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    Cancer Technologies

    (F-204) Mechanical Disruption by Focused Ultrasound Increase ERα Expression in Tamoxifen resistant Breast Cancer Cells

    Saturday, October 14, 2023
    9:30 AM – 10:30 AM PDT
    Location: Exhibit Hall - Row F - Poster # 204
    Introduction:: Tamoxifen is the most commonly used anti-cancer therapeutic agent in estrogen receptor positive (ER+) breast cancer, which accounts for ~70% of all cases 1. Recently, it is even suggested that women at high risk for breast cancer be prescribed Tamoxifen as a preventative 2. However, one third of patients will relapse within 15 years even if treated with tamoxifen for up to 5 years 3. Tumors that are initially responsive to tamoxifen develop resistance, leading to aggressive phenotypes 4. There is a critical need to understand the underlying mechanisms and identify therapies capable of overcoming endocrine therapy resistance, which impact up to 25% of all breast cancer patients 5. We hypothesized that mechanical vibration induced by focused ultrasound (FUS) re-sensitizes breast cancer cells to tamoxifen by inducing ERα expression. 

    Materials and Methods:: To test our hypothesis, we exposed resistant and non-resistant breast cancer cells and normal mammary epithelial cells to FUS and/or Tamoxifen. Cell viability post-exposure was measured using Annexin V / Propidium Iodide apoptotic kit. WST-8 and crystal violet assays were used to assess cell proliferation. The ERα expression in untreated and treated cells was measured by quantitative real-time PCR analysis, performed using PowerUp SYBR Green Master Mix ( Thermo Fisher Scientific, Waltham, MA). Total RNA from cells was extracted with RNeasy Kit (Qiagen, Valencia, CA, USA) with a DNase 1 digestion (Qiagen). qScript cDNA SuperMix (Quantabio, Beverly, MA, USA ) was used to synthesize cDNA from cellular RNA. Primers were made for GAPDH (F-5'-ATC GTG GAA GGA CTC ATG ACC ACA-3', R-5'-CCT GCT TCA CCA CCT TCT TGA TGT-3') and ERα (F-5’-ACA TGG ACA CCT CCC AGT C-3’, R-5’-ACA GAC TAA CAC AGC CCA TC-3’).

    Results, Conclusions, and Discussions:: A few mechanisms have been identified for how cancers develop resistance to estrogen receptor impairment, which include ER downregulation and increased activation of alternative pro-survival signaling pathways. To address this issue, we utilized mechanochemical disruption via Tamoxifen and FUS to broadly disrupt pro-survival signaling and re-sensitize breast cancer cells to Tamoxifen. Not only did this combination significantly reduce the viability and proliferative potentials of T-47D breast cancer cells, but it was able to significantly reduce the number of viable tamoxifen-resistant cells, T-47D Tam1. FUS increased the ERα expression in both T-47D and T-47D Tam1 cells. FUS alone or in combination with tamoxifen had no effect on the viability of normal breast epithelial cells, MCF-10A. 

    Acknowledgements (Optional): : The authors thank Mark Mondrinos and Omar Ahmad for their help with RT-PCR analysis.

    References (Optional): :

    1. Harvey JM, Clark GM, Osborne CK, Allred DC. Estrogen receptor status by immunohistochemistry is superior to the ligand-binding assay for predicting response to adjuvant endocrine therapy in breast cancer. J Clin Oncol 1999; 17(5): 1474-81. 




    2. Smith SG, Foy R, McGowan JA, et al. Prescribing tamoxifen in primary care for the prevention of breast cancer: a national online survey of GPs' attitudes. Br J Gen Pract 2017; 67(659): e414-e27. 




    3. Early Breast Cancer Trialists' Collaborative G, Davies C, Godwin J, et al. Relevance of breast cancer hormone receptors and other factors to the efficacy of adjuvant tamoxifen: patient-level meta-analysis of randomised trials. Lancet 2011; 378(9793): 771-84. 




    4. Hiscox S, Morgan L, Barrow D, Dutkowskil C, Wakeling A, Nicholson RI. Tamoxifen resistance in breast cancer cells is accompanied by an enhanced motile and invasive phenotype: inhibition by gefitinib ('Iressa', ZD1839). Clin Exp Metastasis 2004; 21(3): 201-12. 




    5. Musgrove EA, Sutherland RL. Biological determinants of endocrine resistance in breast cancer. Nat Rev Cancer 2009; 9(9): 631-43.