Molecular Immunology Unit, Hospital Universitario Puerta de Hierro Majadahonda, 28222 Majadahonda, Madrid, Spain.
Proc Natl Acad Sci U S A. 2013 Aug 20;110(34):13791-6. doi: 10.1073/pnas.1300013110. Epub 2013 Aug 5.
Antibody cancer therapies rely on systemically accessible targets and suitable antibodies that exert a functional activity or deliver a payload to the tumor site. Here, we present proof-of-principle of in vivo selection of human antibodies in tumor-bearing mice that identified a tumor-specific antibody able to deliver a payload and unveils the target antigen. By using an ex vivo enrichment process against freshly disaggregated tumors to purge the repertoire, in combination with in vivo biopanning at optimized phage circulation time, we have identified a human domain antibody capable of mediating selective localization of phage to human prostate cancer xenografts. Affinity chromatography followed by mass spectrometry analysis showed that the antibody recognizes the proteasome activator complex PA28. The specificity of soluble antibody was confirmed by demonstrating its binding to the active human PA28αβ complex. Whereas systemically administered control phage was confined in the lumen of blood vessels of both normal tissues and tumors, the selected phage spread from tumor vessels into the perivascular tumor parenchyma. In these areas, the selected phage partially colocalized with PA28 complex. Furthermore, we found that the expression of the α subunit of PA28 [proteasome activator complex subunit 1 (PSME1)] is elevated in primary and metastatic human prostate cancer and used anti-PSME1 antibodies to show that PSME1 is an accessible marker in mouse xenograft tumors. These results support the use of PA28 as a tumor marker and a potential target for therapeutic intervention in prostate cancer.
抗体癌症疗法依赖于可系统获得的靶点和合适的抗体，这些抗体能够在肿瘤部位发挥功能活性或传递有效载荷。在这里，我们提出了在荷瘤小鼠中体内选择人抗体的原理验证，鉴定了一种能够传递有效载荷的肿瘤特异性抗体，并揭示了靶抗原。通过使用针对新鲜分离的肿瘤的体外富集过程来清除库，结合优化的噬菌体循环时间的体内生物淘选，我们已经鉴定出一种能够介导噬菌体对人前列腺癌异种移植物选择性定位的人源单域抗体。亲和层析和质谱分析表明，该抗体识别蛋白酶体激活复合物 PA28。通过证明其与活性人 PA28αβ 复合物结合，证实了可溶性抗体的特异性。而系统给予的对照噬菌体局限于正常组织和肿瘤血管的管腔中，所选噬菌体从肿瘤血管扩散到血管周围的肿瘤实质中。在这些区域，所选噬菌体与 PA28 复合物部分共定位。此外，我们发现蛋白酶体激活复合物亚单位 1（PSME1）的α亚基在原发性和转移性人前列腺癌中的表达升高，并使用抗 PSME1 抗体表明 PSME1 是小鼠异种移植肿瘤中可及的标志物。这些结果支持将 PA28 用作肿瘤标志物和前列腺癌治疗干预的潜在靶点。
