The Anticancer Activity of Hypericin in Photodynamic Therapy

Photodynamic therapy (PDT) is a cancer treatment that requires the interaction of a photosensitizer (PS), light and oxygen. A PS is characterised as a non-toxic drug or dye which is excited using light from a laser source at a specific wavelength. The excited PS will react with oxygen present in biological tissue to produce reactive oxygen species (ROS) that destroys cancerous cells by inducing cell death. The PS uptake by cancerous tissue in combination with localised light delivery makes PDT an effective oncology treatment that prevents damage to surrounding normal healthy tissue. To date, most photosensitizers (PSs) for PDT have been chemically synthesized and modified to satisfy the demands for an ideal PS. However, a naturally occurring red plant pigment (Hypericin) has drawn increased interest recently as a new generation PDT drug. It is known to have high quantum yields, tumor selectivity and low production costs. Other beneficial properties of hypericin include low photobleaching, low cytotoxicity in the absence of light and no mutagenicity. Several in vitro and in vivo studies have established its anticancer potential upon irradiation with laser light.