Anticancer activity of undecapeptide analogues derived from antimicrobial peptide, Brevinin-1EMa

Application Value of Antimicrobial Peptides in Gastrointestinal Tumors

Gastrointestinal cancer is a common clinical malignant tumor disease that seriously endangers human health and lacks effective treatment methods. As part of the innate immune defense of many organisms, antimicrobial peptides not only have broad-spectrum antibacterial activity but also can specifically kill tumor cells. The positive charge of antimicrobial peptides under neutral conditions determines their high selectivity to tumor cells. In addition, antimicrobial peptides also have unique anticancer mechanisms, such as inducing apoptosis, autophagy, cell cycle arrest, membrane destruction, and inhibition of metastasis, which highlights the low drug resistance and high specificity of antimicrobial peptides. In this review, we summarize the related studies on antimicrobial peptides in the treatment of digestive tract tumors, mainly oral cancer, esophageal cancer, gastric cancer, liver cancer, pancreatic cancer, and colorectal cancer. This paper describes the therapeutic advantages of antimicrobial peptides due to their unique anticancer mechanisms. The length, net charge, and secondary structure of antimicrobial peptides can be modified by design or modification to further enhance their anticancer effects. In summary, as an emerging cancer treatment drug, antimicrobial peptides need to be further studied to realize their application in gastrointestinal cancer diseases.

Brevinin-2PN, an antimicrobial peptide identified from dark-spotted frog (Pelophylax nigromaculatus), exhibits wound-healing activity

Brevinins exhibit a wide range of structural features and strong biological activities. Brevinin-2, derived from several amphibians, has shown antimicrobial activities. However, little is known about the wound-healing activity of brevinin-2. In this study, brevinin-2 cDNA was identified from the skin transcriptome of the dark-spotted frog (Pelophylax nigromaculatus) and it comprises a signal peptide, a propeptide, and a mature peptide. Sequence alignment with brevinin-2 derived from other amphibians showed variability of the mature peptide, and the presence of a C-terminal cyclic heptapeptide domain (Cys-Lys-Xaa4-Cys) in the mature peptide. Dark-spotted frog brevinin-2 belonged to the brevinin-2 cluster and was closely related to brevinin-2HB1 from Pelophylax hubeiensis. Synthetic dark-spotted frog brevinin-2 mature peptide (brevinin-2PN) exhibited antibacterial activity against several pathogens by destroying cell membrane integrity and hydrolysis of genomic DNA. Brevinin-2PN exhibited significant wound-healing activity by accelerating the healing of human skin fibroblast cell scratches, influencing cell migration, and stimulating gene expression of growth factors.

Membrane disruptive action of cationic anti-bacterial peptide B1CTcu3

A twenty-two-residue peptide Brevinin1 Clinotarsus curtipus-3 (B1CTcu3), identified from the skin secretion of frog Clinotarsus curtipes of the Western Ghats, exhibited a broad range of antibacterial activity against Gram-negative and Gram-positive bacteria, including the methicillin-resistant Staphylococcus aureus (MRSA). It showed anti-biofilm activity even at sub-Minimum Inhibitory Concentration (sub-MIC) against Pseudomonas aeruginosa and Staphylococcus aureus. Analysis of the scanning electron microscopic (SEM) images, confocal images, flow cytometric data and the effect of salt concentration on antibacterial potency suggests that the killing action of the peptide is through the membranolytic process. Single channel electric recording confirmed that the peptide elicited pores on the bacterial cell membrane as it induces a heterogeneous channel in the lipid bilayer.  It also showed cytotoxicity against MDA-MB-231 breast cancer cell with IC50 of 25µM. B1CTcu3 peptide could serve as the template for next-generation antibacterial agents, particularly against antibiotic resistant pathogenic bacteria.

Ethnopharmacological study of natural products used for traditional cancer therapy in Algeria

Traditional and complementary medicine constitutes an important, and often underestimated, source of healthcare for multiple diseases including cancer. However, little is known about the ethnomedical knowledge and practices in Northern Africa. The main objective of this study is to identify and analyze the variety of natural products used in Algerian ethnopharmacology for cancer therapy. For this purpose, semi-structured interviews with 225 traditional healers, herbalists and practitioners were realized in twelve locations in Algeria throughout field studies performed from June 2015 to July 2019. Interviews covered popular and vernacular names of the natural product, mode of use and administration, dose, period of treatment, toxicity and side effects among other data. The obtained results reveal the use of 113 medicinal plants (belonging to 53 families and 104 genera), 10 animal species and various products and by-products from different origins such as honey, olive oil, thorns, urine, milk, animal fat and the alkaline water of Zamzam. Basing on the frequency of citation (FC), use reports (UR) and use value (UV), the most used natural products for cancer treatment are honey (FC = 181, UR = 194, UV = 0.65), Nigella sativa L. (FC = 131, UR = 152, UV = 0.54), Aristolochia longa L. (FC = 118, UR = 144, UV = 0.51), Berberis vulgaris L. (FC = 111, UR = 142, UV = 0.51), Curcuma longa L. (FC = 107, UR = 121, UV = 0.43), Trigonella foenum-graecum L. (FC = 102; UR = 119, UV = 0.43), Citrus limon (L.) Obseck (FC = 97, UR = 120, UV = 0.43), Artemisia herba-alba Asso (FC = 92, UR = 115, UV = 0.41) and the holy water 'Zamzam' (FC = 110, UR = 110, UV = 0.43) respectively. Mixtures of two or more ingredients were frequently used. The use of Pelophylax saharicus skin' was reported for the first time for the treatment of visible tumors and skin cancer. This is the first study documenting the traditional uses of various natural products for cancer treatment in Algeria. Our findings are relevant to document the traditional uses of numerous natural products and to provide background basis to search for novel compounds for cancer therapy.

Characterisation of a novel peptide, Brevinin-1H, from the skin secretion of Amolops hainanensis and rational design of several analogues

As drug-resistant bacteria have become a serious health problem and have caused thousands of deaths, finding new antibiotics has become an urgent research priority. A novel antimicrobial peptide, named Brevinin-1H, was identified in the skin secretion of Amolops hainanensis through 'shotgun' cloning. It has broad-spectrum antimicrobial activity against tested micro-organisms and has anticancer cell activity. To improve its bioactivity and decrease its cytotoxicity, two structural analogues-Brevinin-1Ha and Brevinin-1HY-were designed based on the secondary structure of the natural peptide. Brevinin-1HY, in which tyrosine substituted Pro¹¹ , had similar activity to the natural peptide against Gram-negative bacteria and cancer cells, but showed a dramatic increase in haemolytic activity and cytotoxicity at its minimum inhibitory concentration. Brevinin-1Ha, which transferred the Rana-box from the C-terminal to a central position, had significantly decreased haemolytic activity, but also in antimicrobial and anticancer activity. The present data suggest that increasing the proportion of α-helix structure in an AMP can increase its target micro-organism bioactivity to some extent.

Biophysical studies on the antimicrobial activity of linearized esculentin 2EM

Linearized esculentin 2 EM (E2EM-lin) from the frog, Glandirana emeljanovi was highly active against Gram-positive bacteria (minimum lethal concentration ≤ 5.0 μM) and strongly α-helical in the presence of lipid mimics of their membranes (>55.0%). The N-terminal α-helical structure adopted by E2EM-lin showed the potential to form a membrane interactive, tilted peptide with an hydrophobicity gradient over residues 9 to 23. E2EM-lin inserted strongly into lipid mimics of membranes from Gram-positive bacteria (maximal surface pressure changes ≥5.5 mN m^-1), inducing increased rigidity (C_s^-1 ↑), thermodynamic instability (ΔG_mix < 0 → ΔG_mix > 0) and high levels of lysis (>50.0%). These effects appeared to be driven by the high anionic lipid content of membranes from Gram-positive bacteria; namely phosphatidylglycerol (PG) and cardiolipin (CL) species. The high levels of α-helicity (60.0%), interaction (maximal surface pressure change = 6.7 mN m^-1) and lysis (66.0%) shown by E2EM-lin with PG species was a major driver in the ability of the peptide to lyse and kill Gram-positive bacteria. E2EM-lin also showed high levels of α-helicity (62.0%) with CL species but only low levels of interaction (maximal surface pressure change = 2.9 mN m^-1) and lysis (21.0%) with the lipid. These combined data suggest that E2EM-lin has a specificity for killing Gram-positive bacteria that involves the formation of tilted structure and appears to be primarily driven by PG-mediated membranolysis. These structure/function relationships are used to help explain the pore forming process proposed to describe the membranolytic, antibacterial action of E2EM-lin.

Evaluating the Bioactivity of a Novel Broad-Spectrum Antimicrobial Peptide Brevinin-1GHa from the Frog Skin Secretion of Hylarana guentheri and Its Analogues

Many antimicrobial peptides (AMPs) have been identified from the skin secretion of the frog Hylarana guentheri (H.guentheri), including Temporin, Brevinin-1, and Brevinin-2. In this study, an antimicrobial peptide named Brevinin-1GHa was identified for the first time by using ‘shotgun’ cloning. The primary structure was also confirmed through mass spectral analysis of the skin secretion purified by reversed-phase high-performance liquid chromatography (RP-HPLC). There was a Rana-box (CKISKKC) in the C-terminal of Brevinin-1GHa, which formed an intra-disulfide bridge. To detect the significance of Rana-box and reduce the hemolytic activity, we chemically synthesized Brevinin-1GHb (without Rana-box) and Brevinin-1GHc (Rana-box in central position). Brevinin-1GHa exhibited a strong and broad-spectrum antimicrobial activity against seven microorganisms, while Brevinin-1GHb only inhibited the growth of Staphylococcus aureus (S. aureus), which indicates Rana-box was necessary for the antimicrobial activity of Brevinin-1GHa. The results of Brevinin-1GHc suggested transferring Rana-box to the central position could reduce the hemolytic activity, but the antimicrobial activity also declined. Additionally, Brevinin-1GHa demonstrated the capability of permeating cell membrane and eliminating biofilm of S. aureus, Escherichia coli (E. coli), and Candida albicans (C. albicans). The discovery of this research may provide some novel insights into natural antimicrobial drug design.

Biological Properties, Current Applications and Potential Therapeautic Applications of Brevinin Peptide Superfamily

The Brevinin peptides are antimicrobial agents obtained from frog skin secretions. Brevinin-2R has attracted many attentions due to its very low hemolytic activity, cationic property, and high affinity to cancer cells. Moreover, it has shown little toxicity against normal mammalian cells, while having killed several tumor cell lines by activation of lysosome-mitochondrial death pathway. In this review, we introduced the Brevinin superfamily with a focus on its therapeutic applications. Next, some unique properties of Brevinins were briefly discussed, including their ability to stimulate insulin secretion, dendritic cell maturation, and wound healing. In this context, we also provide information about the decoration of nanoparticles, such as cerium nano-oxide, by Brevinins. Finally, we addressed their potential for anti-tumor and drug design applications.

Electrical potentiation of the membrane permeabilization by new peptides with anticancer properties

New polycationic peptides were designed on the basis of 16-mer and 14-mer fragments of the peptide BTM-P1, derived from the Cry11Bb protoxin. The peptides caused mitochondrial, but not red blood cell membrane permeabilization. Conjugation of the cell penetrating hepta-arginine vector to their N- or C-termini through two glycine residues resulted in more active peptides, which also permeabilized the red blood cells with a relatively high plasma membrane potential generated in the presence of valinomycin. The efficiency of the peptides was remarkably higher in the lower ionic strength media. The capability of the plasma membrane permeabilization of the normal red blood cells by the designed conjugated peptides and by known anticancer peptide R7-KLA was also strongly potentiated by the external electrical pulses applied to the cell suspension. These results open the new avenues of the local destruction of solid tumors using the combined "peptide--electrical pulses" synergistic treatment. The designed peptides were active against the human leukemia Jurkat cells but not against the normal wild type CHO cells.