PARP1 and ovarian carcinoma: If oxidative stress mediates the antiproliferative effect of PARP inhibition on ovarian cancer cells, PARP1 inhibition or depletion would be expected to render ovarian cancer cells more sensitive to exogenous H2O2. Indeed, H2O2 caused a more pronounced decrease in colony formation when PARP1 was inhibited or depleted (Fig. 5F and 5G).