The cytotoxic effect against the breast cancer cell line MDA-MB-468 of the palindromic peptide LfcinB (21–25)Pal: 1RWQWRWQWR9 and its analogous peptides, obtained via alanine scanning, was evaluated.

The palindromic nonapeptide H‐1RWQWRWQWR9‐NH2 (LfcinB (21–25)Pal) was synthetize and scaled following the good manufacturing practices (GMP) guidelines to obtained batches up to 1 g of pure peptide which evidencing their synthetic viability. Its cytotoxic effect was tested against breast cancer cell lines MDA‐MB‐231 and MCF‐7 and was dependent on concentration against both. The IC50 values were 135 μM and 66 μM, respectively. Against MCF‐7 the peptide exerts its greater cytotoxic effect at 135 μM, diminishing their cell viability to 21%. Furthermore, the palindromic peptide did not exhibit a significant cytotoxic effect against the nontumorigenic cells MCF‐12, BMEC (bovine mammary epithelial cells) or fibroblast, which confirms its selectivity. The cancerous cells treated at 135 μM for 2 h exhibited morphological changes like cellular shrinkage and rounded forms. Trough flow cytometry assays we evidence that 73% of the events were related to late apoptosis, and cells that exhibited mitochondrial membrane depolarization also had an increase in the relative expression of caspase‐3. Our results suggest that the LfcinB (21–25)Pal peptide has a cytotoxic effect against MCF‐7 mainly through apoptotic events which makes it a promising candidate for therapeutic agent.

The reaction between L-cysteine (Cys) and 6-maleimidohexanoic acid (Mhx) in an aqueous medium at different levels of pH was analyzed via RP-HPLC, finding the presence of two reaction products throughout the evaluated pH range. By means of solid-phase extraction (SPE), it was possible to separate the products and obtain isolated profiles enriched up to 80%. The products were analyzed individually through mass spectrometry, DAD-HPLC, NMR 1H, 13C, and two-dimensional evidence of isomerization between the hydrogen atoms of the α-amino and the thiol group present in the cysteine. Thus, it was concluded that the products obtained corresponded to a mixture of the isomer Cys-S-Mhx, where the adduct is formed by a thioether bond, and the isomer Cys-NH-Mhx, in which the union is driven by the amino group. We consider that the phenomenon of isomerization is an important finding, since it has not previously been reported for this reaction.

: Over the last few years, short peptides have become a powerful tool in basic and applied research, with different uses like diagnostic, antimicrobial peptides, human health promoters or bioactive peptides, therapeutic treatments, templates for peptidomimetic design, and peptide-based vaccines. In this endeavor, different approaches and technologies have been explored, such as bioinformatics, large-scale peptide synthesis, omics sciences, structure-activity relationship studies, and a biophysical approach, among others, seeking to obtain the shortest sequence with the best activity. The advantage of short peptides lies in their stability, ease of production, safety, and low cost. There are many strategies for designing short peptides with biomedical and industrial applications (targeting the structure, length, charge, or polarity) or as a starting point for improving their properties (sequence data base, de novo sequences, templates, or organic scaffolds). In peptide design, it is necessary to keep in mind factors such as the application (peptidomimetic, immunogen, antimicrobial, bioactive, or proteinprotein interaction inhibitor), the expected target (membrane cell, nucleus, receptor proteins, or immune system), and particular characteristics (shorter, conformationally constrained, cycled, charged, flexible, polymerized, or pseudopeptides). This review summarizes the different synthetic approaches and strategies used to design new peptide analogs, highlighting the achievements, constraints, and advantages of each.