Dysregulation of the epigenome is implicated in initiation and progression of variety of cancers and their acquired resistance to chemotherapy. As such targeting epigenetic regulators has the potential to modulate cancer cell biology and their sensitivity to chemotherapy and/or radiation. Our studies demonstrates that silencing of the epigenetic regulator Nucleosome Remodeling Factor (NURF) sensitizes breast tumor cells to chemotherapy and enhances the anti-tumor immune response. A screen of a variety of chemotherapeutic agents shows that NURF KD cells are selectively sensitized to Topo II inhibitors, which includes doxorubicin. NURF KD increases DNA damage (gamma H2AX staining) and autophagy (acridine orange staining) in breast tumor cells exposed to doxorubicin (Dox) and enhances growth inhibition as well as suppressing the ability of the cells to recover proliferative capacity. Increased autophagy as well as breast tumor sensitization to doxorubicin were observed using a small molecule inhibitor of NURF, suggesting that NURF can also be targeted pharmacologically. Our studies suggest that enhanced autophagy may be a primary contributor to chemo sensitivity in NURF KD cells. Studies are currently underway to confirm the role of autophagy in chemosensitization in- vitro and enhanced immune response in-vivo using autophagy deficient cells (through ATG silencing). Doxorubicin produces profound DNA damage and promotes immunogenic cell death enhanced by NURF KD. Increased cell autonomous antitumor effects by doxorubicin in concert with increased cell non-autonomous antigenicity could help to achieve tumor regression, reduce metastasis, and possibly promote long term remission in breast cancer. Citation Format: Liliya Tyutyunyk, Joseph Landry, David Gewirtz, Nga Dao. Role of epigenetic remodeling in sensitizing triple-negative breast cancer cells to treatment through enhanced chemotherapy-induced autophagy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1330.
Dysregulation of the epigenome is implicated in initiation and progression of variety of cancers and their acquired resistance to chemotherapy. As such, targeting epigenetic regulators has the potential to modulate tumor cell biology and reestablish tumor cell sensitivity to chemotherapy and/or radiation. Our studies demonstrate that silencing of the epigenetic regulator Nucleosome Remodeling Factor (NURF) sensitizes breast tumor cells to chemotherapy and enhances the anti-tumor immune response. Compared to controls, NURF KD 4T1 breast tumor cells exposed to doxorubicin (Dox) show increased DNA damage (gamma H2AX staining) and autophagy (acridine orange staining) in vitro and enhanced growth inhibition both in vitro and in vivo. NURF KD also sensitizes 4T1 cells to doxorubicin stimulated Natural Killer (NK) cell antitumor activity ex vivo, which is associated with a cytokine/chemokine secreted by doxorubicin exposed NURF KD cells; potential candidates are CCL5, TNFa and CCL2. The importance of NK cells for the enhanced growth control of doxorubicin treated NURF KD cells was confirmed using a mAb depletion approach. Autophagy may be instrumental in NK cell activation and elimination of tumor cell targets by mediating cytokine secretion. Sensitization of NURF KD 4T1 cells to doxorubicin, both increased autophagy and enhanced NK cell activity, were also observed using a small molecule inhibitor of NURF, suggesting that NURF can also be targeted pharmacologically. Our studies suggest that enhanced doxorubicin induced DNA damage and autophagy (cell autonomous effects) and NK cell cytotoxic activity (cell non-autonomous affects) may be primary contributors to immune sensitization in NURF KD cells. Increased cell autonomous antitumor effects by doxorubicin in concert with increased cell non-autonomous immunogenicity could help to achieve tumor regression, reduce metastasis, and possibly promote long term remission in breast cancer. Citation Format: Liliya Tyutyunyk, David A. Gewirtz, Joseph Landry, Nga Dao. Suppression of epigenetic regulator NURF leads to autophagy mediated chemo-and immune sensitization of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4272.
Despite the ability of chemotherapy (and/or radiation) to eliminate the majority of tumor cells, some residual surviving cells may be able to escape cell death by entering into a prolonged senescence-based growth arrest. In addition to apoptosis, the majority of anti-cancer therapies induce senescence that has long been considered to be a favorable outcome of treatment due to its perceived irreversibility. However, accumulating studies in the literature demonstrate that therapy induced senescence may reflect one form of tumor dormancy and disease recurrence, when senescent cells are able to regain proliferative capacity. Tumor cells that escape dormancy often demonstrate an aggressive phenotype and are refractory to further treatment. Senescent cells are characterized by a specific (though often heterogeneous) secretory profile (Senescence Associated Secretory Phenotype or SASP), some components of which have been shown to promote tumorigenesis and may assist in neoplastic escape after therapy. In the current work, we evaluated the capacity of the BCL protein family inhibitor, ABT 263, to selectively clear breast tumor cells induced into senescence by doxorubicin. MDA-MB231-231 human breast cancer cells (a model of triple negative breast cancer) were induced into senescence upon exposure to a clinical concentration of the chemotherapeutic agent, doxorubicin (Dox). While a fraction of the MDA-MB-231 cell population underwent cell death, a large subpopulation entered into a state of prolonged growth arrest that lasted for several days, after which time the cells recovered proliferative capacity and formed colonies. At the time points when cells were arrested, prominent Senescence Associated β-Galactosidase staining marker indicative of senescence. In addition, tumor tissue collected from mice that received injections of Dox also were positive for β-Galactosidase staining. Cells induced into senescence and treated with ABT263 for 18 hours showed a significant increase in apoptosis and did not regain colony forming capabilities. We therefore postulate that senescence and escape from senescence may represent a form of tumor dormancy and disease recurrence, respectively. Consequently, if Therapy Induced Senescence is a deleterious outcome of treatment, it is of importance to identify strategies that might prevent senescent cells from neoplastic escape and induce cell death in order to completely eliminate residual tumors and thereby interfere with disease recurrence. Citation Format: Liliya Tyutyunyk, Tareq Saleh, David A. Gewirtz. Selective clearance of cells undergoing therapy-induced senescence in a model of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 899.
Cytotoxic chemotherapy has been shown to enhance tumor cell immunogenicity by promoting the secretion of damage-associated molecular pattern (DAMP) molecules which, in turn, stimulates the immune response. These effects can be further stimulated by combining chemotherapy with an immunotherapy designed to enhance effector cell (CD8 T cell or NK cell) anti-tumor activity. Our studies demonstrate that knockdown of the epigenetic regulator NURF increases DNA damage (gamma H2AX staining) and autophagy (acridine orange staining) in breast tumor cells exposed to doxorubicin and enhances growth inhibition as well as suppressing the capacity of the cells to recover and proliferate. Similar increases in autophagy were observed using a small molecule inhibitor of NURF, suggesting that NURF can be targeted therapeutically. Sensitization was not observed with ionizing radiation or cisplatin. Studies are in progress to assess the nature of autophagy in the NURF KD and NURF WT cells, distinguishing between the cytoprotective, cytotoxic, cytostatic and nonprotective forms. How NURF regulates doxorubicin induced DNA damage is being investigated by mapping sites of damage genome wide. It is anticipated that enhanced cell autonomous tumor cell sensitivity in concert with improvements in tumor cell antigenicity (cell non-autonomous sensitization) achieved by NURF depletion could improve anti-tumor immunogenicity, achieve tumor regression, reduce metastasis, and possibly achieve long term remission in breast cancer. Citation Format: Liliya Tyutyunyk, Joseph Landry, Tareq Saleh, David Gewirtz. Synergistic effects of chemotherapy-induced autophagy and epigenetic remodeling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3314. doi:10.1158/1538-7445.AM2017-3314
Despite the ability of chemotherapy (and/or radiation) to eliminate the majority of tumor cells, some residual surviving cells may be able to escape cell death by entering into a prolonged growth arrest from which they can ultimately re-emerge and proliferative . In this study, we evaluated two mechanisms, autophagy and senescence, that in theory could allow tumor cells to escape apoptotic cell death, and which therefore might be responsible for cancer recurrence. 4T1 murine breast cancer cells exposed to the chemotherapeutic agent, Adriamycin (doxorubicin), underwent both autophagy and senescence. Senescence induced by anticancer drugs or radiation is a state of prolonged growth arrest that is thought to be irreversible and is considered an alternative (but nevertheless desirable) response to apoptosis. Our studies, however, suggest that Therapy Induced Senescence (TIS) is reversible and serves as a mechanism of evading cell death. When subjected to acute treatment with Adriamycin, some of the 4T1 cells underwent apoptosis; however, a large population entered into a state of prolonged growth arrest that lasted for several days, after which time the cells recovered proliferative capacity and formed colonies. At the time points when cells were arrested, prominent Senescence Associated β-Galactosidase staining and polyploidy were detected, markers indicative of senescence. Inhibition of autophagy did not prevent the tumor cells from undergoing senescence and later escaping growth arrest. To further establish the reversibility of senescence, senescent cells that were isolated by Flow Cytometry (based on their enlarged morphology and detection of a fluorescent β-Gal substrate (C12FDG)), plated and monitored over time; these cells were also shown to recover, as was the case from with the non-sorted senescent cells. Sorted and isolated senescent cells implanted into either NSG (immunodeficient) or syngeneic (immunocompetent) mice also recovered and developed into tumors; recovery was accelerated in the NSG mice, suggesting that the immune system may (at least transiently) recognize and eliminate the tumor cells either at senescence or during recovery from senescence. Senescent cells are characterized by a specific (though often heterogeneous) secretory profile (Senescence Associated Secretory Phenotype or SASP), some components of which have been shown to promote tumorigenesis and may assist in neoplastic escape after therapy. Furthermore, senescence and escape from senescence may represent a form of tumor dormancy and disease recurrence, respectively. Therefore, it is important to treat Therapy Induced Senescence as a deleterious outcome of treatment and identify strategies that might prevent senescent cells from neoplastic escape and induce cell death to completely eliminate residual tumors. Citation Format: Liliya Tyutyunyk, Joseph Landry, Tareq Saleh, David Gewirtz. Reversibility of chemotherapy-induced senescence in breast tumor cells in culture and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 460.
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