Near infrared light-triggered nanoparticles using singlet oxygen photocleavage for drug delivery systems

Drug delivery systems (DDSs) have showed a reduced systemic toxicity and enhanced therapeutic efficacy over conventional cancer treatments. However, after reaching the damaged tissue, DDSs should present a trigger release of the encaged therapeutics. Among all methodologies for a controlled release system, the use of light in NIR window (650-900 nm) shows the most appropriate characteristics for biological applications (e.g. bio-compatibility with tissues). This review is focused on NIR responsive approaches for DDSs intermediated by a photosensitizer (PS) using nanoparticles (NP) that possess oxidation sensitive segments. After excited by light, the PS generates singlet oxygen species which interact with a sensitive segment, causing bond cleavage or hydrophobicity change in NP followed by the release of entrapped therapeutics. The most relevant sensitive segments addressed in this work are: olefin (lipid, vinyl ether, vinyl disulfide, and aminoacrylate), thioketal, selenium and hydrophobicity changeable polymers (tellurium, poly(propylene sulfide), imidazole and nitroimidazole). The chemical structure of the sensitive segment, the available strategies for nanoparticle formation and DDSs in vitro and in vivo studies are also critically discussed. These NIR responsive DDSs have enormous potential as a tool for a controlled spatial-temporal drug release with capacity to overcome the drawbacks of the others specificity target DDSs (such as pH, temperature and ROS). In order to reach the pharmacological market, the light sensibility of the labile segments should increase for the range of wavelengths used and more biological test should be addressed.