Angela A. Salim

Potential of Cyclopenta[b]benzofurans from Aglaia Species in Cancer Chemotherapy

During the past few years, a group of cyclopenta[b]benzofurans from the plant genus Aglaia has received broad scientific attention as interesting natural product lead compounds with potential anticancer and insecticidal activities. Since the first cyclopenta[b]benzofuran derivative, rocaglamide, from Aglaia elliptifolia, was found to exhibit antileukemic activity in a murine in vivo model, the genus Aglaia has been subjected to further investigation. Over 40 cyclopenta[b]benzofurans have been tested against different human cancer cell lines, and the cumulative results provide some important clues as to how to improve their activity through modification of their chemical structures. The semisynthesis and total synthesis of the cyclopenta[b]benzofurans have been conducted. Although the ultimate molecular target(s) responsible for their antiproliferative activity has not yet been identified, studies on their cellular mechanism of action have demonstrated that some of these compounds inhibit TNF-alpha or PMA-induced NF-kappaB activity in T-lymphocytes and induce apoptosis in different human cancer cell lines. Based on the published data thus far, cyclopenta[b]benzofurans offer excellent potential as therapeutic agent candidates in cancer chemotherapy, even if much work still remains to be done for their further development.

Staurosporines Disrupt Phosphatidylserine Trafficking and Mislocalize Ras Proteins

Background: Ras proteins must be plasma membrane-localized for biological activity. Results: A high content screen identified staurosporines as inhibitors of Ras plasma membrane localization and K-Ras signal transmission by disrupting endosomal recycling of phosphatidylserine. Conclusion: Staurosporines are novel inhibitors of phosphatidylserine trafficking. Significance: Ras trafficking pathways and Ras spatiotemporal organization on the plasma membrane are valid targets for anti-Ras drug development. Oncogenic mutant Ras is frequently expressed in human cancers, but no anti-Ras drugs have been developed. Since membrane association is essential for Ras biological activity, we developed a high content assay for inhibitors of Ras plasma membrane localization. We discovered that staurosporine and analogs potently inhibit Ras plasma membrane binding by blocking endosomal recycling of phosphatidylserine, resulting in redistribution of phosphatidylserine from plasma membrane to endomembrane. Staurosporines are more active against K-Ras than H-Ras. K-Ras is displaced to endosomes and undergoes proteasomal-independent degradation, whereas H-Ras redistributes to the Golgi and is not degraded. K-Ras nanoclustering on the plasma membrane is also inhibited. Ras mislocalization does not correlate with protein kinase C inhibition or induction of apoptosis. Staurosporines selectively abrogate K-Ras signaling and proliferation of K-Ras-transformed cells. These results identify staurosporines as novel inhibitors of phosphatidylserine trafficking, yield new insights into the role of phosphatidylserine and electrostatics in Ras plasma membrane targeting, and validate a new target for anti-Ras therapeutics.

Antioxidant and cytoprotective compounds from Berberis vulgaris (barberry).

Activity‐guided fractionation of an EtOAc‐soluble partition of the MeOH extract from the root bark of Berberis vulgaris L. (barberry), using a hydroxyl radical‐scavenging assay, led to the isolation and identification of three phenolic compounds of a previously known structure, N‐(p‐trans‐coumaroyl)tyramine, cannabisin G and (±)‐lyoniresinol. Of these, cannabisin G and (±)‐lyoniresinol exhibited antioxidant activity in this bioassay. Furthermore, it was found that cannabisin G showed cytoprotective activity in cultured MCF‐7 cells modulated by hydrogen peroxide. Copyright

Potential Anticancer Activity of Naturally Occurring and Semisynthetic Derivatives of Aculeatins A and B from Amomum aculeatum

Activity-guided fractionation of hexanes- and CHCl 3-soluble extracts of Amomum aculeatum leaves, collected in Indonesia, led to the isolation of three new dioxadispiroketal-type ( 3- 5) and two new oxaspiroketal-type ( 6 and 7) derivatives. Nine semisynthetic derivatives ( 1a- 1h and 2a) of the parent compounds, aculeatins A ( 1) and B ( 2), were prepared. All isolates and semisynthetic compounds were tested against a small panel of human cell lines. Of these, aculeatin A ( 1; ED 50 0.2-1.0 microM) was found to be among the most cytotoxic of the compounds tested and was further evaluated in an in vivo hollow fiber assay; it was found to be active against MCF-7 (human breast cancer) cells implanted intraperitoneally at doses of 6.25, 12.5, 25, and 50 mg/kg. However, when 1 was tested using P388 lymphocytic leukemia and human A2780 ovarian carcinoma in vivo models, it was deemed to be inactive at the doses used.

Lamellarin O, a Pyrrole Alkaloid from an Australian Marine Sponge, Ianthella sp., Reverses BCRP Mediated Drug Resistance in Cancer Cells

ATP binding cassette (ABC) transporters, such as P-gp, BCRP and MRP1, can increase efflux of clinical chemotherapeutic agents and lead to multi-drug resistance (MDR) in cancer cells. While the discovery and development of clinically useful inhibitors has proved elusive to date, this molecular target nevertheless remains a promising strategy for addressing and potentially overcoming MDR. In a search for new classes of inhibitor, we used fluorescent accumulation and efflux assays supported by cell flow cytometry and MDR reversal assays, against a panel of sensitive and MDR human cancer cell lines, to evaluate the marine sponge co-metabolites 1–12 as inhibitors of P-gp, BCRP or MRP1 initiated MDR. These studies identified and characterized lamellarin O (11) as a selective inhibitor of BCRP mediated drug efflux. A structure–activity relationship analysis inclusive of the natural products 1–12 and the synthetic analogues 13–19, supported by in silico docking studies, revealed key structural requirements for the lamellarin O (11) BCRP inhibitory pharmacophore.

Chemical inhibition of bacterial protein tyrosine phosphatase suppresses capsule production

Capsule polysaccharide is a major virulence factor for a wide range of bacterial pathogens, including Streptococcus pneumoniae. The biosynthesis of Wzy-dependent capsules in both Gram-negative and –positive bacteria is regulated by a system involving a protein tyrosine phosphatase (PTP) and a protein tyrosine kinase. However, how the system functions is still controversial. In Streptococcus pneumoniae, a major human pathogen, the system is present in all but 2 of the 93 serotypes found to date. In order to study this regulation further, we performed a screen to find inhibitors of the phosphatase, CpsB. This led to the observation that a recently discovered marine sponge metabolite, fascioquinol E, inhibited CpsB phosphatase activity both in vitro and in vivo at concentrations that did not affect the growth of the bacteria. This inhibition resulted in decreased capsule synthesis in D39 and Type 1 S. pneumoniae. Furthermore, concentrations of Fascioquinol E that inhibited capsule also lead to increased attachment of pneumococci to a macrophage cell line, suggesting that this compound would inhibit the virulence of the pathogen. Interestingly, this compound also inhibited the phosphatase activity of the structurally unrelated Gram-negative PTP, Wzb, which belongs to separate family of protein tyrosine phosphatases. Furthermore, incubation with Klebsiella pneumoniae, which contains a homologous phosphatase, resulted in decreased capsule synthesis. Taken together, these data provide evidence that PTPs are critical for Wzy-dependent capsule production across a spectrum of bacteria, and as such represents a valuable new molecular target for the development of anti-virulence antibacterials.

Wollamides: Antimycobacterial Cyclic Hexapeptides from an Australian Soil Streptomyces

A soil Streptomyces nov. sp. (MST-115088) isolated from semiarid terrain near Wollogorang Station, Queensland, returned two known and two new examples of a rare class of cyclic hexapeptide, desotamides A and B (1 and 2) and E and F (3 and 4), respectively, together with two new d-Orn homologues, wollamides A and B (5 and 6). Structures were assigned by detailed spectroscopic and C3 Marfeys analysis. The desotamides/wollamides exhibit growth inhibitory activity against Gram-positive bacteria (IC50 0.6-7 μM) and are noncytotoxic to mammalian cells (IC50 >30 μM). The wollamides exhibit antimycobacterial activity (IC50 2.8 and 3.1 μM), including reduction in the intracellular mycobacterial survival in murine bone marrow-derived macrophages.

C3 and 2D C3 Marfey’s methods for amino acid analysis in natural products

We validate the improved resolution and sensitivity of the C3 Marfeys method, including an ability to resolve all Ile isomers, against an array of amino acids commonly encountered in natural products and by comparison to an existing Marfeys method. We also describe an innovative 2D C3 Marfeys method as an analytical approach for determining the regiochemistry of enantiomeric amino acid residues in natural products. The C3 and 2D C3 Marfeys methods represent valuable tools for probing and defining the stereocomplexity of hydrolytically accessible amino acid residues in natural products.

Parguerenes: Marine red alga bromoditerpenes as inhibitors of P-glycoprotein (ABCB1) in multidrug resistant human cancer cells

High intrinsic or acquired expression of membrane spanning, adenosine triphosphate binding cassette (ABC) transporter proteins, such as P-glycoprotein (P-gp), in cancers represents a major impediment to chemotherapy, with accelerated drug efflux leading to multi-drug resistance (MDR). Although ABC transporter inhibitors offer the prospect of reversing the MDR phenotype, no inhibitors have advanced to the clinic. We employed a range of intracellular fluorescence and radio-ligand accumulation and efflux assays, together with cytotoxicity and MDR reversal assays, as well as flow cytometry, fluorescence microscopy and radioimmunoprecipitation, to discover and evaluate new P-gp inhibitors from a unique library of southern Australian and Antarctic marine natural products. This study successfully characterized two rare bromoditerpenes, parguerenes I and II, sourced from a southern Australian collection of the red alga Laurencia filiformis, as P-gp inhibitors. We determined that the parguerenes were non-cytotoxic, dose-dependent inhibitors of P-gp mediated drug efflux, that modify the extracellular antibody binding epitope of P-gp in a manner that differs markedly from that of the known inhibitors verapamil and cyclosporine A. We confirmed that parguerenes were capable of reversing P-gp mediated vinblastine, doxorubicin and paclitaxel MDR, that inhibitory properties span both P-gp and multidrug resistant protein 1 (MRP1), but do not extend to breast cancer resistance protein (BCRP), and that parguerene II is superior (more potent) to verapamil. Our investigations validate the proposition that marine natural products can deliver new ABC transporter inhibitor scaffolds, with structure characteristics fundamentally different from existing inhibitor classes.

STRUCTURE AND FUNCTION OF PLANT TOXINS (WITH EMPHASIS ON CYSTINE KNOT TOXINS)

Plant toxins are substances produced and secreted by plants to defend themselves against predators. In a broad sense, this includes all substances that have a toxic effect on targeted organisms, whether they are microbes, other plants, insects, or higher animals. Plant toxins have a diverse range of structures, from small organic molecules through to proteins. This review gives an overview of the various classes of plant toxins but focuses on an interesting class of protein-based plant toxins containing a cystine knot motif. This structural motif confers exceptional stability on proteins containing it and is associated with a wide range of biological activities. The biological activities and structural stability offer many potential applications in the pharmaceutical and agricultural fields. One particularly exciting prospect is in the use of protein-based plant toxins as molecular scaffolds for displaying pharmaceutically important bioactivities. Future applications of plant toxins are likely to involve genetic engineering techniques and “molecular pharming” approaches.