Akabani Gamal, Carlin Sean, Welsh Phil, Zalutsky Michael R
Department of Radiology, Duke University Medical Center, P.O. Box 3808, Durham, NC 27710, USA.
Nucl Med Biol. 2006 Apr;33(3):333-47. doi: 10.1016/j.nucmedbio.2005.12.006. Epub 2006 Mar 9.
Radioimmunotherapy with anti-HER2 monoclonal antibodies (mAbs) such as trastuzumab is a promising strategy for treating HER2-positive breast and ovarian carcinoma patients. The objective of this study was to determine the cytotoxic effectiveness of trastuzumab labeled with the 7.2-h half-life alpha-particle emitter 211At.
Experiments were performed on SKBr-3, BT-474 and the transfected MCF7/HER2-18 human breast carcinoma cell lines. Intrinsic radiosensitivity was determined after exposure to external beam irradiation. The cytotoxicity of 211At-labeled trastuzumab was measured by clonogenic assays. The distribution of HER2 receptor expression on the cell lines was measured using fluorescence-activated cell sorting. A pharmacokinetic (PK)/microdosimetric model was established to assess the effects of specific activity (SA), HER2 receptor expression and absorbed dose on survival fraction (SF).
With external beam irradiation, the 2-Gy SF for BT-474, SKBr-3 and MCF7/HER2-18 cells was 0.78, 0.53 and 0.64 Gy, respectively. Heterogeneous HER2 expression was observed, with a subpopulation of cells lacking measurable receptor (14.5%, SKBr-3; 0.34%, MCF-7/HER2; 1.73%, BT-474). When plotted as a function of activity concentration, SF curves were biphasic and inversely proportional to SA; however, when the model was applied and absorbed doses calculated, the SF curve was monoexponential independent of SA. Thus, the PK model was able to demonstrate the effects of competition between cold and labeled mAb. These studies showed that the relative biological effectiveness of 211At-labeled trastuzaumab was about 10 times higher than that of external beam therapy.
These in vitro studies showed that 211At-labeled trastuzumab mAb is an effective cytotoxic agent for the treatment of HER2-positive tumor cells. The SA of the labeled mAb and the homogeneity of HER2 receptor expression are important variables influencing the efficiency of cell killing.
用抗HER2单克隆抗体（mAb）如曲妥珠单抗进行放射免疫治疗是治疗HER2阳性乳腺癌和卵巢癌患者的一种有前景的策略。本研究的目的是确定用半衰期为7.2小时的α粒子发射体211At标记的曲妥珠单抗的细胞毒性效果。
在SKBr-3、BT-474和转染的MCF7/HER2-18人乳腺癌细胞系上进行实验。暴露于外照射后测定内在放射敏感性。通过克隆形成试验测量211At标记的曲妥珠单抗的细胞毒性。使用荧光激活细胞分选测量HER2受体在细胞系上的表达分布。建立药代动力学（PK）/微剂量模型以评估比活度（SA）、HER2受体表达和吸收剂量对存活分数（SF）的影响。
在外照射下，BT-474、SKBr-3和MCF7/HER2-18细胞的2-Gy存活分数分别为0.78、0.53和0.64 Gy。观察到HER2表达异质性，有一部分细胞缺乏可测量的受体（SKBr-3为14.5%；MCF-7/HER2为0.34%；BT-474为1.73%）。当以活性浓度为函数绘制时，存活分数曲线呈双相且与比活度成反比；然而，当应用该模型并计算吸收剂量时，存活分数曲线呈单指数形式，与比活度无关。因此，PK模型能够证明冷抗体和标记抗体之间竞争的影响。这些研究表明，211At标记的曲妥珠单抗的相对生物有效性比外照射治疗高约10倍。
这些体外研究表明，211At标记的曲妥珠单抗mAb是治疗HER2阳性肿瘤细胞的有效细胞毒性剂。标记mAb的比活度和HER2受体表达的同质性是影响细胞杀伤效率的重要变量。
