Colin Skene

Marine nematocides: Tetrahydrofurans from a southern Australian brown alga, Notheia anomala

Chemical analysis of N. anomala collected off rock platforms along the southern coast of Australia yielded a cis-dihydroxytetrahydrofuran (2), the structure for which was assigned by spectroscopic analysis, chemical derivatization and biomimetic synthesis. Tetrahydrofurans from Notheia anomola are reported for the first time as potent and selective inhibitors of the larval development of parasitic nematodes. SAR observations are made on a selection of natural, semi-synthetic and synthetic tetrahydrofurans

Aspergillicins A–E: five novel depsipeptides from the marine-derived fungus Aspergillus carneus

A search for new antiparasitic agents from a strain of the fungus Aspergillus carneus isolated from an estuarine sediment collected in Tasmania, Australia, yielded the known terrestrial fungal metabolite marcfortine A (1) as an exceptionally potent antiparasitic agent. This study also yielded a series of new depsipeptides, aspergillicins A-E (2-6) and the known terrestrial fungal metabolite acyl aszonalenin (7). Marcfortine A (1) and acyl aszonalenin (7) were identified by spectroscopic analysis, with comparison to literature data. Complete stereostructures were assigned to aspergillicins A-E (2-6) on the basis of detailed spectroscopic analysis, together with ESIMS analysis of the free amino acids generated by acid hydrolysis, and HPLC analysis of Marfey derivatives prepared from the acid hydrolysate. The peptide amino acid sequence for all aspergillicins was unambiguously assigned by MS(n) ion-trap ESI mass spectrometry.

Esmodil: An Acetylcholine Mimetic Resurfaces in a Southern Australian Marine Sponge Raspailia (Raspailia) SP

Bioassay directed fractionation of a Raspailia (Raspailia) sp. (Order Poecilosclerida; Family Raspailiidae) collected during scientific trawling operations off the Northern Rottnest Shelf yielded as nematocidal agents the known metabolites, phorboxazoles A (1) and B (2). Further examination revealed the new natural product but known synthetic compound, esmodil (3). The structure for 3 was confirmed by spectroscopic analysis and total synthesis.

Plasmid breakage by 125I-labelled DNA ligands: Effect of DNA-iodine atom distance on breakage efficiency

Purpose: The aim of the study is to establish the relationship between the efficiency of DNA double-stranded breakage by 125I-labelled DNA ligands and the distance from the decaying atom to the helical axis. Materials and methods: Two new iodinated minor groove binding ligands were synthesized which, on the basis of molecular modelling studies, place the iodine atom at different distances from the DNA helical axis (namely 7.4 and 11.2 A°). Plasmid DNA breakage experiments, in both buffer-only and buffer + 2M dimethylsulfoxide (DMSO), were used to determine the efficiency of induction of internal double-stranded breaks (DSB) of the two new ligands, as well as that for 125I-Hoechst 33258, which is characterized by a helical axis-iodine atom distance of 9.1 A°. Results: The results showed a progressive decrease in the efficiency of DNA DSB induction with the axis-iodine atom distance, for both incubation conditions. The distance-damage relationship was somewhat steeper than previously predicted from the theoretical studies by Humm and Charlton, based on radical-mediated damage. Another distinctive trend was revealed by comparison of breakage efficiency with and without DMSO. The extent of DMSO protection increased significantly with DNA-iodine distance. Conclusions: The steeper than predicted decrease in DSB induction with DNA-iodine distance is consistent with a substantial contribution to DNA breakage of the charge neutralization effect (arising from the transient positive charge left on the daughter Te atom), and the expectation that this contribution would be very dependent on the distance of the site of hole injection from the base-pair π-stack. An important caveat to the results and conclusions is the need to confirm the estimated helical axis-iodine distances with X-ray crystallography studies, and for further exemplification with a more extensive collection of DNA ligands.

The biomimetic synthesis of marine epoxylipids: Bisepoxides to tetrahydrofurans

The biomimetic synthesis of novel lipids 1, 2, 8 and 10 obtained from the southern Australian marine brown alga Notheia anomala has been achieved, and features the acid mediated conversion of methylene interrupted bisepoxides to tetrahydrofurans

Tumour targeting of Auger emitters using DNA ligands conjugated to octreotate

Abstract Purpose: The objective of the study was to conjugate the DNA binding ligand para-[125I]-iodoHoechst to octreotate, and to explore the tumour targeting potential of this conjugate in the octreotate-somatostatin receptor system. Methods: We synthesized a Hoechst analogue containing a tri-butylstannyl group in the para position of phenyl ring, conjugated it to the N-terminal amino group of octreotate and prepared 125I-labelled conjugate by iododestannylation. We used the somatostatin receptor (SSTR2) over-expressing cell line A427-7 derived from its parent A427 human non-small cell lung carcinoma cell line to investigate SSTR2 affinity and receptor-mediated internalisation of the conjugate, and the mouse A427-7 tumour xenograft model for in vivo biodistribution studies of the radiolabelled conjugate. Results: A method was developed for convenient preparation of high specific activity radioiodinated conjugate which retains affinity for somatostatin receptors and is internalised into A427-7 SSTR2 over-expressing cells via a receptor-mediated mechanism. The conjugate accumulates in mouse A427-7 tumour xenografts following intravenous administration. Conclusions: A dual targeting strategy for Auger endoradiotherapy, in which a DNA ligand is used to target the Auger decay to DNA, in conjunction with receptor-mediated targeting to specific receptors, using a labelled DNA ligand/peptide conjugate, has been demonstrated for the octreotate-somatostatin receptor system.

Macrophage migration inhibitory factor is required for NLRP3 inflammasome activation

Macrophage migration inhibitory factor (MIF) exerts multiple effects on immune cells, as well as having functions outside the immune system. MIF can promote inflammation through the induction of other cytokines, including TNF, IL-6, and IL-1 family cytokines. Here, we show that inhibition of MIF regulates the release of IL-1α, IL-1β, and IL-18, not by affecting transcription or translation of these cytokines, but via activation of the NLRP3 inflammasome. MIF is required for the interaction between NLRP3 and the intermediate filament protein vimentin, which is critical for NLRP3 activation. Further, we demonstrate that MIF interacts with NLRP3, indicating a role for MIF in inflammasome activation independent of its role as a cytokine. These data advance our understanding of how MIF regulates inflammation and identify it as a factor critical for NLRP3 inflammasome activation.MIF is a cytokine best known for its modulatory effect on expression of proinflammatory cytokines. Here the authors show that MIF facilitates the NLRP3–vimentin interaction, resulting in Nlrp3 inflammasome activation.

Hyperconjugation Involving Strained Carbon–Carbon Bonds. Structural Analysis of Ester and Ether Derivatives and One-Bond 13C–13C Coupling Constants of α- and β-Nopinol

σ(C-C)-σ*(C-O) interactions involving the strained carbon-carbon bonds of α- and β-nopinol, and their ester and ether derivatives have been demonstrated in the solid state using the variable oxygen probe. These hyperconjugative interactions are manifested as a strong response of the C-OR bond distance to the electron demand of the OR substituent. Although the effects upon the donor C-C bond distances are not large enough to be measurable by X-ray crystallography, they do result in systematic and measurable effects on the (13)C-(13)C one-bond coupling constants. For the donor C-C bond, coupling constants decrease, consistent with weakening of this bond, while the intervening C-C bond coupling constants increase, consistent with bond strengthening, as the electron demand of OR increases.

Strand breakage by decay of DNA-bound 124I provides a basis for combined PET imaging and Auger endoradiotherapy

Abstract Purpose DNA ligands labelled with 125I induce cytotoxic DNA double-strand breaks (DSB), suggesting a potential for Auger endoradiotherapy. Since the 60-day half-life of 125I is suboptimal for therapy, we have investigated another Auger-emitter 124I, with shorter half-life (4.18 days), and the additional feature of positron-emission, enabling positron emission tomography (PET) imaging. The purpose of this study was to compare the two radionuclides on the basis of DNA DSB per decay. Materials and methods Using a 124I- (or 125I)-labelled minor groove binding DNA ligand, we investigated DNA breakage using the plasmid DNA assay. Biodistribution of the conjugate of the labelled ligand with transferrin was investigated in nude mice bearing a K562 human lymphoma xenograft. Results The probability of DSB per decay was 0.58 and 0.85 for 124I and 125I, respectively, confirming the therapeutic potential of the former. The crystal structure of the ligand DNA complex shows the iodine atom deep within the minor groove, consistent with the high efficiency of induced damage. Biodistribution studies, including PET imaging, showed distinctive results for the conjugate, compared to the free ligand and transferrin, consistent with receptor-mediated delivery of the ligand. Conclusions Conjugation of 124I-labelled DNA ligands to tumor targeting peptides provides a feasible strategy for Auger endoradiotherapy, with the advantage of monitoring tumor targeting by PET imaging.

Triple targeting of Auger emitters using octreotate conjugated to a DNA-binding ligand and a nuclear localizing signal.

Abstract Purpose: We investigated the effect of incorporation of a nuclear localization signal (NLS) into a conjugate comprising the DNA binding ligand para-iodoHoechst (PIH) and octreotate on its DNA binding and affinity to the somatostatin receptor (SSTR). Confirmation of these properties would support development of similar conjugates labelled with Auger emitters for their potential in Auger endoradiotherapy. Materials and methods: We synthesized conjugates of PIH and octreotate (PO) or PIH and NLS (PN) and a conjugate comprising PIH, NLS and octreotate (PNO). DNA-binding characteristics of PIH and conjugates were assessed using synthetic DNA oligonucleotides employing spectrophotometric titration of ligand solutions with DNA. We used membranes from the type 2 SSTR (SSTR2) overexpressing human non-small cell lung cancer cell line A427-7 to investigate the binding affinity of PNO. Results: We demonstrated PN and PNO retain specific high affinity DNA-binding properties observed for PIH, and acquire an additional non-specific binding capacity. No DNA binding was observed for PO. PNO retains its binding affinity for SSTR. Conclusions: The DNA-binding properties of PNO and its affinity for SSTR suggests that it could potentially be used for tumour-specific delivery of PIH labelled with an Auger emitter in SSTR expressing tumours.