We have in the present study explored the anticancer activity against human Burkitt's lymphoma cells (Ramos) of a series of small linear and cyclic tetrapeptides containing a β2,2-amino acid with either two 2-naphthyl-methylene or two para-CF3-benzyl side chains, along with their interaction with the main plasma protein human serum albumin (HSA). The cyclic and more amphipathic tetrapeptides revealed a notably higher anticancer potency against Ramos cells [50% inhibitory concentration (IC50) 11–70 μM] compared to the linear tetrapeptide counterparts (IC50 18.7 to >413 μM). The most potent cyclic tetrapeptide c3 had a 16.5-fold preference for Ramos cells compared to human red blood cells, whereas the cyclic tetrapeptide c1 both showed low hemolytic activity and displayed the overall highest (2.9-fold) preference for Ramos cells (IC50 23 μM) compared to healthy human lung fibroblast cells (MRC-5). Investigating the interaction of selected tetrapeptides and recently reported hexapeptides with HSA revealed that the peptides bind to drug site II of HSA in the 22–28 μM range, disregarding size and overall structure. NMR and in silico molecular docking experiments identified the lipophilic residues as responsible for the interaction, but in vitro studies showed that the anticancer potency of the peptides varied in the presence of HSA and that c3 remained the most potent peptide. Based on our findings, we call for implementing serum albumin binding in development of anticancer peptides, as it may have implications for future administration and systemic distribution of peptide-based cancer drugs. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.
Detection of structure–activity relationship of anticancer potency and selectivity for linear and cyclic tetrapeptides containing an achiral β2,2-amino acid are reported. Pharmacokinetic investigation of the interaction with the major transporter protein human serum albumin shows binding to drug site II is exclusively through the hydrophobic parts of the peptides and is in the micromolar range. In vitro testing indicates in vivo implication for the potency of these peptides when human serum albumin is present.