Fischer Thomas, Doll Christian, Jacobs Stefan, Kolodziej Angela, Stumm Ralf, Schulz Stefan
Department of Pharmacology and Toxicology, Friedrich-Schiller-University, Nonnenplan 4, 07743 Jena, Germany.
J Clin Endocrinol Metab. 2008 Nov;93(11):4519-24. doi: 10.1210/jc.2008-1063. Epub 2008 Aug 12.
The overexpression of somatostatin receptor 2 (sst2) in neuroendocrine tumors is the molecular basis for diagnostic and therapeutic application of the stable somatostatin analog octreotide. Recent evidence has shown that the immunocytochemical evaluation of sst2A status is of value for predicting response to octreotide therapy and disease prognosis. However, due to the lack of monoclonal and limited availability of specific polyclonal anti-sst2A antibodies, only very few patients can currently benefit from in vitro sst2 evaluation.
In the present study, we extensively characterized the novel rabbit monoclonal anti-sst2A antibody (clone UMB-1) using tissues from sst2-deficient mice and their wild-type littermates. UMB-1 was then subjected to a comparative study of immunohistochemistry on a series of histological specimens from formalin-fixed, paraffin-embedded human tumors and adjacent normal tissues.
Immunoprecipitation experiments unequivocally demonstrated that UMB-1 selectively detected its cognate sst2A and did not cross-react with other proteins present in crude tissue homogenates. The UMB-1 monoclonal antibody, when compared with currently available polyclonal antisera, yielded several times more effective immunohistochemical staining of fixed-embedded tissues with a predominance of plasma membrane staining and very low cytoplasmic signal even without heat-based antigen retrieval. In addition, dual immunofluorescence revealed for the first time that the sst2A is present on not only gastrin-containing but also ghrelin-containing cells in human gastric mucosa.
Thus, the rabbit monoclonal antibody UMB-1 may prove of great value in the assessment of sst2A status in human neuroendocrine tumors during routine histopathological examination.
神经内分泌肿瘤中生长抑素受体2（sst2）的过表达是稳定型生长抑素类似物奥曲肽诊断和治疗应用的分子基础。最近的证据表明，sst2A状态的免疫细胞化学评估对于预测奥曲肽治疗反应和疾病预后具有重要价值。然而，由于缺乏单克隆抗体且特异性多克隆抗sst2A抗体的可用性有限，目前只有极少数患者能够从体外sst2评估中获益。
在本研究中，我们使用sst2基因缺陷小鼠及其野生型同窝小鼠的组织，对新型兔单克隆抗sst2A抗体（克隆UMB-1）进行了广泛的特性鉴定。然后，UMB-1在一系列来自福尔马林固定、石蜡包埋的人类肿瘤及相邻正常组织的组织学标本上进行了免疫组织化学比较研究。
免疫沉淀实验明确表明，UMB-1能选择性检测其同源的sst2A，且不与粗组织匀浆中存在的其他蛋白质发生交叉反应。与目前可用的多克隆抗血清相比，UMB-1单克隆抗体对固定包埋组织的免疫组织化学染色效果提高了数倍，主要为质膜染色，即使不进行热抗原修复，细胞质信号也非常低。此外，双重免疫荧光首次揭示，sst2A不仅存在于人类胃黏膜中含胃泌素的细胞上，也存在于含胃饥饿素的细胞上。
因此，兔单克隆抗体UMB-1在常规组织病理学检查中评估人类神经内分泌肿瘤的sst2A状态方面可能具有重要价值。
