Preliminary Application Evaluation Of ¹⁸F-labeled Hippuric Acid Analogs And Aminooxy Acetic Acid Derivative Renal Dynamic PET Imaging Agents

Objective:Dynamic renoscintigraphy can continuously display double kidney blood perfusion,renal parenchyma morphology and function and urinary tract morphology and drainage function,has the characteristics of safety,non-invasive,convenient and information uniformity,more has the advantage of showing kidney function,is one of the most important examination methods of urinary system.At present,the most commonly used renal imaging agents are single-photon radionuclide imaging agents,while positron radionuclide imaging agents are mostly in the stage of pre-clinical research,and rarely used in the clinical work of renal dynamic imaging.In addition,compared with single-photon emission Computed tomography（SPECT）,positron emission tomography（PET）can provide not only higher spatial resolution but also many quantitative parameters.In this study,two positron labeled renal imaging agents were preliminarily evaluated.In the first part,a previously synthesized ¹⁸F-labeled hippuric acid analogs(6-[¹⁸F]FPyGly)was used to evaluate renal function in rats with different severity of diabetic nephropathy,and the results were compared with the results of Scr and BUN in rats,which were confirmed by histopathology.In the second part,this study synthesized¹⁸F-labeled aminoxy acetic acid derivative(¹⁸F-FDG-AOA)using ¹⁸F-FDG as labeled auxiliary group by radiochemical labeling of aminoxy acetic acid through oxime reaction,and conducted preliminary evaluation on its biological distribution,in vitro stability and rat kidney micro-PET/CT imaging.Methods:Evaluation of renal function in diabetic nephropathy model rats by 6-[¹⁸F]FPyGly micro-PET/CT dynamic renal imaging:twenty 8-week-old male SD rats were purchased and randomly divided into 4 groups according to feeding time and feed type（n=5）,group1:healthy control group（HC）;Group 2:diabetic nephropathy model group（DNM）,fed with high glucose and high fat;Group 3:routine feed,diabetic nephropathy model group（RDNM）,high glucose and high fat feeding+routine feed feeding;Group 4:the high fat and high sugar,diabetic nephropathy model group（HDNM）,high sugar and high fat feed.Renal function parameters of dynamic renal imaging:curve peak counts（P,）Time of max(T_max),time from Max to 1/2Max(C_1/2)and curve height at the time of15min/peak counts（15min/Peak ratio）were obtained from 6-[¹⁸F]FPyGly micro-PET/CT imaging data.After micro-PET/CT dynamic renal imaging,blood was collected from the posterior ophthalmic artery of the rats,and Scr and BUN values were measured.By correlation analysis and difference comparison,the specificity and sensitivity of renal function parameters of dynamic renal imaging and the concentration of Scr and BUN on renal function evaluation of rats with different severity of diabetic nephropathy were compared.Synthesis and preliminary application of ¹⁸F-FDG-AOA,a novel renal imaging agent:Using 2-¹⁸F-fluoro-2-deoxy-d-glucose(¹⁸F-FDG)as the labeled supplement,¹⁸F-FDG-AOA was synthesized by reacting with Aminooxyacetic Acid（AOA）into oxime.The crude product was purified by Sep Pak QMA column,and TLC thin layer scanner was used to detect whether the radiochemical purity reached the radiochemical purity of injection.The biological distribution experiment and abnormal toxicity experiment of ¹⁸F-FDG-AOA were carried out in healthy ICR mouses,the stability of ¹⁸F-FDG-AOA was detected under different PH values,and the preliminary application study of renal function evaluation of ¹⁸F-FDG-AOA was carried out in healthy SD rats by micro-PET/CT dynamic renal imaging.Results:The parameters used to evaluate renal function from 6-[¹⁸F]FPyGly micro-PET/CT dynamic renal imaging mainly include T_max,C_1/2,P and 15min/Peak ratio.There were significant differences in T_max,P,Scr and BUN between group 1 and group 2.There was no significant difference in C_1/2 and 15min/Peak ratio between group 1 and group 2.In diabetic nephropathy models with different severity（group 2,group 3 and Group 4）,renal function parameters T_max,C_1/2,P and 15min/Peak ratio increased gradually among and P decreased gradually among the three groups the three groups,while P and15min/Peak ratio showed significant differences among the three groups.T_max and C_1/2were significantly different only between group 2 and group 3,and between group 2 and group 4.The levels of Scr and BUN increased,but there was no significant difference in Scr among the three groups,and there was a significant difference in BUN between group 2 and group 4.Statistical results showed that P,T_max,C_1/2 and 15min/Peak ratio had higher specificity than Scr and BUN in monitoring renal function of diabetic nephropathy model rats.The pathological changes of glomerulus,tubules and interstitium of rats in the three groups were gradually aggravated,which was consistent with the changes of renal function parameters.The radio-chemical Yield（RCY）of ¹⁸F-FDG-AOA was 64±10%.The radio-chemical purity of ¹⁸F-FDG-AOA was more than 98%after purification by Sep Pak QMA column.In vivo biological distribution results showed that:After injection,¹⁸F-FDG-AOA is distributed in the whole body with blood circulation,mainly in the blood and kidney.The radioactivity of the kidney and blood continues to decline over time,and basically reaches the tissue background level within 60min.The radioactivity distribution of all organs remains at a low level all the time,and a small amount is absorbed in bone tissue,but the radioactivity gradually decreases over time.Micro-PET/CT dynamic renal imaging of rats showed that,10min after injection,the development of both renal cortices was clear,and the imaging agent was concentrated in the bladder.Peripheral liver and spleen tissues had little uptake of the imaging agent.After 60min,both renal cortices were still clearly developed.Conclusion:6-[¹⁸F]FPyGly micro-PET/CT dynamic renal imaging parameters P,T_max,C_1/2 and15min/Peak ratio have higher specificity in monitoring renal dysfunction in diabetic nephropathy rats than concentrations of Scr and BUN,and can indirectly reflect renal pathological changes.Among the parameters,renal function parameters P and 15min/Peak ratio have better efficacy in the evaluation of renal function changes in diabetic nephropathy model rats.¹⁸F-FDG-AOA was successfully prepared by the reaction of ¹⁸F-FDG as labeled auxiliary group and aminoxy acetic acid with oxime.The labeling method was simple and the labeling rate was high.The results of biological distribution showed that the imaging agent was mainly distributed in blood and kidney,and the distribution of other organs and tissues was very low.Preliminary rat micro-PET/CT imaging results showed that18F-FDG-AOA was excreted through the kidney and had very low peripheral background,which has the potential to develop into a new PET renal function imaging agent.However,the longer mechanism between kidney retention and 18F-FDG-AOA needs further study.