The challenge of liposome targeting in vivo

The ability to “target” drugs to specific cells within the body has long been one of the most cherished goals in therapeutics. Ever since Ehrlich2 foresaw the usc of “bodies which possessed a particular affinity for a certain organ… as carriers by which to bring therapeutic active groups to the organ in question,” considerable ingenuity has been devoted to the study of this challenging problem 35 When the first reports describing the use of liposomes as drug carriers were published in the early 1970s they attracted considerable interest. This interest stemmed in large part from proposals that liposomes might be “targeted” to specific cell types in vivo by constructing liposomes bearing “cell recognition” molecules that could interact selectively with surface determinants on the desired target cell(s). Fascination with this concept, and its seemingly unlimited applications, was not confined to the scientific literature. Numerous newspaper and magazine articles for the general public, as well as segments for television news and science shows, were prepared, some as recently as late 1982,6 describing how liposomes equipped with molecular “zip codes” could serve as “guided missiles” to target drugs and how this approach was about to “revolutionize” drug therapy and the treatment of many important diseases (the terms cited above in quotation marks appear consistently in such articles and should not be viewed by the reader as representative of the terms used routinely by the authors' in describing liposome-cell interactions).