Modulation of the Anti-Tumor Efficacy of Photodynamic Therapy by Nitric OxideReport as inadecuate


Modulation of the Anti-Tumor Efficacy of Photodynamic Therapy by Nitric Oxide


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Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA





Academic Editor: Michael R. Hamblin

Abstract Nitric oxide NO produced by nitric oxide synthase NOS enzymes is a free radical molecule involved in a wide variety of normophysiologic and pathophysiologic processes. Included in the latter category are cancer promotion, progression, and resistance to therapeutic intervention. Animal tumor photodynamic therapy PDT studies several years ago revealed that endogenous NO can reduce PDT efficacy and that NOS inhibitors can alleviate this. Until relatively recently, little else was known about this anti-PDT effect of NO, including: a the underlying mechanisms; b types of NOS involved; and c whether active NO was generated in vascular cells, tumor cells, or both. In addressing these questions for various cancer cell lines exposed to PDT-like conditions, the author’s group has made several novel findings, including: i exogenous NO can scavenge lipid-derived free radicals arising from photostress, thereby protecting cells from membrane-damaging chain peroxidation; ii cancer cells can upregulate inducible NOS iNOS after a PDT-like challenge and the resulting NO can signal for resistance to photokilling; iii photostress-surviving cells with elevated iNOS-NO proliferate and migrate-invade more aggressively; and iv NO produced by photostress-targeted cells can induce greater aggressiveness in non-targeted bystander cells. In this article, the author briefly discusses these various means by which NO can interfere with PDT and how this may be mitigated by use of NOS inhibitors as PDT adjuvants. View Full-Text

Keywords: nitric oxide NO; inducible nitric oxide synthase iNOS; PDT resistance; post-PDTcell growth-migration-invasion; PDT bystander effects nitric oxide NO; inducible nitric oxide synthase iNOS; PDT resistance; post-PDTcell growth-migration-invasion; PDT bystander effects





Author: Albert W. Girotti

Source: http://mdpi.com/



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