A class of substances known as photocages contain “photosensitive groups, also known as ‘photoremovable protecting groups’, from which target substances are released upon exposure to specific wavelengths of light”. The photosensitive groups physically and chemically protect the target from being released until the molecule undergoes photoreaction. Due to these interactions with light, they are commonly used molecules in photopharmacology. More recently, they have played an important role in photoactivated chemotherapy (PACT). In PACT, photocages utilize a photoremovable protecting group that protects cytotoxic drugs until the bond is cleaved via light interaction and the cytotoxic drug is released. Some well-known photocages include “o-nitrobenzyl derivatives, coumarin derivatives, BODIPY, xanthene derivatives, quinone and diarylenes derivatives”. However, there are limitations with using photocages in clinical applications as there are not many PPGs that can be used in vivo. This is due to PPG-payload conjugates needing to have acceptable solubility and biological inertness for biocompatibility and the need for efficient uncaging above 600 nm.
Figure 5. Example of a photocage release system activated by NIR