Fatty acid conjugated EPI-X4 derivatives with increased activity and in vivo stability

Dysregulation of the CXCL12/CXCR4 axis is implicated in autoimmune, inflammatory, and oncogenic diseases, positioning CXCR4 as a pivotal therapeutic target. We evaluated optimized variants of the specific endogenous CXCR4 antagonist, EPI-X4, addressing existing challenges in stability and potency. Our structure-activity relationship study investigates the conjugation of EPI-X4 derivatives with long-chain fatty acids, enhancing serum albumin interaction and receptor affinity. Molecular dynamic simulations revealed that the lipid moieties stabilize the peptide-receptor interaction through hydrophobic contacts at the receptor's N-terminus, anchoring the lipopeptide within the CXCR4 binding pocket and maintaining essential receptor interactions. Accordingly, lipidation resulted in increased receptor affinities and antagonistic activities. Additionally, by interacting with human serum albumin lipidated EPI-X4 derivatives displayed sustained stability in human plasma and extended circulation times in vivo. Selected candidates showed significant therapeutic potential in human retinoblastoma cells in vitro and in ovo, with our lead derivative exhibiting higher efficacies compared to its non-lipidated counterpart. This study not only elucidates the optimization trajectory for EPI-X4 derivatives but also underscores the intricate interplay between stability and efficacy, crucial for delineating their translational potential in clinical applications.