Page - (000355) - in Biomedical Chemistry: Current Trends and Developments

anticancer drugs, frequently associated to low therapeutic efficacy (Siegel, 2011). Another factor that needs to be considered for drug delivery is the physicochemical properties of the drugs themselves. Many of the anticancer drugs used in the clinic at the present are rather hydrophobic, and thus, their poor solubility may lead to local toxicity associated with the fact that they may not be soluble enough to go through the aqueous environment surrounding the tumor cells and cross the cell membrane to ultimately reach the intracellular targets (Owen, 2012). On the other hand, successful utilization of hydrophilic drugs (e.g., macromolecules such as proteins or nucleic acids) has been stalled by a number of obstacles, such as poor cell internalization, because of their inability to cross the lipid bilayer of the cell membrane, as well as short half-life in the bloodstream, due to poor stability against proteolytic and hydrolytic degradation (Fattal, 2009; Ishihara, 2010; Sun, 2014). Therefore, by applying nanotechnology, many scientists have focused on investigating new ways to develop novel drug delivery systems with the aim to maintain high therapeutic drug levels at the malignant cell sites and as low as possible in healthy cells, hence overcoming and improving the poor physicochemical properties of the drug (Grinberg, 2014; Sun, 2014). For this purpose, several strategies to both target the tumor site and release the drug(s) in a controlled fashion have been developed in order to selectively deliver therapeutic cargos over time. In this section, we will briefly focus on the most recent controlled release strategies and give some examples of the nanosystems used to achieve the abovementioned aims. It is possible to fine-tune and control the release of payloads from the nanocarrier through diverse mechanisms. For example, for porous materials, controlling the pore size and the surface chemistry of the pore walls can lead to different diffusion release profiles, either improving or sustaining the release of the loaded cargos. Porous hollow Fe3O4 nanoparticles were able to provide the delivery of cisplatin via a slow diffusion-controlled process, exhibiting different kinetic profiles of cisplatin depending of the pore gap sizes (Cheng, 2009). Porous silicon (PSi) materials are another good example of a biomaterial widely used for biomedical applications (Santos, 2014). The small and tunable size of