- Increased PARP activity is one of the mechanisms by which tumor cells avoid apoptosis caused by DNA damaging agents, and drug resistance has been linked to higher expressions of PARP in cancer cells. This differential expression of PARP supports the observed selectivity of PARP inhibitors to affect proliferating tumor cells. AZD2281 is an orally administered potent inhibitor of PARP-1 and PARP-2, and its combination with cisplatin and gemcitabine may overcome some of the resistance associated with these agents.