⁶⁸Ga-DOTA-TFpep Targeting the Thomsen-Friedenreich Antigen for PET Imaging

As an important tumor-associated carbohydrate antigen, the Thomsen-Friedenreich (T or TF) antigen has become an attractive target for tumor diagnosis and treatment. However, there has been very limited success in developing peptide- and small-molecule-based radiopharmaceuticals for this important target. Currently, only ⁶⁴Cu-NO2A-TFpep has been reported as a radiolabeled peptide targeting the TF antigen, and it shows a low tumor-to-liver ratio due to ⁶⁴Cu retention in the liver. In this study, a novel PET probe targeting the TF antigen (DOTA-TFpep) was synthesized using 2,2',2″,2‴-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) chelator for increasing the hydrophilic property and for radiolabeling with different radionuclides. DOTA-TFpep was then radiolabeled with ⁶⁸Ga for positron emission tomography (PET) imaging of breast tumors expressing the TF antigen. ⁶⁸Ga-DOTA-TFpep was confirmed by radio-HPLC with a purity greater than 98% and high stability in PBS. Immunofluorescence analysis confirmed the TF antigen expression of 4T1 and K1 cell lines. Cell uptake studies confirmed its targeting specificity. Further in vivo biodistribution studies in high (4T1) and low (K1) TF antigen-expression xenograft models demonstrated the favorable pharmacokinetics property of the probe. PET imaging and biodistribution showed that ⁶⁸Ga-DOTA-TFpep exhibited specific tumor uptake. Moreover, compared with the widely studied ⁶⁴Cu-NO2A-TFpep, ⁶⁸Ga-DOTA-TFpep showed lower liver uptake and a higher tumor-to-liver ratio (1.31 ± 0.20 for ⁶⁴Cu-NO2A-TFpep and 0.48 ± 0.15 for ⁶⁸Ga-DOTA-TFpep at 120 min after injection). In summary, this study demonstrates the synthesis and evaluation of the TF antigen-targeting probe ⁶⁸Ga-DOTA-TFpep. It shows favorable in vivo tumor imaging properties, highlighting it as a promising molecular probe targeting the TF antigen.