Emerging Combination Strategy: FANCI Inhibition Induces PARP1 Redistribution to Enhance Efficacy of PARP Inhibitors in Breast Cancer

Abstract Background While PARP inhibitors have made advancements in the treatment of breast cancer, challenges such as chemotherapy resistance and limited application persist. FANCI, a DNA repair protein associated with breast cancer development, represents a potential target for novel combination therapeutic strategies. However, the role of FANCI in breast cancer and its impact on the efficacy of PARP inhibitors require further investigation. Methods In this study, we analyzed FANCI expression in breast cancer tissues and cell lines, and its correlation with clinical parameters and patient prognosis. Lentiviral vectors were utilized and functional assays were performed to evaluate the effects of FANCI modulation on breast cancer cell growth and metastasis. Co-immunoprecipitation assays and protein interaction analysis were conducted to identify the interaction between FANCI and PARP1 and determine the specific binding region. The functionality and nuclear distribution of PARP1 were assessed upon FANCI modulation. Finally, the sensitivity of breast cancer cells to the PARP inhibitor talazoparib upon FANCI knockdown was evaluated in vitro and in vivo . Results Our findings demonstrated that FANCI was overexpressed in breast cancer and associated with poor prognosis. FANCI significantly promoted breast cancer cell proliferation both in vitro and in vivo . We identified the interaction between FANCI and PARP1, specifically at the FANCI HD2 binding site. FANCI inhibition led to reduced nuclear localization of PARP1 and decreased PARP1 activity. Importantly, combination treatment with FANCI knockdown and talazoparib significantly inhibited cancer growth in vitro and in vivo . Additionally, we found that the CDK4/6 inhibitor palbociclib, which effectively suppresses FANCI protein expression, exhibited a robust synergistic effect with talazoparib both in vitro and in vivo . Conclusion FANCI is a novel therapeutic target for breast cancer. Inhibition of FANCI regulates PARP1 redistribution and activity, making cells more responsive to PARP inhibitors. This combination therapeutic strategy shows potential in enhancing the effectiveness of PARP inhibitors for breast cancer treatment, regardless of BRCA mutations.