Foundations of Pretargeted Radioimmunotherapy

描述(申请人提供)：将电离辐射的细胞杀伤量输送到肿瘤是抗体导向放射免疫疗法(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辐射剂量。前靶向RIT(PRIT)旨在通过分离肿瘤靶向和放射性核素传递的药代动力学来克服这一限制。这份重新提交的更新提案的主要观点是，PRIT的原则是合理的，但为了充分发挥其潜力，必须优化蛋白质靶向制剂，并且必须对肿瘤渗透的药代动力学进行严格的工程分析。该项目汇集了生物工程和核医学的教员，共同开发必要的试剂和剂量策略，使PRIT发挥最大的效果。在之前的项目期间，双特异性抗体(BsAbs)被设计成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。给出了新的数据，证明了bsAbs的稳健表达和溶解特性。小鼠异种移植模型中的生物分布研究有助于为所提出的优化预靶向给药策略建立参数。理论分析提供了抗体结合、扩散、内吞、毛细血管外溢和全身清除之间的平衡预测，这些平衡共同决定了抗体进入肿瘤的程度。这一基本上完整的肿瘤微分布理论不仅限于PRIT，而且对所有基于抗体的疗法都是显著的。在下一个项目期间，PRIT方案将在数学建模的指导下，在移植肿瘤的小鼠中进行优化。关键变量是肿瘤抗原选择(A33 vs.CEA)；双特异性抗体的推注剂量；血池阻断/清除剂的推注剂量；清除剂和随后的放射性金属螯合物注射的等待时间；以及放射性金属螯合物的推注剂量大小。蛋白质工程方法将进一步改善抗体对肿瘤的摄取。一个新的目标是评估对移植瘤小鼠的毒性和抗肿瘤效果。通过强调原则而不是特别的经验修修补补，这些研究的目的是建立一个坚实的科学基础，以此为基础来开发PRIT。这样制定的方法应该更容易推广。该项目有强大的势头，有才华的研究生充分投入到每一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.