title: Combinatorial treatment of mammospheres with trastuzumab and salinomycin efficiently targets HER2-positive cancer cells and cancer stem cells.
abstract: A major obstacle in the successful treatment of cancer is the occurrence of chemoresistance. Cancer cells surviving chemotherapy and giving rise to a recurrence of the tumor are termed cancer stem cells and can be identified by elevated levels of certain stem cell markers. Eradication of this cell population is a priority objective in cancer therapy. Here, we report elevated levels of stem cell markers in MCF-7 mammospheres. Likewise, an upregulation of HER2 and its differential expression within individual cells of mammospheres was observed. Sorting for HER2(high)  and HER2(low)  cells revealed an upregulation of stem cell markers NANOG, OCT4 and SOX2 in the HER2(low)  cell fraction. Accordingly, HER2(low)  cells also showed reduced proliferation, ductal-like outgrowths and an increased number of colonies in matrigel. Xenografts from subcutaneously injected HER2(low)  sorted cells exihibited earlier onset but slower growth of tumors and an increase in stem cell markers compared to tumors developed from the HER2(high)  fraction. Treatment of mammospheres with salinomycin reduced the expression of SOX2 indicating a selective targeting of cancer stem cells. Trastuzumab however, did not reduce the expression of SOX2 in mammospheres. Furthermore, a combinatorial treatment of mammospheres with trastuzumab and salinomycin was superior to single treatment with each drug. Thus, targeting HER2 expressing tumors with anti-HER2 therapies will not necessarily eliminate cancer stem cells and may lead to a more aggressive cancer cell phenotype. Our study demonstrates efficient killing of both HER2 positive cells and cancer stem cells, hence opening a possibility for a new combinatorial treatment strategy.
authors.affiliation: Pharmaceutical Biotechnology, Department of Pharmacy, Ludwig-Maximilians Universität München, Munich, Germany.
authors.forename: Prajakta S
authors.initials: PS
authors.lastname: Oak
authors.forename: Florian
authors.initials: F
authors.lastname: Kopp
authors.forename: Chitra
authors.initials: C
authors.lastname: Thakur
authors.forename: Joachim W
authors.initials: JW
authors.lastname: Ellwart
authors.forename: Ulf R
authors.initials: UR
authors.lastname: Rapp
authors.forename: Axel
authors.initials: A
authors.lastname: Ullrich
authors.forename: Ernst
authors.initials: E
authors.lastname: Wagner
authors.forename: Pjotr
authors.initials: P
authors.lastname: Knyazev
authors.forename: Andreas
authors.initials: A
authors.lastname: Roidl
mesh_terms: D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage / Q000494:pharmacology; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D001483:Base Sequence; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D017931:DNA Primers; D005260:Female; D006801:Humans; D014411:Neoplastic Stem Cells / Q000187:drug effects*; D011714:Pyrans / Q000008:administration & dosage / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D000068878:Trastuzumab; D000095662:Polyether Polyketides
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D017931:DNA Primers; D011714:Pyrans; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C010327:salinomycin; D000095662:Polyether Polyketides