First 18F-labeled ligand for PET imaging of uPAR: In vivo studies in human prostate cancer xenografts

Abstract

Urokinase-type plasminogen activator receptor (uPAR) is overexpressed in human prostate cancer and uPAR has been found to be associated with metastatic disease and poor prognosis. AE105 is a small linear peptide with high binding affinity to uPAR. We synthesized an N-terminal NOTA-conjugated version (NOTA-AE105) for development of the first 18F-labeled uPAR positron-emission-tomography PET ligand using the Al18F radiolabeling method. In this study, the potential of 18F-AlF-NOTA-AE105 to specifically target uPAR-positive prostate tumors was investigated. Methods NOTA-conjugated AE105 was synthesized and radiolabeled with 18F-AlF according to a recently published optimized protocol. The labeled product was purified by reverse phase high performance liquid chromatography RP-HPLC. The tumor targeting properties were evaluated in mice with subcutaneously inoculated PC-3 xenografts using small animal PET and ex vivo biodistribution studies. uPAR-binding specificity was studied by coinjection of an excess of a uPAR antagonist peptide AE105 analogue (AE152). Results NOTA-AE105 was labeled with 18F-AlF in high radiochemical purity (> 92%) and yield (92.7%) and resulted in a specific activity of greater than 20 GBq/μmol. A high and specific tumor uptake was found. At 1 h post injection, the uptake of 18F-AlF-NOTA-AE105 in PC-3 tumors was 4.22 ± 0.13%ID/g. uPAR-binding specificity was demonstrated by a reduced uptake of 18F-AlF-NOTA-AE105 after coinjection of a blocking dose of uPAR antagonist at all three time points investigated. Good tumor-to-background ratio was observed with small animal PET and confirmed in the biodistribution analysis. Ex vivo uPAR expression analysis on extracted tumors confirmed human uPAR expression that correlated close with tumor uptake of 18F-AlF-NOTA-AE105. Conclusion The first 18F-labeled uPAR PET ligand, 18F-AlF-NOTA-AE105, has successfully been prepared and effectively visualized noninvasively uPAR positive prostate cancer. The favorable in vivo kinetics and easy production method facilitate its future clinical translation for identification of prostate cancer patients with an invasive phenotype and poor prognosis.

Dosimetry of 64Cu-DOTA-AE105, a PET tracer for uPAR imaging

“…Based on the small linear peptide AE105 with high affinity for uPAR, 64 Cu-DOTA-AE105 is one of several promising uPAR PET tracers recently developed in our group [15][16][17][18][19]. Before considering translation into human use, estimates of human dosimetry are important.…”

Safety, Dosimetry, and Tumor Detection Ability of 68Ga-NOTA-AE105: First-in-Human Study of a Novel Radioligand for uPAR PET Imaging

“…Accordingly, we have for several years focused on development of radioligands based on the high-affinity peptide antagonist AE105 for PET imaging of uPAR expression (12)(13)(14)(15)(16)(17). We recently published results from a promising first-in-human study with 64 Cu-DOTA-AE105 showing high uptake in both primary tumor lesions and lymph node metastases paralleled with high uPAR expression in excised tumor tissue, thereby providing evidence for uPAR PET imaging in cancer patients (4).…”

Prostate cancer relevant antigens and enzymes for targeted drug delivery

“…A number of approaches have been investigated to target uPA/uPAR for diagnosis 118, 119 as well as for the targeted delivery of drug to prostate cancer cells. 117 Several uPAR-specific peptides 106, 120, 121 and a monoclonal anti-uPAR antibody 122 have been identified and used for targeting uPAR-overexpressing cancer cells 123124 including prostate cancer cells.…”