Targeting Human Cancers with Hemizygous Deletion of TP53

 描述（由申请人提供）TP 53是一种众所周知的肿瘤抑制基因，在大多数人肿瘤中经常由于突变或缺失而失活。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信号传导的复杂性，没有有效的基于p53的疗法已经成功地转化为临床癌症治疗。因此，识别由TP 53缺失或突变赋予的脆弱性是靶向人类癌症中的p53异常的主要挑战。我们证明，TP 53的基因组缺失经常包括邻近的必需基因，使癌细胞与半合子TP 53缺失易受进一步抑制的这些基因。POLR 2A被鉴定为在人类癌症中总是与TP 53共缺失的基因。TP 53/POLR 2A的半合子丢失发生在53%的结直肠癌（CRC）、62%的乳腺癌、75%的卵巢癌和41%的胰腺癌中。POLR 2A编码RNA聚合酶II复合物的最大催化亚基。它被α-鹅膏毒肽特异性抑制，α-鹅膏毒肽是一种在死帽蘑菇（鹅膏菌）中发现的环状8-aa肽毒素。POLR 2A在人结直肠癌（CRC）中的表达水平与其基因拷贝数密切相关。P0 LR 2A的抑制以p53非依赖性方式选择性地抑制具有半合子TP 53缺失的CRC细胞的增殖、存活和致瘤潜力。由于α-鹅膏蕈碱的肝毒性，其先前的临床应用受到限制。游离α-鹅膏毒肽通过与肝细胞特异性转运蛋白OATP 1B 3相互作用导致肝细胞凋亡和坏死（10）。然而，当与抗体偶联时，α-鹅膏蕈碱不再是OATP 1B 3的底物。因此，基于α-鹅膏菌素的抗体药物缀合物（ADC）是具有显著降低的毒性的高效治疗剂。我们的研究已经表明，低剂量的α-鹅膏菌素缀合的抗EpCAM（上皮细胞粘附分子）抗体导致具有POLR 2A半合子缺失的人CRC的鼠模型中的完全肿瘤消退。该应用中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。已经有关于基于我们的工作启动临床试验的可能性的讨论。我们 提出人类癌症中TP 53的半合子缺失在正常细胞和癌细胞之间产生了治疗窗口，并且PORL 2A是具有这种基因组改变的癌症中的新的可药用靶标。

 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.