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New Horizons in Cancer Biology

Development and Characterization of Novel Endoxifen-Resistant Breast Cancer Cell Lines Highlight Numerous Differences from Tamoxifen-Resistant Models

Calley J. Jones, Malayannan Subramaniam, Michael J. Emch, Elizabeth S. Bruinsma, James N. Ingle, Matthew P. Goetz and John R. Hawse
Calley J. Jones
1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota.
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Malayannan Subramaniam
1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota.
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Michael J. Emch
1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota.
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Elizabeth S. Bruinsma
1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota.
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James N. Ingle
2Department of Oncology, Mayo Clinic, Rochester, Minnesota.
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  • ORCID record for James N. Ingle
Matthew P. Goetz
2Department of Oncology, Mayo Clinic, Rochester, Minnesota.
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John R. Hawse
1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota.
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  • For correspondence: hawse.john@mayo.edu
DOI: 10.1158/1541-7786.MCR-20-0872
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Abstract

Despite the availability of drugs that target ERα-positive breast cancer, resistance commonly occurs, resulting in relapse, metastasis, and death. Tamoxifen remains the most commonly-prescribed endocrine therapy worldwide, and “tamoxifen resistance” has been extensively studied. However, little consideration has been given to the role of endoxifen, the most abundant active tamoxifen metabolite detected in patients, in driving resistance mechanisms. Endoxifen functions differently from the parent drug and other primary metabolites, including 4-hydroxy-tamoxifen (4HT). Many studies have shown that patients who extensively metabolize tamoxifen into endoxifen have superior outcomes relative to patients who do not, supporting a primary role for endoxifen in driving tamoxifen responses. Therefore, “tamoxifen resistance” may be better modeled by “endoxifen resistance” for some patients. Here, we report the development of novel endoxifen-resistant breast cancer cell lines and have extensively compared these models to 4HT and fulvestrant (ICI)-resistant models. Endoxifen-resistant cells were phenotypically and molecularly distinct from 4HT-resistant cells and more closely resembled ICI-resistant cells overall. Specifically, endoxifen resistance was associated with ERα and PR loss, estrogen insensitivity, unique gene signatures, and striking resistance to most FDA-approved second- and third-line therapies. Given these findings, and the importance of endoxifen in the efficacy of tamoxifen therapy, our data indicate that endoxifen-resistant models may be more clinically relevant than existing models and suggest that a better understanding of endoxifen resistance could substantially improve patient care.

Implications: Here we report on the development and characterization of the first endoxifen-resistant models and demonstrate that endoxifen resistance may better model tamoxifen resistance in a subset of patients.

Footnotes

  • Note: Supplementary data for this article are available at Molecular Cancer Research Online (http://mcr.aacrjournals.org/).

  • Mol Cancer Res 2021;XX:XX–XX

  • Received October 6, 2020.
  • Revision received January 25, 2021.
  • Accepted February 19, 2021.
  • Published first February 24, 2021.
  • ©2021 American Association for Cancer Research.
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This OnlineFirst version was published on March 26, 2021
doi: 10.1158/1541-7786.MCR-20-0872

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Development and Characterization of Novel Endoxifen-Resistant Breast Cancer Cell Lines Highlight Numerous Differences from Tamoxifen-Resistant Models
Calley J. Jones, Malayannan Subramaniam, Michael J. Emch, Elizabeth S. Bruinsma, James N. Ingle, Matthew P. Goetz and John R. Hawse
Mol Cancer Res March 26 2021 DOI: 10.1158/1541-7786.MCR-20-0872

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Development and Characterization of Novel Endoxifen-Resistant Breast Cancer Cell Lines Highlight Numerous Differences from Tamoxifen-Resistant Models
Calley J. Jones, Malayannan Subramaniam, Michael J. Emch, Elizabeth S. Bruinsma, James N. Ingle, Matthew P. Goetz and John R. Hawse
Mol Cancer Res March 26 2021 DOI: 10.1158/1541-7786.MCR-20-0872
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Molecular Cancer Research
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