Foundations of Pretargeted Radioimmunotherapy

描述（由申请人提供）：向肿瘤提供细胞杀伤剂量的电离辐射是抗体定向放射免疫治疗（RIT）的目标。然而，在实践中，对健康骨髓和肾脏的附带损害限制了最大放射剂量。预靶向RIT （PRIT）旨在通过分离肿瘤靶向和放射性核素递送的药代动力学来克服这一限制。这项重新提交的更新提案的总体观点是，PRIT的原理是合理的，但为了充分发挥其潜力，蛋白质靶向剂必须优化，肿瘤穿透的药代动力学必须经过严格的工程分析。该项目汇集了生物工程和核医学的教师，共同开发基本试剂和剂量策略，以使PRIT发挥最大的作用。在之前的项目期间，双特异性抗体（bsAbs）被设计为对螯合金属离子和肿瘤抗原（特别是结直肠癌抗原A33或CEA）具有皮摩尔亲和力。提出了新的数据，证明了bsab的稳健表达和溶解度特性。在小鼠异种移植物模型中的生物分布研究有助于建立预靶向给药策略优化的参数。理论分析提供了抗体结合、扩散、内吞摄取、毛细血管外渗和全身清除之间平衡的预测，这些平衡共同决定了抗体进入肿瘤的距离。这个本质上完整的肿瘤微分布理论不仅局限于PRIT，而且对所有基于抗体的治疗都很重要。在下一个项目期间，将在数学建模的指导下，优化肿瘤移植小鼠的PRIT方案。关键变量为肿瘤抗原选择（A33 vs. CEA）；双特异性抗体的起始剂量；血池阻断/清除剂的剂量；使用清除剂和随后使用放射性金属螯合物的等待时间；以及放射性金属螯合物的大剂量。在抗体肿瘤摄取方面的进一步改进将通过蛋白质工程方法来追求。为评价异种肿瘤移植小鼠的毒性和抗肿瘤效果增加了新的目的。通过强调原则而不是临时的经验修补，这些研究旨在为发展PRIT建立坚实的科学基础。这样制定的方法应该更容易推广。该项目势头强劲，有才华的研究生充分参与到每个具体目标的工作中。

DESCRIPTION (provided by applicant): Delivery of cell-killing doses of ionizing radiation to tumors is the objective of antibody-directed radioimmunotherapy (RIT). In practice, however, collateral damage to healthy bone marrow and kidneys limits the maximum delivered radiation dose. Pretargeted RIT (PRIT) aims to overcome this limitation by separating the pharmacokinetics of tumor targeting and radionuclide delivery. The overarching perspective of this resubmitted renewal proposal is that the principle of PRIT is sound, but that to reach its full potential the protein targeting agents must be optimized, and the pharmacokinetics of tumor penetration must be subjected to rigorous engineering analysis. This project brings together faculty from Biological Engineering and Nuclear Medicine to collaboratively develop essential reagents and dosing strategies to enable PRIT to be maximally effective. In the previous project period, bispecific antibodies (bsAbs) were engineered with picomolar affinity both to chelated metal ions and to tumor antigens (specifically, the colorectal carcinoma antigens A33 or CEA). New data is presented that demonstrates the robust expression and solubility characteristics of the bsAbs. Biodistribution studies in mouse xenograft models helped establish the parameters for the proposed optimization of pretargeting dosing strategies. Theoretical analyses have provided predictions of the balances amongst antibody binding, diffusion, endocytic uptake, capillary extravasation, and systemic clearance that together determine how far antibodies reach into tumors. This essentially complete tumor microdistribution theory is not limited to PRIT, but is salient for all antibody-based therapeutics. In the next project period, PRIT protocols will be optimized in tumor-xenografted mice, guided by mathematical modeling. Key variables are tumor antigen choice (A33 vs. CEA); bolus dose of the bispecific antibody; bolus dose of a blood pool blocking/clearing agent; waiting time for administration of the clearing agent and subsequent radiometal chelate administration; and bolus dose size of the radiometal chelate. Further improvements in antibody tumor uptake will be pursued by protein engineering methods. A new aim has been added to evaluate toxicity and anti-tumor efficacy in tumor-xenografted mice. By emphasizing principles over ad hoc empirical tinkering, these studies are aimed at establishing a firm scientific foundation from which to develop PRIT. The approaches thus developed should be more readily generalizable. The project has strong momentum and talented graduate students fully engaged in work on each of the Specific Aims.