Changes in SPECT imaging of 99mTc-labeled cyclic nonapeptide CGRRAGGSC in nude mice bearing human non-small cell lung cancer A549

ZHAO Guotai; LI Chunming; LUO Yuyu; LIU Yinshuo; GUO Shuang; ZHANG Qinliang

doi:10.20258/j.cnki.1006-9011.2026.01.030

Abstract：Objective To investigate the SPECT imaging changes of the radionuclide 99mTc-labeled cyclic nonapeptide CGRRAGGSC(99mTc-DTPA-CGRRAGGSC)in nude mice bearing human non-small cell lung cancer A549 cells.Methods 99mTc-DTPA-CGRRAGGSC was prepared using the stannous chloride reduction method.The radiochemical purity and stability of the labeled product in PBS and serum were determined by high performance liquid chromatography(HPLC).The binding ability of the labeled product to A549 cells in vitro was assessed by chemical fluorescence receptor binding localization assay and binding competition inhibition assay.A549 cells were subcutaneously implanted to establish a tumor-bearing nude mouse model.The labeled product was injected via the tail vein,and the mice were sacrificed at 0.5,1.0,2.0,4.0,6.0,and 8.0 h post-injection.Tissues including brain,heart,liver,lung,kidney,muscle,bone,and tumor were collected for radioactivity counting.The percentage of injected dose per gram of tissue(％ID/g)was calculated to observe the biodistribution of the labeled product in tumor-bearing nude mice.SPECT imaging was performed to visualize the labeled product in nude mice,and the target-to-nontarget ratio(T/NT)of mean radioactivity in the tumor region versus the contralateral symmetric non-target region was calcu-lated.Results The radiochemical purity of 99mTc-DTPA-CGRRAGGSC was 96.8％.The radiochemical purity of the labeled product in serum was lower than that in PBS immediately and at 3.0 h after labeling(all P<0.05),while no significant difference was observed between serum and PBS at 6.0 and 12.0 h(all P>0.05).Chemical fluorescence receptor binding localization assay showed that the 99mTc-DTPA-CGRRAGGSC-FITC complex bound to A549 cells exhibited yellow-green fluorescence,but no fluo-rescence was observed when bound to AT Ⅱ cells.Chemical fluorescence receptor binding competition inhibition assay showed that the 99mTc-DTPA-CGRRAGGSC-FITC complex bound to A549 cells exhibited green fluorescence,which weakened after the addition of a competitive inhibitor.The radioactivity in tumor tissue was higher than that in blood,brain,heart,liver,lung,kid-ney,muscle,and bone at 1.0,2.0,4.0,6.0,and 8.0 h after injection(all P<0.05).At 8.0 h post-injection,tumor tissue still maintained high radioactivity,while radioactivity in vital tissues and organs gradually decreased compared to that at 0.5 h(all P<0.05).Throughout SPECT imaging,mild whole-body visualization of tumor-bearing nude mice was observed and gradually faded.At 0.5 h post-injection,the bladder and tumor site were visualized.At 2.0 h post-injection,the tumor site was clearly visualized with distinct boundaries,reaching the most significant visualization at 4.0 h,which persisted until 8.0 h.Bladder visualization gradually faded at 4.0 h.The T/NT ratio first increased and then decreased over time post-injection,with the T/NT at 6.0 h being higher than that at other time points(all P<0.05).Conclusion 99mTc-DTPA-CGRRAGGSC is easy to prepare,exhibits good biological stability,and shows favorable targeting to nude mice bearing human non-small cell lung cancer A549 cells.Its radioac-tivity metabolizes rapidly in non-target areas without obvious abnormal accumulation.