Preclinical Characterization of Phage Display Derived Bicyclic Peptides for PET Imaging of MMP14 Expressing Tumors

Objectives: Metastatic dissemination requires the migration of tumor cells through the surrounding extracellular matrix. Matrix metalloproteinases (MMP) play a particular role in extracellular matrix remodeling resulting in the intravasation of tumor cells into blood or lymphatic vessels. In the present work, novel phage display derived bicyclic peptides directed against the tumor associated matrix metalloproteinase 14 (MMP-14, also known as MT1-MMP) were identified, and preclinically characterized with regard to their clinical potential as PET imaging agent. Methods: The phage display derived bicyclic peptides were preclinically characterized with regard to binding affinity and specificity to MMP-14. The optimal variant was subsequently conjugated to DOTA and radiolabelled with Ga-68 or Lu-177, respectively. Organ distribution, dose study and μPET imaging was performed using MMP-14+ HT1080 tumor-bearing nude mice. Results: The final DOTA-conjugated bicyclic compound N266 showed a high proteolytic stability and an affinity of 0.94 ± 0.08 nM to MMP-14. Organ distribution at 1 h p.i. of the optimal dose of 150 pmol showed a high MMP14-specific tumor uptake of 12.02 ± 2.37 %ID/g (0.12 ± 0.06 %ID/g for non-binding scrambled variant). The radiopharmaceutical candidate showed fast background clearance (< 1 %ID/g for all organs except the kidneys) resulting in high imaging contrast in the μPET studies as early as 30 minutes post injection. Conclusion: Clinically, the overexpression of MMP-14 is associated with early death of cancer patients and correlates with lymph node metastases, progression, invasion, tumor size and poor clinical stage. Thus, the characterized radiopharmaceutical targeting specifically MMP-14 might represent a highly promising tool for future clinical PET imaging and therapeutic management of patients.