Concept:
Targeted drug delivery refers to a system where a therapeutic agent is directed towards a specific site or organ in the body.
The aim is to concentrate the drug in the tissues of interest while reducing its concentration in non-target tissues, thereby optimizing therapeutic effects and minimizing side effects.
Approaches:
Targeted drug delivery is a method to deliver the drug specifically to its site of action, minimizing side effects and improving therapeutic efficacy.
Here are some of the main approaches to targeted drug delivery:
1. Passive Targeting:
This relies on the natural differences between normal and pathological tissues, especially in terms of their vasculature.
For instance: The Enhanced Permeability and Retention (EPR) effect in tumor tissues allows nanoparticles to accumulate in tumor sites due to leaky vasculature and poor lymphatic drainage.
Nanoparticles, such as liposomes, are often used in this approach.
2. Active Targeting:
This involves the use of specific ligands (like antibodies or peptides) that can recognize and bind to receptors or other molecules that are overexpressed on diseased cells, but not on healthy cells.
For example: Using monoclonal antibodies attached to liposomes to target cancer cells specifically.
3. Magnetic Drug Targeting:
This employs magnetically responsive particles that are guided to the site of interest using an external magnetic field.
The magnetic particles can either carry the drug or induce hyperthermia in tumor tissues.
4. pH-sensitive drug delivery:
Diseased tissues, like tumor, often have a different pH compared to normal tissues.
This difference can be exploited by designing drug delivery systems that release the drug at a specific pH.
5. Thermo-sensitive drug delivery:
Certain drug carriers can be designed to release their drug load upon experiencing a specific temperature.
This can be combined with external heating methods to target the drug release to a specific site.
6. Ultrasound-triggered drug delivery:
Ultrasound waves can be used to release drug molecules from carriers at the target site.
This approach is particularly beneficial for localized treatment with minimal systemic exposure.
7. Enzyme-responsive drug delivery:
In certain diseases, specific enzymes are overexpressed. Drug delivery systems can be designed to release the drug upon interaction with these enzymes.
8. Electro-responsive drug delivery:
This approach involves using electrical currents to facilitate the release or penetration of drugs at the target site.
9. Gene-directed enzyme prodrug therapy (GDEPT):
This is a two-step system. Firstly, genes that encode for enzymes are delivered to tumor cells.
Once expressed, these enzymes can convert a non-toxic prodrug into its toxic form, specifically targeting the tumor cells.
10. Stimuli-responsive polymers:
These are polymers that undergo a physicochemical change in response to certain stimuli like pH, temperature, or light.
They can be employed to design drug delivery systems that release their drug load upon experiencing a specific stimulus.