Haubner Roland, Kuhnast Bertrand, Mang Christian, Weber Wolfgang A, Kessler Horst, Wester Hans-Jürgen, Schwaiger Markus
Department of Nuclear Medicine, Technische Universität München, 81675 München, Germany.
Bioconjug Chem. 2004 Jan-Feb;15(1):61-9. doi: 10.1021/bc034170n.
It has been demonstrated in various murine tumor models that radiolabeled RGD-peptides can be used for noninvasive determination of alphavbeta3 integrin expression. Introduction of sugar moieties improved the pharmacokinetic properties of these peptides and led to tracer with good tumor-to-background ratios. Here we describe the synthesis, radiolabeling, and the metabolic stability of a glycosylated RGD-peptide ([18F]Galacto-RGD) and give first radiation dose estimates for this tracer. The peptide was assembled on a solid support using Fmoc-protocols and cyclized under high dilution conditions. It was conjugated with a sugar amino acid, which can be synthesized via a four-step synthesis starting from pentaacetyl-protected galactose. For radiolabeling of the glycopeptide, 4-nitrophenyl-2-[18F]fluoropropionate was used. This prosthetic group allowed synthesis of [18F]Galacto-RGD with a maximum decay-corrected radiochemical yield of up to 85% and radiochemical purity >98%. The overall radiochemical yield was 29 +/- 5% with a total reaction time including final HPLC preparation of 200 +/- 18 min. The metabolic stability of [18F]Galacto-RGD was determined in mouse blood and liver, kidney, and tumor homogenates 2 h after tracer injection. The average fraction of intact tracer in these organs was approximately 87%, 76%, 69%, and 87%, respectively, indicating high in vivo stability of the radiolabeled glycopeptide. The expected radiation dose to humans after injection of [18F]Galacto-RGD has been estimated on the basis of dynamic PET studies with New Zealand white rabbits. According to the residence times in these animals the effective dose was calculated using the MIRDOSE 3.0 program as 2.2 x 10(-2) mGy/MBq. In conclusion, [18F]Galacto-RGD can be synthesized in high radiochemical yields and radiochemical purity. Despite the time-consuming synthesis of the prosthetic group 185 MBq of [18F]Galacto-RGD, a sufficient dose for patient studies, can be produced starting with approximately 2.2 GBq of [18F]flouride. Moreover, the fast excretion, the suitable metabolic stability and the low estimated radiation dose allow to evaluate this tracer in human studies.
在多种小鼠肿瘤模型中已证实，放射性标记的RGD肽可用于无创测定αvβ3整合素的表达。引入糖部分改善了这些肽的药代动力学特性，并产生了具有良好肿瘤与本底比值的示踪剂。在此，我们描述了一种糖基化RGD肽（[18F]半乳糖-RGD）的合成、放射性标记及代谢稳定性，并给出了该示踪剂的首次辐射剂量估计。该肽使用Fmoc方案在固相载体上组装，并在高稀释条件下环化。它与一种糖氨基酸偶联，该糖氨基酸可通过从五乙酰保护的半乳糖开始的四步合成法合成。为了对糖肽进行放射性标记，使用了4-硝基苯基-2-[18F]氟丙酸酯。该前体基团使得[18F]半乳糖-RGD的合成具有高达85%的最大衰变校正放射化学产率和>98%的放射化学纯度。总放射化学产率为29±5%，包括最终HPLC制备在内的总反应时间为200±18分钟。在示踪剂注射后2小时，在小鼠血液、肝脏、肾脏和肿瘤匀浆中测定了[18F]半乳糖-RGD的代谢稳定性。在这些器官中完整示踪剂的平均比例分别约为87%、76%、69%和87%，表明放射性标记糖肽在体内具有高稳定性。基于对新西兰白兔的动态PET研究，估计了注射[18F]半乳糖-RGD后对人类的预期辐射剂量。根据这些动物体内的停留时间，使用MIRDOSE 3.0程序计算有效剂量为2.2×10(-2) mGy/MBq。总之，[18F]半乳糖-RGD能够以高放射化学产率和放射化学纯度合成。尽管前体基团的合成耗时，但从约2.2 GBq的[18F]氟化物开始，可以生产出185 MBq的[18F]半乳糖-RGD，这对于患者研究来说是足够的剂量。此外，快速排泄、合适的代谢稳定性和低估计辐射剂量使得该示踪剂能够在人体研究中进行评估。
