title: Metformin-induced preferential killing of breast cancer initiating CD44+CD24-/low cells is sufficient to overcome primary resistance to trastuzumab in HER2+ human breast cancer xenografts.
abstract: Trastuzumab-refractory breast cancer stem cells (CSCs) could also explain the high rate of primary resistance to single-agent trastuzumab in HER2 gene-amplified breast cancer patients.  The identification of agents with strong selective toxicity for trastuzumab-resistant breast CSCs may have tremendous relevance for how HER2+ breast cancer patients should be treated.  Using the human breast cancer cell line JIMT-1, which was established from the pleural metastasis of a patient who was clinically resistant to trastuzumab ab initio, we examined whether preferential killing of the putative CD44+CD24-/low breast CSC population might be sufficient to overcome primary resistance to trastuzumab in vivo.  Because recent studies have shown that the anti-diabetic biguanide metformin can exert antitumor effects by targeted killing of CSC-like cells, we explored whether metformin's ability to preferentially kill breast cancer initiating CD44+CD24-/low cells may have the potential to sensitize JIMT-1 xenograft mouse models to trastuzumab. Upon isolation for breast cancer initiating CD44+CD24-/low cells by employing magnetic activated cell sorting, we observed the kinetics of metformin-induced killing drastically varied among CSC and non-CSC subpopulations. Metformin's cell killing effect increased dramatically by more than 10-fold in CD44+CD24-/low breast CSC cells compared to non-CD44+CD24-/low immunophenotypes. While seven-weeks treatment length with trastuzumab likewise failed to reduce tumor growth of JIMT-1 xenografts, systemic treatment with metformin as single agent resulted in a significant two-fold reduction in tumor volume. When trastuzumab was combined with concurrent metformin, tumor volume decreased sharply by more than four-fold. Given that metformin-induced preferential killing of breast cancer initiating CD44+CD24-/low subpopulations is sufficient to overcome in vivo primary resistance to trastuzumab, the incorporation of metformin into trastuzumab-based regimens may provide a valuable strategy for treatment of HER2+ breast cancer patients.
authors.affiliation: Translational Research Laboratory, Catalan Institute of Oncology (ICO), Girona, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Cufi
authors.forename: Bruna
authors.initials: B
authors.lastname: Corominas-Faja
authors.forename: Alejandro
authors.initials: A
authors.lastname: Vazquez-Martin
authors.forename: Christina
authors.initials: C
authors.lastname: Oliveras-Ferraros
authors.forename: Joan
authors.initials: J
authors.lastname: Dorca
authors.forename: Joaquim
authors.initials: J
authors.lastname: Bosch-Barrera
authors.forename: Begoña
authors.initials: B
authors.lastname: Martin-Castillo
authors.forename: Javier A
authors.initials: JA
authors.lastname: Menendez
mesh_terms: D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051927:CD24 Antigen / Q000378:metabolism; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005260:Female; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D008687:Metformin / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D051379:Mice; D008819:Mice, Nude; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D000068878:Trastuzumab; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D051927:CD24 Antigen; D018960:Hyaluronan Receptors; D008687:Metformin; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C508053:ERBB2 protein, human