N-methylsansalvamide a peptide analogues. Potent new antitumor agents

Anti-cancer properties of Sansalvamide A, its derivatives, and analogs: an updated review

As peptide-based therapies gain recognition for their potential anti-cancer activity, cyclic peptides like Sansalvamide A, a marine-derived cyclic depsipeptide, have emerged as a potential anti-cancer agent due to their potent activity against various cancer types in preclinical studies. This review offers a comprehensive overview of Sansalvamide A, including its sources, structure-activity relationship, and semi-synthetic derivatives. The review also aims to outline the mechanisms through which Sansalvamide A and its analogs exert their anti-proliferative effects and to discuss the need for enhancements in pharmacokinetic profiles for better clinical utility. An extensive literature search was conducted, focusing on studies that detailed the anti-cancer activity of Sansalvamide A, its pharmacokinetics, and mechanistic pathways. Data from both in vitro and in vivo studies were collated and analyzed. Sansalvamide A and its analogs demonstrated significant anti-cancer activity across various cancer models, mediated through Hsp 90 inhibition, Topoisomerase inhibition, and G0/G1 cell cycle arrest. However, their pharmacokinetic properties were identified as a significant limitation, requiring improvement for effective clinical translation. Despite its notable anti-cancer effects, the utility of Sansalvamide A is currently limited by its pharmacokinetic characteristics. Therefore, while Sansalvamide A exhibits promise as an anti-cancer agent, there is a compelling need for further clinical and toxicological studies and optimization of its pharmacokinetic profile to fully exploit its therapeutic potential alongside modern cancer therapies.

Exploring Cyclic Peptide Nanotube Stability Across Diverse Lipid Bilayers and Unveiling Water Transport Dynamics

Cyclic Peptide Nanotubes (CPNTs) have emerged as compelling candidates for various applications, particularly as nanochannels within lipid bilayers. In this study, the stability of two CPNTs, namely 8 × [(Cys-Gly-Met-Gly)2] and 8 × [(Gly-Leu)4], are comprehensively investigated across different lipid bilayers, including 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a mixed model membrane (POPE/POPG), and a realistic yeast model membrane. The results demonstrate that both CPNTs maintain their tubular structures in all lipid bilayers, with [(Cys-Gly-Met-Gly)2] showing increased stability over an extended period in these lipid membranes. The insertion of CPNTs shows negligible impact on lipid bilayer properties, including area per lipid, volume per lipid, and bilayer thickness. The study demonstrates that the CPNT preserves its two-line water movement pattern within all the lipid membranes, reaffirming their potential as water channels. The MSD curves further reveal that the dynamics of water molecules inside the nanotube are similar for all the bilayer systems with minor differences that arise due to different lipid environments.

Secondary Metabolites of Biscogniauxia: Distribution, Chemical Diversity, Bioactivity, and Implications of the Occurrence

The genus Biscogniauxia, a member of the family Xylariaceae, is distributed worldwide with more than 50 recognized taxa. Biscogniauxia species is known as a plant pathogen, typically acting as a parasite on tree bark, although certain members of this genus also function as endophytic microorganisms. Biscogniauxia endophytic strain has received attention in many cases, which includes constituent research leading to the discovery of various bioactive secondary metabolites. Currently, there are a total of 115 chemical compounds belonging to the class of secondary metabolites, and among these compounds, fatty acids have been identified. In addition, the strong pharmacological agents of this genus are (3aS,4aR,8aS,9aR)-3a-hydroxy-8a-methyl-3,5-dimethylenedecahydronaphto [2,3-b]furan-2(3H)-one (HDFO) (antifungal), biscopyran (phytotoxic activity), reticulol (antioxidant), biscogniazaphilone A and B (antimycobacterial), and biscogniauxone (Enzyme GSK3 inhibitor). This comprehensive research contributes significantly to the potential discovery of novel drugs produced by Biscogniauxia and holds promise for future development. Importantly, it represents the first-ever review of natural products originating from the Biscogniauxia genus.

Therapeutic potential of marine peptides in malignant melanoma

Malignant melanoma is the most dangerous type of skin cancer. It is becoming more common globally and is increasingly resistant to treatment options. Despite extensive research into its pathophysiology, there are still no proven cures for metastatic melanoma. Unfortunately, current treatments are frequently ineffective and costly, and have several adverse effects. Natural substances have been extensively researched for their anti-MM capabilities. Chemoprevention and adjuvant therapy with natural products is an emerging strategy to prevent, cure or treat melanoma. Numerous prospective drugs are found in aquatic species, providing a plentiful supply of lead cytotoxic chemicals for cancer treatment. Anticancer peptides are less harmful to healthy cells and cure cancer through several different methods, such as altered cell viability, apoptosis, angiogenesis/metastasis suppression, microtubule balance disturbances and targeting lipid composition of the cancer cell membrane. This review addresses marine peptides as effective and safe treatments for MM and details their molecular mechanisms of action.

Influence of salt and temperature on the self-assembly of cyclic peptides in water: a molecular dynamics study

It is found in the literature that cyclic peptides (CPs) are able to self-assemble in water to form cyclic peptide nanotubes (CPNTs) and are used extensively in the field of nanotechnology. Several factors influence the formation and stability of these nanotubes in water. However, an extensive study of the contribution of several important factors is still lacking. The purpose of this study is to explore the effect of temperature and salt (NaCl) on the association tendency of CPs. Furthermore, the self-association behavior of CPs in aqueous solutions at various temperatures is also thoroughly discussed. Cyclo-[(Asp-D-Leu-Lys-D-Leu)₂] is considered for this study and a series of classical molecular dynamics (MD) simulations at three different temperatures, viz. 280 K, 300 K, and 320 K, both in pure water and in NaCl solutions of different concentrations are carried out. The calculations of radial distribution functions, preferential interaction parameters, cluster formation and hydrogen bonding properties suggest a strong influence of NaCl concentration on the association propensity of CPs. Low NaCl concentration hinders CP association while high NaCl concentration facilitates the association of CPs. Besides this, the association of CPs is found to be enhanced at low temperature. Furthermore, the thermodynamics of CP association is predominantly found to be enthalpy driven in both the presence and absence of salt. No crossover between enthalpy and entropy in CP association is observed. In addition, the MM-GBSA method is used to investigate the binding free energies of the CP rings that self-assembled to form nanotube like structures at all three temperatures.

Marine Natural Products with Activities against Prostate Cancer: Recent Discoveries

Prostate cancer is the most common cancer in men, with over 52,000 new cases diagnosed every year. Diagnostics and early treatment are potentially hindered by variations in screening protocols, still largely reliant on serum levels of acid phosphatase and prostate-specific antigen, with tumour diagnosis and grading relying on histopathological examination. Current treatment interventions vary in terms of efficacy, cost and severity of side effects, and relapse can be aggressive and resistant to the current standard of care. For these reasons, the scientific community is looking for new chemotherapeutic agents. This review reports compounds and extracts derived from marine organisms as a potential source of new drugs against prostate cancer. Whilst there are several marine-derived compounds against other cancers, such as multiple myeloma, leukemia, breast and lung cancer, already available in the market, the presently collated findings show how the marine environment can be considered to hold potential as a new drug source for prostate cancer, as well. This review presents information on compounds presently in clinical trials, as well as new compounds/extracts that may enter trials in the future. We summarise information regarding mechanisms of action and active concentrations.

Depsipeptides Targeting Tumor Cells: Milestones from In Vitro to Clinical Trials

Cancer is currently considered one of the most threatening diseases worldwide. Diet could be one of the factors that can be enhanced to comprehensively address a cancer patient's condition. Unfortunately, most molecules capable of targeting cancer cells are found in uncommon food sources. Among them, depsipeptides have emerged as one of the most reliable choices for cancer treatment. These cyclic amino acid oligomers, with one or more subunits replaced by a hydroxylated carboxylic acid resulting in one lactone bond in a core ring, have broadly proven their cancer-targeting efficacy, some even reaching clinical trials and being commercialized as "anticancer" drugs. This review aimed to describe these depsipeptides, their reported amino acid sequences, determined structure, and the specific mechanism by which they target tumor cells including apoptosis, oncosis, and elastase inhibition, among others. Furthermore, we have delved into state-of-the-art in vivo and clinical trials, current methods for purification and synthesis, and the recognized disadvantages of these molecules. The information collated in this review can help researchers decide whether these molecules should be incorporated into functional foods in the near future.

Therapeutic Potential of Marine Peptides in Prostate Cancer: Mechanistic Insights

Prostate cancer (PCa) is the leading cause of cancer death in men, and its treatment is commonly associated with severe adverse effects. Thus, new treatment modalities are required. In this context, natural compounds have been widely explored for their anti-PCa properties. Aquatic organisms contain numerous potential medications. Anticancer peptides are less toxic to normal cells and provide an efficacious treatment approach via multiple mechanisms, including altered cell viability, apoptosis, cell migration/invasion, suppression of angiogenesis and microtubule balance disturbances. This review sheds light on marine peptides as efficacious and safe therapeutic agents for PCa.

Photoinduced Synthesis of Methylated Marine Cyclopeptide Galaxamide Analogs with Isoindolinone as Anticancer Agents

The methylation of amino acid residues has played an important role in the biological function of bioactive peptides. In this paper, various methyl-modified and stereostructural-modified marine cyclopeptide galaxamide analogs with isoindolinone were synthesized by a photoinduced single electron transfer cyclization reaction. It was found that the single-methyl substitution was beneficial for the bioactivity of cyclic analogs with isoindolinone fragments, and the influence of methylation on bioactivity is uncertain and is sometimes case-specific. The compound with a single methyl group at Gly5 (compound 8) showed the strongest antiproliferative activity against HepG-2 cells. The tumor cell apoptosis, cell cycle, mitochondrial membrane potential, intracellular Ca2+ concentration and lactate dehydrogenase activity have been studied extensively to evaluate the antitumor potential of compound 8. Western blotting tests showed that compound 8 could decrease the MDM2 level and increase p53 levels efficiently. Careful molecular docking suggested that cyclic peptide 8 could bind firmly with MDM2 oncoprotein, indicating that MDM2 may be a potential drug target of the prepared peptides.

Natural heat shock protein 90 inhibitors in cancer and inflammation

Heat shock protein (HSP)90 is the most abundant HSPs, which are chaperone molecules whose major roles are cell protection and maintenance by means of aiding the folding, the stabilization and the remodeling of a wide range of proteins. A few hundreds of proteins depend on HSP90 chaperone activity, including kinases and transcriptional factors that play essential roles in cancer and inflammation, so that HSP90-targeted therapies have been considered as a potential strategy for the treatment of cancer and inflammatory-associated diseases. HSP90 inhibition by natural, semi-synthetic and synthetic compounds have yield promising results in pre-clinical studies and clinical trials for different types of cancers and inflammation. Natural products are a huge source of biologically active compounds widely used in drug development due to the great diversity of their metabolites which are capable to modulate several protein functions. HSP90 inhibitors have been isolated from bacteria, fungi and vegetal species. These natural compounds have a noteworthy ability to modulate HSP90 activity as well as serve as scaffolds for the development of novel synthetic or semi-synthetic inhibitors. Over a hundred clinical trials have evaluated the effect of HSP90 inhibitors as adjuvant treatment against different types of tumors and, currently, new studies are being developed to gain sight on novel promising and more effective approaches for cancer treatment. In this review, we present the naturally occurring HSP90 inhibitors and analogues, discussing their anti-cancer and anti-inflammatory effects.

Targeting hsp90 family members: A strategy to improve cancer cell death

A crucial process in biology is the conversion of the genetic information into functional proteins that carry out the genetic program. However, a supplementary step is required to obtain functional proteins: the folding of the newly translated polypeptides into well-defined, three-dimensional conformations. Proteins chaperones are crucial for this final step in the readout of genetic information, which results in the formation of functional proteins. In this review, a special attention will be given to the strategies targeting hsp90 family members in order to increase cancer cell death. We argue that disruption of hsp90 machinery and the further client protein degradation is the main consequence of hsp90 oxidative cleavage taking place at the N-terminal nucleotide-binding site. Moreover, modulation of Grp94 expression will be discussed as a potential therapeutic goal looking for a decrease in cancer relapses.

Fermentative Production of N-Methylglutamate From Glycerol by Recombinant Pseudomonas putida

N-methylated amino acids are present in diverse biological molecules in bacteria, archaea and eukaryotes. There is an increasing interest in this molecular class of alkylated amino acids by the pharmaceutical and chemical industries. N-alkylated amino acids have desired functions such as higher proteolytic stability, enhanced membrane permeability and longer peptide half-lives, which are important for the peptide-based drugs, the so-called peptidomimetics. Chemical synthesis of N-methylated amino acids often is limited by incomplete stereoselectivity, over-alkylation or the use of hazardous chemicals. Here, we describe metabolic engineering of Pseudomonas putida KT2440 for the fermentative production of N-methylglutamate from simple carbon sources and monomethylamine. P. putida KT2440, which is generally recognized as safe and grows with glucose and the alternative feedstock glycerol as sole carbon and energy source, was engineered for the production of N-methylglutamate using heterologous enzymes from Methylobacterium extorquens. About 3.9 g L⁻¹N-methylglutamate accumulated within 48 h in shake flask cultures with minimal medium containing monomethylamine and glycerol. A fed-batch cultivation process yielded a N-methylglutamate titer of 17.9 g L⁻¹.

PET imaging of Hsp90 expression in pancreatic cancer using a new 64Cu-labeled dimeric Sansalvamide A decapeptide

Heat shock protein 90 (Hsp90) plays a vital role in the progress of malignant disease and elevated Hsp90 expression has been reported in pancreatic cancer. In this study, we radiolabeled a dimeric Sansalvamide A derivative (Di-San A1) with ⁶⁴Cu, and evaluated the feasibility of using ⁶⁴Cu-Di-San A1 for PET imaging of Hsp90 expression in a mouse model of pancreatic cancer. A macrocyclic chelator NOTA (1,4,7-triazacyclononane-1,4,7-trisacetic acid) was conjugated to Di-San A1. ⁶⁴Cu-Di-San A1 was successfully prepared in a radiochemical yield > 97% with a radiochemical purity > 98%. ⁶⁴Cu-Di-San A1 is stable in PBS and mouse serum with > 92% of parent probe intact after 4 h incubation. The cell binding and uptake revealed that ⁶⁴Cu-Di-San A1 binds to Hsp90-positive PL45 pancreatic cancer cells, and the binding can be effectively blocked by an Hsp90 inhibitor (17AAG). For microPET study, ⁶⁴Cu-Di-San A1 shows good in vivo performance in terms of tumor uptake in nude mice bearing PL45 tumors. The Hsp90-specific tumor activity accumulation of ⁶⁴Cu-Di-San A1 was further demonstrated by significant reduction of PL45 tumor uptake with a pre-injected blocking dose of 17AAG. The ex vivo PET imaging and biodistribution results were consistent with the quantitative analysis of PET imaging, demonstrating good tumor-to-muscle ratio (5.35 ± 0.46) of ⁶⁴Cu-Di-San A1 at 4 h post-injection in PL45 tumor mouse xenografts. ⁶⁴Cu-Di-San A1 allows PET imaging of Hsp90 expression in PL45 tumors, which may provide a non-invasive method to quantitatively characterize Hsp90 expression in pancreatic cancer.

Evidence for Ion-Templation During Macrocyclooligomerization of Depsipeptides

The ion-mediated Mitsunobu macrocyclooligomerization (M-MCO) reaction of hydroxy acid depsipeptides provides small collections of cyclic depsipeptides with good mass recovery. The approach can produce good yields of a single macrocycle or provide rapid access to multiple oligomeric macrocycles in good overall yield. While Lewis acidic alkali metal salts are known to play a role in the outcome of MCO reactions, it is unclear whether their effect is due to an organizational (e.g., templating) mechanism. Isothermal titration calorimetry (ITC) was used to study macrocycle-metal ion binding interactions, and this report correlates these thermodynamic measurements to the (kinetically determined) size distributions of depsipeptides formed during a Mitsunobu-based macrocyclooligomerization (MCO). Key trends have been identified in quantitative metal ion-cyclic depsipeptide binding affinity ( Ka), enthalpy of binding (Δ H), and stoichiometry of complexation across discrete series of macrocycles, and they provide the first analytical platform to rationally select a metal-ion template for a targeted size regime of cyclic oligomeric depsipeptides.

Structural Diversity and Biological Activities of Cyclic Depsipeptides from Fungi

Cyclic depsipeptides (CDPs) are cyclopeptides in which amide groups are replaced by corresponding lactone bonds due to the presence of a hydroxylated carboxylic acid in the peptide structure. These peptides sometimes display additional chemical modifications, including unusual amino acid residues in their structures. This review highlights the occurrence, structures and biological activities of the fungal CDPs reported until October 2017. About 352 fungal CDPs belonging to the groups of cyclic tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, and tridecadepsipeptides have been isolated from fungi. These metabolites are mainly reported from the genera Acremonium, Alternaria, Aspergillus, Beauveria, Fusarium, Isaria, Metarhizium, Penicillium, and Rosellina. They are known to exhibit various biological activities such as cytotoxic, phytotoxic, antimicrobial, antiviral, anthelmintic, insecticidal, antimalarial, antitumoral and enzyme-inhibitory activities. Some CDPs (i.e., PF1022A, enniatins and destruxins) have been applied as pharmaceuticals and agrochemicals.

Cytotoxicity Study of Cyclopentapeptide Analogues of Marine Natural Product Galaxamide towards Human Breast Cancer Cells

Herein, we report the cytotoxicity of cyclopentapeptide analogues of marine natural product galaxamide towards breast carcinoma cells and the underlying mechanisms. We examined the effect of the novel galaxamide analogues on cancer cell proliferation by MTT assay and also further examined the most active compound for morphological changes using Hoechst33342 staining technique, induction of apoptosis, cell cycle phases, mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) generation using flow cytometry in human breast cancer MCF-7 cells in vitro. Galaxamide and its analogues effectively induced toxicity in human hepatocellular carcinoma HepG2, human breast carcinoma MCF-7, human epitheloid cervix carcinoma HeLa, and human breast carcinoma MB-MDA-231 cell lines. Amongst them, compound 3 exhibited excellent toxicity towards MCF-7 cells. This galaxamide analogue significantly induced apoptosis in a dose-dependent manner in MCF-7 cells involves cell cycle arrest in the G1 phase, a reduction of MMP, and a marked increase in generation of ROS. Particularly, compound 3 of galaxamide analogues might be a potential candidate for the treatment of breast cancer.

Aspersymmetide A, a New Centrosymmetric Cyclohexapeptide from the Marine-Derived Fungus Aspergillus versicolor

A new centrosymmetric cyclohexapeptide, aspersymmetide A (1), together with a known peptide, asperphenamate (2), was isolated from the fungus Aspergillus versicolor isolated from a gorgonian coral Carijoa sp., collected from the South China Sea. The chemical structure of 1 was elucidated by analyzing its NMR spectroscopy and MS spectrometry data, and the absolute configurations of the amino acids of 1 were determined by Marfey's method and UPLC-MS analysis of the hydrolysate. Aspersymmetide A (1) represents the first example of marine-derived centrosymmetric cyclohexapeptide. Moreover, 1 exhibited weak cytotoxicity against NCI-H292 and A431 cell lines at the concentration of 10 μM.

d-Amino Acid Position Influences the Anticancer Activity of Galaxamide Analogs: An Apoptotic Mechanism Study

Galaxamide, an extract from Galaxaura filamentosa, is a cyclic pentapeptide containing five l-leucines. Due to the particular cyclic structure and the excellent anticancer activity, synthesis of Galaxamide and its analogs and their subsequent bio-applications have attracted great attention. In the present work, we synthesized six Galaxamide analogs by replacing one of the l-leucines with phenylalanine and varying the d-amino acid position. The anticancer effect of the synthesized Galaxamide analogs was tested against four in vitro human cancer cell lines, human hepatocellular cells (HepG₂), human breast cancer cell (MCF-7), human breast adenocarcinoma cells (MDA-MB-435) and a human cervical carcinoma cell line (Hela). Results showed that Galaxamide analogs with different d-amino acid positions displayed distinct anticancer potential. The Galaxamide analog containing d-amino acid at position 5 (Analog-6) presented the strongest anticancer activity. The mechanism study revealed that Analog-6 could cause the early apoptosis of HepG₂ cells by inhibiting their growth in the sub-G1 stage of the cell cycle and induce the chromatin condensation and fragmentation, which can be seen as 68% of HepG₂ cells inhibited in the sub-G1 stage. Moreover, a mitochondria-mediated pathway was found to be involved in the apoptotic process of Analog-6 on HepG₂ cells.

OSMAC approach leads to new fusarielin metabolites from Fusarium tricinctum

Using the OSMAC (One Strain MAny Compounds) approach, the fungal endophyte Fusarium tricinctum was cultivated on fruit and vegetable juice-supplemented solid rice media. This led to an up to 80-fold increase in the accumulation of the new natural product fusarielin J (1), as well as to the induction of two new natural products fusarielin K (2) and fusarielin L (3) and the known derivatives fusarielins A (4) and B (5). Compounds 2-5 were not detected when the fungus was grown on rice media lacking either fruit or vegetable juice. The highest increase in the accumulation of compound 1 was observed in the presence of apple and carrot juice, whereas the stimulating effect was weaker for banana juice. Compound 1 exhibited cytotoxicity against the human ovarian cancer cell line A2780, with an IC₅₀ value of 12.5 μM.

Biscogniauxone, a New Isopyrrolonaphthoquinone Compound from the Fungus Biscogniauxia mediterranea Isolated from Deep-Sea Sediments

The properties and the production of new metabolites from the fungal strain LF657 isolated from the Herodotes Deep (2800 m depth) in the Mediterranean Sea are reported in this study. The new isolate was identified as Biscogniauxia mediterranea based on ITS1-5.8S-ITS2 and 28S rRNA gene sequences. A new isopyrrolonaphthoquinone with inhibitory activity against glycogen synthase kinase (GSK-3β) was isolated from this fungus. This is the first report of this class of compounds from a fungus isolated from a deep-sea sediment, as well as from a Biscogniauxia species.

Design and Synthesis of Analogues of Marine Natural Product Galaxamide, an N-methylated Cyclic Pentapeptide, as Potential Anti-Tumor Agent in Vitro

Herein, we report design and synthesis of novel 26 galaxamide analogues with N-methylated cyclo-pentapeptide, and their in vitro anti-tumor activity towards the panel of human tumor cell line, such as, A549, A549/DPP, HepG2 and SMMC-7721 using MTT assay. We have also investigated the effect of galaxamide and its representative analogues on growth, cell-cycle phases, and induction of apoptosis in SMMC-7721 cells in vitro. Reckon with the significance of conformational space and N-Me aminoacid (aa) comprising this compound template, we designed the analogues with modification in N-Me-aa position, change in aa configuration from l to d aa and substitute one Leu-aa to d/l Phe-aa residue with respective to the parent structure. The efficient solid phase parallel synthesis approach is employed for the linear pentapeptide residue containing N-Me aa, followed by solution phase macrocyclisation to afford target cyclo pentapeptide compounds. In the present study, all galaxamide analogues exhibited growth inhibition in A549, A549/DPP, SMMC-7721 and HepG2 cell lines. Compounds 6, 18, and 22 exhibited interesting activities towards all cell line tested, while Compounds 1, 4, 15, and 22 showed strong activity towards SMMC-7221 cell line in the range of 1–2 μg/mL IC₅₀. Flow cytometry experiment revealed that galaxamide analogues namely Compounds 6, 18, and 22 induced concentration dependent SMMC-7721 cell apoptosis after 48 h. These compounds induced G0/G1 phase cell-cycle arrest and morphological changes indicating induction of apoptosis. Thus, findings of our study suggest that the galaxamide and its analogues 6, 18 and 22 exerted growth inhibitory effect on SMMC-7721 cells by arresting the cell cycle in the G0/G1 phase and inducing apoptosis. Compound 1 showed promising anti-tumor activity towards SMMC-7721 cancer cell line, which is 9 and 10 fold higher than galaxamide and reference DPP (cisplatin), respectively.

Toward structure prediction of cyclic peptides

Cyclic peptides are a promising class of molecules that can be used to target specific protein-protein interactions. A computational method to accurately predict their structures would substantially advance the development of cyclic peptides as modulators of protein-protein interactions. Here, we develop a computational method that integrates bias-exchange metadynamics simulations, a Boltzmann reweighting scheme, dihedral principal component analysis and a modified density peak-based cluster analysis to provide a converged structural description for cyclic peptides. Using this method, we evaluate the performance of a number of popular protein force fields on a model cyclic peptide. All the tested force fields seem to over-stabilize the α-helix and PPII/β regions in the Ramachandran plot, commonly populated by linear peptides and proteins. Our findings suggest that re-parameterization of a force field that well describes the full Ramachandran plot is necessary to accurately model cyclic peptides.

Novel cyclic pentapeptide H-15 induces differentiation and inhibits proliferation in murine melanoma B16 cells

Sansalvamide A is a cyclic depsipeptide that is isolated from a marine fungus of the Fusarium genus. Sansalvamide A exhibits significant antitumor ability. The molecular formula and molecular weight of the novel sansalvamide A derivative H-15 are C₂₉H₄₄BrN₅O₆ and 637.2475, respectively. In the present study, H-15 was found to inhibit the proliferation and induce the differentiation of murine melanoma B16 cells. A sulforhodamine B colorimetric assay was used to measure the inhibitory effects of 0.1, 1, 10, 50 and 100 µM H-15 on the B16 cells, and the results revealed that the inhibitory effects of H-15 exerted on the B16 cells occurred in a concentration-dependent manner. In addition, the growth curve model of the B16 cells treated with 50 µM H-15 revealed that the effect of H-15 was also time-dependent. The differentiation morphology of the B16 cells was observed subsequent to treating the cells with H-15. An optical microscope was used to observe the differentiation morphology of the cells. In addition, melanin secretion increased in the B16 cells treated with 50 µM H-15. The expression levels of tyrosinase (TYR) were assayed by western blot analysis, and it was found that the cells treated with 50 µM H-15 for 48 h exhibited increased expression of TYR. The results of the present study indicated that H-15 may induce the differentiation of B16 cells.

Liquid chromatography coupled to different atmospheric pressure ionization sources-quadrupole-time-of-flight mass spectrometry and post-column addition of metal salt solutions as a powerful tool for the metabolic profiling of Fusarium oxysporum

Fusarium oxysporum L11 is a non-pathogenic soil-borne fungal strain that yielded an extract that showed antifungal activity against phytopathogens. In this study, reversed-phase high-performance liquid chromatography (RP-HPLC) coupled to different atmospheric pressure ionization sources-quadrupole-time-of-flight mass spectrometry (API-QTOF-MS) was applied for the comprehensive profiling of the metabolites from the extract. The employed sources were electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). Post-column addition of metal solutions of Ca, Cu and Zn(II) was also tested using ESI. A total of 137 compounds were identified or tentatively identified by matching their accurate mass signals, suggested molecular formulae and MS/MS analysis with previously reported data. Some compounds were isolated and identified by NMR. The extract was rich in cyclic peptides like cyclosporins, diketopiperazines and sansalvamides, most of which were new, and are reported here for the first time. The use of post-column addition of metals resulted in a useful strategy for the discrimination of compound classes since specific adducts were observed for the different compound families. This technique also allowed the screening for compounds with metal binding properties. Thus, the applied methodology is a useful choice for the metabolic profiling of extracts and also for the selection of metabolites with potential biological activities related to interactions with metal ions.

Cyclic depsipeptides as potential cancer therapeutics

Cyclic depsipeptides are polypeptides in which one or more amino acid is replaced by a hydroxy acid, resulting in the formation of at least one ester bond in the core ring structure. Many natural cyclic depsipeptides possessing intriguing structural and biological properties, including antitumor, antifungal, antiviral, antibacterial, anthelmintic, and anti-inflammatory activities, have been identified from fungi, plants, and marine organisms. In particular, the potent effects of cyclic depsipeptides on tumor cells have led to a number of clinical trials evaluating their potential as chemotherapeutic agents. Although many of the trials have not achieved the desired results, romidepsin (FK228), a bicyclic depsipeptide that inhibits histone deacetylase, has been shown to have clinical efficacy in patients with refractory cutaneous T-cell lymphoma and has received Food and Drug Administration approval for use in treatment. In this review, we discuss antitumor cyclic depsipeptides that have undergone clinical trials and focus on their structural features, mechanisms, potential applications in chemotherapy, and pharmacokinetic and toxicity data. The results of this study indicate that cyclic depsipeptides could be a rich source of new cancer therapeutics.

Cyclodepsipeptides: a rich source of biologically active compounds for drug research

Faced with the need to find new drugs for all kinds of diseases, science sees that Nature offers numerous classes of compounds showing an impressively high biological potential. Among those are the cyclodepsipeptides, hybrid structures composed of amino and hydroxy acids. In the past decades numerous cyclodepsipeptides have been isolated and their potential as drugs has been studied extensively. For several cyclodepsipeptides total syntheses both in solution and on solid-phase have been established, allowing the production of combinatorial libraries. In addition, the biosynthesis of specific cyclodepsipeptides has been elucidated and used for the chemoenzymatic preparation of nonnatural analogues. This review summarizes the recent literature on cyclic tetra- to decadepsipeptides, composed exclusively of α-amino- and α-hydroxy acids.

A novel cyclic pentapeptide, H-10, inhibits B16 cancer cell growth and induces cell apoptosis

Sansalvamide A, a cyclic depsipeptide isolated from a marine fungus of the Fusarium genus, exhibits significant antitumor activity. In the present study, H-10 (molecular formula, C₃₈H₅₅N₅O₆; molecular weight, 677.8732), a novel sansalvamide A derivative, demonstrated an inhibitory effect on the proliferation of murine melanoma B16 cells. It was confirmed that H-10 induced the apoptosis of the B16 cells. The inhibitory rate of various concentrations of H-10 on the B16 cells was measured by sulforhodamine B colorimetric assay, and the results revealed that the inhibitory effect of H-10 on the B16 cells occurred in a concentration-dependent manner. In addition, a growth curve model of the B16 cells treated with 50 μM H-10 revealed that the effect of H-10 also occurred in a time-dependent manner. The apoptotic morphology of the B16 cells was observed using an optical microscope. Following the treatment of the cells with 50 μM H-10 for 24 h, the cell apoptosis rate was analyzed using flow cytometry. The expression levels of caspase-3, -8 and -9 were analyzed by western blot analysis, and the results indicated that H-10 may induce the apoptosis of B16 cells.

Consecutive isocyanide-based multicomponent reactions: synthesis of cyclic pentadepsipeptoids

The synthesis of six cyclic depsipeptoids inspired by the natural depsipeptide sansalvamide A is described. An efficient and fast synthetic strategy was developed using a combination of consecutive isocyanide-based multicomponent reactions (Ugi and Passerini reactions). This methodology can be used to access a variety of cyclic oligodepsipeptoids.

Solid-phase peptide synthesis (SPPS), C-terminal vs. side-chain anchoring: a reality or a myth

Here we review the strategies for the solid-phase synthesis of peptides starting from the side chain of the C-terminal amino acid. Furthermore, we provide experimental data to support that C-terminal and side-chain syntheses give similar results in terms of purity. However, the stability of the two bonds that anchor the peptide to the polymer may determine the overall yield and this should be considered for the large-scale production of peptides. In addition, resins/linkers which do not subject to side reactions can be preferred for some peptides.

N-Triethylene glycol (N-TEG) as a surrogate for the N-methyl group: application to Sansalvamide A peptide analogs

Here we studied the N-triethylene glycol (N-TEG) group as a surrogate for the N-Me group in Sansalvamide A peptide. The five N-TEG and N-Me analogs of this cyclic pentapeptide were synthesized, and their biological activity, lipophilicity and conformational features were compared.

N-2-Hydroxybenzaldehyde acylhydrazone–Fe(iii) complex: synthesis, crystal structure and its efficient and selective N-methylation

The n-acylhydrazone–Fe(iii) complexes permit ligand's amide N to be easily methylated and suppress the O-methylation side reactions of phenol.

Mixed ligand complexation of some transition metal ions in solution and solid state: spectral characterization, antimicrobial, antioxidant, DNA cleavage activities and molecular modeling

Equilibrium studies of Ni(II), Cu(II) and Zn(II) mixed ligand complexes involving a primary ligand 5-fluorouracil (5-FU; A) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L-histidine (his) as co-ligands(B) were carried out pH-metrically in aqueous medium at 310±0.1K with I=0.15 M (NaClO4). In solution state, the stoichiometry of MABH, MAB and MAB2 species have been detected. The primary ligand(A) binds the central M(II) ions in a monodentate manner whereas him, bim, hist and his co-ligands(B) bind in mono, mono, bi and tridentate modes respectively. The calculated ΔlogK, logX and logX' values indicate higher stability of the mixed ligand complexes in comparison to binary species. Stability of the mixed ligand complex equilibria follows the Irving-Williams order of stability. In vitro biological evaluations of the free ligand(A) and their metal complexes by well diffusion technique show moderate activities against common bacterial and fungal strains. Oxidative cleavage interaction of ligand(A) and their copper complexes with CT DNA is also studied by gel electrophoresis method in the presence of oxidant. In vitro antioxidant evaluations of the primary ligand(A), CuA and CuAB complexes by DPPH free radical scavenging model were carried out. In solid, the MAB type of M(II)5-FU(A)his(B) complexes were isolated and characterized by various physico-chemical and spectral techniques. Both the magnetic susceptibility and electronic spectral analysis suggest distorted octahedral geometry. Thermal studies on the synthesized mixed ligand complexes show loss of coordinated water molecule in the first step followed by decomposition of the organic residues subsequently. XRD and SEM analysis suggest that the microcrystalline nature and homogeneous morphology of MAB complexes. Further, the 3D molecular modeling and analysis for the mixed ligand MAB complexes have also been carried out.

Identification of a novel gene product expressed by Trichinella spiralis that binds antiserum to Sp2/0 myeloma cells

To obtain novel antigen genes for use as an anti-tumor vaccine, a Trichinella spiralis cDNA expression library was constructed from muscle larvae RNA and screened with sera from Balb/C mice injected with Sp2/0 myeloma cells. One positive clone was obtained after three rounds of immunoscreening of the cDNA expression library and was subsequently excised in vivo using the ExAssist helper phage with SOLR strain. A full-length gene was amplified using 5'-RACE technology and analyzed by BLAST, Protein Analysis System of ELM, and DNAStar Software. The sequencing results showed that the fragment was 569 bp in length and contained an open reading frame. It was predicted that the full-length gene encoded 136 amino acids. This gene, TS2, contained four putative N-Arg dibasic convertase (nardilysine) cleavage sites, one peptide C-terminal amidation site, and one glycosaminoglycan attachment site. Six antibody epitopes were predicted by bioinformatic analysis.

Synthesis and evaluation of biotinylated sansalvamide A analogs and their modulation of Hsp90

Described are the syntheses of three sansalvamide A derivatives that contain biotinylated tags at individual positions around the macrocycle. The tagged derivatives indicated in protein pull-down assays that they bind to Hsp90 at the same binding site (N-Middle domain) as the San A-amide peptide. Further, these compounds inhibit binding between Hsp90 and multiple C-terminal client proteins. This interaction is unique to the San A analogs indicating they can be tuned for selectivity against Hsp90 client/co-chaperone proteins.

New methodology for the N-alkylation of 2-amino-3-acylthiophenes

2-Amino-3-acylthiophenes are known to allosterically modulate the A(1) adenosine receptor and are also used as intermediates in the synthesis of therapeutic agents and pharmacophores such as thienoazepines and thienopyrimidines. The N-alkylation of 2-aminothiophenes has been notoriously difficult to accomplish under mild conditions and there are very few examples of N-alkylated 2-aminothiophenes in the literature, all of which use forcing conditions to effect the alkylation. Here we describe the synthesis of such compounds under mild conditions utilising 2-carbamoylamino and 2-acylamino-3-acylthiophenes with caesium carbonate, and tetrabutylammonium iodide in DMF.

Design and synthesis of Hsp90 inhibitors: exploring the SAR of Sansalvamide A derivatives

Utilizing the structure-activity relationship we have developed during the synthesis of the first two generations and mechanism of action studies that point to the interaction of these molecules with the key oncogenic protein Hsp90, we report here the design of 32 new Sansalvamide A derivatives and their synthesis. Our new structures, designed from previously reported potent compounds, were tested for cytotoxicity on the HCT116 colon cancer cell line, and their binding to the biological target was analyzed using computational studies involving blind docking of derivatives using Autodock. Further, we show new evidence that our molecules bind directly to Hsp90 and modulate Hsp90's binding with client proteins. Finally, we demonstrate that we have integrated good ADME properties into a new derivative.