Mitochondrial Reactive Oxygen Species and Photodynamic Therapy

Worldwide, the number of cancer cases is increasing. Typically, they are treated by either surgery or chemotherapy. However, these treatments may be undesirable in elderly patients or those who are under medication with antiplatelet drugs. Photodynamic therapy (PDT) represents a potentially attractive treatment option for these types of patients, since it does not involve surgery and has considerably reduced side effects compared to chemotherapy. Porphyrin, one of the most commonly used photosensitizers, has the convenient property of cancer-specific accumulation and therefore, is commonly used in PDT. However, the mechanism by which this cancer-specific accumulation occurs remains unclear. We previously reported that a heme-transport protein, HCP1, was capable of transporting porphyrin compounds. HCP1 expression is associated with increased hypoxia, although the detailed mechanism by which this regulation occurs is also unknown. Here, we review available data on the mechanism of regulation of HCP1 expression through mitochondrial reactive oxygen species (mitROS). Specifically, cancer cells show increased expression of HCP1 compared to normal cells and this over-expression is reduced in cancer cells over-expressing the mitROS scavenging enzyme manganese superoxide dismutase (MnSOD). Thus we conclude that mitROS is involved in regulating HCP1 expression.