Synthesis and Evaluation of (68)Ga-labeled uPAR Targeted Peptides for PET Imaging of Glioblastoma

1361 Objectives Urokinase plasminogen activator receptor (uPAR) is overexpressed in various cancers including in glioblastoma (GBM) and is an established biomarker for metastatic potential. The linear peptide AE105 (Ac-Asp-Cha-Phe-(D)Ser-(D)Arg-Tyr-Leu-Trp-Ser) has high affinity for uPAR and (68)Ga-labeled NODAGA-conjugated AE105-imaging probes have previously shown promising results for non-invasive uPAR detection using PET in human cancer xenograft mice models. Our aim is to characterize, using small-animal PET/CT, two new (68)Ga-NODAGA-conjugated AE105-probes with 1) a carbohydrate chain (AOC-probe) and 2) a polyethylene-glycole chain (PEG-probe) linking AE105 and NODAGA for imaging of GBM. Methods Syntheses of the probes were done using standard Fmoc solid-phase peptide chemistry. For in-vitro characterization, uptake and blocking studies in uPAR positive U87MG (glioblastoma) cells, serum stability and octanol-water partition coefficient (logP) were done. To characterize the tumor targeting properties, in-vivo static PET/CT-imaging (n=3) and ex-vivo biodistribution (n=3) to specific organs collected after sacrifice were performed for both probes in U87MG tumor-bearing nude mice. Results (68)Ga-labeling gave high yield (>85 %) with high purity (>95 %) determined by radio-HPLC. Octanol-water partition coefficient (logP) was significantly lower for the PEG-probe (-0.93 vs. -0.32, p Conclusions The PEG-probe and AOC-probe both had desirable in- vitro performance. As expected from its more hydrophilic structure, the logP coefficient of the PEG-probe was more negative than of the AOC-probe. PET/CT imaging showed a higher tumor-to-liver ratio of the PEG-probe than of the AOC-probe in U87MG-tumor bearing mice. Biodistribution analysis showed a significantly better in-vivo performance of the PEG-probe with a higher tumor uptake and a tendency of higher tumor-to-liver ratio than of the AOC-probe. The PEG-probe tumor uptake was also comparable to previously reported values for (68)Ga-NODAGA-conjugated AE105-probes. The results are encouraging and warrant further investigation of the probes for uPAR targeted PET imaging of GBM. RESEARCH SUPPORT: This work was supported, in part, by the Office of Science (BER), U.S. Department of Energy (DE-SC0008397) and the Lundbeck Foundation Clinical Research Fellowship Grant. $$graphic_0563E073-7519-4A93-A5E1-F57ABB2E34D0$$