Drug targeting strategies in cancer treatment: an overview.

Classic chemotherapy his little or no specificity for cancer cells, normally resulting in low accumulation at the tumor region (inefficacy), and in severe side effects (toxicity). This challenge has resulted in the development of several deliver strategies for chemotherapy agents to improve their concentration at the tumor site, simultaneously increasing their anticancer efficacy, while reducing the associated adverse systemic effects. In this work, the potential of drug delivery strategies involving the use of nanocarriers for controlling the biodistribution of antitumor drugs is deeply revised: passive targeting (through the enhanced permeability and retention effect, EPR effect) and active targeting (including stimuli-sensitive carriers and ligand-mediated delivery). Special attention will be also focussed on the recent approaches for overcoming multi-drug resistence. Finally, a general view of the problem of "nanotoxicity" in cancer treatment is also given.