Near-infrared uncaging or photosensitizing dictated by oxygen tension

Abstract

Existing strategies that use tissue-penetrant near-infrared light for the targeted treatment of cancer typically rely on the local generation of reactive oxygen species. This approach can be impeded by hypoxia, which frequently occurs in tumour microenvironments. Here we demonstrate that axially unsymmetrical silicon phthalocyanines uncage small molecules preferentially in a low-oxygen environment, while efficiently generating reactive oxygen species in normoxic conditions. Mechanistic studies of the uncaging reaction implicate a photoredox pathway involving photoinduced electron transfer to generate a key radical anion intermediate. Cellular studies demonstrate that the biological mechanism of action is O ₂-dependent, with reactive oxygen species-mediated phototoxicity in normoxic conditions and small molecule uncaging in hypoxia. These studies provide a near-infrared light-targeted treatment strategy with the potential to address the complex tumour landscape through two distinct mechanisms that vary in response to the local O ₂ environment.

Abstract

The generation of reactive oxygen species (ROS) in photodynamic cancer treatments is limited by low intraturmoural oxygen availability. Here the authors show that irradiation of a silicon phthalocyanine leads to uncaging of a biologically active molecule or to ROS formation in an oxygen-dependent manner.