Photodynamic therapy and nitric oxide

Abstract

Photodynamic therapy (PDT) is a clinically approved, minimally invasive therapeutic treatment that exerts a selectively cytotoxic activity towards cancer cells. This technique involves administration of a photosensitizer followed by irradiation at a wavelength corresponding to its absorbance band. In the presence of oxygen, a cascade of stress oxidative reactions leads to direct tumor cell death, damage to the microvasculature and induction of a local inflammatory reaction. Clinical studies showed that PDT can be curative particularly in early-stage tumors. Moreover, with many cancers becoming resistant to treatment, PDT offers a mechanistically distinct alternative, mitigating chemoresistance but also synergizing with chemotherapy and molecularly targeted therapies. A well-known phrase of Tayyaba Hasan, one of the experts in PDT, stated "with PDT no matter what you do, if you are lucky, there is a prodeath response, simultaneously, there is a prosurvival molecular response, which mitigates the desidered outcome with PDT". These opposing molecular responses represent the challenge for basic science researchers and clinicians to enhance the photodynamic-mediated chemicals. Noteworthy, one of the major effectors that modulate the efficacy of PDT is nitric oxide, whose role will be discussed in this chapter.