Department of Biomedical Radiation Sciences, Uppsala University, Uppsala, Sweden.
J Nucl Med. 2012 Jun;53(6):953-60. doi: 10.2967/jnumed.111.101527. Epub 2012 May 14.
Radionuclide imaging of cancer-associated molecular alterations may contribute to patient stratification for targeting therapy. Scaffold high-affinity proteins, such as Affibody molecules, are a new, promising class of probes for in vivo imaging.
The effects of human epidermal growth factor receptor 2 (HER2) affinity and binding site composition of HER2-binding Affibody molecules, and of the HER2 density on the tumor targeting, were studied in vivo. The tumor uptake and tumor-to-organ ratios of Affibody molecules with moderate (dissociation constant [K(D)] = 10(-9) M) or high (K(D) = 10(-10) M) affinity were compared between tumor xenografts with a high (SKOV-3) and low (LS174T) HER2 expression level in BALB/C nu/nu mice. Two Affibody molecules with similar affinity (K(D) = 10(-10) M) but having alternative amino acids in the binding site were compared.
In SKOV-3 xenografts, uptake was independent of affinity at 4 h after injection, but high-affinity binders provided 2-fold-higher tumor radioactivity retention at 24 h. In LS174T xenografts, uptake of high-affinity probes was already severalfold higher at 4 h after injection, and the difference was increased at 24 h. The clearance rate and tumor-to-organ ratios were influenced by the amino acid composition of the binding surface of the tracer protein.
The optimal affinity of HER2-binding Affibody molecules depends on the expression of a molecular target. At a high expression level (>10(6) receptors per cell), an affinity in the low-nanomolar range is sufficient. At moderate expression, subnanomolar affinity is desirable. The binding site composition can influence the imaging contrast. This information may be useful for development of imaging agents based on scaffold affinity proteins.
研究了人表皮生长因子受体 2（HER2）亲和力和 HER2 结合型 Affibody 分子的结合位构效关系，以及 HER2 密度对肿瘤靶向的影响，探讨了高亲和力（解离常数 [K(D)] = 10(-9) M）和中等亲和力（K(D) = 10(-10) M）HER2 结合型 Affibody 分子在高表达（SKOV-3）和低表达（LS174T）HER2 肿瘤异种移植鼠模型中的体内靶向性。比较了两种具有相似亲和力（K(D) = 10(-10) M）但结合位氨基酸不同的 Affibody 分子。
在 SKOV-3 肿瘤中，注射后 4 h 摄取与亲和力无关，但高亲和力结合物在 24 h 时提供了 2 倍更高的肿瘤放射性保留。在 LS174T 肿瘤中，高亲和力探针在注射后 4 h 时摄取已经高出数倍，在 24 h 时差异更大。清除率和肿瘤与器官比值受示踪蛋白结合表面氨基酸组成的影响。
HER2 结合型 Affibody 分子的最佳亲和力取决于靶分子的表达。在高表达水平（>10(6)个受体/细胞）时，低纳摩尔范围的亲和力就足够了。在中等表达水平时，亚纳摩尔亲和力是理想的。结合位构效关系可以影响成像对比度。这些信息可能有助于基于支架亲和力蛋白开发成像剂。
