Evasion of a Single-Step, Chemotherapy-Induced Senescence in Breast Cancer Cells: Implications for Treatment Response

Abstract

Purpose:The purpose of this study is to define the mechanistic basis for recovery of proliferative capacity in breast tumor cells after chemotherapy. Here, we test the hypothesis that evasion of senescence confers resistance to chemotherapeutic drugs and ionizing radiation. Experimental Design: MCF-7 cells were treated with a single, clinically relevant dose (0.75-1.0 Amol/L) of Adriamycin. Two weeks following induction of senescence, clonal outgrowths were expanded and characterized in terms of senescence-associated B-galactosidase activity, gene expression profiles (Affymetrix U95 probe sets, Affymetrix, Santa Clara, CA) with confirmatory Western analyses, and telomerase activity following a second drug treatment. Levels of intracellular Adriamycin, as well as cross-resistance to other therapeutic agents, were also determined to define the resistance phenotype. Results: A senescence-resistant (SR) clone (clone 2) was identified that was largely refractory to both Adriamycin-induced and g-irradiation^induced senescence. Clone 2 continued to proliferate and maintain high levels of telomerase activity following a second drug treatment, when treated parental cells expressed very low levels of telomerase and many positive cell cycle regulators. SR clone 2 also expressed substantially more cdc-2 than parental cells and undetectable levels of MDR1, showed an intact p53 checkpoint and only a modestly lower level of intracellular drug accumulation, while exhibiting cross-resistance to other topoisomerase inhibitors. Conclusions: SR clone 2 is intrinsically resistant to DNA damage^induced senescence perhaps through an ability to prevent down-regulation of cdc-2. Telomerase is a marker of proliferative recovery for breast cancer cells after chemotherapy exposure. Evasion or escape from a single-step, drug-induced senescence may represent a unique and previously unrecognized drug-resistance phenotype.

Autophagy, senescence and tumor dormancy in cancer therapy

“…3,[9][10][11][12] Finally, a recent report presents evidence for apoptosis that is dependent on prior autophagy. The transient arrest and renewed tumor growth that has been interpreted as tumor dormancy by Lu et al 2 is also a common observation in other xenograft models treated with chemotherapy or radiation; 19,20 our own studies in cell culture [21][22][23] also support the concept of drug and radiation induced senescence in tumor cells that is succeeded by proliferative recovery. We believe that this profile of response in tissue culture as well as xenograft models could prove to be a corollary of tumor dormancy and disease recurrence in the patient.…”

“…Alternatively, autophagy may be succeeded by a second type of protective response, that of senescence, where the cells remain metabolically active but where the bulk of the population is unable to return to the cell cycle. Whether protection is conferred by autophagy, senescence or both, our own work [21][22][23] as well as that of others 27,28 and the studies by Lu et al 2 support the clinically relevant concept that at least a small subpopulation of tumor cells may regain the ability to reenter the cell cycle.…”

Resistance to discodermolide, a microtubule-stabilizing agent and senescence inducer, is 4E-BP1–dependent

“…Finally, these data and that of others challenge the dogma that senescence is an irreversible process (21,40). Although we cannot exclude that our AD32 cells originated from a population that bypassed disco-induced senescence, we consider this highly unlikely as cells were cloned at multiple steps throughout selection and the period required for AD32 cells to emerge was extremely long.…”

Cancer stem cells and escape from drug-induced premature senescence in human lung tumor cells: Implications for drug resistance and in vitro drug screening models

“…However, more recent data show that exposure to low doses of different antitumor agents leads to growth arrest of tumor cells, without signs of cell death, where cells acquire morphological and biochemical features of senescent cells. [2][3][4][5][6][7][8] This process resembles replicative senescence, 9 but is induced primarily in tumor cells with functional p53 and is termed drug-induced premature senescence (DIPS) or pseudo-senescence (reviewed in ref. 10).…”