Anti-proliferative effects of new staurosporine derivatives isolated from a marine ascidian and its predatory flatworm

Translating molecular insights into clinical success: alkaloid-based therapies for leukemia

Alkaloids, a diverse class of naturally occurring compounds, have shown significant potential in the treatment of leukemia by targeting key molecular pathways and cellular mechanisms. This review discusses several potent alkaloids, such as homoharringtonine, chaetominine, matrine, and jerantinine B, which induce apoptosis, cell cycle arrest, and autophagy and inhibit signaling pathways including PI3K/Akt/mTOR, MAPK, and NF-κB. For instance, homoharringtonine induces apoptosis in acute myeloid leukemia (AML) cells via the SP1/TET1/5hmC/FLT3/MYC axis, while chaetominine enhances chemosensitivity by inhibiting the PI3K/Akt/Nrf2 pathway. In addition, targeting leukemia stem cells (LSCs) with alkaloids such as zalypsis offers promise due to its ability to induce apoptosis without significantly affecting normal hematopoietic stem cells. The modulation of the immune response, such as the inhibition of NF-κB activation by noscapine, further underscores the potential of alkaloids in overcoming treatment resistance. Various studies have demonstrated the efficacy of alkaloids across different leukemia types. For example, jerantinine B targets AML cells, while vincristine has shown success in lymphocytic leukemia. Clinical trials have also highlighted the benefits of alkaloids, including homoharringtonine, which achieved a 79.9% complete remission rate in AML patients. However, adverse effects such as neutropenia and hepatotoxicity necessitate careful management. Collectively, these findings emphasize the need for further research into alkaloid-based combination therapies to enhance efficacy and minimize toxicity, providing a promising avenue for innovative leukemia treatments.

Generation of streptocarbazoles with cytotoxicities by pathway engineering and insights into their biosynthesis

Streptocarbazoles are a class of indolocarbazole (ICZ) compounds produced by Streptomyces strains that feature unique cyclic N-glycosidic linkages between the 1,3-carbon atoms of the glycosyl moiety and the two indole nitrogen atoms. Although several streptocarbazole compounds display effective cytotoxic activity, their biosynthesis remains unclear. Herein, through the inactivation of the aminotransferase gene spcI in the staurosporine biosynthetic gene cluster spc followed by heterologous expression, two new streptocarbazole derivatives (1 and 3) and three known ICZs (2, 4, and 5) were generated. Their structures were determined by a combination of spectroscopic methods, circular dichroism measurements, and single-crystal X-ray diffraction. Compounds 1-4 displayed moderate cytotoxicity against HCT-116 cell line, and compounds 3 and 4 were effective against Huh 7 cell line. Double-gene knockout experiments allowed us to propose a biosynthetic pathway for streptocarbazole productions. Furthermore, by overexpression of the involving key enzymes, the production of streptocarbazoles 1 and 3 were improved by approximately 1.5-2.5 fold.

IMPORTANCE

Indolocarbazoles (ICZs) are a group of antitumor agents, with several analogs used in clinical trials. Therefore, the identification of novel ICZ compounds is important for drug discovery. Streptocarbazoles harbor unique N-glycosidic linkages (N13-C1' and N12-C3'), distinguishing them from the representative ICZ compound staurosporine; however, their biosynthesis remains unclear. In this study, two new streptocarbazoles (1 and 3) with cytotoxic activities were obtained by manipulating the staurosporine biosynthetic gene cluster spc followed by heterologous expression. The biosynthetic pathway of streptocarbazoles was proposed, and their productions were improved through the overexpression of the key enzymes involved. This study enriches the structural diversity of ICZ compounds and would facilitate the discovery of new streptocarbazoles via synthetic biological strategies.

Multifunctional role of natural products for the treatment of Parkinson's disease: At a glance

Natural substances originating from plants have long been used to treat neurodegenerative disorders (NDs). Parkinson's disease (PD) is a ND. The deterioration and subsequent cognitive impairments of the midbrain nigral dopaminergic neurons distinguish by this characteristic. Various pathogenic mechanisms and critical components have been reported, despite the fact that the origin is unknown, such as protein aggregation, iron buildup, mitochondrial dysfunction, neuroinflammation and oxidative stress. Anti-Parkinson drugs like dopamine (DA) agonists, levodopa, carbidopa, monoamine oxidase type B inhibitors and anticholinergics are used to replace DA in the current treatment model. Surgery is advised in cases where drug therapy is ineffective. Unfortunately, the current conventional treatments for PD have a number of harmful side effects and are expensive. As a result, new therapeutic strategies that control the mechanisms that contribute to neuronal death and dysfunction must be addressed. Natural resources have long been a useful source of possible treatments. PD can be treated with a variety of natural therapies made from medicinal herbs, fruits, and vegetables. In addition to their well-known anti-oxidative and anti-inflammatory capabilities, these natural products also play inhibitory roles in iron buildup, protein misfolding, the maintenance of proteasomal breakdown, mitochondrial homeostasis, and other neuroprotective processes. The goal of this research is to systematically characterize the currently available medications for Parkinson's and their therapeutic effects, which target diverse pathways. Overall, this analysis looks at the kinds of natural things that could be used in the future to treat PD in new ways or as supplements to existing treatments. We looked at the medicinal plants that can be used to treat PD. The use of natural remedies, especially those derived from plants, to treat PD has been on the rise. This article examines the fundamental characteristics of medicinal plants and the bioactive substances found in them that may be utilized to treat PD.

Natural Products from Actinomycetes Associated with Marine Organisms

The actinomycetes have proven to be a rich source of bioactive secondary metabolites and play a critical role in the development of pharmaceutical researches. With interactions of host organisms and having special ecological status, the actinomycetes associated with marine animals, marine plants, macroalgae, cyanobacteria, and lichens have more potential to produce active metabolites acting as chemical defenses to protect the host from predators as well as microbial infection. This review focuses on 536 secondary metabolites (SMs) from actinomycetes associated with these marine organisms covering the literature to mid-2021, which will highlight the taxonomic diversity of actinomycetes and the structural classes, biological activities of SMs. Among all the actinomycetes listed, members of Streptomyces (68%), Micromonospora (6%), and Nocardiopsis (3%) are dominant producers of secondary metabolites. Additionally, alkaloids (37%), polyketides (33%), and peptides (15%) comprise the largest proportion of natural products with mostly antimicrobial activity and cytotoxicity. Furthermore, the data analysis and clinical information of SMs have been summarized in this article, suggesting that some of these actinomycetes with multiple host organisms deserve more attention to their special ecological status and genetic factors.

Anticancer Potential of Compounds from the Brazilian Blue Amazon

"Blue Amazon" is used to designate the Brazilian Economic Exclusive Zone, which covers an area comparable in size to that of its green counterpart. Indeed, Brazil flaunts a coastline spanning 8000 km through tropical and temperate regions and hosting part of the organisms accredited for the country's megadiversity status. Still, biodiversity may be expressed at different scales of organization; besides species inventory, genetic characteristics of living beings and metabolic expression of their genes meet some of these other layers. These metabolites produced by terrestrial creatures traditionally and lately added to by those from marine organisms are recognized for their pharmaceutical value, since over 50% of small molecule-based medicines are related to natural products. Nonetheless, Brazil gives a modest contribution to the field of pharmacology and even less when considering marine pharmacology, which still lacks comprehensive in-depth assessments toward the bioactivity of marine compounds so far. Therefore, this review examined the last 40 years of Brazilian natural products research, focusing on molecules that evidenced anticancer potential-which represents ~ 15% of marine natural products isolated from Brazilian species. This review discusses the most promising compounds isolated from sponges, cnidarians, ascidians, and microbes in terms of their molecular targets and mechanisms of action. Wrapping up, the review delivers an outlook on the challenges that stand against developing groundbreaking natural products research in Brazil and on a means of surpassing these matters.

From Seabed to Bedside: A Review on Promising Marine Anticancer Compounds

The marine environment represents an outstanding source of antitumoral compounds and, at the same time, remains highly unexplored. Organisms living in the sea synthesize a wide variety of chemicals used as defense mechanisms. Interestingly, a large number of these compounds exert excellent antitumoral properties and have been developed as promising anticancer drugs that have later been approved or are currently under validation in clinical trials. However, due to the high need for these compounds, new methodologies ensuring its sustainable supply are required. Also, optimization of marine bioactives is an important step for their success in the clinical setting. Such optimization involves chemical modifications to improve their half-life in circulation, potency and tumor selectivity. In this review, we outline the most promising marine bioactives that have been investigated in cancer models and/or tested in patients as anticancer agents. Moreover, we describe the current state of development of anticancer marine compounds and discuss their therapeutic limitations as well as different strategies used to overcome these limitations. The search for new marine antitumoral agents together with novel identification and chemical engineering approaches open the door for novel, more specific and efficient therapeutic agents for cancer treatment.

Marine-Derived Natural Compounds for the Treatment of Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder caused by the loss of dopaminergic neurons, leading to the motor dysfunctions of patients. Although the etiology of PD is still unclear, the death of dopaminergic neurons during PD progress was revealed to be associated with the abnormal aggregation of α-synuclein, the elevation of oxidative stress, the dysfunction of mitochondrial functions, and the increase of neuroinflammation. However, current anti-PD therapies could only produce symptom-relieving effects, because they could not provide neuroprotective effects, stop or delay the degeneration of dopaminergic neurons. Marine-derived natural compounds, with their novel chemical structures and unique biological activities, may provide anti-PD neuroprotective effects. In this study, we have summarized anti-PD marine-derived natural products which have shown pharmacological activities by acting on various PD targets, such as α-synuclein, monoamine oxidase B, and reactive oxygen species. Moreover, marine-derived natural compounds currently evaluated in the clinical trials for the treatment of PD are also discussed.

Staurosporine Derivatives Generated by Pathway Engineering in a Heterologous Host and Their Cytotoxic Selectivity

Two new staurosporine derivatives, staurosporines M1 and M2 (4 and 5), in addition to five previously reported metabolites (1-3, 6, and 7), were generated by the heterologous expression of engineered spc gene clusters in Streptomyces coelicolor M1146. The structures of these derivatives were determined by a combination of spectroscopic methods and CD measurement. Compounds 1, 2, 4, and 5 showed effective activities against three tumor cell lines (HCT-116, K562, and Huh 7.5), and 3 was active against HCT-116 and K562 cells. In addition, compounds 3 and 5 showed undetectable toxicity up to 100 μM toward the normal hepatic cell line LO₂. Based on the IC₅₀ values, their structure and activity relationships are discussed.

Marine-derived protein kinase inhibitors for neuroinflammatory diseases

Neuroinflammation is primarily characterized by overexpression of proinflammatory mediators produced by glial activation or immune cell infiltration. Several kinases have been shown to be critical mediators in neuroinflammation. One of the largest groups of kinases is protein kinases, which have been the second most studied group of drug targets after G-protein-coupled receptors. Thus far, most of the approved kinase inhibitor drugs are adenosine triphosphate-competitive inhibitors with various off-target liabilities because of cross-reactivities; however, marine-derived compounds provide opportunities for discovering allosteric kinase inhibitors. This review summarizes the potential of marine-derived protein kinase inhibitors in the field of neuroinflammatory diseases, such as Parkinson disease, Alzheimer disease, multiple sclerosis, and pain. The previous studies from 1990 to 2017 in this review have shown that marine-derived protein kinase inhibitors have great potential to elicit anti-neuroinflammatory or neuroprotective responses in in vitro and in vivo models of neuroinflammatory diseases. This suggests that further exploration and investigation of these marine-derived protein kinase inhibitors on neuroinflammatory diseases are warranted. Therefore, this review may inspire further discovery of new protein kinase inhibitors from a marine origin and additional neuroscience studies focusing on these valuable marine-derived protein kinase inhibitors.

Natural Products Diversity of Marine Ascidians (Tunicates; Ascidiacea) and Successful Drugs in Clinical Development

This present study reviewed the chemical diversity of marine ascidians and their pharmacological applications, challenges and recent developments in marine drug discovery reported during 1994-2014, highlighting the structural activity of compounds produced by these specimens. Till date only 5% of living ascidian species were studied from <3000 species, this study represented from family didemnidae (32%), polyclinidae (22%), styelidae and polycitoridae (11-12%) exhibiting the highest number of promising MNPs. Close to 580 compound structures are here discussed in terms of their occurrence, structural type and reported biological activity. Anti-cancer drugs are the main area of interest in the screening of MNPs from ascidians (64%), followed by anti-malarial (6%) and remaining others. FDA approved ascidian compounds mechanism of action along with other compounds status of clinical trials (phase 1 to phase 3) are discussed here in. This review highlights recent developments in the area of natural products chemistry and biotechnological approaches are emphasized.

Diversity of Actinobacteria Associated with the Marine Ascidian Eudistoma toealensis

Ascidians have yielded a wide variety of bioactive natural products. The colonial ascidian Eudistoma toealensis from Micronesia has been identified as the source of a series of staurosporine derivatives, though the exact origin of these derivatives is still unknown. To identify known staurosporine-producing microbes associated with E. toealensis, we analyzed with 16S rRNA gene tag pyrosequencing the overall bacterial community and focused on potential symbiotic bacteria already known from other ascidians or other marine hosts, such as sponges. The described microbiota was one of very high diversity, comprising 43 phyla: two from archaea, 34 described bacterial phyla, and seven candidate bacterial phyla. Many bacteria, which are renowned community members of other ascidians and marine holobionts, such as sponges and corals, were also part of the E. toealensis microbial community. Furthermore, two known producers of indolocarbazoles, Salinispora and Verrucosispora, were found with high abundance exclusively in the ascidian tissue, suggesting that microbial symbionts and not the organism itself may be the true producers of the staurosporines in E. toealensis.

Nitric oxide synthesis inhibition and cytotoxicity of Korean horse mussel Modiolus modiolus extracts on cancer cells in culture

The Korean horse mussel extract was purified and fractionated by a bioassay-guided purification step. The final fraction contained seven steroid and one polycyclic aromatic compounds, in which cholest-7-en-3-ol, (3β,5α)- (58.7 %) was a main component followed by ergosta-7,22dien-3-ol (3β,5α,22E) (13.0 %). This extract exhibited strong anti-inflammatory activity determined solely through the nitric oxide inhibition assay in a dose-dependant manner with the IC50 value of 9.6 µg/mL and no cytotoxic effect on the macrophages. Moreover, it also exhibited strong cytotoxicity with the IC50 values of 21.4, 36.4, and 37.1 µg/mL against AGS, DLD-1, and HeLa cells, respectively. These results indicated that the horse mussel extract might be a functional ingredient in the prevention of inflammation and human cancers.

Structure elucidation and anticancer activity of 7-oxostaurosporine derivatives from the Brazilian endemic tunicate Eudistoma vannamei

The present study reports the identification of two new staurosporine derivatives, 2-hydroxy-7-oxostaurosporine (1) and 3-hydroxy-7-oxostaurosporine (2), obtained from mid-polar fractions of an aqueous methanol extract of the tunicate Eudistoma vannamei, endemic to the northeast coast of Brazil. The mixture of 1 and 2 displayed IC₅₀ values in the nM range and was up to 14 times more cytotoxic than staurosporine across a panel of tumor cell lines, as evaluated using the MTT assay.

Structure of pseudocerosine, an indolic azafulvene alkaloid from the flatworm Pseudoceros indicus

The rim of the tunic of the flatworm Pseudoceros indicus is characterized by blue dots on a white background. The isolation and structure elucidation of the blue pigment is reported. It is shown by extensive analysis of spectroscopic data to be an indolic azafulvene, which has been named pseudocerosine.

Protein kinase inhibition of clinically important staurosporine analogues

The isolation in 1977 of the microbial alkaloid staurosporine inaugurated research into several distinct series of related natural and synthetic compounds. This has especially included research into applications as anticancer drugs, beginning with the observation of low nanomolar inhibition of protein kinases. At present, several staurosporine cognates are in advanced clinical trials as anticancer agents, with the potential to join the 10 other protein kinase inhibitors now approved for clinical use. Staurosporine is a broadly selective and potent protein kinase inhibitor, with submicromolar binding to the vast majority of the protein kinases tested, and binding most of them more tightly than 100 nM. Crystal structures have shown the extended buried surface area interactions between the protein kinase adenine binding site and the extended aromatic plane of the inhibitor, together with protein-saccharide interactions in the ribose binding site. Together with structures of closely related analogues, there are now some 70 X-ray crystal structures in the Protein Data Bank that enable analysis of target binding properties of the clinical compounds. In this manuscript we review the discovery of these compounds, revisit crystal structures and review the observed interactions. These support the interpretation of kinase selectivity profiles of staurosporine and its analogues, including midostaurin (PKC412), for which a co-crystal structure is not yet available. Further, the mix of purely natural, biosynthetically and chemically modified compounds described here offer insights into prospects and strategies for drug discovery via bioprospecting.

Indolocarbazole natural products: occurrence, biosynthesis, and biological activity

The indolocarbazole family of natural products, including the biosynthetically related bisindolylmaleimides, is reviewed (with 316 references cited). The isolation of indolocarbazoles from natural sources and the biosynthesis of this class of compounds are thoroughly reviewed, including recent developments in molecular genetics, enzymology and metabolic engineering. The biological activities and underlying modes of action displayed by natural and synthetic indolocarbazoles is also presented, with an emphasis on the development of analogs that have entered clinical trials for its future use against cancer or other diseases.

Marine pharmacology in 2001-2: antitumour and cytotoxic compounds

During 2001 and 2002, marine antitumour pharmacology research aimed at the discovery of novel antitumour agents was published in 175 peer-reviewed articles. The purpose of this paper is to present a structured Review of the antitumour and cytotoxic properties of 97 marine natural products, many of them novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids, and peptides. The organisms yielding these bioactive compounds comprise a taxonomically diverse group of marine invertebrate animals, algae, fungi and bacteria. Antitumour pharmacological studies were conducted with 30 structurally characterised natural marine products in a number of experimental and clinical models which further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines was reported for 67 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy, is the fact that marine anticancer research was sustained by a collaborative effort, involving researchers from Australia, Brazil, Canada, Denmark, Egypt, France, Germany, Italy, Japan, Netherlands, New Zealand, The Philippines, Russia, Singapore, South Korea, Thailand, Taiwan, Turkey, Spain, Switzerland, Taiwan, Thailand, Turkey, and the United States. Finally, this 2001-2 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine antitumour agents has continued at the same pace as during 1998, 1999 and 2000.

Marine Alkaloid Polycarpine and Its Synthetic Derivative Dimethylpolycarpine Induce Apoptosis in JB6 Cells Through p53- and Caspase 3-Dependent Pathways

PURPOSE

Polycarpine from ascidian Polycarpa aurata was previously found to be active against different human tumor cells. In this study, we investigated the antitumor mechanisms of polycarpine and its synthetic derivative, desmethoxyethoxy-polycarpine (dimethylpolycarpine), through the induction of apoptosis. This new knowledge regarding the proapoptotic action of polycarpine and dimethylpolycarpine should lead to a better understanding of their effects and development of a new class of anticancer drugs.

METHODS

Apoptosis was clearly observed by flow cytometry and Western blotting using an antibody against cleaved caspase-3 as an apoptotic marker.

RESULTS

Polycarpines differentially activated p38 kinase, JNKs, and ERKs in JB6 Cl 41 cells. The polycarpines-induced apoptosis was decreased in cells expressing a dominant-negative mutant of JNK. Both compounds stimulated p53-dependent transcriptional activity and phosphorylation. Induction of p53-phosphorylation at serine 15 was suppressed in JNKI and JNK2 knockout cells. Furthermore, polycarpines were unable to induce apoptosis in p53-deficient MEFs in contrast to a strong induction of apoptosis in wild type MEFs, suggesting that p53 is involved in apoptosis induced by polycarpines. The p53 phosphorylation in turn was mediated by activated JNKs.

CONCLUSIONS

These results indicate that all three MAPK signaling pathways are involved in the response of JB6 cells to treatment with polycarpines. Evidence also supports a proapoptotic role of the JNKs signaling pathway in vivo and clearly indicates that JNKs are required for phosphorylation of c-Jun, activation of p53, and subsequent apoptosis induced by polycarpines.

Differential effects of staurosporine and its analogues on chemokine release by promyelocytic leukemia cell line NB-4

The protein kinase inhibitor staurosporine elicits multiple responses in various systems. We evaluated nine naturally occurring staurosporine derivatives as modulators of chemokine production by monitoring the secretion of interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) in the cell line NB-4. Several staurosporines increased, dose- and time-dependently, the IL-8 and MCP-1 concentration in the cell culture supernatants and three derivatives strongly inhibited proliferation of the NB-4 cells. By comparing the efficiency of these analogues at the same concentration, the lead compound staurosporine (STS-1) was the best inducer of chemokine secretion, whereas 3-hydroxystaurosporine (STS-3) was the most potent growth inhibitor. Besides the staurosporines, also 12-O-tetradecanoyl phorbol acetate (TPA) and tumor necrosis factor-alpha (TNFalpha) strongly increased the IL-8 and MCP-1 secretion of NB-4 cells. Several staurosporine analogues clearly inhibited the TPA-induced but enhanced the TNFalpha-mediated chemokine increase. These effects, namely the increase of chemokines in untreated or TNFalpha-treated cells and the inhibition of chemokine release in TPA-treated cells, cannot be explained by the exclusive inhibition of protein kinase C (PKC). It may indicate that staurosporines are additionally involved in activation of the PKC-triggered chemokine production.

Bioactive natural products from marine invertebrates and associated fungi

Marine natural products with their unique structural features and pronounced biological activities continue to provide lead structures in the search for new drugs from nature. Invertebrates such as sponges, tunicates, mollusks and others that are either sessile or slow moving and mostly lack morphological defense structures have so far provided the largest number of marine-derived secondary constituents including some of the most interesting drug candidates. This review highlights recent research findings of our group related to natural products from marine invertebrates. Areas that are covered include ecological functions of secondary constituents from sponges against predatory fish, the search for new pharmacologically active constituents from sponges and tunicates, and sponge-associated fungi as an evolving source for new bioactive natural products.

The K252a derivatives, inhibitors for the PAK/MLK kinase family selectively block the growth of RAS transformants

BACKGROUND

Oncogenic RAS mutants such as v-Ha-RAS activate members of Rac/CDC42-dependent kinases (PAKs) and appear to contribute to the development of more than 30% of all human cancers. PAK1 activation is essential for oncogenic RAS transformation, and several chemical compounds that inhibit Tyr kinases essential for the RAS-induced activation of PAK1 strongly suppress RAS transformation either in cell culture or in vivo (nude mice). Although we have developed a cell-permeable PAK-specific peptide inhibitor called WR-PA18, so far no chemical (metabolically stable) compound has been developed that directly inhibits PAK1 in a highly selective manner. Thus, we have explored such a PAK1 inhibitor(s) among synthetic derivatives of an adenosine triphosphate antagonist.

RESULTS

From the naturally occurring adenosine triphosphate antagonist K252a, we have developed two bulky derivatives, called CEP-1347 and KT D606 (a K252a dimer), which selectively inhibit PAKs or mixed-lineage kinases both in vitro and in cell culture and convert v-Ha-RAS-transformed NIH 3T3 cells to flat fibroblasts similar to the parental normal cells. Furthermore, these two K252a analogues suppress the proliferation of v-Ha-RAS transformants, but not the normal cells.

CONCLUSION

These bulky adenosine triphosphate antagonists derived from K252a or related indolocarbazole compounds such as staurosporine would be potentially useful for the treatment of RAS/ PAK1-induced cancers, once their anti-PAK1 activity is significantly potentiated by a few additional chemical modifications at the sugar ring suggested in this paper.

Further new staurosporine derivatives from the ascidian Eudistoma toealensis and its predatory flatworm Pseudoceros sp

Three new indolocarbazole alkaloids, 3-hydroxy-4'-N-methylstaurosporine (3), 3-hydroxy-4'-N-demethylstaurosporine (4), and 3'-demethoxy-3'-hydroxy-4'-N-demethylstaurosporine (5), were isolated from the marine ascidian Eudistoma toealensis and its predatory flatworm Pseudoceros sp. in addition to two known staurosporines. The structures were determined by 1D and 2D homonuclear and 1H-detected heteronuclear NMR spectroscopy and from comparisons with published data. CD measurements for these five staurosporine derivatives, as well as the previously described seven staurosporines, are reported, confirming that all derivatives possess the 2'S,3'R,4'R,6'R configuration.