CD45 Pretargeted Radioimmunotherapy for AML

描述（由申请人提供）：常规化疗治愈率仅为25-45%的新诊断急性髓性白血病（AML）患者和<5%的复发性AML患者。同种异体干细胞移植（SCT）的高剂量放化疗将新诊断的AML的治愈率提高到50-60%，对复发的AML的治愈率提高到20-30%，然而，很明显需要改进治疗。我们的团队之前已经记录了将放射标记的抗CD45单克隆抗体（Ab）纳入AML的SCT调节方案的前景，但毒性仍然很高，对于新诊断的AML，使用直接放射标记的抗hcd45 Ab和SCT的治愈率仍然只有65%，对于复发的AML，治愈率仍然低于30%。在这项应用中，我们研究了一种新的方法，利用重组四价单链抗体- sa融合蛋白（scFv）4SA，靶向人hCD45（一种树突状n -乙酰半乳糖胺“清除剂”和放射性标记的dota生物素），为AML提供放射免疫治疗（RIT）。这种多步骤的抗CD45“预靶向”方法被假设可以放大传递到AML细胞的辐射量，减少传递到肝脏、肺和其他正常器官的辐射量，并显着减弱输注相关的毒性。在Aim 1中，我们将研究抗hcd45 (scFv)4SA融合蛋白和放射生物素在胸腺和SCID小鼠模型白血病异种移植物中的药代动力学和生物分布，并将比较预先靶向RIT与传统抗cd45 RIT的生物分布、毒性、疗效和剂量。在Aim 2中，我们将比较传统KIT和预靶向RIT在严格的同基因小鼠白血病模型中的相对优点，使用Aim 1中描述的方法，使用Ab和（scFv）4SA融合蛋白直接针对小鼠mCD45。在Aim 3中，我们将利用连续定量伽马相机成像、血液采样、活检、放射自显影和尸检，评估针对hCD45的（scFv）4SA和放射性生物素成分在非人灵长类动物（猕猴）中的安全性、药代动力学和生物分布。在Aim 4中，我们将为抗人CD45 (scFv)4SA融合蛋白生成一个主细胞库，并生产、纯化和表征足够的材料，以启动AML预靶向方法的I期和II期临床试验。我们假设，与传统的RIT相比，本提案中定义的预靶向策略将提高肿瘤与正常器官吸收辐射的比率，从而提高反应率和反应持续时间，同时毒性比目前可行的要小。我们期望将这些临床前实验的结果快速转化为人类AML的临床RIT项目。

DESCRIPTION (provided by applicant): Conventional chemotherapy cures only 25-45% of patients with newly diagnosed acute myeloid leukemia (AML) and <5% of patients with relapsed AML. High dose chemoradiotherapy with allogeneic stem cell transplantation (SCT) improves the rates of cure to 50-60% for newly diagnosed AML and 20-30% for relapsed AML, however, it is clear that improved therapy is needed. Our group has previously documented the promise of incorporating radiolabeled anti- CD45 monoclonal antibodies (Ab) into SCT conditioning regimens for AML, but toxicity remains high and cure rates are still only 65% for newly diagnosed AML and <30% for relapsed AML using directly radiolabeled anti-hCD45 Ab and SCT. In this application, we investigate a novel approach to delivering radioimmunotherapy (RIT) for AML using a recombinant tetravalent single chain antibody-SA fusion protein, (scFv)4SA, directed against human hCD45, a dendrimeric N-acetylgalactosamine-containing "clearing agent" and radiolabeled-DOTA-biotin. This multi-step anti- CD45 "pretargeting" approach is hypothesized to amplify the amount of radiation delivered to AML cells, decrease the amount of radiation delivered to the liver, lungs, and other normal organs, and markedly attenuate infusion-related toxicities. In Aim 1, we will investigate the pharmacokinetics and biodistributions of an anti-hCD45 (scFv)4SA fusion protein and radiobiotin in leukemia xenografts in athymic and SCID mouse models and will compare the biodistributions, toxicities, efficacies and dosimetries achieved with pretargeted RIT with those using conventional anti-CD45 RIT. In Aim 2, we will compare the relative merits of conventional KIT and pretargeted RIT in a rigorous, syngeneic murine leukemia model using an Ab and an (scFv)4SA fusion protein directed against murine mCD45 using the approaches described in Aim 1. In Aim 3, we will evaluate the safety, pharmacokinetics, and biodistributions of both the (scFv)4SA directed to hCD45 and the radiobiotin component in non-human primates (macaques), using serial quantitative gamma camera imaging, blood sampling, biopsies, radioautography, and necropsy. In Aim 4, we will generate a Master Cell Bank for the anti-human CD45 (scFv)4SA fusion protein and produce, purify and characterize sufficient material to initiate Phase I & II clinical trials of the pretargeting approach in AML. We hypothesize that the pretargeting strategies defined in this proposal will improve the tumor-to-normal organ ratios of absorbed radiation compared with conventional RIT, allowing improvement in response rates and response durations with less toxicity than is currently feasible. We anticipate rapid translation of the results of these preclinical experiments into our clinical RIT program for human AML.