Prosthetic radiolabeling of the Tenascin-C-binding aptamer TTA-01 with fluorine-18 using [18F]FPyMe

Objectives TTA-01 is a size-minimized (39 mer, 13.4 kDa), chemically modified RNA aptamer that binds to the fibrinogen-like domain of human Tenascin-C, a hexameric glycoprotein, primarily located in the extracellular matrix and involved in tumorigenesis. The 5’ end was derivatized with a hexyl-aminolinker bearing an N2S peptidyl chelating moiety (mercaptoacetyl-(Gly)₂) for the labeling with radiometals but offering also the possibility of a prosthetic labeling with fluorine-18 using [¹⁸F]FPyME du to the presence of a free sulfhydryl function. This fluorine-18-labeling is presented herein.

Methods [¹⁸F]FPyME was prepared using a three-step radiochemical pathway already reported. [¹⁸F]FPyME, after HPLC-purification, was conjugated with TTA-01 (0.650-0.850 mg) in 1 mL of a 1/9 (v/v) mixture of DMSO and 0.1 M aq. PBS (pH 7.5) at room temperature for 15 min. c-[¹⁸F]TTA-01 (the product of TTA-01 coupling with [¹⁸F]FPyME) was then purified by semipreparative C-18 HPLC. c-[¹⁸F]TTA-01 was finally formulated in aq. 0.9% NaCl.

Results Typically, 5.2-7.5 GBq of pure [¹⁸F]FPyME could be obtained after HPLC in 110 min starting from a cyclotron production batch of 37-51 GBq of [¹⁸F]fluoride. Conjugation of [¹⁸F]FPyME with TTA-01 was achieved in ndc 50-70% yield and c-[¹⁸F]TTA-01 was easily purified from non-reacted [¹⁸F]FPyME using HPLC. Routinely, 0.6-1.4 GBq of HPLC-purified and formulated c-[¹⁸F]TTA-01 could be obtained in 65-75 minutes starting from the above-mentioned [¹⁸F]FPyME batch.

Conclusions The fluorine-18-labeled reagent [¹⁸F]FPyME has been succesfully used for the prosthetic labeling of the Tenascin-C-binding aptamer TTA-01.