Targeting Human Cancers with Hemizygous Deletion of TP53

 说明书(申请人提供)TP53是一种众所周知的肿瘤抑制基因，在大多数人类肿瘤中经常因突变或缺失而失活。人们已经做出了巨大的努力来恢复癌症治疗中的P53活性。然而，由于P53信号的复杂性，目前还没有有效的基于P53的治疗方法被成功地转化为临床癌症治疗。因此，识别TP53缺失或突变导致的易损性是针对人类癌症中P53突变的主要挑战。我们证明，TP53的基因组缺失经常包括邻近的必需基因，使具有半合子缺失的癌细胞容易受到这些基因的进一步抑制。POLR2A是一种在人类癌症中总是与TP53共缺失的基因。在53%的结直肠癌(CRC)、62%的乳腺癌、75%的卵巢癌和41%的胰腺癌中，TP53/POLR2A基因发生半合子缺失。POLR2A编码RNA聚合酶II复合体最大的催化亚基。它被α-Amanitin特异性地抑制，Amanitin是一种在死亡帽蘑菇中发现的环状8-AA多肽毒素。POLR2A在结直肠癌中的表达水平与其基因拷贝数密切相关。抑制POLR2A以非p53依赖的方式选择性地抑制TP53半合子缺失的结直肠癌细胞的增殖、存活和致瘤潜能。以往α-Amanitin的临床应用因其肝脏毒性而受到限制。游离α-Amanitin通过与肝细胞特异性转运蛋白OATP1B3(10)相互作用，引起肝细胞的凋亡和坏死。然而，当α-Amanitin与抗体结合时，不再是OATP1B3的底物。因此，以α-Amanitin为基础的抗体药物结合物(ADC)是一种毒性显著降低的高效治疗药物。我们的研究表明，在POLR2A半合子缺失的人结直肠癌小鼠模型中，低剂量的α-Amanitin偶联的抗EPCAM(上皮细胞黏附分子)抗体可以导致肿瘤完全消退。该申请的临床前研究最近发表在《自然》杂志上，为未来的临床试验提供了基础。基于我们的工作，已经有关于启动临床试验的可能性的讨论。我们 提出在人类癌症中TP53的半合子缺失在正常细胞和癌细胞之间创造了一个治疗窗口，并且PORL2A是具有这种基因组改变的癌症的一个新的和可用药的靶点。

 DESCRIPTION (provided by applicant) TP53, a well-known tumor suppressor gene, is frequently inactivated by mutation or deletion in a majority of human tumors. A tremendous effort has been made to restore p53 activity in cancer therapies. However, no effective p53-based therapy has been successfully translated into clinical cancer treatment due to the complexity of p53 signaling. Therefore, identification of vulnerabilities conferred by TP53 deletion or mutation is a major challenge to target p53 aberrancy in human cancer. We demonstrate that genomic deletion of TP53 frequently encompasses neighboring essential genes, rendering cancer cells with hemizygous TP53 deletion vulnerable to further suppression of such genes. POLR2A is identified as such a gene that is always co-deleted with TP53 in human cancers. Hemizygous loss of TP53/POLR2A occurs in 53% of colorectal cancers (CRC), 62% of breast cancers, 75% of ovarian cancers, and 41% of pancreatic cancers. POLR2A encodes the largest and catalytic subunit of RNA polymerase II complex. It is specifically inhibited by α-Amanitin, a cyclic 8-aa peptide toxin found in the death cap mushroom (Amanita phalloides). POLR2A expression levels are tightly correlated with its gene copy numbers in human colorectal cancer (CRC). Suppression of POLR2A selectively inhibits proliferation, survival and tumorigenic potential of CRC cells with hemizygous TP53 loss in a p53- independent manner. Previous clinical applications of α-Amanitin have been limited due to its liver toxicity. Free α-Amanitin causes apoptosis and necrosis of hepatocytes by interacting with the hepatocyte-specific transporting protein OATP1B3 (10). However, α-Amanitin is no longer substrate for OATP1B3 when coupled to antibodies. Therefore, α-Amanitin-based antibody drug conjugates (ADCs) are highly effective therapeutic agents with significantly reduced toxicity. Our study has shown that low doses of α-Amanitin-conjugated anti- EpCAM (Epithelial Cell Adhesion Molecule) antibody lead to complete tumor regression in murine models of human CRC with hemizygous deletion of POLR2A. The preclinical studies in this application were recently published in Nature, which provide the foundation for future clinical trials. There is already discussion regarding the potential for initiation of a clinical trial based on our work. We propose that hemizygous deletion of TP53 in human cancers creates a therapeutic window between normal and cancer cells, and that PORL2A is a novel and druggable target in cancers with such genomic alterations.