Nanosystems in drug targeting: Opportunities and challenges

The long cherished goal of targeting drugs to specific sites in the body, where the pharmacological action is desired and sparing other tissues has been actively pursued all these years. The concept of 'magic bullets' given by Ehrlich has now seen a metamorphosis to 'magic wands', in the form of targeted drug delivery systems. The magic, all due to the specific targeting ligands which guide the drug carriers to the molecular targets be it on cell surface or nuclear membranes. Nanosystems including the nano-sized (<1000 nm) drug carrier systems, such as polymeric nanoparticles, liposomes, micelles and polymer-drug conjugates are the vanguards of this ever-evolving field. Targeting drugs to specific sites, and maintaining pharmacologically relevant drug levels at the site for a period required for desired therapeutic action is what makes the nanosystems - the burgeoning magic wands. Substantial challenges still exist in terms of biological barriers. Nevertheless, the approaches like directly reaching the target using catheters, or using exogenous guiding mechanisms (magnetic fields and ultrasound), and exploiting the accessible targets on vascular endothelium are emerging as new and promising trends. It is conceivable, that despite all the formidable challenges, interplay of different disciplines ranging from engineering to biology will make the dream of drug targeting come true!