Improved positron emission tomography imaging of glioblastoma cancer using novel 68Ga-labeled peptides targeting the urokinase-type plasminogen activator receptor (uPAR)

Abstract

The urokinase-type plasminogen activator receptor (uPAR) is overexpressed in several cancers including glioblastoma (GBM) and is an established biomarker for metastatic potential. The uPAR-targeting peptide AE105-NH (Ac-Asp-Cha-Phe-(D)Ser-(D)Arg-Tyr-Leu-Trp-Ser-CONH) is a promising candidate for non-invasive positron emission tomography (PET) imaging of uPAR. Despite the optimal physical properties of Ga for peptide-based PET imaging, low tumor uptakes have previously been reported usingGa-labeled AE105-NH-based tracers. In an attempt to optimize the tumor uptake, we developed three novel tracers with alkane (AOC) and polyethylene glycol (PEG) spacers inserted between AE105-NH and the radio metal chelator 2-(4,7-bis(carboxymethyl)-1,4,7-triazonan-1-yl)pentanedioic acid (NODAGA). The resulting tracers NODAGA-AOC-AE105-NH, NODAGA-PEG-AE105-NH and NODAGA-PEG-AE105-NH were compared to the non-spacer version, NODAGA-AE105-NH. Following radiolabeling with Ga, we evaluated the in vitro and in vivo performance in mice bearing subcutaneous tumors derived from the uPAR-expressing human GBM cell line U87MG. In vivo PET/CT imaging showed that introduction of PEG spacers more than doubled the in vivo tumor uptake after 1 h compared with the non-spacer version:Ga-NODAGA-PEG-AE105-NH (2.08 ± 0.37%ID/g) and Ga-NODAGA-PEG-AE105-NH (2.01 ± 0.22%ID/g) vs. Ga-NODAGA-AE105-NH (0.70 ± 0.40%ID/g), p < 0.05. In addition, Ga-NODAGA-PEG-AE105-NH showed significantly higher (p < 0.05) tumor-to-background contrast (3.68 ± 0.23) than the other tracers. The specific tumor-targeting property of Ga-NODAGA-PEG-AE105-NH was established by effectively blocking the tumor uptake with co-injection of unlabeled AE105-NH (1 h: unblocked 2.01 ± 0.22%ID/g vs. blocked 1.24 ± 0.09%ID/g, p < 0.05). Ex vivo biodistribution confirmed the improved tumor uptakes of the PEG-modified tracers. Ga-NODAGA-PEG-AE105-NH is thus a promising candidate for human translation for PET imaging of GBM.

Optimization and Evaluation of Al18F Labeling Using a NOTA—or RESCA1-Conjugated AE105 Peptide Antagonist of uPAR

“…AE105mut is used as negative control, and AE105 is used as positive control. The conjugation of the large chelators, NOTA or RESCA1, to the small uPAR-targeting 9-mer AE105 has as expected, a penalty on the binding to uPAR, but the interactions are still in the low nM range (15,16).…”

Novel dual-function near-infrared II fluorescence and PET probe for tumor delineation and image-guided surgery

“…2d and S13 † ). Briefly, CHS2 was then incubated with 68 Ga [2 mCi] under mild conditions for 15 min according to a previously reported method, 41 and purified by RP-HPLC resulting in over 95% purity (Fig. S14 † ).…”

Angiogenesis-Related Gene Signature-Derived Risk Score for Glioblastoma: Prospects for Predicting Prognosis and Immune Heterogeneity in Glioblastoma

“…In the present study, three genes (PLAUR, ITGA5, and FMOD) were finally identified to be key hub genes through construction of a PPI network and screening hub genes with Cytoscape software. PLAUR, which is also known as CD87, UPAR, URKR, and U-PAR, is found to be overexpressed in multiple cancers including GBM, and contributes to tumor angiogenesis, cell migration, and invasion (Raghu et al, 2011;Raghu et al, 2012;Schuler et al, 2012;Hu et al, 2015;Loft et al, 2017). It encodes urokinase-type plasminogen activator receptor (uPAR), a GPI-anchored cell membrane receptor, which could bind with urokinase (uPA) and stimulate the intracellular signals associated with tumorigenesis.…”