Marine-Derived Anticancer Agents Targeting Apoptotic Pathways: Exploring the Depths for Novel Cancer Therapies.

Extensive research has been conducted on the isolation and study of bioactive compounds derived from marine sources. Several natural products have demonstrated potential as inducers of apoptosis and are currently under investigation in clinical trials. These marine-derived compounds selectively interact with extrinsic and intrinsic apoptotic pathways using a variety of molecular mechanisms, resulting in cell shrinkage, chromatin condensation, cytoplasmic blebs, apoptotic bodies, and phagocytosis by adjacent parenchymal cells, neoplastic cells, or macrophages. Numerous marine-derived compounds are currently undergoing rigorous examination for their potential application in cancer therapy. This review examines a total of 21 marine-derived compounds, along with their synthetic derivatives, sourced from marine organisms such as sponges, corals, tunicates, mollusks, ascidians, algae, cyanobacteria, fungi, and actinobacteria. These compounds are currently undergoing preclinical and clinical trials to evaluate their potential as apoptosis inducers for the treatment of different types of cancer. This review further examined the compound's properties and mode of action, preclinical investigations, clinical trial studies on single or combination therapy, and the prospective development of marine-derived anticancer therapies.

Synergy between Genome Mining, Metabolomics, and Bioinformatics Uncovers Antibacterial Chlorinated Carbazole Alkaloids and Their Biosynthetic Gene Cluster from Streptomyces tubbatahanensis sp. nov., a Novel Actinomycete Isolated from Sulu Sea, Philippines.

In this study, a novel actinomycete strain, DSD3025T, isolated from the underexplored marine sediments in Tubbataha Reefs Natural Park, Sulu Sea, Philippines, with the proposed name Streptomyces tubbatahanensis sp. nov., was described using polyphasic approaches and characterized using whole-genome sequencing. Its specialized metabolites were profiled using mass spectrometry and nuclear magnetic resonance analyses, followed by antibacterial, anticancer, and toxicity screening. The S. tubbatahanensis DSD3025T genome was comprised of 7.76 Mbp with a 72.3% G+C content. The average nucleotide identity and digital DNA-DNA hybridization values were 96.5% and 64.1%, respectively, compared with its closest related species, thus delineating the novelty of Streptomyces species. The genome encoded 29 putative biosynthetic gene clusters (BGCs), including a BGC region containing tryptophan halogenase and its associated flavin reductase, which were not found in its close Streptomyces relatives. The metabolite profiling unfolded six rare halogenated carbazole alkaloids, with chlocarbazomycin A as the major compound. A biosynthetic pathway for chlocarbazomycin A was proposed using genome mining, metabolomics, and bioinformatics platforms. Chlocarbazomycin A produced by S. tubbatahanensis DSD3025T has antibacterial activities against Staphylococcus aureus ATCC BAA-44 and Streptococcus pyogenes and showed antiproliferative activity against colon (HCT-116) and ovarian (A2780) human cancer cell lines. Chlocarbazomycin A exhibited no toxicity to liver cells but moderate and high toxicity to kidney and cardiac cell lines, respectively. IMPORTANCE Streptomyces tubbatahanensis DSD3025T is a novel actinomycete with antibiotic and anticancer activities from Tubbataha Reefs Natural Park, a United Nations Educational, Scientific and Cultural Organization World Heritage Site in Sulu Sea and considered one of the Philippines' oldest and most-well-protected marine ecosystems. In silico genome mining tools were used to identify putative BGCs that led to the discovery of genes involved in the production of halogenated carbazole alkaloids and new natural products. By integrating bioinformatics-driven genome mining and metabolomics, we unearthed the hidden biosynthetic richness and mined the associated chemical entities from the novel Streptomyces species. The bioprospecting of novel Streptomyces species from marine sediments of underexplored ecological niches serves as an important source of antibiotic and anticancer drug leads with unique chemical scaffolds.

Recent Advances of Marine Sponge-Associated Microorganisms as a Source of Commercially Viable Natural Products.

Many industrially significant compounds have been derived from natural products in the environment. Research efforts so far have contributed to the discovery of beneficial natural products that have improved the quality of life on Earth. As one of the sources of natural products, marine sponges have been progressively recognised as microbial hotspots with reports of the sponges harbouring diverse microbial assemblages, genetic material, and metabolites with multiple industrial applications. Therefore, this paper aims at reviewing the recent literature (primarily published between 2016 and 2022) on the types and functions of natural products synthesised by sponge-associated microorganisms, thereby helping to bridge the gap between research and industrial applications. The metabolites that have been derived from sponge-associated microorganisms, mostly bacteria, fungi, and algae, have shown application prospects especially in medicine, cosmeceutical, environmental protection, and manufacturing industries. Sponge bacteria-derived natural products with medical properties harboured anticancer, antibacterial, antifungal, and antiviral functions. Efforts in re-identifying the origin of known and future sponge-sourced natural products would further clarify the roles and significance of microbes within marine sponges.

Antibiotic Isoflavonoids, Anthraquinones, and Pterocarpanoids from Pigeon Pea (Cajanus cajan L.) Seeds against Multidrug-Resistant Staphylococcus aureus.

Cajanus cajan L. (pigeon pea, locally known in the Philippines as kadios) seed is a functional food with health benefits that extend beyond their nutritional value. C. cajan seeds contain highly diverse secondary metabolites with enriched beneficial properties, such as antibacterial, anticancer, and antioxidant activities. However, the antibacterial activities of secondary metabolites from Philippine-grown C. cajan, against multidrug-resistant Staphylococcus aureus have not been thoroughly described. Here, we investigated the in vitro antibacterial properties of C. cajan seed against multidrug-resistant S. aureus ATCC BAA-44 (MDRSA) and three other S. aureus strains (S. aureus ATCC 25923, S. aureus ATCC 6538, and coagulase-negative S. aureus) and, subsequently, identified the antibiotic markers against S. aureus strains using mass spectrometry. Secondary metabolites from C. cajan seeds were extracted using acetone, methanol, or 95% ethanol. Antibacterial screening revealed antibiotic activity for the C. cajan acetone extract. Bioassay-guided purification of the C. cajan acetone extract afforded three semi-pure high-performance liquid chromatography (HPLC) fractions exhibiting 32-64 µg/mL minimum inhibitory concentration (MIC) against MDRSA. Chemical profiling of these fractions using liquid chromatography mass spectrometry (LCMS) identified six compounds that are antibacterial against MDRSA. High-resolution mass spectrometry (HRMS), MS/MS, and dereplication using Global Natural Products Social Molecular Networking (GNPS)™, and National Institute of Standards and Technology (NIST) Library identified the metabolites as rhein, formononetin, laccaic acid D, crotafuran E, ayamenin A, and biochanin A. These isoflavonoids, anthraquinones, and pterocarpanoids from C. cajan seeds are potential bioactive compounds against S. aureus, including the multidrug-resistant strains.

Insights into the Variation in Bioactivities of Closely Related Streptomyces Strains from Marine Sediments of the Visayan Sea against ESKAPE and Ovarian Cancer.

Marine sediments host diverse actinomycetes that serve as a source of new natural products to combat infectious diseases and cancer. Here, we report the biodiversity, bioactivities against ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) and ovarian cancer, and metabolites variation among culturable actinomycetes isolated from the marine sediments of Visayan Sea, Philippines. We identified 15 Streptomyces species based on a 16S rRNA gene sequence analysis. The crude extracts of 10 Streptomyces species have inhibited the growth of ESKAPE pathogens with minimum inhibitory concentration (MIC) values ranging from 0.312 mg/mL to 20 mg/mL depending on the strain and pathogens targeted. Additionally, ten crude extracts have antiproliferative activity against A2780 human ovarian carcinoma at 2 mg/mL. To highlight, we observed that four phylogenetically identical Streptomyces albogriseolus strains demonstrated variation in antibiotic and anticancer activities. These strains harbored type I and II polyketide synthase (PKS) and non-ribosomal synthetase (NRPS) genes in their genomes, implying that their bioactivity is independent of the polymerase chain reaction (PCR)-detected bio-synthetic gene clusters (BGCs) in this study. Metabolite profiling revealed that the taxonomically identical strains produced core and strain-specific metabolites. Thus, the chemical diversity among these strains influences the variation observed in their biological activities. This study expanded our knowledge on the potential of marine-derived Streptomyces residing from the unexplored regions of the Visayan Sea as a source of small molecules against ESKAPE pathogens and cancer. It also highlights that Streptomyces species strains produce unique strain-specific secondary metabolites; thus, offering new chemical space for natural product discovery.

Multimeric TAT peptides are effective in vitro inhibitors of Staphylococcus saprophyticus.

TAT (48-60) is a tridecapeptide from the envelope protein of HIV that was previously shown to possess cell-penetrating properties and antibacterial activity, making it a potential drug delivery agent for anticancer drugs and as antibacterial compound. Previous reports indicated that dimerization enhances the desired bioactivity of TAT; hence, we sought to synthesize multimeric TAT peptides. Herein, we describe the effects of multimerization on the antibacterial activity and secondary structure of the peptide. Terminal modifications such as N-acetylation and C-amidation were employed in the design. TATp monomer, dimer, and tetramer were synthesized using solid-phase peptide synthesis, purified by reversed-phase HPLC, and then characterized by mass spectrometry. Multimerization of the peptide did not change the secondary structure conformation. The CD analysis revealed a polyproline-II conformation for all peptide designs. Thus, this study provides a method of increasing the biological activity of the peptide by multimerization while retaining the secondary conformation of its monomeric unit. Furthermore, the bacteria Staphylococcus saprophyticus was found to be susceptible to the dimer and tetramer, with MIC50 of 12.50 µm and <1.56 µm, respectively. This suggests a structure-activity relationship whereby the antibacterial activity increases with increase in valency.

Anthracycline Shunt Metabolites From Philippine Marine Sediment-Derived Streptomyces Destroy Cell Membrane Integrity of Multidrug-Resistant Staphylococcus aureus.

The rise of antibiotic resistance (ABR) and the drying up of the pipeline for the development of new antibiotics demands an urgent search for new antibiotic leads. While the majority of clinically available antibiotics were discovered from terrestrial Streptomyces, related species from marine sediments as a source of antibiotics remain underexplored. Here, we utilized culture-dependent isolation of thirty-five marine sediment-derived actinobacterial isolates followed by a screening of their antibacterial activity against multidrug-resistant S. aureus ATCC BAA-44. Our results revealed that the crude extract of Streptomyces griseorubens strain DSD069 isolated from marine sediments collected in Romblon, Philippines displays the highest antibacterial activity, with 96.4% growth inhibition. The S. aureus ATCC BAA-44 cells treated with crude extract of Streptomyces griseorubens strain DSD069 showed cell membrane damage as demonstrated by (a) leakage and loss of vital cell constituents, including DNA and proteins, (b) irregular shrinkage of cells, and (c) increase membrane permeability. The antibiotic compounds were identified as Bisanhydroaklavinone and 1-Hydroxybisanhydroaklavinone with MIC value of 6.25 µg/mL and 50.00 µg/mL, respectively. Bisanhydroaklavinone and 1-Hydroxybisanhydroaklavinone are shunt metabolites in the biosynthesis of anticancer anthracycline derivatives namely doxorubicin, daunorubicin, and cinerubins. It is rare, however, that shunt metabolites are accumulated during fermentation of marine sediment-derived Streptomyces strain without genetic modification. Thus, our study provides evidence that natural bacterial strain can produce Bisanhydroaklavinone and 1-Hydroxybisanhydroaklavinone as antibiotic leads to combat ABR.

Nipah virus attachment glycoprotein stalk C-terminal region links receptor binding to fusion triggering.

UNLABELLED: Membrane fusion is essential for paramyxovirus entry into target cells and for the cell-cell fusion (syncytia) that results from many paramyxoviral infections. The concerted efforts of two membrane-integral viral proteins, the attachment (HN, H, or G) and fusion (F) glycoproteins, mediate membrane fusion. The emergent Nipah virus (NiV) is a highly pathogenic and deadly zoonotic paramyxovirus. We recently reported that upon cell receptor ephrinB2 or ephrinB3 binding, at least two conformational changes occur in the NiV-G head, followed by one in the NiV-G stalk, that subsequently result in F triggering and F execution of membrane fusion. However, the domains and residues in NiV-G that trigger F and the specific events that link receptor binding to F triggering are unknown. In the present study, we identified a NiV-G stalk C-terminal region (amino acids 159 to 163) that is important for multiple G functions, including G tetramerization, conformational integrity, G-F interactions, receptor-induced conformational changes in G, and F triggering. On the basis of these results, we propose that this NiV-G region serves as an important structural and functional linker between the NiV-G head and the rest of the stalk and is critical in propagating the F-triggering signal via specific conformational changes that open a concealed F-triggering domain(s) in the G stalk. These findings broaden our understanding of the mechanism(s) of receptor-induced paramyxovirus F triggering during viral entry and cell-cell fusion. IMPORTANCE: The emergent deadly viruses Nipah virus (NiV) and Hendra virus belong to the Henipavirus genus in the Paramyxoviridae family. NiV infections target endothelial cells and neurons and, in humans, result in 40 to 75% mortality rates. The broad tropism of the henipaviruses and the unavailability of therapeutics threaten the health of humans and livestock. Viral entry into host cells is the first step of henipavirus infections, which ultimately cause syncytium formation. After attaching to the host cell receptor, henipaviruses enter the target cell via direct viral-cell membrane fusion mediated by two membrane glycoproteins: the attachment protein (G) and the fusion protein (F). In this study, we identified and characterized a region in the NiV-G stalk C-terminal domain that links receptor binding to fusion triggering via several important glycoprotein functions. These findings advance our understanding of the membrane fusion-triggering mechanism(s) of the henipaviruses and the paramyxoviruses.

Acute stressor exposure modifies plasma exosome-associated heat shock protein 72 (Hsp72) and microRNA (miR-142-5p and miR-203).

Exosomes, biologically active nanoparticles (40-100 nm) released by hematopoietic and non-hematopoietic cells, contain a variety of proteins and small, non-coding RNA known as microRNA (miRNA). Exposure to various pathogens and disease states modifies the composition and function of exosomes, but there are no studies examining in vivo exosomal changes evoked by the acute stress response. The present study reveals that exposing male Fisher 344 rats to an acute stressor modulates the protein and miRNA profile of circulating plasma exosomes, specifically increasing surface heat shock protein 72 (Hsp72) and decreasing miR-142-5p and -203. The selected miRNAs and Hsp72 are associated with immunomodulatory functions and are likely a critical component of stress-evoked modulation of immunity. Further, we demonstrate that some of these stress-induced modifications in plasma exosomes are mediated by sympathetic nervous system (SNS) activation of alpha-1 adrenergic receptors (ADRs), since drug-mediated blockade of the receptors significantly attenuates the stress-induced modifications of exosomal Hsp72 and miR-142-5p. Together, these findings demonstrate that activation of the acute stress response modifies the proteomic and miRNA profile of exosomes released into the circulation.

Multivalency amplifies the selection and affinity of bradykinin-derived peptides for lipid nanovesicles.

The trimer of a bradykinin derivative displayed a more than five-fold increase in binding affinity for phosphatidylserine-enriched nanovesicles as compared to its monomeric precursor. The nanovesicle selection is directly correlated with multivalency, which amplifies the electrostatic attraction. This strategy may lead to the development of novel molecular probes for detecting highly curved membrane bilayers.

Computationally designed peptide inhibitors of the ubiquitin E3 ligase SCF(Fbx4).

A structure-based computational approach was used to rationally design peptide inhibitors that can target an E3 ligase (SCF(Fbx4) )-substrate (TRF1) interface and subsequent ubiquitylation. Characterization of the inhibitors demonstrates that our sequence-optimization protocol results in an increase in peptide-TRF1 affinity without compromising peptide-protein specificity.

MARCKS-ED peptide as a curvature and lipid sensor.

Membrane curvature and lipid composition regulates important biological processes within a cell. Currently, several proteins have been reported to sense and/or induce membrane curvatures, e.g., Synaptotagmin-1 and Amphiphysin. However, the large protein scaffold of these curvature sensors limits their applications in complex biological systems. Our interest focuses on identifying and designing peptides that can sense membrane curvature based on established elements observed in natural curvature-sensing proteins. Membrane curvature remodeling also depends on their lipid composition, suggesting strategies to specifically target membrane shape and lipid components simultaneously. We have successfully identified a 25-mer peptide, MARCKS-ED, based on the effector domain sequence of the intracellular membrane protein myristoylated alanine-rich C-kinase substrate that can recognize PS with preferences for highly curved vesicles in a sequence-specific manner. These studies further contribute to the understanding of how proteins and peptides sense membrane curvature, as well as provide potential probes for membrane shape and lipid composition.

Targeting the lateral interactions of transmembrane domain 5 of Epstein-Barr virus latent membrane protein 1.

The lateral transmembrane protein-protein interaction has been regarded as "undruggable" despite its importance in many biological processes. The homo-trimerization of transmembrane domain 5 (TMD-5) of latent membrane protein 1 (LMP-1) is critical for the constitutive oncogenic activation of the Epstein-Barr virus (EBV). Herein, we report a small molecule agent, NSC 259242 (compound 1), to be a TMD-5 self-association disruptor. Both the positively charged acetimidamide functional groups and the stilbene backbone of compound 1 are essential for its inhibitory activity. Furthermore, cell-based assays revealed that compound 1 inhibits full-length LMP-1 signaling in EBV infected B cells. These studies demonstrated a new strategy for identifying small molecule disruptors for investigating transmembrane protein-protein interactions.

The remarkable stability of chimeric, sialic acid-derived alpha/delta-peptides in human blood plasma.

Peptides are labile toward proteolytic enzymes, and structural modifications are often required to prolong their metabolic half-life and increase resistance. One modification is the incorporation of non-alpha-amino acids into the peptide to deter recognition by hydrolytic enzymes. We previously reported the synthesis of chimeric alpha/delta-peptides from glutamic acids (Glu) and the sialic acid derivative Neu2en. Conformational analyses revealed these constructs adopt secondary structures in water and may serve as conformational surrogates of polysialic acid. Polysialic acid is a tumor-associated polysaccharide and is correlated with cancer metastasis. Soluble polysialic acid is rapidly cleared from the blood limiting its potential for vaccine development. One motivation in developing structural surrogates of polysialic acid was to create constructs with increased bioavailability. Here, we report plasma stability profiles of Glu/Neu2en alpha/delta-peptides. DOTA was conjugated at the peptide N-termini by solid phase peptide synthesis, radiolabeled with (111)In, incubated in human blood plasma at 37 degrees C, and their degradation patterns monitored by cellulose acetate electrophoresis and radioactivity counting. Results indicate that these peptides exhibit a long half-life that is two- to three-orders of magnitude higher than natural alpha-peptides. These findings provide a viable platform for the synthesis of plasma stable, sialic acid-derived peptides that may find pharmaceutical application.

Synthesis and structural characterization of sialic acid-glutamic acid hybrid foldamers as conformational surrogates of alpha-2,8-linked polysialic acid.

Surface expression of alpha-(2,8)-linked polymers of sialic acid in adult tissues has been correlated with metastasis of several human cancers. One approach to chemotherapeutic intervention against the spread of these cancers involves the development of immunogenic molecules that elicit an antibody response against alpha-(2,8)-linked polysialic acids. Naturally occurring polysialic acids are not viable candidates because they are present during embryonic development and are recognized as self by the immune system. These natural polymers also have poor pharmacokinetic properties because they are readily degraded by neuraminidase enzymes. We have been interested in developing structural surrogates of polysialic acids in an effort to overcome these limitations. Reported herein are microwave-assisted solid-phase peptide syntheses and structural characterization studies of a series of alpha/delta hybrid peptides derived from Fmoc-Neu2en and Fmoc-Glu(OtBu)-OH. Conformational experiments including circular dichroism, NH/ND exchange, and ROESY in aqueous solution were performed to study the secondary structures of these hybrid foldamers. ROESY data were analyzed with the assistance of XPLOR-NIH that was modified to include parameter and topology files to accommodate unnatural amino acids and the delta amide linkages. The results indicate that stable secondary structure is dependent upon both the amino acid sequence and the configuration of Glu. The most stable foldamer was composed of a total of 6 residues beginning with L-Glu at the carboxy terminus and alternating Neu2en and L-Glu residues. In water, this foldamer adopts a right-handed helical conformation with 3.7 residues per turn, 7.4 A pitch, 5.8 A diameter, and a length of 18.5 A, which is stabilized by both classical C=O...H-N backbone interactions and by pyranose ring O and L-Glu HN H-bonding. These structural features orient the L-Glu carboxylates along the helical backbone with a periodicity that matches the carboxylate positions along the reported G2(+) left-handed helix of alpha-(2,8)-polysialic acid. However, the charge density of the foldamer is one-half that of the natural polymer. These findings provide a fundamental understanding of the factors that influence stable secondary structure in hybrid Neu2en/Glu systems, and the tools we have developed establish a viable platform for the rational design of alpha-(2,8)-polysialic acid surrogates.

Drug development from marine natural products.

Drug discovery from marine natural products has enjoyed a renaissance in the past few years. Ziconotide (Prialt; Elan Pharmaceuticals), a peptide originally discovered in a tropical cone snail, was the first marine-derived compound to be approved in the United States in December 2004 for the treatment of pain. Then, in October 2007, trabectedin (Yondelis; PharmaMar) became the first marine anticancer drug to be approved in the European Union. Here, we review the history of drug discovery from marine natural products, and by describing selected examples, we examine the factors that contribute to new discoveries and the difficulties associated with translating marine-derived compounds into clinical trials. Providing an outlook into the future, we also examine the advances that may further expand the promise of drugs from the sea.