Unravel the role of CD276 and determine efficacy of CD276-targeted therapy on Merkel cell carcinoma progression and metastasis

默克尔细胞癌（MCC）是一种侵袭性皮肤神经内分泌癌， 晚期疾病的存活率低于18%，死亡率比黑素瘤高3倍。MCC 不成比例地，主要影响65岁以上的白人男性，他们在 退伍军人中已确诊5000多例新的MCC病例。因此，MCC有一个 对退伍军人健康和VA医疗保健系统的影响越来越大。尽管免疫疗法获得批准， 治疗转移性MCC仍然是一个挑战。因此，我们不得不寻求新的疗法来克服 耐药性，或作为由于以下原因不适合免疫治疗的MCC患者的确定性治疗 合并症。 在本提案中，我们将与遇到大多数退伍军人MCC患者的VA医疗中心合作， 定义B7-H3（由CD276编码）在大型退伍军人患者队列中MCC患者生存中的作用。 此外，我们将确定CD276靶向治疗的疗效，因为它的过表达与CD276靶向治疗相关。 在包括MCC在内的无数晚期人类癌症中结果不佳。我们的合作者圣克鲁瓦博士 美国国家癌症研究所开发了一种新的抗体-药物缀合物（ADC，m276-SL-PBD）， CD276抗体与细胞毒性DNA结合剂PBD。值得注意的是，m276-SL-PBD赋予稳健的抗肿瘤活性。 在一系列临床前模型中，包括我们的MCC细胞系衍生的异种移植物中， (CDX)模型（导致本提案的初步数据）。值得注意的是，m276-SL-PBD有效地防止了 通过直接根除异质癌细胞，包括癌症干细胞、肿瘤血管 和肿瘤间质细胞，其中CD276上调被赋予。因此，我们假设m276-SL-PBD是 一种具有持续反应的上级抗MCC药物，强调了MCC的新治疗进展。 为了克服障碍，我们成功建立了MCC临床前的独特而强大的模型， 研究包括多种原代MCC细胞系、CDX和患者肿瘤来源的异种移植物（PDX）模型， 重建人体免疫系统为了模拟临床情况，我们首先建立了人类转移性肿瘤， 小鼠皮下接种后具有自发内脏播散倾向的MCC细胞系。 由于其有限的资源，我们将利用基于单小鼠测试（SMT）的PDX试验策略， 越来越多地用于更好地捕获肿瘤间异质性，并产生高度临床相关的临床前 证据基于SMT的研究的成本效益允许涵盖大型肿瘤患者队列 并评估患者之间的异质性药物效应，这在罕见癌症中特别重要 临床前研究，包括MCC。 因此，利用我们非常强大的患者MCC衍生模型，我们处于理想的位置， 拟定的研究：1）确定m276-SL-PBD的安全性、疗效和直接药物作用， 鉴定MCC CDX模型和转移模型中治疗反应的生物标志物; 2）确定 m276-SL-PBD的治疗功效及其对一组PDX小鼠中MCC肿瘤微环境的影响 模型; 3）确定CD276对退伍军人患者MCC存活率的影响。调查结果将在近期 通过为包括VA医疗保健系统在内的立即确证性临床试验奠定基础， 最终改善退伍军人患这种致命皮肤癌的机会。

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine cancer of the skin with a dismal five-year survival rate of less than 18% in advanced disease and a mortality rate 3-times higher than melanoma. MCC disproportionately and predominantly affects Caucasian males older than 65, who are well represented among Veterans, and more than 5000 new MCC cases have been diagnosed among Veterans. Hence, MCC has a growing impact on Veterans’ health and VA healthcare system. Notwithstanding the approval of immunotherapy, treating metastatic MCC remains a challenge. Thus, we are compelled to seek novel therapies to overcome resistance, or to serve as definitive treatments for MCC patients who are ineligible for immunotherapy due to comorbidities. In this proposal, we will collaborate with VA Medical Centers encountering most Veteran MCC patients to define the role of B7-H3 (encoded by CD276) in MCC patient survival in a large cohort of Veteran patients. Moreover, we will determine the efficacy of CD276-targeted therapy, as its overexpression has been associated with poor outcome in a myriad of advanced human cancer including MCC. Our collaborator, Dr. St. Croix at the National Cancer Institute, has developed a novel antibody-drug conjugate (ADC, m276-SL-PBD), which couples CD276 antibody with a cytotoxic DNA-binding agent PBD. Notably, m276-SL-PBD confers robust anti-tumor activities and long-term durability in a range of preclinical models, including our MCC cell line-derived xenograft (CDX) models (preliminary data leading to this proposal). Remarkably, m276-SL-PBD effectively prevents resistance by directly eradicating heterogenous cancer cells including cancer stem cells, tumor vasculatures and tumor stromal cells, where CD276 upregulation is endowed. Therefore, we postulate that m276-SL-PBD is a superior anti-MCC drug with sustainable response, underscoring a novel therapeutic advance in MCC. To overcome barriers, we have successfully established unique and robust models for MCC preclinical studies including multiple primary MCC cell lines, CDX, and patient tumor-derived xenograft (PDX) models with reconstituted human immune system. To simulate clinical scenario, we have first established human metastatic MCC cell lines with propensity for spontaneous visceral dissemination after subcutaneous inoculation in mice. Due to its finite resource, we will utilize single mouse testing (SMT)-base PDX trial strategies that are increasingly used to better capture inter-tumor heterogeneity and generate highly clinically relevant preclinical evidence. The cost-effectiveness of SMT-based studies allow to encompass a large cohort of patient tumors and evaluate heterogeneous drug effects across patients, which is of particular importance in rare cancer preclinical studies including MCC. Hence leveraging our singularly powerful patient MCC-derived models, we are ideally positioned to pursue proposed studies: 1) to determine safety, therapeutic efficacy, and direct drug effects of m276-SL-PBD and identify biomarkers for treatment response in MCC CDX models and metastatic models; 2) to determine therapeutic efficacy of m276-SL-PBD and its effects on MCC tumor microenvironment in a panel of PDX mouse models; 3) to define the impact of CD276 in MCC survival in Veteran patients. Findings will have near-term impact by setting the stage for an immediate confirmatory clinical trial inclusive of VA healthcare systems to ultimately improve access for Veterans suffering from this deadly skin cancer.