Bisindole Compounds Research Articles

Emission-based sensing of cobalt (II) and vitamin B12 via a bis-indole derivative.

In this study, a bis-indole compound was synthesized, characterized by 1H NMR, Fourier transform infrared, and mass spectroscopic measurements and used as a selective and efficient probe for the spectrofluorimetric analysis of Co (II). The cobalt-induced quenching in the emission maximum at 567 nm was considered as the analytical signal in calibration studies. When encapsulated in a polymethyl methacrylate (PMMA) matrix, the bis-indole compound exhibited a limit of detection (LOD) of 3.60 × 10-11 M for Co (II). Vitamin B12, which contains a cobalt ion in the center of a corrin ring in its structure, was also successfully quantified using the same probe. The bis-indole compound showed a linear response based on quenching for increasing concentrations of vitamin B12, partially mimicking the contracted tetrapyrrole ring found naturally in the center of vitamin B12. The LOD for vitamin B12 was found to be 76 nm. Promising photophysical properties of the proposed probe, including high molar extinction coefficient, considerable quantum yield (0.46 and 0.64 in tetrahydrofuran and PMMA, respectively), high Stoke's shift and satisfactory photostability, make it a good choice for fluorescence-based Co (II) determination. The ML3-type stoichiometry of the complex between the dye and cobalt was elucidated both by Job's method and by high-resolution mass spectrometry (HR-MS).

The Sources, Structures and Cytotoxicity of Animal-Derived Bisindole Compounds.

Bisindole compounds constitute a significant class of natural compounds distinguished by their characteristic bisindole structure and renowned for their anticancer properties. Over the past four decades, researchers have isolated 229 animal-derived bisindole compounds (ADBCs) from various animals. These compounds demonstrate a wide range of pharmacological properties, including cytotoxicity, antibacterial, antifungal, antiviral, and other activities. Notably, among these activities, cytotoxicity emerges as the most prominent characteristic of ADBCs. This review also summarizes the structureactivity relationship (SAR) studies associated with the cytotoxicity of these compounds and explores the druggability of these compounds. In summary, our objective is to provide an overview of the research progress concerning ADBCs, with the aim of fostering their continued development and utilization.

Marine-Derived Bisindoles for Potent Selective Cancer Drug Discovery and Development.

Marine-derived bisindoles exhibit structural diversity and exert anti-cancer influence through multiple mechanisms. Comprehensive research has shown that the development success rate of drugs derived from marine natural products is four times higher than that of other natural derivatives. Currently, there are 20 marine-derived drugs used in clinical practice, with 11 of them demonstrating anti-tumor effects. This article provides a thorough review of recent advancements in anti-tumor exploration involving 167 natural marine bisindole products and their derivatives. Not only has enzastaurin entered clinical practice, but there is also a successfully marketed marine-derived bisindole compound called midostaurin that is used for the treatment of acute myeloid leukemia. In summary, investigations into the biological activity and clinical progress of marine-derived bisindoles have revealed their remarkable selectivity, minimal toxicity, and efficacy against various cancer cells. Consequently, they exhibit immense potential in the field of anti-tumor drug development, especially in the field of anti-tumor drug resistance. In the future, these compounds may serve as promising leads in the discovery and development of novel cancer therapeutics.

Abstract 2713: Modulation of the blood-tumor barrier by 6-bromoindirubin acetoxime increases intra-tumoral drug accumulation and extends survival in murine glioblastoma models

Abstract Introduction: Glioblastoma (GBM) is the most frequent primary malignant adult brain tumor. Median survival is ~15 months after diagnosis. Therapies to effectively manage glioblastoma are hindered due to the presence of the blood-tumor barrier (BTB). Indirubins are 3,2’-bisindole compounds of the Indigo naturalis used in traditional Chinese medicine to treat proliferative diseases. Herein, we demonstrate that systemic delivery of 6-bromoindirubin-3’-acetoxime (BIA), an indirubin derivative, increases cisplatin delivery to GBM tumors through alteration of the BTB integrity and synergy of BIA with platinum therapeutics to potentiate anti-tumor killing. Methods: Pre-clinical studies involved G9-pCDH glioblastoma cell line implantation in naïve nude mice. Cisplatin uptake 24 hours after BIA tail-vein administration into healthy brain and GBM murine tumors was assessed via inductively-coupled plasma mass spectrometry (ICP-MS). DNA-damage was assessed by γH2AX immunofluorescence. BIA combination with cisplatin in vitro studies were performed via luminescent viability assays. Treatment of human cerebrovascular endothelial cells (HCMEC/D3) with BIA for BBB studies in vitro involved trans-endothelial electrical resistance (TEER) measurement, transcriptome analysis, VE-cadherin western blotting and immunofluorescence. Results: Combined addition of cisplatin and BIA showed enhanced anti-GBM killing effects than cisplatin alone in G9-pCDH (IC50 cisplatin=1, BIA+cisplatin=0.2), G34-pCDH (IC50 cisplatin=3, BIA+cisplatin=1.7) and G30-LRP (IC50 cisplatin=1, BIA+cisplatin=0.3) lines. Efficacy studies using the G9-pCDH xenograft murine model showed extended survival when using cisplatin in combination with BIA (median 27d, p=0.0016) when compared to cisplatin (18.5d), BIA (21.5d) and control (18d). Increased intra-tumoral accumulation of cisplatin was observed when used in combination with BIA (mean 100 pg/mg, p=0.012) rather than cisplatin alone (5 pg/mg). No increased platinum uptake was seen in healthy brain tissue under any conditions. γH2AX foci in tumor were more frequent in the BIA and cisplatin combination arm (p=0.0086) than each single agent and control groups. Evaluation of HCMEC/D3 cells treated with BIA showed a decrease in TEER levels (p<0.001) and transcriptomic dysregulation of members of the WNT pathway and downregulation of VE-cadherin (~4-fold). BIA exerted cytoskeleton changes in HCMEC/D3 cells and decreased VE-cadherin expression at the protein level and its distribution on cellular surface, suggesting loss of adherens junctions as a potential mechanism for BIA-induced permeability of the BTB. Conclusion: Overall, our data support the applicability of BIA for modulating the BTB permeability and increasing intra-tumoral drug accumulation for improving GBM therapeutic efficacy. Citation Format: Jorge L. Jimenez Macias. Modulation of the blood-tumor barrier by 6-bromoindirubin acetoxime increases intra-tumoral drug accumulation and extends survival in murine glioblastoma models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2713.

Synthesis of New Methoxy Actived Mono and Bis-indole Compounds

An indole hydrazone has successfully been synthesized employing Schiff base reaction conditions starting from 4,6-dimethoxy-2,3-diphenylindole-7-carbaldehyde with hydrazine hydrate. The reaction of this compound with acetone yielded indole based imine compound. The structure of targeted compound was identified by mass and 1H spectroscopy along with single crystal X-ray diffraction technique. Also, bromination of bis-indole with N-bromo succinimide was produced corresponding bromo bis-indol derivative.

Structure-guided engineering of a flavin-containing monooxygenase for the efficient production of indirubin

Indirubin is a bisindole compound for the treatment of chronic myelocytic leukemia. Here, we presented a structure-guided method to improve the activity of a flavin-containing monooxygenase (bFMO) for the efficient production of indirubin in Escherichia coli. A flexible loop interlocked with the active pocket through a helix and the substrate tunnel rather than the active pocket in bFMO were identified to be two reconfigurable structures to improve its activity, resulting in K223R and N291T mutants with enhanced catalytic activity by 2.5- and 2.0-fold, respectively. A combined modification at the two regions (K223R/D317S) achieved a 6.6-fold improvement in catalytic efficiency (kcat/Km) due to enhancing π–π stacking interactions stabilization. Finally, an engineered E. coli strain was constructed by metabolic engineering, which could produce 860.7 mg/L (18 mg/L/h) indirubin, the highest yield ever reported. This work provides new insight into the redesign of FMOs to boost their activities and an efficient approach to produce indirubin.Graphical

DNA-Binding Properties of Bis-N-substituted Tetrandrine Derivatives.

A series of bis-N-substituted tetrandrine derivatives carrying different aromatic substituents attached to both nitrogen atoms of the natural alkaloid were studied with double-stranded model DNAs (dsDNAs) to examine the binding properties and mechanism. Variable-temperature molecular recognition studies using UV–vis and fluorescence techniques revealed the thermodynamic parameters, ΔH, ΔS, and ΔG, showing that the tetrandrine derivatives exhibit high affinity toward dsDNA (K ≈ 105–107 M–1), particularly the bis(methyl)anthraquinone (BAqT) and bis(ethyl)indole compounds (BInT). Viscometry experiments, ethidium displacement assays, and molecular modeling studies enabled elucidation of the possible binding mode, indicating that the compounds exhibit a synergic interaction mode involving intercalation of one of the N-aryl substituents and interaction of the molecular skeleton in the major groove of the dsDNA. Cytotoxicity tests of the derivatives with tumor and nontumor cell lines demonstrated low cytotoxicity of these compounds, with the exception of the bis(methyl)pyrene (BPyrT) derivative, which is significantly more cytotoxic than the remaining derivatives, with IC50 values against the LS-180, A-549, and ARPE-19 cell lines that are similar to natural tetrandrine. Finally, complementary electrochemical characterization studies unveiled good electrochemical stability of the compounds.

A bis indole analog molecule fluorescent probe for living cell staining

In this study, the fluorescent probe property of a bis indole compound (5,14-dimethyl-5,6,7,8,9,14-hexahydroindolo [2 ', 3′: 3,4] cycloocta [1,2-b] indole), a Caulerpin derivative, which is a member of the indole family, was investigated. For this purpose, firstly, the fluorescence character of the molecule was investigated by absorption and fluorescence spectroscopy techniques in both solvent and surfactant environments. Afterwards, the cytotoxicity of the molecule was tested on the human colon cancer HT-29 cells and breast cancer MCF-7 cells as well as mouse fibroblast 3T3-L1 cells. After determining that the molecule has no cytotoxic effect against all the tested cell lines by 100 µM, the cell staining feature of the probe was examined. The obtained data showed us that the molecule, whose confocal microscopy images were taken at 360 nm excitation wavelength, stained the cell cytoplasm. In addition, optical absorption spectra, oscillator strength (f), transition configuration and transition characteristics of the Ars-In in different solvents were investigated at the theoretical level using Time Dependent-Density Functional Theory (TD-DFT). In conclusion, these results confirm that this indole derivative molecule could be evaluated as an effective fluorescence probe for biological systems.

Bisindole compound 4ae ameliorated cognitive impairment in rats with vascular dementia by anti-inflammation effect via microglia cells

Neuroinflammation is considered as an important mechanism of vascular dementia (VaD). Our primary study showed that the bisindole analogue (2-(2-(bis(5-chloro-1H-indol-3-yl)methyl)phenoxy)aniline, compound 4ae) had great anti-inflammation in zebrafish. Rat model of permanent occlusion of the bilateral common carotid arteries (2-vessel occlusion, 2VO) was utilized to evaluate the neuroprotective effect of 4ae. Our results showed that 4ae treatment effectively reduced Iba-1 positive microglia cells in cerebral cortex and hippocampus after cerebral ischemia. Compared with the model group, neuroinflammation characterized by Interleukin (IL)-6 and tumor necrosis factor (TNF)-α, oxidative stress characterized by reactive oxygen species (ROS) and superoxide dismutase (SOD) were both improved significantly after treatment with 4ae. Moreover, 4ae treatment significantly reversed ischemia-induced ACE enhancement, while notably increased the level of ACE2. To further elucidate the role of 4ae on neuroinflammation, we investigated the effects of 4ae on lipopolysaccharide (LPS)-induced inflammation in BV2 microglia cells, a kind of innate immune cells in central nervous system. The results demonstrated that the expressions of CD11b, TNFα and IL-6 and the level of ROS were up-regulated after treatment with LPS. More importantly, 4ae was able to block the activation of BV2 by reducing ROS production and the expression of inflammatory cytokines. In addition, our results suggested that 4ae inhibited the inflammatory response mediated by microglia cells by inhibiting NF-κB. This anti-inflammatory effect on microglia may be a potential mechanism for the neuroprotective effect of 4ae in VaD.

Inhibition potential evaluation of two synthetic bis-indole compounds on amyloid fibrillation: a molecular simulation study

Protein aggregation is known as the main mechanism of amyloid fibrillation in amyloidosis diseases. Recent studies confirmed that compounds with one or two indole rings have inhibitory potential against amyloid fibrillation. Herein, the interaction of two similar compounds ‘bis(indolyl)-2-methyl-phenyl-methene’ and ‘bis(indolyl)-2-chloro-phenyl-methene’ with an amyloid core model was investigated. To this aim, molecular docking and all-atom molecular dynamics (MD) simulations were used. Docking results between aggregation-prone region (APR) of hen egg-white lysozyme (HEWL) and either of ligands showed that they interact with different residues of the APR (amyloid fibril nucleus). According to MD results, bis(indolyl)-2-methyl-phenyl-methene made a distance between the two cores, which was 1.5 times greater than that bis(indolyl)-2-chloro-phenyl-methene made. Analysis of RMSD/RMSF values revealed that bis(indolyl)-2-methyl-phenyl-methene stabilized strands of A and B, while destabilized strands C and D. The hydrophobic ‘methyl’ functional group in bis(indolyl)-2-methyl-phenyl-methene facilitate its deep penetration between core nuclei, via destabilizing outer strands of C and D. Considering this fact that results of this study are in agreement with experimental findings, details of the discovered mechanism of interaction between ligands and HEWL’s APR would be inspiring for further anti-fibrillation drug designs. Communicated by Ramaswamy H. Sarma

Computer-aided discovery of bis-indole derivatives as multi-target drugs against cancer and bacterial infections: DFT, docking, virtual screening, and molecular dynamics studies

Recently, more complex diseases of seemingly incurable pathology have demonstrated the need for potent and multi-target drugs. Specific to many cancers and bacterial diseases, more than 100 bis-indole compounds along with a commercialized drug, olaparib are screened against fifteen protein targets (eleven cancer and four bacterial), which have direct roles in tumorigenesis, cancer progression, or pathogenesis. Successive refinements are performed employing the density functional theory (DFT), pharmacokinetics, and virtual screening. Eight potential drugs, of which three as multi-target agents against both bacteria and cancer, are shortlisted. Molecular dynamics simulation was employed to check the stability of the discovered drugs in their docked configurations along with principal component analysis and molecular mechanics Poisson-Boltzmann surface area-based binding free energy calculation. All of these complexes have lower binding free energies. During dynamics, after some initial run, the root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), and radius of gyration (Rg) of every shortlisted target-drug complex quickly reach a plateau, indicating the stability of the docked complex and potential inhibitory property of the shortlisted drugs. A proposed drug can unprecedentedly inhibit six targets. Due to the presence of prevailing bis-indole-scaffold as evident in many well-known drugs, the shortlisted compounds can be envisaged to emerge as very effective drugs for cancers and bacterial infections, which encourages experimental studies to validate them.

Generation of indole derivatives by an endophytic fungus Chaetomium sp. through feeding 1,2-dimethylindole

Through feeding 1,2-dimethylindole, two new bisindoles, chaetoindolone E and F (1 and 2) and five known indole derivatives (3–7) were isolated from the cultures of an endophytic fungus Chaetomium sp. The structures of these compounds were elucidated based on HR-MS, NMR and single-crystal X-ray crystallography. Compounds 1 and 2 were undescribed before, compounds 3–7 were first reported from natural sources, and NMR spectrums of compounds 4 and 5 were first reported. The cytotoxity of the bisindole compounds (1–3) was also tested.

Antibacterial Evaluation of Novel Substituted Cycloheptaindoles in Staphylococcus and Enterococcus Strains.

Due to emerging resistances against antibiotics there is a strong need to find novel antibacterial agents with a novel structure to prevent early resistance developments. Bisindole compounds with antibacterial activities which formally result from the reaction of an aldehyde with indole motivated to investigate the reaction of a dialdehyde and indole to give novel structures with potential antibacterial activities. Compounds were yielded by chemical synthesis and purified using column chromatography. The antibacterial activity was determined as minimal inhibitory growth activity in cultures of Gram-positive strains of Staphylococcus aureus and Enterococcus species. Cyclohepta[2,3-b]indoles have been yielded in a one-step reaction procedure with indole substitutions at the cycloheptane central core matching a solution for achieving fused novel cycloalkane indoles with functionalized residues of promising biological activity. So far fused cycloalkane indoles have not been available in a one-step procedure and moreover, core functionalizations have been additional challenges. Various indole substitutions have been done to provide a first set of compounds. Substituent-dependent effects have been suggested to influence the antibacterial activity and first compounds were identified with specific Staphylococcus activities and Enterococcus species effects towards Enterococcus faecalis as critical pathogens in the hospital with upcoming resistances against standard antibiotics.

High-throughput screening of bioactive compounds via new catalytic reaction in the pooled mixture.

To increase the chances of finding new candidate molecules with medicinal properties, while expending less resource and effort, the present study used pooled substrates as starting materials. A bisindole compound that showed inhibitory activity was then isolated from the mixture, and the activity was improved by optimizing the substituents on the indole skeleton.

Convenient Synthesis of 6,7,12,13-Tetrahydro-5H-Cyclohepta[2,1-b:3,4-b']diindole Derivatives Mediated by Hypervalent Iodine (III) Reagent.

Bisindolyl alkaloids represent a large family of natural and synthetic products that display various biological activities. Among the bisindole compounds, 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b’]diindoles have received little attention. Only two methods have been developed for the construction of the 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b’]diindole scaffold thus far, including the classical Fischer indole synthesis conducted by reacting indole-fused cycloheptanone and hydrazines, and the condensation reaction to build the seven-membered ring. Here, we report for the first time a new route to synthesize 6,7,12,13-tetrahydro-5H-cyclohepta[2,1-b:3,4-b’]diindoles through intramolecular oxidative coupling of 1,3-di(1H-indol-3-yl)propanes in the presence of PIFA, DDQ and TMSCl with moderate to excellent yields.

Investigation of the molecular characteristics of bisindole inhibitors as HIV-1 glycoprotein-41 fusion inhibitors

In previous work, we described 6-6‘-bisindole compounds targeting a hydrophobic pocket on the N-heptad repeat region of viral glycoprotein-41 as effective inhibitors of HIV-1 fusion. Two promising compounds with sub-micromolar IC50's contained a benzoic acid group and a benzoic acid ester attached at the two indole nitrogens. Here we have conducted a thorough structure-activity relationship (SAR) study evaluating the contribution of each of the ring systems and various substituents to compound potency. Hydrophobicity, polarity and charge were varied to produce 35 new compounds that were evaluated in binding, cell-cell fusion and viral infectivity assays. We found that (a) activity based solely on increasing hydrophobic content plateaued at ∼ 200 nM; (b) the bisindole scaffold surpassed other heterocyclic ring systems in efficacy; (c) a polar interaction possibly involving Gln575 in the pocket could supplant less specific hydrophobic interactions; and (d) the benzoic acid ester moiety did not appear to form specific contacts with the pocket. The importance of this hydrophobic group to compound potency suggests a mechanism whereby it might interact with a tertiary component during fusion, such as membrane. A promising small molecule 10b with sub-μM activity was discovered with molecular weight <500 da and reduced logP compared to earlier compounds. The work provides insight into requirements for small molecule inhibition of HIV-1 fusion.

Indirubin ameliorates imiquimod-induced psoriasis-like skin lesions in mice by inhibiting inflammatory responses mediated by IL-17A-producing γδ T cells

ObjectivesIndirubin (IR) is a bisindole compound extracted from the leaves of Chinese herb Indigo Naturalis. Indigo Naturalis has been widely used in traditional Chinese medicine to treat inflammatory and autoimmune diseases. Psoriasis is a chronic immune-mediated inflammatory skin disease in which γδ T cells play an important role. This study aims to determine the immunoregulatory effects and the underlying mechanisms of Indirubin in psoriasis-related inflammatory responses. MethodsBALB/c mice with imiquimod (IMQ)-induced psoriasis-like dermatitis were treated with saline (Model), 1 mg/kg methotrexate (MTX) that serves as a positive control, or 12.5, 25 and 50 mg/kg Indirubin(IR) intragastrically. Keratinocytes proliferation, inflammatory cells infiltration, the expression of inflammatory cytokines and Jak/Stat pathway-related proteins in the skin lesion were examined. The abundance of γδ T cells in lymph nodes and spleen was determined by flow cytometry. The IL-17 expression and secretion, and the activation of Jak3/Stat3 pathways in in vitro cultured γδ T cell were tested. ResultsIndirubin ameliorated keratinocyte proliferation, reduced the infiltration of CD3+ T cells, IL-17 A-producing γδ T cells, and CD11b+ neutrophils, inhibited the mRNA expression of Il1, Il6, Il23, Il17a and Il22, and the protein expression of Jak/Stat pathway-related molecules in the skin lesion. Indirubin also reduced the abundance of γδ T cell and CCR6+ γδ T cells (the major IL-17 A producer) in spleen and lymph nodes. In cultured γδ T cells, Indirubin inhibited the mRNA expression of Il17a and Ifng, and the secretion of IL-17 A, while suppressed the activation of Jak3/Stat3 pathways. ConclusionIndirubin alleviates IMQ-induced psoriasis-like dermatitis mainly through reducing the inflammatory responses mediated by IL-17 A-producing γδ T cells involving Jak3/Stat3 activation. Our results highlighted the novel mechanisms by which Indirubin ameliorates psoriasis-related inflammatory responses, supporting its therapeutic potential.

Fe-catalyzed regioselective Friedel–Crafts hydroxyalkylation of N -substituted glyoxylamide with indoles

An efficient regioselective Friedel–Crafts hydroxyalkylation of N-substituted glyoxylamide with various indoles catalyzed by Lewis acids was developed. The reactions proceeded smoothly at room temperature and the 2-hydroxy-2-(1H-indol-3-yl)-N-substituted acetamide resulted from the reactions catalyzed by FeSO4 were synthesized in excellent yields (up to 93%). While the bisindole compounds were obtained when FeCl3 was used as a catalyst in excellent yields (up to 92%). A possible mechanism was proposed.

Regioselective Friedel–Crafts Reactions of N-Substituted Glyoxylamide with Indoles Catalyzed by Brønsted Acid

An efficient regioselective Friedel–Crafts reaction of a series of N-substituted glyoxylamide with indoles catalyzed by Brønsted acid was developed. The reactions proceeded smoothly at room temperature and the corresponding N-substituted 2-hydroxy-2-(1<i>H</i>-indol-3-yl) acetamides were afforded in moderate to good yields (up to 89%). When 2 M HCl was used, the bisindole compounds were obtained in good to excellent yield (up to 91%) resulting from a double Friedel–Crafts reaction.

Novel synthetic bis-indolic derivatives with antistaphylococcal activity, including against MRSA and VISA strains.

We report the synthesis, antibacterial activity and toxicity of 24 bis-indolic derivatives obtained during the development of new ways of synthesis of marine bis-indole alkaloids from the spongotine, topsentin and hamacanthin classes. Innovative ways of synthesis and further structural optimizations led to bis-indoles presenting either the 1-(1H-indol-3'-yl)-1,2-diaminoethane unit or the 1-(1H-indol-3-yl)ethanamine unit. MIC determination was performed for reference and clinical strains of Staphylococcus aureus and CoNS species. MBC, time-kill kinetics, solubility, hydrophobicity index, plasma protein-binding and cytotoxicity assays were performed for lead compounds. Inhibition of the S. aureus NorA efflux pump was also tested for bis-indoles with no antistaphylococcal activity. Lead compounds were active against both S. aureus and CoNS species, with MICs between 1 and 4 mg/L. Importantly, the same MICs were found for MRSA and vancomycin-intermediate S. aureus strains. Early concentration-dependent bactericidal activity was observed for lead derivatives. Compounds with no intrinsic antibacterial activity could inhibit the S. aureus NorA efflux pump, which is involved in resistance to fluoroquinolones. At 0.5 mg/L, the most effective compound led to an 8-fold reduction of the ciprofloxacin MIC for the SA-1199B S. aureus strain, which overexpresses NorA. However, the bis-indole compounds displayed a high hydrophobicity index and high plasma protein binding, which significantly reduced antibacterial activity. We have synthesized and characterized novel bis-indole derivatives as promising candidates for the development of new antistaphylococcal treatments, with preserved activity against MDR S. aureus strains.