Pharmacological Activities of Extracts and Compounds Isolated from Mediterranean Sponge Sources

Marine pharmacology is an exciting and growing discipline that blends blue biotechnology and natural compound pharmacology together. Several sea-derived compounds that are approved on the pharmaceutical market were discovered in sponges, marine organisms that are particularly rich in bioactive metabolites. This paper was specifically aimed at reviewing the pharmacological activities of extracts or purified compounds from marine sponges that were collected in the Mediterranean Sea, one of the most biodiverse marine habitats, filling the gap in the literature about the research of natural products from this geographical area. Findings regarding different Mediterranean sponge species were individuated, reporting consistent evidence of efficacy mainly against cancer, infections, inflammatory, and neurological disorders. The sustainable exploitation of Mediterranean sponges as pharmaceutical sources is strongly encouraged to discover new compounds.

Investigating the Antiparasitic Potential of the Marine Sesquiterpene Avarone, Its Reduced form Avarol, and the Novel Semisynthetic Thiazinoquinone Analogue Thiazoavarone

The chemical analysis of the sponge Dysidea avara afforded the known sesquiterpene quinone avarone, along with its reduced form avarol. To further explore the role of the thiazinoquinone scaffold as an antiplasmodial, antileishmanial and antischistosomal agent, we converted the quinone avarone into the thiazinoquinone derivative thiazoavarone. The semisynthetic compound, as well as the natural metabolites avarone and avarol, were pharmacologically investigated in order to assess their antiparasitic properties against sexual and asexual stages of Plasmodium falciparum, larval and adult developmental stages of Schistosomamansoni (eggs included), and also against promastigotes and amastigotes of Leishmania infantum and Leishmania tropica. Furthermore, in depth computational studies including density functional theory (DFT) calculations were performed. A toxic semiquinone radical species which can be produced starting both from quinone- and hydroquinone-based compounds could mediate the anti-parasitic effects of the tested compounds.

Dictyoceratidan poisons: Defined mark on microtubule-tubulin dynamics

Tubulin/microtubule assembly and disassembly is characterized as one of the chief processes during cell growth and division. Hence drugs those perturb these process are considered to be effective in killing fast multiplying cancer cells. There is a collection of natural compounds which disturb microtubule/tubulin dis/assemblage and there have been a lot of efforts concerted in the marine realm too, to surveying such killer molecules. Close to half the natural compounds shooting out from marine invertebrates are generally with no traceable definite mechanisms of action though may be tough anti-cancerous hits at nanogram levels, hence fatefully those discoveries conclude therein without a capacity of translation from laboratory to pharmacy. Astoundingly at least 50% of natural compounds which have definite mechanisms of action causing disorders in tubulin/microtubule kinetics have an isolation history from sponges belonging to the Phylum: Porifera. Poriferans have always been a wonder worker to treat cancers with a choice of, yet precise targets on cancerous tissues. There is a specific order: Dictyoceratida within this Phylum which has contributed to yielding at least 50% of effective compounds possessing this unique mechanism of action mentioned above. However, not much notice is driven to Dictyoceratidans alongside the order: Demospongiae thus dictating the need to know its select microtubule/tubulin irritants since the unearthing of avarol in the year 1974 till date. Hence this review selectively pinpoints all the compounds, noteworthy derivatives and analogs stemming from order: Dictyoceratida focusing on the past, present and future.

In vitro avarol does affect the growth of Candida sp

This work extends in vitro screening of antimicrobial activity of avarol, the marine natural product firstly isolated from the Mediterranean sponge Dysidea avara. Its anticandidial activity was evaluated by microdilution method against eight Candida strains, two ATCC and six clinical ones. At a different extent this compound was proven to be active against all the strains tested (MIC 0.8-6.0 μg/mL and MFC 1.6-12.0 μg/mL, respectively). According to the best of our knowledge, this is the first report on avarol activity towards any yeast strain which may be of relevance for Alzheimer's disease. Indeed, avarol derivatives showing moderate AChE activity should be screened for anticandidial activity both in vitro and in vivo.

Further in vitro biological activity evaluation of amino-, thio- and ester-derivatives of avarol

The acetylcholinesterase inhibitory and/or antitumour activities of amino-, thio- and ester-derivatives of avarol selected were evaluated for the first time at in vitro conditions. Avarol-3',4'-dithioglycol (1) and avarol-4'-(3)mercaptopropionic acid (3) were shown to be the best inhibitors of the enzyme tested (0.50 µg and IC50 0.05 mM and 0.50 µg and IC50 0.12 mM, respectively), while 4'-tryptamine-avarone (9) and avarol-3'-(3)mercaptopropionic acid (2) exhibited the highest cytotoxicity against the human breast T-47D cancer cell line (IC50 0.66 µg/mL and 1.25 µg/mL, respectively). According to experimental data obtained, the sesquiterpenoid hydroquinone structure of bioactive avarol derivatives may inspire development of new pharmacologically useful substances to be used in the treatment of Alzheimer's disease and/or human breast tumour.

Evaluation of HIV-1 inhibition by stereoisomers and analogues of the sesquiterpenoid hydroquinone peyssonol A

Peyssonol A, a brominated natural product with documented anti-HIV-1 activity, was synthesized racemically along with 6 isomers and 15 truncated analogues and synthetic precursors. These compounds were screened in a cell-based assay against a recombinant HIV-1 strain to investigate structure-activity relationships. The results obtained suggest that both the aliphatic and aromatic domains of peyssonol A are responsible for its potency, while the stereochemical configuration of the substituents on the aliphatic domain, including their bromine atom, are largely irrelevant. Although none of the analogues tested were as potent as the parent natural product, several exhibited greater therapeutic indices due to reduced cytotoxicity, noting that nearly all compounds tested were measurably cytotoxic.

Cytotoxic terpene quinones from marine sponges

The 1,4-benzoquinone moiety is a common structural feature in a large number of compounds that have received considerable attention owing to their broad spectrum of biological activities. The cytotoxic and antiproliferative properties of many natural sesquiterpene quinones and hydroquinones from sponges of the order Dictyoceratida, such as avarol, avarone, illimaquinone, nakijiquinone and bolinaquinone, offer promising opportunities for the development of new antitumor agents. The present review summarizes the structure and cytotoxicity of natural terpenequinones/hydroquinones and their bioactive analogues and derivatives.

Antiviral lead compounds from marine sponges

Marine sponges are currently one of the richest sources of pharmacologically active compounds found in the marine environment. These bioactive molecules are often secondary metabolites, whose main function is to enable and/or modulate cellular communication and defense. They are usually produced by functional enzyme clusters in sponges and/or their associated symbiotic microorganisms. Natural product lead compounds from sponges have often been found to be promising pharmaceutical agents. Several of them have successfully been approved as antiviral agents for clinical use or have been advanced to the late stages of clinical trials. Most of these drugs are used for the treatment of human immunodeficiency virus (HIV) and herpes simplex virus (HSV). The most important antiviral lead of marine origin reported thus far is nucleoside Ara-A (vidarabine) isolated from sponge Tethya crypta. It inhibits viral DNA polymerase and DNA synthesis of herpes, vaccinica and varicella zoster viruses. However due to the discovery of new types of viruses and emergence of drug resistant strains, it is necessary to develop new antiviral lead compounds continuously. Several sponge derived antiviral lead compounds which are hopedto be developed as future drugs are discussed in this review. Supply problems are usually the major bottleneck to the development of these compounds as drugs during clinical trials. However advances in the field of metagenomics and high throughput microbial cultivation has raised the possibility that these techniques could lead to the cost-effective large scale production of such compounds. Perspectives on biotechnological methods with respect to marine drug development are also discussed.

Synthesis and biological activity of derivatives of the marine quinone avarone

Nine alkyl(aryl)thio derivatives of the marine sesquiterpene quinone avarone were synthesized by nucleophilic addition of thiols or thiophenol to avarone. In most cases only one regioisomer was obtained. Their cytotoxic activities, brine shrimp lethality and antibacterial activity were evaluated, as well as those of some previously synthesized avarone derivatives. Anti-HIV activity of two derivatives was tested. Electrochemical properties were determined for all the derivatives in order to obtain more accurate information on structure-activity relationships. Most derivatives showed cytotoxic activity against tumor cell lines, with IC(50) values less than 10 microM for some of them, in particular those with electron-donating substituents. The most active compound was 4'-(methylamino)avarone, with IC(50) value of 2.4 microM to melanoma Fem-X cells, and no cytotoxicity to normal lymphocytes.

Evaluation of the activity of the sponge metabolites avarol and avarone and their synthetic derivatives against fouling micro- and macroorganisms

The sesquiterpene hydroquinone avarol (1) was isolated from the marine sponge Dysidea avara, whereas the corresponding quinone, avarone (2), was obtained by oxidation of avarol, and the significantly more lipophilic compounds [3'-(p-chloro-phenyl)avarone (3), 3',4'-ethylenedithioavarone (4), 4'-isopropylthioavarone (5), 4'-tert-butylthioavarone (6), 4'-propylthioavarone (7), 4'-octylthioavarone (8)] were obtained by nucleophilic addition of thiols or p-chloroaniline to avarone. All these compounds were tested, at concentrations ranging from 0.5 to 50 microg/mL, for their effect on the settlement of the cyprid stage of Balanus amphitrite, for toxicity to both nauplii and cyprids and for their growth inhibitory activity on marine bacteria (Cobetia marina, Marinobacterium stanieri, Vibrio fischeri and Pseudoalteromonas haloplanktis) and marine fungi (Halosphaeriopsis mediosetigera, Asteromyces cruciatus, Lulworthia uniseptata and Monodictys pelagica).

Reactivity and biological activity of the marine sesquiterpene hydroquinone avarol and related compounds from sponges of the order Dictyoceratida

A review of results of bioactivity and reactivity examinations of marine sesquiterpene (hydro)quinones is presented. The article is focused mostly on friedo- rearranged drimane structural types, isolated from sponges of the order Dictyoceratida. Examples of structural correlations are outlined. Available results on the mechanism of redox processes and examinations of chemo- and regioselectivity in addition reactions are presented and, where possible, analyzed in relation to established bioactivities. Most of the bioactivity examinations are concerned with antitumor activities and the mechanism thereof, such as DNA damage, arylation of nucleophiles, tubulin assembly inhibition, protein kinase inhibition, inhibition of the arachidonic cascade, etc. Perspectives on marine drug development are discussed with respect to biotechnological methods and synthesis. Examples of the recognition of validated core structures and synthesis of structurally simplified compounds retaining modes of activity are analyzed.

Potential antipsoriatic avarol derivatives as antioxidants and inhibitors of PGE(2) generation and proliferation in the HaCaT cell line

The synthesis and structure-activity relationships for a series of 14 new avarol derivatives as antioxidants and inhibitors of cell proliferation and PGE(2) generation in human keratinocytes are described. Compound 6 (thiosalicylic derivative) was the most potent inhibitor of superoxide generation in human neutrophils and also potently inhibited PGE(2) generation in the human keratinocyte HaCaT cell line. Compound 7(3'-methylaminoavarone) presented the best antiproliferative profile, by the inhibition of (3)H-thymidine incorporation in HaCaT cells, with potency similar to the reference compound anthralin. None of the avarol derivatives showed any sign of cytotoxicity measured as LDH release in treated keratinocytes. The potency and pharmacological profile of derivatives are also discussed.

New selective cytotoxic diterpenylquinones and diterpenylhydroquinones

A new series of diterpenylquinone/hydroquinones has been prepared by Diels-Alder cycloaddition between three labdanic diterpenoids (myrceocommunic acid, methyl myrceocommunate, and myrceocommunyl acetate) and p-benzoquinone or 1,4-naphthoquinone. Influences of the quinone/hydroquinone fragment and other structural features, such as the different functionalities in the terpenic core, are considered in relation to the cytotoxicity toward neoplastic cells and the selectivity of these diterpenylnaphthoquinones/hydroquinones and anthraquinones. Several compounds showed IC50 values under the micromolar level, and four of these derivatives were evaluated at the NCI screening panel. The results showed an important selectivity toward renal cancer lines, identifying these compounds as a very promising group of antineoplastics.

Avarol and avarone, two new anti-inflammatory agents of marine origin

The anti-inflammatory activity of avarol and avarone, sesquiterpenoid derivatives from the Mediterranean sponge Dysidea avara, was investigated. Both compounds potently inhibited paw oedema induced by carrageenan (approximated ED50 = 9.2 and 4.6 mg/kg, p.o., respectively) as well as ear oedema induced by 12-O-tetradecanoylphorbol acetate (TPA; ED50 = 97 and 397 micrograms/ear, respectively) in mice, with effects comparable to those of indomethacin. In A23187-stimulated rat peritoneal leukocytes, avarol showed an IC50 = 0.6 and 1.4 microM for inhibition of leukotriene B4 and thromboxane B2 release, respectively, with avarone showing a slightly lower potency. Both marine metabolites failed to show xanthine oxidase inhibitory activity or superoxide scavenging effects but were potent inhibitors of superoxide generation in rat peritoneal leukocytes activated by different stimuli, with an IC50 below the microM range. Only avarol was able to inhibit human recombinant synovial phospholipase A2 activity with an IC50 = 158 microM, and thus this compound showed a potency higher than that of mepacrine. Avarol and avarone effectively control acute inflammation in experimental models after either oral or topical administration and their anti-inflammatory activity may result from inhibition of eicosanoid release and depression of superoxide generation in leukocytes.

Arylation of sulfhydryl groups in vitro by the naturally occurring sesquiterpenoid benzoquinone avarone

Avarone (AQ) is a naturally occurring sesquiterpenoid benzoquinone possessing antileukaemic activity. Its reactivity towards glutathione (GSH) and protein sulfhydryl (SH) groups was investigated. The stoichiometry of AQ reaction with GSH at [GSH]/[AQ] ratios lower than unity proved to be 1:2 (thiol:quinone), consistent with the formation of the corresponding hydroquinone (avarol) as well as a quinone-thioether in the reaction. Conversely, when the [GSH]/[AG] ratio was higher than unity, a hydroquinone-thioether was the only reaction product. AQ/protein interaction was also investigated by using bovine serum albumin (BSA) as model compound. As observed with GSH, arylation rather than oxidation of SH groups appeared to be the mechanism responsible for the AQ-induced depletion of protein SH groups. However, AQ proved to be less effective in depleting BSA sulfhydryls than that of GSH. AQ disappearance after BSA addition was greater than expected on the basis of the total SH groups depleted, if a stoichiometric ratio 1:2 (thiol:quinone) was assumed. It also occurred in the presence of BSA with blocked SH groups, thus suggesting that AQ may react with other nucleophilic protein residues, such as amino or imino groups. When HepG2 cells were exposed to AQ, depletion of both protein SH groups and GSH occurred. However, in contrast to the above, AQ proved to be more effective, probably because of its lipophilic nature, in depleting protein SH groups than GSH. Also, in intact cells AQ appeared to arylate both SH and other nucleophilic groups in proteins. This mechanism may play a major role in AQ-induced cytotoxicity.