An esculentin-1 homolog from a dark-spotted frog (Pelophylax nigromaculatus) possesses antibacterial and immunoregulatory properties.

BACKGROUND: Esculentin-1, initially discovered in the skin secretions of pool frogs (Pelophylax lessonae), has demonstrated broad-spectrum antimicrobial activity; however, its immunomodulatory properties have received little attention. RESULTS: In the present study, esculentin-1 cDNA was identified by analysing the skin transcriptome of the dark-spotted frog (Pelophylax nigromaculatus). Esculentin-1 from this species (esculentin-1PN) encompasses a signal peptide, an acidic spacer peptide, and a mature peptide. Sequence alignments with other amphibian esculentins-1 demonstrated conservation of the peptide, and phylogenetic tree analysis revealed its closest genetic affinity to esculentin-1P, derived from the Fukien gold-striped pond frog (Pelophylax fukienensis). Esculentin-1PN transcripts were observed in various tissues, with the skin exhibiting the highest mRNA levels. Synthetic esculentin-1PN demonstrated antibacterial activity against various pathogens, and esculentin-1PN exhibited bactericidal activity by disrupting cell membrane integrity and hydrolyzing genomic DNA. Esculentin-1PN did not stimulate chemotaxis in RAW264.7, a murine leukemic monocyte/macrophage cell line. However, it amplified the respiratory burst and augmented the pro-inflammatory cytokine gene (TNF-α and IL-1ß) expression in RAW264.7 cells. CONCLUSIONS: This novel finding highlights the immunomodulatory activity of esculentin-1PN on immune cells.

Purification, conformational analysis and cytotoxic activities of host-defense peptides from the Tungara frog Engystomops pustulosus (Leptodactylidae; Leiuperinae).

The amphibian family Leptodactylidae is divided into three sub-families: Leiuperinae, Leptodactylinae, and Paratelmatobiinae. Host-defense peptides (HDPs) present in the skins of frogs belonging to the Leptodactylinae have been studied extensively, but information is limited  regarding peptides from Leiuperinae species. Peptidomic analysis of norepinephrine-stimulated skin secretions from the Tungara frog Engystomops pustulosus (Leiuperinae) collected in Trinidad led to the isolation and structural characterization of previously undescribed pustulosin-1 (FWKADVKEIG KKLAAKLAEELAKKLGEQ), [Q28E] pustulosin-1 (pustulosin-2), and pustulosin-3 (DWKETAKELLKKIGAKVAQVISDKLNPAPQ). The primary structures of these peptides do not resemble those of previously described frog skin HDPs. In addition, the secretions contained tigerinin-1EP (GCKTYLIEPPVCT) with structural similarity to the tigerinins previously identified in skin secretions from frogs from the family Dicroglossidae. Pustulosin-1 and -3 adopted extended α-helical conformations in 25% trifluoroethanol-water and in the presence of cell membrane models (sodium dodecylsulfate and dodecylphosphocholine micelles). Pustulosin-1 and -3 displayed cytotoxic activity against a range of human tumor-derived cell lines (A549, MDA-MB-231, and HT29), but their therapeutic potential for development into anti-cancer agents is limited by their comparable cytotoxic activity against non-neoplastic human umbilical vein endothelial cells. The peptides also displayed weak antimicrobial activity against Escherichia coli (MIC = 125 µM) but were inactive against Staphylococcus aureus. Tigerinin-1EP was inactive against both the tumor-derived cells and bacteria.

Benzyl stapled modification and anticancer activity of antimicrobial peptide A4K14-Citropin 1.1.

A4K14-Citropin 1.1 (GLFAVIKKVASVIKGL-NH2) is a derived antimicrobial peptide (AMP) with a more stable α-helical structure at the C-terminal compared to prototype Citropin 1.1 which was obtained from glandular skin secretions of Australian freetail lizards. In a previous report, A4K14-Citropin 1.1 has been considered as an anti-cancer lead compound. However, linear peptides are difficult to maintain stable secondary structure, resulted in poor pharmacokinetic properties. In this study, we designed and synthesized a series of benzyl-stapled derivatives of A4K14-Citropin 1.1. And their physical and chemical properties, as well as biological activity, were both explored. The result showed that AC-CCSP-2-o and AC-CCSP-3-o exhibited a higher degree of helicity and greater anti-cancer activity compared with the prototype peptide. Besides, there was no significant difference in the hemolytic effect between the stapled peptides and the prototype peptide. AC-CCSP-2-o and AC-CCSP-3-o could serve as promising anti-cancer lead compounds for the novel anti-cancer drug development.

Design and modification of frog skin peptide brevinin-1GHa with enhanced antimicrobial activity on Gram-positive bacterial strains.

Naturally occurring frog skin peptides are one of largest sources of antimicrobial peptides that have many advantages including high potency, broad spectrum of targets and low susceptibility to multiple drug-resistance bacteria. However, they also have disadvantages such as hemolytic activity, low stability and high production costs. For these reasons, various strategies have been applied to overcome these drawbacks restricting their use in clinical trials. Previously reported brevinin-1GHa (BR-1GHa) is a 24 amino acid long antimicrobial peptide isolated from Hylarana guentheri with hemolytic activity. To enhance the antimicrobial activity of this peptide and to reduce its hemolytic activity, we designed five new temporin like analogues and examined their bioactivities. Temporins are another class of frog skin peptides without hemolytic activity and shorter than brevinins. When the antimicrobial activities of new analogues were examined against a panel of microorganisms, BR-1GHa-3, in which two alanine residues in the truncated version of BR-1GHa were replaced with leucine, exhibited significantly improved antimicrobial activity against Gram-positive bacterial strains (e.g., S. aureus ATCC 29213 and E. casseliflavus ATCC 700327) with lower hemolytic activity compared to the BR-1GHa peptide. Furthermore, BR-1GHa-4 analogue, in which Gly3 was replaced with Pro, did not show any hemolytic activity except for highest (128 µM) concentration tested and have a strong antimicrobial effect on Gram-positive bacteria (e.g., E. faecalis ATCC 51299 and B. cereus ATCC 13061).

Broad-Spectrum Antiviral Activity of the Amphibian Antimicrobial Peptide Temporin L and Its Analogs.

The COVID-19 pandemic has evidenced the urgent need for the discovery of broad-spectrum antiviral therapies that could be deployed in the case of future emergence of novel viral threats, as well as to back up current therapeutic options in the case of drug resistance development. Most current antivirals are directed to inhibit specific viruses since these therapeutic molecules are designed to act on a specific viral target with the objective of interfering with a precise step in the replication cycle. Therefore, antimicrobial peptides (AMPs) have been identified as promising antiviral agents that could help to overcome this limitation and provide compounds able to act on more than a single viral family. We evaluated the antiviral activity of an amphibian peptide known for its strong antimicrobial activity against both Gram-positive and Gram-negative bacteria, namely Temporin L (TL). Previous studies have revealed that TL is endowed with widespread antimicrobial activity and possesses marked haemolytic activity. Therefore, we analyzed TL and a previously identified TL derivative (Pro3, DLeu9 TL, where glutamine at position 3 is replaced with proline, and the D-Leucine enantiomer is present at position 9) as well as its analogs, for their activity against a wide panel of viruses comprising enveloped, naked, DNA and RNA viruses. We report significant inhibition activity against herpesviruses, paramyxoviruses, influenza virus and coronaviruses, including SARS-CoV-2. Moreover, we further modified our best candidate by lipidation and demonstrated a highly reduced cytotoxicity with improved antiviral effect. Our results show a potent and selective antiviral activity of TL peptides, indicating that the novel lipidated temporin-based antiviral agents could prove to be useful additions to current drugs in combatting rising drug resistance and epidemic/pandemic emergencies.

A cellular endolysosome-modulating pore-forming protein from a toad is negatively regulated by its paralog under oxidizing conditions.

Endolysosomes are key players in cell physiology, including molecular exchange, immunity, and environmental adaptation. They are the molecular targets of some pore-forming aerolysin-like proteins (ALPs) that are widely distributed in animals and plants and are functionally related to bacterial toxin aerolysins. ßγ-CAT is a complex of an ALP (BmALP1) and a trefoil factor (BmTFF3) in the firebelly toad (Bombina maxima). It is the first example of a secreted endogenous pore-forming protein that modulates the biochemical properties of endolysosomes by inducing pore formation in these intracellular vesicles. Here, using a large array of biochemical and cell biology methods, we report the identification of BmALP3, a paralog of BmALP1 that lacks membrane pore-forming capacity. We noted that both BmALP3 and BmALP1 contain a conserved cysteine in their C-terminal regions. BmALP3 was readily oxidized to a disulfide bond-linked homodimer, and this homodimer then oxidized BmALP1 via disulfide bond exchange, resulting in the dissociation of ßγ-CAT subunits and the elimination of biological activity. Consistent with its behavior in vitro, BmALP3 sensed environmental oxygen tension in vivo, leading to modulation of ßγ-CAT activity. Interestingly, we found that this C-terminal cysteine site is well conserved in numerous vertebrate ALPs. These findings uncover the existence of a regulatory ALP (BmALP3) that modulates the activity of an active ALP (BmALP1) in a redox-dependent manner, a property that differs from those of bacterial toxin aerolysins.

Mind the GAP: Purification and characterization of urea resistant GAPDH during extreme dehydration.

The African clawed frog (Xenopus laevis) withstands prolonged periods of extreme whole-body dehydration that lead to impaired blood flow, global hypoxia, and ischemic stress. During dehydration, these frogs shift from oxidative metabolism to a reliance on anaerobic glycolysis. In this study, we purified the central glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to electrophoretic homogeneity and investigated structural, kinetic, subcellular localization, and post-translational modification properties between control and 30% dehydrated X. laevis liver. GAPDH from dehydrated liver displayed a 25.4% reduction in maximal velocity and a 55.7% increase in its affinity for GAP, as compared to enzyme from hydrated frogs. Under dehydration mimicking conditions (150 mM urea and 1% PEG), GAP affinity was reduced with a Km value 53.8% higher than controls. Frog dehydration also induced a significant increase in serine phosphorylation, methylation, acetylation, beta-N-acetylglucosamination, and cysteine nitrosylation, post-translational modifications (PTMs). These modifications were bioinformatically predicted and experimentally validated to govern protein stability, enzymatic activity, and nuclear translocation, which increased during dehydration. These dehydration-responsive protein modifications, however, did not appear to affect enzymatic thermostability as GAPDH melting temperatures remained unchanged when tested with differential scanning fluorimetry. PTMs could promote extreme urea resistance in dehydrated GAPDH since the enzyme from dehydrated animals had a urea I50 of 7.3 M, while the I50 from the hydrated enzyme was 5.3 M. The physiological consequences of these dehydration-induced molecular modifications of GAPDH likely suppress GADPH glycolytic functions during the reduced circulation and global hypoxia experienced in dehydrated X. laevis.

Novel antimicrobial cruzioseptin peptides extracted from the splendid leaf frog, Cruziohyla calcarifer.

Antimicrobial peptides (AMPs) constitute part of a broad range of bioactive compounds present on diverse organisms, including frogs. Peptides, produced in the granular glands of amphibian skin, constitute a component of their innate immune response, providing protection against pathogenic microorganisms. In this work, two novel cruzioseptins peptides, cruzioseptin-16 and -17, extracted from the splendid leaf frog Cruziohyla calcarifer are presented. These peptides were identified using molecular cloning and tandem mass spectrometry. Later, peptides were synthetized using solid-phase peptide synthesis, and their minimal inhibitory concentration and haemolytic activity were tested. Furthermore, these two cruzioseptins plus three previously reported (CZS-1, CZS-2, CZS-3) were computationally characterized. Results show that cruzioseptins are 21-23 residues long alpha helical cationic peptides, with antimicrobial activity against E. coli, S. aureus, and C. albicans and low haemolytic effect. Docking results agree with the principal action mechanism of cationic AMPs that goes through cell membrane disruption due to electrostatic interactions between cationic residues in the cruzioseptins and negative phosphate groups in the pathogen cell membrane. An action mechanism through enzymes inhibition was also tried, but no conclusive results about this mechanism were obtained.

C-terminus amidation influences biological activity and membrane interaction of maculatin 1.1.

Cationic antimicrobial peptides have been investigated for their potential use in combating infections by targeting the cell membrane of microbes. Their unique chemical structure has been investigated to understand their mode of action and optimize their dose-response by rationale design. One common feature among cationic AMPs is an amidated C-terminus that provides greater stability against in vivo degradation. This chemical modification also likely modulates the interaction with the cell membrane of bacteria yet few studies have been performed comparing the effect of the capping groups. We used maculatin 1.1 (Mac1) to assess the role of the capping groups in modulating the peptide bacterial efficiency, stability and interactions with lipid membranes. Circular dichroism results showed that C-terminus amidation maintains the structural stability of the peptide (α-helix) in contact with micelles. Dye leakage experiments revealed that amidation of the C-terminus resulted in higher membrane disruptive ability while bacteria and cell viability assays revealed that the amidated form displayed higher antibacterial ability and cytotoxicity compared to the acidic form of Mac1. Furthermore, 31P and 2H solid-state NMR showed that C-terminus amidation played a greater role in disturbance of the phospholipid headgroup but had little effect on the lipid tails. This study paves the way to better understand how membrane-active AMPs act in live bacteria.

Linearized esculentin-2EM shows pH dependent antibacterial activity with an alkaline optimum.

Here the hypothesis that linearized esculentin 2EM (E2EM-lin) from Glandirana emeljanovi possesses pH dependent activity is investigated. The peptide showed weak activity against Gram-negative bacteria (MLCs ≥ 75.0 µM) but potent efficacy towards Gram-positive bacteria (MLCs ≤ 6.25 µM). E2EM-lin adopted an α-helical structure in the presence of bacterial membranes that increased as pH was increased from 6 to 8 (↑ 15.5-26.9%), whilst similar increases in pH enhanced the ability of the peptide to penetrate (↑ 2.3-5.1 mN m-1) and lyse (↑ 15.1-32.5%) these membranes. Theoretical analysis predicted that this membranolytic mechanism involved a tilted segment, that increased along the α-helical long axis of E2EM-lin (1-23) in the N → C direction, with - < µH > increasing overall from circa - 0.8 to - 0.3. In combination, these data showed that E2EM-lin killed bacteria via novel mechanisms that were enhanced by alkaline conditions and involved the formation of tilted and membranolytic, α-helical structure. The preference of E2EM-lin for Gram-positive bacteria over Gram-negative organisms was primarily driven by the superior ability of phosphatidylglycerol to induce α-helical structure in the peptide as compared to phosphatidylethanolamine. These data were used to generate a novel pore-forming model for the membranolytic activity of E2EM-lin, which would appear to be the first, major reported instance of pH dependent AMPs with alkaline optima using tilted structure to drive a pore-forming process. It is proposed that E2EM-lin has the potential for development to serve purposes ranging from therapeutic usage, such as chronic wound disinfection, to food preservation by killing food spoilage organisms.

Design, synthesis, and anti-tumor activities of novel Brevinin-1BYa peptidomimetics.

Brevinin-1BYa is an amphibian skin-derived peptide that exhibits promising anti-microbial activity against gram-positive and -negative bacteria. However, the anti-tumor activity of Brevinin-1BYa remains unclear, and, more importantly, its therapeutic application is limited owing to its poor protease and reduction stability. In this study, a series of novel Brevinin-1BYa derivatives, including O-linked N-acetyl-glucosamine glyclopeptides and disulfide bond mimetics, were designed and synthesized. Additionally, their anti-tumor activity against human prostate cancer cell line C4-2B, human NSCLC cell line A549 (adenocarcinoma), and human hepatoma cells line HuH-7 was investigated. Among these, the thioether bridge substituted peptidomimetic Brevinin-1BYa-3 displayed improved reduction stability, more stable secondary structure, greater protease stability, and increased anti-tumor activity compared with the original peptide, rendering it a promising leading compound for drug development, particularly for applications against malignant tumors.

Evaluation of antimicrobial and anticancer activities of three peptides identified from the skin secretion of Hylarana latouchii.

The skins of frogs of the family Ranidae are particularly rich sources of biologically active peptides, among which antimicrobial peptides (AMPs) constitute the major portion. Some of these have attracted the interest of researchers because they possess both antimicrobial and anticancer activities. In this study, with 'shotgun' cloning and MS/MS fragmentation, three AMPs, homologues of family brevinin-1 (brevinin-1HL), and temporin (temporin-HLa and temporin-HLb), were discovered from the skin secretion of the broad-folded frog, Hylarana latouchii. They exhibited various degrees of antimicrobial and antibiofilm activities against test microorganisms and hemolysis on horse erythrocytes. It was found that they could induce bacteria death through disrupting cell membranes and binding to bacterial DNA. In addition, they also showed different potencies towards human cancer cell lines. The secondary structure and physicochemical properties of each peptide were investigated to preliminarily reveal their structure-activity relationships. Circular dichroism spectrometry showed that they all adopted a canonical α-helical conformation in membrane-mimetic solvents. Notably, the prepropeptide of brevinin-1HL from H. latouchii was highly identical to that of brevinin-1GHd from Hylarana guentheri, indicating a close relationship between these two species. Accordingly, this study provides candidates for the design of novel anti-infective and antineoplastic agents to fight multidrug-resistant bacteria and malignant tumors and also offers additional clues for the taxonomy of ranid frogs.

Aggregation and Its Influence on the Bioactivities of a Novel Antimicrobial Peptide, Temporin-PF, and Its Analogues.

Temporin is an antimicrobial peptide (AMP) family discovered in the skin secretion of ranid frog that has become a promising alternative for conventional antibiotic therapy. Herein, a novel temporin peptide, Temporin-PF (TPF), was successfully identified from Pelophylax fukienensis. It exhibited potent activity against Gram-positive bacteria, but no effect on Gram-negative bacteria. Additionally, TPF exhibited aggregation effects in different solutions. Three analogs were further designed to study the relationship between the aggregation patterns and bioactivities, and the MD simulation was performed for revealing the pattern of the peptide assembly. As the results showed, all peptides were able to aggregate in the standard culture media and salt solutions, especially CaCl2 and MgCl2 buffers, where the aggregation was affected by the concentration of the salts. MD simulation reported that all peptides were able to form oligomers. The parent peptide assembly depended on the hydrophobic interaction via the residues in the middle domain of the sequence. However, the substitution of Trp/D-Trp resulted in an enhanced inter-peptide interaction in the zipper-like domain and eliminated overall biological activities. Our study suggested that introducing aromaticity at the zipper-like domain for temporin may not improve the bioactivities, which might be related to the formation of aggregates via the inter-peptide contacts at the zipper-like motif domain, and it could reduce the binding affinity to the lipid membrane of microorganisms.

Amino acid residues important for D-galactose recognition by the F-type lectin, Ranaspumin-4.

F-type lectins are typically L-fucose binding proteins with characteristic L-fucose-binding and calcium-binding sequence motifs, and an F-type lectin fold. An exception is Ranaspumin-4, an F-type lectin of the Tungra frog, Engystomops pustulosus. Ranaspumin-4 is D-galactose specific and does not bind to L-fucose although it has the conserved L-fucose binding sequence motif and shares overall sequence similarity with other F-type lectins. Here, we report the detailed glycan-binding profile of wild-type Ranaspumin-4 using hemagglutination inhibition assays, flow cytometry assays and enzyme-linked lectin assays, and identify residues important for D-galactose recognition using rational site-directed mutagenesis. We demonstrate that Ranaspumin-4 binds to terminal D-galactose in α or ß linkage with preference for α1-3, α1-4, ß1-3, and ß1-4 linkages. Further, we find that a methionine residue (M31) in Ranaspumin-4 that occurs in place of a conserved Gln residue (in other F-type lectins), supports D-galactose recognition. Resides Q42 and F156 also likely aid in D-galactose recognition.

Peptide derivatives of dermaseptin S4 in fresh bovine semen for bacterial contamination control: Physicochemical and structural characterization, antibacterial potency, and effects on red blood and sperm cells.

The objectives of this study were to examine the physicochemical and structural properties of peptide derivatives of dermaseptin S4, investigate their detrimental effects on red blood and sperm cells and ascertain their antibacterial potency to control bacterial contaminants in fresh bovine semen. The dermaseptin S4 peptide derivatives used in this study were K4S4, S4(5-28), S4(5-28)a, K20S4(5-28), K4S4(1-16)a, K4S4(1-15)a and K4S4(1-15). Peptides K4S4, S4(5-28)a, K20S4(5-28), K4S4(1-15)a and K4S4(1-16)a, with a higher positive charge, were the most potent against the bacterial strains tested, with the lowest minimum inhibitory concentration (MIC), whereas S4(5-28) and K4S4(1-15), with a lower positive charge, showed the highest MIC (p < .01). Haemolysis percentage depended on peptide concentration (p < .01). The K4S4 was the most powerful haemolytic peptide, showing the highest haemolysis percentage at all peptide concentrations (p < .01). In contrast, S4(5-28), S4(5-28)a, K20S4(5-28) and K4S4(1-15) were not able to produce 50% cell lysis up to 100 µM (p < .01). All peptides reduced sperm motility in a dose-dependent manner when used in concentrations from 16 to 64 µM (p < .01). The highest reduction was seen due to K4S4 activity, and the lowest reductions of sperm motility were observed due to K4S4(1-16)a and K4S4(1-15)a activity (p < .01). Hence, we can conclude that K4S4(1-16)a and K4S4(1-15)a at a concentration of approximately 15 µM are the most promising peptides as antibacterial agents in fresh bovine semen, because at this concentration, they showed the most potent antibacterial activity against evaluated strains without significant effects on haemolysis or a reduction in sperm motility.

Conceptual DFT-Based Computational Peptidology of Marine Natural Compounds: Discodermins A-H.

A methodology based on the concepts that arise from Density Functional Theory named Conceptual Density Functional Theory (CDFT) was chosen for the calculation of some global and local reactivity descriptors of the Discodermins A-H family of marine peptides through the consideration of the KID (Koopmans in DFT) technique that was successfully used in previous studies of this kind of molecular systems. The determination of active sites of the studied molecules for different kinds of reactivities was achieved by resorting to some CDFT-based descriptors like the Fukui functions as well as the Parr functions derived from Molecular Electron Density Theory (MEDT). A few properties identified with their ability to behave as a drug and the bioactivity of the peptides considered in this examination were acquired by depending on a homology model by studying the correlation with the known bioactivity of related molecules in their interaction with various biological receptors. With the further object of analyzing their bioactivity, some parameters of usefulness for future QSAR studies, their predicted biological targets, and the ADME (Absorption, Distribution, Metabolism, and Excretion) parameters related to the Discodermins A-H pharmacokinetics are also reported.

In Silico Discovery of Antimicrobial Peptides as an Alternative to Control SARS-CoV-2.

A serious pandemic has been caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The interaction between spike surface viral protein (Sgp) and the angiotensin-converting enzyme 2 (ACE2) cellular receptor is essential to understand the SARS-CoV-2 infectivity and pathogenicity. Currently, no drugs are available to treat the infection caused by this coronavirus and the use of antimicrobial peptides (AMPs) may be a promising alternative therapeutic strategy to control SARS-CoV-2. In this study, we investigated the in silico interaction of AMPs with viral structural proteins and host cell receptors. We screened the antimicrobial peptide database (APD3) and selected 15 peptides based on their physicochemical and antiviral properties. The interactions of AMPs with Sgp and ACE2 were performed by docking analysis. The results revealed that two amphibian AMPs, caerin 1.6 and caerin 1.10, had the highest affinity for Sgp proteins while interaction with the ACE2 receptor was reduced. The effective AMPs interacted particularly with Arg995 located in the S2 subunits of Sgp, which is key subunit that plays an essential role in viral fusion and entry into the host cell through ACE2. Given these computational findings, new potentially effective AMPs with antiviral properties for SARS-CoV-2 were identified, but they need experimental validation for their therapeutic effectiveness.

Investigating the theragnostic potential of 131I-caerin peptide in thyroid cancer.

OBJECTIVE: Caerin is a new peptide with tumour toxicity and its uptake by tumour cells is independent of the sodium iodide symporter (NIS). Thyroid cancer is the most common cancers of endocrine malignancy. Radioiodine (131I)-refractory thyroid cancer is the most lethal subtype of the thyroid cancers and remains a clinical challenge. In the current study, we investigated the 131I radiolabeling efficiency of Caerin and the effects of Caerin, 131I-Caerin and free 131I on differentiated and undifferentiated human thyroid cancer cell lines (B-CPAP and CAL-62) in vitro. MATERIALS AND METHODS: Cell Counting Kit-8 was used to assess the cytotoxic effect of Caerin, 131I-Caerin and free 131I on B-CPAP and CAL-62 cells. Laser scanning confocal microscope was exploited to evaluate the uptake and internalization of Caerin by thyroid cancer cells. The Chloramine-T method was used to label the peptide with 131I. And the stability and water partition coefficient (Log P) of 131I-Caerin were studied. RESULTS: Our results demonstrated that Caerin and 131I-Caerin could be accumulated by B-CPAP and CAL-62 cells, resulting in killing of the thyroid cancer cells in vitro. The efficacy of 131I-Caerin is much higher than 131I, especially to undifferentiated CAL-62 cells. The results prove the feasibility of radioiodination of the 131I-Caerin via the Chloramine-T method. Moreover, the result indicate the hydrophobic 131I-Caerin was stable in 72 hours. CONCLUSION: Iodine-131-Caerin can inhibit the cell viability of thyroid cancer and hold certain promise as a theragnostic tool for human thyroid cancers.

Novel peptide dermaseptin-PS1 exhibits anticancer activity via induction of intrinsic apoptosis signalling.

Antimicrobial peptides (AMP) secreted by the granular glands of frog skin have been widely reported to exhibit strong bacteriostatic and bactericidal activities. Many of them have been documented with potent antiproliferative effects on multiple cancer cells, many studies also suggested that AMPs exert their functions via disrupting cell membranes. However, whether and how other cell death induction mechanism is involved in mammalian cancer cells has rarely been investigated. In this study, a novel AMP named Dermaseptin-PS1 was isolated and identified from Phyllomedusa sauvagei, it showed strong antimicrobial activities against three types of microorganisms. In vitro antiproliferative studies on human glioblastoma U-251 MG cells indicated that Dermaseptin-PS1 disrupted cell membranes at the concentrations of 10-5  M and above, while the cell membrane integrity was not affected when concentrations were decreased to 10-6  M or lower. Further examinations revealed that, at the relatively low concentration (10-6  M), Dermaseptin-PS1 induced apoptosis through mitochondrial-related signal pathway in U-251 MG cells. Thus, for the first time, we report a novel frog skin derived AMP with anticancer property by distinct mechanisms, which largely depends on its concentration. Together, our study provides new insights into the mechanism-illustrated drug design and the optimisation of dose control for cancer treatment in clinic.

The defensive system of tree frog skin identified by peptidomics and RNA sequencing analysis.

The diversity of defensive peptides from skin of amphibians has been demonstrated. These peptides may have resulted from the diversity of microorganisms encountered by amphibians. In this study, peptidomics and RNA sequencing analyses were used to study deeply the defensive peptides of the skin secretions from Polypedates megacephalus. A total of 99 defensive peptides have been identified from the skin secretions. Among these peptides, 3 peptides were myotropical peptides and 34 peptides classified as protease inhibitor peptides. 5 lectins, 8 antimicrobial peptides, 26 immunomodulatory peptides, 10 wound-healing peptides and 13 other bioactive peptides were identified as belonging to the innate immune system. One antimicrobial peptide Pm-amp1 showed high similarity to antimicrobial peptide marcin-18. This peptide was successfully expressed and showed moderate activity against four tested strains. These identified peptides highlight the extensive diversity of defensive peptides and provide powerful tools to understand the defense weapon of frog.