Application Of A Novel Glucagon-like Peptide-1 Receptor Probe In PET Imaging Of Pheochromocytoma

Objective:Noninvasivediagnosisofpheochromocytoma?Pheochromacytoma,PHEO?is a major challenge in clinic.Glucagon-like peptide-1receptor?GLP-1R?is overexpressed in pheochromocytoma and becomes a specific target for the tumor.Exendin-4 is a GLP-1R agonist and its radiolabeled analogues have been used to detect the levels of GLP-1R.A novel Positron Emission Computed Tomography?PET?probe,⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4,was prepared for imaging pheochromocytoma.The feasibility of the probe in the diagnosis of pheochromocytoma was investigated by in vitro and in vivo study.Methods:The precursor,NOTA-MAL-Cys³⁹-exendin-4,was prepared by coupling Cys³⁹-exendin-4 with a bifunctional chelating agent NOTA-Maleimide?NOTA-MAL?,and ⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4 was obtained by one-step reaction.HPLC was used to determine the radiochemical purity of the probe.The receptor affinity was investigated by in vitro cell uptake study.A model of pheochromocytoma?high and low differentiation PC-12?was established to evaluate the pharmacokinetic properties of the probe in vivo by micro PET imaging combining with biodistribution.The results were compared with the commonly used tumor imaging agents ¹⁸F-FDG and ¹³¹I-MIBG.In addition,the safety of the probes was also evaluated.Results:TheyieldofNOTA-MAL-Cys³⁹-exendin-4was60%?70%.⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4 could be prepared within 30 min,with a labeling yield of 91.6±2.8%and radiochemical purity was greater than 95%.The uptake values of the probe in PC-12 high and low differentiation cells were 0.90±0.07%AD/10⁶cells and 1.84±0.21%AD/10⁶cells respectively.The cell uptake values was significantly blocked by excessive Cys³⁹-exendin-4 and decreased to 0.24±0.10%AD/10⁶cells and 0.47±0.02%AD/10⁶cells respectively.Immunohistochemical?IHC?staining revealed that higher expression of GLP-1R was found in PC-12 low differentiation pheochromocytoma than those in high differentiation pheochromocytoma.Micro PETimagingshowedthat⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4 was specifically concentrated more in the former than that in the latter.A significant difference was found between the uptake values in two tumors.At 30 min,60 min and 120 min postinjection,the uptake values of⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4 in PC-12 poorly differentiated and highly differentiated pheochromocytoma were 1.88±0.10%ID/g?1.53±0.13%ID/g?1.15±0.16%ID/g and 1.09±0.03%ID/g?0.91±0.01%ID/g?0.71±0.01%ID/g respectively.On the country,no significant differences were observed in the tumors imaged with ¹⁸F-FDG or ¹³¹I-MIBG at 60min postinjection.Biodistribution verified that the probe was mainly excreted by the kidney and less absorbed in the liver.It was showed that ⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4 was metabolized faster in blood,and the half-life of distribution and elimination in mice were 3.16 min and 14.52 min respectively.Conclusion:⁶⁸Ga-NOTA-MAL-Cys³⁹-exendin-4 is easily to be obtained by a simple synthesis procedure with high radiochemical purity,good targeting,and safety.It may provide a non-invasive method for diagnosis of pheochromocytoma in clinic.