Photodynamic inhibition of acetylcholinesterase after two-photon excitation of copper tetrasulfophthalocyanine

Sequential two-photon (2-γ) activated copper tetrasulfophthalocyanine (CuPcS4) was shown capable of inactivating acetylcholinesterase (ACE). ACE activity was measured photometrically by the Ellman method. Simultaneous irradiation of ACE in the presence of CuPcS4 with 514 nm (183 mW/cm2) and 670 nm (86 mW/cm2) continuous wave (CW) light induced a 20–50% increase in enzyme inhibition as compared to one-photon (1-γ) irradiation, using either 514- or 670-nm (CW) light at the same fluences. The enzyme activity was not affected by CuPcS4 or light alone, decreased linearly with the irradiation time, and was shown to be oxygen-dependent. We conclude that the photoinactivation of ACE with sequential 2-γ irradiation involves reactive oxygen species produced by the interaction of the upper excited Tn state of CuPcS4 with molecular oxygen. As CuPcS4 shows little activity as a conventional 1-γ photosensitizer, unwanted side effects such as prolonged skin sensitivity are eliminated rendering 2-γ photodynamic therapy advantageous for the treatment of selected medical applications.