Development Of Two 18 F-labeled Targeted Follicle Stimulating Hormone Receptor Imaging Agents And Imaging Studies In Prostate Cancer

Purpose: Follicle stimulating hormone receptor?FSHR?is selectively expressed in endothelial cells of prostate cancer?PCa?and involves in tumorigenesis and development.FSHR has become an important target for diagnosis and therapy of PCa.FSH1?YTRDLVYKDPARPKIQKTCTF?which is a FSHR specific antagonist was prepared in our previous study as a targeting ligand to develop a new PET?Positron Emission Computed Tomography?probe ¹⁸F-Al-NOTA-MAL-FSH1,prostate tumor xenograft model is clearly visible,however,the fast clear from tumor tissue may weaken the performance of the probe in vivo.Nine-arginine?R9?is a kind of cell penetrating peptides?CPPs?,has strong penetration ability and contributes to enhance the penetrability of tracer and extend residence time.In this study,R9 modified FSH1 peptides?R9-FSH1?was radiosynthesized and used to PCa imaging to determine the targeting and performance of the new tracer in vivo.Methods: ¹⁸F-Al and NOTA-MAL was combined firstly,then conjugated with R9-FSH1 to obtain ¹⁸F-Al-NOTA-MAL-R9-FSH1.The oil-water partition coefficient and PC-3 cell experiments in vitro were performed.Balb/c nude mice bearing human PCa were used for in vivo study.Results: The yield of ¹⁸F-Al-NOTA-MAL was 8%,R9-FSH1 was labeled by ¹⁸F-Al-NOTA-MAL within 2 h and the non-decay corrected yield were 4.01 ± 0.54%(based on ¹⁸F-Al-NOTA-MAL),the radiochemical purity was > 95% and the specific activity was about 0.22 GBq/?mol.The oil-water partition coefficient for ¹⁸F-Al-NOTA-MAL-R9-FSH1 was-2.29 ± 0.17.¹⁸F-Al-NOTA-MAL-R9-FSH1 indicated the highly specific FSHR targeting in human prostate cancer PC-3 cells through the cell experiments in vitro.Tumors were clearly visualized with good contrast to background through micro PET.ROI analysis showed the tumor uptake of ¹⁸F-Al-NOTA-MAL-R9-FSH1 were 1.54 ± 0.03,0.84 ± 0.19,0.22 ± 0.07 %ID/g,at 30,60 and 120 min postinjection?p.i.?,respectively.The biodistribution studies of ¹⁸F-Al-NOTA-MAL-R9-FSH1 were consistent with the micro PET findings.¹⁸F-Al-NOTA-MAL-R9-FSH1 showed the accumulation of tumor were 1.69 ± 0.14,0.77 ± 0.09,0.19 ± 0.03 %ID/g,respectively,at 30,60,120 min p.i..FSHR-binding specificity was also demonstrated by reduced tumor uptake after coinjection excessive unlabeled R9-FSH1.Conclusions: ¹⁸F-Al-NOTA-MAL-R9-FSH1 can be radiolabeled successfully and used for micro PET imaging in human prostate tumor models.These preclinical studies may contribute to improve the further development of FSHR-targeting PET probes.Purpose: Follicle stimulating hormone receptor?FSHR?is selectively high-expressed in endothelial cells of prostate cancer?PCa?,and brings an important biological significance on tumorigenesis,development and metastasis.Hence,FSHR is a promising target for diagnosis and therapy of PCa.In our previous study,we developed a new PET?Positron Emission Computed Tomography?probe ¹⁸F-Al-NOTA-MAL-FSH1,micro PET showed the tumor was visible,however,the unfavourable abdominal background may hamper the translation of the probe in clinical.GGGRDN?Gly-Gly-Gly-Arg-Asp-Asn?is a new hydrophilic linker and has been proven to improve the imaging quality of Bombesin peptides.In this study,GGGRDN modified FSH1 peptides?GGGRDN-FSH1?was radiosynthesized and used to PCa imaging to determine the targeting and performance of the new tracer in vivo.Methods: NOTA-MAL-GGGRGDN-FSH1 was designed and then labeled with Al18 F.The in vitro stability studies were determined in PBS and human serum,the oil-water partition coefficient and cell experiments in vitro were performed.Balb/c nude mice bearing human PCa were used for in vivo study.Results : NOTA-MAL-GGGRDN-FSH1 was obtained with ⁵0% yield.GGGRDN-FSH1 was labeled by 18 F within 20 min,and the non-decay corrected yield was 41.46 ± 10.36%(Based on ¹⁸F),the radiochemical purity was > 95% and the specific activity was at least 50 GBq/?mol.¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 kept stable for at least 2 h.The oil-water partition coefficient for ¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 were-1.18 ± 0.17.In vitro experiments indicated ¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 owned the highly specific FSHR targeting in human prostate cancer PC-3 cells.Tumors were clearly visualized with good contrast to background through micro PET.ROI analysis showed the tumor uptakes of ¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 were 2.68 ± 0.52,1.97 ± 0.61,1.26 ± 0.21 %ID/g,at 30,60 and 120 min postinjection?p.i.?,respectively.The biodistribution studies of ¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 were consistent with the micro PET findings.¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 showed the accumulation of liver and intestine were 0.47 ± 0.11,0.12 ± 0.03 %ID/g,respectively,at 60 min p.i..FSHR-binding specificity was also demonstrated by reduced tumor uptake after coinjection excessive unlabeled GGGRDN-FSH1.Conclusions: Preclinical studies have shown that ¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 could be radiolabeled with Al18 F successfully in one-step method and contributed to prostate tumor imaging.¹⁸F-Al-NOTA-MAL-GGGRDN-FSH1 appears to be a promising molecular imaging tracer for FSHR-positive tumors.