Targeting Shared Vulnerabilities in Alternate Telomere Lengthening (ALT) Cancers

摘要 端粒是在染色体末端具有TTAGGG DNA重复序列的核蛋白，其保护编码DNA不受染色体的损伤。 腐蚀和检测作为DNA损伤。端粒的维持是癌细胞无限增殖所必需的 容量大多数癌症通过核糖核蛋白端粒酶的激活来维持其端粒。癌症低或无 端粒酶活性通常利用另一种机制来延长其端粒，即端粒替代延长（ALT） 其中端粒通过同源端粒DNA重组来维持，但其机制仍然很差 明白ALT+肿瘤含有染色体外端粒DNA C环，（用独特的PCR检测法检测） 提供了一种特异性和敏感的ALT生物标志物。采用C环分析，我们调查了各种儿童 和成人癌症，发现11种癌症组织学ALT阳性率为10%至74%，另外5种癌症组织学ALT阳性率为10%至74%。 ALT+的组织学有1 - 5%。ALT癌症的临床结局较差，无论组织学如何，ALT + 相对于端粒酶+癌症，癌细胞系表现出对DNA损伤剂的高抗性。ALT癌症 功能失调的端粒，这提供了独特的脆弱性，可以作为新的治疗目标。我们最近 证明ALT神经母细胞瘤中ATM激酶的高活化导致对DNA损伤化疗的耐药性， 可以用临床阶段ATM抑制剂AZD 0156逆转。根据我们的数据，我们假设ALT+癌症 对标准疗法的抗性的共同机制和可用于治疗的共同弱点。 加强ALT+癌症生物学的研究，发现和验证新的治疗靶点，并能够比较 ALT+癌症在一系列的组织学，我们已经组装了一个大面板ALT+患者来源的细胞系（PDCL） 以及患者来源的异种移植物（PDX）和比较物端粒酶+PDCL和PDX，包括儿科癌症 （神经母细胞瘤、横纹肌肉瘤、骨肉瘤）和成人癌症（三阴性乳腺癌、结肠癌、软 组织肉瘤）。使用这一独特的患者衍生模型，我们将证明ATM激酶激活 端粒功能障碍是ALT+癌症的共同特征（与组织学无关）。我们将演示 临床阶段的研究药物利用ALT+癌症中的高ATM激酶活化（ATM激酶 抑制剂AZD 1390和p53激活剂APR-246）联合伊立替康在ALT + 相对于端粒酶+比较物的癌症。对于选定组织学的细胞系和异种移植物，我们将确定是否 AZD 1390可以逆转对伊立替康的耐药性。我们假设ALT+癌症耐受ATM激活， 在某些实施方案中，通过APR-246恢复功能的p53将被ATM激活（磷酸化）。我们将 证明APR-246（单独使用或与伊立替康联合使用）相对于 端粒酶+癌细胞系和异种移植物。该项目将证明， ALT+癌细胞对ATM激酶的依赖性在一系列癌症组织学中对于ALT+癌是常见的。数据 该项目的研究将为寻求招募ALT+癌症患者的组织学不可知临床试验的发展提供信息 其易于用稳健的肿瘤生物标志物识别。

Abstract Telomeres are nucleoproteins with TTAGGG DNA repeats at the ends of chromosomes that protect coding DNA from erosion and detection as DNA damage. Telomere maintenance is necessary for cancer cells to have unlimited proliferation capacity. Most cancers maintain their telomeres via activation of the ribonucleoprotein telomerase. Cancers with low or no telomerase activity often use another mechanism to extend their telomeres, the Alternative Lengthening of Telomeres (ALT) in which telomeres are maintained via homologous telomeric-DNA recombination, but the mechanism is still poorly understood. ALT+ tumors contain extra-chromosomal telomeric DNA C-circles, which (detected with a unique PCR assay) provides a specific and sensitive ALT biomarker. Employing the C-circle assay we have surveyed a variety of childhood and adult cancers and found 11 cancer histologies with ALT-positivity ranging from 10% to 74% and an additional 5 cancer histologies with 1 to 5% that are ALT+. ALT cancers have a poor clinical outcome and regardless of histology ALT+ cancer cell lines manifest high resistance to DNA damaging agents relative to telomerase+ cancers. ALT cancers have dysfunctional telomeres, which provides unique vulnerabilities that can serve as novel therapeutic targets. We have recently demonstrated high ATM kinase activation in ALT neuroblastoma leads to resistance to DNA damaging chemotherapy that can be reversed with a clinical-stage ATM inhibitor AZD0156. Based on our data we hypothesize that ALT+ cancers share both common mechanisms of resistance to standard therapies and common vulnerabilities that may be exploited for therapy. To enhance studies of ALT+ cancer biology, discovery and validation of novel therapeutic targets, and to enable comparing ALT+ cancers across a range of histologies we have assembled a large panel of ALT+ patient-derived cell lines (PDCLs) and patient-derived xenografts (PDXs) and comparator telomerase+ PDCLs and PDXs, including pediatric cancers (neuroblastoma, rhabdomyosarcoma, osteosarcoma) and adult cancers (triple negative breast cancer, colon cancer, soft tissue sarcomas). Using this unique panel of patient-derived models we will demonstrate that ATM kinase activation resulting from telomere dysfunction is a common feature of ALT+ cancers (regardless of histology). We will demonstrate that clinical-stage investigational drugs leveraging the high ATM kinase activation in ALT+ cancers (the ATM kinase inhibitor AZD1390 and the p53 activator APR-246) combined with irinotecan have significantly higher activity in ALT+ cancers relative to telomerase+ comparators. For cell lines and xenografts of selected histologies we will determine if AZD1390 can reverse resistance to irinotecan. We hypothesize that ALT+ cancers tolerate ATM activation due to dysfunctional p53, and that p53 restored to functionality by APR-246 will be activated (phosphorylated) by ATM. We will demonstrate that APR-246 (alone or in combination with irinotecan) will be selectively cytotoxic to ALT+ relative to telomerase+ cancer cell lines and xenografts. This project will demonstrate that the unique vulnerability conferred by the dependence of ALT+ cancers cells on ATM kinase is common to ALT+ cancers across a range of cancer histologies. Data from this project will inform development of histology-agnostic clinical trials seeking to enroll patients with ALT+ cancers that are readily identifiable with a robust tumor biomarker.