Lu Yingjuan, Low Philip S
Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette, IN 47907, USA.
Cancer Immunol Immunother. 2002 May;51(3):153-62. doi: 10.1007/s00262-002-0266-6. Epub 2002 Mar 19.
A variety of human cancers overexpress a cell surface receptor with high affinity for the vitamin, folic acid ( K(d) approximately 10(-10)M). Covalent attachment of therapeutic agents to folic acid has been shown to allow efficient targeting of the folate-drug conjugates to folate receptor-expressing cancer cells, with little or no uptake by normal tissues except the kidneys. We report here the use of folate's ability to deliver attached molecules specifically to cancer cells to convert poorly immunogenic tumors into highly immunogenic tissue targets. By linking folic acid to a model hapten, we have been able to decorate folate receptor-expressing cancer cell surfaces with >10(6) haptens/cell in vivo. Following marking of such cells with haptens, the cells are observed to become opsonized with autologous anti-hapten antibodies, which is presumed to mediate cell removal via antibody-dependent cellular cytotoxicity (ADCC). Supplemental administration of low levels of ADCC-activating cytokines [e.g. interleukin-2 (IL-2) and interferon-alpha (IFN-alpha)] has been shown to synergize with the folate-targeted immunotherapy. Thus, using M109 syngeneic lung cancer cells injected intraperitoneally into Balb/c mice that were previously immunized against fluorescein, a significant extension of life span is observed following treatment with folate-fluorescein conjugates, and complete cures are observed upon supplementation with moderate levels of IL-2 and IFN-alpha. Because control tumor-bearing mice treated with the same cytokines but with non-targeted fluorescein show no extension of life span, we conclude that tumor-specific opsonization is an essential step in this immunotherapy. Finally, because the anti-fluorescein antibodies are unable to access the folate receptors on the apical membranes of the kidney proximal tubules, no kidney or other normal tissue cytotoxicity is observed. These data suggest that retargeting of haptens to folate receptor-expressing cancers might constitute a method for mobilizing the immune system specifically against poorly immunogenic tumors.
多种人类癌症过度表达一种对维生素叶酸具有高亲和力的细胞表面受体（解离常数K(d)约为10(-10)M）。已证明将治疗剂与叶酸共价连接可使叶酸 - 药物偶联物有效地靶向表达叶酸受体的癌细胞，除肾脏外正常组织几乎不摄取或不摄取。我们在此报告利用叶酸将附着分子特异性递送至癌细胞的能力，将免疫原性差的肿瘤转化为高免疫原性的组织靶点。通过将叶酸与一种模型半抗原连接，我们已能够在体内用>10(6)个半抗原/细胞修饰表达叶酸受体的癌细胞表面。在用半抗原标记此类细胞后，观察到细胞被自体抗半抗原抗体调理，推测这通过抗体依赖性细胞毒性（ADCC）介导细胞清除。已证明补充低水平的ADCC激活细胞因子[例如白细胞介素 - 2（IL - 2）和干扰素 - α（IFN - α）]与叶酸靶向免疫疗法具有协同作用。因此，使用腹腔内注射到先前已针对荧光素免疫的Balb/c小鼠体内的M109同基因肺癌细胞，在用叶酸 - 荧光素偶联物治疗后观察到寿命显著延长，并且在补充中等水平的IL - 2和IFN - α后观察到完全治愈。由于用相同细胞因子但用非靶向荧光素治疗的对照荷瘤小鼠未显示寿命延长，我们得出结论，肿瘤特异性调理是这种免疫疗法的关键步骤。最后，由于抗荧光素抗体无法接触肾近端小管顶端膜上的叶酸受体，未观察到肾脏或其他正常组织的细胞毒性。这些数据表明，将半抗原重新靶向表达叶酸受体的癌症可能构成一种动员免疫系统特异性对抗免疫原性差的肿瘤的方法。
