Nat. Prod. Bioprospect. DOI 10.1007/s13659-016-0115-5 REVIEW Natural Products Diversity of Marine Ascidians (Tunicates; Ascidiacea) and Successful Drugs in Clinical Development Satheesh Kumar Palanisamy . N. M. Rajendran . Angela Marino Received: 19 November 2016 / Accepted: 14 December 2016 Ó The Author(s) 2017. This article is published with open access at Springerlink.com Abstract This present study reviewed the chemical diversity of marine ascidians and their pharmacological applications, challenges and recent developments in marine drug discovery reported during 1994–2014, highlighting the structural activity of compounds produced by these specimens. Till date only 5% of living ascidian species were studied from\3000 species, this study represented from family didemnidae (32%), polyclinidae (22%), styelidae and polycitoridae (11–12%) exhibiting the highest number of promising MNPs. Close to 580 compound structures are here discussed in terms of their occurrence, structural type and reported biological activity. Anti-cancer drugs are the main area of interest in the screening of MNPs from ascidians (64%), followed by anti-malarial (6%) and remaining others. FDA approved ascidian compounds mechanism of action along with other compounds status of clinical trials (phase 1 to phase 3) are discussed here in. This review highlights recent developments in the area of natural products chemistry and biotechnological approaches are emphasized. Keywords Cancer Á Cytotoxicity Á Diversity Á Metabolites Á Pharmacology 1 Introduction from marine invertebrates, especially sponges, ascidians, bryozoans and molluscs in which some of them are The study of marine natural products (MNPs) is becoming approved by FDA and currently utilized in clinical trials ever more sophisticated and an increasingly collaborative [1]. effort between marine biologist, chemist and pharmacolo- Ascidians or sea squirts (Phylum: Chordata, Class: gist, which involves the discovery of new natural products Ascidiacea) are also known as tunicates due to their to enter preclinical studies and clinical tests. Since the external covering, found tied to rocks and high-current 1990s, several MNPs and their applications towards marine fields. There are approximately 3000 living species of biotechnological and therapeutical potential were reported. ascidians were reported [2]. The production of chemical Large numbers of bioactive compounds were dragged up compounds is principally important for soft bodied ascid- ian species, which use secondary metabolites to deter predatory fishes, to compete for space, to control settlement S. K. Palanisamy (&) Á A. Marino and growth of microbial fauna and other fouling organisms. Department of Chemical, Biological, Pharmaceutical and Ascidians represent the most highly evolved group of Environmental Science, University of Messina, 98166 Messina, Italy marine organisms commonly investigated for identification e-mail: [email protected] of MNPs and provide rich sources of bioactive secondary metabolite with promising potential biomedical applica- N. M. Rajendran tions [3–5]. So far a few novel compounds have been Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, purified and characterized with a view of developing Chinese Academy of Sciences, Beijing 100190, China marine drug discovery. However, the most well known 123 S. K. Palanisamy et al. didemnins has been isolated from whole body homogenates of promising MNPs (Fig. 1). The distribution of chemistry of Caribbean ascidians belonging to the genus of Tridide- class of ascidian MNPs are given in (Fig. 2). Close to 580 nium sp. [6]. More than 80% of new ascidians compounds compound structures are here discussed in terms of their contain nitrogen, and nearly 70% of nitrogenous metabo- occurrence, structural type and reported biological activity. lites are alkaloids [7–9]. These compounds often exhibit a Anti-cancer drugs are the main area of interest in the range of biological activities such as cytotoxicity, antibi- screening of MNPs from ascidians (64%), followed by otic, immunosuppressive activities, inhibition of topoiso- anti-malarial (6%) and remaining others (Fig. 3). The merases and cyclin kinases [10]. On the other hand, non- National Cancer Institute-United states estimate that nitrogenous metabolites are fewer available in ascidians approximately 1% of MNPs showing anti-tumor cytotoxi- and also less significant. Hence, identification of the bio- city properties as against only 0.01% amongst their ter- genetic origin of ascidian natural products is often chal- restrial counterparts. Accordingly, finding MNPs research lenging [11]. The first bioactive metabolite geranyl must being continued to progress to improve existing hydroquinone was isolated from the ascidian Aplidium sp. therapies and to develop novel cures. [12]; only 230 metabolites were isolated from ascidians This review focuses on the chemical diversity of marine during 1974–1992 [3]. ascidians. The recent research on MNPs has been surveyed at At that time, a wide-ranging attention has focused on relatively frequent intervals [4, 5, 9, 13]. Davidson [3] was ascidians because of their biologically active metabolites published the first review on secondary metabolites derived and the chemical diversity of ascidians has become one of ascidians from 1988 to 1993. Additionally, in contrast to the the most significant sources of MNPs. It has been review of ascidian metabolites, the present study provides demonstrated that marine ecosystems are essential pro- complete list of the compounds with biological activities; the ducers of unusual chemical compounds and potent bioac- primary focus of this article is addressed to structures and tivities [4, 5, 9, 13]. Nonetheless, significant research in the properties of promising ascidian metabolites and their bio- area of marine pharmacology is a very recent origin, and logical activities. In this latter regard, anti-bacterial, anti- also few products (or their analogues) have already reached fungi, anti-diabetic, anti-viral, anti-HIV, anti-inflammatory, the market as therapeutic drugs. Indeed, ascidian-derived anti-proliferative, anti-malarial, anti-oxidant, anti-tumor, natural products have yielded promising drug leads, among anti-cancer compounds, described in marine ascidians dur- which ecteinascidin 743 (YondelisÒ) and dehydrodidemnin ing 1994–2014 were reported here in. In this study, we did B (AplidinÒ) are in clinical usage for the treatment of not aim to review proceedings of conference, scientific specific cancers [14, 15]. reports and patent literature. Wherever possible, we made The research attempt on MNPs has not targeted all attempt to focus on their potential biogenesis, chemical marine invertebrates equally. Ascidians are one of the most structure–activity relationships. Nevertheless, the present intensely studied organisms during the 21st century so that study has been mainly focused on their recent developments 572 secondary metabolites were reported from 1994 to in the preclinical studies, biotechnology advances and future 2014. This present study represented MNPs studied from directions of ascidian secondary metabolites. Meanwhile, family didemnidae (32%), polyclinidae (22%), styelidae the possible cytotoxicity and growth inhibition of MNPs is an and polycitoridae (11–12%) exhibiting the highest number identifying and short-listing of a potential drug molecule. Distribution of Chemistry classes of MNPs MNPs reported from the Family Ascidian Alkyl sulfates Pseudodistomidae 3% Saturosporine Steroids 4% Spiroketals Polyketide 5% Perphoridae 2% Clavelinidae Esters 1% 2% 2% 5% 1% Polysachride Pyrocridine Molugulidae Alkene 2% Alkaloids 1% Polyclinidae Ascididae 3% 18% Alkane 1% Peptides 22% 3% Holozoidae 4% Didemnidae 1% β Carboline Indole/ Alkaloids 32% Polycitoridae Alkaloids 48% Cionidae 11% 8% 4% Pyuridae Styelidae 5% 12% Fig. 1 Marine nature products studied from the family ascidian on Fig. 2 Distribution of chemistry class of MNPs with high biomedical 1994–2014 potential application studied from 1994 to 2014 123 Natural Products Diversity Distribution of Drug Class L-histidine (9) and N-(6-bromo-1H-indolyl-3-carbonyl)-L- Anti fungal enduracididine (10) compounds. Furthermore, the other 3% Anti viral 1% metabolites leptoclinidamines A–C (11–13) were reported Anti bacterial 2 14% Anti-HIV from the ascidian L. durus [18] and C -a-D-manno- Anti malarial 3% sylpyranosyl-L-tryptophan (14) was isolated from L. dubius 6% Anti tumor/Cancer Anti diabetic [19]. 64% 1% A new hexacyclic pyridoacridine alkaloid, nordehydro- Anti oxidant cyclodercitin (15) was reported from the ascidians, Aplid- 2% Anti ium sp. and A. cratiferum collected in Great Barrier Reef, inflammatory Australia [20]. Nordehydrocyclodercitin was structurally Central Nervous 3% System related to stellettamine [21] and cyclodercitin [22], which 3% is earlier reported from the sponge metabolites. Compound 16 Fig. 3 Distribution of drug classes of MNPs with high biomedical cycloshermilamine D ( ) was reported from the ascidian potential application studied from 1994 to 2014 Cystodytes violatinctus, it is an analogue of stellettamine with a 6-membered non-aromatic heterocycle in place of This review is restricted to those compounds exhibiting the thiazole ring [23]. Two new pyridoacridine alkaloids promising in vitro activity which was reported during the kuanoniamines E and F (17, 18), a new ring-opened pyri- above period. We listed out 327 anti-tumor/cancer,