Anticancer potency of small linear and cyclic tetrapeptides and pharmacokinetic investigations of peptide binding to human serum albumin

Abstract

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.

An amphipathic cyclic tetrapeptide scaffold containing halogenated β2,2‐amino acids with activity against multiresistant bacteria

“…This procedure reduced the amount of DMF (from 600 to 310 mL) and only minor amounts, if any, of the dimer were observed by HR‐MS in the crude product. The cyclic peptides 5a–d and 6a–d were obtained with yields ranging from 1% to 58%, which was in the same range as reported previously for similar cyclic tetrapeptides . The cyclic tetrapeptides were purified by either C 18 flash chromatography or preparative C 18 reversed‐phase high‐performance liquid chromatography (RP‐HPLC).…”

“…The linear peptides were prepared by microwave solid‐phase peptide synthesis (mw‐SPPS) using precoupled Lys to 2‐chlorotrityl resin for synthesis of the side chain–protected linear precursor peptide H‐Lys(Boc)‐β 2,2 ‐Xaa‐Lys(Boc)‐OH (Scheme ). To our delight, the linear precursor tetrapeptides could be synthesized with HCTU as coupling reagent and microwave heating, compared with the previous method of preactivating with TFFH (fluoro‐ N,N,N′,N′ ‐tetramethyl‐formamidinium hexafluorophosphate) for generating steric unhindered acid fluorides . However, the reaction time for coupling of the steric hindered Fmoc‐β 2,2 ‐amino acids was increased from the standard 5 to 15 minutes (75 ° C mw‐SPPS).…”

“…We have previously described a method for head‐to‐tail cyclization of side chain–protected tetrapeptides to give 5 and 6 after acidic removal of protecting groups . The reported cyclization was performed at low concentration (0.18 mM) in CH 2 Cl 2 :dimethylformamide (DMF) (1:1).…”

“…In the present study, we have incorporated two halogenated α,α‐disubstituted β 2,2 ‐amino acid residues into an amphipathic 13‐membered cyclic tetrapeptide scaffold and explored their antimicrobial activity (Figure ). We have previously shown that such cyclic tetrapeptides can display cytotoxic activity against Ramos cancer cells depending on their amino acid composition . The main aim of the present paper was now to target multiresistant bacteria for scaffold‐based lead compound generation.…”

“…We have previously shown that such cyclic tetrapeptides can display cytotoxic activity against Ramos cancer cells depending on their amino acid composition. 9 The main aim of the present paper was now to target multiresistant bacteria for scaffold-based lead compound generation.…”