Although governments invest billions of dollars in cancer research, cancer remains one of the major causes of death worldwide (Liu et al., 2007). During the last decades, outstanding results have been attained in fundamental cancer biology but, unfortunately, they have not been translated in even distantly comparable progressions in the clinic. The main reason for this gap being the inability to administer therapeutic agents so that they can reach target cells without or with minimal side-effects (Ferrari, 2005). Today, scientists are faced with the recognition that very few molecules reach the desired locations and thus fail to selectively reach the target cells. Consequently, patients experience a very poor quality of life (Ferrari, 2004; Ferrari, 2005; Chan, 2006).