CD45 Pretargeted Radioimmunotherapy for AML

描述(申请人提供)：传统化疗只能治愈25-45%的初诊急性髓系白血病(AML)患者和5%的复发AML患者。大剂量放化疗联合异基因干细胞移植(SCT)可将初诊AML的治愈率提高到50-60%，复发AML的治愈率提高到20%-30%，但显然需要改进治疗方法。我们小组先前已经证明将放射性标记的抗CD45单抗(Ab)整合到急性髓细胞白血病的SCT预适应方案中，但毒性仍然很高，对于新诊断的AML，治愈率仍然只有65%，对于复发的AML，直接使用放射性标记的抗hCD45单抗和SCT的治愈率仍然只有30%。在这项应用中，我们研究了一种新的方法，利用针对人hCD45的重组四价单链抗体-SA融合蛋白(ScFv)4SA，一个含有N-乙酰半乳糖胺的树状大分子“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”方法被认为是为了放大向AML细胞传递的辐射量，减少向肝、肺和其他正常器官传递的辐射量，并显著减轻输液相关的毒性。在目标1中，我们将研究抗hCD45(ScFv)4SA融合蛋白和放射性生物素在裸鼠和SCID小鼠白血病移植瘤中的药代动力学和生物分布，并比较预靶向RIT和常规抗CD45 RIT的生物分布、毒性、疗效和剂量学。在目标2中，我们将使用针对小鼠mCD45的抗体和(ScFv)4SA融合蛋白，在严格的同基因小鼠白血病模型中比较常规试剂盒和预靶向RIT的相对优点。在目标3中，我们将使用一系列定量伽马相机成像、采血、活组织检查、放射自显影和尸检来评估针对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。在目标4中，我们将为抗人CD45(ScFv)4SA融合蛋白建立一个主细胞库，并生产、纯化和鉴定足够的材料，以启动AML前靶向方法的I期和II期临床试验。我们假设，与传统的RIT相比，本方案中定义的预靶向策略将改善吸收辐射的肿瘤与正常器官的比率，从而以比目前可行的更低的毒性提高应答率和反应持续时间。我们预计这些临床前实验的结果将迅速转化为我们针对人类AML的临床RIT计划。

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.