January 16th 2010
Pharmacologic strategies targeting the DNA of tumor cells have been in use for much of the past century for many different cancer types. Radiation has also been a long-employed strategy to cause DNA damage and subsequent tumor cell death. However, the class of agents designed to inhibit the enzyme poly-(ADP-ribose) polymerase (PARP) have taken this a step further-these agents do not damage DNA themselves, but rather, inhibit the repair of DNA via inhibition of the base excision single-strand repair pathway. PARP inhibitors have been shown preclinically and clinically to enhance the affects of chemotherapies known to damage DNA or interefere with DNA replication. However, the most exciting use of PARP inhibitors may be in exploiting the concept of synthetic lethality. In this setting, the concept is based on two factors: (1) BRCA1/2-positive malignancies cannot use one of the major pathways to repair double-strand DNA breaks (ie, homologous recombination), and (2) making the base excision repair pathway nonfunctional via inhibition of PARP leads to tumor cell death, as unrepaired single-strand breaks are converted into double-strand breaks.