Cite this article: Lorente A, Makowski K, Albericio F, Álvarez M (2014) Bioactive Marine Polyketides as Potential and Promising Drugs. Ann Mar Biol Res 1(1): 1003.
*Corresponding author
Álvarez M, Institute for Research in Biomedicine, Baldirii Reixac, 10, 08028, Barcelona, Spain, Tel: 34934037087; E-mail
Keywords•Polyketides•Marine drugs•Cytotoxic•Clinical status
Review Article
Bioactive Marine Polyketides as Potential and Promising DrugsAdriana Lorente1,2#, Kamil Makowski1,3#, Fernando Albericio1,2,4,5 and Mercedes Álvarez1,2,6*1Institute for Research in Biomedicine, Barcelona Science Park-University of Barcelona, Spain2CIBER-BBN, Networking Centre on Bioengineering Biomaterials and Nanomedicine, Spain3Centre for Genomic Regulation, Barcelona, Spain4Department of Organic Chemistry, University of Barcelona, Spain5School of Chemistry, University of Kwa-Zulu-Natal, South Africa6Department of Organic Chemistry, University of Barcelona, Spain#Both authors contributed equally to this work
Abstract
The marine environment offers an extensive source of secondary metabolites with promising biological activities to start drug discovery processes. Marine polyketides are a class of compounds with diverse and interesting biological properties. Their biosynthetic production mechanism of versatile assembly confers these compounds remarkable diversity both in terms of structural complexity and biological activity. This review focuses on marine aliphatic polyketides or mixed non-ribosomal peptide-polyketide compounds in advanced drug discovery stages. The isolation, drug development process, supply sources and clinical status of these polyketide or mixed peptide-polyketide compounds, as well as their potential as drug candidates, is hereby described.
Coenzyme A; DEBS: 6-Deoxyerythronolide B Synthase; DH: Dehydratase; EMEA: European Medicines Agency; ER: Enoyl Reductase; FDA: Food and Drug Administration; GT: Glycosyl Transferases; KR: Ketoreductase; KS: Ketosynthase; MT: Methyl Transferase; NCI: National Cancer Institute; NME: New Molecular Entity; NRP: Non-Ribosomal Peptide; NRPS: Non-Ribosomal Peptide Synthase; OX: Oxygenase; PK: Polyketide; PKS: Polyketide Synthase; TE: Thioesterase
INTRODUCTIONNatural products from terrestrial plants and microorganisms
have long been a traditional source of drugs. They constitute a group of privileged structures because the generation of diversity has occurred in the context of biological utility, meaning that the functional and the biosynthetic routes generating these compounds coevolved with the requirements of ligand functionality. Therefore, natural products are selected by the evolutionary process to interact with a wide variety of proteins and therapeutic targets, and are excellent candidates for drug development processes. Although technology offers a wide range of opportunities, nature is still the most reliable starting point for drug development [1]. Their importance lies not only as a direct
source of new bioactive molecules, but also as an inspiration to create new structures.
Nevertheless, in the current clinical pipeline, the era of the “me-too” or the “me-slightly-better” has arrived [2]. Thus, the discovery of New Molecular Entities (NME) requires innovation. The way to NME is to investigate new possible sources, such as oceans, and to refocus our approach with new ideas and processes because what has worked in the past does not provide innovative results anymore.
Unlike terrestrial sources, the marine habitat has not been as extensively studied; this field awaited refinements in technology to collect organisms from marine sources, and the development of advanced analysis techniques to better understand more complex isolated compounds. Since the 1950s, this field has undergone exponential growth. Considering that water covers around 70% of the earth’s surface and that 32 of the 33 animal phyla are represented in aquatic media, marine habitat represents an unexplored source of new bioactive molecules [3].
Marine organisms produce a large number of structurally diverse secondary metabolites [4] that do not play an essential role in the life of the organism, but rather offer a complementary function as chemical defence against pathogens, in the fierce competition for survival in marine habitats. As a consequence, natural products isolated from marine sources present
Central
Álvarez et al. (2014)Email:
Ann Mar Biol Res 1(1): 1003 (2014) 2/10
novel bioactivities, as a result of sophisticated biosynthetic pathways created through the combination of evolution and thermodynamics.
Among these, marine aliphatic polyketides are a class of compounds that present diverse and interesting biological properties. Due to the versatility of their biosynthetic production mechanism, these compounds exhibit remarkable diversity, both in terms of structural complexity and biological activity. Polyketides are constructed as highly oxygenated stereo chemically-enriched scaffolds, sometimes with the characteristic presence of macrocyclic lactones, cyclic five or six-membered ethers or polyethers that act as a conformational constraint [5,6].
This revision focuses on marine aliphatic polyketides or mixed non-ribosomal peptide-polyketide compounds in advanced drug discovery stages (Table 1). The isolation, drug development process, clinical status and their supply, is described. The potential as drug candidates that this class of compounds represents is outlined.
BIOSYNTHESISPolyketides are a class of secondary metabolites elaborated
from a series of enzymatic transformations upon biosynthetic linear assembly. Polyketide natural products are constructed by large multifunctional protein complexes called polyketide synthases (PKSs) from acetate and propionate building blocks. The PKS and non ribosomal peptide synthase (NRPs) machinery is mainly known to originate from microorganisms [7,8]. Nevertheless, Wang et al. have recently revealed that PKS/NRPS gene clusters are also present in eukaryotes, although their end products are still unknown and so it is their concrete function [9]. Different families of PKSs generate distinct classes of polyketides, but irrespective of the producing organism, polyketides are always formed by decarboxylative Claisen-type 1, 2-head-to-tail condensations of thioesters with malonyl-derived extender units [10,11]. Type I PKSs, or modular PKSs, construct polyoxygenated aliphatic compounds, which is the subject of this review.
The polyketide synthase machinery starts by thioester bond formation between an acyl carrier protein (ACP) domain and a coenzyme A (CoA)-bound starter unit catalyzed by an acyl transferase (AT) domain. A ketosynthase (KS) domain catalyzes the binding of its cysteine-bound malonyl elongation unit to the growing ACP-bound polyketide. Acetate units are loaded successively to cysteine residues of adjacent KS domains, and
the chain is elongated via Claisen condensations through the different protein modules. Complexity and diversity are added to the polyketide chain through ketoreductase (KR), dehydratase (DH), and enoyl reductase (ER) domains, which may or may not be present in each module. Moreover, PKS and non-ribosomal peptide synthase modules can work together to form hybrid PKS-NRPS molecules. The sequence ends in the thioesterase (TE) domain and macrolactones are normally formed upon termination/cyclization. An example of chain elongation, shown in (Figure 1); 6-deoxyerythronolide B synthase (DEBS), is the PKS that forms the backbone of erythromycins and is encoded by the three genes, eryAI-III [12,13].
Once the resulting linear carbon backbone is released from the PKS, the carbon framework is further processed and modified by various tailoring enzymes, which enhance its functionality. This post-PKS processing is another source of diversity in polyketide biosynthesis, as there is enormous scope to produce altered structures. For example, the skeleton can be oxidized or reduced to introduce hydroxy or carbonyl groups (oxygenases [OXs] and ketoreductases [KRs]), methylated at oxygen, nitrogen or carbon centers (methyl transferases [MTs]), or decorated with deoxysugar molecules (glycosyltransferases [GTs]) [14]. The post-PKS processing may also involve the formation of polycyclic ethers, which can occur through a wide variety of transformations, such as epoxide-opening cascades, addition to double bonds or elimination processes of hemi-acetals [15].
All together, the PKS-catalyzed assembly process generates stereochemical diversity, because of carbon–carbon double bonds and the chirality of centers bearing hydroxyl and branching methyl groups. This is one of the more striking features of the efficiency of PKSs. More recently, many aspects of stereochemistry in polyketide biosynthesis have been better explained, [16] but the knowledge around the stereochemical complexity of polyketide biosynthesis is still not completely understood.
SUPPLYThe bottleneck for the development of these compounds is
supply. Isolation from the natural sources often furnishes small amounts of product, which makes the structure determination and preparation of enough sample of compound for clinical trials extremely challenging. In the actual scenario, few marine natural products have arrived at the latter development stage of a drug,
Compound Structure Target Clinical status Disease Area Company
Eribulin Macrocyclic PK Microtubules Approved (2010) Cancer Eisai Co., Ltd.
Bryostatin Macrocyclic PK Protein kinase C Phase I-II Alzheimer National Cancer Institute
Aplidine Macrocyclic mixed PK-NRP Protein Kinases Phase I-III Cancer PharmaMar S.A.
PM060184 Linear PK Microtubules Phase I Cancer PharmaMar S.A.
Salinosporamide A γ-lactam-β-lactone mixed PK-NRP 20S proteasome Phase I Cancer Triphase A.C.
Spongistatin Macrocyclic PK Tubulin Preclinical Cancer National Cancer Institute
Discodermolide Linear PK Microtubules Discontinued Cancer Novartis A.G.
Table 1: Marine polyketides in the clinical pipeline.
Figure 1 Biosynthetic formation of the carbon skeleton of erythromycin and detail of the intermediate reactions.
[17] but many are on their way, a vast number of them being currently under preclinical and clinical trials [18,19].
Aliphatic marine polyketides are no exception, although they present potent bioactivities and excellent pharmacological properties that may well make them suitable for medical use. Their complexity not only makes their supply difficult, but also their structural and stereochemical assignment, which further decelerates their development as drug leads. Nowadays, the main solutions to overcome supply issues are either aquaculture of the producing organism or the application of synthetic or semi synthetic methodologies to produce them in large enough scale
quantities. On the other hand, genetic engineering is starting to offer an alternative for the production of certain metabolites.
Although fauna from the deep sea is usually unculturable, aquaculture of marine invertebrates can be used as supply route by finding the appropriate aquaculture conditions [20]. This is the most straightforward way to obtain gram quantities of a drug candidate in a short period of time, but the fact that production is highly dependent on the external conditions and that this can alter the production of some metabolites should be considered. Moreover, aquaculture usually has an important environmental cost, as farms may have to be located in oceans and the host
Central
Álvarez et al. (2014)Email:
Ann Mar Biol Res 1(1): 1003 (2014) 4/10
media may suffer some alterations.
On the other hand, the design of efficient and stereo selective methodologies to obtain these targets by synthesis or semi-synthesis seems to be a potential option [21,22]. This strategy requires high production yields with minimum synthetic steps. Chemistry attempts both to understand the structures and characteristics of compounds and to create new compounds with desirable properties and functions. Synthesis is a powerful tool to use on behalf of structure determination [23] and supply of material for clinical tests on the development of new bioactive drugs. Nevertheless, as mentioned before, marine polyketide compounds tend to be extremely complex and their synthesis requires the overcoming of the challenges associated with structural complexity and stereochemistry.
Increasing evidence shows that symbiotic microbial organisms are the producers of some bioactive compounds and not the sponge, tunicate, or invertebrate from which they were isolated [24,25]. Specifically, this is stated for compounds derived from polyketide and non-ribosomal peptide biosynthetic pathways, since the producing enzymes are mainly known to originate from microorganisms [7,8]. A possible bacterial origin of some marine natural products could have important implications concerning their drug development, since it may permit fermentation-based production systems, which are superior to current procurement methods.
As genome sequencing is common, rapid and relatively inexpensive, genetic engineering of cells can be successfully applied to the development of strains dedicated to the overproduction of a certain natural product. Unlike their invertebrate hosts, genomes of bacteria are small and their biosynthetic pathways tend to be organized in contiguous regions of DNA (operons), which facilitates cloning of these pathways. A number of studies have been directed towards the identification of symbiotic biosynthetic sources of marine natural products. The most unequivocal evidence to identify them is provided culturing the microbe and showing production of the compound. Nevertheless, marine symbionts are often unable to produce those bioactive compounds under growth conditions. Other strategies have been consequently developed such as localization of compounds in specific invertebrate or symbiont cells, experimental manipulation of symbiont load (for instance by treatment with antibiotics) or detailed analysis of the chemical structures of the bioactive metabolites (finding similarities to known microbial compounds). Finally, isolation of the biosynthetic genes from the symbiont enables definitive proof. Next step is the cloning of the biosynthetic genes. A certain strategy and vector is used depending on the size of the region to be cloned and the proximity of their elements in the genome. Finally, expression of the target gene leads to the production of the natural compound [26]. Although there may be some difficulties, the benefits of cloning and expressing bioactive metabolite genes are enormous. This process allows not only the synthesis of unlimited amounts of compound but also the manipulation of the gene sequences for the production of analogs [27].
Genetic engineering is attracting the attention of many scientists working on marine natural products [28,29]. The predictable relationship between the structure and function
of PKSs and NRPSs has enabled the genetic manipulation of biosynthetic pathways for production of novel variants of naturally occurring compounds. Nevertheless, some limitations may appear using this approach such as inappropriate expression devices, lack of a unique substrate for a pathway enzyme, or autotoxicity of the produced compound to the host [30–32].
RELEVANT POLYKETIDES AS POTENTIAL DRUG CANDIDATESEribulin
Halichondrin B was isolated for the first time from the sponge Halichondriaokadai in 1986 along with other halichondrins and norhalichondrins [33,34]. Halichondrins showed low nanomolar cytotoxic activity; however, supply became a problem for their further development. In 1992, the total synthesis of halichondrin B was reported, but a significant number of synthetic steps were required (almost 90); too many to become an effective source of this compound [35]. Over the course of the drug development program of halichondrin B, scientists at Eisai Co., Ltd. discovered that synthetic analogs of much simpler structures with molecular mass reduced about 30% presented similar pharmacological profiles and eribulin (Figure 2) was targeted as the next drug candidate [36]. A direct comparison of the natural product and eribulin shows that the analog is 30 to 40% more potent as inhibitor of purified tubulin polymerization. In the same study, halichondrin B showed to be slightly more active on a panel of human cancer cell lines as a growth inhibitor, nerveless eribulin still presented sub to low nmol/L IC50 values. On the other hand, in vivo tumor studies show that eribulin is superior and presents less toxicity [37]. Given the lack of intermediates from naturally occurring sources to support a semi-synthetic strategy, eribulin was, and still is, produced by total synthesis, [38] representing a breakthrough on the perception of what a druggable chemical lead should look like.
The mechanism of action of eribulin has not been totally elucidated; however, preclinical studies have shown that its main effect is exerted on microtubule dynamics interruption by suppressing microtubule polymerization and inducing apoptosis [39]. Other eribulin preclinical studies have proven its tumor growth inhibition capacity in colon and breast cancer xenograft models in mice [40]. Clinical trials have demonstrated the feasibility of this compound in advanced breast cancer studies [41]. Further phase III studies have demonstrated that eribulin, like only two other chemotherapeutic agents (anthracycline and taxane), improves overall survival in pretreated patients with advanced breast cancer. After being approved by the FDA (US) and EMEA (Europe), eribulin is now being used for treatment of metastatic breast cancer [42]. Eribulin presents improved survival rates in patients and recent studies have shown that it can be used in combination with trastuzumab–a monoclonal antibody used in chemotherapy in late-stage breast cancer [43]. Other recent studies have shown a synergistic effect in vitro and in vivo with S-1, a three-component oral antitumor drug [44]. All of this together makes eribulin the most developed, fully synthetic derivative of a natural polyketide, already used as a chemotherapy agent with new promising perspectives.
Central
Álvarez et al. (2014)Email:
Ann Mar Biol Res 1(1): 1003 (2014) 5/10
O
OH2N OH
O OH
HO
H
OOO
O
O
Eribulin Mesylate
MsOH
O O
O
O
O
O
OO
O
O
O O
O
HOH
HO
OH
OH
Bryostatin 1
Didemnin B R1 = H; R2 = OHAplidine R1, R2 = O
O
OO
O NH
OHNH
O
ON
ON
O
O
NH
O
O
N
ON
OR1 R2
O
O O O
ONH
HN
OO
NH2
PM060184 X = HPM050489 X = Cl
X
Cl
O
OHO
O
HN
H
Salinosporamide A
Cl OO
O
O
O
OHHO
OH
AcO
OH
HOO
O O
O
OAc
HOO
HO
HH
H
H
H
H
H
Spongistatin 1
O
HO
OOOH
HOOH
O
NH2
(+)-Discodermolide
Figure 2 Structures of relevant polyketides.
Bryostatin
The first members of the bryostatin family were isolated by Pettit and co-workers in 1968 from the invertebrate bryozoans Bugula neritina and Amathiaconvulata, but were not fully characterized until 1982 [45]. Since then, twenty bryostatins have been isolated to date. Bryostatin 1 (Figure 2) is the member of the family that has attracted the most attention, as it shows remarkable in vitro and in vivo anticancer activity with no significant side effects [46]. Studies on its mechanism of action have shown that bryostatin 1 is a protein kinase C modulator and that it inhibits proliferation and promote apoptosis of cells [47].
Bryostatin 1 has been evaluated alone and in combination with other chemotherapeutic agents in phase I and phase II clinical trials for several cancer treatments, but has not been effective enough to progress to phase III clinical trials. Interestingly, bryostatin has had positive results in central
nervous system cancer models and has entered clinical trials for the treatment of Alzheimer’s disease in humans. Furthermore, studies on its application as an HIV inhibitor showed a purging effect of the virus from cellular reservoirs, which may make it useful in combination with some existing treatments [48].
Supply of this macrocyclic polyketide has encountered some difficulties. Marine aquaculture of the bryozoans was achieved, and significant quantities of bryostatin 1 were obtained for the first clinical trials; however, this method was not commercially implemented [20]. Several groups focused their efforts on designing effective synthetic routes to obtain bryostatins and simplified analogs with similar pharmacological profiles, [46,49–51] but until now, none of these strategies have succeeded in bringing a practical method for industrial production, nor any accessible simplified analog with a similar pharmacological profile. Finally, although definitive proof is lacking, there is
Central
Álvarez et al. (2014)Email:
Ann Mar Biol Res 1(1): 1003 (2014) 6/10
evidence suggesting that bryostatins are produced by the bacterial symbiont Candidatus Endobugula sertula [52]. This scenario would mean new possibilities for the supply of bryostatin as it may enable to attain this compound by cloning and biosynthetic expression strategies.
Aplidine
The didemnin family of natural products was isolated from the Caribbean tunicate Trididemmumsolidum in 1981 [53]. Didemnin B (Figure 2) was the most potent analog of this series of compounds and entered clinical trials as an anticancer agent. Nevertheless, this compound showed cardiac and neuromuscular toxicities and the clinical process was discontinued. The family congener aplidine (plitidepsin) (Figure 4) was later isolated from the Mediterranean tunicate Aplidiniumalbicans, [54] which displayed a similar pharmacological profile but less toxicity, and replaced didenmin B in multiple phase I and phase II trials as an anticancer agent [55].
Preclinical studies have shown that aplidine produces apoptosis at nM concentrations. The mechanism of action of aplidine-induced apoptosis was also investigated but it still remains to be fully elucidated. Further, multiple signaling pathways have been shown to be involved in aplidine apoptotic action [56].
Aplidine, administered alone or in combination, is currently undergoing phase I-III clinical trials for the treatment of relapsed/refractory multiple myeloma, non-Hodgkin’s lymphoma, dedifferentiated liposarcoma and metastatic melanoma [57].
Supply of aplidine is currently limited to total synthesis [58]. Although this family of compounds has been the objective of extended investigations concerning total synthesis and preparation of analogs, a practical method to produce this anticancer agent is not yet available [55,59]. Nevertheless, recent discoveries show that the didenmins are produced by the symbiotic marine bacteria Tristrellamobilis and Tristrellabauzanensis and involve a hybrid NRPS-PKS enzyme complex [60]. Thus, the discovery of the didemnin gene cluster may have important long-term implications in the supply of this material.
PM060184
The sponge Lithoplocamialithistoides from Madagascar was the source of two new polyketide compounds: PM060184 and its chloride derivative PM050489 isolated by PharmaMar (Figure 2). Mass spectrometry and careful NMR studies together with additional derivatizations led to the determination of the structure and most of the stereocenter configurations. The presence of amide motifs in their structures suggest that these compounds may originate from a mixed PKS-NRPS enzymatic complex, although their biosynthetic production has not been reported. Both compounds have shown promising subnanomolar activity in human cancer cell lines. For the purpose of drug development and the need for bigger quantities of these products, synthesis had to be employed. Efficient total synthesis at multigram scales was achieved in 18 steps for the longest linear sequences and a total of 35 steps for the total synthesis starting from commercially available 1,3-propanediol, thus,
permitting further preclinical studies. Spectral data comparisons of synthetic and isolated compounds were conducted to elucidate the complete structure [61].
PM060184 is a potent mitotic inhibitor that binds tubulin dimers with low nanomolar affinity and disrupts cellular microtubules by a novel mechanism that has not earlier been described for other tubulin-binding agents. The interaction with a new site in β-tubulin produces alteration of microtubule dynamics and polymer mass which leads to mitotic blockade and as a consequence to apoptosis [62]. Antiproliferative activity was demonstrated in many different human cancer cell lines from different tissues. Moreover, animal studies against several xenograft models in mice clearly demonstrated that it works by reducing the tumor´s growth capacity [62,63]. Currently PM060184 is undergoing phase I clinical trials in late stage cancer patients. Recently, the crystal structure of the complex tubulin-PM060184 was obtained, providing structural information that may further lead to the design and development of new tubulin-binding cytotoxic agents [64].
Salinosporamide A
Salinosporamide A (marizomib; NPI-0052) is γ-lactam-β-lactone isolated by Fenical, Jensen and co-workers from the bacteria Salinosporatropica, which are found in marine sediment collected in the Bahamas (Figure 2) [65]. Extensive labeling studies have shown that biosynthesis of salinosporamide A is due to mixed polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) pathways [66–68].
Salinosporamide A is a novel, potent proteasome inhibitor. It induces apoptosis by a caspase-8 dependent mechanism in multiple myeloma and leukemia cells. Additionally, in the apoptosis of leukemia cells, a reactive oxygen species (ROS)-dependent mechanism is involved. [69,70]
Enzymatic inhibition studies of purified 20S proteasome chymotrypsin-like activity have shown the high potency of this compound with low nanomolar activity (IC50 = 1.3 nM). Furthermore, salinosporamide A has demonstrated strong cytotoxic activity against a panel of human cancer cell lines in the nanomolar range, showing better potency than bortezomib, an FDA approved protease inhibitor used for treating relapsed multiple myeloma and mantle cell lymphoma [65,70].
When both salinosporamide A and bortezomib were examined in normal peripheral blood mononucleated cells, salinosporamide A did not significantly decrease normal lymphocyte viability at the IC50effective against multiple myeloma cells. Bortezomib, however, inhibited proliferation of those normal cells at concentrations close to the IC50 for multiple myeloma cells. These studies suggest that salinosporamide A could be less toxic than bortezomib when extrapolated to in vivo studies [70]. Further in vivo preclinical studies of salinosporamide A have shown that this drug can be administered orally or intravenously [70] and that it affords no significant toxicity [71].
Since 2006 the efficacy and the safety of salinosporamide A as an anticancer drug in patients with multiple myeloma, lymphomas and leukemias have been evaluated in phase I clinical trials. Results of treatment with a 0.5 mg/m2 dose of
Central
Álvarez et al. (2014)Email:
Ann Mar Biol Res 1(1): 1003 (2014) 7/10
salinosporamide A given twice a week suggests anti-myeloma activity, with responses seen in patients in whom bortezomib had previously failed [72–74]. Currently, combination therapies of salinosporamide A with other drugs are under investigation in phase I clinical trials.
Total syntheses of salinosporamide A until 2010 have been reviewed by Potts and Lam [75]. Since then, Romo, [76,77] Chida, [78] Fukuyama [79] and co-workers reported new interesting syntheses of this natural product. However, for clinical supply, salinosporamide A is manufactured through a saline fermentation process. Optimization of this fermentation process was carried out at Nereus Pharmaceuticals and led to production of 450 mg of compound by S. tropica bacteria for every liter of media in shake flask culture. Currently, the drug is manufactured in 500-1500 L industrial fermentors with a 250-300 mg/L yield. This process requires only a single flash chromatography step and further purification by crystallization [75].
Spongistatin
The spongistatins are a family of marine polyketide macrolides with highly complex structures and interesting anticancer properties. Among this family of natural products, Spongistatin 1 (Figure 2) is the most interesting macrocycle because of its extraordinary biological activity. Spongistatin 1 was isolated by Pettit and co-workers from sponges Spirastrella spinispirulifera and Hyrtios [80,81].
Acytotoxic screening study of spongistatin 1 against a panel of 60 human cancer cell lines by the National Cancer Institute (NCI60) had an averaged IC50 value of 0.12 nM and even more potent low picomolar values for other cancer cell lines [80,82,83].
Antiproliferative activity of spongistatin 1 is due to a microtubule targeting mechanism of action, causing mitotic arrest in cancer cells. This polyketide has significant in vivo antitumor activity. Injections of relatively low doses (10 µg/kg) administered each day in the pancreatic cancer xenograft model produced tumor growth inhibition [84]. A different study showed significant tumor suppressing activity against the LOX-IMVI human melanoma xenograft model [83]. Studies of antifungal activity of spongistatin 1 both in vitro and in vivo that involved the testing of the drug against 74 reference strains and clinical isolates showed it to be more potent than amphotericin B (clinically used antifungal drug) in lowering renal and lung infection burdens in mousemodels [85,86].
Many total syntheses of spongistatin 1 have been described [5,87], including a gram-scale synthesis achieved by Smith III [88]. Recently, step-economical and scalable multi-gram synthesis of one of the spiroketal fragments of spongistatin 1 has been reported by Leighton [89].
Despite the high proven efficiency of spongistatin 1, its clinical development is limited by the low quantities available from synthesis and extraction of the sponges, and the high ecological cost that this process implies.
Discodermolide
(+)-Discodermolide (Figure 2) was isolated by Gunasekera and co-workers from the Bahamian deep water sponge
Discodermia dissolute [90]. The structure was elucidated by extensive nuclear magnetic resonance, mass spectroscopy and X-ray crystal structure studies and further confirmed after total synthesis of the (−) and (+)-discodermolide enantiomers. Interestingly, (−)-discodermolide still presents cytotoxic activity, but at higher concentrations when compared to the natural (+)-enantiomer [91,92].
Many total syntheses of (+)-discodermolide were published (reviewed in 2004 by Souza [93]), including gram- and multigram-scale, particularly the preparation of 60 g of this highly stereochemically complex polyketide by workers at Novartis for the supply of phase I clinical trials. Other interesting improved syntheses appeared in the literature after this review [94–98]. Mariculture of Discodermia dissolute sponge was also achieved. For every 1 mL of sponge 8 µg of polyketide were obtained after six months of culturing [99]. This process could still be optimized as an alternative to its synthetic production.
The first biological activity investigation of (+)-discodermolide was related to its strong immunosuppressive effect [93]. It was later also recognized as a cytotoxic agent. (+)-Discodermolide is an antimitotic agent which produces disruption of cellular division by microtubule stabilisation. (+)-Discodermolide is often compared to Taxol (Paclitaxel), a widely used drug in chemotherapy. Both drugs present a similar tubulin-binding mechanism; however, (+)-discodermolide has been described to be more potent and to have higher affinity than paclitaxel. On the other hand, a synergistic effect is observed when these drugs are used together. The presence of low concentrations of paclitaxel amplified the cytotoxicity of discodermolide in the paclitaxel resistant A549-T-12 lung cancer cell line [100]. More recently, Horwitz and co-workers reported a discodermolide-paclitaxel hybrid compound with up to an 8-fold increased potency in vitro [101].
Further development of the drug has shown tumor suppressing activity in the mouse colorectal cancer xenograft model in vivo. Unfortunately, phase I clinical studies have shown mild to moderate toxicity and Novartis has decided to discontinue phase I trials. Nevertheless, the potential of discodermolide as a drug candidate remains a possibility when used in combination with other anticancer compounds [102].
CONCLUSIONTo date, only a few marine polyketide-derived drugs are
considered suitable for medical use. The main cause for the slow development of these compounds is supply. Nevertheless, scientists are starting to overcome these problems, as seen from the examples given above and drug development of these complex compounds is now becoming possible. In the oncoming years more advances on the supply of these materials will appear, especially in the field of genetic engineering through the application of cloning and biosynthetic expression strategies.
It is a fact that the discovery of NME requires innovation and a new mentality approach with new ideas and processes. Scientists have learned over the years how to overcome the problems often associated with marine-derived natural products development. Nevertheless, there is a symbiotic relationship between scientific progress and clinical achievements. Science profits from the
Central
Álvarez et al. (2014)Email:
Ann Mar Biol Res 1(1): 1003 (2014) 8/10
new challenges provided by these complex structures, because “need” stimulates ideas and ideas are converted into innovative technology.
ACKNOWLEDGEMENTSThis study was partially funded by the CICYT (CTQ2009-
07758 and CTQ2012-30930), the Generalitat de Catalunya (2009 SGR 1024), and the Institute for Research in Biomedicine Barcelona (IRB Barcelona).
REFERENCES1. Newman DJ, Cragg GM. Natural products as sources of new drugs over
the 30 years from 1981 to 2010. J Nat Prod. 2012; 75: 311-335.
2. Paul SM, Mytelka DS, Dunwiddie CT, Persinger CC, Munos BH, Lindborg SR. How to improve R&D productivity: the pharmaceutical industry’s grand challenge. Nat Rev Drug Discov. 2010; 9: 203-214.
4. Hughes CC, Fenical W. Antibacterials from the sea. Chemistry. 2010; 16: 12512-12525.
5. Qi Y, Ma S. The medicinal potential of promising marine macrolides with anticancer activity. ChemMedChem. 2011; 6: 399-409.
6. Lorente A, Lamariano-Merketegi J, Albericio F, Álvarez M. Tetrahydrofuran-containing macrolides: a fascinating gift from the deep sea. Chem Rev. 2013; 113: 4567-4610.
7. Weissman KJ. Polyketide biosynthesis: understanding and exploiting modularity. Philos Trans A Math Phys Eng Sci. 2004; 362: 2671-2690.
8. Amoutzias GD, Van de Peer Y, Mossialos D. Evolution and taxonomic distribution of nonribosomal peptide and polyketide synthases. Future Microbiol. 2008; 3: 361-370.
9. Wang H, Fewer DP, Holm L, Rouhiainen L, Sivonen K. Atlas of nonribosomal peptide and polyketide biosynthetic pathways reveals common occurrence of nonmodular enzymes. Proc Natl Acad Sci U S A. 2014; 111: 9259-9264.
11. Weissman KJ. Uncovering the structures of modular polyketide synthases. Nat Prod Rep. 2014.
12. Cortes J, Haydock SF, Roberts GA, Bevitt DJ, Leadlay PF. An unusually large multifunctional polypeptide in the erythromycin-producing polyketide synthase of Saccharopolyspora erythraea. Nature. 1990; 348: 176-178.
13. Bevitt DJ, Cortes J, Haydock SF, Leadlay PF. 6-Deoxyerythronolide-B synthase 2 from Saccharopolyspora erythraea. Cloning of the structural gene, sequence analysis and inferred domain structure of the multifunctional enzyme. Eur J Biochem. 1992; 204: 39-49.
14. Rix U, Fischer C, Remsing LL, Rohr J. Modification of post-PKS tailoring steps through combinatorial biosynthesis. Nat Prod Rep. 2002; 19: 542-580.
15. Domínguez de María P, van Gemert RW, Straathof AJ, Hanefeld U. Biosynthesis of ethers: unusual or common natural events? Nat Prod Rep. 2010; 27: 370-392.
16. Kwan DH, Schulz F. The stereochemistry of complex polyketide biosynthesis by modular polyketide synthases. Molecules. 2011; 16: 6092-6115.
17. Mayer AM, Glaser KB, Cuevas C, Jacobs RS, Kem W, Little RD. The
odyssey of marine pharmaceuticals: a current pipeline perspective. Trends Pharmacol Sci. 2010; 31: 255-265.
18. Cragg GM, Grothaus PG, Newman DJ. New horizons for old drugs and drug leads. J Nat Prod. 2014; 77: 703-723.
19. Newman DJ, Cragg GM. Marine-sourced anti-cancer and cancer pain control agents in clinical and late preclinical development. Mar Drugs. 2014; 12: 255-278.
20. Mendola D, Naranjo Lozano SA, Duckworth A, Osinga R. The promise of aquaculture for delivering sustainable supplies of new drugs from the sea: Examples from in-sea, and tank-based invertebrate culture projects from around the world. Front Mar Biotechnol. 2006: 21–72.
21. Paterson I, Findlay AD. Recent Advances in the Total Synthesis of Polyketide Natural Products as Promising Anticancer Agents. Aust J Chem. 2009; 62: 624-638.
23. Suyama TL, Gerwick WH, McPhail KL. Survey of marine natural product structure revisions: a synergy of spectroscopy and chemical synthesis. Bioorg Med Chem. 2011; 19: 6675-6701.
24. Piel J. Bacterial symbionts: prospects for the sustainable production of invertebrate-derived pharmaceuticals. Curr Med Chem. 2006; 13: 39-50.
25. Newman DJ, Giddings L-A. Natural products as leads to antitumor drugs. Phytochem Rev. 2013; 13: 123–137.
26. Hildebrand M, Waggoner LE, Lim GE, Sharp KH, Ridley CP, Haygood MG. Approaches to identify, clone, and express symbiont bioactive metabolite genes. Nat Prod Rep. 2004; 21: 122-142.
27. Nikolouli K, Mossialos D. Bioactive compounds synthesized by non-ribosomal peptide synthetases and type-I polyketide synthases discovered through genome-mining and metagenomics. Biotechnol Lett. 2012; 34: 1393–1403.
28. Lane AL, Moore BS. A sea of biosynthesis: marine natural products meet the molecular age. Nat Prod Rep. 2011; 28: 411-428.
29. Dunlap WC, Battershill CN, Liptrot CH, Cobb RE, Bourne DG, Jaspars M. Biomedicinals from the phytosymbionts of marine invertebrates: a molecular approach. Methods. 2007; 42: 358-376.
30. Winter JM, Tang Y. Synthetic biological approaches to natural product biosynthesis. Curr Opin Biotechnol. 2012; 23: 736-743.
31. Fisch KM. Biosynthesis of natural products by microbial iterative hybrid PKS–NRPS. RSC Adv. 2013; 3: 18228 -18247.
32. Ongley SE, Bian X, Neilan BA, Müller R. Recent advances in the heterologous expression of microbial natural product biosynthetic pathways. Nat Prod Rep. 2013; 30: 1121-1138.
33. Uemura Daisuke, Takahashi Kanji, Yamamoto T, Katayam C, Tanaka J, Okumura Y, et al. Norhalichondrin A: An Antitumor Polyether Macrolide from a Marine Sponge. J Am Chem Soc. 1985; 107: 4796–4798.
34. Hirata Y, Uemura D. Halichondrins - antitumor polyether macrolides from a marine sponge. Pure Appl Chem. 1986; 58: 701–710.
35. Aicher TD, Buszek KR, Fang FG, Forsyth CJ, Jung SH, Kishi Y, et al. Total synthesis of halichondrin B and norhalichondrin B. J Am Chem Soc. 1992; 114: 3162–3164.
36. Wang Y, Habgood GJ, Christ WJ, Kishi Y, Littlefield BA, Yu MJ. Structure-activity relationships of halichondrin B analogues: modifications at C.30-C.38. Bioorg Med Chem Lett. 2000; 10: 1029-1032.
37. Dabydeen DA, Burnett JC, Bai R, Verdier-Pinard P, Hickford SJ, Pettit
GR. Comparison of the activities of the truncated halichondrin B analog NSC 707389 (E7389) with those of the parent compound and a proposed binding site on tubulin. Mol Pharmacol. 2006; 70: 1866-1875.
38. Yu MJ, Zheng W, Seletsky BM. From micrograms to grams: scale-up synthesis of eribulin mesylate. Nat Prod Rep. 2013; 30: 1158-1164.
39. Smith JA, Wilson L, Azarenko O, Zhu X, Lewis BM, Littlefield BA. Eribulin binds at microtubule ends to a single site on tubulin to suppress dynamic instability. Biochemistry. 2010; 49: 1331-1337.
40. Towle MJ, Salvato KA, Budrow J, Wels BF, Kuznetsov G, Aalfs KK. In vitro and in vivo anticancer activities of synthetic macrocyclic ketone analogues of halichondrin B. Cancer Res. 2001; 61: 1013-1021.
41. Gourmelon C, Frenel JS, Campone M. Eribulin mesylate for the treatment of late-stage breast cancer. Expert Opin Pharmacother. 2011; 12: 2883-2890.
42. Pean E, Klaar S, Berglund EG, Salmonson T, Borregaard J, Hofland KF, et al. The European medicines agency review of eribulin for the treatment of patients with locally advanced or metastatic breast cancer: summary of the scientific assessment of the committee for medicinal products for human use. Clin Cancer Res. 2012; 18: 4491-4497.
43. Mukai H, Saeki T, Shimada K, Naito Y, Matsubara N, Nakanishi T. Phase 1 combination study of Eribulin mesylate with trastuzumab for advanced or recurrent human epidermal growth factor receptor 2 positive breast cancer. Invest New Drugs. 2014.
44. Terashima M, Sakai K, Togashi Y, Hayashi H, De Velasco MA, Tsurutani J. Synergistic antitumor effects of S-1 with eribulin in vitro and in vivo for triple-negative breast cancer cell lines. Springerplus. 2014; 3: 417.
45. Pettit GR, Herald CL, Doubek DL, Herald DL, Arnold E, Clardy J. Isolation and structure of bryostatin 1. J Am Chem Soc. 1982; 104: 6846–6848.
46. Hale KJ, Hummersone MG, Manaviazar S, Frigerio M. The chemistry and biology of the bryostatin antitumour macrolides. Nat Prod Rep. 2002; 19: 413-453.
47. Kortmansky J, Schwartz GK. Bryostatin-1: a novel PKC inhibitor in clinical development. Cancer Invest. 2003; 21: 924-936.
48. Kollár P, Rajchard J, Balounová Z, Pazourek J. Marine natural products: bryostatins in preclinical and clinical studies. Pharm Biol. 2014; 52: 237-242.
49. Hale KJ, Manaviazar S. New approaches to the total synthesis of the bryostatin antitumor macrolides. Chem Asian J. 2010; 5: 704-754.
51. Irie K, Yanagita RC. Synthesis and biological activities of simplified analogs of the natural PKC ligands, bryostatin-1 and aplysiatoxin. Chem Rec. 2014; 14: 251-267.
53. Rinehart KL, Gloer JB, Cook JC, Mizsak SA, Scahill TA. Structures of the didemnins, antiviral and cytotoxic depsipeptides from a Caribbean tunicate. J Am Chem Soc. 1981; 103: 1857–1859.
54. Urdiales JL, Morata P, Núñez De Castro I, Sánchez-Jiménez F. Antiproliferative effect of dehydrodidemnin B (DDB), a depsipeptide isolated from Mediterranean tunicates. Cancer Lett. 1996; 102: 31-37.
55. Lee J, Currano JN, Carroll PJ, Joullié MM. Didemnins, tamandarins and
related natural products. Nat Prod Rep. 2012; 29: 404-424.
56. Humeniuk R, Menon LG, Mishra PJ, Saydam G, Longo-Sorbello GS, Elisseyeff Y, et al. Aplidin synergizes with cytosine arabinoside: functional relevance of mitochondria in Aplidin-induced cytotoxicity. Leukemial. 2007; 21: 2399–2405.
57. Plummer R, Lorigan P, Brown E, Zaucha R, Moiseyenko V, Demidov L. Phase I-II study of plitidepsin and dacarbazine as first-line therapy for advanced melanoma. Br J Cancer. 2013; 109: 1451-1459.
58. Jou G, González I, Albericio F, Lloyd-Williams P, Giralt E. Total Synthesis of Dehydrodidemnin B. Use of Uronium and Phosphonium Salt Coupling Reagents in Peptide Synthesis in Solution. J Org Chem. 1997; 62: 354-366.
59. Oliveira H, Thevenot J, Garanger E, Ibarboure E, Calvo P, Aviles P. Nano-encapsulation of plitidepsin: in vivo pharmacokinetics, biodistribution, and efficacy in a renal xenograft tumor model. Pharm Res. 2014; 31: 983-991.
60. Xu Y, Kersten RD, Nam SJ, Lu L, Al-Suwailem AM, Zheng H. Bacterial biosynthesis and maturation of the didemnin anti-cancer agents. J Am Chem Soc. 2012; 134: 8625-8632.
61. Martín MJ, Coello L, Fernández R, Reyes F, Rodríguez A, Murcia C. Isolation and first total synthesis of PM050489 and PM060184, two new marine anticancer compounds. J Am Chem Soc. 2013; 135: 10164-10171.
62. Martínez-Díez M, Guillén-Navarro MJ, Pera B, Bouchet BP, Martínez-Leal JF, Barasoain I, et al. PM060184, a new tubulin binding agent with potent antitumor activity including P-glycoprotein over-expressing tumors. Biochem Pharmacol. 2014; 88: 291–302.
63. Pera B, Barasoain I, Pantazopoulou A, Canales A, Matesanz R, Rodriguez-salarichs J, et al. New Interfacial Microtubule Inhibitors of Marine Origin, PM050489/ PM060184, with Potent Antitumor Activity and a Distinct Mechanism. 2013; 8: 2084–2094.
64. Prota AE, Bargsten K, Diaz JF, Marsh M, Cuevas C, Liniger M. A new tubulin-binding site and pharmacophore for microtubule-destabilizing anticancer drugs. Proc Natl Acad Sci U S A. 2014; 111: 13817-13821.
65. Feling RH, Buchanan GO, Mincer TJ, Kauffman CA, Jensen PR, Fenical W. Salinosporamide A: a highly cytotoxic proteasome inhibitor from a novel microbial source, a marine bacterium of the new genus salinospora. Angew Chem Int Ed Engl. 2003; 42: 355-357.
66. Gulder TA, Moore BS. Salinosporamide natural products: Potent 20 S proteasome inhibitors as promising cancer chemotherapeutics. Angew Chem Int Ed Engl. 2010; 49: 9346-9367.
67. Beer LL, Moore BS. Biosynthetic convergence of salinosporamides A and B in the marine actinomycete Salinispora tropica. Org Lett. 2007; 9: 845-848.
68. Eustáquio AS, McGlinchey RP, Liu Y, Hazzard C, Beer LL, Florova G. Biosynthesis of the salinosporamide A polyketide synthase substrate chloroethylmalonyl-coenzyme A from S-adenosyl-L-methionine. Proc Natl Acad Sci U S A. 2009; 106: 12295-12300.
69. Miller CP, Ban K, Dujka ME, McConkey DJ, Munsell M, Palladino M. NPI-0052, a novel proteasome inhibitor, induces caspase-8 and ROS-dependent apoptosis alone and in combination with HDAC inhibitors in leukemia cells. Blood. 2007; 110: 267-277.
70. Chauhan D, Catley L, Li G, Podar K, Hideshima T, Velankar M. A novel orally active proteasome inhibitor induces apoptosis in multiple myeloma cells with mechanisms distinct from Bortezomib. Cancer Cell. 2005; 8: 407-419.
KC. Pharmacodynamic and efficacy studies of the novel proteasome inhibitor NPI-0052 (marizomib) in a human plasmacytoma xenograft murine model. Br J Haematol. 2010; 149: 550-559.
72. Richardson PG, Spencer A, Cannell P, Harrison SJ, Catley L, Underhill C, et al. Phase 1 Clinical Evaluation of Twice-Weekly Marizomib (NPI-0052), a Novel Proteasome Inhibitor, in Patients with Relapsed/Refractory Multiple Myeloma (MM). ASH Annu Meet Abstr. 2011; 118: 302.
73. Allegra A, Alonci A, Gerace D, Russo S, Innao V, Calabrò L. New orally active proteasome inhibitors in multiple myeloma. Leuk Res. 2014; 38: 1-9.
74. Potts BC, Albitar MX, Anderson KC, Baritaki S, Berkers C, Bonavida B. Marizomib, a proteasome inhibitor for all seasons: preclinical profile and a framework for clinical trials. Curr Cancer Drug Targets. 2011; 11: 254-284.
75. Potts BC, Lam KS. Generating a generation of proteasome inhibitors: from microbial fermentation to total synthesis of salinosporamide a (marizomib) and other salinosporamides. Mar Drugs. 2010; 8: 835-880.
76. Nguyen H, Ma G, Romo D. A(1,3)-strain enabled retention of chirality during bis-cyclization of beta-ketoamides: total synthesis of (-)-salinosporamide A and (-)-homosalinosporamide A. Chem Commun (Camb). 2010; 46: 4803-4805.
77. Nguyen H, Ma G, Gladysheva T, Fremgen T, Romo D. Bioinspired total synthesis and human proteasome inhibitory activity of (-)-salinosporamide A, (-)-homosalinosporamide A, and derivatives obtained via organonucleophile promoted bis-cyclizations. J Org Chem. 2011; 76: 2-12.
78. Kaiya Y, Hasegawa J, Momose T, Sato T, Chida N. Total synthesis of (-)-salinosporamide A. Chem Asian J. 2011; 6: 209-219.
79. Satoh N, Yokoshima S, Fukuyama T. Total synthesis of (-)-salinosporamide A. Org Lett. 2011; 13: 3028-3031.
80. Pettit GR, Chicacz ZA, Gao F, Herald CL, Boyd MR, Schmidt JM, et al. Isolation and structure of spongistatin 1. J Org Chem 1993; 58: 1302–1304.
81. von Schwarzenberg K, Vollmar AM. Targeting apoptosis pathways by natural compounds in cancer: marine compounds as lead structures and chemical tools for cancer therapy. Cancer Lett. 2013; 332: 295-303.
82. Bai R, Cichacz ZA, Herald CL, Pettit GR, Hamel E. Spongistatin 1, a highly cytotoxic, sponge-derived, marine natural product that inhibits mitosis, microtubule assembly, and the binding of vinblastine to tubulin. Mol Pharmacol. 1993; 44: 757-766.
83. Xu Q, Huang KC, Tendyke K, Marsh J, Liu J, Qiu D. In vitro and in vivo anticancer activity of (+)-spongistatin 1. Anticancer Res. 2011; 31: 2773-2779.
84. Rothmeier AS, Schneiders UM, Wiedmann RM, Ischenko I, Bruns CJ, Rudy A. The marine compound spongistatin 1 targets pancreatic tumor progression and metastasis. Int J Cancer. 2010; 127: 1096-1105.
85. Pettit RK, Woyke T, Pon S, Cichacz ZA, Pettit GR, Herald CL. In vitro and in vivo antifungal activities of the marine sponge constituent spongistatin. Med Mycol. 2005; 43: 453-463.
86. Cheung RC, Wong JH, Pan WL, Chan YS, Yin CM, Dan XL. Antifungal and antiviral products of marine organisms. Appl Microbiol Biotechnol. 2014; 98: 3475-3494.
87. Morris JC, Nicholas GM, Phillips AJ. Marine natural products: synthetic aspects. Nat Prod Rep. 2007; 24: 87-108.
88. Smith AB, Sfouggatakis C, Risatti CA, Sperry JB, Zhu W, Doughty VA. Spongipyran Synthetic Studies. Evolution of a Scalable Total Synthesis of (+)-Spongistatin 1. Tetrahedron. 2009; 65: 6489-6509.
89. Reznik SK, Leighton JL. Toward a more step-economical and scalable synthesis of spongistatin 1 to facilitate cancer drug development efforts. Chem Sci. 2013; 4: 1497-1501.
90. Gunasekera SP, Gunasekera M, Longley RE, Pierce F, Schulte GK. Discodermolide: A New Bioactive Polyhydroxylated Lactone from the Marine Sponge Discodermia dissoluta. J Org Chem 1990; 55: 4912–4915.
91. Nerenberg JB, Hung DT, Somers PK, Schreiber SL. Total synthesis of the immunosuppressive agent (-)-discodermolide. J Am Chem Soc. 1993; 115: 12621–12622.
92. Hung DT, Nerenberg JB, Schreiber SL. Distinct binding and cellular properties of synthetic (+)- and (-)-discodermolides. Chem Biol. 1994; 1: 67-71.
93. De Souza MV. (+)-discodermolide: a marine natural product against cancer. ScientificWorldJournal. 2004; 4: 415-436.
94. Arefolov A, Panek JS. Crotylsilane reagents in the synthesis of complex polyketide natural products: total synthesis of (+)-discodermolide. J Am Chem Soc. 2005; 127: 5596-5603.
95. Smith AB 3rd, Freeze BS, Xian M, Hirose T. Total synthesis of (+)-discodermolide: a highly convergent fourth-generation approach. Org Lett. 2005; 7: 1825-1828.
96. de Lemos E, Porée FH, Commerçon A, Betzer JF, Pancrazi A, Ardisson J. alpha-Oxygenated crotyltitanium and dyotropic rearrangement in the total synthesis of discodermolide. Angew Chem Int Ed Engl. 2007; 46: 1917-1921.
97. Paterson I, Lyothier I. Total synthesis of (+)-discodermolide: an improved endgame exploiting a Still-Gennari-type olefination with a C1-C8 beta-ketophosphonate fragment. Org Lett. 2004; 6: 4933-4936.
98. Yu Z, Ely RJ, Morken JP. Synthesis of (+)-discodermolide by catalytic stereoselective borylation reactions. Angew Chem Int Ed Engl. 2014; 53: 9632-9636.
99. Ruiz C, Valderrama K, Zea S, Castellanos L. Mariculture and natural production of the antitumoural (+)-discodermolide by the Caribbean marine sponge Discodermia dissoluta. Mar Biotechnol (NY). 2013; 15: 571-583.
100. Martello LA, McDaid HM, Regl DL, Yang CP, Meng D, Pettus TR. Taxol and discodermolide represent a synergistic drug combination in human carcinoma cell lines. Clin Cancer Res. 2000; 6: 1978-1987.
101. Smith AB, Sugasawa K, Atasoylu O, Yang CP, Horwitz SB. Design and synthesis of (+)-discodermolide-paclitaxel hybrids leading to enhanced biological activity. J Med Chem. 2011; 54: 6319-6327.
102. Molinski TF, Dalisay DS, Lievens SL, Saludes JP. Drug development from marine natural products. Nat Rev Drug Discov. 2009; 8: 69-85.
Lorente A, Makowski K, Albericio F, Álvarez M (2014) Bioactive Marine Polyketides as Potential and Promising Drugs. Ann Mar Biol Res 1(1): 1003.
