DNA directed damage using a brominated DAPI derivative.

Photodynamic therapy (PDT) is a clinically approved cancer treatment that uses light, oxygen and a photosensitizer to produce localized reactive oxygen species (ROS). Due to the short lifetime of ROS, the location of the photosensitizer in the cell is believed to be the key determinant governing the outcome of PDT. To explore the effect of direct association between a photosensitizer and DNA a well know DNA-binding dye, DAPI, was converted into a photosensitizer. Br-DAPI - unlike native DAPI - upon irradiation produces ROS. We demonstrate that the ROS are only effective in inducing dsDNA breaks when Br-DAPI is bound to DNA. In cancer cells (A549) Br-DAPI causes rapid light dependent cell death. This work supports the design of photosensitizers which bind with high affinity to the DNA of target cells for potentially more effective PDT.