PHARMACOLOGICAL MODULATION OF POLY(ADP-RIBOSE) METABOLISM

 描述（由申请人提供）分子靶向癌症疗法已经彻底改变了这种异质性和日益普遍的疾病的治疗。遗传不稳定性是许多癌症的标志，这些癌症产生突变以支持不受控制的肿瘤生长和对化疗的抗性。这些肿瘤中潜在的DNA修复缺陷可以用于肿瘤选择性治疗，阻断关键的剩余DNA修复功能，引发灾难性损伤和细胞死亡。这一想法得到了聚（ADP-核糖）聚合酶1（PARP 1）抑制剂治疗BRCA 1或BRCA 2突变的乳腺癌和卵巢癌的临床成功的证实。然而，这些BRCA缺陷型肿瘤仅占少数癌症，因此重要的是要确定与分子靶向治疗相结合的合成致死性肿瘤的其他生理缺陷。此外，目前的PARP抑制剂具有剂量限制性毒性，这可能是由于对大型PARP超家族其他成员的脱靶效应造成的。作为PARP抑制剂的替代品，我们使用高通量筛选来鉴定人聚（ADP-核糖）糖水解酶PARG的选择性抑制剂。PARG是一种单基因酶，其去除由PARP 1修饰的蛋白质的聚（ADP-核糖）翻译后修饰。PARG的基因敲低使癌细胞对DNA损伤剂和辐射敏感，并且表型模仿PARP 1酶抑制剂在BRCA缺陷癌细胞中的肿瘤特异性杀伤作用。在本申请中，我们提出了通过结构指导的化学合成和体外测试来提高小分子PARG抑制剂的效力和选择性的实验，并将选定的化合物推进到乳腺癌培养细胞和异种移植模型中的肿瘤杀伤活性的临床前试验。我们将合成利用PARG活性位点的独特特征的类似物的集中文库，并筛选小分子片段文库以鉴定可以纳入我们的抑制剂设计策略的新化学型和相互作用。PARG的选择性抑制剂将是对损伤DNA的癌症化疗剂的细胞应答的有用探针，并且通过利用许多肿瘤的基因组不稳定表型，其本身可能是有用的癌症疗法。

 DESCRIPTION (provided by applicant) Molecularly-targeted cancer therapies have revolutionized the treatment of this heterogeneous and increasingly prevalent disease. Genetic instability is a hallmark of many cancers that generates mutations to support uncontrolled tumor growth and resistance to chemotherapies. The underlying DNA repair defects in these tumors can be exploited in tumor-selective therapies that block critical remaining DNA repair functions to trigger catastrophic damage and cell death. This idea is borne out by the clinical successes of inhibitors of poly(ADP-ribose) polymerase 1 (PARP1) to treat breast and ovarian cancers with mutations in BRCA1 or BRCA2. However, these BRCA-deficient tumors account for a minority of cancers so it is important to identify other physiological defects of tumors that are synthetically lethal in combination with molecularly targeted therapies. Additionally, the current PARP inhibitors suffer from dose-limiting toxicities, which may result from off-target effects on other members of the large PARP superfamily. As an alternative to PARP inhibitors, we used high-throughput screening to identify selective inhibitors of the human poly(ADP-ribose) glycohydrolase PARG. PARG is a monogenic enzyme that removes the poly(ADP-ribose) posttranslational modification of proteins modified by PARP1. A genetic knockdown of PARG sensitizes cancer cells to DNA damaging agents and radiation and phenocopies the tumor-specific killing effects of PARP1 enzymatic inhibitors in BRCA- deficient cancer cells. In this application, we propose experiments to improve the potency and selectivity of small molecule PARG inhibitors through structure-guided chemical synthesis and testing in vitro, and to advance selected compounds to preclinical trials of tumor killing activity in cultured cells and xenograft models of breast cancer. We will synthesize focused libraries of analogs that exploit unique features of the PARG active site and screen small molecule fragment library to identify new chemotypes and interactions that can be incorporated into our inhibitor design strategy. Selective inhibitors of PARG will be useful probes of cellular responses to cancer chemotherapeutics that damage DNA, and may be useful cancer therapies in their own right by exploiting the genomic instability phenotype of many tumors.