Casalini P, Luison E, Ménard S, Colnaghi M I, Paganelli G, Canevari S
Oncologia Sperimentale E, Istituto Nazionale Tumori, Milan, Italy.
J Nucl Med. 1997 Sep;38(9):1378-81.
Radioimmunodetection of tumor can be improved by introducing a two-step system in which radiolabeled streptavidin is administrated after the injection of a biotinylated monoclonal antibody (MAb) (two-step) or radiolabeled biotin is injected after biotinylated MAb and avidin (three-step). The anti-carcinoembryonic antigen (CEA) MAb FO23C5 has been recently exploited in a three-step protocol based on the avidin-biotin system. The anti-folate receptor (FR) MAb MOv18 has proven suitable for radioimmunodetection of ovarian cancer using directly radiolabeled MAb or in a two-step method. In this study, we analyzed the suitability of MOv18 in a three-step protocol in ovarian carcinoma patients and the internalization events after formation of the MOv18-avidin complex.
Selected patients with documented metastatic lesions were enrolled in a three-step radioimaging analysis with biotinylated MOv18 and FO23C5, avidin and (111)In-labeled biotin. Two-step internalization experiments were conducted in vitro with MOv18 and MOv19 MAbs on the FR-overexpressing IGROV1 cell line and with the anti-CEA MAb FO23C5 on the LS174T cell line. Cells were incubated sequentially with biotinylated MAb and 125I-labeled streptavidin or with 125I-biotinylated MAb and cold streptavidin.
In the in vivo study, SPECT revealed the majority of metastatic lesions in patients injected with biotinylated MOv18; however, the tumor-to-background ratio was relatively low. In the in vitro study, a consistent internalization was induced by antigen-biotinylated MAb-streptavidin complex formation at the cell surface in both antigenic systems analyzed. However, the extent of internalization was lower in the CEA model.
The internalization ability of avidin suggests its potential clinical application for delivering toxic agents in a two-step approach (biotinylated MAb + avidin conjugate). The suitability of a given MAb for three-step clinical applications (biotinylated MAb + avidin + biotin) should be previously investigated by using appropriate in vitro experiments.
通过引入两步系统可改善肿瘤的放射免疫检测，在该系统中，注射生物素化单克隆抗体（MAb）后给予放射性标记的链霉亲和素（两步法），或者在生物素化MAb和抗生物素蛋白后注射放射性标记的生物素（三步法）。抗癌胚抗原（CEA）单克隆抗体FO23C5最近已被用于基于抗生物素蛋白-生物素系统的三步方案中。抗叶酸受体（FR）单克隆抗体MOv18已被证明适用于使用直接放射性标记的单克隆抗体或两步法进行卵巢癌的放射免疫检测。在本研究中，我们分析了MOv18在卵巢癌患者三步方案中的适用性以及MOv18-抗生物素蛋白复合物形成后的内化事件。
选择有记录的转移病灶患者，用生物素化的MOv18和FO23C5、抗生物素蛋白和（111）In标记的生物素进行三步放射成像分析。在体外对FR过表达IGROV1细胞系用MOv18和MOv19单克隆抗体以及对LS174T细胞系用抗CEA单克隆抗体FO23C5进行两步内化实验。细胞依次与生物素化单克隆抗体和125I标记的链霉亲和素孵育，或与125I-生物素化单克隆抗体和冷链霉亲和素孵育。
在体内研究中，SPECT显示注射生物素化MOv18的患者中大多数转移病灶；然而，肿瘤与背景的比值相对较低。在体外研究中，在分析的两种抗原系统中，抗原-生物素化单克隆抗体-链霉亲和素复合物在细胞表面形成均诱导了一致的内化。然而，CEA模型中的内化程度较低。
抗生物素蛋白的内化能力表明其在两步法（生物素化单克隆抗体+抗生物素蛋白缀合物）中递送毒性剂的潜在临床应用。给定单克隆抗体在三步临床应用（生物素化单克隆抗体+抗生物素蛋白+生物素）中的适用性应事先通过适当的体外实验进行研究。
