Conclusion
BCY18469 demonstrated high affinity, specific targeting of EphA2, a favorable biodistribution profile, and clearance through renal pathways. These findings underscore the potentially important role of bicyclic peptides in advancing radiotheranostic approaches and encourage additional translational research.
Methods
The EphA2-targeting Bicycle® peptide BCY18469 was identified through phage-display and chemically optimized. BCY18469 was radiolabeled with 68Ga, 177Lu and 111In. The physicochemical properties, binding affinity and internalization as well as specificity of the peptide were evaluated in vitro. In vivo PET/MR and SPECT/CT imaging studies were performed using [68Ga]Ga-BCY18469 and [111In]In-BCY18469, respectively, along with biodistribution of [177Lu]Lu-BCY18469 up to 24 h post injection in HT1080- and PC-3-tumor bearing BALB/c nu/nu EphA2-overexpressing xenograft mouse models.
Results
The EphA2-targeting bicyclic peptide BCY18469 showed high binding affinity toward human and mouse EphA2 (1.9 and 3.8 nM, respectively). BCY18469 specifically bound and internalized into EphA2-expressing HT1080 cells. Imaging studies showed high tumor enrichment at early time-points (SUV of 1.7 g/mL at 1 h p.i. and 1.2 g/mL at 2 h p.i. in PET/MRI, HT1080 xenograft) with tumor contrast as early as 5 min p.i. and kidney-mediated clearance. Biodistribution studies revealed high early tumor uptake (19.5 ± 3.5 %ID/g at 1 h p.i., HT1080 xenograft) with SPECT/CT imaging further confirming these findings (5.7 ± 1.5 %ID/g at 1 h p.i., PC-3 xenograft).