Comparative Studies of Three Pairs of α- and γ-Conjugated Folic Acid Derivatives Labeled with Fluorine-18

详细信息    查看全文

• 作者：Silvan D. Boss ; Thomas Betzel ; Cristina Müller ; Cindy R. Fischer ; Stephanie Haller ; Josefine Reber ; Viola Groehn ; Roger Schibli ; Simon M. Ametamey
• 刊名：Bioconjugate Chemistry
• 出版年：2016
• 出版时间：January 20, 2016
• 年：2016
• 卷：27
• 期：1
• 页码：74-86
• 全文大小：688K
• ISSN：1520-4812

文摘

The folate receptor (FR) is upregulated in various epithelial cancer types (FR α-isoform), while healthy tissues show only restricted expression. FR-targeted imaging using folate radiopharmaceuticals is therefore a promising approach for the detection of FR-positive cancer tissue. Almost all folate-based radiopharmaceuticals have been prepared by conjugation at the γ-carboxylic functionality of the glutamate moiety of folic acid. In this work, three pairs of fluorinated α- and γ-conjugated folate derivatives were synthesized and their in vitro and in vivo properties compared. The syntheses of all six regioisomers were obtained in good chemical yields using a multistep synthetic approach including the highly selective Cu(I)-catalyzed 1,3-dipolar cycloaddition. The radiosyntheses of the α- and γ-conjugated ¹⁸F-labeled folate derivatives were accomplished in moderate to good radiochemical yields, high radiochemical purities (>95%), and specific activities ranging from 25 to 196 GBq/μmol. In vitro, all folate derivatives showed high binding affinity to the FR-α (IC₅₀ = 1.4–2.2 nM). In vivo PET imaging and biodistribution studies in FR-positive KB tumor-bearing mice demonstrated similar FR-specific tumor uptake for both regioisomers of each pair of compounds. However, FR-unspecific liver uptake was significantly lower for the α-regioisomers compared to the corresponding γ-regioisomers. In contrast, kidney uptake was up to 50% lower for the γ-regioisomers than for the α-regioisomers. These results show that the site of conjugation in the glutamyl moiety of folic acid has a significant impact on the in vivo behavior of ¹⁸F-based radiofolates, but not on their in vitro FR-binding affinity. These findings may potentially stimulate new directions for the design of novel ¹⁸F-labeled folate-based radiotracers.