Tumour-specific uptake of anti-cancer drugs: the future is here.

A challenge of anti-cancer treatment is the specific delivery of the drugs in order to avoid deleterious effects on normal cells. In fact, anti-cancer drugs have potent effects also on normal cells due to the strong similarity of the mechanisms of growth regulation of normal cells if compared to their transformed counterparts. The recent developments in nanotechnology allow the old Ehrlich's dream to deliver anti-cancer drugs in tumour tissue through their encapsulation in drug delivery systems (DDS). In the present review we analyze the different reasons to encapsulate an anti-tumour drug in DDS including eventual damages induced by their extravasation or by eccipients used to their solubilisation, the rapid break-down of the drug in vivo and the specific bio-distribution of the drug in tumour tissues. The delivery strategies of anti-cancer drugs are based upon the particular structure of tumour neo-angiogenic vessels that allow the passive targeting or enhanced permeability and retention (EPR). In order to avoid the entrapping of DDS in reticulo-endothelial system the nanoparticles can be modified with the addition on their surface of inert polyetilenglicole (PEG) molecules that inhibit the opsonisation of DDS by macrophages. The addition of targeting moieties, antibodies or Fab fragments or small peptides and aptamers, on the surface of DDS can allow the active targeting of DDS to tumour cells. In conclusion, a new avenue in anti-cancer treatment has been disclosed with the use of DDS.