Modification at the C9 position of the marine natural product isoaaptamine and the impact on HIV-1, mycobacterial, and tumor cell activity

Manzamine A reduces androgen receptor transcription and synthesis by blocking E2F8-DNA interactions and effectively inhibits prostate tumor growth in mice

The androgen receptor (AR) is the main driver in the development of castration-resistant prostate cancer, where the emergence of AR splice variants leads to treatment-resistant disease. Through detailed molecular studies of the marine alkaloid manzamine A (MA), we identified transcription factor E2F8 as a previously unknown regulator of AR transcription that prevents AR synthesis in prostate cancer cells. MA significantly inhibited the growth of various prostate cancer cell lines and was highly effective in inhibiting xenograft tumor growth in mice without any pathophysiological perturbations in major organs. MA suppressed the full-length AR (AR-FL), its spliced variant AR-V7, and the AR-regulated prostate-specific antigen (PSA; also known as KLK3) and human kallikrein 2 (hK2; also known as KLK2) genes. RNA sequencing (RNA-seq) analysis and protein modeling studies revealed E2F8 interactions with DNA as a potential novel target of MA, suppressing AR transcription and its synthesis. This novel mechanism of blocking AR biogenesis via E2F8 may provide an opportunity to control therapy-resistant prostate cancer over the currently used AR antagonists designed to target different parts of the AR gene.

Manzamine-A Alters In Vitro Calvarial Osteoclast Function

Manzamine-A is a marine-derived alkaloid that has demonstrated antimalarial and antiproliferative properties and is an emerging drug lead compound as a possible intervention in certain cancers. This compound has been found to modulate SIX1 gene expression, a target that is critical for the proliferation and survival of cells via various developmental pathways. As yet, little research has focused on manzamine-A and how its use may affect tissue systems including bone. Here we hypothesized that manzamine-A, through its interaction with SIX1, would alter precursor cells that give rise to the bone cell responsible for remodeling: the osteoclast. We further hypothesized reduced effects in differentiated osteoclasts, as these cells are generally not mitotic. We interrogated the effects of manzamine-A on preosteoclasts and osteoclasts. qrtPCR, MTS cell viability, Caspase 3/7, and TRAP staining were used as a functional assay. Preosteoclasts show responsiveness to manzamine-A treatment exhibited by decreases in cell viability and an increase in apoptosis. Osteoclasts also proved to be affected by manzamine-A but only at higher concentrations where apoptosis was increased and activation was reduced. In summary, our presented results suggest manzamine-A may have significant effects on bone development and health through multiple cell targets, previously shown in the osteoblast cell lineage, the cell responsible for mineralized tissue formation, and here in the osteoclast, the cell responsible for the removal of mineralized tissue and renewal via precipitation of bone remodeling.

Informatics and Computational Approaches for the Discovery and Optimization of Natural Product-Inspired Inhibitors of the SARS-CoV-2 2'-O-Methyltransferase

The urgent need for new classes of orally available, safe, and effective antivirals─covering a breadth of emerging viruses─is evidenced by the loss of life and economic challenges created by the HIV-1 and SARS-CoV-2 pandemics. As frontline interventions, small-molecule antivirals can be deployed prophylactically or postinfection to control the initial spread of outbreaks by reducing transmissibility and symptom severity. Natural products have an impressive track record of success as prototypic antivirals and continue to provide new drugs through synthesis, medicinal chemistry, and optimization decades after discovery. Here, we demonstrate an approach using computational analysis typically used for rational drug design to identify and develop natural product-inspired antivirals. This was done with the goal of identifying natural product prototypes to aid the effort of progressing toward safe, effective, and affordable broad-spectrum inhibitors of Betacoronavirus replication by targeting the highly conserved RNA 2'-O-methyltransferase (2'-O-MTase). Machaeriols RS-1 (7) and RS-2 (8) were identified using a previously outlined informatics approach to first screen for natural product prototypes, followed by in silico-guided synthesis. Both molecules are based on a rare natural product group. The machaeriols (3-6), isolated from the genus Machaerium, endemic to Amazonia, inhibited the SARS-CoV-2 2'-O-MTase more potently than the positive control, Sinefungin (2), and in silico modeling suggests distinct molecular interactions. This report highlights the potential of computationally driven screening to leverage natural product libraries and improve the efficiency of isolation or synthetic analog development.

Aaptocarbamates A-G, chlorinated terpene carbamates with antiosteoclastogenic activities from the marine sponge Aaptos sp

Six undescribed chlorinated sesquiterpene carbamates, aaptocarbamates A-F, and a chlorinated tris-norsesquiterpene carbamate, aaptocarbamate G, were isolated from the marine sponge Aaptos sp. collected in Indonesia. Aaptocarbamates D-F and G possess tetrahydrofurans and a tetrahydrofuranone, respectively. The relative configurations of the tetrahydrofuran units were determined by the NOE correlations and DFT-based calculation of the 13C chemical shifts. This is the first time that chlorinated terpene carbamates have been reported from natural sources. Various aaptamine derivatives have been reported from the Aaptos sponges so far, the isolation of chlorinated terpene carbamates is very rare. Aaptocarbamates A, B, and D showed 60% inhibition of the RANKL-induced formation of multinucleated osteoclasts in RAW264 macrophages at 20 μM.

New Guanidine Alkaloids Batzelladines O and P from the Marine Sponge Monanchora pulchra Induce Apoptosis and Autophagy in Prostate Cancer Cells

Two new guanidine alkaloids, batzelladines O (1) and P (2), were isolated from the deep-water marine sponge Monanchora pulchra. The structures of these metabolites were determined by NMR spectroscopy, mass spectrometry, and ECD. The isolated compounds exhibited cytotoxic activity in human prostate cancer cells PC3, PC3-DR, and 22Rv1 at low micromolar concentrations and inhibited colony formation and survival of the cancer cells. Batzelladines O (1) and P (2) induced apoptosis, which was detected by Western blotting as caspase-3 and PARP cleavage. Additionally, induction of pro-survival autophagy indicated as upregulation of LC3B-II and suppression of mTOR was observed in the treated cells. In line with this, the combination with autophagy inhibitor 3-methyladenine synergistically increased the cytotoxic activity of batzelladines O (1) and P (2). Both compounds were equally active in docetaxel-sensitive and docetaxel-resistant prostate cancer cells, despite exhibiting a slight p-glycoprotein substrate-like activity. In combination with docetaxel, an additive effect was observed. In conclusion, the isolated new guanidine alkaloids are promising drug candidates for the treatment of taxane-resistant prostate cancer.

Review on marine sponge alkaloid, aaptamine: A potential antibacterial and anticancer drug

In recent years, biological macromolecules have piqued the interest of researchers owing to their vast variety of biological uses. As a result, the marine sponge is a multicellular heterotrophic parazoan with chemicals for defence against predator assaults, biofouling and microbial diseases. These priceless molecules are known as secondary metabolites, and they are essential for survival in a highly competitive environment. So far, over 5,000 marine natural compounds have been extracted from marine sponges, making them an excellent option for drug formulation. One among them is, aaptamine, a marine alkaloid with a benzo[de][1,6]-napthyridine framework extensively distributed in marine sponges. Due to this reason, aaptamine has been intensively researched for various biological purposes, including cancer and protease inhibition, offering fresh insights into novel treatments. Keeping this in mind, we reviewed the biological significance of the marine sponge alkaloid aaptamine.

Effects of Sponge-Derived Alkaloids on Activities of the Bacterial α-D-Galactosidase and Human Cancer Cell α-N-Acetylgalactosaminidase

During a search for glycosidase inhibitors among marine natural products, we applied an integrated in vitro and in silico approach to evaluate the potency of some aaptamines and makaluvamines isolated from marine sponges on the hydrolyzing activity of α-N-acetylgalactosaminidase (α-NaGalase) from human cancer cells and the recombinant α-D-galactosidase (α-PsGal) from a marine bacterium Pseudoalteromonas sp. KMM 701. These alkaloids showed no direct inhibitory effect on the cancer α-NaGalase; but isoaaptamine (2), 9-demethylaaptamine (3), damirone B (6), and makaluvamine H (7) reduced the expression of the enzyme in the human colorectal adenocarcinoma cell line DLD-1 at 5 μM. Isoaaptamine (2), 9-demethylaaptamine (3), makaluvamine G (6), and zyzzyanone A (7) are slow-binding irreversible inhibitors of the bacterial α-PsGal with the inactivation rate constants (k_inact) 0.12 min⁻¹, 0.092 min⁻¹, 0.079 min⁻¹, and 0.037 min⁻¹, as well as equilibrium inhibition constants (K_i) 2.70 µM, 300 µM, 411 µM, and 105 µM, respectively. Docking analysis revealed that these alkaloids bind in a pocket close to the catalytic amino acid residues Asp451 and Asp516 and form complexes, due to π-π interactions with the Trp308 residue and hydrogen bonds with the Lys449 residue. None of the studied alkaloids formed complexes with the active site of the human α-NaGalase.

Aromatic Ring Substituted Aaptamine Analogues as Potential Cytotoxic Agents against Extranodal Natural Killer/T-Cell Lymphoma

A chemical modification study was conducted on the marine natural product aaptamine (1), isolated from the marine sponge Aaptos aaptos. Thirty new derivatives substituted by various aromatic rings at the 3- and 7-positions of aaptamine were prepared by bromination, followed by the Suzuki coupling reaction. Sixteen compounds displayed cytotoxicities to four cancer cell lines (IC₅₀ < 10 μM). In particular, compound 5i demonstrated a significant antiproliferative effect on the extranodal natural killer/T-cell lymphoma (ENKT) cell line SNK-6 with an IC₅₀ value of 0.6 μM. Additionally, compound 5i showed cytotoxicities to multiple lymphoma cell lines, including Ramos, Raji, WSU-DLCL2, and SU-DHL-4 cells.

Aaptodines A-D, Spiro Naphthyridine-Furooxazoloquinoline Hybrid Alkaloids from the Sponge Aaptos suberitoides

LC-MS-oriented fractionation of the sponge Aaptos suberitoides resulted in the isolation of four heptacyclic alkaloids, aaptodines A-D (1-4), which contain 9,10-dihydrofuro[2,3-f][1,3]oxazolo[5,4-h]quinolone and 7,8-dihydrocyclopenta[de][1,6]naphthyridine subunits with a spiro carbon atom. The structures were determined on the basis of NMR spectroscopic and single-crystal X-ray diffraction data analysis aided by electronic circular dichroism calculations and Mosher's method. A biosynthetic pathway for the formation of aaptodines A-D is postulated. Aaptodine D exhibits potent inhibition against osteoclast formation.

3-(Phenethylamino)demethyl(oxy)aaptamine as an anti-dormant mycobacterial substance: Isolation, evaluation and total synthesis

3-(Phenethylamino)demethyl(oxy)aaptamine (1) was re-discovered from the marine sponge of Aaptos sp. as an anti-dormant mycobacterial substance through the bioassay-guided separation. Compound 1 showed potent anti-microbial activity against Mycobacterium bovis BCG with a minimum inhibitory concentration of 0.75 µg/mL under both aerobic conditions and hypoxic conditions inducing dormant state. Compound 1 was also effective against pathogenic M. tuberculosis strains including clinical multidrug-resistant strains. Furthermore, the successful total syntheses of 1 and its analog 3-aminodemethyl(oxy)aaptamine (2) afford sufficient quantities for further biological studies.

Aaptamine-Related Alkaloid from the Marine Sponge Aaptos aaptos

A new aaptamine-related alkaloid, 1,3-dioxolo [4,5- d] benzo [ de]-1,6-naphthyridine (methylenedioxyaaptamine, 1), was isolated from the organic extracts of the Bornean marine sponge Aaptos aaptos, together with a known aaptamine derivative, 8,9,9-trimethoxy-9 H-benzo [ de]-1,6-naphthyridine (2). The structure of compound 1 was elucidated by interpretation of its spectroscopic data. Two compounds were tested for their cytotoxic potentials against adult T-cell leukemia (ATL) cells, and compound 1 showed moderate cytotoxic potential.

New Drugs from the Sea: Pro-Apoptotic Activity of Sponges and Algae Derived Compounds

Natural compounds derived from marine organisms exhibit a wide variety of biological activities. Over the last decades, a great interest has been focused on the anti-tumour role of sponges and algae that constitute the major source of these bioactive metabolites. A substantial number of chemically different structures from different species have demonstrated inhibition of tumour growth and progression by inducing apoptosis in several types of human cancer. The molecular mechanisms by which marine natural products activate apoptosis mainly include (1) a dysregulation of the mitochondrial pathway; (2) the activation of caspases; and/or (3) increase of death signals through transmembrane death receptors. This great variety of mechanisms of action may help to overcome the multitude of resistances exhibited by different tumour specimens. Therefore, products from marine organisms and their synthetic derivates might represent promising sources for new anticancer drugs, both as single agents or as co-adjuvants with other chemotherapeutics. This review will focus on some selected bioactive molecules from sponges and algae with pro-apoptotic potential in tumour cells.

Potential Secondary Metabolites from Marine SpongeAaptos aaptosfor Atherosclerosis and Vibriosis Treatments

Natural products play a crucial role in drug discovery. In the last decade, the advent of marine natural product research has produced a remarkable number of compounds, particularly those isolated from marine sponges, with a broad range of activities for the treatment of human and animal diseases. In this study, five known alkaloids namely aaptamine (1), 9-demethylaaptamine (2), 4- N-methylaaptamine (3), 9-methoxyaaptamine (4), 9-demethyloxyaaptamine (5), an uncommon amide in sponge, 4-hydroxybenzamide (6) and 3 β,5α-cholesterol (7) were isolated from the butanol extract of Aaptos aaptos (Schmidt, 1864) by bioactivity-guided isolation. Their structures were determined based on a detailed analysis of their 1D and 2D spectroscopic NMR and EIMS spectral data as well as comparison with literature data. Cytotoxic activity and anti-atherosclerotic property of the compounds were determined based on their ability to increase the transcriptional activity of SRB1 promoter and PPRE in human liver HepG2 cell line. The results showed that compounds 4 and 7 exhibited cytotoxic effects and compounds 1–4 and 7 increased the transcriptional activity of SRB1 promoter and PPRE. This suggests that compounds isolated from A. aaptos may have potential as anti-cancer agents and to reduce the progression of atherosclerosis. In addition, the compounds 1–4 displayed antibacterial activity against shrimp pathogenic bacteria, Vibrio harveyi and Vibrio sp. This suggests that the compounds have potential as vibriosis treatment.

Guanidine Alkaloids from the Marine Sponge Monanchora pulchra Show Cytotoxic Properties and Prevent EGF-Induced Neoplastic Transformation in Vitro

Guanidine alkaloids from sponges Monanchora spp. represent diverse bioactive compounds, however, the mechanisms underlying bioactivity are very poorly understood. Here, we report results of studies on cytotoxic action, the ability to inhibit EGF-induced neoplastic transformation, and the effects on MAPK/AP-1 signaling of eight rare guanidine alkaloids, recently isolated from the marine sponge Monanchora pulchra, namely: monanchocidin A (1), monanchocidin B (2), monanchomycalin C (3), ptilomycalin A (4), monanchomycalin B (5), normonanchocidin D (6), urupocidin A (7), and pulchranin A (8). All of the compounds induced cell cycle arrest (apart from 8) and programmed death of cancer cells. Ptilomycalin A-like compounds 1–6 activated JNK1/2 and ERK1/2, following AP-1 activation and caused p53-independent programmed cell death. Compound 7 induced p53-independent cell death without activation of AP-1 or caspase-3/7, and the observed JNK1/2 activation did not contribute to the cytotoxic effect of the compound. Alkaloid 8 induced JNK1/2 (but not ERK1/2) activation leading to p53-independent cell death and strong suppression of AP-1 activity. Alkaloids 1–4, 7, and 8 were able to inhibit the EGF-induced neoplastic transformation of JB6 P⁺ Cl41 cells. Our results suggest that investigated guanidine marine alkaloids hold potential to eliminate human cancer cells and prevent cancer cell formation and spreading.

Antileishmanial drug discovery: comprehensive review of the last 10 years

This review covers the current aspects of leishmaniasis including marketed drugs, new antileishmanial agents, and possible drug targets of antileishmanial agents.

Aaptamine derivatives with antifungal and anti-HIV-1 activities from the South China Sea sponge Aaptos aaptos

Five new alkaloids of aaptamine family, compounds (1–5) and three known derivatives (6–8), have been isolated from the South China Sea sponge Aaptos aaptos. The structures of all compounds were unambiguously elucidated by spectroscopic analyses, as well as by comparison with the literature data. Compounds 1–2 are characterized with triazapyrene lactam skeleton, whereas compounds 4–5 share an imidazole-fused aaptamine moiety. These compounds were evaluated in antifungal and anti-HIV-1 assays. Compounds 3, 7, and 8 showed antifungal activity against six fungi, with MIC values in the range of 4 to 64 μg/mL. Compounds 7–8 exhibited anti-HIV-1 activity, with inhibitory rates of 88.0% and 72.3%, respectively, at a concentration of 10 μM.

Aaptamines, marine spongean alkaloids, as anti-dormant mycobacterial substances

A new aaptamine class alkaloid, designated 2-methoxy-3-oxoaaptamine (1), together with seven known aaptamines (2-8) were isolated from a marine sponge of Aaptos sp. as anti-mycobacterial substances against active and dormant bacilli. The chemical structure of 1 was determined on the basis of spectroscopic analysis. Compound 1 was anti-mycobacterial against Mycobacterium smegmatis in both active growing and dormancy-inducing hypoxic conditions with a minimum inhibitory concentration (MIC) of 6.25 μg/ml, and compounds 2, 5, 6, and 7 showed anti-mycobacterial activities under hypoxic condition selectively, with MIC values of 1.5-6.25 μg/ml.

Suberitine A-D, four new cytotoxic dimeric aaptamine alkaloids from the marine sponge Aaptos suberitoides

Suberitine A-D (1-4), four new bis-aaptamine alkaloids with two aaptamine skeleton units, 8,9,9-trimethoxy-9H-benzo[de][1,6]-naphthyridine and demethyl(oxy)-aaptamine, linked through a rare C-3-C-3' or C-3-C-6' σ-bond between the 1,6-naphthyridine rings, together with two known monomers 5 and 6, were isolated from the marine sponge Aaptos suberitoides. Their structures were elucidated using NMR spectroscopy. Compounds 2 and 4 showed potent cytotoxicity against P388 cell lines, with IC(50) values of 1.8 and 3.5 μM, respectively.

Three New Aaptamines from the Marine Sponge Aaptos sp. and Their Proapoptotic Properties

Three new aaptamine-type alkaloids, 2,3-dihydro-2,3-dioxoaaptamine (1), 6 -( N-morpholinyl)-4,5-dihydro-5-oxo-demethyl(oxy)aaptamine (2) and 3-(methylamino)demethyl(oxy)aaptamine (3), along with known aaptamines were isolated from the sponge Aaptos sp. Their structures were determined on the basis of detailed analysis of their 1D and 2D NMR spectroscopic and mass spectral data. The isolated compounds induced apoptosis in human leukemia THP-1 cells.

Antiviral lead compounds from marine sponges

Marine sponges are currently one of the richest sources of pharmacologically active compounds found in the marine environment. These bioactive molecules are often secondary metabolites, whose main function is to enable and/or modulate cellular communication and defense. They are usually produced by functional enzyme clusters in sponges and/or their associated symbiotic microorganisms. Natural product lead compounds from sponges have often been found to be promising pharmaceutical agents. Several of them have successfully been approved as antiviral agents for clinical use or have been advanced to the late stages of clinical trials. Most of these drugs are used for the treatment of human immunodeficiency virus (HIV) and herpes simplex virus (HSV). The most important antiviral lead of marine origin reported thus far is nucleoside Ara-A (vidarabine) isolated from sponge Tethya crypta. It inhibits viral DNA polymerase and DNA synthesis of herpes, vaccinica and varicella zoster viruses. However due to the discovery of new types of viruses and emergence of drug resistant strains, it is necessary to develop new antiviral lead compounds continuously. Several sponge derived antiviral lead compounds which are hopedto be developed as future drugs are discussed in this review. Supply problems are usually the major bottleneck to the development of these compounds as drugs during clinical trials. However advances in the field of metagenomics and high throughput microbial cultivation has raised the possibility that these techniques could lead to the cost-effective large scale production of such compounds. Perspectives on biotechnological methods with respect to marine drug development are also discussed.

Aaptamine, an alkaloid from the sponge Aaptos suberitoides, functions as a proteasome inhibitor

Aaptamine (1), isoaaptamine (2), and demethylaaptamine (3) were isolated from the marine sponge Aaptossuberitoides collected in Indonesia as inhibitors of the proteasome. They inhibited the chymotrypsin-like and caspase-like activities of the proteasome with IC(50) values of 1.6-4.6 microg/mL, while they showed less inhibition of the trypsin-like activity of the proteasome. The three compounds showed cytotoxic activities against HeLa cells, but their cytotoxicity did not correlate with their potency as proteasome inhibitors, strongly suggesting that their proteasomal inhibitory activity is dispensable to their cytotoxicity.

New innovations for an old infection: antimalarial lead discovery from marine natural products during the period 2003–2008

Malaria remains one of the most serious global infectious diseases, with an estimated 2 billion people at risk and 1 million deaths annually. Drug resistance is hampering the effectiveness of many current antimalarial therapies and resistant strains of the parasite are now known for almost all classes of antimalarial compounds. Owing to a lack of concerted drug-discovery efforts over the last 30 years, the development pipeline is limited and the identification of new antimalarial lead compounds is a pressing concern. The development of new antimalarials that exhibit novel modes of action is of critical importance if the devastating effects of malaria are to be controlled. Natural products have traditionally played an important role in antimalarial drug development and the marine environment represents an underexplored resource in this regard. This review covers developments in the field of antimalarial drug discovery from marine sources between January 2003 and December 2008 and offers a comprehensive overview of all marine-derived compounds from this period. Marine natural products represent an emerging opportunity in the development of new antimalarial lead compounds. This review provides examples of several recent lead discovery projects that show promise in this regard and presents a perspective on areas of possible future study.

Cytotoxic aaptamines from Malaysian Aaptos aaptos

In a preliminary screen, Aaptos aaptos showed significant cytotoxic activity towards a panel of cell lines and was thus subjected to bioassay-guided isolation of the bioactive constituents. In addition to the known aaptamine, two new derivatives of the alkaloid were isolated from the bioactive chloroform fraction of the crude methanolic extract. Detailed analysis by NMR and mass spectroscopy enabled their identification to be 3-(phenethylamino)demethyl(oxy)aaptamine and 3-(isopentylamino)demethyl(oxy) aaptamine. The cytotoxic activities of the three alkaloids were further evaluated against CEM-SS cells.

Antiviral and anticancer optimization studies of the DNA-binding marine natural product aaptamine

Aaptamine has potent cytotoxicity that may be explained by its ability to intercalate DNA. Aaptamine was evaluated for its ability to bind to DNA to validate DNA binding as the primary mechanism of cytotoxicity. Based on UV-vis absorbance titration data, the K(obs) for aaptamine was 4.0 (+/-0.2) x 10(3) which was essentially equivalent to the known DNA intercalator N-[2-(diethylamino)ethyl]-9-aminoacridine-4-carboxamide. Semi-synthetic core modifications were performed to improve the general structural diversity of known aaptamine analogs and vary its absorption characteristics. Overall, 26 aaptamine derivatives were synthesized which consisted of a simple homologous range of mono and di-N-alkylations as well as some 9-O-sulfonylation and bis-O-isoaaptamine dimer products. Each product was evaluated for activity in a variety of whole cell and viral assays including a unique solid tumor disk diffusion assay. Details of aaptamine's DNA-binding activity and its derivatives' whole cell and viral assay results are discussed.