Foundations of Pretargeted Radioimmunotherapy

描述（由申请方提供）：向肿瘤递送细胞杀伤剂量的电离辐射是抗体导向放射免疫治疗（RIT）的目的。然而，在实践中，对健康骨髓和肾脏的附带损害限制了最大的辐射剂量。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。 该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，必须优化蛋白质靶向剂，并且必须对肿瘤渗透的药代动力学进行严格的工程分析。该项目汇集了来自生物工程和核医学的教师，共同开发必要的试剂和剂量策略，使PRIT能够最大限度地发挥作用。 在之前的项目期间，双特异性抗体（bsAb）被工程化为对螯合金属离子和肿瘤抗原（具体地，结肠直肠癌抗原A33或CEA）具有皮摩尔亲和力。提供了新的数据，其证明了bsAb的稳健表达和溶解性特征。在小鼠异种移植模型中的生物分布研究有助于建立所提出的优化预靶向给药策略的参数。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的平衡的预测，这些平衡共同决定了抗体到达肿瘤的程度。这种基本上完整的肿瘤微分布理论并不限于PRIT，而是对所有基于抗体的疗法都很重要。 在下一个项目期间，PRIT方案将在数学建模的指导下在肿瘤异种移植小鼠中进行优化。关键变量是肿瘤抗原选择（A33相对于CEA）;双特异性抗体的推注剂量;血池阻断/清除剂的推注剂量;给予清除剂和随后的放射性金属螯合物给予的等待时间;和放射性金属螯合物的推注剂量大小。抗体肿瘤摄取的进一步改善将通过蛋白质工程方法来追求。增加了一个新的目标，以评估肿瘤异种移植小鼠的毒性和抗肿瘤疗效。 通过强调原则而不是临时的经验修补，这些研究的目的是建立一个坚实的科学基础，从发展PRIT。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每一个具体目标的工作。 公共卫生相关性：该项目汇集了来自生物工程和核医学的教师，以优化有毒辐射对肿瘤的输送。该方法的原理被称为“预靶向”，其中工程蛋白质在肿瘤内积累，随后捕获随后施用的放射性金属。数学建模和蛋白质生物技术是该项目的重要组成部分。

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. PUBLIC HEALTH RELEVANCE: This project brings together faculty from Biological Engineering and Nuclear Medicine to optimize delivery of toxic radiation to tumors. The principle of the method is termed "pretargeting", in which engineered proteins accumulate within tumors and subsequently capture radioactive metals administered later. Mathematical modeling and protein biotechnology are essential components of the project.