Radiochemical Synthesis of 4-[18F]FluorobenzylAzide and Its Conjugation with EGFR-Specific Aptamers

Central nervous system tumors related to gliomas are of neuroectodermal origin and cover about 30% of all primary brain tumors. Glioma is not susceptible to any therapy and surgical attack remains one of the main approaches to its treatment. Preoperative tumor imaging methods, such as positron emission tomography (PET), are currently used to distinguish malignant tissue to increase the accuracy of glioma removal. However, PET is lacking a specific visualization of cells possessing certain molecular markers. Here, we report an application of aptamers to enhancing specificity in imaging tumor cells bearing the epidermal growth factor receptor (EGFR). Glioblastoma is characterized by increased EGFR expression, as well as mutations of this receptor associated with active division, migration, and adhesion of tumor cells. Since 2021, EGFR has been included into the WHO classification of gliomas as a molecular genetic marker. To obtain conjugates of aptamers GR20 and GOL1-specific to EGFR, a 4-[F-18]fluorobenzylazide radiotracer was used as a synthon. For the production of the synthon, a method of automatic synthesis on an Eckert & Ziegler research module was adapted and modified using spirocyclic iodonium ylide as a precursor. Conjugation of 4-[F-18]fluorobenzylazide and alkyne-modified aptamers was carried out using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) with/without the TBTA ligand. As a result, it was possible to obtain F-18-labelled conjugates with 97% radiochemical purity for [F-18]FB-GR20 and 98% for [F-18]FB-GOL1. The obtained conjugates can be used for further studies in PET analysis on model animals with grafted glioblastoma.

Automated summary

Central nervous system tumors related to gliomas account for about 30% of all primary brain tumors. Surgical attack is the main treatment approach as there is no effective therapy for glioma. The use of PET imaging methods, such as positron emission tomography, can enhance the accuracy of glioma removal by distinguishing malignant tissue. However, PET lacks specific visualization of cells with certain molecular markers. In this study, aptamers were used to enhance specificity in imaging tumor cells bearing the epidermal growth factor receptor (EGFR). Conjugates of aptamers specific to EGFR were successfully obtained and can be used for further PET analysis on model animals with grafted glioblastoma.