Epstein Alan L, Mizokami Myra M, Li Jiali, Hu Peisheng, Khawli Leslie A
Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
J Natl Cancer Inst. 2003 May 21;95(10):741-9. doi: 10.1093/jnci/95.10.741.
The cytokine interleukin 2 (IL-2) is involved in the activation of T cells and has been shown to play a central role in cancer immunotherapy. The full therapeutic potential of IL-2, however, has not been realized because of its dose-limiting systemic toxicity. We sought to identify a region of IL-2 that is responsible for the induction of vasopermeability (leaky tumor endothelium), a property associated with the toxicity of the molecule.
Intact IL-2 or overlapping synthetic peptides of IL-2 that were chemically conjugated to tumor-targeting monoclonal antibodies (TNT-1 or Lym-1) were injected into groups of mice (n = 4) that had previously been xenotransplanted with human tumor cells (ME-180 cervical carcinoma and Raji lymphoma). Two hours later, mice received intravenous injections of radiolabeled tracer antibody, and 3 days later they were subjected to biodistribution analysis to measure the ability of each immunoconjugate to enhance tumor uptake of the tracer antibody (i.e., vasopermeability activity). The cytokine activity of the immunoconjugates was determined by assaying their ability to promote the proliferation of a mouse IL-2-dependent cell line.
Pretreatment of mice with an antibody/IL-2 immunoconjugate resulted in an approximately fourfold increase in radiolabeled tracer antibody uptake in the xenograft tumor as compared with uptake in mice injected with antibody alone. One synthetic fragment consisting of amino acids 22-58 contained 100% of the vasopermeability activity of IL-2 and was designated permeability-enhancing peptide (PEP). PEP had vasopermeability activity only when conjugated to a tumor-targeting antibody, had maximal activity as a dimer, and was devoid of cytokine activity.
The identification of PEP should aid in the discovery of ways to decrease the toxicity of IL-2. Moreover, PEP is a promising candidate for the generation of agents that can enhance the delivery of antibodies and drugs to tumors.
细胞因子白细胞介素2（IL-2）参与T细胞的激活，并且已证明在癌症免疫治疗中起核心作用。然而，由于其剂量限制性全身毒性，IL-2的全部治疗潜力尚未实现。我们试图确定IL-2中负责诱导血管通透性（肿瘤内皮渗漏）的区域，这是一种与该分子毒性相关的特性。
将完整的IL-2或与肿瘤靶向单克隆抗体（TNT-1或Lym-1）化学偶联的IL-2重叠合成肽注射到预先异种移植了人肿瘤细胞（ME-180宫颈癌和Raji淋巴瘤）的小鼠组（n = 4）中。两小时后，小鼠接受放射性标记的示踪抗体静脉注射，三天后对它们进行生物分布分析，以测量每种免疫偶联物增强示踪抗体在肿瘤中的摄取能力（即血管通透性活性）。通过测定免疫偶联物促进小鼠IL-2依赖细胞系增殖的能力来确定其细胞因子活性。
与单独注射抗体的小鼠相比，用抗体/IL-2免疫偶联物预处理小鼠后，异种移植肿瘤中放射性标记的示踪抗体摄取量增加了约四倍。一个由氨基酸22-58组成的合成片段包含IL-2的100%血管通透性活性，被命名为通透性增强肽（PEP）。PEP仅在与肿瘤靶向抗体偶联时具有血管通透性活性，作为二聚体时具有最大活性，并且没有细胞因子活性。
PEP的鉴定应有助于发现降低IL-2毒性的方法。此外，PEP是生成可增强抗体和药物向肿瘤递送的药物的有希望的候选物。
