- [Resource Hub](/) - [Publication](/?resource-type=publication#library) - Pure estrogen receptor antagonists potentiate capecitabine activity in ESR1-mutant breast cancer # Pure estrogen receptor antagonists potentiate capecitabine activity in ESR1-mutant breast cancer Grinshpun A, Russo D, Ma W, Verma A, Hermida-Prado F, Sherman S, et al. npj Breast Cancer . 2024;10(1):42. DOI [10.1038/s41523-024-00647-1](https://doi.org/10.1038/s41523-024-00647-1). PMID 38851818. PMCID PMC11162492. How to cite ### AMA Grinshpun A, Russo D, Ma W, Verma A, Hermida-Prado F, Sherman S, et al. Pure estrogen receptor antagonists potentiate capecitabine activity in ESR1-mutant breast cancer. npj Breast Cancer . 2024;10(1):42. doi:10.1038/s41523-024-00647-1 ### APA Grinshpun, A., Russo, D., Ma, W., Verma, A., Hermida-Prado, F., Sherman, S., et al. (2024). Pure estrogen receptor antagonists potentiate capecitabine activity in ESR1-mutant breast cancer. npj Breast Cancer , 10(1), 42. https://doi.org/10.1038/s41523-024-00647-1 ### BibTeX @article{grinshpun2024pure, title = {Pure estrogen receptor antagonists potentiate capecitabine activity in ESR1-mutant breast cancer}, author = {Grinshpun, A and Russo, D and Ma, W and Verma, A and Hermida-Prado, F and Sherman, S and others}, journal = {npj Breast Cancer}, volume = {10}, number = {1}, pages = {42}, year = {2024}, doi = {10.1038/s41523-024-00647-1}, pmid = {38851818} } Estrogen receptor-positive breast cancers often stop responding to hormone therapy, and one of the most common reasons is a mutation in the ESR1 gene that keeps the receptor switched on. Once that happens, patients usually move to chemotherapy, but the mutant receptor can blunt the chemotherapy response too. This preclinical study asked whether keeping the mutant receptor blocked with a pure ER antagonist such as fulvestrant makes chemotherapy work better. In ESR1-mutant cell lines and a patient-derived xenograft, adding fulvestrant to the chemotherapy drug capecitabine suppressed tumor growth that neither drug controlled alone. Cyclic multiplexed imaging of the treated tumors showed the combination lowered proliferation in individual cancer cells across the whole tumor. [Read publication at npj Breast Cancer](https://pmc.ncbi.nlm.nih.gov/articles/PMC11162492/) ## Key findings - In ESR1-mutant cells, a pure ER antagonist turned chemotherapy synergistic. In MCF7 cells carrying the Y537S ER mutation, fulvestrant combined with 5-fluorouracil, doxorubicin, or paclitaxel produced synergistic Bliss scores (above 10), while wild-type-ER cells showed only additive effects, and the synergistic activity depended on intact P53. - Fulvestrant plus capecitabine suppressed tumor growth only in the mutant model. In a Y537S ESR1-mutant patient-derived xenograft, neither drug alone slowed growth, yet the combination significantly reduced tumor volume by day 28 across four treatment arms of 5 to 8 mice each. - Single-cell imaging traced the benefit to reduced proliferation in every cell, whatever its ER level. A Multivariate Proliferation Index built from five markers (Ki-67, PCNA, MCM2, p21, p27) scored each cell; the combination cut the proliferative fraction as early as day 10, and by day 28 that reduction held in both ER-low and ER-high cells. ## CyteFinder in the methods “FFPE slides were baked at 60 °C for 30 min, dewaxed using Bond Dewax solution at 72 °C, and antigen retrieval was performed with Epitope Retrieval 1 solution at 100 °C for 20 min using the BOND RX Automated IHC/ISH Stainer. Antibodies for each cycle were diluted in Odyssey Blocking Buffer and incubated overnight at 4 °C in the dark (used antibody list in Supplementary Data 2 ). After antibody incubation, slides were stained with Hoechst 33342 for 10 min at room temperature. Slides were cover slipped using 20–50% glycerol solution (Sigma, G5516) in PBS. Images were taken using DAPI, FITC, Cy3, and Cy5 channels either on the RareCyte CyteFinder (20×/0.75NA objective). After imaging, fluorophores were inactivated (4.5% H 2 O 2 , 20 mM NaOH in PBS, 45 min) under LED lights, and the next cycle was performed.” — Grinshpun et al., npj Breast Cancer (2024), Methods, “Cyclic immunofluorescence (CyCIF)” ## Why it matters for CyteFinder users If you are weighing CyteFinder for tissue imaging, notice the question it answered here. A bulk stain can tell you that a tumor carries less Ki67 after treatment, but it cannot tell you whether that drop came from every cell or only from the cells that already expressed little ER. The CyteFinder did the cyclic multiplexed imaging that settled it: FFPE tumor sections were stained, imaged across the DAPI, FITC, Cy3, and Cy5 channels at 20×/0.75NA, then re-stained over successive cycles, so five proliferation and arrest markers were recorded on the same cells. From those registered images the authors built a per-cell Multivariate Proliferation Index and sorted single cells into ER-low and ER-high groups. That is what let them show the combination reduces proliferation across the whole tumor rather than selecting one population. For your own work, the point is that every marker sits on one section, so you read proliferation and arrest together and can make a claim about single cells, not about a slide average. 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