Marine Sponges as a Drug Treasure

Abstract

Marine sponges have been considered as a drug treasure house with respect to great potential regarding their secondary metabolites. Most of the studies have been conducted on sponge’s derived compounds to examine its pharmacological properties. Such compounds proved to have antibacterial, antiviral, antifungal, antimalarial, antitumor, immunosuppressive, and cardiovascular activity. Although, the mode of action of many compounds by which they interfere with human pathogenesis have not been clear till now, in this review not only the capability of the medicinal substances have been examined in vitro and in vivo against serious pathogenic microbes but, the mode of actions of medicinal compounds were explained with diagrammatic illustrations. This knowledge is one of the basic components to be known especially for transforming medicinal molecules to medicines. Sponges produce a different kind of chemical substances with numerous carbon skeletons, which have been found to be the main component interfering with human pathogenesis at different sites. The fact that different diseases have the capability to fight at different sites inside the body can increase the chances to produce targeted medicines.

INTRODUCTION

Sponges are spineless animals belong to phylum, “the pore bearers” (Porifera), serve as most primitive multicelled animals, existing for millions of year ago. Marine sponges are soft bodied, sessile and filter feeders assembling small particles of food from sea water rising through their bodies (Hadas et al., 2009; Ramel, 2010). All over the world, marine sponges are the member of benthic communities of a marine environment, including its biomass as well as its ability to promote pelagic and benthic processes (Maldonado et al., 2005), also provide habitat for other organisms (Hultgren and Duffy, 2010). Marine life is a massive source for the synthesis of novel molecules and it need to be studied. According to evolutionary history, marine microorganisms are more diversified than terrestrial microorganisms. Marine sponges frequently produce bioactive compounds as compared to other living microorganisms. Because sponges cannot move and lack physical defenses, they are highly susceptible to marine predators such as fish, turtles, and invertebrates. Thus, it is not surprising that sponges have developed a wide suite of defensive chemicals to deter predators (Thomas et al., 2010). They also use their defensive chemicals to keep the offspring of small plants and animals (fouling organisms) from settling onto their outer surfaces (Mol et al., 2009; Hertiani et al., 2010). These sessile animals are a prolific source of a huge diversity of secondary metabolites that has been discovered over the past 50 years (Faulkner, 2002; Blunt et al., 2005; Laport et al., 2009; Hertiani et al., 2010; Proksch et al., 2010). The bioactive compounds are very diverse in both structure and bioactivity. The known species of sponges are more than 8000 (Van soest et al., 2014) widely distributed in sea and freshwater environment (Hooper and van Soest, 2002).

In the early 1950s, pharmaceutical interest among sponges have been started and it has started by the investigation of the nucleosides spongouridine and spongothymidine in the marine sponge i.e. Cryptotethya crypta (Bergmann and Feeney, 1950; 1951). These nucleosides were the basic root for the synthesis of ara-A, an antiviral drug and ara-C, the first marine-derived anticancer agent (Proksch et al., 2002). Currently, ara-C used in the treatment of lymphoma and leukemia, a part of this one of its fluorinated derivative also permitted for the treatment of lung, pancreatic (Momparler, 2013), breast and bladder cancer (Schwartsmann, 2000). On the other hand, it also been revealed that lower invertebrates have more lipid components such as sterols, fatty acids and other unsaponifiable elements as compared to vertebrate animals (Bergmann and Swift, 1951; Piel, 2004). Up till now approximately 20,000 bioactive compounds have been found in marine organisms (Hu et al., 2011). However, most of these biologically active compounds, which are predominantly terpenoids and alkaloids, have been isolated from sponges (Leal et al., 2012). Regarding the diversity of marine compounds, sponges are the most important producer. Every year around 5300 different natural products and new compounds have been isolated from marine sponges (Faulkner, 2000; 2001; 2002). Sponges are most abundantly produce novel compounds, including more than 200 novel metabolites, every year (Blunt et al., 2006; Turk et al., 2013). About 300 novel compounds were reported in 2011 from the phylum Porifera (Blunt et al., 2013). Moreover, some of the sponge-derived substances are however in a process of a clinical and pre-clinical trial (e.g., as anti-inflammatory or anticancer agents) in comparison of those substances that derived from different marine phylum (Blunt et al., 2005: Martins et al., 2014).

Sponge-derived or other marine microorganism’s associated bioactive substances have possessed antibacterial, antiviral, antifungal, antimalarial, anthelminthic, immunosuppressive, muscle relaxants and anti-inflammatory activities. Sponge substances have remarkable chemical diversity. A part of uncommon nucleosides, marine sponges also able to produce other classes of amino acid derivatives including cyclic peptides, alkaloids, sterols, terpenes, fatty acids, peroxides, etc. (Fig. 1) (Donia and Hamann, 2003; Blunt et al., 2005, 2006; Sipkema et al., 2005; Piel, 2006). Although few representatives from sponges are approved as drugs, hundreds of new compounds with interesting pharmacological activities are discovered from sponges every year. Several sponge-derived compounds are already in clinical trials as agents against cancer, microbial infections, inflammation and other diseases. However, in many cases drug development is severely hampered by the limited supply of the respective compounds, as they are often present only in minute amounts in the sponge tissue. These reasons have moved the pharmaceutical drug discovery programs away from natural products in favor of synthetic approaches. However, the abundance of synthetic compounds with similar chemical functional groups and, therefore, limited chemical diversity has renewed interest in nature as a good resource for finding new fascinating leads to be applied to design the next generation of drugs.

Fig. 1.

The chemical structure of sponge derived molecules. (A) Xestospongin C (Xestospongia sp./macrocyclic bis-oxaquinolizidine. (B) Ara-A (Cryptotethia crypta/unusal nucleoside). (C) Contignasterol (Petrosia contignata/oxygenated sterol). (D) Jaspamide (Hemiastrella minor/macrocyclic lactam/lactone). (E) Manolide (Sesterterpenoids/Luffariella variabilis sp). (F) Agelasphin (Agelas mauritianus/agalactosy-ceramide).

In most cases development and production of sponge-derived drugs is hindered by environmental concerns and technical problems associated with harvesting large amounts of sponges. The presence of possibly producing microbial symbionts is therefore especially intriguing, as a sustainable source of sponge-derived drug candidates could be generated by establishing a symbiont culture or by transferring its biosynthetic genes into culturable bacteria. For example, Manzamine alkaloids, the promising leads for extended preclinical assessment against malaria, tuberculosis and HIV, have been previously isolated from sponge Acanthostrongylophora sp. and have also been isolated from the associated microorganism Micromonospora sp. (Hill et al., 2005). A dinoflagellate Prorocentrum lima produces okadaic acid (Morton et al., 1998), first isolated from the host sponge Halichondria okadai (Kobayashi and Ishibashi, 1993). A Vibrio sp. produces peptide, andrimid and brominated biphenyl ethers (Maria et al., 2011) that was purified from the sponge Hyatella sp. extract (Oclarit et al., 1994) and sponge Dysidea sp. (Elyakov et al., 1991).Thus, the microbial association that occurs on or in sponges could be of great interest as a solution of the supply problem of most of pharmaceutical compounds produced by sponges.

Therefore, the main focus of this review is to highlight the survey of discoveries of products derived from marine sponges which displayed in vivo potency or effective in vitro activity against infectious and parasitic diseases, including protozoal, bacterial, fungal and viral infections and their mode of action by which they interpose with the pathogenesis of human diseases. The knowledge of mechanisms of actions is very necessary for the development of the drug from a bioactive compound. For example, many secondary metabolites inhibit the growth of cancer cell lines or show the highest degree of antibiosis activity, but they do not prove that they are fit as anti-cancer or anti-microbial agents because they may exhibit severe adverse effects. Our objective was to highlight the compounds by disease type, their mode of action and the greatest potential to drive towards clinically useful treatments.

ANTIBACTERIAL ACTIVITY

At the beginning of the twenty century, the first antibiotics detection left the scientific and social society untrained, when the antibiotic-resistant bacteria emerged. This antibiotic-resistance bacterium has multiplied very swiftly and creates a considerable problem while both Staphylococcus aureus and some pathogenic bacteria are involved in causing the infections. According to Davies and Davies (Rice, 2006), lately vancomycin became ineffective to cure the infections caused by methicillin-resistant S. aureus (MRSA). The importance of drug-resistant bacterial infection has produced an imperative requirement for the quick and sustained development of new antibiotics classes, which may keep pace with the varying face of bacterial antibiotic vulnerability. Therefore, the first precedence of a biochemical research community is the innovation and improvement of new antibiotics.

The marine sponges crude extracts exhibited a low level of anti-bacterial activity against marine bacteria while a high level of antibacterial activity was exhibited against terrestrial bacteria (Amade et al., 1982; 1987; McCaffrey and Endeau, 1985; Uriz et al., 1992; Xue et al., 2004). The antimicrobial screenings of crude extracts from 101 Arctic sponges against bacteria associated with opportunistic infections showed that about 10% of the sponges yielded significant antimicrobial activities, with IC50 values from 0.2 to 5 μg/mL (Turk et al., 2013). In every year, some new molecules containing antibiotic properties are introduced, but in marine sponges, their ubiquity is on the top.

After an early screening test by Burkholder and Xue (Burkholder and Ruetzler, 1969; Xue et al., 2004), it was noted that 18 sponges out of 31 exhibited antibacterial effect while some of them were very strong against Gram-positive and Gram-negative bacteria. It was observed that marine sponges screening test for an antibacterial activity directed to both the isolation and characterization of a wide range of active substances, containing some promising therapeutic (Mayer and Hamann, 2004; Moura et al., 2006; Mayer et al., 2011). Marine sponges produced up to 800 antibiotic substances (Torres et al., 2002), while some other antibacterial agents have also been identified from sponges by marine natural products community. However, no antibacterial product was reported yet in the discovered marine natural product but many of them are under investigation in current research. More or less isolated marine sponges substances with antibacterial activity are shown in (Table 1). Manoalide, one of the first sesterterpenoids to be isolated from a marine sponge Luffariella variabilis, was found to be an antibiotic (Fig. 1) (de Silva and Scheuer, 1980). This is the only example of antibiotic sesterterpenoid discovered so far.

Table 1.

Examples of antibacterial compounds

Substance	Chemistry	Species	Activity Spectrum	MIC Value	References
Discodermins B, C and D	Cyclic peptide	Discodermia kiiensis/Lithistida	Antibacterial (B. subtilis)	3 μg/ml	Matsunaga et al., 1985
Arenosclerins A–C	Alkyl pepridine alkaloid	Arenosclera brasiliensis	S. aureus, P. aeruginosa, M. tuberculosis	16 μg/ml*, 30 μg/ml**	Torres et al., 2002
Haliclona cyclamine E	Alkylpiperidine alkaloids	Arenosclera brasiliensis	S. aureus, P. aeruginosa	8 μg/ml*	Torres et al., 2002
CvL	Lectine	Cliona varians	S. aureus, B. subtilis	16 μg/ml*	Moura et al., 2006
Axinellamines B–D	Imidazo-azolo-imidazole alkaloid	Axinella sp./Halichondrida	H. Pylori, M. Luteus	16.7 μg/ml***	Urban et al., 1999
Caminosides A–D	Glycolipids	Caminus sphaeroconia	E. coli, S. aureus	16 μg/ml*	Linington et al., 2006
6-hydroxymanzamine E	Alkaloid	Acanthostrongylophora sp.	M. tuberculosis	0.9 μg/ml**	Rao et al., 2004
Cribrostatin 3	Alkaloid	Cribrochalina sp.	N.gonorrheae (antibiotic resistant strain)	-	Petit and Knight, 2002
Cribrostatin 6	Alkaloid	Cribrochalina sp.	S. pneumoniae (anitibiotic resistant strain)	≤2	Pettit et al., 2004
Isojaspic acid, cacospongin D and jaspaquinol	Meroditerpenes	Cacospongia sp.	S. epidermidis	20 μg/ml	Rubio et al., 2007
Isoaaptamine	Alkaloid	Aaaptos aaptos	S. aureus	3.7 μg/ml	Jang et al., 2007
(−)-Microcionin-1	Terpenoid	Fasciospongia sp	M. Luteus	6 μg/ml	Gaspar et al., 2008

^*S. aureus

^**M. tuberculosis,

^***M. luetus

ANTIVIRAL ACTIVITY

The officially approved antiviral drug armamentarium for clinical use contains approximately 40 substances and most of them were discovered recently. It was reported that half of the recently discovered substances are used for the human immunodeficiency virus (HIV) infection treatment (De Clercq, 2004; Yasuhara-Bell and Lu, 2010). The significance of new antiviral agents development help to increase the number of available drugs becomes clear. It was observed that the adenovirus serotype 5 (AdV-5) is much constant in the environment for long time, and connected to respiratory infections with no special cure (Wiedbrauk and Johnston, 1992; Sipkema et al., 2005). There are some viruses such as rotaviruses, which are mainly responsible for sever gastroenteritis in human and animals. The treatment of diarrhea is only possible by symptomatic, which may cause the infection of children and immune compromised patients even it can lead to death (White and Fenner, 1986; Grimwood and Lambert, 2009).

Some new approaches being use to introduce new antiviral agents from marine sources and many promising therapeutic leads because sponges are one of the rich source of antiviral property compounds (Table 2). Maximum quantities of HIV-inhibiting compounds were introduced, while they do not reflect greater potential of sponges to fight against AIDS compared with other viral diseases. Researchers use screening techniques for anti-HIV activity has led to introducing of different compounds, although the system of inhibition is still not clear. It has been reported recently by many researchers that HIV-inhibiting compounds were produced by different sponges (Ford et al., 1999; Qureshi and Faulkner, 1999; Yasuhara-Bell and Lu, 2010; Sagar et al., 2010). For instance, avarol is a compound which inhibits the progression of HIV infection up to some extent. The data form in vitro experiment and animal show that avarol combines have very useful properties and increase humoral immune response (Muller et al., 1987; Amigó et al., 2007). HIV inhibits completely by avarol and blocking the production of natural UAG suppressor glutamine transfer tRNA. After viral infection, the production of tRNA is up-regulated, which is necessary for the viral protease and viral proliferation synthesis. The low Concentration of avarol 0.3 and 0.9 μM resulted in 50 and 80% of inhibition of virus released from infected cells (Muller et al., 1987). Moreover, the derivatives of avarol such as 6′-hydroxy avarol and 3′-hydroxy avarone were noted as very strong inhibitors of HIV reverse transcriptase (Fig. 2). Avarol play very important role during the early stages of HIV infection and it also has a specific target for antiviral drugs, while it convert the viral genomic RNA into pro-viral double-stranded DNA, and later on it integrated into the host chromosomal DNA (Loya and Hizi, 1990).

Table 2.

Examples of antiviral compounds

Substances	Chemistry	Species	Action spectrum	References
4-Methylaaptamine	Alkaloid	Aaptos aaptos	Anti-viral (HSV-1)	Souza et al., 2007
Papuamides A–D	Cyclic depsipeptides	Theonella sp.	Anti-viral (HIV-1)	Ford et al., 1999
Ara-A	Nucleoside	Cryptotethya crypta	HSV-1, HSV-2, VZV	Faulkner, 2002
Avarol	Sesquiterpene hydroquinone	Dysidea avara	HIV-1,UAG suppressor Glutamine tRNA inhibitor	Muller et al., 1987
Haplosamates A and B	Sulfamated steroid	Xestospongia sp./Haplosclerida	Anti-viral (HIV-1Integrase inhibitor)	Qureshi and Faulkner, 1999
Dragmacidin F	Alkaloid	Halicortex sp.	HIV-1	Cutignano et al., 2000
Hamigeran B	Phenolic Macrolide	Hamigera tarangaensis	Anti-viral (herpes and polio virus)	Wellington et al., 2000
Mycalamide A–B	Nucleosides	Mycale sp.	A59 coronavirus, (HSV-1)	Perry et al., 1990
Mirabamides A, C and D	Peptide	Siliquariaspongia mirabilis	Antiviral (HIV-1)	Plaza et al., 2007
Oroidin	Alkaloid	Stylissa carteri	Antiviral (HIV-1)	O’Rourke et al., 2016

Fig. 2.

Molecular structures of avarol (a: R1 = H) and 6¢- hydroxy avarol (A: R1 = OH) and avarone (B: R1 = H) and 3¢- hydroxy avarone (B: R1 = OH).

Another important antiviral discovery from marine source reported is the nucleoside ara A (vidarabine) which was isolated from Cryptotethya crypta sponge and was first synthesized in 1960 (Walter, 2005). Ara-A is an arabinosyl nucleosides which inhibits viral DNA synthesis (Bergmann and Swift, 1951; Blunt et al., 2006; Sagar et al., 2010). Research proved that our biological systems can recognize nucleoside base just after sugar moiety modifications, then chemists started to replace the pentoses by acyclic entities or with sugar molecules, it lead to the development of azidothymidine (zidovudine) drug. An examples of semisynthetic arabinosyl nucleosides modification are Ara-A, acyclovir, ara-C (Fig. 1, 3) and azidothymidine are in clinical use (De Clercq et al., 2002; Sagar et al., 2010).

Fig. 3.

Molecular structure of Acyclovir and Ara-c (Acyclovir is a drug of choice for Herpes virus).

ANTIFUNGAL ACTIVITY

In the last decades, the fungal infection (especially invasive mycoses) dramatically increased in those individuals suffering from AIDS, immune depressants, hematological malignancies, and transplant recipients, increased the need of new antifungals (García-Ruiz et al., 2004; Pontón et al., 2000). Fungal infection remains a major direct cause of death for those patients who are treated for malignant disease (Sandven, 2000; Ellis et al., 2000). Fungal causing malignant diseases are a major cause of life threatening diseases as well as resistance to them is a major problem (García-Ruiz et al., 2004; Giusiano et al., 2004; Walsh et al., 2004; Giusiano et al., 2005). Immunocompromised patients are mainly infected by Candida, Aspergillus, Cryptococcus and other opportunistic fungi. Currently using fungicides are less diversified than antimicrobial substances and their use is restricted because of biological system toxicity (Rahden-Staron, 2002).

Jaspamide is the first example of cyclodepsipeptide 19-membered macrocyclic depsipeptide (Fig. 1) isolated from the sponges Jaspis sp has a selective in vitro antifungal activity with MIC of 25 μg/ml against C. albicans while in vivo topical activity of a 2% solution against Candida vaginal infection in mice (Zabriskie et al., 1986; Ebada et al., 2009). The other examples of important antifungals examined in vitro with MIC values have been listed (Table 3).

Table 3.

Examples of antiviral compounds

Substances	Chemistry	Species	Action spectrum	MIC value	References
Jaspamide	Macrocyclic depsipeptide	Jaspis sp	C.albicans	25 μg/ml*	Zabriskie et al., 1986
Eurysterols A–B	Sterols	Euryspongia sp	C.albicans, Amphoterician B-resistant	62.5 μg/ml*, 15.6 μg/ml	Boonlarppradab and Faulkner, 2007
Naamine D	Imidazole alkaloid	Leucetta cf. chagosensis	C.neoformans	6.25 μg/ml**	Dunbar et al., 2000
Mirabilin B	Tricyclic guanidine alkaloid	Monanchora unguifera	C.neoformans	7.0 μg/ml**	Hua et al., 2004
Hamacanthin A	Indole alkaloid	Spongosorities sp.	C.albicans	6.25 μg/ml*	Oh et al., 2006
Macanthins A–B	Indole alkaloid	Spongosorities sp.	C.albicans, C.neoformans	1.6 μg/ml*, 6.2 μg/ml**	Oh et al., 2006
Agelasines and agelasimines	Purine derivative	Agelas sp.	C.krusei	15.6 μg/ml	Vik et al., 2007

MIC: Minimum Inhibitory Concentration,

^*C. albicans,

^**C. neoformans.

ANTIMALARIAL PROPERTIRES

In sub- Saharan Africa, malaria is a predominant disease including that it is also serious public health problem in some areas of South America and Southeast Asia. Most of the malaria related deaths are caused by Plasmodium falciparum parasite (Mishra et al., 1999; Caraballo and King, 2014; WHO, 2015). Recently, most widely disseminated malarial species all over the world is Plasmodium vivax. P. vivax is the predominant specie in the Asia and America, while in Brazil this species represents around 80% of clinical issue annually (Brazilian Health Ministry, 2002). Sub-Saharan Africa carries a disproportionately high share of the global malaria burden. In 2015, the region was home to 88% of malaria cases and 90% of malaria deaths (Baird, 2013; WHO, 2015). During last decades, some of the antimicrobial compounds have been derived from sponges (Table 4, Fig. 4). Increasing resistance among Plasmodium strains created a need to discover new antimalarial compounds. Plasmodium falciparum has become resistant toward chloroquinone, pyrimethamine, and sulfadoxine (Bwijo et al., 2003). In vitro, selective antimalarial activity against Plasmodium falciparum has been recorded by different isonitrilese, isothiocyanates and terpenoid isocyanates from Cymbastela hooperi (Konig et al., 1996). Including that a number of free carboxylic acids (Diacarnus levii) after esterification were used as precursors to synthesize some new cyclic norditerpene peroxides. These epidioxy-substituted norsesterterpenes and norditerpenes endoperoxides from marine sponge Diacarnus megaspinorhabdosa showed antimalarial activity against both chloroquine-resistant P. falciparum and chloroquine-sensitive (D Ambrosio et al., 1998; Yang et al., 2014).

Table 4.

Examples of anti-malarial compounds

Substances	Chemistry	Species	Action spectrum	IC50 value	References
Monamphilectine A	Antimalarial β-lactam	Hymeniacidon sp	P. falciparum	0.6 μM***	Avilés and Rodriguez, 2010
Manzamine A	Alkaloids	e.g., Haliclona sp./ Haplosclerida Cymbastela hooperi/Halichondrida Diacarnus levii/Poecilosclerida	T. gondii, P. berghei, P. falciparum	4.5 ng/ml***	D Ambrosio et al., 1998
Kalihinol A	Isonitril-containing kalihinane diterpenoid	Acanthella sp./Halichondrida	P. falciparum	0.0005 μg/ml**	Ang et al., 2001
Diisocyanoadociane	Tetracyclic diterpene	Cymbastela hooperi	P. falciparum	0.005 μg/ml**	Miyaoka et al., 1998
Halichondramide	Macrolides		P. falciparum	0.002 μg/ml**	Konig et al., 1996
Sigmosceptrellin-B	Norsesterterpene acid	Diacarnus erythraeanus	T. gondii, P. falciparum	1200 ng/ml*	Konig et al., 1996
(E)-Oroidin	Alkaloids	Agelas oroides	P. falciparum	0.30 μg/ml**	Yousaf et al., 2002
Plakortin and dihydroplakortin	Cycloperoxidase	Plakortis simplex	P. falciparum	1263-1117 nM*	Tasdemir et al., 2007

IC₅₀: Inhibitory Concentration,

^*P. falciparum (D10),

^**P. falciparum (D6 clone),

^***Chloroquine-resistant P. falciparum (W2). [h] Fattorusso et al., 2002.

Fig. 4.

Structure of Antimalarial compounds; Manzamine A; Monamphilectine A; Kalihinol A.

The most capable and promising antimalarial compound, manzamines have been isolated from a number of sponges (Sakai et al., 1986; Yousaf et al., 2002; Fattorusso and Taglialatela, 2009). Manzamine A displayed a potent in vitro activity against P. falciparum (D6clone), with MIC of 0.0045 μg/ml (Sakai et al., 1986; Ashok et al., 2014). According to research antimalarial activity of manzamine A is due to enhancing immune response (Ang et al., 2001).

ANTI-INFLAMMATORY ACTIVITY

Body inflammation is caused by physical or chemical damage or due to infection. In this case, blood is oozing out from blood vessels into tissues (Tan et al., 1997; Franceschi and Campisi, 2014). Manolide is the first sesterterpenoids anti-inflammatory drug derived from marine sponges with several other pharmaceutical properties (Mayer and Jacobs, 1998). Its Anti-inflammatory action is basically an irreversible inhibition of the release of arachidonic acid from phospholipid membrane by the mechanism of preventing the phospholipase A2 enzyme from the binding to the membrane of phospholipid, the reason is that it increases the concentration of intracellular arachidonic acid that results in the upregulation of the inflammation mediators synthesis as a leukotrienes and prostaglandins. The Mode of action of sponge-derived anti-inflammatory substances has different from other non-steroidal anti-inflammatory drugs (NSAIDS). Only a few of sponge-derived substances have the capability to inhibit lipoxygenase, another enzyme which is involved in the inflammatory response (Carroll et al., 2001) (Fig. 5).

Fig. 5.

Diagrammatic process of Inflammatory cascade inside the cell. Phospholipase A2 (PLA2) catalyzes the release of membrane-bound arachidonic acid (AA) to free arachidonic acid. Arachidonic acid is then converted to leukotrienes and prostaglandins by lipoxygenase (LOX) and cyclooxygenase-2 (COX-2), respectively. Sponge derived anti-inflammatory substances are mainly inhibitors of PLA2 or LOX, while nonsteroidal anti-inflammatory drugs (NSAID) inhibit COX-2, but also the constitutive COX-1.

ANTITUMOR ACTIVITY

In the tumor development protein kinase C (PKC) is an essential factor (Bradshaw et al., 1993; Kang, 2014). Many of the sponge-derived substances are PKC inhibitors. Worldwide, PKC inhibitors have attracted interest because of providing evidence, that extreme levels of PKC enzymes are involved in the pathogenesis of psoriasis, arthritis and especially in the development of tumor (Bradshaw et al., 1993; Kang, 2014). PKC serve as a receptor for tumor-promoting phorbol esters by the binding prevention of carcinosarcoma cells with Endothelium (Liu et al., 1991; Kang, 2014).

Fucosyltransferase inhibitors, like octa and nonaprenylhydroquinone sulfates, which were derived from Sarcotragus sp. (Wakimoto et al., 1999), may be capable candidates for regulating inflammatory processes like arthritis or for opposing tumor growth.

There are many other sponge derived compounds having anti-tumor potency with different kind of mechanisms of actions (Table 5). These are divided into three types.

Table 5.

Examples of anti-tumor compounds

Compound	Chemistry	Species/order	Mode of action	References
Isoaaptamine	Benzonaphthyridine alkaloid	Aaptos aaptos/Hadromerida	Protein kinase C inhibitor	Fedoreev et al., 1988
Debromohymenialdisine	Pyrrole-guanidine alkaloid, prenylhydroquinone derivative	Hymeniacidonaldis/Halichondrida	Protein kinase C inhibitor	Kitagawa et al., 1983
Adociasulfates	Triterpenoid hydroquinones	Sarcotragus sp./ Dictyoceratida Haliclona (aka Adocia) sp./Haplosclerida	A1, 3-fucosyltransferase inhibitor Kinesin motor protein inhibitors	Zapolska-Downar et al., 2001
Discodermolide	Linear tetraene lactone	Discodermia dissolute/ Lithistida	Stabilization of microtubules	Ter Haar et al., 1996
Peloruside A	Macrocyclic lactone	Mycdle hentschett/ Poecilosclerida	Stabilization of microtubules	Hood et al., 2002
Elenic acid	Alkylphenol	Plakinastrella sp./ Homosclerophorida	Topoisomerase II inhibitor	Hood et al., 2002
Naamine D	Imidazole alkaloid	Leucetta cf. chagosensis	Nitric oxide synthetase inhibitor	Juagdan et al., 1995
Agelasphin (KRN7000)	a-Galactosylceramide	Agelas mauritianus / Agelasida	NKT cell activator	Shimosaka, 2002
Crambescidins 1–4	Pentacyclic guanidine derivative	Crambe crambe/Poecilosclerida	Ca2+/channel blocker	Jares-Erijman et al., 1991
Discorhabdin D	Fused pyrrolophenanthroline alkaloid	Latrunculia brevis/Poecilosclerida; Prianos sp./Haplosclerida	Unknown	Perry et al., 1990
Glaciasterols A and B	9, 11-Secosterol	Aplysilla glacialis/Dendroceratida	Unknown	Pika et al., 1992
Durumolides A–C	Terpenoid	Lobophytum duru	Inducible NOS and COX-2 inhibition	Cheng et al., 2008
Plakortide P	Polyketide	Plakortis angulospiculatus	TXB2 inhibition	Kossuga et al., 2008
24-methoxypetrosaspongia C	Sesterterpenes	Hyrtios erectus	Unknown	Elhady et al., 2016

Non-specific inhibitors

Nonspecific anti-tumor inhibitors are important compounds to treat cancer but in unusual conditions because these compounds also have toxic effects on healthy cells of a body. Example is adociasulfates (titerpenoid hydroquinones), isolated from Haticlona sp. Etc (Blackburn et al., 1999; Zapolska-Downar et al., 2001) and they are protein inhibitors by binding to microtubule binding site “locking up” protein motor function and there by blocking cell division.

Specific inhibitors

Specific inhibitors are specifically active against the tumor. For example, agosterol A derived from marine spongia can reverse the over appearance of membrane glycoproteins. These proteins are responsible for multidrug resistance in human carcinoma cells. Another example belongs to these inhibitors group is salicylihamide A. The first natural isolated from cinachyrella spp. is 6- hydroximino-4-en-3 (Griffith and Gross, 1996).

Inhibitors of a cancer cell of certain types

Growth inhibitory active compounds against tumor cell line have been isolated but its mechanism of action is still unknown. For example Discorhabdin D (Perry et al., 1990) etc.

IMMUNE SUPPRESSIVE ACTIVITY

Nitric oxide synthetase inhibitors, as anti-cancer agents are also responsible for the immune system suppression by downregulating the T-cells (Griffith and Gross, 1996). The ratio of Immune system suppression is very highly desired in case of hypersensitivity to antigens (e.g. allergies) medicines or organ transplantations. The cases in which patients receive any donor organ have to persist on life-long medication to prevent rejection by the body immune system as a foreign agent, and for that reasons, it is very important that these medicines should be specific suppressors. To prevent this autoimmune body defensive response and rejection of the donor organ, therefore, now it is a very crucial need for new specific immunosuppressors. A number of new biomolecules with strong immunosuppressive activities, which interfere at different sites of the immune response system have been discovered in marine sponges.

Dysidea sp have a large contribution in the portion of biomolecules (Mayer et al., 2000; 2004; 2011). 3 polyoxygenated sterols derived from Dysidea sp. in North Australia having a strong selective immunosuppressive capability of blocking the binding of interleukin 8 (IL-8), a cytokine that attracts neutrophil into tissue injury site, to the IL-8 receptor (de Almeida Leone et al., 2000). Thus, these polyoxygenated sterols have a specific selective inhibition on primary immune response (Fig. 6). Correspondingly, Pateamine A derived from Mycale sp., are the selective inhibitors of the production of interleukin 2 (IL-2), IL-2 helps in activation of B cells and T resting cells leading to cause antigen-antibody reaction and produce Secondary immune response.(Romo et al., 1998; Pattenden et al., 2004). Some examples for these suppressants are mentioned in Table 6, Fig. 6.

Fig. 6.

Diagrammatic representation of body immune response towards antigen capturing by Macrophages. The macrophages and T-helper cells secrete many interleukins (IL-x) or macrophage activation factor (MAF), to trigger primary immune response with the help of neutrophils, or the secondary immune response by activating the B and resting T-cells. The activated B cells secrete antibodies which bind to macrophages that already have phagocytized an antigen, and then killed by T-killer cells. The sign shows the sponge derived substances.

Table 6.

Examples of immunosuppressive compounds

Compounds	Chemistry	Species/ order	Mode of action	References
Simplexides	Glycolopids	Plakortis simplex/Homosclerophorida	Inhibitors of T cell proliferation	Costantino et al., 1999
Polyoxygenated sterols	Sterol	Dysidea sp./Dendroceratida	IL 8 inhibitor	de Almeida Leone et al., 2000
Contignasterol	Oxygenated sterol	Petrosia contignata/Haplosclerida	Histamine release inhibitor	Takei et al., 1994
Pateamine A	Thiazole macrolide	Mycale sp./Poecilosclerida	IL-2 inhibitor	Northcote et al., 1991
Iso-iantheran A	Polyketide	Ianthella quadrangulata	Ionotropic P2Y11 receptor activation	Greve et al., 2007

CARDIOVASCULAR AGENTS

Some of the very common blood-related diseases like diabetes, thrombosis, atherosclerosis etc. have been treated by some marine sponge’s derived substances (Table 7, Fig. 7). The mechanism of blood coagulation is managed by a complex photolytic cascade that leads to the production of fibrin. Fibrin, a major component responsible for blood coagulation has been generated by the peptide cleaving of fibrinogen by thrombin (Kołodziejczyk and Ponczek, 2013). Cyclotheonamide A, isolated from marine sponges Theonella sp (Maryanoff et al., 1993) is an unusual class of Serine protease (an enzyme responsible for the conversion of fibrinogen into fibrin) inhibitor and is a drug of choice for thrombosis (Maryanoff et al., 1993; Schaschke and Sommerhoff, 2010). Eryloside F derived from Eryltus formosus sp. was found to be a potent Thrombin-receptor antagonist (Shuman et al., 1993; Stead et al., 2000; Kalinin et al., 2012). Thrombin receptor plays a central role not only in thrombosis but also the main agent to cause atherosclerosis (Fig. 7) (Chackalamannil, 2001; Ikenaga et al., 2016). Atherosclerosis is a disease in which plaque (fats, cholesterol, and calcium etc.) builds up layer by layer inside the arteries and resulting by narrowing of the arteries, causing a barrier to blood circulation leading to serious problems including heart attack, stroke or maybe death (Zapolska-Downar et al., 2001; Ikenaga et al., 2016).

Table 7.

Cardiovascular compound examples

Compounds	Chemistry	Species/ order	Mode of action	References
Cyclotheonamide A	Cyclic pentapeptide	Theonella sp./Lithistida	Serine protease inhibitor	Maryanoff et al., 1993
Eryloside F	Penasterol disaccharide	Eryltus formosus/Astrophorida	Thrombin receptor antagonist	Stead et al., 2000
Halichlorine	Cyclic aza Polyketide	Halichondria okadai/Halichondria	VCAM 1* inhibitor	Arimoto et al., 1998

^*VCAM: vascular cell adhesion molecule.

Fig. 7.

Blood coagulation (Thrombosis) and atherosclerosis (arterial disease characterized by the deposition of plaques of fatty material on their inner walls) pathway in vivo showing central role played by Thrombin. X111 represent fibrin stabilizing factor (enzyme responsible for blood coagulation). The Sign shows the sponge derived compounds.

ANTIHELMINTHIC ACTIVITY

A new macrocyclic polyketide lactam tetramic acid, geodin A Magnesium salt, isolated from the marine sponge Geodia sp. exhibited a remarkable nematocidal activity with (LD99=14 μg/ml) against Haemonchus contortus (Capon et al., 1999). The mode of action of the pure Geodin A is not explored yet. Two more studies contributed to the search of novel anthelmintic marine sponge derived products during 2005–6. Two novel alkaloidal betaines (−)-echinobetaine A (1) and (+)-echinobetaine B (2), isolated from marine sponge Echinodictyum sp proved to be a nematocidal with (LD99=83 and 8.3 μg/ mL, respectively) against commercial livestock parasite Haemonchus contortus (Capon et al., 2005). Unfortunately, the mode of action of these compounds was also undetermined. (+)-echinobetaine B’s nematocidal potency was comparable to that of “two commercially available synthetic anthelmintic, closantel and levamisole” (Capon et al., 2005).

MUSCLE RELAXANT

Continuous muscles activation caused by disturbances in the neuromuscular communication that result in muscular stress (Lundberg et al., 1995; Edgar et al., 2002; Hibbs and Zambon, 2011). Muscle relaxants are divided into two parts; centrally and peripherally active. Centrally active can mediate neuromuscular communication while peripherally relaxants are used for local muscle relaxation like stroke or during surgery (Frakes, 2001; Hibbs and Zambon, 2011) Xestospongin C (Fig. 1) isolated from marine sponge Xestospongia sp is a potent α-receptor’s IP₃ (Inositol triphosphate) inhibitor and Ca²⁺ (calcium channel) blocker (Quinn et al., 1980; Gafni et al., 1997; Miyamoto et al., 2000). IP₃ is a secondary messenger molecule used in signal transduction and it diffuses throughout the cell and increases the Ca²⁺ level and resulting cause’s smooth muscles contraction (Fig. 8) (Quinn et al., 1980; Nausch et al., 2010). S1319 isolated from a Dysidea sp. (Suzuki et al., 1999) is another substance with a remarkable muscle relaxing capability. Its mechanism of action is to agonist the β-Adrenoreceptor. β-Adrenoreceptors are of two types β-1 and β-2. β-1 receptors are available in heart increases heart rate, myocardial contractility and increases conduction velocity while β-2 receptors are available in lungs and uterus responsible for dilation of bronchial smooth muscles, dilation of blood vessels in skeletal smooth muscles and relaxation of uterus muscles (Dennedy et al., 2002; Barrese and Taglialatela, 2013). S1319 have the uterus relaxing capability which can be therapeutically used at infant’s delivery time (Dennedy et al., 2002) and bronchodilation property which can be used as antiasthmatic (Suzuki et al., 1999). However, because of their low selectivity, they have some side effects like activation of β-1 receptors resulting arterial hypertension, tachycardia and coronary heart disease (Borchard, 1998). Therefore, there is a desired continued research in interest to find selective β-agonists.

Fig. 8.

The mechanism of adrenergic receptors. A represent α-receptors and trigger the IP₃ (Inositol triphosphate) which then increase the Ca²⁺ level in cytoplasm and causing muscles contraction. B represents β-adrenoreceptors. The represents Marine compounds. Xestospongin C inhibit the phospholipase enzyme which play a key role in activation of IP₃ (Inositol triphosphate) and block Ca²⁺ channels. S1319 B-2 receptor agonist resulting Bronchodilation and uterus relaxation.

CONCLUSION

Sponge-derived substances span a wide range of chemistry (e.g., alkaloid, peptide, terpenoid and polyketides) with an equally variety of biotechnological properties (e.g., Antibacterial, antifungal, antiviral, immunosuppressive, cardiovascular and anti-parasitic) (Ang et al., 2001; Torres et al., 2002). The relationship between the chemistry of the secondary metabolites originated from marine sponges and their mode of action on disease in vivo is mostly not obvious (interaction with DNA to combat tumors, or inhibition of α/β receptors to provide muscle relaxation). Moreover, in drug discovery, it is frequently observed that a certain series of compounds that exhibited the most potent inhibitors in vitro turned out not to be the drug of choice in vivo. It is likely that for every compound prior to coming out to the market, its profile should be with a distinct chemistry, improved bioavailability with lesser side effects.

Now, there are some significant reports of activities from a particular class of metabolites, the manzamines from marine sponges as potential drugs that might be effective against HIV (Muller et al., 1987), malaria (Konig et al., 1996), tuberculosis (Schwartsmann, 2000) and some other diseases. Other substances with best anti-pathogenic profiles like ara-A, ara-C, acyclovir are in clinical use and are all examples of products originated from marine sponges (Muller et al., 1987).

The potency of sponge-derived medicines lies in the fact that each of these thousands of metabolites and their derivatives has its own specific dose-related efficacy, inhibitory effect, and potential side effects that determine its suitability for medicinal use. Unfortunately, these secondary metabolites are usually present in very trace amounts, and natural stocks are too small which is one of the major obstacles in sustaining the development of widely available medicines. An example is avarol (D.avara sponge), a potent anti-HIV drug (Muller et al., 1987), that was in preclinical assessment. However, further studies on this natural product stopped due to an insufficient amount of sponge for its isolation (Müller et al., 2004). In addition, the active core or skeleton of these compounds may be used as a vehicle to generate derivatives with their own distinct efficacy and side effects. Therefore, the most significant challenge in the transformation of bioactive molecules into medicines is now to screen the drug treasure house of sponges and elect those that illustrate a precise mode of action with the desired characteristics towards a disease. A major question for the future still persists, how to actually prepare the potential novel drugs in a bulk quantity.