Construction and Preliminary Evaluation of Multivalent LLP2A Derivatives Targeting VLA-4 in Melanoma

The high-affinity ligand LLP2A targeting α₄β₁ integrin (VLA-4) has shown promise for molecular imaging, but its monomeric form exhibits rapid clearance and limited tumor retention, restricting its therapeutic potential. This study aimed to develop multimeric LLP2A probes with improved tumor uptake and retention.

Seven structurally distinct multimeric LLP2A derivatives were designed and synthesized, and their in vivo performance was compared with the monomeric analogue T4 in B16F10 melanoma mice using PET imaging, SPECT/CT imaging, biodistribution and therapy evaluation.

Among the synthesized probes, LLP2A-Pol-1 showed the highest tumor uptake (%ID/g, 7.89 ± 0.50 vs 2.40 ± 0.48 at 1 h in PET imaging; approximately 3-fold higher than the monomer) and maintained high tumor activity up to 24-48 h postinjection, markedly improving tumor retention over the monomer (%ID/mL, 2.45 ± 0.39 vs 0.17 ± 0.04 at 48 h in SPECT/CT imaging). In a B16F10 therapy study, [¹⁷⁷Lu]Lu-LLP2A-Pol-1 significantly delayed tumor growth.

A multimeric LLP2A probe with significantly enhanced tumor uptake and retention was successfully identified, providing a promising candidate for melanoma theranostics.