POLQ Synthetic Lethality in HR-Deficient Pancreatic Adenocarcinoma

胰腺导管腺癌(PDA)是一种高度致命的人类恶性肿瘤，通常在 晚期，已知对化疗和电离辐射基本无反应。最新基因组学 PDA的特征表明，20%-25%的PDA存在基因的反复突变，包括 BRCA1/2、PALB2和ATM，它们对DNA的一种重要形式同源重组(HR)至关重要 修理。在许多患者中，这些可能是生殖系突变。这一PDA子组被称为HR缺陷PDA， 已经成为一种明确的生物实体，与化疗耐药性的增加和更具侵略性的 病程。 在这些肿瘤中观察到的HR缺陷使细胞对PARP抑制剂和 含铂疗法。尽管如此，正如在许多其他靶向治疗的情况下观察到的那样，只有一小部分 HR缺陷患者肿瘤对PARP抑制有反应。更重要的是，许多最初有反应的患者 最终往往会产生抵触和进步。因此，能够有效对抗HR的新疗法-- 有缺陷的PDA，单独或与PARP抑制剂或其他联合方案联合使用是迫切的 需要的。 我们最近确定，HR通路的失活与其过度表达有关 聚合酶Theta(POLƟ，也称为POLQ)。POLQ是调节一种替代物的关键酶 DNA修复途径，称为选择性非同源末端连接途径(Alt-NHEJ)。数据来自 我们的小组指出，在有缺陷的HR的设置中，Alt-NHEJ成为负责 修复DNA断裂。此外，我们还表明，在HR缺陷的肿瘤细胞中，POLQ抑制表现出 人工合成致死表型，在HR完整的细胞中未观察到。在这项提案中，我们提出了令人兴奋的新数据 在缺乏BRCA1、BRCA2、ATM和PALB2基因的PDA细胞中，POLQ的敲除是合成致命的。 在体内，POLQ基因敲除显著抑制了BRCA2和ATM缺陷肿瘤细胞的生长。此外， POLQ基因敲除显著上调HR缺陷型PDA的cGAS-STING通路并促进T细胞 渗透。 在这里，我们计划研究POLQ在胰腺癌生物学中的独特作用以及它作为一个新的 HR缺陷型胰腺癌的治疗靶点。我们还将评估联合应用的抗肿瘤效果。 POLQ抑制：i)当前标准的细胞毒化疗，ii)PARP抑制，以及iii) 免疫疗法。该提案的一个重要目标是为概念验证生成一组数据， 靶向POLQ是HR缺陷型胰腺癌有价值的治疗策略，POLQ抑制剂就是 目前正在开发中，用于临床。

Pancreatic ductal adenocarcinoma (PDA) is a highly lethal human malignancy, typically diagnosed at an advanced stage and known to be largely unresponsive to chemotherapy and ionizing radiation. Recent genomic characterization of PDA reveals that between 20-25 % of PDA harbor recurrent mutations in genes, including BRCA1/2, PALB2, and ATM, which are critical for homologous recombination (HR), an important form of DNA repair. In many patients, these may be germline mutations. This subgroup of PDAs, termed HR-deficient PDA, has emerged as a defined biological entity associated with increased chemoresistance and a more aggressive disease course. The defects in HR observed in these tumors impart cells with a specific vulnerability to PARP inhibitors and platinum-containing therapy. Still, as observed in the case of many other targeted therapies, only a fraction of HR-defective patient tumors respond to PARP inhibition. More so, many patients that initially respond eventually often develop resistance and progress. Therefore, novel therapies which can be effective against HR- defective PDA, alone or in combination with PARP inhibitors or other combinatorial regimens, are urgently needed. We have recently determined that inactivation of the HR pathway is associated with overexpression of polymerase theta (PolƟ, also known as POLQ) in PDA. POLQ is a key enzyme that regulates an alternative pathway of DNA repair, known as the alternative non-homologous end-joining (Alt-NHEJ) pathway. Data from our group indicates that in the setting of defective HR, Alt-NHEJ becomes a critical pathway responsible for the repair of DNA breaks. Furthermore, we show that POLQ inhibition in HR-defective tumor cells demonstrates a synthetic lethality phenotype, not observed in cells with intact HR. In this proposal, we present exciting new data that knockdown of POLQ is synthetically lethal in PDA cells deficient for Brca1, Brca2, Atm, and Palb2 genes. POLQ knockdown significantly inhibited growth of both Brca2- and Atm-deficient tumors cells in vivo. Further, POLQ knockdown significantly upregulated the cGAS-STING pathway in HR-deficient PDA and promoted T cell infiltration. Here, we plan to examine the unique role of POLQ in pancreatic cancer biology and its role as a novel therapeutic target in HR-defective pancreatic cancers. We will also evaluate the antitumor effect of combining POLQ inhibition with: i) current standard cytotoxic chemotherapies, ii) PARP inhibition, and iii) immunotherapy. An important goal of this proposal is to generate a set of data for proof-of-concept that targeting POLQ in a valuable therapeutic strategy in HR-defective pancreatic cancer, as POLQ inhibitors are currently in development for clinical use.