Active drug targeting: Lessons learned and new things to consider

There is "hype" surrounding passive and active drug targeting of diseased tissues in vivo. The most common example of passive targeting is the utilisation of the "enhanced permeation and retention" phenomenon to target solid tumours and inflamed tissues. Alternatively, targeting moieties or "ligands" could be conjugated to the delivery system offering "actively" targeted delivery systems. The targets are usually receptors that are up-regulated in the biological areas of interest. Targeted drug delivery has been proposed to treat many diseases, such as cardiovascular diseases and diabetes. However, the most important application of targeted drug delivery is to treat cancerous tumours. Standardisation of in vitro and in vivo assays currently in place to assess the targeting efficiency of such systems is of utmost importance since heterogeneity in targeting assays and target validation could easily bias conclusions made affecting the future perspective of the field of active drug targeting. (C) 2013 Published by Elsevier B.V.