Preparation And Biological Evaluation Of Novel PET Imaging Agents Targeting Hormone Receptor Of Breast Cancer

Breast cancer is the most common cancer among the female and also the main cause of cancer death for women in the world.Estrogen receptor(ER)and progesterone receptor(PR)are overexpressed in most human breast cancers and therefore they become important prognostic factors for directing therapy of breast cancer.Currently,the most commonly used method for detecting ER expression is immunohistochemistry(IHC)assay.However,IHC assay displays some disadvantages,such as invasive procedure of biopsies and low sensitivity.Positron emission tomography(PET)is a noninvasive imaging technology,which can assess the entire lesion in real time,quantify tracer accumulation and offer highly sensitive images of various kinds of cancers.Among some imaging agents of ER or PR,16?-18F-fluoroestradiol(18F-FES)and 21-18F-fluoro-furanyl-norprogesterone(18F-FFNP)are known as the most studied ER and PR PET imagimg agents,respectively.However,the radiosyntheses of 18F-FES and 18F-FFNP always require two steps and semi-prep high-performance liquid chromatography(HPLC)is also necessary for the further purification,resulting in a low radiochemical yield(RCY)for the long time of radiosynthesis.These challenges for 18F-labeling limit the clinical application of 18F-FES and 18F-FFNP.Hence,a facile 18F-labeling approach is needed for these radiotracers,which is significant to promote the clinical application of such imging agents.Therefore,in this paper,two novel imaging agents of ER,18F-AmBF3-ES and 18F-AmBF3-TEG-ES,and a novel imaging agent of PR,18F-AmBF3-PT,are designed and radiosynthesized using one-step 18F-labeling method.The purpose is to obtain novel breast cancer imaging agents with high target selectivity and simple 18F-labeling process.Firstly,three precursors AmBF3-ES,AmBF3-TEG-ES and AmBF3-PT were synthesized through multi-reactions,such as nucleophilic substitution,quaternization,click reaction,and so on.The structures of the products were characterized by elemental analysis,IR spectrum,ESI mass spectrum and nuclear magnetic resonance(1H-NMR,13C-NMR and 19F-NMR).Three radiotracers 18F-Am BF3-ES,18F-AmBF3-TEG-ES and 18F-AmBF3-PT were successfully prepared by one-step 18F-19 F isotope exchange reaction.The conditions for the radiolabeling of the tracers were optimal and determined as follows,the reaction temperature was 80 °C and the reaction time was 30 min.Under the optimal condition,the radiochemical yields of 18F-AmBF3-ES,18F-AmBF3-TEG-ES and 18F-AmBF3-PT were 65%,61% and 68%,respectively.The radiochemical purities(RCPs)of the three tracers were more than 98% within the total reaction time of 40 min.The stability studies indicated that 18F-AmBF3-ES,18F-AmBF3-TEG-ES and 18F-AmBF3-PT remained stable in PBS and serum for at least 4 h.The octanol-water partition coefficients,cell cytotoxicity,cell uptake and block studies and PET imaging of T47 D xenografted mice were performed for biological evaluation of 18F-AmBF3-ES,18F-AmBF3-TEG-ES and 18F-AmBF3-PT.Judged from the octanol-water partition coefficients,the imaging agents 18F-AmBF3-ES and 18F-AmBF3-TEG-ES for targeting ER were lipophilic and hydrophilic,respectively.The results of cell cytotoxicity assay indicated the cold precursors AmBF3-ES and AmBF3-TEG-ES showed little effect on the cell viability and exhibited good biocompatibility.The results of cell uptake and block studies indicated that the radiotracer 18F-AmBF3-ES and 18F-AmBF3-TEG-ES could selectively target ER.PET imaging of T47 D xenografted mice showed that 18F-AmBF3-ES and 18F-AmBF3-TEG-ES had selective uptake in ER+ breast cancer,and the tumor-to-muscle ratios were 2.46 and 1.90,respectively.It is suggested that 18F-AmBF3-ES and 18F-AmBF3-TEG-ES exhibited affinity for ER and the PET imaging effect of 18F-AmBF3-ES was superior to 18F-AmBF3-TEG-ES.According to the measured octanol-water partition coefficient,the PR-targeting agent,18F-AmBF3-PT was lipophilic.The results of cell cytotoxicity assay also indicated that the cold precursor AmBF3-PT exhibited good biocompatibility.In the cell uptake and block studies,the radiotracer 18F-AmBF3-PT showed specifc binding to PR.The specific uptake of 18F-AmBF3-PT in PR+ breast cancer was confirmed by PET imaging of xenografted mice.The tumor-to-muscle ratio was 2.18,which demonstrated the specifc binding of 18F-AmBF3-PT to PR.In summary,the novel ER PET imaging agents,18F-AmBF3-ES and 18F-AmBF3-TEG-ES and the PR PET imaging agent 18F-AmBF3-PT could be successfully prepared in high yields through one step 18F-19 F isotope exchange reaction,obviating drying of the 18F-fluoride ion and semi-prep HPLC purification.These radiotracers showed negligible cytotoxicity,high serum stability and specific binding for ER or PR,which imply that the radiotracers 18F-AmBF3-ES and 18F-AmBF3-TEG-ES are promising ER-targeting PET imaging agents and 18F-AmBF3-PT is a promising PR-targeting PET agent for imaging breast cancer.