Contrast enhancement in MRI using magnetization or saturation transfer techniques promises better sensitivity, and faster acquisition compared to T₁ or T₂ contrast. This work reports the synthesis and evaluation of 5-HT_1A targeted PARACEST MRI contrast agent using 1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide (DO3AM) as the bifunctional chelator, and 5-HT_1A-antagonist methoxyphenyl piperazine (MPP) as a targeting unit. The multi-step synthesis led to the MPP conjugated DO3AM with 60% yield. CEST-related physicochemical parameters were evaluated after loading DO3AM-MPP with paramagnetic MRI active lanthanides: Gadolinium (Gd-DO3AM-MPP) and Europium (Eu-DO3AM-MPP). Luminescence lifetime measurements with Eu-DO3AM-MPP and computational DFT studies using Gd-DO3AM-MPP revealed the coordination of one water molecule (q=1.43) with metal-water distance (r_M-H₂O) of 2.7 Å and water residence time (τ_m) of 0.23 ms. The dissociation constant of K_d 62 ± 0.02 pM as evaluated from fluorescence quenching of 5-HT_1A (protein) and docking score of -4.81 in theoretical evaluation reflect the binding potential of the complex Gd-DO3AM-MPP with the receptor 5-HT_1A. Insights of the docked pose reflect the importance of NH₂ (amide) and aromatic ring in Gd-DO3AM-MPP while interacting with Ser 374 and Phe 370 in the antagonist binding pocket of 5-HT_1A. Gd-DO3AM-MPP shows longitudinal relaxivity 5.85 mM^-1s^-1 with a water residence lifetime of 0.93 ms in hippocampal homogenate containing 5-HT_1A. The potentiometric titration of DO3AM-MPP showed strong selectivity for Gd³⁺ over physiological metal ions such as Zn²⁺ and Cu²⁺. The in vitro and in vivo studies confirmed the minimal cytotoxicity and presential binding of Gd-DO3AM-MPP with 5-HT_1A receptor in the hippocampus region of the mice. Summarizing, the complex Gd-DO3AM-MPP can have a potential for CEST imaging of 5-HT_1A receptors.

与 T ₁或 T ₂对比相比，使用磁化或饱和转移技术的 MRI 对比度增强有望提供更好的灵敏度和更快的采集。这项工作报告了使用 1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetamide (DO3AM) 作为双功能螯合剂和 5-HT _1A合成和评估 5-HT _1A靶向 PARACEST MRI 造影剂-拮抗剂甲氧基苯基哌嗪 (MPP) 作为靶向单元。多步合成导致 MPP 共轭 DO3AM 的产率为 60%。在用顺磁 MRI 活性镧系元素加载 DO3AM-MPP 后评估 CEST 相关的物理化学参数：钆 (Gd-DO3AM-MPP) 和铕 (Eu-DO3AM-MPP)。使用 Eu-DO3AM-MPP 的发光寿命测量和使用 Gd-DO3AM-MPP 的计算 DFT 研究揭示了一个水分子 (q=1.43) 与2.7 Å 的金属-水距离 (r _M -H ₂ O) 和水驻留的协调0.23 毫秒的时间 (τ _m )。从 5-HT _{1A 的}荧光猝灭评估的 K _d 62 ± 0.02 pM的解离常数(蛋白质) 和理论评估中的对接分数 -4.81 反映了复合物 Gd-DO3AM-MPP 与受体 5-HT _1A的结合潜力。对接姿势的见解反映了 NH ₂（酰胺）和芳香环在 Gd-DO3AM-MPP 中的重要性，同时与 5-HT _1A的拮抗剂结合口袋中的 Ser 374 和 Phe 370 相互作用。Gd-DO3AM-MPP在含有 5-HT _{1A 的}海马匀浆中显示出 5.85 mM ^-1 s ^{-1 的}纵向弛豫时间和 0.93 ms 的水驻留寿命。DO3AM-MPP 的电位滴定显示对 Gd ^{3+ 的}选择性强于生理金属离子如 Zn ²⁺和 Cu ²⁺。这体外和体内研究证实了 Gd-DO3AM-MPP 与小鼠海马区5-HT _1A受体的最小细胞毒性和目前结合。总之，复合物 Gd-DO3AM-MPP 具有对 5-HT _1A受体进行 CEST 成像的潜力。