The Study Of PET New Molecular Probes Targeting On Hsp90 For Diagnosis Of Early Pancreatic Cancer

BackgroundDetection of early pancreatic cancer is still a challenge nowadays.Positron emission tomography?PET?is a newly emerged molecular imaging modality,which can offer functional information of the disease and detect the expression of indicative molecular targets in vivo non-invasively.¹⁸F-FDG is a non-specific PET tracer in oncology,increased glucose metabolism of mass pancreatitisis is the main source of false-positive PET findings in pancreatic cancer.Receptor imaging has advantages of high sensitivity,specificity and accuracy.Heat Shock Protein 90?Hsp90?is overexpressed in the majority of cancers,including pancreatic cancer,but with low expression in pancreatitisis.Dimer-Sansalvamide A cyclodecapeptide is an Hsp90 inhibitor,which can bind to Hsp90 with high specificity and affinity.PurposeIn this study,Hsp90 was used as the imaging target,which is highly expressed in pancreatic cancer,and NOTA-Dimer-Sansalvamide A cyclodecapeptide was labeled using radionuclide⁶⁴Cu/¹⁸F.The purpose of the study is to explore the feasibility of the PET imaging of Hsp90expression for diagnosis and differential diagnosis of early pancreatic cancer.MethodsA macrocyclic chelator NOTA?1,4,7-triazacyclononane-1,4,7-trisacetic acid?was conjugated to NOTA-Dimer-Sansalvamide A.⁶⁴Cu/¹⁸F-NOTA-Dimer-Sansalvamide A were successfully prepared,and evaluated their characteristics such as in vitro stability.PL45 cell uptake assay,MicroPET imaging of nude mice bearing PL45 pancreatic cancer and block studies confirmed the binding specificity.Meanwhile,an inflammation model?induced with turpentine?was used as a contrast.MicroPET imaging was performed to detect the difference of Hsp90 expression in pancreatic cancer and inflammation after tail vein injection.Results⁶⁴Cu-NOTA-Dimer-Sansalvamide A was labled in a radiochemical yield>97%with a radiochemical purity>98%.It was stable in PBS and mouse serum with>92%of parent probe intact after 4 h incubation.The cell binding and uptake revealed that ⁶⁴Cu-NOTA-Dimer-Sansalvamide A binded to Hsp90-positive PL45 pancreatic cancer cells,and the binding can be effectively blocked by an Hsp90 inhibitor?17AAG?.For MicroPET study,⁶⁴Cu-NOTA-Dimer-Sansalvamide A showed good in vivo performance in terms of tumor uptake in nude mice bearing PL45 tumors at 2 h and 4 h?2.97±0.58%ID/g and 2.87±0.60%ID/g respectively?.The Hsp90-specific tumor activity accumulation of ⁶⁴Cu-NOTA-Dimer-Sansalvamide A was further demonstrated by significant reduction of PL45 tumor uptake with a pre-injected blocking dose of17AAG.The ex vivo PET imaging and biodistribution results were consistent with the quantitative analysis of PET imaging,demonstrating good tumor-to-muscle ratio?5.35±0.46?of⁶⁴Cu-NOTA-Dimer-Sansalvamide A at 4 h post-injection in PL45 pancreatic cancer xenografts.¹⁸F-NOTA-Dimer-Sansalvamide A was synthesized with a 32.7%radiochemical yield and>99%purity.The in vitro cell uptake and block study confirmed the binding specificity of¹⁸F-NOTA-Dimer-Sansalvamide A and Hsp90.Furthermore,Hsp90 expression was imaged with MicroPET in pancreatic cancer xenografts.And sterile inflammation mice in the left calf muscle were also established as a contrast.All the mice received an intravenous bolus of¹⁸F-NOTA-Dimer-Sansalvamide A,and images were scanned at 1 h,2 h time points.The new probe demonstrated prominent tumor uptake in the pancreatic cancer xenografts?4.00±0.88%ID/g,5.80±0.94%ID/g?,and the inflammatory thigh showed little uptake?0.85±0.006%ID/g,1.50±0.20%ID/g?at 1 h and 2 h after injection,respectively.The difference was statistically significant?p<0.05?.The biodistribution results were consistent with the quantitative analysis of PET imaging,demonstrating good tumor-to-muscle ratio?5.85±1.69?of ¹⁸F-NOTA-Dimer-Sansalvamide A at 2 h post-injection in PL45 pancreatic cancer xenografts.Conclusions⁶⁴Cu/¹⁸F-NOTA-Dimer-Sansalvamide A are specific molecular probes targeting on Hsp90,which allow PET imaging of Hsp90 expression in pancreatic cancer xenografts,and have potential for diagnosis and differential diagnosis of early pancreatic cancer.