Abstract 136: Doxorubicin-induced senescence as a mechanism of resistance in TNBC cell lines
Authors: Smoots Stephen G. , Schreiber Anna R. , Yacob Betelehem , Dominguez Adrian , Levandowski Cecilia , Pitts Todd M. , Diamond Jennifer R. 
Published: June 2022

Abstract
Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer which lacks HER2 overexpression, as well estrogen and progesterone receptor expression. TNBC constitutes 10-15% of all breast cancers but has a worse prognosis due to limited treatment options and high rates of metastatic recurrence. Doxorubicin (dox) remains one of the most active chemotherapy agents for the treatment of TNBC, although de novo and acquired resistance to chemotherapy remains a major challenge. The purpose of this work was to characterize dox resistant cell phenotypes and investigate treatment-induced senescence in p53-mutated (Mut) and wildtype (WT) TNBC cell lines.
Methods: A panel of 12 TNBC cell lines (p53 WT and p53 Mut) were exposed to dox (0-5 uM) for 72 hours and cellular proliferation was determined using the Cell Titer Glo assay. A subset of sensitive and resistant cell lines were treated with dox (0.1, 0.25 uM) or vehicle control and apoptosis was determined by flow cytometry (Annexin-V) at 24 and 48 hrs. Cells were treated with dox or control for 24 hrs and western blotting was performed for mediators of apoptosis. Senescence was analyzed by ß-galactosidase staining following treatment with dox for 3-14 days. shRNA knockdown (KD) of p53 was performed in the CAL-51 (p53 WT cell line) and cells were subject to investigations above.
Results: Doxorubicin treatment resulted in decreased cellular proliferation and increased apoptosis as assessed by Annexin-V expression in a subset of p53 WT and p53 Mut cell lines. Treatment with dox resulted in an increase in the pro-apoptotic proteins BID and p21, as well as a decrease in VAMP in sensitive cell lines. In a subset of cell lines resistant to dox treatment, we observed an increase in cells demonstrating phenotypic features of senescence and ß -galactosidase staining. We observed a decrease in p16 with dox treatment in the CAL-51 (p53 WT cell line) compared to an increase following treatment in p53 Mut cell lines. KD of p53 resulted in an increase in senescent cells following treatment with low dose dox.
Conclusions: Treatment with doxorubicin resulted in different terminal cell phenotypes in TNBC cell lines with apoptosis observed in p53 WT and Mut cell lines. Senescence was observed in resistant cells and KD of p53 increased dox-induced senescence, confirming a role for p53 in mediating terminal cell fate. Efforts are ongoing to understand the role of mutant p53 in mediating terminal cell fate in response to dox and rational combinations to overcome dox-induced senescence may be clinically active in metastatic TNBC.
Citation Format: Stephen G. Smoots, Anna R. Schreiber, Betelehem Yacob, Adrian Dominguez, Cecilia Levandowski, Todd M. Pitts, Jennifer R. Diamond. Doxorubicin-induced senescence as a mechanism of resistance in TNBC cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 136.