The synthetic lethality of PARP1 and BRCA1/2 seen in tumor cells (Bryant et al., 2005; Farmer et al., 2005) has led to intensive investigations of developing PARP inhibitors to treat cancers with deficiencies in BRCA or other DNA repair genes such as p53 (Williamson et al., 2012), MRE11 (Vilar et al., 2011), PTEN (Mendes-Pereira et al., 2009), MTA2 (Shi et al., 2021) and so on (Lord et al., 2008; Tutt et al., 2010; Cardnell et al., 2013; Kaufman et al., 2015; de Bono et al., 2017; Scott, 2017; Hoy, 2018; Litton et al., 2018). Here, PARP1 is linked to cancer.