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Cancers 2016, 8(10), 96; doi:10.3390/cancers8100096

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

Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
Academic Editor: Michael R. Hamblin
Received: 30 August 2016 / Revised: 12 October 2016 / Accepted: 14 October 2016 / Published: 20 October 2016
(This article belongs to the Special Issue Photodynamic Cancer Therapy)
View Full-Text   |   Download PDF [1262 KB, uploaded 20 October 2016]   |  

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) type(s) 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
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Girotti, A.W. Modulation of the Anti-Tumor Efficacy of Photodynamic Therapy by Nitric Oxide. Cancers 2016, 8, 96.

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