News & Events

When

Date - March 8, 2017
1:00 pm

What

Ph.D. Literature Seminar – 751

Abstract:

Photodynamic therapy (PDT) is a promising alternative to treat cancers and other diseases. Briefly, PDT uses light to activate an otherwise non-toxic compound, the photosensitizer (PS), resulting in the formation of reactive species that elicits a biological response. Unlike other treatments, PDT has the advantage of low systemic toxicity and minimum invasiveness. Furthermore, PDT can induce an immune response while destroying tumor tissue. Porphyrin derivatives were among the first class of PS to be studied, including the drug Photofrin, which was the first to be approved for use. While Photofrin is still used for cancer treatment, it has some substantial drawbacks, including prolonged photosensitivity. An ideal PS must: (1) have little to no dark toxicity, (2) be highly toxic when activated by light, (3) selective for and retained in target tissue, (4) be rapidly excreted from the body to avoid systemic toxicity, (5) have a high quantum yield for some photochemical event (e.g., generation of singlet oxygen), and (6) have strong absorbance within the 600-800nm phototherapeutic window where light penetrates deepest into tissue.  The inability of most PSs to date to exhibit these ideal characteristics has held back the use of PDT as a mainstream cancer treatment.

Polypyridyl ruthenium(II) complexes are of particular interest for these reasons. In the past, PDT has largely relied on excited state molecular oxygen (¹O₂) to damage cancer cells via type I and II photochemical processes. However, since solid tumors tend to be hypoxic, this is an inherently poor strategy. Our group has been developing PSs that switch reactive modality depending on the availability of O₂. We have also been investigating the largely neglected aspect of the effects of the light dose (wavelength, irradiance, etc.), especially in in vitro biological assays. This seminar will discuss the background of PDT and significant contributions Dr. Glazer’s (University of Kentucky) and the late Dr. Brewer’s (Virgina Tech.) research groups have made in the field. In addition, our novel approaches to overcome the challenges that have held back this form of cancer treatment will be highlighted.