Targeting therapy-induced senescence across multiple breast cancer subtypes in a metastatic bone-like microenvironment

Chemotherapeutic treatment of breast cancer with Doxorubicin (DOX) can induce tumor and stromal cell senescence leading to therapy-resistance. Senescence-associated secretory phenotype (SASP) promotes secretion of pro-inflammatory and tumorigenic factors causing systemic inflammation. Combined, this can result in immune suppression, tumor growth and secondary spread of cancer. Targeting and removing senescent and cancerous cells using a combination of chemotherapeutic and senolytic drugs may reduce systemic inflammation, improve therapeutic efficacy, and prevent metastasis. Exposure of triple-negative breast cancer (MDA-MB-231), hormone-responsive (MCF-7) and HER2+ (MDA-MB-453) cells, and primary spine osteoblasts to DOX showed significant induction of p21-positive senescent cells. DOX and senolytics (RG-7112, o-Vanillin) treatment of co-culture spheroids showed a significant additive effect in reducing tumor sphere viability and growth, indicating reduced metastatic potential. This was correlated with reduced SASP in triple-negative and hormone responsive lines and decreased levels of senescent cells in all subtypes and primary stromal cells, while proliferation was decreased, and apoptosis increased across all breast cancer subtypes. Future chemotherapeutic treatment in breast cancer models may be optimized by adding senolytic drugs to more effectively clear senescent tumor and stromal cells, reducing risk for relapse and metastatic potential, while allowing for tissue regeneration in the bone metastatic environment.