Nitric oxide modulates tumor cell death induced by photodynamic therapy through a cGMP-dependent mechanism, R.D. Almeida et al

Photodynamic therapy (PDT) of cancer is a very promising technique based on the formation of singlet oxygen induced by a sensitizer after irradiation with visible light. The stimu-lation of tumor growth by nitric oxide (NO) was reported re-cently, and NO was shown to have a protective effect against PDT-induced tumor death. We investigated a putative direct effect of NO on tumor cell death induced by PDT, using the human lymphoblastoid CCRF-CEM cells and bisulfonated aluminum phthalocyanine (AlPcS2) as a sensitizer. Cells were incubated with AlPcS2 in the presence or absence of NO donors ((Z)-1-[(2-aminoethyl)-N-(2-ammonioethyl)ami-no]diazen-1-ium-1,2-diolate, hydroxylamine and S-nitroso-N-acetylpenicillamine) or L-arginine. Under these conditions, in the absence of NO donors or L-arginine the cells died rapidl