Project 2: Next Generation TOP1 Inhibition for the Treatment of Ovarian Cancer

摘要-项目2 DNA修复酶聚（ADP-核糖）聚合酶1（PARP 1）的抑制剂在同源物中具有高度活性， 同源重组（HR）缺陷型卵巢癌，尤其是BRCA 1或BRCA 2（BRCA 1/2）穆塔- 选择。然而，即使在这种情况下，40-80%的病例成为PARP抑制剂（PARPi）耐药，最常见的是， 这是恢复HR的遗传或生化变化的结果。在卵巢癌的其他基因组亚群中， PARPi抗性甚至更为普遍。观察到，获得性PARPi的最常见机制 耐药性不是由于不能抑制PARP 1引起的，这增加了PARP 1可能潜在地被 如果可以确定合适的组合，则在这种情况下用作化学增敏剂。因此 本项目旨在提高PARPi rucaparib的疗效，并通过将其与一种 第三代拓扑异构酶I（TOP1）抑制剂（TOP1 i）。最近的研究表明， 制剂如PLX 038，TOP1 i 7-乙基-10-甲基-N-（2-甲基-2-氧代-N- 羟基喜树碱（SN-38），在骨髓毒性方面比传统TOP1 is更低， 临床前癌症模型。我们的初步研究表明，包括PLX 038在内的TOP1 is缓释剂， 对测试的七种PARPi耐药卵巢癌患者来源的异种移植物（PDX）中的五种具有活性。此外，委员会认为， 使用独特的抗体检测TOP1-DNA共价复合物（TOP1 ccs），这是中间体， TOP1 i诱导的杀伤过程，我们已经表明，TOP1 ccs减少或检测不到的PDX， 对TOP1 i/PARPi组合具有耐药性，为了解卵巢癌耐药性提供了起点 这种治疗。总的来说，这些结果导致了一个假设，即一个容易识别的HR子集- 熟练的卵巢癌将表现出持续的抗肿瘤效果时，治疗的下一代 TOP1 i单独或与PARPi组合。为了验证这一假设，我们现在建议i）评估疗效 PLX 038单独和与PARPi rucaparib组合，在基因组学分析的高级别恶性肿瘤队列中， 对单一药物PARPis具有内在或获得性耐药性的浆液性卵巢癌PDX，以确定谱 可能从PLX 038或其组合中受益的卵巢癌; ii）确定 PDX和细胞系中对TOP1 i/PARPi组合的抗性;以及iii）检查TOP1 i/PARPi组合与PDX和细胞系中的细胞毒性之间的关联。 药物稳定的TOP1-DNA共价复合物在肿瘤细胞中的形成和卵巢癌的反应 在II期临床试验中，患者接受PLX 038/rucaparib组合。总的来说，这些研究不仅 深入了解影响卵巢癌患者对第3代TOP1 i反应的基因组和生化因素。 癌症，但也确定是否有可能使用PARPis作为化学增敏剂的设置， 它们不再作为单一药剂而活跃。如果成功的话，这个项目将为日益增长的 患有PARPi耐药卵巢癌的女性人数。

ABSTRACT – PROJECT 2 Inhibitors of the DNA repair enzyme poly(ADP-ribose) polymerase 1 (PARP1) are highly active in homol- ogous recombination (HR)-deficient ovarian cancers, especially those with BRCA1 or BRCA2 (BRCA1/2) muta- tions. Even in this setting, however, 40-80% of cases become PARP inhibitor (PARPi) resistant, most often as a result of genetic or biochemical changes that restore HR. Among other genomic subsets of ovarian cancer, PARPi resistance is even more prevalent. The observation that most common mechanisms of acquired PARPi resistance do not result from a failure to inhibit PARP1 raises the possibility that PARPis can potentially be utilized as chemosensitizing agents in this setting if suitable combinations can be identified. Accordingly, the present project seeks to enhance the efficacy of the PARPi rucaparib and extend its use by combining it with a 3rd generation topoisomerase I (TOP1) inhibitor (TOP1i). Recent studies have shown that nanoparticle formulations such as PLX038, a polyethylene glycol-conjugated ultra-long acting form of the TOP1i 7-ethyl-10- hydroxycamptothecin (SN-38), exhibit less marrow toxicity and greater efficacy than conventional TOP1is in preclinical cancer models. Our preliminary studies show that sustained release TOP1is, including PLX038, are active against five of seven PARPi-resistant ovarian cancer patient-derived xenografts (PDXs) tested. Moreover, using a unique antibody that detects TOP1-DNA covalent complexes (TOP1ccs), which are intermediates in the TOP1i-induced killing process, we have shown that TOP1ccs are diminished or undetectable in PDXs that are resistant to the TOP1i/PARPi combination, providing a starting point for understanding ovarian cancer resistance to this treatment. Collectively, these results lead to the hypothesis that a readily identifiable subset of HR- proficient ovarian cancers will exhibit sustained antitumor effects when treated with a next generation TOP1i alone or in combination with a PARPi. To test this hypothesis, we now propose to i) assess the efficacy of PLX038, alone and in combination with the PARPi rucaparib, in a cohort of genomically profiled high grade serous ovarian cancer PDXs with intrinsic or acquired resistance to single agent PARPis to identify the spectrum of ovarian cancers that could potentially benefit from PLX038 or the combination; ii) identify mechanisms of resistance to the TOP1i/PARPi combination in PDXs and cell lines; and iii) examine the association between the formation of drug-stabilized TOP1-DNA covalent complexes in tumor cells and the response of ovarian cancer patients to the PLX038/rucaparib combination in a phase II clinical trial. Collectively, these studies will not only provide insight into the genomic and biochemical factors that affect response to a 3rd generation TOP1i in ovarian cancer, but also determine whether it is possible to use PARPis as chemosensitizing agents in settings where they are no longer active as single agents. If successful, this project will point to a new therapy for the growing number of women with PARPi-resistant ovarian cancer.