PET Molecular Probes Targeting Folate Receptor

Folic acid can combine specifically with folate receptors (FRs) which are overexpressed on the epithelial cells of the tumor. The FRs are confirmed to be the tumor-associated antigens that bind folate and folate conjugates with very high affinity and shuttle these bound molecules inside cells via an endocytic mechanism．The FR-α is a target of critical value for nuclear imaging through using folate-based radiotracers as it is expressed on several tumor types. Moreover, employment of folate radiopharmaceuticals for imaging of inflammatory diseases by targeting at FR-β on activated macrophages holds promise as a further field of application. Based on these, more and more researches focus on folate conjugates labeled with radionuclides for nuclear medicine imaging (including single photon emission computed tomography (SPECT) and positron emission tomography (PET). These folate molecular probes are applied not only in cancer imaging but also in inflammation imaging. Hence, folate-based imaging agents may be useful for selection of patients who could profit from such new therapy concepts and for monitoring response to a particular treatment. This review was focused on the preparation and preclinical biological evaluation of the molecular probes which were labeled by positron nuclides （¹⁸F, ¹²⁴I, ⁶⁸Ga, ⁴⁴Sc, ¹⁵²Tb）, and the clinical application of these molecular probes were discussed.