Cancerous Cell Death from Sensitizer Free Photoactivation of Singlet Oxygen

Abstract

Singlet oxygen (¹O₂) is an electronic state of molecular oxygen which plays a major role in many chemical and biological photo-oxidation processes. It has a high chemical reactivity which is commonly harnessed for therapeutic issues. Indeed, ¹O₂ is believed to be the major cytotoxic agent in photodynamic therapy. In this treatment of cancer, ¹O₂ is created, among other reactive species, by an indirect transfer of energy from light to molecular oxygen via excitation of a photosensitizer (PS). This PS is believed to be necessary to obtain an efficient ¹O₂ production. In this paper, we demonstrate that production of ¹O₂ is achieved in living cells from PS-free 1270 nm laser excitation of molecular oxygen. The quantity of ¹O₂ produced in this way is sufficient to induce an oxidative stress leading to cell death. Other effects such as thermal stress are discriminated and we conclude that cell death is only due to ¹O₂ creation. This new simplified scheme of ¹O₂ activation can be seen as a breakthrough for phototherapies of malignant diseases and/or as a noninvasive possibility to generate reactive oxygen species in a tightly controlled manner.