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INTRODUCTION
Marine macroalgae also known as seaweeds represent a vast, multifaceted, and largely untapped reservoir of natural bioactive compounds with significant therapeutic potential (Monroy-García et al., 2025). These multicellular photosynthetic organisms, encompassing brown (Phaeophyceae), red (Rhodophyta), and green (Chlorophyta) lineages, thrive across diverse marine environments and have evolved remarkable chemical defenses against predators, microbial pathogens, and environmental stressors (L. Pereira, 2021; Premarathna et al., 2022). This evolutionary pressure has endowed them with complex secondary metabolites, including polyphenols, sulfated polysaccharides, carotenoids, terpenoids, and peptides that possess potent biological activities such as antioxidant, antiviral, anti-inflammatory, and notably, antiparasitic effects (Kumar et al., 2021; Leandro et al., 2019). Despite considerable exploration of macroalgae for applications in nutraceuticals and oncology, their role in controlling parasitic diseases remains underexplored (Adarshan et al., 2023). Increasing resistance to frontline antiparasitic agents for diseases such as malaria, leishmaniasis, Chagas disease, and schistosomiasis underscores the urgent necessity for novel chemical scaffolds with alternative mechanisms of action (Njoroge et al., 2014). Marine macroalgae and their microbial metabolites offer a promising frontier in this context, providing both novel chemical diversity and ecological sustainability (Vicente et al., 2021). Traditional usage of certain seaweed species as deworming agents, such as Digenea simplex against human intestinal nematodes, and the nematocidal properties found in Notheia anomala extracts illustrate the ethnopharmacological relevance of these organisms (Bonde et al., 2021). More recently, in vivo and in vitro studies have confirmed significant antiparasitic activity from cold-water brown algae species (e.g., Laminaria digitata, Saccharina latissima) against gastrointestinal nematodes like Ascaris suum and Teladorsagia circumcincta (Bonde et al., 2023). Moreover, compounds such as Sulfoquinovosyl Diacylglycerols (SQDGs) identified in Lobophora variegata demonstrate potent inhibition of anaerobic protozoa including Giardia intestinalis, Entamoeba histolytica, and Trichomonas vaginalis (Cantillo-Ciau et al., 2010). These findings highlight the functional relevance of macroalgal metabolites against a broad spectrum of parasitic taxa and emphasize their potential as sources of antiparasitic drug leads. However, sustainability challenges, such as low natural abundance, inefficient extraction protocols, and variable compound yields, have hindered systematic drug discovery efforts from macroalgae. Advances in green extraction technologies, aquaculture systems, and synthetic biology are now offering viable solutions to these limitations (Nurkolis, 2025; Samoraj et al., 2024). This review aims to comprehensively explore the phytochemistry, pharmacology, and toxicological attributes of marine macroalgal metabolites with demonstrated anti-parasitic activity. This review also elaborates current knowledge across redox-stressed habitats, analyze structure-activity relationships of key compounds, and critically assess translational feasibility, including extraction scalability, mechanistic targets, and cytotoxicity profiles.
SURVEY OF ANTIPARASITIC MARINE MICROBIAL METABOLITES
Marine Microbial Metabolites Active Against Pathogenic Protozoa
Marine microbial ecosystems represent a prolific and evolutionarily distinct reservoir of secondary metabolites with broad-spectrum activity against human protozoan pathogens such as Plasmodium, Trypanosoma, Leishmania, and Toxoplasma gondii. These parasites, responsible for a significant global disease burden, particularly in tropical and developing regions, exhibit increasing drug resistance and necessitate new therapeutic scaffolds. Marine-derived actinomycetes, cyanobacteria, and sponge-associated bacteria have yielded structurally unique compounds including alkaloids, depsipeptides, nucleoside analogs, and polyketides, each with targeted or multitarget anti-protozoal actions (Ameen et al., 2021; Davies-Bolorunduro et al., 2021).
Ionophoric and Kinase-Inhibiting Depsipeptides: Valinomycin and Staurosporine
Valinomycin, a cyclic dodecadepsipeptide produced by Streptomyces spp. from Mediterranean sponges, demonstrates potent ionophoric activity by disrupting mitochondrial potassium gradients, leading to loss of membrane potential and parasite death. It is highly active against T. brucei (IC50 ≈ 3.2 nM) and Leishmania major (IC50 < 110 nM), exhibiting a selectivity index (SI) >100 (Andersson et al., 1998; New Molecular Entities and Structure–Activity Relationships of Drugs Designed by the Natural Product Derivatization Method from, 2010 to 2018, 2021). Staurosporine, an indolocarbazole also from marine Streptomyces, inhibits protein kinases in T. brucei (IC50 ≈ 5.3 μM), affecting cell cycle progression and inducing apoptosis via caspase-like pathways (Stepczynska et al., 2001). Both represent bioactive leads with defined mechanisms, though staurosporine’s moderate host toxicity remains a developmental constraint.
Broad-Spectrum Nucleoside Analogue: Tubercidin and Derivatives
Tubercidin, a C7-deazaadenosine analog from marine Streptomyces and sponge symbionts, disrupts purine salvage pathways essential in protozoan parasites. It exhibits potent inhibition across Trypanosoma brucei, Trypanosoma cruzi, Leishmania spp., and Toxoplasma gondii, with IC50 values between 0.06-0.30 μM. Tubercidin-treated murine models showed complete clearance of bloodstream trypanosomes without notable toxicity (Drew et al., 2003). However, its non-specificity toward mammalian purine transporters necessitates prodrug development or derivatization. 3′-deoxytubercidin analogs are under evaluation for improved selectivity (Fiuza et al., 2022).
Mitochondrial Disruptors: Renieramycin A and Araguspongin C
Renieramycin A, a tetrahydroisoquinoline alkaloid from Xestospongia spp., exhibits anti-leishmanial activity with an IC50 ≈ 0.2 µg/mL. Araguspongin C, another sponge alkaloid, induces parasite clearance in L. donovani-infected hamsters (~39% reduction in liver burden) (Fang et al., 2021). These compounds act primarily through mitochondrial membrane disruption and ROS generation, leading to parasite apoptosis without triggering host cell necrosis. Their safety profiles, along with synthetic accessibility, support further preclinical development (Fonseca-Silva et al., 2011).
DNA Synthesis Inhibitor: Marinopyrrole A
Marinopyrrole A, an aromatic heterocycle from Streptomyces sp., inhibits T. gondii tachyzoites with an IC50 of 0.31 μM by intercalating into DNA and stalling replication forks. However, serum binding (>20%) reduces efficacy, indicating the need for optimized formulation or analog development. This pharmacokinetic limitation is being addressed through nanoparticle encapsulation strategies (Guo et al., 2024; Martens et al., 2022).
Protease Inhibitors: Gallinamide A and Related Lipodepsipeptides
Gallinamide A, isolated from Schizothrix and Symploca cyanobacteria, exhibits targeted inhibition of falcipain and cruzain cysteine proteases. It demonstrates efficacy against P. falciparum (IC50 ≈ 8.4 μM) and L. donovani (~9.3 μM), although it is inactive against T. cruzi, likely due to lack of compound permeability or target engagement (Barbosa Da Silva et al., 2022; Miller et al., 2014). Gallinamide binds irreversibly to parasite cysteine proteases through its α, β-unsaturated carbonyl moiety, inducing proteolytic dysfunction and starvation (Boudreau et al., 2019).
Cytoskeletal Disruptors: Oroidin and Analogues
Oroidin, a bromopyrrole alkaloid from Agelas sponges, displays moderate multi-protozoan activity (P. falciparum, T. brucei, T. cruzi, L. donovani) with IC50 ranging from 10-50 μM. It disrupts cytoskeletal integrity and mitochondrial morphology (Scala et al., 2010). SAR studies show that halogenation and amide modifications enhance selectivity and potency, suggesting a promising scaffold for further lead optimization.
Marine Microbial Metabolites Against Anaerobic Protozoa
Anaerobic protozoa, including Entamoeba histolytica, Giardia intestinalis, and Trichomonas vaginalis, cause widespread gastrointestinal and urogenital infections, particularly in low-resource settings. Their unique metabolic adaptations such as reliance on fermentation, hydrogenosomes, and non-canonical redox enzymes offer distinctive drug targets. Marine-derived microbial compounds, particularly glycolipids and non-ribosomal peptides, have shown activity through mechanisms involving oxidative stress, transcriptional suppression, and cytoskeletal collapse (Priya et al., 2008; Sabatke et al., 2021).
Glycolipid-Mediated Membrane Disruption: Sulfoquinovosyldiacylglycerols (SQDGs)
SQDGs, primarily isolated from the brown alga Lobophora variegata but associated with epiphytic microbial consortia, exhibit potent in vitro activity (1-5 µg/mL crude extracts) against Giardia, Entamoeba, and Trichomonas. These sulfonated glycolipids incorporate into parasite membranes, inducing oxidative membrane damage and lytic death. The palmitoyl myristoyl variant shows the highest potency, and liposomal formulations are under exploration to enhance delivery and specificity (Estrella-Parra et al., 2022; Kini et al., 2020).
Transcriptional and Proteasomal Inhibitors: Tirandamycins and Carmaphycins
Tirandamycin B, a tetrahydrofuran-containing polyketide from Streptomyces spp., inhibits parasite RNA polymerases, impairing gene expression in anaerobic protozoa (Reusser, 1970). Similarly, carmaphycin B, a β-lactone containing peptide from marine cyanobacteria, disrupts proteasomal function. Although IC50 values for anaerobic protozoa remain limited in literature, mechanistic studies confirm host-independent targeting of conserved parasite machinery. Resistance profiling is needed to fully determine therapeutic viability (A. R. Pereira et al., 2012).
Actin-Binding Peptides: Jasplakinolide, Symplocamide A, and Venturamides
Depsipeptides such as jasplakinolide (from Jaspis sp.), symplocamide A, and venturamides target cytoskeletal actin filaments, causing impaired motility, division, and encystation in anaerobic parasites. Jasplakinolide stabilizes F-actin, leading to morphological disarray and inhibition of phagocytosis in Entamoeba histolytica. These mechanisms are relevant across multiple protozoan genera, and although cytotoxicity must be carefully managed, analog development may allow improved selectivity (Bubb et al., 1994; Posey & Bierer, 1999).
Marine Microbial Metabolites Targeting Helminths (Trematodes and Other Endoparasites)
Helminthic infections particularly those caused by Schistosoma species, affect over 200 million people worldwide and contribute to significant morbidity, especially in tropical and subtropical regions. Current treatments rely heavily on praziquantel and albendazole, both of which face emerging resistance and fail to target larval or migratory stages (Utzinger & Keiser, 2004). Marine-derived microbial metabolites offer novel structural templates and mechanisms to combat helminthic infections, with some already showing efficacy in disrupting egg-laying, reproductive organ function, or tegument integrity of helminths (König et al., 2006).
Naphthacene Glycosides: SF2446A2 from Marine Streptomyces
SF2446A2 is a naphthacene glycoside isolated from Streptomyces sp. derived from Mediterranean sponges. It demonstrates potent phenotypic activity against adult Schistosoma mansoni. At a concentration of 50 µM, SF2446A2 completely abolished egg-laying within 72 hours in ex vivo assays and induced severe tegumental damage, gonadal degeneration, and disorganization of oogenesis and spermatogenesis (Reimer et al., 2015). Histological evaluation of treated worms revealed vacuolation of gonadal tissues, erosion of the syncytial tegument, and disruption of musculature, effects not typically observed with praziquantel. The compound likely acts on nuclear or mitochondrial DNA replication pathways or through oxidative stress induction, although the precise molecular mechanism remains to be fully elucidated (Winkelmann et al., 2021).
Multitarget Nucleoside Analog: Tubercidin as a Dual Anti-Protozoal and Anti-Helminthic Agent
Although primarily characterized as an anti-protozoal agent, tubercidin a nucleoside analog produced by Streptomyces and marine sponge symbionts has shown significant cross-activity against helminths. In murine models of S. mansoni infection, tubercidin treatment resulted in parasite clearance and reversal of hepatosplenomegaly, suggesting systemic efficacy. The compound likely inhibits DNA and RNA synthesis in schistosomes via its incorporation into nucleic acid chains, ultimately leading to parasite apoptosis. Moreover, in vivo tolerability studies demonstrated acceptable host safety, though caution is warranted due to its narrow therapeutic index. Its dual action across multiple parasitic phyla underscores its potential as a lead for developing broad-spectrum antiparasitic agents, particularly in co-endemic settings (Biabani et al., 2002; Pimentel-Elardo et al., 2010).
Perspective: Marine Actinomycete and Cyanobacterial Libraries for Anti-Helminth Discovery
The activity of tubercidin against S. mansoni opens the door to systematic screening of marine actinomycete and cyanobacterial metabolite libraries for anti-helminthic candidates. Genome mining of Salinispora, Micromonospora, and Nocardiopsis strains has revealed numerous biosynthetic gene clusters (BGCs) encoding PKS-NRPS hybrids, which may yield analogs capable of targeting schistosome tegument integrity, neuromuscular transmission, or reproductive processes. Furthermore, cyanobacterial depsipeptides and indole alkaloids known to modulate actin cytoskeleton or proteasome function in protozoa may show cross-activity against helminths due to conserved cellular machinery. Such structural scaffolds have yet to be systematically tested in Schistosoma, Brugia, or Echinococcus models, representing a major knowledge gap and an opportunity for future exploration. Table 1 describes a comparison of various marine metabolite’s sources, targets, efficacy, and selectivity, and Figure 1 depicts the comparison potency between some marine microbial antiparasitic metabolites.
| Compound | Source Organism | Target Parasite(s) | In vitro Potency (IC50/EC50) | Host Cytotoxicity/SI | Proposed Mechanism of Action | References |
|---|---|---|---|---|---|---|
| Valinomycin | Streptomyces sp. from marine sponge | T. brucei, L. major | 3.2 nM (T. brucei), <110 nM (L. major) | CC50 >10 µM; SI >100 | Ionophore disrupting K⁺ homeostasis in protozoa | (Pimentel-Elardo et al., 2010) |
| Staurosporine | Marine Streptomyces | T. brucei | 5.3 µM | Moderate cytotoxicity | Protein kinase inhibition | (Cartuche et al., 2019; Choi et al., 2024) |
| Tubercidin | Marine sponge symbiont | T. cruzi, L. donovani, S. mansoni | 0.06-0.30 µM | Good tolerability in mice | Purine analog-nucleoside metabolism inhibition | (Choi et al., 2024; Orhan et al., 2010) |
| Renieramycin A | Marine sponge (Xestospongia) | L. amazonensis | ~0.2 µg/mL | Low cytotoxicity | Mitochondrial dysfunction | (Halim et al., 2011) |
| Marinopyrrole A | Marine Streptomyces | T. gondii | 0.31 µM | IC50 ↑ in serum >20% | DNA synthesis inhibition | (Martens et al., 2022) |
| Gallinamide A | Schizothrix / Symploca (cyanobacteria) | P. falciparum, L. donovani | 8.4 µM (Pf), 9.3 µM (Ld) | Minimal cytotoxicity | Irreversible cathepsin L inhibition | (Tan & Salleh, 2024) |
| Oroidin | Sponge (Agelas spp.) | P. falciparum, T. brucei, L. donovani | 10-50 µM | Low-moderate toxicity | Cytoskeletal disruption | (Gribble, 2015; Mayer et al., 2019) |
| SQDG lipids | Brown alga Lobophora variegata | Entamoeba, Giardia, Trichomonas | 1-5 µg/mL (crude), pure not defined | Not reported | Membrane perturbation, oxidative stress induction | (Cantillo-Ciau et al., 2010) |
| SF2446A2 | Marine Streptomyces | S. mansoni | Functional inhibition (50 µM) | No major host toxicity noted | Tegumental and gonadal tissue degeneration | (Cantillo-Ciau et al., 2010; Reimer et al., 2015) |
MAJOR MARINEDERIVED MICROBIAL METABOLITES WITH ANTIPARASITIC POTENTIAL
Marine-derived microorganisms, particularly those associated with sponges, sediments, and cyanobacteria, have emerged as prolific sources of structurally diverse and pharmacologically potent natural products. Several of these microbial metabolites have demonstrated significant anti-parasitic activities against a broad range of protozoan parasites including Plasmodium spp., Leishmania spp., Trypanosoma spp., and Toxoplasma gondii. Figure 2 depicts the chemical structures of major marine derived metabolites. These compounds span multiple phytochemical categories such as alkaloids, polyketides, macrolides, lipodepsipeptides, and β-lactones, each exhibiting unique structural scaffolds and mechanisms of action. Despite promising in vitro and some in vivo results, many of these metabolites remain underexplored in terms of pharmacokinetics, toxicity, and translational viability. The following Table 2 categorizes these compounds based on their phytochemical class, microbial source, parasitic target, and key pharmacological activities.
| Phytoconstituent Class | Compound Name | Source | Parasite Target | Pharmacological Activity | References |
|---|---|---|---|---|---|
| βCarboline Alkaloids | Manzamine A; 8hydroxymanzamine; Manzamine F | Spongeassociated (Haliclona, Xestospongia etc.) microbial symbionts | P. berghei (rodent malaria) (nanomolar IC50); also, Leishmania, T. brucei | Very potent antiplasmodial, induces morphological parasite damage | (El-Desoky & Tsukamoto, 2020; Kokkaliari et al., 2021; Rao et al., 2003) |
| Pyrrole / Imidazole / Indole Alkaloids | Calothrixin A, Calothrixin B; Oroidin (and analogues) | Marine cyanobacteria (e.g., Calothrix, Lyngbya) | P. falciparum, T. cruzi, T. brucei, L. donovani | Moderate-to-potent activity; oroidin analogues inhibit T. brucei rhodesiense etc. | (Rickards et al., 1999; Xu et al., 2016; Zidar et al., 2014) |
| Macrolide / Cyclic Peptides | Cyclomarin A; Lyngbyabellin A; Salinipostins A | Marine actinomycetes (Salinispora tropica, Lyngbya, others) | P. falciparum (W2, D6, K1 strains) | Cyclomarin targets PfAp3Ase; salinipostins inhibit serine hydrolases; potent nanomolar activity | (Jensen et al., 2015a, 2015b; Y. Lee et al., 2017) |
| βLactone / Proteasome Inhibitors | Salinosporamide A (Marizomib) and analogues | Salinispora tropica and S. arenicola | P. falciparum in vitro antimalaria screens | Also, in oncological trials; mechanism proteasome inhibition | (Jensen et al., 2015a; Sülzen et al., 2025) |
| Lipodepsipeptides | Gallinamide A (Symplostatin4) | Marine cyanobacteria (Schizothrix, Symploca) | P. falciparum (IC50 ~8.4 µM), L. donovani (~9.3 µM) | Selective cysteine protease inhibitor (cathepsin/cruzain) | (Stolze et al., 2012) |
| Glycosylated Polyketides / Siderophores | Actinosporin A | Spongeassociated Actinobacteria | T. brucei (antitrypanosomal) | Unique glycosylated scaffold; early-stage lead | (Gonçalves et al., 2022; Selim et al., 2021) |
| Nucleoside Analogue | Tubercidin (and derivatives e.g., 3′deoxytubercidin) | Streptomyces spp., cyanobacteria, sponge symbionts | T. cruzi (antitrypanosomal), antiprotozoal | Potent antitrypanosomal; some derivatives show low host toxicity | (Nwoke et al., 2024) |
PHYTOCHEMISTRY AND STRUCTURAL DIVERSITY
In recent years, marinederived microbial sources, especially sponge‐associated microorganisms, sedimentderived actinomycetes, and cyanobacteria (e.g. Calothrix, Streptomyces, Salinispora, Moorea), have become increasingly recognized as fertile reservoirs for structurally diverse antiparasitic metabolites. Isolation typically begins with collection of marine sponges or sediments, followed by stringent pretreatment protocols (e.g. dry heat, freezethaw, selective antibiotic pretreatment) and highthroughput cultivation using media optimized with seawater, specific carbon sources, and inhibitors to suppress fast‐growing contaminants, facilitating recovery of rare genera such as Salinispora and marine Streptomyces spp (J. Chen et al., 2021; J. Kuo et al., 2019; Shrestha et al., 2021). From these biosources, diverse compound classes have emerged. Salinispora tropica and S. arenicola yield halogenated γlactamβlactone bicyclic compounds such as salinosporamide A (marizomib), produced via a hybrid PKSNRPS gene cluster featuring an irondependent halogenase responsible for chlorination of an unactivated methyl precursor. Likewise, Streptomyces species associated with sponges (e.g. S. tateyamensis, S. marinus) deliver alkaloids (tubercidin), polyketides (tirandamycin B), angucyclinones, glutarimides, and glycosylated polyenes with antiparasitic or enzyme inhibitory activity (Bauman et al., 2022; Gulder & Moore, 2010).
Biosynthetic Gene Clusters and Isolation Strategies
Environmental sampling of sponges, sediments, or cyanobacterial mats is followed by selective cultivation and genomic screening for PKS/NRPS gene clusters (Agrawal et al., 2017). For example, in Salinispora sp., gene architecture comprises a PKS module synthesizing polyketide backbone, an NRPS module incorporating the amino acid βhydroxycyclohexenylalanine, and a nonheme iron halogenase that installs the chlorine in salinosporamide A (Rocha-Martin et al., 2014). Similarly, gene clusters encoding cyclomarin in Salinispora spp. combine NRPS modules with unusual tailoring domains to produce a cyclic peptide scaffold. Mapping these BGCs allows prediction of structural modification and tailoring enzymes that drive halogenation, glycosylation, or macrocyclization (Pimentel-Elardo et al., 2012). Figure 3 depicts the biosynthetic gene clusters for Salinosporamide and Cyclomarin.
Structural Diversity and Unique Motifs
Marine microbial metabolites display notable structural uniqueness; Halogenated scaffolds, such as salinosporamide A, featuring a chlorinated bicyclic γlactamβlactone core. Enediyne and polyene motifs, as seen in angucyclinones or tirandamycin derivatives (Wang et al., 2021). Cyclic peptides and depsipeptides, exemplified by cyclomarin, lyngbyabellins, and analogues like homiamides (depsipeptides from Streptomyces ROA065). Glycolipid headgroups, including glycosidic sphingolipids from cyanobacteria and sponge symbionts, some of which display antiGiardia effect (though not detailed here) and possess unique βglycoside linkages (Moore, 1996). Structural features are often correlated with bioactivity; for example, the halogen substitution in salinosporamide analogues significantly enhances proteasome inhibitory potency, while removal or alteration of the halogen diminishes target affinity.
Structure Activity Relationships (SAR) Insights
Salinosporamide analogues (B-J, bromosalinosporamide, thioester derivatives)
Modifications at the halogen-bearing carbon or alkyl branch yield analogues with altered proteasome inhibition profiles. Retention of the bicyclic core structure with chlorine increases potency, whereas substitution often reduces selectivity index (Potts & Lam, 2010).
Lyngbyabellin analogues from cyanobacterial peptides
Variations in side chain length and cyclization status (macrocycle vs depsiforms) influence cytotoxicity and target selectivity, implying fine structural tuning can enhance parasite selectivity (Fathoni et al., 2020; Yokokawa et al., 2001).
Depsipeptides like homiamides A-C
Changes in amino acid sequence or hydroxylation pattern influence antibacterial activity and cytotoxicity moderately but may indicate how to engineer antiparasitic efficacy (Kim et al., 2024).
Tirandamycin B vs A
The keto-enol positional isomerism dramatically affects inhibitory activity against Brugia malayi AsntRNA synthetase; B (1keto4′enol) is active (IC50 ≈ 30 μM), whereas A shows different bacterial enzyme targeting and less antiparasitic activity (Pang et al., 2021; Zhao et al., 2014).
Table 3 describes that structural features and SAR of various marine-derived microbial metabolites with antiparasitic potential, and Figure 4 depicts the structure and SAR of Analog modifications of those marine microbial metabolites.
| Compound | Key Structural Motif | SAR/Analog Modifications | Effect on Potency or Selectivity | References |
|---|---|---|---|---|
| Salinosporamide A/B/J | Halogenated γlactamβlactone bicyclic | Variation of halogen (Cl, Br), butyrate substitutions | ClA most potent; Br or nonhalogen lower activity | (Agarwal et al., 2017; Sülzen et al., 2025) |
| Cyclomarin analogues | Cyclic peptide scaffold | Tailoring side chains, ring size | Affects selectivity vs parasite proteasome | (Kazmaier & Junk, 2021; Ribeiro et al., 2023) |
| Lyngbyabellins | Macrocyclic depsipeptide | Side chain hydroxylation, cyclodepsipeptide variants | Alters cytotoxicity/selectivity indices | (Alvarez-Sánchez et al., 2024; Fathoni et al., 2020) |
| Tirandamycin A vs B | Polyeneketone vs ketoenol | Isomerism between tautomeric forms | B active against parasite enzyme; A less so | (Jiang et al., 2020) |
| Homiamides A-C | Linear/depsipeptide variants | Amino acid substitution, hydroxylation pattern | Modulates antimicrobial but unknown antiparasitic | (Kim et al., 2024) |
PHARMACOLOGY AND MECHANISM OF ACTION
In vitro Efficacy
Marinederived microbial metabolites such as salinosporamide A (marizomib) and gallinamide A, as well as manzamine A, have demonstrated promising inhibitory activity against parasitic protozoa in culture systems. Salinosporamide A, isolated from Salinispora tropica, exhibits potent activity against erythrocytic Plasmodium falciparum (H.-S. Lee & Jeong, 2020). A study reported IC50 in the low-nanomolar range, with comparative assays showing similar potency to proteasome inhibitor MG132 (IC50 ≈ 40 nM) during SYBR Green growth assays (Barzkar et al., 2024; Prudhomme et al., 2008), (Fan et al., 2011). Cytotoxicity in host cells (mammalian) was minimal at these concentrations, yielding favorable selectivity indices (SI not explicitly quantified but inferred based on comparative MG132 data). Gallinamide A, a cyanobacterial depsipeptide, exhibited selective inhibition of P. falciparum W2 chloroquineresistant strain with IC50 ≈ 8.4 µM, and activity against Leishmania donovani (IC50 ~9.3 µM), with moderately low mammalian TC50 (≈ 10.4 µM), yielding SI around ~1.2 (Alvarez-Sánchez et al., 2024). Manzamine A, a spongederived alkaloid, showed ~70 % inhibition of Toxoplasma gondii at approximately 0.1 µM in culture studies, implying IC50 in submicromolar range; cytotoxicity to host cells remained low at these doses (Rubio et al., 2009). Comparative potency against drugresistant versus drugsensitive strains is emerging but limited. For example, salinosporamide A retains activity in P. falciparum strains resistant to conventional antimalarials, due to its mechanism targeting a conserved proteasome, rather than the usual drug transport or target mutations. This suggests minimal crossresistance with chloroquineresistant or artemisininresistant isolates (Rosenthal, 2023). Similarly, gallinamide A remains active against chloroquineresistant strain W2, highlighting its distinct mechanism via cysteine protease inhibition of falcipain homologues. Studies frequently report selectivity index (SI) as ratio of host cell TC50 to parasite IC50; for gallinamide A the SI was below ideal (>10), but for salinosporamide A preliminary data suggest a significantly higher SI based on low cytotoxicity and nanomolar potency (Afonso et al., 2023; Conroy et al., 2014; Ettari et al., 2021).
In vivo & Preclinical Activity
Salinosporamide A has advanced into animal infective models of malaria with notable efficacy. In a murine model using P. yoelii, Salinosporamide A, administered orally at ~130 µg/kg, significantly inhibited parasitemia and prolonged survival compared to untreated controls. This ultralow dose efficacy underscores exceptional potency and pharmacodynamic effect (Prudhomme et al., 2008). Table 4 describes a comparative overview of in vitro, in vivo and mechanistic data of various microbial metabolites.
| Compound | Parasite(s) | In vitro IC50 (Selectivity Index) | In vivo Efficacy (Model, Dose) | Proposed Mechanism | References |
|---|---|---|---|---|---|
| Salinosporamide A | P. falciparum (sensitive/resistant) | ~40 nM; SI high (minimal host toxicity) | P. yoelii mice; 130 µg/kg orally → parasitemia suppressed | Irreversible 20S proteasome inhibitor; cell-cycle arrest | (Krishnan & Williamson, 2018) |
| Gallinamide A | P. falciparum W2 (resistant); L. donovani | ~8.4 µM (SI ~1.2) | No in vivo data yet | Irreversible cysteine protease (falcipain) inhibitor | (Stoye et al., 2019), (Siddiqui et al., 2018) |
| Manzamine A | T. gondii | IC50 ~0.1 µM (~70 % inhibition); SI favorable | Not tested in animal infection models | Membrane disruption; actin/calcium interference | (Hamann, 2007) |
Mechanisms of Action
Proteasome Inhibition by Salinosporamide A
Salinosporamide A exerts its potent activity by irreversibly inhibiting the 20S proteasome in parasite cells. Structural studies reveal that the β-lactone moiety reacts with the nucleophilic Thr1 residue in the proteasome’s catalytic site, forming a stable adduct and permanently disabling proteolytic activity. The adjacent γ-lactam ring and chlorine substituent facilitate precise orientation and internal cyclization, cementing the bond (Groll et al., 2018; Potts & Lam, 2010). Biochemically, treatment with salinosporamide A results in accumulation of ubiquitinated proteins in P. falciparum, indicative of blocked protein turnover. This leads to cell cycle arrest at ring and schizont stages, inhibiting progression through DNA synthesis and schizogony, culminating in parasite death (Lindner et al., 2013; Ponts et al., 2011).
Cysteine Protease (Falcipain) Inhibition by Gallinamide A
Gallinamide A targets cysteine proteases, particularly falcipain enzymes in the malaria parasite, as well as Cathepsin L1 homologues. It binds irreversibly to the active-site cysteine residue, potently inhibiting enzymatic activity (IC50 ~17.6 pM against human Cathepsin L1) (Boudreau et al., 2019; Miller et al., 2014). In parasites, blockade of falcipain prevents hemoglobin digestion within the food vacuole, starving the parasite of essential amino acids and disrupting cellular metabolism, leading to death (Pasupureddy et al., 2019).
Membrane Disruption / Alternative Targets (e.g. Manzamines and Others)
Although the exact molecular targets of manzamine A remain incompletely characterized, its antiparasitic effect is attributed to perturbation of parasite membrane integrity, possible interference with calcium signaling or actin dynamics, and modulation of host immune responses. Its structure, a polycyclic alkaloid scaffold, likely intercalates into lipid bilayers or binds peripheral proteins, destabilizing parasite structural homeostasis at submicromolar concentrations (Hamann, 2007; Peng et al., 2010). Figure 5 depicts the mechanisms of action of marine-derived compounds like Salinosporamide A, Gallinamide A, and Manzamines.
TOXICOLOGY, SAFETY & ADMET
Manzamine A demonstrates appreciable cytotoxicity in multiple mammalian cell types. In differentiated osteoclast progenitors, IC50 values of approximately 1.9-2.5 µM at 24-72 hr were observed, with dosedependent apoptosis confirmed via caspase3/7 assays. Similar potency (~2-3 µM) is consistent across preosteoblast and mature osteoblast lines in MTS assays. These values correspond roughly to ~0.7-2 µg/mL, indicating moderate host cell cytotoxicity at concentrations overlapping antiparasitic doses (manzamine A antimalarial IC50 typically submicromolar) (Maykovich et al., 2024). In contrast, cyclomarin A exhibits substantially lower host cytotoxicity, as minimal inhibition of mammalian cells has been reported at concentrations effective against parasites though explicit CC50 values are less documented than for manzamine.
In vivo Tolerability & Adverse Effects
In murine in vivo antimalarial efficacy studies, manzamine A was used in Swiss albino mice at doses up to 100 µmol/kg (approximately 40-50 mg/kg depending on salt form) administered intraperitoneally or orally over one or two consecutive days. These regimens achieved >90% parasitemia reduction and ~40% survival at 60 days postinfection, with no overt signs of acute toxicity or organ pathology reported in primary study endpoints (Ang et al., 2000; Laport et al., 2009). A recent oncology xenograft study delivered 30 mg/kg manzamine A in tumorbearing mice for multiple weeks; body weight remained stable and serum liver enzymes were comparable between treated and control groups, indicating acceptable tolerability at this dosing level (Melfi et al., 2023).
ADMET Properties
Solubility
Manzamine A is poorly watersoluble, often formulated as oil suspensions or with Tween for in vivo dosing; specific solubility metrics remain unreported (Palem et al., 2017).
Metabolic stability & halflife
In vivo pharmacokinetic profiling in antimalarial studies revealed detectable plasma concentrations peaking at maximum 4 hr and persisting at quantifiable levels at 48 hr postinjection, suggesting slow clearance and long systemic exposure (Looareesuwan et al., 2002; White, 2013).
Structure-derived liabilities
Analogue SAR studies (amidation at βcarboline positions) reduced cytotoxicity while retaining activity; for example, certain position8 amides dosed at 30 mg/kg orally suppressed parasitemia by ~62% with no apparent toxicity, suggesting that structural optimization can improve ADMET profiles (Karan et al., 2020; Uddin et al., 2020). For pentabromopseudilin, while highly potent in vitro, its high halogen content (>70% bromine) raises concerns regarding potential bioaccumulation, offtarget toxicity, and limited metabolic clearance (Bond et al., 2013). Historical data indicate in vitro activity at submicromolar IC50, but early therapeutic developments failed in animal studies and no modern ADMET or in vivo mammalian safety data are available (Janse van Rensburg et al., 2023). Table 5 describes the summary of toxicity and ADMET properties of some marine microbial metabolites with anti-parasitic activity.
| Compound | Cytotoxicity (CC50/SI) | In vivo Toxicity Signs | ADMET Characteristics | References |
|---|---|---|---|---|
| Manzamine A | IC50 ~1.9-2.5 µM in mammalian cells; SI 2-10 | Well tolerated up to ~50 mg/kg; stable weight, normal liver enzymes | Poor aqueous solubility; long halflife (~48 hr); plasma peak at 4 hr | (Ang et al., 2000; Ashok et al., 2015; Hamann, 2007) |
| Cyclomarin A | Minimal reported cytotoxicity; high selectivity | No published in vivo toxicity data | Likely favorable; low halogen load; limited data | (Taylor et al., 2022; Vasudevan et al., 2013) |
| Pentabromopseudilin | IC50 ~0.1 μM bacterial/mammalian; low SI | No modern in vivo data reported | Extremely halogenated; potential bioaccumulation, metabolic liability | (S. Chen & Li, 2025; D. T. F. Kuo et al., 2022) |
FUTURE DIRECTIONS
Future efforts to translate marine-derived microbial metabolites into clinically relevant antiparasitic therapies must prioritize an integrated and multidisciplinary approach. The first imperative is to optimize compound accessibility through synthetic biology and metabolic engineering. Expression of biosynthetic gene clusters in heterologous hosts such as Streptomyces, E. coli, or Saccharomyces cerevisiae, coupled with promoter engineering and chassis optimization, can overcome the supply limitations of rare marine microbes. Equally important is the rational design of semi-synthetic analogues using medicinal chemistry and Structure-Activity Relationship (SAR) insights to improve pharmacokinetics, solubility, and target specificity while minimizing host cytotoxicity. In parallel, there is an urgent need for standardized in vivo validation pipelines. Most compounds currently lack robust preclinical studies across parasitic models. Establishing comparative efficacy data, toxicity thresholds, and therapeutic windows using murine models of malaria, leishmaniasis, and trypanosomiasis will provide foundational data required for IND-enabling studies. Moreover, collaborative screening platforms that pair phenotypic high-content assays with transcriptomics, proteomics, and chemical genomics will be critical for target deconvolution and resistance profiling. From a translational perspective, regulatory and environmental frameworks must also be proactively addressed. As marine resources fall under international conventions like the Nagoya Protocol, ensuring ethical bioprospecting, traceability, and benefit-sharing will be essential for sustainable drug development. Additionally, public-private partnerships should be fostered to de-risk early-phase development of marine microbial metabolites, particularly for neglected tropical diseases. Finally, the field would benefit from a global marine metabolite repository that integrates genomic, chemical, and pharmacological metadata, enabling data-driven prioritization and accelerating lead progression. By systematically overcoming these challenges, marine microbial metabolites can be repositioned from underutilized biological assets to next-generation antiparasitic therapies with broad global health impact.
CONCLUSION
Marine-derived microbial metabolites have emerged as a promising frontier in the discovery of novel anti-parasitic agents. Over the last two decades, scientific advancements in marine microbiology, natural product chemistry, and pharmacology have converged to uncover a wide array of structurally unique compounds with activity against protozoan and helminthic parasites. These include alkaloids, cyclic peptides, macrolides, lipodepsipeptides, and proteasome inhibitors, many of which exhibit submicromolar potency and high selectivity against key human parasites such as Plasmodium falciparum, Leishmania donovani, Trypanosoma brucei, and Toxoplasma gondii. Notable examples such as salinosporamide A, gallinamide A, and manzamine A have demonstrated mechanism-based activity targeting proteasomes, cysteine proteases, and cell membranes, respectively. Importantly, several of these agents show low cytotoxicity and promising therapeutic indices in vitro, with a few also validated in in vivo models. Despite this strong potential, the translational progress of these compounds remains limited. None have yet entered clinical trials for anti-parasitic indications, primarily due to challenges such as low natural abundance, difficult cultivation of marine microorganisms, biosynthetic complexity, and incomplete ADMET profiles. However, advances in genome mining, heterologous gene cluster expression, and semi-synthetic derivatization are beginning to resolve these barriers. The collective evidence compiled in this review highlights the underexplored but highly valuable space of marine microbial metabolites. They are poised to significantly expand the therapeutic toolkit for combating parasitic diseases, especially in the context of rising drug resistance and limited current options.