Marine Organisms As a Source of New Anticancer Agents

Marine-derived anticancer agents Review

Marine organisms as a source of new anticancer agents

Gilberto Schwartsmann, Adriana Brondani da Rocha, Roberto GS Berlinck and Jose Jimeno

Various active anticancer agents are derived from plants and terrestrial microorganisms. The isolation of C-nucleosides from the Caribbean sponge, Cryptotheca crypta, four decades ago, provided the basis for the synthesis of cytarabine, the first marine- derived anticancer agent to be developed for clinical use. Cytarabine is currently used in the routine treatment of patients with leukaemia and lymphoma. Gemcitabine, one of its fluorinated derivatives, has also been approved for use in patients with pancreatic, breast, bladder, and non-small-cell lung cancer. Over the past decade, several new experimental anticancer agents derived from marine

sources have entered preclinical and clinical trials. © Pharma Mar SA This field has expanded significantly as a result of Figure 1. The Mediterranean tunicate Aplidium albicans. improvements in the technology of deep-sea collection, extraction, and large-scale production Over the past few years, about 3000 new compounds from through aquaculture and synthesis. In this paper, various marine sources (Figure 1) have been described and examples of marine-derived experimental agents that some have entered clinical trials.6 This activity has been are currently undergoing preclinical and early clinical largely due to improvements in the technologies involved in evaluation are briefly discussed. A summary of the deep-sea sample collection and large-scale drug production available information on the results of phase I and II through aquaculture and drug synthesis7 which took place trials of agents such as aplidine, ecteinascidin-734 in the 1980s. These developments suggest that, in the (ET-734), dolastatin 10 and bryostatin 1 is also future, the oceans will become an important source of novel presented. chemical classes not found in the terrestrial environment Lancet Oncol 2001; 2: 221–25 (Table 2).8,9

Since ancient times, we have relied on nature for our basic New agents undergoing clinical evaluation needs – food, protection, clothing, transport and Tunicate derivatives pharmaceuticals.1,2 The medical armamentarium includes Of the marine-derived compounds that have entered phase many examples of important agents that were first isolated I and II trials as antitumour agents, didemnin B, aplidine, from plants and microorganisms and that are now in and ET-743 are derived from tunicates.9 Didemnin B is a routine clinical use. In the field of anticancer therapy, many cyclic depsipeptide isolated from the tunicate Trididemnum active cytotoxic agents were originally developed from solidum. It has shown impressive antitumour activity in natural sources (Table 1).2,3 human tumour models in vitro as well as in tumours Until recently, the only major contribution to growing in athymic mice.10 In initial clinical trials, patients anticancer therapy from the sea was the synthetic with various solid tumours or non-Hodgkin lymphoma nucleoside analogue cytarabine, which is commonly used in the treatment of leukaemia and lymphoma. The GS is at the South-American Office for Anticancer Drug development of cytarabine was initially inspired by a series Development (SOAD), Comprehensive Cancer Center (CINCAN), The Lutheran University (ULBRA), Brazil; AbdR is doing a of C-nucleoside-derived compounds isolated from the Postgraduate Course in Medicine (HCPA-UFRGS), Porto Alegre, Caribbean sponge Cryptotheca crypta. More recently, a Brazil; RGSB is in the Department of Chemistry, University of São fluorinated derivative of cytarabine, gemcitabine, has Carlos (USP), Brazil; JJ is at PharmaMar SA R&D, Tres Cantos, shown significant activity in patients with solid tumours, Madrid, Spain. such as pancreatic, breast, bladder, and non-small-cell lung Correspondence: Professor G Schwartsmann, MD, PhD, cancer.4,5 Postgraduate Course in Medicine (UFRGS), Porto Alegre, Brazil Hospital de Clinicas de Porto Alegre, Rua Ramiro Barcelos 2350, The oceans cover about 70% of the earth’s surface, and 3º Leste Porto Alegre – RS – Brazil, CEP 90000. the marine environment includes tremendous biodiversity; Tel: +55 51 3168012. Fax: +55 51 3317143. all but two of the 28 major animal phyla are represented. Email: [email protected]/[email protected]

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Table 1. Cytotoxic agents developed from natural sources Table 2. Marine-derived experimental anticancer agents

Agent Oncological use Natural source Organism Group Metabolite Location Etoposide Testicular tumours, Podophyllum Trididemnum soldium Tunicate Didemnin B Caribbean small-cell lung cancer peltatum, Bugula neritina Bryozoan Bryostatin 1 Gulf of Podophyllum California emodi Ecteinascidia turbinata Tunicate Ecteinascidin-743 Caribbean Cytarabine Leukaemias and non- Cryptotheca Hodgkin lymphomas crypta Halichondria okadai Sponge Halichondrin B Okinawa Vinblastine Hodgkin’s disease, Catharanthus Dolabella auricularia Sea hare Dolastatin 10 Indian Ocean non-Hodgkin roseus Portieria hornemannii Red alga Halomon Phillipines lymphoma, germ-cell tumours, Aplidium albicans Tunicate Aplidine Mediterranean Kaposi’s sarcoma and Aplysia kurodai Sea hare Aplyronine A Japan breast cancer Elysia rubefescens Mollusc Kahalalide F Hawaii Vincristine Acute leukaemia, Hodgkin’s Catharanthus disease, non-Hodgkin roseus Mycale sp. Sponge Mycaperoxide B Thailand lymphoma, rhabdo- Micromonospora Actinomycete Thiocoraline Mozambique myosarcoma, Wilm’s tumour marina Strait Gemcitabine Pancreatic, bladder, breast Cryptotheca Ascidian didemnum Tunicate Granulatimide Brazil and non-small-cell lung cancer crypta granulatum Vinorelbine Activity in breast and non- Catharanthus small-cell lung cancer roseus malignant melanoma, tumours of neuroendocrine origin, Paclitaxel Ovarian, breast, lung cancer, Taxus brevifolia 14–16 and others and medullary carcinoma of the thyroid. The main toxic Docetaxel Ovarian, breast, and Taxus baccata effects observed so far have been nausea and vomiting, lung cancers by age 70 myalgia, transient disturbance of liver function, and local irritation at the injection site. Muscular toxicity was circumvented by the concomitant administration of were given a short intravenous infusion of didemnin B L-carnitine (E Raymond, unpublished). Aplidine will start every 3 weeks, and antitumour effects were observed. phase II trials in various solid tumours in the near future. However, severe neuromuscular and cardiotoxic effects led The ecteinascidins are derived from the Caribbean to the discontinuation of clinical trials.11,12 tunicate Ecteinascidia turbinata (Figure 2) and also show Another depsipeptide, dehydrodidemnin B, was significant antitumour activity in both murine and human subsequently isolated from the Mediterranean tunicate, tumour cell lines.17 Of the many ecteinascidins that have Aplidium albicans (Figure 1) and later called aplidine. The been isolated, ET-743 was selected for clinical trials preclinical findings for aplidine suggested potentially high (Figure 3). It is a tetrahydroisoquinoline alkaloid that acts anticancer activity against various different, rapidly by selective alkylation of guanine residues in the DNA proliferating tumour types, as a result of interference with minor groove.18 It therefore differs from the other DNA- cell-cycle progression at G1.13 Aplidine appears to be more alkylating agents so far introduced in the clinic. It also active than didemnin B in preclinical models and so far has interacts with nuclear proteins.19 not shown evidence of life-threatening neuromuscular The main drug-induced toxic effects of ET-743 in early toxicity. Because aplidine appears to have higher clinical trials were pancytopenia, fatigue, emesis and antitumour activity in preclinical models after longer drug transaminitis. Local toxicity was also observed in patients exposure, phase I trials were initiated at various drug who received short-term intravenous administration. There schedules, ie 1 h, 3 h, 24 h and 72 h intravenous infusions. were objective and long-lasting tumour responses in Notably, antitumour activity was observed in patients with patients with advanced resistant mesenchymal tumours, advanced solid tumours, such as renal-cell carcinoma, breast cancer, melanoma and ovarian cancer included in phase I clinical trials of ET-743.20,21 Initial results from pilot phase II trials for ET-743 confirm its therapeutic potential in various soft tissue sarcomas and breast cancer. 22–26

Dolastatins The dolastatins are cytotoxic cyclic and linear peptides derived from the sea hare, Dolabella auricularia (Figure 4), a mollusc found in the Indian Ocean. Dolastatins 10 and 15 are small peptides; dolastatin 10 was selected for clinical trials because of its more favourable preclinical profile.27 It inhibits microtubule assembly, causing cells to accumulate in metaphase28,29 and is extremely potent in vitro. Dolastatin 10 caused bone-marrow toxicity in initial clinical trials, as

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algae (cyanobacteria).43 Depsipeptide (NSC 630176) is a MeO bicyclic peptide isolated from a strain of Chromobacterium HO OH violaceum. It decreases mRNA expression of the c-MYC OAc oncogene and inhibits the growth of Ha-RAS-transformed NIH-3T3 cell line, RAS-1, causing cell-cycle arrest at MeO N Me G0–G1.44 It acts as an inhibitor of a histone deacetylase.45 Depsipeptide showed cytotoxic activity in N various human solid-tumour cell lines in vitro and also in O OH athymic mice.46 Phase I trials of depsipeptide will begin O O soon. S O Other compounds in preclinical development MeO New classes of anticancer drugs isolated from marine NH organisms in different parts of the world show cytotoxic activity in a variety of preclinical models. Discodermolide, a HO metabolite of the deep-sea sponge Discodermia dissolute Figure 3. Chemical structure of ET-743. collected in the waters of the Bahamas, induces microtubule stabilisation.47,48 patients with a range of solid tumours, but so far no Halichondrin B was initially purified from the sponge significant antitumour activity has been seen.30–33 Halichondria okadai in Japan and has shown in vivo activity in melanoma and leukaemia models. It can also be obtained Bryostatins from the deep-water sponge Lissodendoryx, which is found Bryostatin 1 is a macrocyclic natural lactone isolated from in New Zealand. This compound is also active in various the marine bryozoan, Bugula neritina (Figure 5). It human tumour-cell models in vitro and in vivo and appears modulates the activity of protein kinase C (PKC), lacks to interfere with microtubule function.49 tumour-promoting activity and shows differentiation- The Brazilian tunicate, Ascidian didemnum granulatum, inducing effects in various in vitro and in vivo models.34,35 It is the source of the aromatic alkaloids granulatimide and also has immunomodulatory properties, including the isogranulatimide, which appear to act as G2 checkpoint induction of cytokine release and expansion of tumour- inhibitors.50 These compounds have been synthesised, and specific lymphocyte populations.36,37 several analogues are being developed for further testing. In Bryostatin 1 has shown antitumour activity in phase I addition, new bisindole alkaloids of the topsentin and trials in patients with malignant melanoma, lymphoma, hamacanthin classes have been isolated from the and ovarian carcinoma and is undergoing broad phase II Mediterranean sponge Rhaphisia lacazei, and these evaluation. The main toxic effects in initial clinical trials compounds also showed significant antiproliferative were myalgia, local phlebitis, fatigue, nausea and vomiting, activity against a series of human cell lines in vitro.51 and thrombocytopenia. Bryostatin 1 showed no significant Five new sesquiterpenes, parahigginols, and objective antitumour activity in phase I and II trials in parahigginic acid, have been isolated from a Taiwanese patients with advanced solid tumours, including renal-cell marine sponge Parahigginsia sp. Initial studies revealed that and non-small-cell lung cancer, and malignant these compounds were cytotoxic against murine P-388 and melanoma.38–41 However, it was shown to induce cell human KB16, A549, and HT-29 tumour cells.52 Another differentiation in patients with refractory chronic group of marine compounds, the makaluvamines, also lymphocytic leukaemia. A phenotype resembling hairy-cell show significant antitumour activity in animal models, leukaemia was observed following the administration of probably through the induction of dose-dependent DNA bryostatin 1 in one patient, who regained sensitivity to 2- cleavage via topoisomerase II.53 chlorodeoxyadenoside (2-CdA) treatment.42 Dinoflagellates, unicellular marine protozoons, produce A new class of bryostatin analogues, which retain the some of the largest and most complex polyketides identified putative recognition domain of the bryostatins, but are to date. The biological activities of these molecules are quite simplified through deletions and modifications in the C1- diverse.54 More recently, the manipulation of the C14 spacer domain, have been designed by use of computer biosynthetic pathways of microbial polyketides through models. All these analogues are bound strongly to a mixture of PKC isozymes, and several show significant growth- inhibitory activity against human cancer cell lines in vitro. This work constitutes an important step towards the development and understanding of simplified, synthetically accessible analogues of the bryostatins as potential chemotherapeutic agents.34

Depsipeptide (NSC 630176) A large number of structurally novel, biologically active cyclic peptides and depsipeptides are found in blue-green Figure 4. The sea hare Dolabella auricularia.

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metabolic diversity, which is ready to be exploited and which will certainly make anticancer drug discovery even more challenging in the next few years.

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