Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Mol Pharm. 2011 Jun 6;8(3):767-73. doi: 10.1021/mp100382m. Epub 2011 Apr 21.
Noninvasive measurement of human islet cell mass in pancreas or following islet transplantation by nuclear imaging has yet to be achieved. It has been shown using mouse tumor models that pretargeting imaging strategies are sensitive and can greatly increase target to nontarget signal ratios. The objective now is to demonstrate the specific pretargeting of human islet cells in mice. Our pretargeting strategy uses an anti-human islet cell antibody HPi1, conjugated to a phosphorodiamidate morpholino oligomer (MORF) that binds specifically to a (99m)Tc labeled complementary MORF (cMORF). Sensitivity and specificity of the pretargeting were first validated in culture using a human beta cell line (betalox5) and a negative control human cell line (HEK293). Pretargeting was then used to target and visualize these two cell lines and human islets transplanted subcutaneously in NOD-scid IL2rγ(null) mice. In culture, (99m)Tc accumulation on the betalox5 cells pretargeted by MORF-HPi1 was 100-fold higher than on untreated betalox5 cells or following treatment with native HPi1 and much higher than on the MORF-HPi1 pretargeted control HEK293 cells. Small animal imaging readily localized the transplanted betalox5 cells and human islets, but not the HEK293 cells. Ex vivo counting demonstrated 3-fold higher (99m)Tc accumulation in the transplanted betalox5 cells and human islets than in the control HEK293 cells. The target accumulation was also shown to increase linearly with increased numbers of the implanted betalox5 cells. These results demonstrate specific binding of radioactivity and successful imaging of human betalox5 cells and human islets transplanted in mice. Thus MORF/cMORF pretargeting may be useful to measure noninvasively human islet cell mass within the pancreas or following islet transplantation.
目前，还无法通过核成像技术无创性地测量胰腺中的人胰岛细胞量或胰岛移植后的人胰岛细胞量。利用小鼠肿瘤模型表明，前靶向成像策略具有较高的灵敏度，可极大地提高靶标与非靶标信号的比值。目前的目标是证明在小鼠中对人胰岛细胞进行特异性前靶向。我们的前靶向策略使用了一种抗人胰岛细胞抗体 HPi1，将其与特异性结合（99m）Tc 标记的互补 MORF（cMORF）的磷酰胺二酯吗啉寡聚物（MORF）偶联。在使用人β细胞系（betalox5）和阴性对照人细胞系（HEK293）进行培养时，首先验证了前靶向的敏感性和特异性。然后，将前靶向用于靶向和可视化这两种细胞系以及皮下移植到 NOD-scid IL2rγ（null）小鼠中的人胰岛。在培养中，经 MORF-HPi1 前靶向的 betalox5 细胞上（99m）Tc 的积累比未经处理的 betalox5 细胞或用天然 HPi1 处理后的细胞高 100 倍，比经 MORF-HPi1 前靶向的对照 HEK293 细胞高得多。小动物成像很容易定位移植的 betalox5 细胞和人胰岛，但不能定位 HEK293 细胞。体外计数表明，移植的 betalox5 细胞和人胰岛中的（99m）Tc 积累比对照 HEK293 细胞高 3 倍。还表明，靶标积累随植入的 betalox5 细胞数量的增加呈线性增加。这些结果表明放射性的特异性结合以及成功地对小鼠中移植的人 betalox5 细胞和人胰岛进行了成像。因此，MORF/cMORF 前靶向可能有助于在胰腺内或胰岛移植后非侵入性地测量人胰岛细胞量。
