National Institutes of Health (NIH) researchers have discovered a significant new mechanism of action for a class of chemotherapy drugs known as poly (ADP-ribose) polymerase inhibitors, or PARP inhibitors. They have also identified differences in the toxic capabilities of three drugs in this class which are currently being tested in clinical trials. The study, by scientists at the National Cancer Institute (NCI), part of NIH, and their colleagues, appeared in Cancer Research, Nov 1, 2012.