Radiolabeling and initial biological evaluations of [⁶⁴Cu]NOTA-Pep-1L for imaging Glioblastoma (GBM )

Objectives IL-13Rα2 is a tumor restricted receptor that we identified to be present in a number of cancers, including in the vast majority of GBM, High-Grade Gliomas and malignant melanoma. In past work, we have targeted this receptor for diagnostic and therapeutic purposes using IL-13-derived agents. In this work, we examined for the first time the cell and in vivo tumor binding property of ⁶⁴Cu-Pep-1L, a novel peptide discovered to bind IL-13Rα2 (Neuro Oncol. 2012 14(1):6-18. PMID: 21946118).

Methods NOTA-conjugated peptide was commercially purchased from CPC scientific ltd. The conjugated ligand was radiolabeled with ⁶⁴Cu with high purity and reaction progress was monitored by radio-TLC. The in vitro reactivity and specificity were determined using G48a GBM cells, high expressors of IL-13Rα2. The data were expressed as %ID/mg of protein present in each well with p values ≤ .05 considered statistically significant. Standard biodistribution studies were performed using female nude mice bearing flank G48a tumor cells.

Results [⁶⁴Cu]NOTA-Pep-1L was radiolabeled with high radiochemical purity and specific activity. Cell uptake assay in G48a cells demonstrated high uptake, which was significantly blocked by unlabeled Pep-1L, demonstrating specificity. Importantly, the uptake was maintained over time and was still present at high levels at 4 h, which is expected due to known internalization properties of Pep-1L. Initial in vivo tumor uptake studies in tumor-bearing mice demonstrated that [⁶⁴Cu]NOTA-Pep-1L specifically bound to tumors at 24 h, which was blocked (3-fold blockade) by pre-injecting unlabeled peptide.

Conclusions [⁶⁴Cu]NOTA-Pep-1L demonstrated high radioactive uptake using an in vitro cell uptake assay and also demonstrated specific tumor uptake in the tumor bearing nude mice. Quantitative biodistrubution, tumor uptake and MicroPET imaging studies are currently underway to further assess the utility of Pep-1L in imaging GBM.