title: Targeting homologous recombination and telomerase in Barrett's adenocarcinoma: impact on telomere maintenance, genomic instability and tumor growth.
abstract: Homologous recombination (HR), a mechanism to accurately repair DNA in normal cells, is deregulated in cancer. Elevated/deregulated HR is implicated in genomic instability and telomere maintenance, which are critical lifelines of cancer cells. We have previously shown that HR activity is elevated and significantly contributes to genomic instability in Barrett's esophageal adenocarcinoma (BAC). The purpose of this study was to evaluate therapeutic potential of HR inhibition, alone and in combination with telomerase inhibition, in BAC. We demonstrate that telomerase inhibition in BAC cells increases HR activity, RAD51 expression, and association of RAD51 to telomeres. Suppression of HR leads to shorter telomeres as well as markedly reduced genomic instability in BAC cells over time. Combination of HR suppression (whether transgenic or chemical) with telomerase inhibition, causes a significant increase in telomere attrition and apoptotic death in all BAC cell lines tested, relative to either treatment alone. A subset of treated cells also stain positive for β-galactosidase, indicating senescence. The combined treatment is also associated with decline in S-phase and a strong G2/M arrest, indicating massive telomere attrition. In a subcutaneous tumor model, the combined treatment resulted in the smallest tumors, which were even smaller (P=0.001) than those that resulted from either treatment alone. Even the tumors removed from these mice had significantly reduced telomeres and evidence of apoptosis. We therefore conclude that although telomeres are elongated by telomerase, elevated RAD51/HR assist in their maintenance/stabilization in BAC cells. Telomerase inhibitor prevents telomere elongation but induces RAD51/HR, which contributes to telomere maintenance/stabilization and prevention of apoptosis, reducing the efficacy of treatment. Combining HR inhibition with telomerase renders telomeres more vulnerable to degradation and significantly increases/expedites their attrition, leading to apoptosis. We therefore demonstrate that a therapy targeting HR and telomerase has the potential to prevent both tumor growth and genomic evolution in BAC.
authors.affiliation: 1] Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA [2] Department of Clinical Laboratory, Fudan University Shanghai Cancer Center and Shanghai Medical School, Shanghai, China.
authors.forename: R
authors.initials: R
authors.lastname: Lu
authors.affiliation: Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Pal
authors.affiliation: Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA.
authors.forename: L
authors.initials: L
authors.lastname: Buon
authors.affiliation: Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Nanjappa
authors.affiliation: 1] Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA [2] Department of Medicine, Harvard Medical School, Boston, MA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Shi
authors.affiliation: 1] Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA [2] Department of Medicine, Harvard Medical School, Boston, MA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Fulciniti
authors.affiliation: 1] Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA [2] Department of Medicine, Harvard Medical School, Boston, MA, USA.
authors.forename: Y-T
authors.initials: YT
authors.lastname: Tai
authors.affiliation: Department of Clinical Laboratory, Fudan University Shanghai Cancer Center and Shanghai Medical School, Shanghai, China.
authors.forename: L
authors.initials: L
authors.lastname: Guo
authors.affiliation: Department of Clinical Laboratory, Fudan University Shanghai Cancer Center and Shanghai Medical School, Shanghai, China.
authors.forename: M
authors.initials: M
authors.lastname: Yu
authors.affiliation: Department of Nucleic Acid Chemistry, Geron Corporation, Menlo Park, CA, USA.
authors.forename: S
authors.initials: S
authors.lastname: Gryaznov
authors.affiliation: 1] Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA [2] Department of Medicine, Harvard Medical School, Boston, MA, USA.
authors.forename: N C
authors.initials: NC
authors.lastname: Munshi
authors.affiliation: Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Shammas
mesh_terms: D000230:Adenocarcinoma / Q000150:complications / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols; D001471:Barrett Esophagus / Q000150:complications* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D004938:Esophageal Neoplasms / Q000150:complications / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology*; D055786:Gene Knockout Techniques; D042822:Genomic Instability / Q000187:drug effects*; D059765:Homologous Recombination / Q000187:drug effects*; D006801:Humans; D008297:Male; D051379:Mice; D009841:Oligonucleotides / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use; D051135:Rad51 Recombinase / Q000172:deficiency / Q000235:genetics; D019098:Telomerase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016615:Telomere / Q000187:drug effects* / Q000235:genetics
chemical_list: D004791:Enzyme Inhibitors; C505952:GRN163L peptide; D009841:Oligonucleotides; D011743:Pyrimidines; D051135:Rad51 Recombinase; D019098:Telomerase; C498826:nilotinib