Salinosporamide A: a highly cytotoxic proteasome inhibitor from a novel microbial source, a marine bacterium of the new genus salinospora

Enantioselective total synthesis of (-)-Salinosporamide A (NPI-0052)

A novel enantioselective total synthesis of 20S proteasome inhibitor Salinosporamide A (NPI-0052; 1) is presented. Key features include intramolecular aldol cyclization of 6 to simultaneously generate the three chiral centers of advanced intermediate 5, cyclohexene ring addition using B-2-cyclohexen-1-yl-9-BBN, and inversion of the C-5 stereocenter by oxidation followed by enantioselective enzymatic reduction.

Concise total synthesis of (+/-)-salinosporamide A, (+/-)-cinnabaramide A, and derivatives via a bis-cyclization process: implications for a biosynthetic pathway?

4-Alkylidene-beta-lactones (hetero ketene dimers) and alpha-amino acids are useful precursors for total syntheses of the beta-lactone-containing proteasome inhibitors salinosporamide A, cinnabaramide A, and derivatives. A key step is a nucleophile-promoted, bis-cyclization of keto acids that simultaneously generates the gamma-lactam and beta-lactone of these natural products. This reaction sequence may have implications for the biosynthesis of these natural products.

Chemical Investigations of a Deep Water Marine-Derived Fungus: Simple Amino Acid Derivatives from an Arthrinium sp

The saltwater culture of an Arthrinium sp. derived from a marine sediment collected at −550 meters was a source of tyrosol (1) and a new compound, tyrosol carbamate (2). This is only the third report of novel secondary metabolites discovered from the saltwater culture of a deep-water marine-derived fungus.

Effects of halogens on the production of salinosporamides by the obligate marine actinomycete Salinispora tropica

We examined the effects of halogens on the production of salinosporamide A (NPI-0052) by the obligate marine actinomycete Salinispora tropica NPS465, specifically the production of analogs containing halogens other than chlorine. Adding NaF, NaBr and NaI directly to the production medium prepared in seawater containing -3% NaCl did not induce the production of the corresponding analogs. Replacing seawater with 2-3% NaI in the production medium enhanced the production of NPI-0052 by 2.1 fold. Replacing seawater with 2-3% NaBr in the production medium suppressed the production of NPI-0052 but induced the production of a brominated analog at very low yield. Using a stepwise enrichment of bromide in the seed cultures in order to reduce the chloride ion carried over to the production medium, the production of the brominated analog was enhanced by 4 fold. We also demonstrated that the growth of this obligate marine actinomycete is dependent upon sodium concentration, not chloride concentration.

A new proteasome inhibitor, TP-110, induces apoptosis in human prostate cancer PC-3 cells

Proteasome inhibitors are useful in the treatment of cancer. Recently, we found a new proteasome inhibitor, TP-110, derived from tyropeptin A produced by Kitasatospora sp. Here we report that TP-110 induces apoptosis in human prostate cancer PC-3 cells. TP-110 showed strong cytotoxicity to PC-3 cells (IC(50)=0.05 muM). It increased the number of cells in the G(2)-M phase and increased the accumulated amounts of the p21 and p27 proteins, which are negative regulators of cell cycle progression. Furthermore, it induced apoptosis along with chromatin condensation and DNA fragmentation in PC-3 cells, and TP-110-induced apoptosis appeared to be associated with caspase activation. Additionally, TP-110 inhibited not only the degradation of IkappaB and the nuclear translocation of nuclear factor-kappaB (NF-kappaB), but also the DNA binding activity of NF-kappaB. These results indicate that TP-110 shows a strong growth inhibition and apoptosis in PC-3 cells.

Expeditious access to unprotected racemic pyroglutamic acids

A series of biologically intriguing pyroglutamic acids were synthesized in racemic form by employing indole-isonitrile and ammonium acetate in the Ugi 4-center-3-component reaction of gamma-ketoacids.

Thalassospiramides A and B, immunosuppressive peptides from the marine bacterium Thalassospira sp

[structure: see text] Two new cyclic peptides, thalassospiramides A and B (1 and 2), were isolated from a new member of the marine alpha-proteobacterium Thalassospira. The thalassospiramides, the structures of which were assigned by combined spectral and chemical methods, bear unusual gamma-amino acids and show immunosuppressive activity in an interleukin-5 production inhibition assay (IC50 = 5 muM for thalassospiramide B).

NPI-0052, a novel proteasome inhibitor, induces caspase-8 and ROS-dependent apoptosis alone and in combination with HDAC inhibitors in leukemia cells

The proteasome has been successfully targeted for the treatment of multiple myeloma and mantle cell lymphoma; however, in other hematologic malignancies, bortezomib has been less effective as a single agent. Here, we describe effects of NPI-0052, a novel proteasome inhibitor, in leukemia model systems. In cell lines, NPI-0052 inhibits all 3 proteolytic activities associated with the proteasome: chymotrypsin-, trypsin-, and caspase-like. NPI-0052 also induces DNA fragmentation in leukemia lines and in mononuclear cells from a Ph + acute lymphoblastic leukemia (ALL) patient. Caspase-3 activation by NPI-0052 was seen in wild-type Jurkat cells, but was significantly lessened in Fas-associated death domain (FADD)-deficient or caspase-8-deficient counterparts. NPI-0052-induced apoptosis was further probed using caspase-8 inhibitors, which were more protective than caspase-9 inhibitors. N-acetyl cysteine (NAC) also conferred protection against NPI-0052-induced apoptosis, indicating a role for oxidative stress by NPI-0052. In support of the drug's in vitro activities, biweekly treatment with NPI-0052 lessened total white blood cell (WBC) burden over 35 days in leukemic mice. Interestingly, combining NPI-0052 with either MS-275 or valproic acid (VPA) induced greater levels of cell death than the combination of bortezomib with these histone deacetylase inhibitors (HDACi). These effects of NPI-0052, alone and in combination with HDACi, warrant further testing to determine the compound's clinical efficacy in leukemia.

Unique butyric acid incorporation patterns for salinosporamides A and B reveal distinct biosynthetic origins

Feeding sodium butyrate (0.25-1 mg/ml) to cultures of Salinispora tropica NPS21184 enhanced the production of salinosporamide B (NPI-0047) by 319% while inhibiting the production of salinosporamide A (NPI-0052) by 26%. Liquid chromatography mass spectrometry analysis of the crude extract from the strain NPS21184 fed with 0.5 mg/ml sodium [U-(13)C(4)]butyrate indicated that butyrate was incorporated as a contiguous four-carbon unit into NPI-0047 but not into NPI-0052. Nuclear magnetic resonance analysis of NPI-0047 and NPI-0052 purified from the sodium [U-(13)C(4)]butyrate-supplemented culture extract confirmed this incorporation pattern. The above finding is the first direct evidence to demonstrate that the biosynthesis of NPI-0047 is different from NPI-0052, and NPI-0047 is not a precursor of NPI-0052.

NPI-0052 enhances tumoricidal response to conventional cancer therapy in a colon cancer model

PURPOSE

In the current study, we examine the effects of a novel proteasome inhibitor, NPI-0052 (salinosporamide A), on proteasome function and nuclear factor-kappaB activation and evaluate its ability to enhance treatment response in colon cancer xenografts when administered orally.

EXPERIMENTAL DESIGN

The effects of treatment on nuclear factor-kappaB activation, cell cycle regulation, and apoptosis were determined. The pharmacodynamic effect of NPI-0052 on 20S proteasome function was assayed in vivo following oral and i.v. drug administration and compared with treatment with bortezomib. The effect of combined treatment with chemotherapy was determined in a colon cancer xenograft model.

RESULTS

We found that NPI-0052 is a potent, well-tolerated proteasome inhibitor that has pharmacodynamic properties distinct from bortezomib in that it achieves significantly higher and more sustained levels of proteasome inhibition. When combined with chemotherapy, NPI-0052 increases apoptosis and shifts cells toward G2 cell cycle arrest. When added to chemotherapy in vivo [using combinations of 5-fluorouracil (5-FU), CPT-11, Avastin (bevacizumab), leucovorin, and oxaliplatin], NPI-0052 significantly improved the tumoricidal response and resulted in a 1.8-fold increased response to CPT-11, 5-FU, and leucovorin triple-drug combination (P=0.0002, t test), a 1.5-fold increased response to the oxaliplatin, 5-FU, and leucovorin triple-drug combination (P=0.013, t test), and a 2.3-fold greater response to the CPT-11, 5-FU, leucovorin, and Avastin regimen (P=0.00057).

CONCLUSIONS

The high level of proteasome inhibition achieved by NPI-0052 is well tolerated and significantly improves the tumoricidal response to multidrug treatment in a colon cancer xenograft model. Further evaluation of this novel proteasome inhibitor in clinical trials is indicated.

Arenicolides A-C, 26-membered ring macrolides from the marine actinomycete Salinispora arenicola

Chemical evaluation of the saline fermentation broth of several strains of the obligate marine actinomycete Salinispora arenicola has led to the identification of three new macrolide polyketides designated arenicolides A-C (1-3). The planar structures, elucidated via spectroscopic and chemical methods, consist of 26-membered polyunsaturated macrolactones containing repeating vicinal hydroxyl methoxyl moieties. The relative and absolute stereochemistries of 1-3 were assigned by a combination of J-based configurational analyses and chemical derivatization.

Cinnabaramides A-G: analogues of lactacystin and salinosporamide from a terrestrial streptomycete

The cinnabaramides A-G (1-7) were isolated from a terrestrial strain of Streptomyces as potent and selective inhibitors of the human 20S proteasome. Their chemical and biological properties resemble those of salinosporamide A, a recently identified lead compound from an obligate marine actinomycete, which is currently under development as an anticancer agent. Cinnabaramides F and G (6, 7) combine essential structural features of salinosporamide A and lactacystin and show about equal potency in vitro, with IC50 values in the 1 nM range. The properties and phylogenetic position of the producer organism, the production and isolation of compounds 1-7, their structure elucidation by MS and NMR, and their biological activities are reported. Additionally, an X-ray crystal structure was obtained from cinnabaramide A (1).

Salinosporamides D-J from the marine actinomycete Salinispora tropica, bromosalinosporamide, and thioester derivatives are potent inhibitors of the 20S proteasome

Salinosporamide A (NPI-0052; 3), a highly potent inhibitor of the 20S proteasome, is currently in phase I clinical trials for the treatment of cancer. During the course of purifying multigram quantities of 3 from Salinispora tropica fermentation extracts, several new salinosporamides were isolated and characterized, most of which represent modifications to the chloroethyl substituent at C-2. Specifically, 3 was isolated along with the known compound salinosporamide B (4), the previously undescribed methyl congener salinosporamide D (7), and C-2 epimers of 3 and 7 (salinosporamides F (9) and G (10), respectively). Salinosporamide I (13), in which the methyl group at the ring junction is replaced with an ethyl group, and the C-5 deshydroxyl analogue salinosporamide J (14), were also identified. Replacement of synthetic sea salt with sodium bromide in the fermentation media produced bromosalinosporamide (12), 4, and its C-2 epimer (11, salinosporamide H). In addition to these eight new salinosporamides, several thioester derivatives were generated semisynthetically. IC50 values for cytotoxicity against human multiple myeloma cell line RPMI 8226 and inhibition of the chymotrypsin-like (CT-L) activity of purified rabbit 20S proteasomes were determined for all compounds. The results indicate that thioesters may directly inhibit the proteasome, albeit with reduced potency compared to their beta-lactone counterparts.

Total Synthesis of Marinomycins A−C and of Their Monomeric Counterparts Monomarinomycin A and iso-Monomarinomycin A

Marinomycins A-C (1-3), and their monomeric analogues monomarinomycin A (m-1) and iso-monomarinomycin A (m-2), were synthesized by a convergent strategy from key building blocks ketophosphonate 5, aldehyde 6, and dienyl bromide carboxylic acid 7. The first attempt to construct marinomycin A [1, convertible to marinomycins B (2) and C (3) by light] by direct Suzuki-type dimerization/cyclization of boronic acid dienyl bromide 4 led to premature ring closure to afford, after global desilylation, monomarinomycin A (m-1) and iso-monomarinomycin A (m-2) in good yield and only small amounts (< or =2%) of the desired product. A subsequent stepwise approach based on Suzuki-type couplings improved considerably the overall yield of marinomycin A (1), and hence of marinomycins B (2) and C (3). Alternative direct dimerization approaches based on the Stille and Heck coupling reactions also led to monomarinomycins A (m-1 and m-2), but failed to deliver useful amounts of marinomycin A (1).

Marine natural products

This review covers the literature published in 2005 for marine natural products, with 704 citations (493 for the period January to December 2005) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (812 for 2005), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Total Synthesis of Lactacystin and Salinosporamide A

Lactacystin and salinosporamide A are fascinating molecules with regard to both their chemical structures and biological activities. These naturally occurring compounds are potent and selective proteasome inhibitors. The molecular structures are characterized by their densely functionalized gamma-lactam cores. The structure and biological properties of these two compounds are attracting the attention of many chemists as challenging synthetic targets. We discuss their synthetic strategies in this review.

(3R,4aR,5S,6R)-6-Hydroxy-5-methylramulosin: a New Ramulosin Derivative from a Marine-Derived Sterile Mycelium

(3R,4aR,5S,6R)-6-Hydroxy-5-methylramulosin (1) was isolated from a culture of a sterile mycelium, which was derived from the green alga, Codium fragile, along with (-)-5-methylmellein (2), (-)-5-hydroxymethylmellein (3), and (-)-(3R,4R)-cis-4-hydroxy-5-methylmellein (4). The absolute configuration of 1 was determined by the NMR data along with the lactone sector rule by circular dichroism (CD). Compound 1 exhibited moderate cytotoxic activity against HeLa cells.

Monodictyquinone A: a New Antimicrobial Anthraquinone from a Sea Urchin-Derived Fungus Monodictys sp

A new antimicrobial anthraquinone, 1,8-dihydroxy-2-methoxy-6-methylanthraquinone, monodictyquinone A (1), was isolated from a culture of a marine-derived fungus of the genus Monodictys which was isolated from the sea urchin, Anthocidaris crassispina, along with three known compounds, pachybasin (2), chrysophanol (3), and emodin (4).

Comparison of biochemical and biological effects of ML858 (salinosporamide A) and bortezomib

Strains within the genus Salinospora have been shown to produce complex natural products having antibiotic and antiproliferative activities. The biochemical basis for the cytotoxic effects of salinosporamide A has been linked to its ability to inhibit the proteasome. Synthetically accessible salinosporamide A (ML858) was used to determine its biochemical and biological activities and to compare its effects with those of bortezomib. ML858 and bortezomib show time- and concentration-dependent inhibition of the proteasome in vitro. However, unlike bortezomib, which is a reversible inhibitor, ML858 covalently binds to the proteasome, resulting in the irreversible inhibition of 20S proteasome activity. ML858 was equipotent to bortezomib in cell-based reporter stabilization assays, but due to intramolecular instability is less potent in long-term assays. ML858 failed to maintain levels of proteasome inhibition necessary to achieve efficacy in tumor models responsive to bortezomib. Our results show that ML858 and bortezomib exhibit different kinetic and pharmacologic profiles and suggest that additional characterization of ML858 is warranted before its therapeutic potential can be fully appreciated.

Nocardia asteroides strain GUH-2 induces proteasome inhibition and apoptotic death of cultured cells

Many bacterial pathogens have the ability to induce apoptosis in their hosts. It was previously shown that Nocardia asteroides strain GUH-2, a Gram-positive facultatively intracellular pathogen, is capable of inducing the apoptotic death of dopaminergic cells in the murine brain and in PC12 cells, a rat cell line. In this study, the apoptosis-inducing potential of N. asteroides GUH-2 was further explored using HeLa cells, a human epithelial cell line. HeLa cells were incubated for 5h with live nocardiae, heat-killed bacteria, or unconcentrated nocardial culture filtrate, and changes to the cells were monitored. Consistent with the previous studies, N. asteroides GUH-2 induced DNA fragmentation and apoptosis in HeLa cells. Caspase activation and disruption of the mitochondrial membrane potential were also investigated to determine their roles in the induction of cell death. In all these experiments, significant changes were only induced by live nocardiae. A recent publication demonstrated that systemic administration of proteasome inhibitors can induce a Parkinsonian syndrome in rats that includes intraneuronal inclusions and characteristic behavioral alterations. Similar effects have been observed in mice and monkeys infected with N. asteroides GUH-2. In addition, some reports have shown that proteasome inhibition causes apoptotic death of affected cells. We therefore investigated the ability of N. asteroides GUH-2 to inhibit proteasome activity. Proteasome activity was significantly reduced, suggesting that this mechanism may be involved in the induction of apoptosis by these bacteria.

Species-specific secondary metabolite production in marine actinomycetes of the genus Salinispora

Here we report associations between secondary metabolite production and phylogenetically distinct but closely related marine actinomycete species belonging to the genus Salinispora. The pattern emerged in a study that included global collection sites, and it indicates that secondary metabolite production can be a species-specific, phenotypic trait associated with broadly distributed bacterial populations. Associations between actinomycete phylotype and chemotype revealed an effective, diversity-based approach to natural product discovery that contradicts the conventional wisdom that secondary metabolite production is strain specific. The structural diversity of the metabolites observed, coupled with gene probing and phylogenetic analyses, implicates lateral gene transfer as a source of the biosynthetic genes responsible for compound production. These results conform to a model of selection-driven pathway fixation occurring subsequent to gene acquisition and provide a rare example in which demonstrable physiological traits have been correlated to the fine-scale phylogenetic architecture of an environmental bacterial community.

Cyanosporasides A and B, chloro- and cyano-cyclopenta[a]indene glycosides from the marine actinomycete "Salinispora pacifica"

[structure: see text] Two structurally novel cyclopenta[a]indene glycosides, cyanosporasides A and B (1 and 2) have been isolated from the culture broth of a new species of the obligate marine actinomycete genus Salinispora. The structures and absolute stereochemistries of these compounds were determined by spectral and chemical methods. The cyanosporasides possess a new 3-keto-pyranohexose sugar as well as a cyano- and chloro-substituted cyclopenta[a]indene ring system. The cyanosporasides are proposed to be cyclization products of an enediyne precursor.

Therapeutic potential of natural product signal transduction agents

Modern drug discovery embraces a strategy of targeting cellular signal transduction pathways as a means of finding new therapeutic agents. Historically, natural products derived from microorganisms have played an important role as drug leads and clinical candidates under this paradigm. The future drug potential of natural products as signal transduction agents looks promising, as illustrated by two key examples. First, substantial advances have been made in the development of inhibitors based on immunophilin ligand polyketides, which target the TOR-mediated pathways and can modulate processes including cell proliferation and cell-cycle arrest. Second, the discovery of natural product inhibitors of the ubiquitin-proteasome proteolytic signal transduction pathway represents an emerging field. Given these examples, together with the diversity of as yet undiscovered agents, natural product signal transduction agents offer great potential for future drug discovery efforts.

Daryamides A-C, weakly cytotoxic polyketides from a marine-derived actinomycete of the genus Streptomyces strain CNQ-085

In the course of our continuing search for new antitumor-antibiotics from marine-derived actinomycete bacteria, four new cytotoxic compounds, designated as daryamides A (1), B (2), and C (3) and (2E,4E)-7-methylocta-2,4-dienoic acid amide (4), were isolated from the culture broth of a marine-derived Streptomyces strain CNQ-085. The structures of these new compounds were assigned by detailed interpretation of spectroscopic data. The relative configuration of 1 was determined by comprehensive NMR analysis, while the absolute configuration of 1 was determined as 4S,5R using the modified Mosher method. The daryamides show weak to moderate cytotoxic activity against the human colon carcinoma cell line HCT-116 and very weak antifungal activities against Candida albicans.

A novel proteasome inhibitor NPI-0052 as an anticancer therapy

Proteasome inhibitor Bortezomib/Velcade has emerged as an effective anticancer therapy for the treatment of relapsed and/or refractory multiple myeloma (MM), but prolonged treatment can be associated with toxicity and development of drug resistance. In this review, we discuss the recent discovery of a novel proteasome inhibitor, NPI-0052, that is distinct from Bortezomib in its chemical structure, mechanisms of action, and effects on proteasomal activities; most importantly, it overcomes resistance to conventional and Bortezomib therapies. In vivo studies using human MM xenografts shows that NPI-0052 is well tolerated, prolongs survival, and reduces tumour recurrence. These preclinical studies provided the basis for Phase-I clinical trial of NPI-0052 in relapsed/refractory MM patients.

Bohemamines from a marine-derived Streptomyces sp

Investigation of the culture extracts of a marine-derived Streptomyces sp. led to the isolation of three new bohemamine-type pyrrolizidine alkaloids, bohemamine B (1), bohemamine C (2), and 5-chlorobohemamine C (3). The structures were elucidated using NMR methods, and the relative stereochemistry was determined using double-pulsed-field-gradient spin echo (DPFGSE) NOE studies.

Protein-reactive natural products

Researchers in the post-genome era are confronted with the daunting task of assigning structure and function to tens of thousands of encoded proteins. To realize this goal, new technologies are emerging for the analysis of protein function on a global scale, such as activity-based protein profiling (ABPP), which aims to develop active site-directed chemical probes for enzyme analysis in whole proteomes. For the pursuit of such chemical proteomic technologies, it is helpful to derive inspiration from protein-reactive natural products. Natural products use a remarkably diverse set of mechanisms to covalently modify enzymes from distinct mechanistic classes, thus providing a wellspring of chemical concepts that can be exploited for the design of active-site-directed proteomic probes. Herein, we highlight several examples of protein-reactive natural products and illustrate how their mechanisms of action have influenced and continue to shape the progression of chemical proteomic technologies like ABPP.

Oceans and human health: Emerging public health risks in the marine environment

There has been an increasing recognition of the inter-relationship between human health and the oceans. Traditionally, the focus of research and concern has been on the impact of human activities on the oceans, particularly through anthropogenic pollution and the exploitation of marine resources. More recently, there has been recognition of the potential direct impact of the oceans on human health, both detrimental and beneficial. Areas identified include: global change, harmful algal blooms (HABs), microbial and chemical contamination of marine waters and seafood, and marine models and natural products from the seas. It is hoped that through the recognition of the inter-dependence of the health of both humans and the oceans, efforts will be made to restore and preserve the oceans.

New bisanthraquinone antibiotics and semi-synthetic derivatives with potent activity against clinical Staphylococcus aureus and Enterococcus faecium isolates

The escalation of antibiotic resistance among Gram-positive pathogens presents increasing treatment challenges and requires the development of innovative therapeutic agents. Here, we present the antimicrobial properties of structurally unusual bisanthraquinone metabolites produced by a marine streptomycete and four semi-synthetic derivatives. Biological activities were measured against clinically derived isolates of vancomycin-resistant Enterococcus faecium (VRE), and methicillin-susceptible, methicillin-resistant, and tetracycline-resistant Staphylococcus aureus (MSSA, MRSA, and TRSA, respectively). The most potent antibiotic displayed MIC(50) values of 0.11, 0.23, and 0.90microM against a panel (n=25 each) of clinical MSSA, MRSA, and VRE, respectively, and was determined to be bactericidal by time-kill analysis.

Marine pharmacology in 2003–2004: Anti-tumour and cytotoxic compounds

During 2003 and 2004, marine pharmacology research directed towards the discovery and development of novel anti-tumour agents was published in 163 peer-reviewed articles. The purpose of this review is to present a structured assessment of the anti-tumour and cytotoxic properties of 150 marine natural products, many of which are novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids and peptides. The organisms yielding these bioactive marine compounds include invertebrate animals, algae, fungi and bacteria. Anti-tumour pharmacological studies were conducted with 31 structurally defined marine natural products in a number of experimental and clinical models that further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines was reported for 119 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy is the fact that marine anti-cancer research was sustained by a global collaborative effort, involving researchers from Australia, Austria, Canada, China, Egypt, France, Germany, Italy, Japan, Mexico, the Netherlands, New Zealand, Papua New Guinea, the Philippines, South Africa, South Korea, Spain, Switzerland, Taiwan, Thailand and the United States of America (USA). Finally, this 2003-2004 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine anti-tumour agents continued at the same pace as during 1998-2002.

The proteasome inhibitor NPI-0052 is a more effective inducer of apoptosis than bortezomib in lymphocytes from patients with chronic lymphocytic leukemia

Proteasome inhibitors are potent inducers of apoptosis in isolated lymphocytes from patients with chronic lymphocytic leukemia (CLL). However, the reversible proteasome inhibitor bortezomib (PS-341; Velcade) did not display substantial antitumor activity in CLL patients. Here, we compared the effects of bortezomib and a new irreversible proteasome inhibitor (NPI-0052) on 20S chymotryptic proteasome activity and apoptosis in isolated CLL cells in vitro. Although their steady-state (3 hours) IC(50)s as proteasome inhibitors were similar, NPI-0052 exerted its effects more rapidly than bortezomib, and drug washout experiments showed that short exposures to NPI-0052 resulted in sustained (> or =24 hours) 20S proteasome inhibition, whereas 20S activity recovered in cells exposed to even 10-fold higher concentrations of bortezomib. Thus, brief (15 minutes) pulses of NPI-0052 were sufficient to induce substantial apoptosis in CLL cells, whereas longer exposure times (> or =8 hours) were required for commitment to apoptosis in cells exposed to equivalent concentrations of bortezomib. Commitment to apoptosis seemed to be related to caspase-4 activation, in that cells exposed to bortezomib or NPI-0052 could be saved from death by addition of a selective caspase-4 inhibitor up to 8 hours after drug exposure. Our results show that NPI-0052 is a more effective proapoptotic agent than bortezomib in isolated CLL cells and suggest that the chemical properties of NPI-0052 might also make it an effective therapeutic agent in CLL patients.

A concise total synthesis of salinosporamide A

A concise and straightforward 14-step total synthesis of (+/-)-salinosporamide A, based on a diastereoselective acid-catalysed intramolecular cyclisation of to the pyrrolidinone , and a regioselective reduction of the malonate derivative 8b to the aldehyde 9, is described.

Structure and Total Synthesis of Aspernigerin: A Novel Cytotoxic Endophyte Metabolite

Aspernigerin (1), a novel cytotoxic alkaloid consisting of an unprecedented structural framework has been isolated from the extract of a culture of Aspergillus niger IFB-E003, an endophyte in Cyndon dactylon. Its structure was elucidated on the basis of comprehensive NMR spectral analysis and confirmed by single-crystal X-ray analysis. Aspernigerin (1) has been shown to be cytotoxic to the tumor cell lines nasopharynyeal epidermoid KB, cervical carcinoma Hela, and colorectal carcinoma SW1116 with corresponding IC(50) values of 22, 46, and 35 microM, respectively. A feasible total synthetic route for aspernigerin (1) has been established for further pharmacological research.

Discovery of novel metabolites from marine actinomycetes

Recent findings from culture-dependent and culture-independent methods have demonstrated that indigenous marine actinomycetes exist in the oceans and are widely distributed in different marine ecosystems. There is tremendous diversity and novelty among the marine actinomycetes present in marine environments. Progress has been made to isolate novel actinomycetes from samples collected at different marine environments and habitats. These marine actinomycetes produce different types of new secondary metabolites. Many of these metabolites possess biological activities and have the potential to be developed as therapeutic agents. Marine actinomycetes are a prolific but underexploited source for the discovery of novel secondary metabolites.

Sporolides A and B: structurally unprecedented halogenated macrolides from the marine actinomycete Salinispora tropica

[structure: see text] Analysis of the fermentation broth of a strain of the marine actinomycete Salinispora tropica has led to the isolation of two unprecedented macrolides, sporolides A (1) and B (2). The structures and absolute stereochemistries of both metabolites were elucidated using a combination of NMR spectroscopy and X-ray crystallography.

New drugs from marine microbes: the tide is turning

This is a mini-review demonstrating that investigation of the genomics of marine microbes from all three domains has the potential to revolutionize the search for secondary metabolites originally thought to be the product of marine invertebrates. The basis for the review was a symposium at the 2005 Annual Meeting of the SIM covering some aspects of the potential for marine microbes to be the primary producers of such metabolites. The work reported at that symposium has been integrated into a fuller discussion of current published literature on the subject with examples drawn from bacteria, cyanophytes and fungi.

Marinomycins A-D, antitumor-antibiotics of a new structure class from a marine actinomycete of the recently discovered genus "marinispora"

Four antitumor-antibiotics of a new structure class, the marinomycins A-D (1-4), were isolated from the saline culture of a new group of marine actinomycetes, for which we have proposed the name "Marinispora". The structures of the marinomycins, which are unusual macrodiolides composed of dimeric 2-hydroxy-6-alkenyl-benzoic acid lactones with conjugated tetraene-pentahydroxy polyketide chains, were assigned by combined spectral and chemical methods. In room light, marinomycin A slowly isomerizes to its geometrical isomers marinomycins B and C. Marinomycins A-D show significant antimicrobial activities against drug resistant bacterial pathogens and demonstrate impressive and selective cancer cell cytotoxicities against six of the eight melanoma cell lines in the National Cancer Institute's 60 cell line panel. The discovery of these new compounds from a new, chemically rich genus further documents that marine actinomycetes are a significant resource for drug discovery.

Crystal Structures of Salinosporamide A (NPI-0052) and B (NPI-0047) in Complex with the 20S Proteasome Reveal Important Consequences of β-Lactone Ring Opening and a Mechanism for Irreversible Binding

The crystal structures of the yeast 20S proteasome core particle (CP) in complex with Salinosporamides A (NPI-0052; 1) and B (4) were solved at <3 angstroms resolution. Each ligand is covalently bound to Thr1O(gamma) via an ester linkage to the carbonyl derived from the beta-lactone ring of the inhibitor. In the case of 1, nucleophilic addition to the beta-lactone ring is followed by addition of C-3O to the chloroethyl group, giving rise to a cyclic ether. The crystal structures were compared to that of the omuralide/CP structure solved previously, and the collective data provide new insights into the mechanism of inhibition and irreversible binding of 1. Upon opening of the beta-lactone ring, C-3O assumes the position occupied by a water molecule in the unligated enzyme and hinders deacylation of the enzyme-ligand complex. Furthermore, the resulting protonation state of Thr1NH2 deactivates the catalytic N-terminus.

Drug discovery from natural products

Natural product compounds are the source of numerous therapeutic agents. Recent progress to discover drugs from natural product sources has resulted in compounds that are being developed to treat cancer, resistant bacteria and viruses and immunosuppressive disorders. Many of these compounds were discovered by applying recent advances in understanding the genetics of secondary metabolism in actinomycetes, exploring the marine environment and applying new screening technologies. In many instances, the discovery of a novel natural product serves as a tool to better understand targets and pathways in the disease process. This review describes recent progress in drug discovery from natural sources including several examples of compounds that inhibit novel drug targets.