Marine-derived anticancer agents in clinical trials

A review on marine source as anticancer agents

This review investigates the potential of natural compounds obtained from marine sources for the treatment of cancer. The oceans are believed to contain physiologically active compounds, such as alkaloids, nucleosides, macrolides, and polyketides, which have shown promising effects in slowing human tumor cells both in vivo and in vitro. Various marine species, including algae, mollusks, actinomycetes, fungi, sponges, and soft corals, have been studied for their bioactive metabolites with diverse chemical structures. The review explores the therapeutic potential of various marine-derived substances and discusses their possible applications in cancer treatment.

Marine-Derived Anticancer Agents Targeting Apoptotic Pathways: Exploring the Depths for Novel Cancer Therapies

Extensive research has been conducted on the isolation and study of bioactive compounds derived from marine sources. Several natural products have demonstrated potential as inducers of apoptosis and are currently under investigation in clinical trials. These marine-derived compounds selectively interact with extrinsic and intrinsic apoptotic pathways using a variety of molecular mechanisms, resulting in cell shrinkage, chromatin condensation, cytoplasmic blebs, apoptotic bodies, and phagocytosis by adjacent parenchymal cells, neoplastic cells, or macrophages. Numerous marine-derived compounds are currently undergoing rigorous examination for their potential application in cancer therapy. This review examines a total of 21 marine-derived compounds, along with their synthetic derivatives, sourced from marine organisms such as sponges, corals, tunicates, mollusks, ascidians, algae, cyanobacteria, fungi, and actinobacteria. These compounds are currently undergoing preclinical and clinical trials to evaluate their potential as apoptosis inducers for the treatment of different types of cancer. This review further examined the compound's properties and mode of action, preclinical investigations, clinical trial studies on single or combination therapy, and the prospective development of marine-derived anticancer therapies.

Therapeutic potential of marine macrolides: An overview from 1990 to 2022

The sea is a vast ecosystem that has remained primarily unexploited and untapped, resulting in numerous organisms. Consequently, marine organisms have piqued the interest of scientists as an abundant source of natural resources with unique structural features and fascinating biological activities. Marine macrolide is a top-class natural product with a heavily oxygenated polyene backbone containing macrocyclic lactone. In the last few decades, significant efforts have been made to isolate and characterize macrolides' chemical and biological properties. Numerous macrolides are extracted from different marine organisms such as marine microorganisms, sponges, zooplankton, molluscs, cnidarians, red algae, tunicates, and bryozoans. Notably, the prominent macrolide sources are fungi, dinoflagellates, and sponges. Marine macrolides have several bioactive characteristics such as antimicrobial (antibacterial, antifungal, antimalarial, antiviral), anti-inflammatory, antidiabetic, cytotoxic, and neuroprotective activities. In brief, marine organisms are plentiful in naturally occurring macrolides, which can become the source of efficient and effective therapeutics for many diseases. This current review summarizes these exciting and promising novel marine macrolides in biological activities and possible therapeutic applications.

Tandem construction of biological relevant aliphatic 5-membered N-heterocycles

Nature often uses cascade reactions in a highly stereocontrolled manner for assembly structurally diverse nitrogen-containing heterocyclic scaffolds, i.e. secondary metabolites, important for medicinal chemistry and pharmacy. Five-membered nitrogen-containing heterocycles as standalone rings, as well as spiro and polycyclic systems are pharmacophores of drugs approved in various therapies, i.a. antibacterial or antiviral, antifungal, anticancer, antidiabetic, as they target many key enzymes. Furthermore, a large number of pyrrolidine derivatives are currently considered as drug candidates. Cascade transformations, also known as domino or tandem reactions, offer straightforward methods to build N-heterocyclic libraries of the great structural variety desired for drawing SAR conclusions. The tandem transformations are often atom economic and time-saving because they are performed as the one-pot, so no need for purification after each 'virtual' step and the limited necessity of protective groups are characteristic for these processes. Thus, the same results as in classical multistep synthesis can be achieved at markedly lower costs and shorter time, which is in line with modern green chemistry rules. Great advantage of cascade reactions is often reflected in their high regio- and stereoselectivities, enabling the preparing of the heterocyclic compound better fitted to the expected target in cells. This review reveals the biological relevance of N-heterocyclic scaffolds based on saturated 5-membered rings since we showed a number of examples of approved drugs together with the recent biologically attractive leading structures of drug candidates. Next, novel cascade synthetic procedures, taking into account the structure of the reactants and reaction mechanisms, enabling to obtain biological-relevant heterocyclic frameworks with good yields and relatively high stereoselectivity, were reviewed and compared. The review covers the advances of designing biological active N-heterocycles mainly from 2018 to 2021, whereas the synthetic part is focused on the last 7 years.

Drug delivery systems for cancer treatment: a review of marine-derived polysaccharides

Abstract:

Cancer is a disease characterized by uncontrolled cell proliferation and the spread of cells to other tissues and remains one of the worldwide problems waiting to be solved. There are various treatment strategies for cancer, such as chemotherapy, surgery, radiotherapy, and immunotherapy, although it varies according to its type and stage. Many chemotherapeutic agents have limited clinical use due to lack of efficacy, off-target toxicity, metabolic instability, or poor pharmacokinetics. One possible solution to this high rate of clinical failure is to design drug delivery systems that deliver drugs in a controlled and specific manner and are not toxic to normal cells. Marine systems contain biodiversity, including components and materials that can be used in biomedical applications and therapy. Biomaterials such as chitin, chitosan, alginate, carrageenan, fucoidan, hyaluronan, agarose, and ulvan obtained from marine organisms have found use in DDSs today. These polysaccharides are biocompatible, non-toxic, biodegradable, and cost-effective, making them ideal raw materials for increasingly complex DDSs with a potentially regulated release. In this review, the contributions of polysaccharides from the marine environment to the development of anticancer drugs in DDSs will be discussed.

Physcion and Physcion 8-O-β-D-glucopyranoside: Natural Anthraquinones with Potential Anticancer Activities

Nature has provided prodigious reservoirs of pharmacologically active compounds for drug development since times. Physcion and physcion 8-O-β-D-glucopyranoside (PG) are bioactive natural anthraquinones which exert anti-inflammatory and anticancer properties with minimum or no adverse effects. Moreover, physcion also exhibits anti-microbial and hepatoprotective properties, while PG is known to have anti-sepsis as well as ameliorative activities against dementia. This review aims to highlight the natural sources and anticancer activities of physcion and PG, along with associated mechanisms of actions. On the basis of the literature, physcion and PG regulate multitudinous cell signaling pathways through the modulation of various regulators of cell cycle, protein kinases, microRNAs, transcriptional factors, and apoptosis linked proteins resulting in the effective killing of cancerous cells in vitro as well as in vivo. Both compounds effectively suppress metastasis, furthermore, physcion acts as an inhibitor of 6PGD and also plays an important role in chemosensitization. This review article suggests that physcion and PG are potent anticancer drug candidates, but further investigations on their mechanism of action and pre-clinical trials are mandatory in order to comprehend the full potential of these natural cancer killers in anticancer remedies.

Marine Cyanobacteria and Microalgae Metabolites-A Rich Source of Potential Anticancer Drugs

Cancer is at present one of the utmost deadly diseases worldwide. Past efforts in cancer research have focused on natural medicinal products. Over the past decades, a great deal of initiatives was invested towards isolating and identifying new marine metabolites via pharmaceutical companies, and research institutions in general. Secondary marine metabolites are looked at as a favorable source of potentially new pharmaceutically active compounds, having a vast structural diversity and diverse biological activities; therefore, this is an astonishing source of potentially new anticancer therapy. This review contains an extensive critical discussion on the potential of marine microbial compounds and marine microalgae metabolites as anticancer drugs, highlighting their chemical structure and exploring the underlying mechanisms of action. Current limitation, challenges, and future research pathways were also presented.

Modulation of the tumor microenvironment by natural agents: implications for cancer prevention and therapy

The development of cancer is not just the growth and proliferation of a single transformed cell, but its surrounding environment also coevolves with it. Indeed, successful cancer progression depends on the ability of the tumor cells to develop a supportive tumor microenvironment consisting of various types of stromal cells. The interactions between the tumor and stromal cells are bidirectional and mediated through a variety of growth factors, cytokines, metabolites, and other biomolecules secreted by these cells. Tumor-stromal crosstalk creates optimal conditions for the tumor growth, metastasis, evasion of immune surveillance, and therapy resistance, and its targeting is being explored for clinical management of cancer. Natural agents from plants and marine life have been at the forefront of traditional medicine. Numerous epidemiological studies have reported the health benefits imparted on the consumption of certain fruits, vegetables, and their derived products. Indeed, a significant majority of anti-cancer drugs in clinical use are either naturally occurring compounds or their derivatives. In this review, we describe fundamental cellular and non-cellular components of the tumor microenvironment and discuss the significance of natural compounds in their targeting. Existing literature provides hope that novel prevention and therapeutic approaches will emerge from ongoing scientific efforts leading to the reduced tumor burden and improve clinical outcomes in cancer patients.

Retracted Article: The synthesis and biological activity of marine alkaloid derivatives and analogues

The ocean is the origin of life, with a unique ecological environment, which has given birth to a wealth of marine organisms. The ocean is an important source of biological resources and tens of thousands of monomeric compounds have been separated from marine organisms using modern separation technology. Most of these monomeric compounds have some kind of biological activity that has attracted extensive attention from researchers. Marine alkaloids are a kind of compound that can be separated from marine organisms. They have complex and special chemical structures, but at the same time, they can show diversity in biological activities. The biological activities of marine alkaloids mainly manifest in the form of anti-tumor, anti-fungus, anti-viral, anti-malaria, and anti-osteoporosis properties. Many marine alkaloids have good medicinal prospects and can possibly be used as anti-tumor, anti-viral, and anti-fungal clinical drugs or as lead compounds. The limited amounts of marine alkaloids that can be obtained by separation, coupled with the high cytotoxicity and low selectivity of these lead compounds, has restricted the clinical research and industrial development of marine alkaloids. Marine alkaloid derivatives and analogues have been obtained via rational drug design and chemical synthesis, to make up for the shortcomings of marine alkaloids; this has become an urgent subject for research and development. This work systematically reviews the recent developments relating to marine alkaloid derivatives and analogues in the field of medical chemistry over the last 10 years (2010–2019). We divide marine alkaloid derivatives and analogues into five types from the point-of-view of biological activity and elaborated on these activities. We also briefly discuss the optimization process, chemical synthesis, biological activity evaluation, and structure–activity relationship (SAR) of each of these compounds. The abundant SAR data provides reasonable approaches for the design and development of new biologically active marine alkaloid derivatives and analogues.

The ocean is the origin of life, with a unique ecological environment, which has given birth to a wealth of marine organisms.

Large-Scale Production of Bioactive Terrein by Aspergillus terreus Strain S020 Isolated from the Saudi Coast of the Red Sea

The diversity of symbiotic fungi derived from two marine sponges and sediment collected off Obhur, Jeddah (Saudi Arabia), was investigated in the current study. A total of 23 isolates were purified using a culture-dependent approach. Using the morphological properties combined with internal transcribed spacer-rDNA (ITS-rDNA) sequences, 23 fungal strains (in the majority Penicillium and Aspergillus) were identified from these samples. The biological screening (cytotoxic and antimicrobial activities) of small-scale cultures of these fungi yielded several target fungal strains which produced bioactive secondary metabolites. Amongst these isolates, the crude extract of Aspergillus terreus strain S020, which was cultured in fermentation static broth, 21 L, for 40 days at room temperature on potato dextrose broth, displayed strong antimicrobial activities against Pseudomonas aeruginosa and Staphylococcus aureus and significant antiproliferative effects on human carcinoma cells. Chromatographic separation of the crude extract by silica gel column chromatography indicated that the S020 isolate could produce a series of chemical compounds. Among these, pure crystalline terrein was separated with a high yield of 537.26 ± 23.42 g/kg extract, which represents the highest fermentation production of terrein to date. Its chemical structure was elucidated on the basis of high-resolution electrospray ionization mass spectrometry (HRESIMS) or high-resolution mass spectrometry (HRMS), 1D, and 2D NMR spectroscopic analyses and by comparison with reported data. The compound showed strong cytotoxic activity against colorectal carcinoma cells (HCT-116) and hepatocellular carcinoma cells (HepG2), with IC₅₀ values of 12.13 and 22.53 µM, respectively. Our study highlights the potential of A. terreus strain S020 for the industrial production of bioactive terrein on a large scale and the importance of future investigations of these strains to identify the bioactive leads in these fungal extracts.

Anti-proliferative and anti-inflammatory activities of the sea cucumber Holothuria polii aqueous extract

Objective:

Sea cucumbers are considered among the most important functional foods. Following bioassay guided fractionation, we assessed the anti-proliferative and anti-inflammatory activities of Holothuria polii (H. polii) extracts.

Methods:

Sea cucumber ethanolic extract and the partially purified aqueous fractions were assessed for their anti-proliferative activities. These latter bioactivities were evaluated in the highly invasive MDA-MB-231 human breast cancer cells in two-dimensional and three-dimensional cultures using trypan blue exclusion assay. The tumor-suppressive effects of sea cucumber ethanolic extract and aqueous fractions were assayed by measuring the trans-well invasion of MDA-MB-231 cells and the expression of some epithelial mesenchymal transition markers using quantitative reverse-transcription polymerase chain reaction and western blot analysis. The anti-inflammatory activity of the aqueous fraction was tested by measuring the secreted levels of interleukin-6, nitric oxide, and matrix metalloproteinase 9 in endotoxin-induced mammary epithelial SCp2 cells and interleukin-1β in phorbol-12-myristate-13-acetate-activated human monocytic THP-1 cells.

Results:

Sea cucumber ethanolic extract and the aqueous fraction significantly decreased the proliferation of MDA-MB-231 cells by more than 50% at similar and noncytotoxic concentrations and caused an arrest in the S-phase of the cell cycle of treated cells. In contrast, petroleum ether, chloroform, ethyl acetate, and n-butanol organic fractions did not show any significant activity. Furthermore, sea cucumber ethanolic extract and aqueous fraction reduced the proliferation of MDA-MB-231 cells in three-dimensional cultures by more than 60% at noncytotoxic concentrations. In addition, treatment with these concentrations resulted in the loss of stellate outgrowths in favor of spherical aggregates and a 30% decrease in invasive properties. Both sea cucumber ethanolic extract and aqueous decreased the transcription of vimentin and the protein expression levels of vimentin and N-cadherin in three-dimensional cultures. The aqueous fraction decreased the levels of inflammatory markers interleukin-6, nitric oxide, and matrix metalloproteinase 9 in the mouse mammary SCp2 cells, and the level of interleukin-1β produced by phorbol-12-myristate-13-acetate-activated THP-1 human monocytic cells.

Conclusion:

The data reveal for the first time promising anti-proliferative and anti-inflammatory activities in H. polii water extract in two-dimensional and three-dimensional culture models.

Radiosensitization by Marine Sponge Agelas sp. Extracts in Hepatocellular Carcinoma Cells with Autophagy Induction

Although radiation therapy is an effective treatment modality in many cancers, there is an urgent need to develop therapeutic drugs capable of overcoming radioresistance or minimizing normal tissue toxicity. A wide variety of marine-derived bioactive compounds have been screened for anti-cancer drug discovery, but little is known regarding radiation therapy applications. In this study, six different extracts of marine sponges collected from the Micronesian sea were screened for anti-cancer and radiosensitizing activity. Two extracts derived from Agelas sponges collected off the coast of Kosrae and Chuuk, the Federated States of Micronesia significantly decreased clonogenic survival of hepatocellular carcinoma (HCC) cells after exposure to ionizing radiation (IR). The Agelas extracts augmented IR-induced apoptosis and accumulation of reactive oxygen species (ROS). Endoplasmic reticulum (ER) stress was increased via unfolded protein response stimulation, which induced autophagy. N-acetylcysteine, a ROS scavenger, diminished ER stress and autophagy induction effects. This result indicated that Agelas extracts may sensitize HCC cells to IR via ROS overproduction in vitro. Our findings suggest that the Agelas sp. may have potential utility in radiosensitizer development.

Jellyfish extract induces apoptotic cell death through the p38 pathway and cell cycle arrest in chronic myelogenous leukemia K562 cells

Jellyfish species are widely distributed in the world's oceans, and their population is rapidly increasing. Jellyfish extracts have several biological functions, such as cytotoxic, anti-microbial, and antioxidant activities in cells and organisms. However, the anti-cancer effect of Jellyfish extract has not yet been examined. We used chronic myelogenous leukemia K562 cells to evaluate the mechanisms of anti-cancer activity of hexane extracts from Nomura's jellyfish in vitro. In this study, jellyfish are subjected to hexane extraction, and the extract is shown to have an anticancer effect on chronic myelogenous leukemia K562 cells. Interestingly, the present results show that jellyfish hexane extract (Jellyfish-HE) induces apoptosis in a dose- and time-dependent manner. To identify the mechanism(s) underlying Jellyfish-HE-induced apoptosis in K562 cells, we examined the effects of Jellyfish-HE on activation of caspase and mitogen-activated protein kinases (MAPKs), which are responsible for cell cycle progression. Induction of apoptosis by Jellyfish-HE occurred through the activation of caspases-3,-8 and -9 and phosphorylation of p38. Jellyfish-HE-induced apoptosis was blocked by a caspase inhibitor, Z-VAD. Moreover, during apoptosis in K562 cells, p38 MAPK was inhibited by pretreatment with SB203580, an inhibitor of p38. SB203580 blocked jellyfish-HE-induced apoptosis. Additionally, Jellyfish-HE markedly arrests the cell cycle in the G0/G1 phase. Therefore, taken together, the results imply that the anti-cancer activity of Jellyfish-HE may be mediated apoptosis by induction of caspases and activation of MAPK, especially phosphorylation of p38, and cell cycle arrest at the Go/G1 phase in K562 cells.

Marine Enzymes in Cancer: A New Paradigm

Over the last decades, the vast chemical and biodiversity of marine environment has been identified as an important source of new anticancer drugs. The evolution of marine life is a result of competition among microorganisms for space and nutrients in the marine environment, which drives marine microorganisms to generate diverse enzyme systems with unique properties to adapt to harsh conditions of ocean. Therefore, marine-derived sources offer novel enzymes endowed with extraordinary properties. Recent advances in cancer therapy have facilitated enzyme therapy as a promising tool. But, the available information on the use of enzymes derived from marine sources as therapeutic agents for cancer therapy is scanty. The potential utility of marine enzymes in cancer therapy will be discussed in this chapter.

Firing the sting: chemically induced discharge of cnidae reveals novel proteins and peptides from box jellyfish (Chironex fleckeri) venom

Cnidarian venom research has lagged behind other toxinological fields due to technical difficulties in recovery of the complex venom from the microscopic nematocysts. Here we report a newly developed rapid, repeatable and cost effective technique of venom preparation, using ethanol to induce nematocyst discharge and to recover venom contents in one step. Our model species was the Australian box jellyfish (Chironex fleckeri), which has a notable impact on public health. By utilizing scanning electron microscopy and light microscopy, we examined nematocyst external morphology before and after ethanol treatment and verified nematocyst discharge. Further, to investigate nematocyst content or "venom" recovery, we utilized both top-down and bottom-up transcriptomics-proteomics approaches and compared the proteome profile of this new ethanol recovery based method to a previously reported high activity and recovery protocol, based upon density purified intact cnidae and pressure induced disruption. In addition to recovering previously characterized box jellyfish toxins, including CfTX-A/B and CfTX-1, we recovered putative metalloproteases and novel expression of a small serine protease inhibitor. This study not only reveals a much more complex toxin profile of Australian box jellyfish venom but also suggests that ethanol extraction method could augment future cnidarian venom proteomics research efforts.

From Land to Sea; Embracing a Renewable Future

The authors discuss the ever increasing role of biological renewable resources in energy, nutrition, and pharmaceuticals; specifically those potentially available deep within the oceans. They provide a list of products already gleaned from this vastly untapped marine environment; discuss the innovations in technology required to effectively explore and prospect the deeper reaches of the ocean; expose the impressive contribution to the economy; and expound the paramount importance of protecting the oceans to ensure the future. Already many new proteins, enzymes, and pharmaceuticals are being developed from the fauna and flora of the forests and relatively shallow economic zones of the ocean. With much of the ocean still an unexplored frontier, the authors hope to promote increased interest in research and development in this arena.

Gracilaria edulis extract induces apoptosis and inhibits tumor in Ehrlich ascites tumor cells in vivo

BACKGROUND

Marine environment is inestimable for their chemical and biological diversity and therefore is an extraordinary resource for the discovery of new anticancer drugs. Recent development in elucidation of the mechanism and therapeutic action of natural products helped to evaluate for their potential activity.

METHODS

We evaluated Gracilaria edulis J. Ag (Brown algae), for its antitumor potential against the Ehrlich ascites tumor (EAT) in vivo and in vitro. Cytotoxicity evaluation of Ethanol Extract of Gracilaria edulis (EEGE) using EAT cells showed significant activity. In vitro studies indicated that EEGE cytotoxicity to EAT cells is mediated through its ability to produce reactive oxygen species (ROS) and therefore decreasing intracellular glutathione (GSH) levels may be attributed to oxidative stress.

RESULTS

Apoptotic parameters including Annexin-V positive cells, increased levels of DNA fragmentation and increased caspase-2, caspase-3 and caspase-9 activities indicated the mechanism might be by inducing apoptosis. Intraperitoneally administration of EEGE to EAT-bearing mice helped to increase the lifespan of the animals significantly inhibited tumor growth and increased survival of mice. Extensive hematology, biochemistry and histopathological analysis of liver and kidney indicated that daily doses of EEGE up to 300 mg/kg for 35 days are well tolerated and did not cause hematotoxicity nor renal or hepatotoxicity.

CONCLUSION

Comprehensive antitumor analysis in animal model and in Ehrlich Ascites Tumor cells was done including biochemical, and pathological evaluations indicate antitumor activity of the extract and non toxic in vivo. It was evident that the mechanism explains the apoptotic activity of the algae extract.

"Head-to-side-chain" cyclodepsipeptides of marine origin

Since the late 1980s, a large number of depsipeptides that contain a new topography, referred to as "head-to-side-chain" cyclodepsipeptides, have been isolated and characterized. These peptides present a unique structural arrangement that comprises a macrocyclic region closed through an ester bond between the C-terminus and a β-hydroxyl group, and terminated with a polyketide moiety or a more simple branched aliphatic acid. This structural pattern, the presence of unique and complex residues, and relevant bioactivity are the main features shared by all the members of this new class of depsipeptides, which are reviewed herein.

Synthesis and antitumor activities of derivatives of the marine mangrove fungal metabolite deoxybostrycin

Deoxybostrycin (1) is an anthraquinone compound derived from the marine mangrove fungus Nigrospora sp. No. 1403 and has potential to be a lead for new drugs because of its various biological properties. A series of new derivatives (2–22) of deoxybostrycin were synthesized. The in vitro cytotoxicity of all the new compounds was tested against MDA-MB-435, HepG2 and HCT-116 cancer cell lines. Most of the compounds exhibit strong cytotoxicity with IC₅₀ values ranging from 0.62 to 10 μM. Compounds 19, 21 display comparable cytotoxicity against MDA-MB-435 to epirubicin, the positive control. The primary screening results indicate that the deoxybostrycin derivatives might be a valuable source of new potent anticancer drug candidates.

Interaction of natural products with cell survival and signaling pathways in the biochemical elucidation of drug targets in cancer

The use of natural products with therapeutic properties is as ancient as human civilization and for a long time mineral, plant and animal products were the main sources of drugs. Worldwide sales of medicinal plants, crude extracts and finished products amounted to US$15 billion in 1999 and it increased to $23 billion in 2002. More interestingly, the influence of natural products upon anticancer drug discovery and design cannot be underestimated. Approximately 60% of all drugs in clinical trials are either a natural product, compounds derived from natural products or contain pharmacophores derived from active natural products. Thus, even today, in the presence of massive numbers of agents from combinatorial libraries, compounds from natural sources are still in the forefront of cancer chemotherapeutics as sources of active drug types, as well as being involved in drug discovery in diseases such as microbial and parasitic infections and the control of cholesterol/lipids, among other functions.

Total synthesis of bryostatins: the development of methodology for the atom-economic and stereoselective synthesis of the ring C subunit

Bryostatins, a family of structurally complicated macrolides, exhibit an exceptional range of biological activities. The limited availability and structural complexity of these molecules makes development of an efficient total synthesis particularly important. This article describes our initial efforts towards the total synthesis of bryostatins, in which chemoselective and atom-economical methods for the stereoselective assembly of the ring C subunit were developed. A Pd-catalyzed tandem alkyne-alkyne coupling/6-endo-dig cyclization sequence was explored and successfully pursued in the synthesis of a dihydropyran ring system. Elaboration of this methodology ultimately led to a concise synthesis of the ring C subunit of bryostatins.

Complementary cell-based high-throughput screens identify novel modulators of the unfolded protein response

Despite advances toward understanding the prevention and treatment of many cancers, patients who suffer from oral squamous cell carcinoma (OSCC) confront a survival rate that has remained unimproved for more than 2 decades, indicating our ability to treat them pharmacologically has reached a plateau. In an ongoing effort to improve the clinical outlook for this disease, we previously reported that an essential component of the mechanism by which the proteasome inhibitor bortezomib (PS-341, Velcade) induced apoptosis in OSCC required the activation of a terminal unfolded protein response (UPR). Predicated on these studies, the authors hypothesized that high-throughput screening (HTS) of large diverse chemical libraries might identify more potent or selective small-molecule activators of the apoptotic arm of the UPR to control or kill OSCC. They have developed complementary cell-based assays using stably transfected CHO-K1 cell lines that individually assess the PERK/eIF2α/CHOP (apoptotic) or the IRE1/XBP1 (adaptive) UPR subpathways. An 66 K compound collection was screened at the University of Michigan Center for Chemical Genomics that included a unique library of prefractionated natural product extracts. The mycotoxin methoxycitrinin was isolated from a natural extract and found to selectively activate the CHOP-luciferase reporter at 80 µM. A series of citrinin derivatives was isolated from these extracts, including a unique congener that has not been previously described. In an effort to identify more potent compounds, the authors examined the ability of citrinin and the structurally related mycotoxins ochratoxin A and patulin to activate the UPR. Strikingly, it was found that patulin at 2.5 to 10 µM induced a terminal UPR in a panel of OSCC cells that was characterized by an increase in CHOP, GADD34, and ATF3 gene expression and XBP1 splicing. A luminescent caspase assay and the induction of several BH3-only genes indicated that patulin could induce apoptosis in OSCC cells. These data support the use of this complementary HTS strategy to identify novel modulators of UPR signaling and tumor cell death.

Chemotherapeutic effects of bioassay-guided extracts of the American cockroach, Periplaneta americana

The organic extract of Periplaneta americana L. (Dictyoptera; Blattidae) has been traditionally used in southwestern China as an alternative medicine against disorders such as hepatitis, trauma, gastric ulcers, burns, and heart disease. The present study describes bioassay-guided purification and chemotherapeutic evaluation of the 60% ethanolic fraction of P americana organic extracts (PAE60). The most effective cytotoxic fraction was determined by way of repeated in vitro screenings against 12 distinct cultured human carcinoma cell lines: Eca 109, BGC823, HO8910, LS174T, CNE, HeLa, K562, PC-3, A549, BEL 7404, HL-60, and KB, followed by in vivo antitumor assays of the lead fraction (PAE60). The complexity of enriched active fraction was qualitatively evaluated using thin layer chromatography. Reconstituted PAE60 was effective at inhibiting HL-60, KB, CNE, and BGC823 cell growth with IC(50) values <20 µg mL-(1). PAE60 reduced tumor growth in S180-bearing immunocompetent mice by 72.62% after 10 days following oral doses of 500 mg kg d-(1) compared with 78.75% inhibition following 40 mg kg d-(1) of cyclophosphamide (CTX). Thymus and spleen indices of S180-bearing mice treated with PAE60 were significantly greater (P < .05) than CTX treatment groups, suggesting potential immunomodulation of antitumor host defenses by PAE60. Antiviral activity was also investigated and PAE60 inhibited herpes simplex type-2 replication (IC(50) = 4.11 ± 0.64 µg mL-(1)) with a selectivity index (CC(50) to IC(50) ratio) of 64.84 in Vero cells but was less effective on type-1 virus (IC(50) of 25.6 ± 3.16 µg mL-(1)). These results support future clinical trials on P. americana as an alternative or complementary medicinal agent.

In vitro evaluation of marine-microorganism extracts for anti-viral activity

Viral-induced infectious diseases represent a major health threat and their control remains an unachieved goal, due in part to the limited availability of effective anti-viral drugs and measures. The use of natural products in drug manufacturing is an ancient and well-established practice. Marine organisms are known producers of pharmacological and anti-viral agents. In this study, a total of 20 extracts from marine microorganisms were evaluated for their antiviral activity. These extracts were tested against two mammalian viruses, herpes simplex virus (HSV-1) and vesicular stomatitis virus (VSV), using Vero cells as the cell culture system, and two marine virus counterparts, channel catfish virus (CCV) and snakehead rhabdovirus (SHRV), in their respective cell cultures (CCO and EPC). Evaluation of these extracts demonstrated that some possess antiviral potential. In sum, extracts 162M(4), 258M(1), 298M(4), 313(2), 331M(2), 367M(1) and 397(1) appear to be effective broad-spectrum antivirals with potential uses as prophylactic agents to prevent infection, as evident by their highly inhibitive effects against both virus types. Extract 313(2) shows the most potential in that it showed significantly high inhibition across all tested viruses. The samples tested in this study were crude extracts; therefore the development of antiviral application of the few potential extracts is dependent on future studies focused on the isolation of the active elements contained in these extracts.

SZ-685C, a marine anthraquinone, is a potent inducer of apoptosis with anticancer activity by suppression of the Akt/FOXO pathway

BACKGROUND AND PURPOSE

The aims of this study were to investigate the anti-cancer activity of SZ-685C, an anthracycline analogue isolated from marine-derived mangrove endophytic fungi, and to explore the molecular mechanisms underlying such activity.

EXPERIMENTAL APPROACH

The effect of SZ-685C on the viability of cancer cell lines was investigated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. SZ-685C-induced apoptosis was assessed by Annexin V-fluorescein isothiocyanate/propidium iodide staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling assay and analysis of caspase activation. The effect of SZ-685C on the Akt/FOXO pathway was studied using Western blotting analysis, and the in vivo anti-tumour efficacy was examined in an MDA-MB-435 breast cancer xenograft model.

KEY RESULTS

SZ-685C suppressed the proliferation of six cancer cell lines derived from human breast cancer, prostate cancer, glioma and hepatoma (IC(50) values ranged from 3.0 to 9.6 microM) and the growth of breast cancer xenografts in mice. SZ-685C had a direct apoptosis-inducing effect through both the extrinsic and intrinsic apoptotic pathways, as shown by activation of caspase-8 and 9 as well as effector caspase-3 and poly (ADP-ribose) polymerase. Phosphorylation of Akt and its downstream effectors, forkhead box protein O1 and forkhead box protein O3a, was down-regulated in SZ-685C-treated cancer cells. Furthermore, the pro-apoptotic protein Bim was up-regulated by SZ-685C treatment consistent with FOXO dephosphorylation.

CONCLUSIONS AND IMPLICATIONS

SZ-685C could induce apoptosis through the Akt/FOXO pathway, which consequently leads to the observed anti-tumour effect both in vitro and in vivo. Our data suggest that SZ-685C may be a potentially promising Akt inhibitor and anti-cancer drug candidate.

Marine actinomycetes: a new source of compounds against the human malaria parasite

Background

Malaria continues to be a devastating parasitic disease that causes the death of 2 million individuals annually. The increase in multi-drug resistance together with the absence of an efficient vaccine hastens the need for speedy and comprehensive antimalarial drug discovery and development. Throughout history, traditional herbal remedies or natural products have been a reliable source of antimalarial agents, e.g. quinine and artemisinin. Today, one emerging source of small molecule drug leads is the world's oceans. Included among the source of marine natural products are marine microorganisms such as the recently described actinomycete. Members of the genus Salinispora have yielded a wealth of new secondary metabolites including salinosporamide A, a molecule currently advancing through clinical trials as an anticancer agent. Because of the biological activity of metabolites being isolated from marine microorganisms, our group became interested in exploring the potential efficacy of these compounds against the malaria parasite.

Methods

We screened 80 bacterial crude extracts for their activity against malaria growth. We established that the pure compound, salinosporamide A, produced by the marine actinomycete, Salinispora tropica, shows strong inhibitory activity against the erythrocytic stages of the parasite cycle. Biochemical experiments support the likely inhibition of the parasite 20S proteasome. Crystal structure modeling of salinosporamide A and the parasite catalytic 20S subunit further confirm this hypothesis. Ultimately we showed that salinosporamide A protected mice against deadly malaria infection when administered at an extremely low dosage.

Conclusion

These findings underline the potential of secondary metabolites, derived from marine microorganisms, to inhibit Plasmodium growth. More specifically, we highlight the effect of proteasome inhibitors such as salinosporamide A on in vitro and in vivo parasite development. Salinosporamide A (NPI-0052) now being advanced to phase I trials for the treatment of refractory multiple myeloma will need to be further explored to evaluate the safety profile for its use against malaria.

Efficacy of selected natural products as therapeutic agents against cancer

With emerging sophistication in the exploration of ocean environment, a number of marine bioactive products have been identified with promising anticancer activity. Many of these are in active phase I or phase II clinical trials or have been terminated because of adverse side effects, mainly hematological in nature. Nonetheless, the information derived has aided enormously in providing leads for laboratory synthesis with modifications in the parent structure affecting compound solubility, absorption, and toxicity, resulting in less severe toxicity while achieving maximum efficacy in smaller doses. We describe herein, a few of the compounds obtained from marine and terrestrial sources [bryostatin 1 ( 1), dolastatin 10 ( 2), auristatin PE ( 3), and combretastatin A4 ( 4)] that have been extensively investigated in our laboratory and continue to be investigated for their sensitization effects with other cytotoxic agents in several different site-specific tumors employing murine models or human subjects.

Natural products as leads to anticancer drugs

Throughout history, natural products have afforded a rich source of compounds that have found many applications in the fields of medicine, pharmacy and biology. Within the sphere of cancer, a number of important new commercialised drugs have been obtained from natural sources, by structural modification of natural compounds, or by the synthesis of new compounds, designed following a natural compound as model. The search for improved cytotoxic agents continues to be an important line in the discovery of modern anticancer drugs. The huge structural diversity of natural compounds and their bioactivity potential have meant that several products isolated from plants, marine flora and microorganisms can serve as "lead" compounds for improvement of their therapeutic potential by molecular modification. Additionally, semisynthesis processes of new compounds, obtained by molecular modification of the functional groups of lead compounds, are able to generate structural analogues with greater pharmacological activity and with fewer side effects. These processes, complemented with high-throughput screening protocols, combinatorial chemistry, computational chemistry and bioinformatics are able to afford compounds that are far more efficient than those currently used in clinical practice. Combinatorial biosynthesis is also applied for the modification of natural microbial products. Likewise, advances in genomics and the advent of biotechnology have improved both the discovery and production of new natural compounds.

In vitro characterization of the human biotransformation pathways of aplidine, a novel marine anti-cancer drug

Aplidine is a potent marine anti-cancer drug and is currently being investigated in phase II clinical trials. However, the enzymes involved in the biotransformation of aplidine and thus its pharmacokinetics are not known yet. To assess the biotransformation pathways of aplidine and their potential implications for human pharmacology and toxicology, the in vitro metabolism of aplidine was characterized using incubations with human plasma, liver preparations, cytochrome P450 (CYP) and uridine diphosphoglucuronosyl transferase (UGT) supersomes in combination with HPLC analysis and cytotoxicity assays with cell lines. Aplidine was metabolised by carboxyl esterases in human plasma. Using CYP supersomes and liver microsomes, it was shown that aplidine was metabolised mainly by CYP3A4 and also by CYP2A6, 2E1 and 4A11. Four metabolites were observed after incubation with human liver microsomes, one formed by CYP2A6 (C-demethylation) and three by CYP3A4 (hydroxylation and/or C-dealkylation). No conjugation was observed in human liver S9 fraction. However, the aplidine metabolites formed by CYP were further conjugated by the phase II enzymes UGT, GST and SULT. In accordance with the findings in microsomes and CYP supersomes, a significant effect of specific CYP2A6, 2E1, 3A4 and 4A11 inhibitors on the cytotoxicity of aplidine in Hep G2 and IGROV-1 cells could be observed. These results provide evidence that CYP3A4 has a major role in metabolising aplidine in vitro with additional involvement of CYP2A6, 2E1, and 4A11. Further, the metabolites formed by CYPs can be conjugated by UGT, SULT and GST. These findings could help interpret the in vivo pharmacokinetics of aplidine.

Characterization of the initial enzymatic steps of barbamide biosynthesis

Barbamide is a mixed polypeptide-polyketide natural product that contains an unusual trichloromethyl group. The origin of the trichloromethyl group was previously shown to be through chlorination of the pro-R methyl group of L-leucine. Trichloroleucine is subsequently decarboxylated and oxidized to trichloroisovaleric acid and then extended with an acetate unit to form the initial seven carbons of barbamide. In this study we used a combination of biosynthetic feeding experiments and enzymatic analysis to characterize the initial steps required for formation of trichloroleucine and its chain-shortened product, trichloroisovaleric acid. Results from isotope-labeled feeding experiments showed that both dichloroleucine and trichloroleucine are readily incorporated into barbamide; however, monochloroleucine is not. This suggests that halogenation of the pro-R methyl group of leucine occurs as two discrete reactions, with the first involving incorporation of at least two halogen atoms and the second converting dichloroleucine to trichloroleucine. Additionally, the initial tandem dichlorination must occur before substrate can be further processed by the remainingbar pathway enzymes. In vitro analysis of the first five open reading frames (ORFs; barA, barB1, barB2, bar C, barD) of the barbamide gene cluster has yielded new insights into the processing of leucine to form the trichloroisovaleryl-derived unit in the final product.

Scale and sustainability of marine bioprospecting for pharmaceuticals

Collecting marine organisms for the discovery and development of pharmaceuticals has been perceived variously as sustaining and threatening conservation. Our initial expectations that marine bioprospecting might pose conservation challenges were largely not confirmed. Thousands of marine species have been collected for initial assessment, but usually only in very small amounts. Very few compounds are sufficiently promising to provoke re-collections, where volumes can be much larger. This is where conservation concerns may arise, particularly if the organism is rare, has a restricted distribution, or is targeted in one narrow area. However, industry generally seeks to avoid dependency on small populations, for economic as well as ecological reasons. Alternative supply strategies to wild capture include synthesis and culture. Mandatory collection protocols and environmental impact (stock) assessments are useful routes for management to achieve sustainable use where extraction is desirable. In general, the scanty information available suggests that marine bioprospecting for pharmaceuticals may have minimal impacts on the environment, particularly compared with those created by other pressures.

The current status of natural products from marine fungi and their potential as anti-infective agents

A growing number of marine fungi are the sources of novel and potentially life-saving bioactive secondary metabolites. Here, we have discussed some of these novel antibacterial, antiviral, antiprotozoal compounds isolated from marine-derived fungi and their possible roles in disease eradication. We have also discussed the future commercial exploitation of these compounds for possible drug development using metabolic engineering and post-genomics approaches.

Antineoplastic agents. 545. Isolation and structure of turbostatins 1-4 from the Asian marine mollusk Turbo stenogyrus

The cancer cell line bioassay-guided separation of an extract from the marine mollusk Turbo stenogyrus led to the isolation of four new cerebrosides designated turbostatins 1-4 (1-4). The structure of each glycolipid was determined by interpreting results of a series of HR-APCI-MS and NMR (1D and 2D) spectral analyses. All four turbostatins exhibited significant (GI50 0.15-2.6 microg/mL) cancer cell growth inhibition against the murine P388 lymphocytic leukemia and a panel of human cancer cell lines.

13-Deoxytedanolide, a marine sponge-derived antitumor macrolide, binds to the 60S large ribosomal subunit

13-Deoxytedanolide is a potent antitumor macrolide isolated from the marine sponge Mycale adhaerens. In spite of its remarkable activity, the mode of action of 13-deoxytedanolide has not been elucidated. [11-3H]-(11S)-13-Deoxydihydrotedanolide derived from the macrolide was used for identifying the target molecule from the yeast cell lysate. Fractionation of the binding protein revealed that the labeled 13-deoxytedanolide derivative strongly bound to the 80S ribosome as well as to the 60S large subunit, but not to the 40S small subunit. In agreement with this observation, 13-deoxytedanolide efficiently inhibited the polypeptide elongation. Interestingly, competition studies demonstrated that 13-deoxytedanolide shared the binding site on the 60S large subunit with pederin and its marine-derived analogues. These results indicate that 13-deoxytedanolide is a potent protein synthesis inhibitor and is the first macrolide to inhibit the eukaryotic ribosome.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) 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 (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.

Isolation and structure of phakellistatin 14 from the Western Pacific marine sponge Phakellia sp

A new cycloheptapeptide, phakellistatin 14, was isolated in 8.8 x 10(-7)% yield from Phakellia sp., a marine sponge from Chuuk, Federated States of Micronesia. The structure (1), cyclo-Phe-beta-OMe-Asp-Ala-Met(SO)-Ala-Ile-Pro, was elucidated by 1D and 2D NMR spectral analyses augmented by HRFABMS. The chirality of each amino acid unit was determined to be S using chiral HPLC methods. Phakellistatin 14 showed cancer cell growth inhibitory activity (ED(50) 5 microg/mL) against the murine lymphocytic leukemia P388 cell line.

Antitumor polyketide biosynthesis by an uncultivated bacterial symbiont of the marine sponge Theonella swinhoei

Bacterial symbionts have long been suspected to be the true producers of many drug candidates isolated from marine invertebrates. Sponges, the most important marine source of biologically active natural products, have been frequently hypothesized to contain compounds of bacterial origin. This symbiont hypothesis, however, remained unproven because of a general inability to cultivate the suspected producers. However, we have recently identified an uncultured Pseudomonas sp. symbiont as the most likely producer of the defensive antitumor polyketide pederin in Paederus fuscipes beetles by cloning the putative biosynthesis genes. Here we report closely related genes isolated from the highly complex metagenome of the marine sponge Theonella swinhoei, which is the source of the onnamides and theopederins, a group of polyketides that structurally resemble pederin. Sequence features of the isolated genes clearly indicate that it belongs to a prokaryotic genome and should be responsible for the biosynthesis of almost the entire portion of the polyketide structure that is correlated with antitumor activity. Besides providing further proof for the role of the related beetle symbiont-derived genes, these findings raise intriguing ecological and evolutionary questions and have important general implications for the sustainable production of otherwise inaccessible marine drugs by using biotechnological strategies.

Marine natural products and related compounds in clinical and advanced preclinical trials

The marine environment has proven to be a very rich source of extremely potent compounds that have demonstrated significant activities in antitumor, antiinflammatory, analgesia, immunomodulation, allergy, and anti-viral assays. Although the case can and has been made that the nucleosides such as Ara-A and Ara-C are derived from knowledge gained from investigations of bioactive marine nucleosides, no drug directly from marine sources (whether isolated or by total synthesis) has yet made it to the commercial sector in any disease. However, as shown in this review, there are now significant numbers of very interesting molecules that have come from marine sources, or have been synthesized as a result of knowledge gained from a prototypical compound, that are either in or approaching Phase II/III clinical trials in cancer, analgesia, allergy, and cognitive diseases. A substantial number of other potential agents are following in their wake in preclinical trials in these and in other diseases.