P62-RNF168 agonist-1 (compound 5a) is a low cytotoxicity P62-RNF168 agonist that enhances the interaction between P62 and RNF168. P62-RNF168 agonist-1 induces a reduction in H2A ubiquitination mediated by RNF168 and impairs homologous recombination-mediated DNA repair. P62-RNF168 agonist-1 also inhibits the growth of xenograft tumors in mice in a dose-dependent manner.