Reactivation of estrogen receptor α by vorinostat sensitizes mesenchymal-like triple-negative breast cancer to aminoflavone, a ligand of the aryl hydrocarbon receptor.
OBJECTIVE
Aminoflavone (AF) acts as a ligand of the aryl hydrocarbon receptor (AhR). Expression of estrogen receptor α (ERα) and AhR-mediated transcriptional induction of CYP1A1 can sensitize breast cancer cells to AF. The objective of this study was to investigate the combined antitumor effect of AF and the histone deacetylase inhibitor vorinostat for treating mesenchymal-like triple-negative breast cancer (TNBC) as well as the underlying mechanisms of such treatment.


METHODS
In vitro antiproliferative activity of AFP464 (AF prodrug) in breast cancer cell lines was evaluated by MTS assay. In vitro, the combined effect of AFP464 and vorinostat on cell proliferation was assessed by the Chou-Talalay method. In vivo, antitumor activity of AFP464, given alone and in combination with vorinostat, was studied using TNBC xenograft models. Knockdown of ERα was performed using specific, small-interfering RNA. Western blot, quantitative RT-PCR, immunofluorescence, and immunohistochemical staining were performed to study the mechanisms underlying the combined antitumor effect.


RESULTS
Luminal and basal A subtype breast cancer cell lines were sensitive to AFP464, whereas basal B subtype or mesenchymal-like TNBC cells were resistant. Vorinostat sensitized mesenchymal-like TNBC MDA-MB-231 and Hs578T cells to AFP464. It also potentiated the antitumor activity of AFP464 in a xenograft model using MDA-MB-231 cells. In vitro and in vivo mechanistic studies suggested that vorinostat reactivated ERα expression and restored AhR-mediated transcriptional induction of CYP1A1.


CONCLUSIONS
The response of breast cancer cells to AF or AFP464 was associated with their gene expression profile. Vorinostat sensitized mesenchymal-like TNBC to AF, at least in part, by reactivating ERα expression and restoring the responsiveness of AhR to AF.
Karmanos Cancer Institute, Wayne State University, Detroit, Michigan, United States of America.
Karri
K
Stark
Angelika
A
Burger
Jianmei
J
Wu
Phillip
P
Shelton
Lisa
L
Polin
Jing
J
Li
D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004357:Drug Synergism; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D005260:Female; D005419:Flavonoids; D005455:Fluorescent Antibody Technique; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology / Q000627:therapeutic use*; D008024:Ligands; D008648:Mesoderm / Q000187:drug effects / Q000473:pathology*; D051379:Mice; D008807:Mice, Inbred BALB C; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D064726:Triple Negative Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000077337:Vorinostat; D023041:Xenograft Model Antitumor Assays
C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D005419:Flavonoids; D006877:Hydroxamic Acids; D008024:Ligands; D018336:Receptors, Aryl Hydrocarbon; C413760:aminoflavone; D000077337:Vorinostat