Chen J, Cheng Z, Hoffman T J, Jurisson S S, Quinn T P
Department of Biochemistry, University of Missouri-Columbia, 65211, USA.
Cancer Res. 2000 Oct 15;60(20):5649-58.
Preliminary reports have demonstrated that (99m)technetium (Tc)-labeled cyclic [Cys(3,4,10), D-Phe7]alpha-MSH(3-13) (CCMSH) exhibits high tumor uptake and retention values in a murine melanoma mouse model. In this report, the tumor targeting mechanism of 99mTc-CCMSH was studied and compared with four other radiolabeled alpha-melanocyte stimulating hormone (alpha-MSH) peptide analogues: 125I-(Tyr2)-[Nle4, D-Phe7]alpha-MSH [125I-(Tyr2)-NDP]; 99mTc-CGCG-NDP; 99mTc-Gly11-CCMSH; and 99mTc-Nle11-CCMSH. In vitro receptor binding, internalization, and cellular retention of radiolabeled alpha-MSH analogues in B16/F1 murine cell line demonstrated that >70% of the receptor-bound radiolabeled analogues were internalized together with the receptor. Ninety % of the internalized 125I-(Tyr2)-NDP, whereas only 36% of internalized 99mTc-CCMSH, was released from the cells into the medium during a 4-h incubation at 37 degrees C. Two mouse models, C57 mice and severe combined immunodeficient (Scid) mice, inoculated s.c. with B16/F1 murine and TXM-13 human melanoma cells were used for the in vivo studies. Tumor uptake values of 11.32 and 2.39 [% injected dose (ID)/g] for 99mTc-CCMSH at 4 h after injection, resulted in an uptake ratio of tumor:blood of 39.0 and 11.5 in murine melanoma-C57 and human melanoma-Scid mouse models, respectively. Two strategies for decreasing the nonspecific kidney uptake of 99mTc-CCMSH, substitution of Lys11 in CCMSH with Gly11 or Nle11, and lysine coinjection, were evaluated. The biodistribution data for the modified peptides showed that Lys11 replacement dramatically decreased the kidney uptake, whereas the tumor uptakes of 99mTc-Nle11- and 99mTc-Gly11-CCMSH were significantly lower than that of 99mTc-CCMSH. Lysine coinjection significantly decreased the kidney uptake (e.g., from 14.6% ID/g to 4.5% ID/g at 4 h after injection in murine melanoma-C57 mice) without significantly changing the value of tumor uptake of 99mTc-CCMSH. In conclusion, the compact cyclic structure of 99mTc-CCMSH, its resistance to degradation, and its enhanced intracellular retention are the major contributing factors to the superior in vivo tumor targeting properties of 99mTc-CCMSH. Lys11 residue in 99mTc-CCMSH is critical to the tumor targeting in vivo, and lysine coinjection rather than lysine replacement can significantly decrease the nonspecific renal radioactivity accumulation without impeding the high melanoma-targeting properties of 99Tc-CCMSH. The metal-cyclized CCMSH molecule displays excellent potential for the development of melanoma-specific diagnostic and therapeutic agents.
初步报告表明，（99m）锝（Tc）标记的环[Cys(3,4,10), D-Phe7]α-MSH(3-13)（CCMSH）在小鼠黑色素瘤小鼠模型中表现出高肿瘤摄取和滞留值。在本报告中，研究了99mTc-CCMSH的肿瘤靶向机制，并与其他四种放射性标记的α-黑素细胞刺激激素（α-MSH）肽类似物进行了比较：125I-(Tyr2)-[Nle4, D-Phe7]α-MSH [125I-(Tyr2)-NDP]；99mTc-CGCG-NDP；99mTc-Gly11-CCMSH；以及99mTc-Nle11-CCMSH。对B16/F-1小鼠细胞系中放射性标记的α-MSH类似物的体外受体结合、内化和细胞滞留研究表明，>70%与受体结合的放射性标记类似物与受体一起内化。在37℃孵育4小时期间，90%内化的125I-(Tyr2)-NDP从细胞释放到培养基中，而只有36%内化的99mTc-CCMSH释放到培养基中。两种小鼠模型，C57小鼠和严重联合免疫缺陷（Scid）小鼠，皮下接种B16/F-1小鼠和TXM-13人黑色素瘤细胞用于体内研究。注射后4小时，99mTc-CCMSH的肿瘤摄取值分别为11.32和2.39 [%注射剂量（ID）/g]，在小鼠黑色素瘤-C57和人黑色素瘤-Scid小鼠模型中，肿瘤与血液的摄取比分别为39.0和11.5。评估了两种降低99mTc-CCMSH非特异性肾脏摄取的策略，即用Gly11或Nle11取代CCMSH中的Lys11，以及共同注射赖氨酸。修饰肽的生物分布数据表明，Lys11取代显著降低了肾脏摄取，而99mTc-Nle11-和99mTc-Gly11-CCMSH的肿瘤摄取明显低于99mTc-CCMSH。共同注射赖氨酸显著降低了肾脏摄取（例如，在小鼠黑色素瘤-C57小鼠中，注射后4小时从14.6% ID/g降至4.5% ID/g），而没有显著改变99mTc-CCMSH的肿瘤摄取值。总之，99mTc-CCMSH紧密的环结构、其抗降解能力以及其增强的细胞内滞留是99mTc-CCMSH体内优异肿瘤靶向特性的主要促成因素。99mTc-CCMSH中的Lys11残基对体内肿瘤靶向至关重要，共同注射赖氨酸而非取代赖氨酸可以显著降低非特异性肾脏放射性积累，而不会妨碍99Tc-CCMSH的高黑色素瘤靶向特性。金属环化的CCMSH分子在黑色素瘤特异性诊断和治疗剂的开发中显示出优异的潜力。
