Dual PARP /Tankyrase Inhibition Enhances Antitumor Efficacy in PTEN ‐Deficient Endometrial Cancer

Endometrial cancer (EC) incidence continues to rise, underscoring the need for effective therapies beyond BRCA-mutant disease. Although PTEN loss, a frequent alteration in EC, has been implicated in impaired homologous recombination and increased sensitivity to PARP inhibitors, responses to PARP inhibitor monotherapy remain variable and are often limited by resistance mechanisms in PTEN-deficient tumours. Here, we show that the dual PARP/tankyrase (TNKS) inhibitor JPI-547 exerts potent antitumor activity, particularly in PTEN-deficient Ishikawa tumours. In vitro, JPI-547 and olaparib more effectively reduced cell survival in PTEN-deficient cells, and combined treatment with olaparib and the TNKS inhibitor XAV-939 induced synergistic cytotoxicity with elevated DNA double-strand breaks. Dual PARP/TNKS inhibition did not further suppress RAD51 but modulated non-homologous end joining and attenuated Wnt/β-catenin signalling in a PTEN-dependent manner. PTEN knockdown further showed enhanced vulnerability to combined targeting. These findings show that JPI-547 enhances antitumor efficacy in PTEN-deficient EC by disrupting DNA repair pathways and Wnt signalling, supporting dual PARP/TNKS inhibition as a potential therapeutic strategy and providing a rationale for further clinical evaluation.