Design and Preclinical Evaluation of Novel uPAR-Targeting Radiopeptides Modified with an Albumin-Binding Entity

Area of Science:

• Radiopharmaceutical chemistry
• Molecular imaging and therapy
• Cancer research

Background:

• The urokinase-type plasminogen activator receptor (uPAR) is a promising target for cancer diagnostics and therapeutics.
• Radiolabeled DOTA-AE105 has been explored for uPAR targeting, but its therapeutic application may be limited by pharmacokinetic properties.

Purpose of the Study:

• To design and evaluate novel uPAR-targeting radiopeptides with improved pharmacokinetic profiles for therapeutic use.
• To synthesize and characterize five new peptides (uPAR-01 to uPAR-05) based on the AE105 backbone, incorporating a DOTA chelator and an albumin-binding moiety.

Main Methods:

• Solid-phase peptide synthesis was employed to create the five novel peptides.
• The synthesized peptides were labeled with Lutetium-177 (¹⁷⁷Lu).
• Stability, uPAR-binding affinity, plasma protein binding, metabolic stability, and tissue distribution in vivo were evaluated for the novel radiopeptides and compared to [¹⁷⁷Lu]Lu-DOTA-AE105.

Main Results:

• The novel ¹⁷⁷Lu-labeled radiopeptides exhibited high stability in saline and biological plasma, outperforming [¹⁷⁷Lu]Lu-DOTA-AE105 in plasma stability.
• uPAR-binding affinities were comparable to [¹⁷⁷Lu]Lu-DOTA-AE105, while plasma protein binding was significantly increased.
• In vivo studies showed reduced blood clearance, enhanced tumor accumulation, and improved metabolic stability for the new radiopeptides, with [¹⁷⁷Lu]Lu-uPAR-02 demonstrating a particularly favorable profile and increased xenograft-to-kidney ratios.

Conclusions:

• The developed uPAR-targeting radiopeptides possess superior metabolic stability and pharmacokinetic properties compared to [¹⁷⁷Lu]Lu-DOTA-AE105.
• These novel radiopeptides, especially [¹⁷⁷Lu]Lu-uPAR-02, show significant potential for targeted radionuclide therapy of uPAR-expressing cancers due to enhanced tumor targeting and retention.