脑胶质母细胞瘤是所有癌症中最致命的之一，其5年生存率仅为6％。由于明显的肿瘤内外异质性，脑胶质母细胞瘤的靶向治疗一直具有挑战性。 TERT启动子突变是脑胶质母细胞瘤中已知的最常见的克隆致癌突变。因此，端粒酶被认为是该肿瘤的有前途的治疗靶标。然而，这种策略的一个重要限制是，在端粒酶消除后，细胞死亡并非立即发生，而是经过数个细胞分裂来达到危急的短端粒酶长度后才会发生。因此，我们假设端粒酶抑制仅在低肿瘤负载脑胶质母细胞瘤中才有效。我们使用CRISPR干扰技术在TERT启动子突变的脑胶质母细胞瘤细胞系和患者来源的模型中降低TERT表达，然后使用串行增殖实验来测量其活力。我们还通过测量端粒长度和染色质桥的形成来评估端粒危机的特征。最后，我们使用Dox诱导的CRISPR干扰系统，在肿瘤形成过程的早期和晚期诱导TERT表达下调。在TERT失活后，脑胶质母细胞瘤细胞随着时间的推移失去了其增殖能力，并出现了端粒危机的证据，其中包括端粒缩短和染色质桥的形成。在体内，只有在肿瘤植入后不久诱导TERT敲除时，肿瘤形成才会被抑制，但是在肿瘤负荷高时却不能。我们的结果支持端粒酶抑制可最有效地治疗低肿瘤负载的脑胶质母细胞瘤，例如在手术去除及放化疗后的辅助治疗中使用。© 作者（们）2023年。由牛津大学出版社代表神经肿瘤学会出版。保留所有权利。有关权限，请发电子邮件至：journals.permissions@oup.com。

Glioblastoma is among the deadliest of all cancers, with 5-year survival rates of only 6%. Glioblastoma targeted therapeutics have been challenging to develop due to significant inter- and intra-tumoral heterogeneity. TERT promoter mutations are the most common known clonal oncogenic mutations in glioblastoma. Telomerase is therefore considered to be a promising therapeutic target against this tumor. However, an important limitation of this strategy is that cell death does not occur immediately after telomerase ablation, but rather after several cell divisions required to reach critically short telomeres. We therefore hypothesize that telomerase inhibition would only be effective in low tumor burden glioblastomas.We used CRISPR interference to knock down TERT expression in TERT promoter-mutant glioblastoma cell lines and patient derived models. We then measured viability using serial proliferation assays. We also assessed for features of telomere crisis by measuring telomere length and chromatin bridge formation. Lastly, we used a doxycycline-inducible CRISPR interference system to knock down TERT expression in vivo early and late in the tumor formation process.Upon TERT inactivation, glioblastoma cells lose their proliferative ability over time and exhibit evidence of telomere crisis with telomere shortening and chromatin bridge formation. In vivo, tumor formation is only inhibited when TERT knockdown is induced shortly after tumor implantation, but not when tumor burden is high.Our results support the idea that telomerase inhibition would be most effective at treating glioblastomas with low tumor burden, for example in the adjuvant setting after surgical debulking and chemoradiation.© The Author(s) 2023. Published by Oxford University Press on behalf of the Society for Neuro-Oncology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.