Abstract P4-06-28: Doxorubicin induces cellular senescence in human breast cancer cells and sensitizes them to cytotoxic T-lymphocytes

[Background]“Cellular senescence” is a state in which cells undergo irreversible cell cycle arrest in response to various cellular stresses. Senescence is induced in not only normal cells but also cancer cells when anti-cancer agents trigger DNA damage. Recent studies have revealed additional feature of senescent cells: increased secretion of various secretory proteins, such as inflammatory cytokines, chemokines, growth factors, and MMPs. This newly recognized senescent phenotype, termed senescence-associated secretory phenotype (SASP), reportedly contribute to tumor recurrence and promotion. Alternatively, senescent cancer cells could be good targets in anti-cancer immunotherapy because they are cell cycle-arrested. [Objective]In this study, we determined whether ”cellular senescence” could be induced by a chemotherapeutic drug doxorubicin (DXR) and whether senescent cancer cells might increase their susceptibility to cytotoxic T-lymphocytes using human breast cancer cells. [Methods and Results]A triple-negative (negative for ER, PR, and HER2) human breast cancer cell line (MDA-MB-231) was used. This cell line was treated with DXR for 2 days and examined for their appearance microscopically. The DXR treatment (500 nM) decreased their proliferating ability and increased their cell size. Colony formation assay revealed that cancer cells significantly decreased the number of colonies even with lower doses (3 nM) of DXR. In immunoblot assay, the DXR treatment increased the protein expression of p21, which inhibits cell cycle. In a flow cytometric assay after staining with SPIDER-β-gal, the DXR treatment (500 nM) increased the expression of β-gal in MDA-MB-231 cells. The induction of SA-β-gal in DXR-treated cancer cells were also confirmed by confocal imaging. In addition, the DXR treatment (500 nM) for 2 days beforehand increased their subsequent ability to produce IL-6 and IL-8. Although the DXR treatment (500 nM) decreased the expression of epidermal growth factor receptor (EGFR) on cancer cells, this treatment sensitized them to anti-EGFR chimeric antigen receptor (CAR) T-lymphocytes in apoptosis assay. [Conclusion]These results suggest that a chemotherapeutic drug DXR can render MDA-MB-231 cells to be senescent and increase their sensitivity to antigen-specific cytotoxic T-lymphocytes. These findings may provide a rationale of combination of chemotherapy and T cell-based anti-cancer immunotherapy. Citation Format: Inao T, Iida Y, Kotani H, Harada M. Doxorubicin induces cellular senescence in human breast cancer cells and sensitizes them to cytotoxic T-lymphocytes [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-06-28.