Morten B. Strøm

Synoxazolidinones A and B: novel bioactive alkaloids from the ascidian Synoicum pulmonaria.

Bioassay-guided fractionation of the sub-Arctic ascidian Synoicum pulmonaria collected off the Norwegian coast led to the isolation of a novel family of brominated guanidinium oxazolidinones named synoxazolidinones A and B (1 and 2). The backbone of the compounds contains a 4-oxazolidinone ring rarely seen in natural products. The structure of the compounds was determined by spectroscopic methods. The synoxazolidinones exhibited antibacterial and antifungal activities.

Antimicrobial Activity of Small β-Peptidomimetics Based on the Pharmacophore Model of Short Cationic Antimicrobial Peptides

We have synthesized a series of small beta-peptidomimetics (M(w) <650) that were based on the minimal pharmacophore model for anti-Staphylococcal activity of short cationic antimicrobial peptides. All beta-peptidomimetics had a net charge of +2 and formed an amphipathic scaffold consisting of an achiral lipophilic beta(2,2)-amino acid coupled to a C-terminal l-arginine amide residue. By varying the lipophilic side-chains of the beta(2,2)-amino acids, we obtained a series of highly potent beta-peptidomimetics with high enzymatic stability against alpha-chymotrypsin and a general low toxicity against human erythrocytes. The most potent beta-peptidomimetics displayed minimal inhibitory concentrations of 2.1-7.2 muM against Staphylococcus aureus, methicillin resistant Staphylococcus aureus (MRSA), methicillin resistant Staphylococcus epidermidis (MRSE), and Escherichia coli. Small amphipathic beta-peptidomimetics may be a promising class of antimicrobial agents by means of having a similar range of potency and selectivity as larger cationic antimicrobial peptides in addition to improved enzymatic stability and lower costs of production.

Screening for antibacterial and antifungal activities in marine benthic invertebrates from northern Norway.

Benthic marine invertebrates collected from sub-Arctic regions of northern Norway, were found to be a promising source of novel bioactive compounds against human and fish pathogenic bacteria and fungi. Lyophilized material from seven species of ascidians, six sponges and one soft alcyonid coral were extracted with 60% acidified acetonitrile (ACN). After separation into an ACN-rich phase (ACN-extract) and an aqueous phase, and subsequent solid-phase extraction of the aqueous phase, fractions differing in polarity were obtained and screened for antibacterial and antifungal activities, along with the more lipophilic ACN-extracts. Antimicrobial activity was determined against two gram-negative, two gram-positive bacteria, and two strains of fungi. Notably, all the invertebrate species in the study showed activity against all four strains of bacteria and the two strains of fungi. In general, the aqueous fractions displayed highest antimicrobial activity, and the most potent extracts were obtained from the colonial ascidian Synoicum pulmonaria which displayed activity against bacteria and fungi at a concentration of 0.02 mg/ml; the lowest concentration tested.

Synthesis of Cationic Antimicrobial β2,2-Amino Acid Derivatives with Potential for Oral Administration

We have prepared a series of highly potent achiral cationic β(2,2)-amino acid derivatives that fulfill the Lipinskis rule of five and that contain the basic structural requirements of short cationic antimicrobial peptides. Highest antimicrobial potency was observed for one of the smallest β(2,2)-amino acid derivatives (M(w) 423.6) exhibiting a MIC of 3.8 μM against methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE), and Staphylococcus aureus, and 7.7 μM against Escherichia coli. The β(2,2)-amino acid derivatives were shown to have similar absorption properties as several commercially available drugs, and the results implied a resembling membrane disrupting mechanism of action as reported for much larger cationic antimicrobial peptides. By their high potency, nontoxicity, absorption properties, and ease of synthesis, the β(2,2)-amino acid derivatives demonstrate a way to modify a vastly investigated class of cationic antimicrobial peptides into small drug-like molecules with high commercial potential.

Anticancer mechanisms of action of two small amphipathic β(2,2)-amino acid derivatives derived from antimicrobial peptides.

We have recently discovered that small antimicrobial β(2,2)-amino acid derivatives (Mw<500) also display activity against cancer cells. To explore their drug potential, we have presently investigated the mechanisms of action of two derivatives BAA-1 (IC(50) 8.1μg/ml) and BAA-2 (IC(50) 3.8μg/ml) on Ramos human Burkitts lymphoma cells. Studies using annexin-V-FITC/propidium iodide staining and flow cytometry revealed essential mechanistic differences, which was confirmed by screening for active caspases, investigation of mitochondrial membrane potential, and electron microscopy studies. Our results indicated that BAA-1 killed Ramos cells by destabilizing the cell membrane, whereas BAA-2 caused apoptosis by the mitochondrial-mediated pathway.

The Antibacterial ent-Eusynstyelamide B and Eusynstyelamides D, E, and F from the Arctic Bryozoan Tegella cf. spitzbergensis

The brominated tryptophan-derived ent-eusynstyelamide B (1) and three new derivatives, eusynstyelamides D, E, and F (2-4), were isolated from the Arctic bryozoan Tegella cf. spitzbergensis. The structures were elucidated by spectroscopic methods including 1D and 2D NMR and analysis of mass spectrometric data. The enantiomer of 1, eusynstyelamide B, has previously been isolated from the Australian ascidian Eusynstyela latericius. Antimicrobial activities are here reported for 1-4, with minimum inhibitory concentrations (MIC) as low as 6.25 μg/mL for 1 and 4 against Staphylococcus aureus. Eusynstyelamides 2 and 3 showed weak cytotoxic activity against the human melanoma A 2058 cell line.

Synthesis of anticancer heptapeptides containing a unique lipophilic β2,2-amino acid building block

We report a series of synthetic anticancer heptapeptides (H‐KKWβ2,2WKK‐NH2) containing eight different central lipophilic β2,2‐amino acid building blocks, which have demonstrated high efficiency when used as scaffolds in small cationic antimicrobial peptides and peptidomimetics. The most potent peptides in the present study had IC50 values of 9–23 µm against human Burkitts lymphoma and murine B‐cell lymphoma and were all nonhaemolytic (EC50 > 200 µm). The most promising peptide 10e also demonstrated low toxicity against human embryonic lung fibroblast cells and peripheral blood mononuclear cells and exceptional proteolytic stability. Copyright

Improved anticancer potency by head‐to‐tail cyclization of short cationic anticancer peptides containing a lipophilic β2,2‐amino acid

We have recently reported a series of synthetic anticancer heptapeptides (H‐KKWβ2,2WKK‐NH2) containing a central achiral and lipophilic β2,2‐amino acid that display low toxicity against non‐malignant cells and high proteolytic stability. In the present study, we have further investigated the effects of increasing the rigidity and amphipathicity of two of our lead heptapeptides by preparing a series of seven to five residue cyclic peptides containing the two most promising β2,2‐amino acid derivatives as part of the central lipophilic core. The peptides were tested for anticancer activity against human Burkitts lymphoma (Ramos cells), haemolytic activity against human red blood cells (RBC) and cytotoxicity against healthy human lung fibroblast cells (MRC‐5). The results demonstrated a considerable increase in anticancer potency following head‐to‐tail peptide cyclization, especially for the shortest derivatives lacking a tryptophan residue. High‐resolution NMR studies and molecular dynamics simulations together with an annexin‐V‐FITC and propidium iodide fluorescent assay showed that the peptides had a membrane disruptive mode of action and that the more potent peptides penetrated deeper into the lipid bilayer. The need for new anticancer drugs with novel modes of action is demanding, and development of short cyclic anticancer peptides with an overall rigidified and amphipathic structure is a promising approach to new anticancer agents. Copyright

Anticancer activity of small amphipathic β2,2-amino acid derivatives

We report the anticancer activity from screening of a series of synthetic β(2,2)-amino acid derivatives that were prepared to confirm the pharmacophore model of short cationic antimicrobial peptides with high anti-Staphylococcal activity. The most potent derivatives against human Burkitts lymphoma (Ramos) cells displayed IC(50) values below 8 μM, and low toxicity against human red blood cells (EC(50) > 200 μM). A more than 5-fold preference for Ramos cancer cells compared to human lung fibroblasts (MRC-5 cells) was also obtained for the most promising β(2,2)-amino acid derivative 3-amino-N-(2-aminoethyl)-2,2-bis(naphthalen-2-ylmethyl)propanamide (5c). Screening of 5c at the National Cancer Institute (NCI, USA) confirmed its anticancer potency and revealed a very broad range of anticancer activity with IC(50) values of 0.32-3.89 μM against 59 different cancer cell lines. Highest potency was obtained against the colon cancer cell lines, a non-small cell lung cancer, a melanoma, and three leukemia cell lines included in the NCI screening panel. The reported β(2,2)-amino acid derivatives constitute a promising new class of anticancer agents based on their high anticancer potency, ease of synthesis, mode-of-action, and optimized pharmacokinetic properties compared to much larger antimicrobial peptides.

Staphylococcus aureus biofilm susceptibility to small and potent β2,2-amino acid derivatives

Small antimicrobial β2,2-amino acid derivatives (Mw < 500 Da) are reported to display high antibacterial activity against suspended Gram-positive strains combined with low hemolytic activity. In the present study, the anti-biofilm activity of six β2,2-amino acid derivatives (A1–A6) against Staphylococcus aureus (ATCC 25923) was investigated. The derivatives displayed IC50 values between 5.4 and 42.8 μM for inhibition of biofilm formation, and concentrations between 22.4 and 38.4 μM had substantial effects on preformed biofilms. The lead derivative A2 showed high killing capacity (log R), and it caused distinct ultrastructural changes in the biofilms as shown by electron and atomic force microscopy. The anti-biofilm properties of A2 was preserved under high salinity conditions. Extended screening showed also high activity of A2 against Escherichia coli (XL1 Blue) biofilms. These advantageous features together with high activity against preformed biofilms make β2,2-amino acid derivatives a promising class of compounds for further development of anti-biofilm agents.