Transcriptomic mechanisms underlying the immune modulating function and therapeutic efficacy of PARP inhibitors

免疫调节功能和治疗效果的转录组学机制 PARP抑制剂 聚（ADP-核糖）聚合酶（PARP）抑制剂（PARPis）被批准用于治疗卵巢癌， 以及BRCA 1或BRCA 2（BRCA 1/2）突变的乳腺癌和胰腺癌。我们目前的理解是， PARPis的主要作用机制之一是通过合成杀伤力，特别是在 具有同源重组修复缺陷（“BRCAness”）的癌症。虽然PARP 1介导的PAR化是 作为基因转录的重要调节因子，PARPi诱导的转录组学变化仍不清楚 有助于其治疗效果。虽然我们的临床前和临床研究评估PARPis联合 程序性细胞死亡配体1（PD-L1）/PD-1抑制剂（PD-1/L1 is）在 在不同的癌症中，患者之间的反应是异质的，令人惊讶的是， 这种组合的益处与已知的PARPis预测生物标志物（如BRCA 1/2）无关 突变这些数据表明PARPis的免疫调节功能可能不同于或 独立于现有的“BRCAness”范例，其是PARPis治疗功效的基础。 为了确定PARPis免疫调节功能的分子机制，我们利用 单细胞RNA测序，以评估PARPis对肿瘤细胞和肿瘤细胞的转录组学影响 免疫微环境令人惊讶的是，我们发现PARPi诱导的PARP 1对DNA的捕获可能 上调B7-H3（CD 276），一种关键的免疫检查点蛋白。根据我们的初步研究， 假设PARPis通过捕获B7-H3基因转录调节癌细胞内在B7-H3表达， PARP 1蛋白与B7-H3启动子区域的连接，这可能是PARP 1蛋白与B7-H3启动子区域的关键调控节点。 PARP的免疫调节功能和治疗效果。我们将使用细胞和动物模型，以及 来自基于PARPi的治疗的临床试验的患者样本来检验该假设。我们将测试三个目标： 目的1：确定PARP转录诱导癌细胞内源性B7-H3的机制 通过PARP 1-染色质捕获表达。目的2：确定B7-H3是否作为关键调控节点发挥作用 PARP在临床前动物模型中的免疫调节功能和功效。目标3： PARPi诱导的B7-H3表达作为确定PARPi作为免疫调节剂的功效的生物标志物 通过分析来自多个临床试验的患者肿瘤和血液样本，我们认为我们的建议 是高度创新的，因为它填补了我们对PARPis治疗效果的知识的关键空白， 免疫调节剂通过转录调控，这超出了目前的机制， PARPis的范例。如果成功，我们的研究将对扩大临床 PARPis作为免疫调节剂的应用，其通过促进抗肿瘤免疫和增强 免疫治疗的功效。这也可能导致合理的PARPi组合的临床开发， B7-H3抑制剂和/或PD-1/L1 i，这取决于个体患者肿瘤的免疫特征。

Transcriptomic mechanisms underlying the immune modulating function and therapeutic efficacy of PARP inhibitors Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPis) are approved for the treatment of ovarian cancer, as well as BRCA1 or BRCA2 (BRCA1/2) mutant breast and pancreatic cancers. Our current understanding is that one of the main mechanisms responsible for the efficacy of PARPis is through synthetic lethality, specifically in cancers with homologous recombination repair defects (‘BRCAness’). While PARP1-mediated PARylation is an essential regulator of gene transcription, it remains unknown how PARPi-induced transcriptomic changes contribute to its therapeutic efficacy. While our preclinical and clinical studies assessing PARPis in combination with programmed cell death-ligand 1 (PD-L1)/PD-1 inhibitors (PD-1/L1is) showed durable responses in different cancers, the responses were heterogeneous between patients, and surprisingly, the therapeutic benefit of this combination did not correlate with known predictive biomarkers for PARPis, such as BRCA1/2 mutations. These data suggest that the immunomodulating function of PARPis may be different from or independent of the existing ‘BRCAness’ paradigm underlying the therapeutic efficacy of PARPis. To determine the molecular mechanisms underlying the immunomodulating function of PARPis, we utilized single-cell RNA sequencing to assess the transcriptomic impact of PARPis on tumor cells and the tumor immune microenvironment. Surprisingly, we identified that PARPi-induced PARP1-trapping to DNA may upregulate B7-H3 (CD276), a key immune checkpoint protein. Based on our preliminary studies, we hypothesize that PARPis transcriptionally regulate cancer-cell intrinsic B7-H3 expression by trapping the PARP1 protein to the B7-H3 promoter region, which may serve as a key regulatory node for the immunomodulating function and therapeutic efficacy of PARPis. We will use cell and animal models, as well as patient specimens from clinical trials of PARPi-based therapies to test this hypothesis. We will test three aims: Aim 1: Determine mechanisms by which PARPis transcriptionally induce cancer cell intrinsic B7-H3 expression through PARP1-chromatin trapping. Aim 2: Determine if B7-H3 functions as a key regulatory node for the immunomodulating function and efficacy of PARPis in preclinical animal models. Aim 3: Validate PARPi-induced B7-H3 expression as a biomarker in determining the efficacy of PARPis as immunomodulating agents by analysing patient tumor and blood samples from multiple clinical trials. We believe that our proposal is highly innovative because it fills key gaps in our knowledge of the therapeutic efficacy of PARPis as immunomodulating agents through transcriptional regulation, which goes beyond the current mechanistic paradigm of PARPis. If successful, our study will have a significant impact on expanding the clinical applications of PARPis as immunomodulating agents by promoting antitumor immunity and enhancing the efficacy of immunotherapy. This may also lead to the clinical development of rational PARPi combinations with an B7-H3 inhibitor and/or a PD-1/L1i, depending on the immune characteristics of the individual patient tumor.