Garg P K, Alston K L, Welsh P C, Zalutsky M R
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Bioconjug Chem. 1996 Mar-Apr;7(2):233-9. doi: 10.1021/bc960001+.
Two peptides of potential utility for targeting melanoma cells, alpha-melanocyte-stimulating hormone (alpha-MSH) and its more potent analogue [Nle4,D-Phe7]-alpha-MSH, were radioiodinated in 45-65% yield using N-succinimidyl 3-[125I]iodobenzoate (SIB). To determine whether this labeling method resulted in improved in vitro and in vivo characteristics, these peptides also were labeled with 131I by direct iodination with the iodogen method. For alpha-MSH, the rapid tissue clearance of both radionuclides in mice was consistent with rapid degradation of the peptide; however, significantly lower levels of 125I were observed in thyroid and stomach, reflecting a greater inertness to deiodination. More extensive comparisons were performed with [Nle4,D-Phe7]-alpha-MSH. The in vitro binding of [Nle4,D-Phe7,Lys11-(125I)IBA]-alpha-MSH (prepared using SIB) to the murine B-16 melanoma cell line, 34.1 +/- 4.7%, was more than twice as high as that for [Tyr2(131I),Nle4,D-Phe7]-alpha-MSH (15.0 +/- 0.1%), and its KD was more than 10-fold lower than that for conventionally labeled peptide (10 +/- 5 versus 140 +/- 14 pM). The normal tissue clearance of [Nle4,D-Phe7,Lys11-(125I)IBA]-alpha-MSH in mice was faster than that of [Tyr2(131I),-Nle4,D-Phe7]-alpha-MSH. The 19-40-fold lower activity concentrations of [Nle4,D-Phe7,Lys11-(125I)IBA]-alpha-MSH in tissues accumulating free iodide (thyroid and stomach) suggest a greater inertness of this peptide to deiodination. The primary urinary catabolite of [Nle4,D-Phe7, Lys11-(125I)IBA]-alpha-MSH was the lysine conjugate of iodobenzoic acid, whereas radioiodide was the chief catabolite generated from [Tyr2(131I),Nle4,D-Phe7]-alpha-MSH. We conclude that further evaluation of [Nle4,D-Phe7,Lys11-(125I)IBA]-alpha-MSH for targeting alpha-MSH receptors is warranted and that SIB may be a useful method for the radioiodination of peptides.
两种对靶向黑色素瘤细胞可能有用的肽，α-黑素细胞刺激素（α-MSH）及其更强效的类似物[Nle4，D-Phe7]-α-MSH，使用N-琥珀酰亚胺基3-[125I]碘苯甲酸酯（SIB）进行放射性碘化，产率为45 - 65%。为了确定这种标记方法是否能改善体外和体内特性，这些肽还通过碘代法直接用131I进行标记。对于α-MSH，两种放射性核素在小鼠体内的快速组织清除与该肽的快速降解一致；然而，在甲状腺和胃中观察到的125I水平显著较低，这反映出其对脱碘的惰性更大。对[Nle4，D-Phe7]-α-MSH进行了更广泛的比较。[Nle4，D-Phe7，Lys11-(125I)IBA]-α-MSH（使用SIB制备）与小鼠B-16黑色素瘤细胞系体外结合率为34.1±4.7%，是[Tyr2(131I)，Nle4，D-Phe7]-α-MSH（15.0±0.1%）的两倍多，其解离常数比传统标记肽低10倍以上（10±5对140±14 pM）。[Nle4，D-Phe7，Lys11-(125I)IBA]-α-MSH在小鼠体内的正常组织清除速度比[Tyr2(131I)，-Nle4，D-Phe7]-α-MSH快。在积累游离碘的组织（甲状腺和胃）中，[Nle4，D-Phe7，Lys11-(125I)IBA]-α-MSH的活性浓度低19 - 40倍，这表明该肽对脱碘的惰性更大。[Nle4，D-Phe7，Lys11-(125I)IBA]-α-MSH的主要尿代谢产物是碘苯甲酸的赖氨酸缀合物，而放射性碘是[Tyr2(131I)，Nle4，D-Phe7]-α-MSH产生的主要代谢产物。我们得出结论，有必要对[Nle4，D-Phe7，Lys11-(125I)IBA]-α-MSH靶向α-MSH受体进行进一步评估，并且SIB可能是一种有用的肽放射性碘化方法。
