PARP1 and cancer: Olaparib inhibits selectively both poly­(ADP-ribose) polymerase1 and 2 (PARP1/2). However, PARP1 isbelieved to account for more than 90% of the total cellular PARP activityand is the most abundantly expressed PARP across many tissues andcan thus be considered as the main contributor to observed proteinlocalizations., PARP enzymes are responsiblefor sensing damaged DNA and catalyzing its repair and are overexpressedin various cancer types.