A novel (68)Ga-labeled pteroic acid-based pet tracer for tumor imaging via the folate receptor.

The folate receptor (FR) is a very attractive target in oncological imaging as it is overexpressed by a variety of cancer types, whereas the expression in healthy tissue is very limited. The synthesis of regioisomeric pure folic acid derivatives normally requires a regioselective approach and does not allow the use of native folic acid (FA). As the pharmacophore of FA is assumed to be pteroic acid, its use without the glutamic acid moiety may enable the possibility to considerably simplify the synthesis of a positron emission tomography (PET) tracer for FR imaging. In this work, DO3A-EA-Pte was successfully synthesized and labeled with (68)Ga. It is stable for up to 3 h in PBS and against transchelation by transferrin. It also displays a lipophilicity that allows the assumption that it will show favorable in vivo characteristics for FR imaging via PET.