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Abstract 2697: Inhibition of estrogen receptor signaling as a strategy for radiosensitization of ER+ breast cancers. Cancer Res 2022. [DOI: 10.1158/1538-7445.am2022-2697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Purpose: The estrogen receptor (ER) is expressed in over 80% of breast tumors and has been shown to be a significant driver of breast cancer (BC) pathogenesis and therefore a target of effective first-line therapies. While both ionizing radiation (RT) and endocrine therapies (ET) are used for the treatment of ER+ BC, the effect of ET on tumor radiosensitization remains unclear, with concerns it may be radioprotective based on G1 cell arrest with ET treatment. Here we assessed the efficacy and mechanism of ER-mediated radiosensitization using various pharmacologic approaches in ER+ BC.
Methods: Radiosensitization with ER inhibitors (tamoxifen [TAM], fulvestrant [FULV], AZD9496) was assessed using clonogenic survival assays. DNA damage was assessed by the neutral comet assay. Efficiency of homologous recombination (HR) or non-homologous end joining (NHEJ) as well as changes in cell cycle, apoptosis, and senescence were assessed. The efficacy of TAM with RT in vivo was assessed with an MCF-7 xenograft model.
Results: The selective estrogen receptor modulator TAM radiosensitized ER+ MCF-7 (enhancement ratio [enhR]: 1.14-1.50) and T47D (enhR: 1.33-1.60) cells but not ER-negative SUM-159 cells (enhR: 0.99-1.02). The selective estrogen receptor degrader (SERD) FULV had similar radiosensitization effects in MCF-7 (enhR: 1.33-1.76) and T47D cells (enhR: 0.97-2.81) with no radiosensitization observed in SUM-159 cells (enhR: 1.01-1.03). The novel oral SERD AZD9496 radiosensitized MCF-7 cells (enhR: 1.36-1.56). MCF-7 cells treated with TAM and RT had an increase in dsDNA breaks compared to RT alone as measured by the comet assay (p<0.05) and a decrease in NHEJ-mediated repair with TAM (p<0.05). No changes were observed in HR-mediated repair by Rad51 foci or a reporter (p=NS). RT alone and in combination with TAM or FULV induced similar levels of cell cycle arrest, suggesting that radiosensitization with the combination therapy is cell-cycle independent. There were no significant changes in apoptosis with TAM, FULV, RT, or the combination (p=NS). Although TAM or FULV did induce senescence, ET with RT increased senescence induction (p<0.05). In vivo, combination RT and TAM led to a significant delay in days to tumor doubling (control: 17, TAM: 40, RT: 32, TAM+RT: undefined; p<0.0001), and a significant difference in tumor growth between mice treated with TAM or RT alone compared combination treatment, with no increased toxicities or skin lesions from the combination treatment. Conclusion: Our data suggest that TAM, FULV, or AZD9496 can radiosensitize ER+ breast tumors, and these agents with RT may be more effective for radiosensitization. This work also supports further clinical investigation of the timing of RT for patients receiving ET, including using ET during RT, especially as initiating ET prior to RT has been increasingly utilized as a bridging therapy followed by concurrent ET+RT during the COVID-19 pandemic.
Citation Format: Anna R. Michmerhuizen, Lynn M. Lerner, Andrea M. Pesch, Connor Ward, Rachel Schwartz, Kari Wilder-Romans, Meilan Liu, Charles Nino, Kassidy Jungles, Ruth Azaria, Alexa Jelley, Nicole Zambrana Garcia, Alexis Harold, Amanda Zhang, Bryan Wharram, Daniel F. Hayes, James M. Rae, Lori J. Pierce, Corey W. Speers. Inhibition of estrogen receptor signaling as a strategy for radiosensitization of ER+ breast cancers [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 2697.
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Abstract 737: Estrogen receptor inhibition with tamoxifen mediates radiosensitization of ER+ breast cancer models. Cancer Res 2021. [DOI: 10.1158/1538-7445.am2021-737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Purpose: Estrogen receptor (ER) expression is present in over 80% of breast tumors and has been shown to be a significant driver of tumor initiation and progression. Therefore, patients with ER-positive (ER+) breast cancers are given first-line therapies which target the ER and downstream ER signaling. Ionizing radiation (RT) has been shown to significantly improve locoregional control and increase overall survival in patients with ER+ breast cancer. Similarly, endocrine therapy (ET) has also been shown to improve metastasis-free and overall survival in women with ER+ breast cancer. While both radiation and ET are used in women with ER+ breast cancer, the effect of endocrine therapies on tumor radiosensitization remains unclear. Here we assessed the efficacy and mechanism of ER inhibition in ER+ breast cancers in combination with radiation therapy.
Methods: Clonogenic survival assays were performed to assess radiosensitization and calculate radiation enhancement ratios (enhR) with the selective estrogen receptor modulator (SERM), tamoxifen, in ER+ MCF-7 and T47D cells or ER-negative (ER-) SUM-159 cells. DNA damage was assessed by yH2AX foci. Efficiency of homologous recombination (HR) or non-homologous end joining (NHEJ) was measured by RAD51 foci or using a pYFP reporter, respectively. Cell cycle effects were measured using flow cytometry with propidium iodide (PI) staining. Apoptosis was assessed by annexin V/PI via flow cytometry. Western blotting was used to quantify expression of proteins and phospho-proteins involved in DNA repair, cell cycle, and apoptosis. An MCF-7 xenograft model was used to assess the efficacy of tamoxifen with RT in vivo.
Results: ER inhibition with tamoxifen radiosensitized ER+ MCF-7 (enhR: 1.14-1.50) and T47D (enhR: 1.33-1.60) cells but not ER- SUM-159 cells (enhR: 0.99-1.02). MCF-7 and T47D cells treated with tamoxifen did not have changes in the kinetics of dsDNA break repair as measured by yH2AX foci (p>0.05) but demonstrated a decrease in NHEJ-mediated repair (p<0.05). No changes were observed in HR-mediated repair by Rad51 foci (p>0.05). While cell cycle arrest was induced at 24 hours after RT, no changes were observed with tamoxifen treatment in combination with RT. In addition, there were no significant changes in apoptosis in MCF-7 or T47D cells with treatment of tamoxifen, radiation, or the combination (p>0.05). In vivo xenograft studies demonstrate a significant delay in time to tumor doubling and a significant difference in tumor growth between mice treated with tamoxifen or RT alone compared to mice treated with tamoxifen and RT.
Conclusion: Our data suggest that tamoxifen may be effectively used to radiosensitize ER+ breast tumors. This work also supports further clinical investigation of the timing of radiation for patients receiving endocrine therapy as concurrent use may be more effective than sequential.
Citation Format: Anna R. Michmerhuizen, Andrea M. Pesch, Rachel Schwartz, Kari Wilder-Romans, Meilan Liu, Ruth Azaria, Alexa Jelley, Lori J. Pierce, Corey W. Speers. Estrogen receptor inhibition with tamoxifen mediates radiosensitization of ER+ breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 737.
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