Poly (ADP-ribose) polymerases (PARPs) are involved in various cellular events, including DNA repair. PARP inhibitors including olaparib and rucaparib, have been specially developed against breast and ovarian cancers deficient in DNA repair systems. In this study, we found that PARP1-defective olaparib-resistant A2780 cells (ola-R cells) cells were still sensitive to two PARP inhibitors, rucaparib and veliparib. Metabolomic analysis revealed that rucaparib suppressed the lactate dehydrogenase (LDH)-mediated conversion of pyruvic acid to lactic acid in A2780 cells, although olaparib did not. The inhibition of LDH by siRNA-mediated knockdown or by LDH inhibitors suppressed the growth of ovarian cancer cells. Our results suggested that the suppression of the LDH-associated pathway contributed to the pharmacological effects of rucaparib. (C) 2019 Elsevier Inc. All rights reserved.