Abstract
A special class of self-assembling peptides has been found to be capable of stabilizing the hydrophobic anticancer agent ellipticine in aqueous solution. Here we study the effect of peptide sequence on the complex formation and its anticancer activity in vitro. Three peptides, EAK16-II, EAK16-IV and EFK16-II, were selected to have either a different charge distribution (EAK16-II vs. EAK16-IV) or a varying hydrophobicity (EAK16-II vs. EFK16-II). Results on their complexation with ellipticine revealed that EAK16-II and EAK16-IV were able to stabilize protonated ellipticine or ellipticine microcrystals depending on the peptide concentration; EFK16-II could stabilize neutral ellipticine molecules and ellipticine microcrystals. These different molecular states of ellipticine were expected to affect ellipticine delivery. The anticancer activity of these complexes was tested against two cancer cell lines: A549 and MCF-7, and related to the cell viability. The viability results showed that the complexes with protonated ellipticine were effective in eradicating both cancer cells (viability <0.05), but their dilutions in water were not stable, leading to a fast decrease in their toxicity. In contrast, the complexes formulated with EFK16-II were relatively stable upon dilution, but their original toxicity was relatively low compared to that with protonated ellipticine. Overall, the charge distribution of the peptides seemed not to affect the complex formation and its therapeutic efficacy in vitro; however, the increase in hydrophobicity of the peptides significantly altered the state of stabilized ellipticine and increased the stability of the complexes. This work provides essential information for peptide sequence design in the development of self-assembling peptide-based delivery of hydrophobic anticancer drugs.
Highlights
Self-assembling peptides are emerging nano-biomaterials with promising biomedical and bioengineering applications [1,2,3]
We report how the subtle differences in the peptide sequence affect the properties of the peptide assemblies, the formation of the peptide-ellipticine complexes, and the cellular toxicity of the complexes
EAK16-IV has a different charge distribution of type IV (2222++++) from EAK16-II as type II (22++22++), while the difference between EFK16-II and EAK16-II is a more hydrophobic residue F replacing A in EAK16-II
Summary
Self-assembling peptides are emerging nano-biomaterials with promising biomedical and bioengineering applications [1,2,3]. They consist of alternating positive and negative charges at physiological conditions, resulting in ionic complementarity These peptides are capable of self-assembling into very stable nanostructures or macroscopic membranes, which can withstand high temperature, extreme pH, many digesting enzymes and denaturation agents [4,5]. They exhibit good biocompatibility with many cultured mammalian cells [6] and no detectable immune responses can be observed when being introduced into animals [4,7,8]. These properties make them ideal materials for tissue scaffolding [9,10,11], regenerative medicine [7,8,12] and drug delivery [13,14,15,16,17]
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