Combination of isorhapontigenin and FSP1 inhibitor suppresses triple negative breast cancer cell progression

Breast cancer is the most frequently diagnosed cancer in women with an estimated 316,950 new cases and 42,170 deaths in the United States in 2025. Approximately 15% of all breast cancers are diagnosed as a malignant subtype known as triple negative breast cancer (TNBC; ER-/PR-/HER2-), which render hormonal therapies ineffective. Combination chemotherapy is the standard-of-care in TNBC patients, but many experience chemoresistance, which accounts for 90% of drug failures in metastatic cancers. Thus, the discovery of new drugs and treatment options is critically needed to improve TNBC patient outcomes. Isorhapontigenin (ISO) is a stilbene derivative from the Chinese herb, Gnetum Cleistostachyun, and has been shown to exert anti-cancer effects in bladder, lung, and prostate cancer, but very few studies have investigated ISO in the context of TNBC. In the present study, we investigated potential anti-cancer effects on MDA-MB-231 and 4T1, human and murine TNBC cell lines, respectively. ISO significantly inhibited the proliferation and clonogenicity of TNBC cells in a dose-dependent manner. In addition, the capacity of cell migration was significantly reduced upon ISO treatment, along with increased expression of claudin-1, a tight-junction marker and tumor-suppressor. Moreover, ISO treatment reduced the size of TNBC spheroids in vitro 3D cancer model, accompanied by decreased expression of cell proliferation markers, PCNA and Ki-67. Further mechanistic studies revealed that ISO treatment significantly increased protein expression of ferroptosis suppressor protein 1 (FSP1), a recently discovered marker of chemoresistance in many cancers. Cycloheximide chase assay and MG132 treatment confirmed that ISO stabilized FSP1 protein stability in the proteasome-dependent manner. Cotreatment of ISO with an FSP1 inhibitor (iFSP1) had significant synergistic effects in reducing TNBC cell proliferation and clonogenicity. In summary, our study demonstrates that ISO inhibits TNBC cancer cell proliferation and migration. Additionally, this is the first study demonstrating the combined treatment of ISO and iFSP1 exerts robust synergistic inhibition of cell proliferation, highlighting ISO as a promising anticancer drug and support its combination with iFSP1 as a novel therapeutic strategy against TNBC.