In a lecture of mine the professor was talking about the issue faced in regards to drug therapy when it comes to targeting lung cells in cystic fibrosis. It was said that if unless the drug gets targeted just for the lungs it could simply travel randomly throughout the body and thus not effectively treat the disease. My question is if cells internalize extracellular signals and travel/respond accordingly why can we simply not coat a drug for cystic fibrosis in extracellular signals that specifically bind to lung cell surface receptors?
Yes you can, in principle, coat the drug particle with ligands such that it will be targeted to specific cell types. This is being considered and actively worked upon for development of targeted drug delivery. However, you should also bear in mind that doing these kinds of coatings would be costly and it would greatly increase the cost of the drug.
At least, in the case of cystic fibrosis or any other disease of the lungs, an easy method of restricting the drug to lungs would be by taking the drug in the form of aerosol, using inhalers.
Mechanism of inhalers.
Picture source: http://www.globalasthmareport.org/management/inhalers.php