Structure-activity relationship study of the tumour-targeting peptide A20FMDV2 via modification of Lys16, Leu13, and N- and/or C-terminal functionality.

The 20-residue linear peptide A20FMDV2 has been shown to exhibit high selectivity and affinity for the tumour-related αvβ6 integrin and has potential as a vector for therapeutic drugs. However, it exhibits poor half-life in plasma in part due to its high susceptibility to serum proteases. In this study fourteen A20FMDV2 analogues incorporating non-proteinogenic substitutes of the native Lys16 and Leu13 residues and six A20FMDV2 analogues containing modified N- and C-termini were synthesised to increase the half-life and activity of A20FMDV2. The analogues incorporating modified terminal motifs of A20FMDV2 were found to strongly bind to the αvβ6 integrin and were subsequently functionalized with the diethylenetriaminepentaacetic acid chelating agent to facilitate coupling with radioactive indium-111 for human plasma stability and in vivo biodistribution studies. A20FMDV2 peptide variants incorporating an N-terminal d-Asn and C-terminal d-Thr exhibited improved relative activity in vitro and were less susceptible to plasma degradation.