Defining the Role of Affinity in Antibody-Based Tumor Targeting and Penetration

描述(由申请人提供)：由于最近在一些恶性肿瘤中证明了它们的有效性，单抗在癌症治疗中正变得越来越重要。大多数开发基于抗体的新分子的努力都集中在识别那些与肿瘤抗原具有最高亲和力的分子上。使用与HER2的同一表位亲和力从1x10-7M到1x10-11M的小的单链抗体(ScFv)分子。我们表明，高亲和力可能会削弱抗体穿透实体肿瘤的能力，导致血管周围定位和潜在的次优治疗效果。这项工作证实了温斯坦提出的“结合部位屏障”假说，即亲和力非常高的抗体穿透实体肿瘤的能力将受到限制。我们早期工作的一个局限性是ScFv会迅速从循环中消除，从而限制了研究肿瘤随时间渗透的能力。我们最近已经产生了上述scFv分子的全长IgG版本，并能够阐明亲和力在肿瘤靶向和渗透中的作用，并确定这一过程的潜在机制。初步数据表明，高亲和力也削弱了Ig对肿瘤的靶向性和穿透性。这一假设是：1)对肿瘤抗原具有很高亲和力的免疫球蛋白分子对实体瘤的穿透能力降低；2)高亲和力抗体对实体瘤穿透能力受限的主要机制是肿瘤细胞的内化和降解；3)低亲和力的免疫球蛋白分子在介导抗肿瘤作用方面可能优于高亲和力抗体。我们将评估结合亲和力、抗原脱落、抗原/单抗内化和正常组织抗原表达对抗HER2单抗的肿瘤靶向性和肿瘤穿透性的影响。我们还将确定亲和力的变化以及随之而来的对肿瘤靶向性和渗透性的影响，是否会影响非偶联抗肿瘤单抗的抗肿瘤效果，从而为指导未来抗肿瘤单抗的合理发展提供信息。这项研究直接关系到公共卫生，因为它将指导癌症治疗新抗体的开发。了解抗体与肿瘤细胞表面靶标的结合强度(亲和力)如何影响抗体进入肿瘤并杀死肿瘤细胞的能力，将使我们能够创造更有效的基于抗体的癌症治疗方法。

DESCRIPTION (provided by applicant): Due to their recent demonstration of efficacy in a number of malignancies, monoclonal antibodies (MAb) are becoming increasingly important in cancer therapy. Most efforts to develop new antibody-based molecules are focused on identifying those with the highest possible affinity for the tumor antigen. Using small, single- chain Fv (scFv) molecules that ranged in affinity for the same epitope of HER2 from 1x10-7 M to 1x10-11 M. We showed that high affinity may impair the ability of an antibody to penetrate into a solid tumor, leading to perivascular localization and potential suboptimal therapeutic efficacy. This work validated a "Binding Site Barrier" hypothesis posed by Weinstein that stated that antibodies of very high affinity would be limited in their ability to penetrate solid tumors. A limitation of our earlier work was that scFv are rapidly eliminated from the circulation, thus limiting the ability to study tumor penetration over time. We have recently generated full-length IgG versions of the scFv molecules described above and are in the position to elucidate the role of affinity in tumor targeting and penetration and determine the mechanisms underlying this process. Preliminary data indicate that high affinity also detracts from tumor targeting and penetration of Ig. The hypotheses underlying this proposal are that 1) IgG molecules with very high affinity for tumor antigen will demonstrate a reduced ability to penetrate into solid tumors, 2) a major mechanism behind the restricted penetration of high affinity antibodies into solid tumors is the internalization and degradation by tumor cells and 3) lower affinity IgG molecules may be superior to higher affinity antibodies in mediating anti-tumor effects. We will evaluate the roles of binding affinity, antigen shedding, antigen/MAb internalization and normal tissue antigen expression on the tumor targeting and tumor penetration of anti-HER2 MAbs. We will also determine if changes in affinity and the attendant impacts on tumor targeting and penetration, influence the anti-tumor efficacy of unconjugated anti-tumor MAbs, thereby providing information that can help guide future rational development of anti-tumor MAbs. This research is directly relevant to public health, as it will guide the development of new antibodies for the treatment of cancer. Learning how the binding strength (affinity) of an antibody for its target on the tumor cell surface affects the ability of the antibody to move into the tumor and kill tumor cells will allow us to create more effective antibody-based treatments for cancer.