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.
Department of Adult Oncology, Harvard (Dana Farber) Cancer Institute and VA Health Care System, Boston, MA, USA.
Oncogene. 2014 Mar 20;33(12):1495-505. doi: 10.1038/onc.2013.103. Epub 2013 Apr 22.
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.
同源重组（HR）是一种在正常细胞中准确修复 DNA 的机制，在癌症中被失调。升高/失调的 HR 与基因组不稳定性和端粒维持有关，这是癌细胞的关键生命线。我们之前已经表明，HR 活性升高并显著促进 Barrett 食管腺癌（BAC）中的基因组不稳定性。本研究的目的是评估 HR 抑制单独和与端粒酶抑制联合治疗 BAC 的潜在治疗效果。我们证明，端粒酶抑制可增加 BAC 细胞中的 HR 活性、RAD51 表达以及 RAD51 与端粒的结合。随着时间的推移，抑制 HR 会导致端粒变短以及 BAC 细胞的基因组不稳定性明显降低。无论使用转基因还是化学方法抑制 HR，与单独治疗相比，都会导致所有测试的 BAC 细胞系中端粒损耗和凋亡死亡的显著增加。一部分处理过的细胞也对β-半乳糖苷酶呈阳性染色，表明衰老。联合治疗还与 S 期下降和强烈的 G2/M 阻滞相关，表明端粒大量损耗。在皮下肿瘤模型中，联合治疗导致的肿瘤最小，比单独治疗的肿瘤还要小（P=0.001）。即使从这些小鼠中取出的肿瘤也有明显缩短的端粒和凋亡的证据。因此，我们得出结论，尽管端粒酶使端粒延长，但升高的 RAD51/HR 有助于 BAC 细胞中端粒的维持/稳定。端粒酶抑制剂可防止端粒延长，但会诱导 RAD51/HR，这有助于端粒的维持/稳定和凋亡的预防，从而降低治疗效果。将 HR 抑制与端粒酶抑制联合使用可使端粒更容易降解，并显著增加/加速其损耗，从而导致凋亡。因此，我们证明针对 HR 和端粒酶的治疗具有预防 BAC 中肿瘤生长和基因组进化的潜力。
