title: Antitumor effect of the mTOR inhibitor everolimus in combination with trastuzumab on human breast cancer stem cells in vitro and in vivo.
abstract: This study evaluated the effects of a mammalian target of mTOR inhibitor everolimus alone or in combination with trastuzumab on stem cells from HER2-overexpressing primary breast cancer cells and the BT474 breast cancer cell line in vitro and in vivo. For the in vitro studies, we sorted ESA(+)CD44(+)CD24(-/low) cells as stem cells from primary breast cancer cells and BT474 cells using flow cytometry. The MTT assay was used to quantify the inhibitory effect of the drugs on total cells and stem cells specifically. Stem cell apoptosis, cell cycle distributions, and their tumorigenicity after treatment were investigated by flow cytometry or soft agar colony formation assays. For the in vivo studies, BALB/c mice were injected with BT474 stem cells, and the different treatments were administered. After necropsy, the expression of Ki67, CD31, AKT1, and phospho-AKT (Thr308) was analyzed by immunohistochemistry. For the in vitro studies, Treatment with everolimus resulted in stem cell growth inhibition in a dose-dependent manner. The combination of everolimus with trastuzumab was more effective at inhibiting cell growth (P < 0.001) and tumorigenicity (P < 0.001) compared with single-agent therapy. In addition, an increase in G1 cell cycle arrest and an increased population of cells in early apoptosis were seen in the combination treatment group compared with either of the single-agent groups (P < 0.01). For the in vivo studies, everolimus plus trastuzumab therapy was much more effective at reducing tumor volume in mice compared with either single agent alone (P < 0.05). Compared with everolimus alone, the combination of everolimus and trastuzumab reduced the expression of Ki67, AKT1, and phospho-AKT (Thr308) (P < 0.05). We conclude that everolimus has effective inhibitory effects on HER2-overexpressing stem cells in vitro and vivo. Everolimus plus trastuzumab is a rational combination treatment that may be promising in human clinical trials.
authors.affiliation: 3rd Department of Breast Cancer, China Tianjin Breast Cancer Prevention, Treatment and Research Center, Tianjin Medical University Cancer Institute and Hospital, West Beihuanhu Rd, Tianjin, 300060, People's Republic of China.
authors.forename: Yuanxi
authors.initials: Y
authors.lastname: Zhu
authors.forename: Xiaobei
authors.initials: X
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Sheng
authors.initials: S
authors.lastname: Zhang
authors.forename: Jingjing
authors.initials: J
authors.lastname: Liu
authors.forename: Yi
authors.initials: Y
authors.lastname: Ma
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D000068338:Everolimus; D005260:Female; D006801:Humans; D020128:Inhibitory Concentration 50; D019394:Ki-67 Antigen / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D014411:Neoplastic Stem Cells / Q000187:drug effects* / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors; D020123:Sirolimus / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000068878:Trastuzumab; D023041:Xenograft Model Antitumor Assays
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000068338:Everolimus; D019394:Ki-67 Antigen; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D000068878:Trastuzumab