Clickable, Hydrophilic Ligand for fac-[MI(CO)3]+ (M = Re/99mTc) Applied in an S-Functionalized 伪-MSH Peptide

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• 作者：Benjamin B. Kasten ; Xiaowei Ma ; Hongguang Liu ; Thomas R. Hayes ; Charles L. Barnes ; Shibo Qi ; Kai Cheng ; Shalina C. Bottorff ; Winston S. Slocumb ; Jing Wang ; Zhen Cheng ; Paul D. Benny
• 刊名：Bioconjugate Chemistry
• 出版年：2014
• 出版时间：March 19, 2014
• 年：2014
• 卷：25
• 期：3
• 页码：579-592
• 全文大小：500K
• 年卷期：v.25,no.3(March 19, 2014)
• ISSN：1520-4812

文摘

The copper(I)-catalyzed azide鈥揳lkyne cycloaddition (CuAAC) click reaction was used to incorporate alkyne-functionalized dipicolylamine (DPA) ligands (1 and 3) for fac-[M^I(CO)₃]⁺ (M = Re/^99mTc) complexation into an 伪-melanocyte stimulating hormone (伪-MSH) peptide analogue. A novel DPA ligand with carboxylate substitutions on the pyridyl rings (3) was designed to increase the hydrophilicity and to decrease in vivo hepatobiliary retention of fac-[^99mTc^I(CO)₃]⁺ complexes used in single photon emission computed tomography (SPECT) imaging studies with targeting biomolecules. The fac-[Re^I(CO)₃(3)] complex (4) was used for chemical characterization and X-ray crystal analysis prior to radiolabeling studies between 3 and fac-[^99mTc^I(OH₂)₃(CO)₃]⁺. The corresponding ^99mTc complex (4a) was obtained in high radiochemical yields, was stable in vitro for 24 h during amino acid challenge and serum stability assays, and showed increased hydrophilicity by log P analysis compared to an analogous complex with nonfunctionalized pyridine rings (2a). An 伪-MSH peptide functionalized with an azide was labeled with fac-[M^I(CO)₃]⁺ using both click, then chelate (CuAAC reaction with 1 or 3 followed by metal complexation) and chelate, then click (metal complexation of 1 and 3 followed by CuAAC with the peptide) strategies to assess the effects of CuAAC conditions on fac-[M^I(CO)₃]⁺ complexation within a peptide framework. The peptides from the click, then chelate strategy had different HPLC t_R鈥檚 and in vitro stabilities compared to those from the chelate, then click strategy, suggesting nonspecific coordination of fac-[M^I(CO)₃]⁺ using this synthetic route. The fac-[M^I(CO)₃]⁺-complexed peptides from the chelate, then click strategy showed >90% stability during in vitro challenge conditions for 6 h, demonstrated high affinity and specificity for the melanocortin 1 receptor (MC1R) in IC₅₀ analyses, and led to moderately high uptake in B16F10 melanoma cells. Log P analysis of the ^99mTc-labeled peptides confirmed the enhanced hydrophilicity of the peptide bearing the novel, carboxylate-functionalized DPA chelate (10a鈥?/b>) compared to the peptide with the unmodified DPA chelate (9a鈥?/b>). In vivo biodistribution analysis of 9a鈥?/b> and 10a鈥?/b> showed moderate tumor uptake in a B16F10 melanoma xenograft mouse model with enhanced renal uptake and surprising intestinal uptake for 10a鈥?/b> compared to predominantly hepatic accumulation for 9a鈥?/b>. These results, coupled with the versatility of CuAAC, suggests this novel, hydrophilic chelate can be incorporated into numerous biomolecules containing azides for generating targeted fac-[M^I(CO)₃]⁺ complexes in future studies.