Development and bioevaluation of ¹⁸F-labeled bivalent cyclic peptides for PET imaging of αvβ6 integrin overexpression

Integrin αvβ6 has emerged as a critical target in cancer diagnostics and therapeutics. In this study, we developed two bivalent ligands, NOTA-(SDM17)₂ and NOTA-(AvB6)₂, for positron emission tomography (PET) imaging of αvβ6 integrins. Surface plasmon resonance (SPR) revealed affinities for NOTA-(SDM17)₂ and NOTA-(AvB6)₂ with KD values of 2.15 μM and 5.21 μM, respectively. Micro-PET imaging demonstrated significantly higher uptake of [¹⁸F]AlF-NOTA-(SDM17)₂ and [¹⁸F]AlF-NOTA-(AvB6)₂ in H2009 tumors (αvβ6-positive) compared to MDA-MB-231 tumors (αvβ6-negative) ([¹⁸F]AlF-NOTA-(SDM17)₂: 3.2 ± 0.3 vs. 0.3 ± 0.07 %ID/g; [¹⁸F]AlF-NOTA-(AvB6)₂: 6.4 ± 0.5 vs. 1.0 ± 0.2 %ID/g at 60 min p.i., P < 0.05). Both bivalent tracers exhibited enhanced tumor uptake and retention relative to their monovalent counterparts ([¹⁸F]AlF-NOTA-SDM17 and [¹⁸F]AlF-NOTA-AvB6) at 60 min p.i., (P < 0.05). Notably, [¹⁸F]AlF-NOTA-(SDM17)₂ demonstrated a superior tumor-to-liver ratio (13.24 vs. 5.93, P = 0.029) and longer retention, as confirmed by in vivo biodistribution studies. These findings highlight the potential of [¹⁸F]AlF-NOTA-(SDM17)₂ and [¹⁸F]AlF-NOTA-(AvB6)₂ as bivalent PET tracers to enhance tumor uptake and prolong retention. Among them, [¹⁸F]AlF-NOTA-(SDM17)₂ shows particular promise for clinical translation due to its higher tumor-to-non-tumor ratio and prolonged retention.