Rational design, synthesis and biological evaluation of dual PARP-1/2 and TNKS1/2 inhibitors for cancer therapy

Poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors are the first and most successful drugs designed to exploit the concept of synthetic lethality (SL) between PARP-1 and BRCA1/2, which provides a novel strategy for tumor treatment. However, narrowed indications and resistance to PARP-1 inhibitors have hampered their further clinical application. Inducing "BRCAness" by targeting other targets, which will directly or indirectly disturb the homologous recombination (HR) repair pathway of double-strand DNA breaks (DSBs), is a promising strategy for expanding the clinical application of PARP-1 inhibitors and overcoming resistance to these inhibitors. Tankyrase1/2 (TNKS1/2) are involved in the nonhomologous end-joining (NHEJ) DNA repair pathway by regulating Wnt/β-catenin signaling. TNKS1/2 can also induce a "BRCAness" phenotype by regulating Wnt signaling, which increases the sensitivity of tumor cells with BRCA proficiency to PARP-1 inhibitors. These results suggest that cotargeting PARP1/2 and TNKS1/2 not only exerts a synergistic effect in the treatment of tumors but also provides a novel strategy for expanding the clinical application of PARP-1 inhibitors and overcoming resistance to PARP-1 inhibitors. Therefore, a series of dual PARP-1/2 and TNKS1/2 inhibitors were rationally designed, synthesized, and evaluated for their pharmacological properties. Among these candidates, compound I-9 showed excellent inhibitory activity as it inhibited PARP-1/2 and TNKS1/2 with IC₅₀ values of 0.25 nM, 1.2 nM, 13.5 nM and 4.15 nM, respectively. I-9 exhibited favorable synergistic antitumor efficacy in both BRCA-mutant and BRCA-wild-type cancer lines. Moreover, I-9 exerted prominent dose-dependent antitumor activity in an HCT116 cell-derived xenograft model and was significantly more efficacious than olaparib and E7449. Overall, the present study indicated that I-9, a dual PARP-1/2 and TNKS1/2 inhibitor, is a novel and promising agent for cancer therapy.