Ong G L, Elsamra S E, Goldenberg D M, Mattes M J
Garden State Cancer Center, Belleville, New Jersey 07109, USA.
Clin Cancer Res. 2001 Jan;7(1):192-201.
Previous studies demonstrated the effective, antigen-specific killing of Raji B-lymphoma cells in vitro by radiolabeled anti-CD74, attributable largely to the high level of uptake, of approximately 10(7) antibody (Ab) molecules/cell/ day. This Ab is rapidly delivered to lysosomes for catabolism, so the radionuclide delivered accumulates primarily in lysosomes. In this study, we have tested Abs that bind to the same target cells in similar amounts, but remain primarily on the cell surface, to compare the potency of radioactivity delivered to the cell surface versus the cytoplasm. The Abs tested were anti-major histocompatibility complex class II and anti-CD20. 111In-labeled conjugates made with these two Abs killed cells very effectively and specifically, with 100% kill of sample of 5 x 10(5) cells. Because these Abs remain primarily on the cell surface, it would be predicted that residualizing radiolabels, which are trapped in lysosomes after Ab catabolism, would not be required, and this was observed, i.e., these two Abs were effective when labeled with either 125I or 131I, using conventional iodination, as well as with the residualizing label 111In-labeled DTPA. These results are in contrast to results obtained with anti-CD74, which required a residualizing radiolabel for effectiveness. The uptake of these radionuclides, in cpm/cell, was monitored, and this allowed estimation of the radiation dose delivered; the cytotoxicity observed was consistent with the estimated radiation dose delivered. To establish the generality of the results, we also demonstrated that 111In-labeled anti-CD74 effectively killed three other B-lymphoma cell lines, in addition to Raji and the adherent melanoma cell line SK-MEL-37. By using more potent radionuclides or conjugates of higher specific activity, this approach might be effective with other, lower density antigens.
先前的研究表明，放射性标记的抗CD74在体外可有效、抗原特异性地杀伤Raji B淋巴瘤细胞，这主要归因于其高水平的摄取，约为每天10⁷个抗体（Ab）分子/细胞。这种抗体迅速被转运至溶酶体进行分解代谢，因此所携带的放射性核素主要在溶酶体中积累。在本研究中，我们测试了能以相似数量结合相同靶细胞但主要保留在细胞表面的抗体，以比较递送至细胞表面与细胞质的放射性的效力。所测试的抗体为抗主要组织相容性复合体II类抗体和抗CD20抗体。用这两种抗体制备的¹¹¹In标记偶联物能非常有效地特异性杀伤细胞，5×10⁵个细胞样本的杀伤率达100%。由于这些抗体主要保留在细胞表面，可以预测，在抗体分解代谢后被困在溶酶体中的残留放射性标记将不再需要，而实际观察到的情况正是如此，即这两种抗体在用常规碘化法标记¹²⁵I或¹³¹I时以及用残留放射性标记¹¹¹In标记的二乙三胺五乙酸（DTPA）时均有效。这些结果与抗CD74的结果形成对比，抗CD74需要残留放射性标记才能发挥效力。监测了这些放射性核素以每分钟计数/细胞表示的摄取量，从而能够估算所递送的辐射剂量；观察到的细胞毒性与估算的辐射剂量一致。为了确定结果的普遍性，我们还证明¹¹¹In标记的抗CD74除了能有效杀伤Raji细胞和贴壁黑色素瘤细胞系SK-MEL-37外，还能有效杀伤另外三种B淋巴瘤细胞系。通过使用更强效放射性核素或更高比活度的偶联物，这种方法可能对其他低密度抗原有效。
