99mTc(CO)3-Labeled 1-(3-Nitropyridin-2-yl) Piperazine as Potential Radioligand for 5-HT7 Receptors

Background and purpose: The serotonin receptor (5-HTR) family includes seven distinct members, with the serotonin seven receptor (5-HT7R) being the newest addition to this family. The 5-HT7R contributes to different physiological and pathological processes including glioblastoma multiforme (GBM). The standard treatment for GBM involves a combination of surgery, radiotherapy and chemotherapy. However, GBM tumors are highly diffuse and exhibit a significant risk of recurrence. As a result, the use of advanced monitoring techniques, such as nuclear medicine imaging, is essential. This study aims to develop an effective radiotracer for imaging 5-HT7R overexpression in GBM by utilizing a radiolabeled aryl piperazine derivative (99mTc(CO)3-[5]). Materials and methods: In this experimental study, compound 5 1-(3-nitropyridin-2-yl) piperazine was designed, synthesized, and characterized, then radiolabeled with fac-[99mTc(CO)3(H2O)3]+ to produce 99mTc(CO)3-[5]. Quality control tests, including high-حperformance liquid chromatography (HPLC) and thin-layer chromatography (TLC) were performed to determine the radiochemical purity. The specific binding study was performed using various cell lines, including U-87 MG, MCF-7, SKBR3, HT-29, and A549. The affinity of 99mTc(CO)3-[5] for 5-HT7R was evaluated using the U87-MG cell line and the maximum binding capacity (Bmax,) and dissociation constant (Kd) were calculated. Results: The initial radiochemical purity of 99mTc(CO)3-[5] was greater than 95% (RCP>95%). This radiotracer displayed moderate affinity for the U87-MG cell line’s 5-HT7R and lower affinity for MCF-7, SKBR3, HT-29, and A549 cell lines. The calculated Bmax, and Kd of the radioligands were 48±9.23nM and 2.94±0.09×105. Conclusion: Compound 5 can be quantitatively radiolabeled with fac-[99mTc(CO)3(H2O)3]+ resulting in the radiotracer (99mTc(CO)3-[5]). The initial radiochemical purity of this radiotracer is approximately 95%; however, its stability decreases over time. 99mTc(CO)3-[5] recognizes the 5-HT7R on the surface of U87-MG cells and binds to this receptor with moderate affinity.