Targeting the interleukin-6 (IL-6)/glycoprotein 130 (GP130) signaling pathway holds significant promise for cancer therapy given its essential role in the survival and progression of various cancer types. We have identified that bazedoxifene (BZA), a Food and Drug Administration (FDA)-approved drug used for the prevention of postmenopausal osteoporosis, when combined with conjugated estrogens in Duavee, also has a novel function as an inhibitor of IL-6/GP130 interaction. BZA is currently under investigation for its potential anticancer therapeutic function through the inhibition of the IL-6/GP130 pathway. Numerous studies have highlighted the efficacy of BZA (monotherapy or combined with other chemotherapy drugs) in impeding progression across multiple cancers. In this review, we mainly focus on the anticancer activity of BZA and the underlying anticancer mechanism through inhibition of the IL-6/GP130 pathway, aiming to provide valuable insights for the design and execution of further research and the potential repositioning of BZA in oncological clinical trials.

Breast cancer gene 1 (BRCA1) is a tumor suppressor gene essential for DNA repair, and its mutations are linked to aggressive breast cancers with poor prognosis. While poly (ADP-ribose) polymerase (PARP) inhibitors benefit some patients with BRCA1-mutant, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer, issues such as limited efficacy and drug resistance persist. This is especially critical for triple-negative breast cancer (TNBC), which lacks targeted therapies. Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors such as abemaciclib—FDA-approved for estrogen receptor (ER)-positive/HER2-negative breast cancer—are emerging as potential treatments for TNBC. We evaluated abemaciclib in BRCA1-mutant TNBC cell lines (SUM149, HCC1937, and MDA-MB-436) and found them to be sensitive to the drug. However, treatment induced cellular senescence and Interleukin-6 (IL-6) secretion, which may promote drug resistance. To address this, we inhibited IL-6 signaling using bazedoxifene or glycoprotein 130 (GP130) siRNA, and both of which enhanced abemaciclib sensitivity. Combination treatment with bazedoxifene and abemaciclib synergistically inhibited cell migration and invasion, and induced apoptosis. In a mammary fat pad TNBC tumor model, the combination treatment significantly suppressed SUM149 tumor growth more than either agent alone. These findings support co-targeting IL-6 and CDK4/6 as a novel therapeutic strategy for BRCA1-mutant TNBC.

Triple-negative breast cancer (TNBC) is a highly aggressive subtype known for its rapid metastatic potential. Despite its severity, treatment options for TNBC remain limited. Olaparib, an FDA-approved PARP inhibitor, has been used to treat germline BRCA-mutated TNBC in both metastatic and high-risk early-stage settings. However, acquired resistance to PARP inhibitors and their limited applicability in non-BRCA TNBCs are now two major growing clinical problems. Activation of the IL-6/STAT3 signaling cascade has been implicated in therapeutic resistance. In this study, we evaluated the combined effects of the PARP inhibitor olaparib and the STAT3 inhibitor LLL12B in human TNBC cell lines with both BRCA mutations and wild-type BRCA status. Our results demonstrate that the PARP inhibitor olaparib can induce increased interleukin-6 (IL-6) in TNBC cells, with ELISA showing a 2- to 39-fold increase across five cell lines. MTT assays revealed that knocking down or inhibiting STAT3, a key downstream effector of the IL-6/GP130 pathway, sensitizes TNBC cells to olaparib. Treatment with either olaparib or LLL12B alone reduced TNBC cell viability, migration, and invasion. Notably, their combined administration produced a markedly enhanced inhibitory effect compared to individual treatments, regardless of BRCA mutation status. These findings highlight the potential of dual PARP and STAT3 inhibition as a novel targeted therapeutic strategy for both BRCA-mutant and BRCA-proficient TNBC.