Abstract 5280: PET imaging of proteolysis: Evaluation of 68Ga-DOTA and 68Ga-NODAGA chelates of an uPAR-specific peptide in a human glioblastoma xenograft model

Abstract

Abstract Background & Aim: The urokinase-type plasminogen activator receptor (uPAR) has been shown to facilitate cancer cell invasion and metastasis. uPAR is over-expressed in various cancers, including human breast, prostate and colorectal cancer, and over-expression has been shown to correlate with poor prognosis. The established correlation between uPAR expression and disease progression provides an opportunity to develop an in vivo imaging agent, which could identify cancer patients at risk. In the present study, we produced and compared two new PET tracers based on 68Ga, the chelators DOTA and NODAGA and the uPAR antagonist peptide AE105 in a human glioblastoma xenograft model using microPET/CT. Method: Both compounds were synthesized using standard Fmoc solid-phase peptide chemistry and subsequently N-terminal conjugated with either DOTA or NODAGA. The conjugated peptides were radiolabeled with 68Ga using a 68Ge/68Ga generator system, which render the production of the tracers independent of a onsite cyclotron. The compounds were evaluated in vitro by surface plasmon resonance against human uPAR and in vivo using micro-positron emission tomography in a mouse model bearing human glioblastoma U87MG xenografts. All findings were validated using uPAR ELISA on tumor tissue and uPAR immnohistochemistry on tumor slides. Results: Both compounds were labeled under mild conditions with high yield and radiochemical purity (>95%). Both compounds showed excellent uPAR binding (IC50 values of 10-15 nM) in vitro, which was identical to the un-conjugated peptide AE105. In vivo, they displayed different tumor uptake, with 68Ga-DOTA-AE105 and 68Ga-NODAGA-AE105 having an uptake of 0.48±0.3 and 2.58±0.02 %ID/g 0.5 hr post injection, respectively. Besides tumor uptake, high uptake in the kidneys was also observed for both compounds. Dynamic PET scans illustrated higher stability in vivo for 68Ga-NODAGA-AE105 compared to 68Ga-DOTA-AE105, thus generating the best tumor-to-background contrast. Conclusion: A new 68Ga-based PET tracer for tumor imaging of human uPAR has been developed. Based on head-to-head comparison, NODAGA seems to be the optimal chelator, giving the highest uptake in tumor tissue. The use of generator-produced 68Ga could further support translation into the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5280. doi:10.1158/1538-7445.AM2011-5280