As of 2021, US Food and Drug Administration (FDA) and European Medicine Agency (EMA) have approved four PARP-1 inhibitors as anti-cancer therapies for breast or ovarian cancer, namely: Olaparib (IC50 = 13 nM), Rucaparib (IC50 = 80 nM), Niraparib (IC50 = 35 nM), and Talazoparib (IC50 = 3 nM) [20]. Here, PARP1 is linked to cancer.