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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.

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Abbreviations

HR:

homologous recombination

BAC:

Barrett’s esophageal adenocarcinoma

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Acknowledgements

We are grateful to Dr David G Beer, Department of Surgery, University of Michigan, Ann Arbor, MI, USA, for providing FLO-1 cells. This work was supported in part by grants from National Cancer Institute R01CA125711 to MAS, from the Department of Veterans Affairs Merit Review Awards (to NCM) and from the National Institutes of Health Grants RO1-1375555, P50-100007 and PO1-78378 to NCM.

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Correspondence to M A Shammas.

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Lu, R., Pal, J., Buon, L. et al. Targeting homologous recombination and telomerase in Barrett’s adenocarcinoma: impact on telomere maintenance, genomic instability and tumor growth. Oncogene 33, 1495–1505 (2014). https://doi.org/10.1038/onc.2013.103

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Keywords

  • homologous recombination
  • telomerase
  • telomeres
  • Barrett’s adenocarcinoma

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