In time- and spatially resolved experiments, singlet molecular oxygen, O(2)(a(1)Delta(g)), was created in a single nerve cell upon irradiation of a sensitizer incorporated in the cell nucleus using a focused laser beam. The singlet oxygen thus produced was detected by its infrared phosphorescence. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extra-cellular environment. These results provide a new perspective for mechanistic studies of photoinduced cell death and intracellular signaling.

The rate of light delivery (fluence rate) plays a critical role in photodynamic therapy (PDT) through its control of tumor oxygenation. This study tests the hypothesis that fluence rate also influences the inflammatory responses associated with PDT. PDT regimens of two different fluences (48 and 128 J/cm 2 ) were designed for the Colo 26 murine tumor that either conserved or depleted tissue oxygen during PDT using two fluence rates (

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen, O(2)(a (1)Delta(g)), is a reactive species involved in many chemical and biological processes. To better understand the roles played by singlet oxygen in biological systems, particularly at the sub-cellular level, optical tools have been developed to create and directly detect this transient state in time- and spatially-resolved experiments from single cells. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extracellular environment. On one hand, these results demonstrate that the behavior of singlet oxygen in an intact cell can be significantly different from that inferred from model bulk studies. More generally, these results provide a new perspective for mechanistic studies of intra- and inter-cellular signaling and events that ultimately lead to photo-induced cell death.

Fluence rate of PDT light delivery exerts far-reaching control upon treatment outcome through its oxygenation modulating properties and possibly other mechanisms yet to be identified. This has been shown to be true in the preclinical and clinical setting. Further development of in situ dosimetry will be necessary to take full advantage of these discoveries.

In time-resolved and spatially resolved experiments, singlet molecular oxygen, O2(a1Deltag), was created in a single nerve cell upon irradiation of a sensitizer incorporated in the cell using a focused laser beam. The singlet oxygen thus produced was detected by its infrared phosphorescence. Data obtained indicate that in both the cytoplasm and the nucleus of the cell, this reactive species is approximately 1-2 orders of magnitude longer-lived than previously believed. The data demonstrate that deactivation of singlet oxygen in the cell is dominated by interactions with the solvent not cellular constituents such as proteins. These results provide a new perspective for mechanistic studies of the role of O2(a1Deltag) in photoinduced cell death and intracellular signaling.