Froidevaux Sylvie, Calame-Christe Martine, Schuhmacher Jochen, Tanner Heidi, Saffrich Rainer, Henze Markus, Eberle Alex N
Laboratory of Endocrinology, Department of Research, University Hospital and University Children's Hospital, Basel, Switzerland.
J Nucl Med. 2004 Jan;45(1):116-23.
Although (18)F-FDG PET is widely used for metastatic melanoma diagnosis, it is less accurate than desirable, particularly for small foci. Since both melanotic and amelanotic melanomas overexpress receptors for alpha-melanocyte-stimulating hormone (alpha-MSH; receptor name, melanocortin type 1 receptor [MC1R]), radiolabeled alpha-MSH analogs are potential candidates for melanoma diagnosis. The aim of this study was to develop a positron emitter-labeled alpha-MSH analog suitable for PET imaging of melanoma metastases.
A short linear alpha-MSH analog, [Nle(4),Asp(5),D-Phe(7)]-alpha-MSH(4-11) (NAPamide), was newly designed and conjugated to the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to enable radiometal incorporation. Compared with our previously reported DOTA-alpha-MSH analog, DOTA-MSH(oct) ([DOTA-betaAla(3),Nle(4),Asp(5),D-Phe(7),Lys(10)]-alpha-MSH(3-10)), the major modification lies in the conjugation of DOTA to the C-terminal end of the peptide via the epsilon-amino group of Lys(11), as opposed to the N-terminal alpha-amino group. After labeling with (111)In, (67)Ga, and the short-lived positron emitter (68)Ga, DOTA-NAPamide was characterized in vitro and in vivo using the mouse melanoma B16F1cell line.
DOTA-NAPamide exhibited an almost 7-fold higher MC1R binding potency as compared with DOTA-MSH(oct). In B16F1 melanoma-bearing mice, both (111)In-DOTA-NAPamide and (67)Ga-DOTA-NAPamide behaved more favorably than (111)In-DOTA-MSH(oct). Both radiopeptides exhibited higher tumor and lower kidney uptake leading to tumor-to-kidney ratios of the 4- to 48-h area under the curve that were 4.6 times ((111)In) and 7.5 times ((67)Ga) greater than that obtained with (111)In-DOTA-MSH(oct). In addition, the 4-h kidney uptake of (67)Ga-DOTA-NAPamide could be reduced by 64% by coinjection of 15 mg L-lysine, without affecting tumor uptake. Skin primary melanoma as well as lung and liver melanoma metastases could be easily visualized on tissue section autoradiographs after systemic injection of (67)Ga-DOTA-NAPamide. The melanoma selectivity of DOTA-NAPamide was confirmed by PET imaging studies using (68)Ga-DOTA-NAPamide. Tumor uptake was found to be highest when the smallest amount of peptide was administered.
DOTA-NAPamide labeled with either (111)In or (67)Ga/(68)Ga is in every way superior to (111)In-DOTA-MSH(oct) in murine models of primary and metastatic melanoma, which makes it a promising agent for melanoma targeting. High-contrast images obtained in PET studies with an experimental tumor model 1 h after injection augurs well for its clinical potential as an imaging tool.
尽管（18）F-FDG PET被广泛用于转移性黑色素瘤的诊断，但其准确性仍不尽人意，尤其是对于小病灶。由于黑色素瘤和无黑色素黑色素瘤均过度表达α-黑素细胞刺激激素（α-MSH；受体名称，黑素皮质素1型受体[MC1R]）的受体，因此放射性标记的α-MSH类似物是黑色素瘤诊断的潜在候选物。本研究的目的是开发一种适用于黑色素瘤转移灶PET成像的正电子发射体标记的α-MSH类似物。
新设计了一种短线性α-MSH类似物[Nle(4),Asp(5),D-Phe(7)]-α-MSH(4-11)（NAPamide），并将其与金属螯合剂DOTA（1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸）偶联，以实现放射性金属掺入。与我们先前报道的DOTA-α-MSH类似物DOTA-MSH(oct)（[DOTA-βAla(3),Nle(4),Asp(5),D-Phe(7),Lys(10)]-α-MSH(3-10)）相比，主要的修饰在于通过Lys(11)的ε-氨基将DOTA与肽的C末端偶联，而不是与N末端的α-氨基偶联。用（111）In、（67）Ga和短寿命正电子发射体（68）Ga标记后，使用小鼠黑色素瘤B16F1细胞系在体外和体内对DOTA-NAPamide进行了表征。
与DOTA-MSH(oct)相比，DOTA-NAPamide的MC1R结合能力高出近7倍。在携带B16F1黑色素瘤的小鼠中，（111）In-DOTA-NAPamide和（67）Ga-DOTA-NAPamide的表现均优于（111）In-DOTA-MSH(oct)。两种放射性肽均表现出较高的肿瘤摄取和较低的肾脏摄取，导致4至48小时曲线下面积的肿瘤与肾脏比值分别比（111）In-DOTA-MSH(oct)高4.6倍（（111）In）和7.5倍（（67）Ga）。此外，通过共同注射15 mg L-赖氨酸，（67）Ga-DOTA-NAPamide的4小时肾脏摄取可降低64%，而不影响肿瘤摄取。全身注射（67）Ga-DOTA-NAPamide后，在组织切片放射自显影片上可以很容易地看到皮肤原发性黑色素瘤以及肺和肝黑色素瘤转移灶。使用（68）Ga-DOTA-NAPamide的PET成像研究证实了DOTA-NAPamide对黑色素瘤的选择性。发现当给予最少量的肽时，肿瘤摄取最高。
在原发性和转移性黑色素瘤的小鼠模型中，用（111）In或（67）Ga/（68）Ga标记的DOTA-NAPamide在各方面均优于（111）In-DOTA-MSH(oct)，这使其成为一种有前景的黑色素瘤靶向剂。在注射后1小时用实验性肿瘤模型进行的PET研究中获得的高对比度图像预示着其作为成像工具的临床潜力良好。
