APOBEC3B enhances the efficacy of PARP inhibitors in elimination of ovarian cancer stem cell

Late detection and tumor recurrence are major factors driving the lethality of high-grade serous ovarian carcinoma (HGSOC). PARP inhibitors (PARPi) have achieved significant clinical efficacy by selectively targeting DNA repair deficiencies in HGSOC patients with BRCA mutations and homologous recombination deficiency (HRD). However, a subset of patients ultimately develops resistance to PARPi, necessitating alternative effective treatment options. The mutational signatures of APOBEC3 family of DNA deaminases are widespread across a broad array of cancer types. Here, we report that cancer stem cell (CSC)-like tumorspheres exhibit reduced A3B expression compared to non-CSC adherent counterparts. Importantly, inhibition of A3B leads to PARPi resistance, elevated frequency of CSCs, and enhanced expression of stemness factors. In addition, we found that high A3B-expressing cells are under strong replication stress and thus synergize efficiently with PARPi. These studies reveal the important role A3B plays in regulating PARPi response.