholera vaccine) more effective. The accepted way of attacking such problems is by the synthesis of selective drugs, i.e., molecules that in theory will interact with the target specifically. However, in spite of some remarkable successes, many disorders afflicting millions are virtually unaffected and it seems that progress will occur in parallel to our understanding of disease at the molecular level. At the same time it is becoming clear that a novel element is needed to add a different dimension to pharmacology. Were one to possess Maxwell’s demon it would be possible to employ him for the carriage of functional molecules through a multitude of passageways and obstacles directly to the area of action.