title: Therapeutic potential of antiviral drugs targeting chemorefractory colorectal adenocarcinoma cells overexpressing endogenous retroviral elements.
abstract: BACKGROUND
  Endoretroviruses account for circa 8 % of all transposable elements found in the genome of humans and other animals. They represent a genetic footprint of ancestral germ-cell infections of exoviruses that is transmittable to the progeny by Mendelian segregation. Traces of human endogenous retroviruses are physiologically expressed in ovarial, testicular and placental tissues as well as in stem cells. In addition, a number of these fossil viral elements have also been related to carcinogenesis. However, a relation between endoretroviruses expression and chemoresistance has not been reported yet.
  
  
  METHODS
  Twenty colorectal carcinoma patient samples were scrutinized for HERV-WE1 and HERV-FRD1 endoretroviruses using immunohistochemical approaches. In order to search for differential expression of these elements in chemotherapy refractory cells, a resistant HCT8 colon carcinoma subline was developed by serial etoposide exposure. Endoretroviral elements were detected by immunocytochemical staining, qPCR and ELISA. IC50-values of antiviral and cytostatic drugs in HCT8 cells were determined by MTT proliferation assay. The antivirals-cytostatics interaction was evaluated by the isobologram method.
  
  
  RESULTS
  In this work, we show for the first time that HERV-WE1, HERV-FRD1, HERV-31, and HERV-V1 are a) simultaneously expressed in treatment-naïve colon carcinoma cells and b) upregulated after cytostatic exposure, suggesting that these retroviral elements are intimately related to chemotherapy resistance. We found a number of antiviral drugs to have cytotoxic activity and the ability to force the downregulation of HERV proteins in vitro. We also demonstrate that the use of different antiviral compounds alone or in combination with anticancer agents results in a synergistic antiproliferative effect and downregulation of different endoretroviral elements in highly chemotherapy-resistant colorectal tumor cells.
  
  
  CONCLUSIONS
  Enhanced HERV-expression is associated with chemoresistance in colon carcinomas which can be overcome by antiviral drugs alone or in combination with anticancer drugs. Therefore, the introduction of antiviral compounds to the current chemotherapy regimens potentially improves patient outcomes.
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany. david.diaz-carballo@marienhospital-herne.de.
authors.forename: David
authors.initials: D
authors.lastname: Díaz-Carballo
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Ali Haydar
authors.initials: AH
authors.lastname: Acikelli
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Klein
authors.affiliation: Institute of Anatomy and Experimental Morphology, University of Duisburg-Essen, Medical School, Essen, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Jastrow
authors.affiliation: Central Animal Laboratory, University of Duisburg-Essen, Medical School, Essen, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Dammann
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wyganowski
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Cihan
authors.initials: C
authors.lastname: Guemues
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Gustmann
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Bardenheuer
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Malak
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Nora Sophia
authors.initials: NS
authors.lastname: Tefett
authors.affiliation: Department of Visceral Surgery, Marienhospital Herne, Ruhr University of Bochum, Medical School, Herne, Germany.
authors.forename: Veria
authors.initials: V
authors.lastname: Khosrawipour
authors.affiliation: Department of Visceral Surgery, Marienhospital Herne, Ruhr University of Bochum, Medical School, Herne, Germany.
authors.forename: Urs
authors.initials: U
authors.lastname: Giger-Pabst
authors.affiliation: Institute of Pathology, Ruhr-University of Bochum, Medical School, Bochum, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tannapfel
authors.affiliation: Institute for Molecular Oncology and Experimental Therapeutics, Division of Oncology and Hematology, Marienhospital Herne, Ruhr University of Bochum, Medical School, Marienhospital Herne, Duengelstr. 33, 44623, Herne, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Strumberg
mesh_terms: D000818:Animals; D000998:Antiviral Agents; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics*; D020077:Endogenous Retroviruses / Q000235:genetics*; D006801:Humans; D015533:Transcriptional Activation
chemical_list: D000998:Antiviral Agents