Targeted drug delivery is a method of delivering medication to a patient in a manner that increases the concentration of the medication in some parts of the body relative to others.
It is sometimes called smart drug delivery in which drug releases from diffusion, degradation, swelling, and affinity-based mechanisms. Some of the common routes of administration include the enteral (gastrointestinal tract), parenteral (via injections), inhalation, transdermal, topical and oral routes.
Targeted drug delivery is an emerging system as a powerful tool for the treatment of cancer because of increased delivery of drugs, as well as genes, to a tumor site with protection from the extracellular environment.
Stimuli-responsive nanogels (NGs) are three-dimensional hydrophilic polymer networks that are formed through covalent linkages or self-assembly processes and are able to change their structural properties in the presence of external stimuli. These NGs have been widely examined as smart drug delivery carriers for a variety of anticancer drugs, as well as genes, because of stability, ease of synthesis, good control over particle size, and easy functionalization. They can control sizes from 5 to 400 nm, followed by different polymerization conditions.
Targeting in nano-enabled drug delivery systems is accomplished by labeling the nanoparticles with receptors or biomolecules that specifically attach them to the target cells or tissues. The most common targeting molecules are antibodies against epithelial growth factor receptors, and anti-epidermal growth factor receptors (EGFR). Because EGFR is expressed in all epithelial cells, this molecule is a special target when delivering drugs to epithelial cells.
Two strategies are widely used for drug targeting to the desired organ/tissue:
- passive targeting
- active targeting
Drug delivery vehicles transport the drug either within or in the vicinity of the target. An ideal drug delivery vehicle is supposed to cross even stubborn sites such as a blood brain barrier. Recently, nano medicine has emerged as the medical application of nanotechnology. Since nanoparticles are very small in size, nano drug delivery can allow for the delivery of drugs with poor solubility in water and also help in avoiding the first pass metabolism of the liver.
The selective delivery of the drugs to specific diseased cells or tissues still is a risky task. Ideally, for target drug delivery systems, the system should be made up of carriers and drugs, where carriers precisely target the desired drug. This issue covers the recent advancements in modern techniques for such purposes.
Delivery of drug carriers to the target cells can be only a part of the whole story of successful drug targeting. Some drug carriers may have to gain access to and get inside the cytoplasm of a target cell in order to release the drug at the optimum rate for pharmacological effectiveness as in the case of gene therapy or treatment with siRNA. In that sense, intracellular targeting is as important as systemic targeting.