Targeting Shared Vulnerabilities in Alternate Telomere Lengthening (ALT) Cancers

摘要 端粒是染色体末端带有TTAGGG DNA重复序列的核蛋白，它保护编码DNA不受 腐蚀和检测作为DNA损伤。端粒维持是癌细胞无限增殖所必需的 容量。大多数癌症通过激活核糖核蛋白端粒酶来维持其端粒。低或无癌症 端粒酶活性通常使用另一种机制来延长端粒，即交替延长端粒(ALT)。 其中端粒是通过同源端粒-DNA重组来维持的，但其机制仍不清楚 明白了。ALT+肿瘤含有染色体外的端粒DNA C环，(用独特的聚合酶链式反应方法检测) 提供了一种特异和敏感的ALT生物标志物。使用C圈分析，我们调查了不同的童年 和成人癌症，发现11个癌症组织的ALT阳性率从10%到74%不等，另外还有5个癌症 ALT+的组织学有1%到5%。ALT癌症的临床结果很差，无论组织学如何，ALT+ 癌细胞株对与端粒酶+癌相关的DNA损伤剂表现出高度的耐药性。ALT癌症有 功能失调的端粒，它提供了独特的脆弱性，可以作为新的治疗靶点。我们最近做了 丙氨酸氨基转移酶神经母细胞瘤的高ATM激酶活性导致对DNA损伤性化疗的抵抗 可以用临床阶段的ATM抑制剂AZD0156逆转。根据我们的数据，我们假设ALT+癌症 既有对标准疗法产生抵抗的常见机制，也有可用于治疗的常见脆弱性。 加强对ALT+癌症生物学的研究，发现和确认新的治疗靶点，并能够进行比较 ALT+癌症跨越一系列组织学我们组装了一大组ALT+患者来源的细胞系(PDCL) 和患者来源的异种移植(PDX)和比较端粒酶+PDCL和PDX，包括儿童癌症 (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、软组织癌) 组织肉瘤)。使用这一独特的患者衍生模型小组，我们将演示ATM激酶激活 端粒功能障碍是ALT+癌症的一个共同特征(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(ATM激酶)的高ATM激酶活性 抑制剂AZD1390和P53激活剂APR-246)与伊立替康联合使用对ALT+有明显更高的活性 与端粒酶+比较器相关的癌症。对于选定组织的细胞系和异种移植，我们将确定 AZD1390可逆转伊立替康的耐药性。我们假设ALT+癌症耐受ATM激活，原因是 功能失调的P53，被APR-246恢复功能的P53将被ATM激活(磷酸化)。我们会 证明APR-246(单独或与伊立替康联合使用)对ALT+具有选择性细胞毒作用 端粒酶阳性癌细胞株和异种移植瘤。该项目将展示由 在一系列癌症组织学中，ALT+癌症细胞对ATM激酶的依赖在ALT+癌症中是常见的。数据 该项目将为寻求招募ALT+癌症患者的组织学不可知临床试验的发展提供信息 它们很容易被一个强大的肿瘤生物标记物识别。

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.