Monocarbonyl analogs of curcumin inhibit growth of antibiotic sensitive and resistant strains of Mycobacterium tuberculosis

Repurposed Drugs and Plant-Derived Natural Products as Potential Host-Directed Therapeutic Candidates for Tuberculosis

Tuberculosis (TB) is one of the leading causes of death due to infectious disease. It is a treatable disease; however, conventional treatment requires a lengthy treatment regimen with severe side effects, resulting in poor compliance among TB patients. Intermittent drug use, the non-compliance of patients, and prescription errors, among other factors, have led to the emergence of multidrug-resistant TB, while the mismanagement of multidrug-resistant TB (MDR-TB) has eventually led to the development of extensively drug-resistant tuberculosis (XDR-TB). Thus, there is an urgent need for new drug development, but due to the enormous expenses and time required (up to 20 years) for new drug research and development, new therapeutic approaches to TB are required. Host-directed therapies (HDT) could be a most attractive strategy, as they target the host defense processes instead of the microbe and thereby may prevent the alarming rise of MDR- and XDR-TB. This paper reviews the progress in HDT for the treatment of TB using repurposed drugs which have been investigated in clinical trials (completed or ongoing) and plant-derived natural products that are in clinical or preclinical trial stages. Additionally, this review describes the existing challenges to the development and future research directions in the implementation of HDT.

Dietary curcumin supplementation attenuates hepatic damage and function abnormality in a chronic corticosterone-induced stress model in broilers

Chronic stress refers to the activation of the hypothalamic-pituitary-adrenal (HPA) axis and elevated blood contents of ACTH and corticosterone (CORT), exhibiting significant adverse effects on health outcomes. Currently, natural polyphenol compounds are increasingly being explored as potential therapeutic agents and have been considered as a treatment option for a variety of stress-induced diseases. Curcumin (CUR) is the main substance in Curcuma longa (Zingiberacea) rhizome that has strong health-beneficial properties. The study aimed to assess the potential protective effects of CUR on hepatic oxidative stress damage and abnormal lipid deposition in a chronic CORT-induced stress (CCIS) model in broilers. One hundred and twenty experimental broilers were randomly divided into 1) control group (CON), 2) CUR group (200 mg/kg feed), 3) CORT group (4 mg/kg BW CORT) and 4) CORT+CUR group (200 mg/kg feed plus 4 mg/kg BW CORT). The liver histology, glycolipid metabolism and oxidative stress were determined. In addition, qPCR was performed to identify shifts in genes expression. Compared with CON group, broilers under CCIS showed a decreased body weight, body weight gain and average daily gain, while dietary CUR significantly reversed these adverse effects. Furthermore, the plasma contents of TCH, TG, HDL-C, LDL-C, TP, GLB and AST were all significantly increased in CCIS broilers, while dietary CUR obviously alleviated the increase of TCH, HDL-C, LDL-C and AST, and relieved the hepatic lipid deposition disorder and liver injury. Moreover, CCIS significantly increased the contents of MDA in both liver and plasma, and decreased the content of plasma SOD, while CUR obviously reversed these changes, showing reduced oxidative stress damage. Finally, the mRNA expressions of FAS, ACC, SCD and the protein level of PPAR-γ were significantly increased, meanwhile the mRNA expression of lipolytic genes ACOX1, ATGL and CPT as well as two major intracellular antioxidant enzymes SOD1 and GPX1 were obviously decreased, while CUR effectively reversed these effects. These results showed that dietary CUR effectively alleviated CCIS-induced body weight loss, hepatic oxidative damage and lipid deposition disorder, suggesting the possible therapeutic effectiveness of CUR against hepatic damage and function abnormality caused by CCIS.

Preliminary insight on diarylpentanoids as potential antimalarials: In silico, in vitro pLDH and in vivo zebrafish toxicity assessment

Malaria remains a major public health problem worldwide, including in Southeast Asia. Chemotherapeutic agents such as chloroquine (CQ) are effective, but problems with drug resistance and toxicity have necessitated a continuous search for new effective antimalarial agents. Here we report on a virtual screening of ∼300 diarylpentanoids and derivatives, in search of potential Plasmodium falciparum lactate dehydrogenase (PfLDH) inhibitors with acceptable drug-like properties. Several molecules with binding affinities comparable to CQ were chosen for in vitro validation of antimalarial efficacy. Among them, MS33A, MS33C and MS34C are the most promising against CQ-sensitive (3D7) with EC50 values of 1.6, 2.5 and 3.1 μM, respectively. Meanwhile, MS87 (EC50 of 1.85 μM) shown the most active against the CQ-resistant Gombak A strain, and MS33A and MS33C the most effective P. knowlesi inhibitors (EC50 of 3.6 and 5.1 μM, respectively). The in vitro cytotoxicity of selected diarylpentanoids (MS33A, MS33C, MS34C and MS87) was tested on Vero mammalian cells to evaluate parasite selectivity (SI), showing moderate to low cytotoxicity (CC50 > 82 μM). In addition, MS87 exhibited a high SI and the lowest resistance index (RI), suggesting that MS87 may exert effective parasite inhibition with low resistance potential in the CQ-resistant P. falciparum strain. Furthermore, the in vivo toxicity of the molecules on early embryonic development, the cardiovascular system, heart rate, motor activity and apoptosis were assessed in a zebrafish animal model. The overall results indicate the preliminary potential of diarylpentanoids, which need further investigation for their development as new antimalarial agents.

Diarylpentanoids, the privileged scaffolds in antimalarial and anti-infectives drug discovery: A review

Asia is a hotspot for infectious diseases, including malaria, dengue fever, tuberculosis, and the pandemic COVID-19. Emerging infectious diseases have taken a heavy toll on public health and the economy and have been recognized as a major cause of morbidity and mortality, particularly in Southeast Asia. Infectious disease control is a major challenge, but many surveillance systems and control strategies have been developed and implemented. These include vector control, combination therapies, vaccine development, and the development of new anti-infectives. Numerous newly discovered agents with pharmacological anti-infective potential are being actively and extensively studied for their bioactivity, toxicity, selectivity, and mode of action, but many molecules lose their efficacy over time due to resistance developments. These facts justify the great importance of the search for new, effective, and safe anti-infectives. Diarylpentanoids, a curcumin derivative, have been developed as an alternative with better bioavailability and metabolism as a therapeutic agent. In this review, the mechanisms of action and potential targets of antimalarial drugs as well as the classes of antimalarial drugs are presented. The bioactivity of diarylpentanoids as a potential scaffold for a new class of anti-infectives and their structure-activity relationships are also discussed in detail.

Arylnitro monocarbonyl curcumin analogues: Synthesis and in vitro antitubercular evaluation

Curcumin is a natural product that has been reported to exhibit myriad pharmacological properties, one of which is antitubercular activity. It demonstrates antitubercular activity by directly inhibiting Mycobacterium tuberculosis (M.tb) and also enhances immune responses that ultimately lead to the elimination of M.tb by macrophages. This natural product is, however, unstable, and several analogues, noticeably monocarbonyl analogues, have been synthesized to overcome this challenge. Curcumin and its monocarbonyl analogues reported so far exhibit moderate antitubercular activity in the range of 7 to 16 μM. Herein, we report a straightforward synthesis of novel monocarbonyl curcumin analogues, their antitubercular activity, and the structure-activity relationship. The hit compound from this study, 3a, exhibits potent MIC₉₀ values in the range of 0.2 to 0.9 μM in both ADC and CAS media.

Antibacterial activity of curcumin and its essential nanoformulations against some clinically important bacterial pathogens: A comprehensive review

Multidrug-resistant bacterial infections can kill 700,000 individuals globally each year and is considered among the top 10 global health threats faced by humanity as the arsenal of antibiotics is becoming dry and alternate antibacterial molecule is in demand. Nanoparticles of curcumin exhibit appreciable broad-spectrum antibacterial activity using unique and novel mechanisms and thus the process deserves to be reviewed and further researched to clearly understand the mechanisms. Based on the antibiotic resistance, infection, and virulence potential, a list of clinically important bacteria was prepared after extensive literature survey and all recent reports on the antibacterial activity of curcumin and its nanoformulations as well as their mechanism of antibacterial action have been reviewed. Curcumin, nanocurcumin, and its nanocomposites with improved aqueous solubility and bioavailability are very potential, reliable, safe, and sustainable antibacterial molecule against clinically important bacterial species that uses multitarget mechanism such as inactivation of antioxidant enzyme, reactive oxygen species-mediated cellular damage, and inhibition of acyl-homoserine-lactone synthase necessary for quorum sensing and biofilm formation, thereby bypassing the mechanisms of bacterial antibiotic resistance. Nanoformulations of curcumin can thus be considered as a potential and sustainable antibacterial drug candidate to address the issue of antibiotic resistance.

Michael acceptor molecules in natural products and their mechanism of action

Purpose: Michael receptor molecules derived from plants are biologically active due to electrophilic groups in their structure. They can target nucleophilic residues on disease-related proteins, with significant therapeutic effects and low toxicity for many diseases. They provide a good option for relevant disease treatment. The aim of this study is to summarize the existing MAMs and their applications, and lay a foundation for the application of Michael receptor molecules in life science in the future. Methods: This review summarizes the published studies on Michael receptor molecules isolated from plants in literature databases such as CNKI, Wanfang Data, PubMed, Web of Science, ScienceDirect, and Wiley. Latin names of plants were verified through https://www.iplant.cn/. All relevant compound structures were verified through PubChem and literature, and illustrated with ChemDraw 20.0. Result: A total of 50 Michael receptor molecules derived from various plants were discussed. It was found that these compounds have similar pharmacological potential, most of them play a role through the Keap1-Nrf2-ARE pathway and the NF-κB pathway, and have biological activities such as antioxidant and anti-inflammatory. They can be used to treat inflammatory diseases and tumors. Conclusion: The Michael receptor molecule has electrophilicity due to its unsaturated aldehyde ketone structure, which can combine with nucleophilic residues on the protein to form complexes and activate or inhibit the protein pathway to play a physiological role. Michael receptor molecules can regulate the Keap1-Nrf2-ARE pathway and the NF-κB pathway. Michael receptor molecules can be used to treat diseases such as inflammation, cancer, oxidative stress, etc.

Developing dietary curcumin mono-carbonyl piperidinone analogs as Nrf2-dependent cytoprotectors against oxidative damage: Structure-activity relationship and mechanisms

Developing nuclear factor erythroid-2 related factor 2 (Nrf2)-dependent cytoprotectors against oxidative damage is of concern because they can effectively reduce the risk of oxidative stress-related diseases, such as cancer and inflammation. This work was aimed to develop more active Nrf2-dependent cytoprotectors than curcumin, a well-known dietary Nrf2 activator and cancer chemopreventive agent. Herein we designed a panel of curcumin-inspired mono-carbonyl piperidinone analogs differentiated by placing distinct electron-withdrawing and electron-donating groups on its two aromatic rings in the ortho, meta, or para position to the linker of α, β-unsaturated piperidinone. Among these, the ortho-fluorine-substituted CN-2F surfaced as a promising lead molecule, which was significantly superior to the parent curcumin in protecting HepG2 cells from oxidative damage induced by tert-butyl hydroperoxide. Mechanically, by virtue of its Michael receptor units and ortho-substituted mode, CN-2F activated Nrf2 signaling by covalently modifying Cys-151 and Cys-288 residues at Keap1, promoting phosphorylation of JNK, ERK and p38, as well as inhibiting Nrf2 degradation. This work reveals the structural determinants and the activity mechanisms of CN-2F as an Nrf2-dependent cytoprotector, and gives useful information on how to design curcumin-inspired Nrf2 activators and cytoprotectors.

Click synthesis of novel dendronized curcumin and analogs. Strengthening of physicochemical properties toward biological applications

Curcumin and its analogs, chalcones, and C5-monocarbonyl are molecules of great therapeutic potential, but their poor stability and hydrophobicity have hampered their extensive use in clinical trials. Therefore, significant efforts have been made in materials science to improve their physicochemical properties. In this study, we propose dendronization as a synthetic strategy to strengthen some physicochemical properties such as solubility and stability of curcumin and analogs, taking advantage of the click chemistry (CuAAC) to attach second-generation polyester dendrons to the unsaturated cores. The dendronization, with the subsequent formation of aromatic triazole groups as linkers, not only modified the solubility and stability of the molecular systems but also favored the diketo tautomeric form of curcumin, as demonstrated spectroscopically. This result is significant since the diketo tautomer, which preserves the antioxidant properties of curcumin, is the most biologically active form. The hydrophobic/hydrophilic balance, achieved after dendronization, allowed the solubilization of the chromophoric molecules in buffered solutions at relevant pH values (7.4 and 6.4). Furthermore, the stability of all molecules was also upgraded since UV-vis absorption spectra did not exhibit modified profiles after 7 days at physiologic pH. From photochemical stability experiments irradiating at 415 nm, the dendritic derivatives containing triazole linkers were more susceptible to being degraded. All derivatives exhibited emission properties according to the length of each conjugate fragment. Fluorescence experiments evidenced the role of dendrons in preventing emission quenching by aggregation and exhibited differentiated emission behavior depending on the linker type (triazole or ester) between the chromophoric core and the polyester dendrons.

Antibiofilm Activity of Azadirachta indica and Catharanthus roseus and Their Synergistic Effects in Combination with Antimicrobial Agents against Fluconazole-Resistant Candida albicans Strains and MRSA

The rapid emergence and spread of antimicrobial resistance has become a global public health concern that threatens the effective treatment of infectious diseases. One major approach adopted to overcome antimicrobial resistance is the use of plant extracts individually and/or with combination of antibiotics with plant extracts, which may lead to new ways of treating infectious diseases and essentially representing a potential area for further future investigations. In this study, the antifungal activities of Azadirachta indica leaf and Catharanthus roseus flower extracts against fluconazole-resistant Candida albicans strains (isolated from pregnant women with vulvovaginal candidiasis) and anti-methicillin-resistant Staphylococcus aureus (MRSA) were evaluated by agar well diffusion, microdilution, and biofilm inhibition assays. Subsequently, the determination of the combined antimicrobial activity of the individual plant extracts with (fluconazole and voriconazole) and (ampicillin, tetracycline, and streptomycin) against C. albicans strains and MRSA, respectively, was evaluated by checkerboard microdilution assay. Results from the study showed that the antimicrobial activity of the two plant extracts determined by time-kill kinetics was fungistatic with their MICs ranging from 0.1 to 4 mg/mL. Interestingly, all extracts were proved as good biofilm inhibitors of resistant C. albicans and MRSA from 10.1 to 98.82%. Their combination interaction with fluconazole, voriconazole, ampicillin, tetracycline, and streptomycin ranged from synergy to antagonism as per the parameters used. Overall, these results showed that A. indica leaf and C. roseus flower extracts have significant antifungal property. Furthermore, A. indica leaf and C. roseus flower extracts alone or in combination with fluconazole and voriconazole could provide a promising approach to the management of candidiasis caused by drug-resistant strains as well as their interaction with the antibacterial agents to combat the common infections caused by MRSA.

Advances in adjunct therapy against tuberculosis: Deciphering the emerging role of phytochemicals

Eastern countries are a major source of medicinal plants, which set up a rich source of ethnopharmacologically known medicines used in the treatment of various diseases. These traditional medicines have been known as complementary, alternative, or nonconventional therapy across globe for ages. Tuberculosis (TB) poses a huge global burden and leads to maximum number of deaths due to an infectious agent. Treatment of TB using Directly Observed Treatment Short-course (DOTS) therapy comprises multiple antibiotics is quite lengthy and causes serious side-effects in different organs. The length of the TB treatment leads to withdrawal from the patients, which paves the way for the emergence of drug resistance in the bacterial population. These concerns related to therapy need serious and immediate interventions. Traditional medicines using phytochemicals has shown to provide tremendous potential in TB treatment, mainly in the eradication of Mycobacterium tuberculosis (M.tb), increasing natural immunity, and managing the side effects of anti-TB drugs. This review describes the antituberculosis potential of selected ethnopharmacologically important phytochemicals as potential immune-modulator and as an adjunct-therapy in TB. This review will be a useful reference for researchers working on ethnopharmacology and will open the door for the discovery of novel agents as an adjunct-therapy to tuberculosis.

Traditional Medicinal Plants as a Source of Antituberculosis Drugs: A System Review

Medicinal plants are the chief components in the different oriental formulations in different traditional medical systems worldwide. As a thriving source of medicine, the medicinal plants with antituberculosis (TB) properties inspire the pharmacists to develop new drugs based on their active components or semimetabolites. In the present review, the anti-TB medicinal plants were screened from the scientific literatures, based on the botanical classification and the anti-TB activity. The obtained anti-TB medicinal plants were categorized into three different categories, viz., 159 plants critically examined with a total 335 isolated compounds, 131 plants with their crude extracts showing anti-TB activity, and 27 plants in literature with the prescribed formula by the traditional healers. Our systemic analysis on the medicinal plants can assist the discovery of novel and more efficacious anti-TB drugs.

Therapeutic Potential of Curcumin as an Antimycobacterial Agent

Curcumin is the principal curcuminoid obtained from the plant Curcuma longa and has been extensively studied for its biological and chemical properties. Curcumin displays a vast range of pharmacological properties, including antimicrobial, anti-inflammatory, antioxidant, and antitumor activity. Specifically, curcumin has been linked to the improvement of the outcome of tuberculosis. There are many reviews on the pharmacological effects of curcumin; however, reviews of the antitubercular activity are comparatively scarcer. In this review, we attempt to discuss the different aspects of the research on the antitubercular activity of curcumin. These include antimycobacterial activity, modulation of the host immune response, and enhancement of BCG vaccine efficacy. Recent advances in the antimycobacterial activity of curcumin synthetic derivatives, the role of computer aided drug design in identifying curcumin targets, the hepatoprotective role of curcumin, and the dosage and toxicology of curcumin will be discussed. While growing evidence supports the use of curcumin and its derivatives for tuberculosis therapy, further preclinical and clinical investigations are of pivotal importance before recommending the use of curcumin formulations in public health.

Monocarbonyl curcuminoids as antituberculosis agents with their moderate in-vitro metabolic stability on human liver microsomes

Tuberculosis, an airborne infectious disease, results in a high morbidity and mortality rate. The continuous emergence of TB resistance strains including MDR (multidrug-resistant tuberculosis), XDR (extensive drug-resistant tuberculosis), and especially TDR (totally drug-resistant tuberculosis) is a major public health threat and has intensified the need to develop new antitubercular agents. A natural product, curcumin, possesses diverse biological activities but suffers due to a lack of water solubility and bioavailability. To overcome these limitations, a series of 17 water-soluble monocarbonyl curcuminoids was synthesized and evaluated for antimycobacterial activity. All compounds exhibited good to moderate anti-TB activity with MIC₉₉ in the range of 3.12-25.0 µM, out of which 7c and 7p were found the most potent compounds with MIC₉₉ in the range of 3.12-6.25 µM. Furthermore, these compounds were observed to be nonhaemolytic, nontoxic, and stable under both physiological as well as reducing conditions. In-vitro metabolic stability data of the representative compound 7p with the human liver microsome revealed that these compounds possess a moderate metabolism with a half-life of 1.2 h and an intrinsic clearance of 1.12 ml/h/mg.

Curcumin Nanoformulations with Metal Oxide Nanomaterials for Biomedical Applications

In the past few decades, curcumin, a natural polyphenolic phytochemical, has been studied for treating a wide variety of diseases. It has shown promising results as a potential curative agent for a variety of diseases. However, its inherent limitations, such as poor aqueous solubility, poor absorbability, fast metabolic rate, and quick elimination from the body, have limited its application beyond preclinical studies. A huge number of studies have been made to address the issues of curcumin and to maximally utilize its potentials. Many review articles have tried to assess and summarize different nanocarriers, especially organic nanocarriers, for nanoformulations with curcumin. Nevertheless, few exclusive reviews on the progress in nanoformulation of curcumin with inorganic nanomaterials have been made. In this review, we present an exclusive summary of the progress in nanoformulation of curcumin with metal oxide nanoparticles. The beneficial feature of the metal oxide nanoparticles used in the curcumin nanoformulation, the different approaches followed in formulating curcumin with the metal oxides, and the corresponding results, protective effect of curcumin from different metal oxide caused toxicities, and concluding remarks are presented in the review.

Antibacterial activity of a new monocarbonyl analog of curcumin MAC 4 is associated with divisome disruption

Curcumin (CUR) is a symmetrical dicarbonyl compound with antibacterial activity. On the other hand, pharmacokinetic and chemical stability limitations hinder its therapeutic application. Monocarbonyl analogs of curcumin (MACs) have been shown to overcome these barriers. We synthesized and investigated the antibacterial activity of a series of unsymmetrical MACs derived from acetone against Mycobacterium tuberculosis and Gram-negative and Gram-positive species. Phenolic MACs 4, 6 and 8 showed a broad spectrum and potent activity, mainly against M. tuberculosis, Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus (MRSA), with MIC (minimum inhibitory concentration) values ranging from 0.9 to 15.6 µg/mL. The investigation regarding toxicity on human lung cells (MRC-5 and A549 lines) revealed MAC 4 was more selective than MACs 6 and 8, with SI (selectivity index) values ranging from 5.4 to 15.6. In addition, MAC 4 did not demonstrate genotoxic effects on A549 cells and it was more stable than CUR in phosphate buffer (pH 7.4) for 24 h at 37 °C. Fluorescence and phase contrast microscopies indicated that MAC 4 has the ability to disrupt the divisome of Bacillus subtilis without damaging its cytoplasmic membrane. However, biochemical investigations demonstrated that MAC 4 did not affect the GTPase activity of B. subtilis FtsZ, which is the main constituent of the bacterial divisome. These results corroborated that MAC 4 is a promising antitubercular and antibacterial agent.

Effects of Curcumin and Its Analogues on Infectious Diseases

Infectious diseases (IDs) are life-threatening illnesses, which result from the spread of pathogenic microorganisms such as bacteria, viruses, fungi, and parasites. IDs are a major challenge for the healthcare systems around the world, leading to a wide variety of clinical manifestations and complications. Despite the capability of frontline-approved medications to partially prevent or mitigate the invasion and subsequent damage of IDs to host tissues and cells, problems such as drug resistance, insufficient efficacy, unpleasant side effects, and high expenses stand in the way of their beneficial applications. One strategy is to evaluate currently explored and available bioactive compounds as possible anti-microbial agents. The natural polyphenol curcumin has been postulated to possess various properties including anti-microbial activities. Studies have shown that it possess pleiotropic effects against bacterial- and parasitic-associating IDs including drug-resistant strains. Curcumin can also potentiate the efficacy of available anti-bacterial and anti-parasitic drugs in a synergistic fashion. In this review, we summarize the findings of these studies along with reported controversies of native curcumin and its analogues, alone and in combination, toward its application in future studies as a natural anti-bacterial and anti-parasitic agent.

Synthesis, pharmacological profile and 2D-QSAR studies of curcumin-amino acid conjugates as potential drug candidates

A series of curcumin bis-conjugates 3a-q, 5a-k and 6a-k were synthesized in good yields utilizing an optimized reaction condition. We explored the effect of different amino acids and protecting groups on biological activities of curcumin. The conjugates were screened for anti-inflammatory, analgesic and antimicrobial properties. Some of the conjugates showed promising biological observations with a potency comparable with the standard references. The variations in biological properties concerning different amino acids and protecting groups are interesting observations. Effects of the synthesized conjugates on splenocytes and the production of nitric oxide by lipopolysaccharide-stimulated peritoneal macrophages are correlated with the observed anti-inflammatory properties. We have also established the safety profile of the most active conjugates. Robust 2D-QSAR studies supported and validated biological data.

Quinoline Based Monocarbonyl Curcumin Analogs as Potential Antifungal and Antioxidant Agents: Synthesis, Bioevaluation and Molecular Docking Study

In search for new fungicidal and free radical scavenging agents, we synthesized a focused library of 2-chloroquinoline based monocarbonyl analogs of curcumin (MACs). The synthesized MACs were evaluated for in vitro antifungal and antioxidant activity. The antifungal activity was evaluated against five different fungal strains such as Candida albicans, Fusarium oxysporum, Aspergillus flavus, Aspergillus niger, and Cryptococcus neoformans, respectively. Most of the synthesized MACs displayed promising antifungal activity compared to the standard drug Miconazole. Furthermore, molecular docking study on a crucial fungal enzyme sterol 14α-demethylase (CYP51) could provide insight into the plausible mechanism of antifungal activity. MACs were also screened for in vitro radical scavenging activity using butylated hydroxytoluene (BHT) as a standard. Almost all MACs exhibited better antioxidant activity compared to BHT.

New potential drug leads against MDR-MTB: A short review

Multidrug resistant Mycobacterium tuberculosis (MDR-MTB) infections have created a critical health problem globally. The appalling rise in drug resistance to all the current therapeutics has triggered the need for identifying new antimycobacterial agents effective against multidrug-resistant Mycobacterium tuberculosis. Structurally unique chemical entities with new mode of action will be required to combat this pressing issue. This review gives an overview of the structures and outlines on various aspects of in vitro pharmacological activities of new antimycobacterial agents, mechanism of action and brief structure activity relationships in the perspective of drug discovery and development. This review also summarizes on recent reports of new antimycobacterial agents.

Synthesis and bioactivity evaluation of penta-1,4-diene-3-one oxime ether derivatives

A series of penta-1,4-diene-3-one oxime ether derivatives were synthesized, and their antiviral and antifungal activities were evaluated. Bioactivity evaluations showed that most target compounds had significant antiviral effects against tobacco mosaic virus (TMV). Among them, (1E,3Z,4E)-1-(4-(benzyloxy)phenyl)-5-(furan-2-yl)penta-1,4-dien-3-one O-(3-fluorobenzyl) oxime (5e) was found to have good curative activity against TMV, with an inhibition rate of 64.6%, which was better than that of ribavirin (45.2%). (1E,3Z,4E)-1-(4-(benzyloxy) phenyl)-5-(furan-2-yl)penta-1,4-dien-3-one O-((6-chloropyridin-3-yl)methyl) oxime (5d) had a remarkable protective effect against TMV, with an inhibitory rate of 66.9%, which was better than that of ribavirin (61.8%). The inhibitory rate of (1E,3Z,4E)-1-(2-(benzyloxy)phenyl)-5-(furan-2-yl)penta-1,4-dien-3-one O-(4-chlorobenzyl) oxime(5m) in inactivation activity against TMV was 87.0%, which was better than that of ribavirin (77.9%). Further molecular docking studies indicated that compound 5m shows strong binding affinities toward the coat protein of tobacco mosaic virus. This result indicates that penta-1,4-diene-3-one oxime ether derivatives can play a significant role in discovering new antiviral agents.

Monocarbonyl Curcumin-Based Molecular Hybrids as Potent Antibacterial Agents

Keeping in view various pharmacological attributes of curcumin, coumarin, and isatin derivatives, triazole-tethered monocarbonyl curcumin-coumarin and curcumin-isatin molecular hybrids have been synthesized and evaluated for their antibacterial potential against Gram-positive (Enterococcus faecalis and Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) human pathogenic bacterial strains. Among all hybrid molecules, A-4 and B-38 showed the most potent antibacterial activity with inhibition zones of 29 and 31 mm along with MIC values of 12.50 and 6.25 μg/mL, respectively. Structure-activity relationship that emerged from biological data revealed that the two-carbon alkyl chain between triazole and coumarin/isatin moiety is well tolerable for the activity. Bromo substitution at the fifth position of isatin, para-cholo substitution in the case of curcumin-isatin, and para-methoxy in the case of curcumin-coumarin hybrids on ring A of curcumin are most suitable groups for the antibacterial activity. Various types of binding interactions of A-4 and B-38 within the active site of dihydrofolate reductase (DHFR) of S. aureus are also streamlined by molecular modeling studies, suggesting their capability in completely blocking DHFR.

Non-antibiotic adjunctive therapy: A promising approach to fight tuberculosis

Tuberculosis (TB) is currently a clinical and public health problem. There is a concern about the emergence and development of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) species. Additionally, the lack of effective vaccines is another limitation to control the related infections. To overcome these problems various approaches have been pursued such as finding novel drug candidates with a new mechanism of action or repurposing conventional antibiotics. However, these strategies are still far from clinical application. Hence, the use of adjunctive therapy has been suggested for TB. In this paper, we review non-antibiotic adjunctive treatment options for TB. Natural products, vitamins, micronutrients, and trace elementals, as well as non-antibiotic drugs, are examples of agents which have been used as adjunctive therapies. The use of these adjunctive therapies has been shown to improve disease outcomes and reduce the adverse effects of antibiotic drugs. Employing these agents, either alone or in combination with antibiotics, might be considered as a promising approach to control TB infections and achieve better clinical outcomes. However, supportive evidence from randomized controlled trials is still scant and merits further investigations.

Phytochemical Evaluation, Embryotoxicity, and Teratogenic Effects of Curcuma longa Extract on Zebrafish (Danio rerio)

Curcuma longa L. is a rhizome plant often used as traditional medicinal preparations in Southeast Asia. The dried powder is commonly known as cure-all herbal medicine with a wider spectrum of pharmaceutical activities. In spite of the widely reported therapeutic applications of C. longa, research on its safety and teratogenic effects on zebrafish embryos and larvae is still limited. Hence, this research aimed to assess the toxicity of C. longa extract on zebrafish. Using a reflux flask, methanol extract of C. longa was extracted and the identification and quantification of total flavonoids were carried out with HPLC. Twelve fertilized embryos were selected to test the embryotoxicity and teratogenicity at different concentration points. The embryos were exposed to the extract in the E3M medium while the control was only exposed to E3M and different developmental endpoints were recorded with the therapeutic index calculated using the ratio of LC50/EC50. C. longa extract was detected to be highly rich in flavonoids with catechin, epicatechin, and naringenin as the 3 most abundant with concentrations of 3,531.34, 688.70, and 523.83μg/mL, respectively. The toxicity effects were discovered to be dose-dependent at dosage above 62.50μg/mL, while, at 125.0μg/mL, mortality of embryos was observed and physical body deformities of larvae were recorded among the hatched embryos at higher concentrations. Teratogenic effect of the extract was severe at higher concentrations producing physical body deformities such as kink tail, bend trunk, and enlarged yolk sac edema. Finally, the therapeutic index (TI) values calculated were approximately the same for different concentration points tested. Overall, the result revealed that plants having therapeutic potential could also pose threats when consumed at higher doses especially on the embryos. Therefore, detailed toxicity analysis should be carried out on medicinal plants to ascertain their safety on the embryos and its development.

Nrf2 is a key factor in the reversal effect of curcumin on multidrug resistance in the HCT‑8/5‑Fu human colorectal cancer cell line

Multidrug resistance (MDR) is a major concern when using chemotherapy for the treatment of patients with colorectal cancer. MDR modulators are agents that can reverse MDR and, thus, enhance the chemosensitivity of tumor cells. The development of MDR modulators can improve the therapeutic efficacies of MDR in cancer. However, few effective MDR modulators have been identified so far. Curcumin has been reported to be an effective compound in the reversal of MDR in colorectal cancer cells. However, the mechanisms associated with the reversal effect of curcumin on MDR and its regulation of target factors in MDR cells remain to be fully elucidated. 3-(4,5-dimethyl-2-thiazol)-2,5-diphenyltetrazolium bromide assays, flow cytometer apoptosis assays as well as mRNA and protein expression assays were performed in the present study, and the results confirmed the reversal effect of curcumin on HCT-8/5-Fu cells and provided evidence that activated nuclear factor erythroid 2-related factor (Nrf2) deficiency induced by the curcumin altered the B-cell lymphoma 2 (Bcl-2) associated X protein/Bcl-2 expression ratio, which led to the induction of apoptosis in HCT-8/5-Fu cells. These results indicated that Nrf2 may have a functional in the reversal effect of curcumin and contribute, at least in part, to the outcomes of chemotherapy in patients with MDR.

Biological evaluation of novel curcumin-pyrazole-mannich derivative active against drug-resistant Mycobacterium tuberculosis

AIM

Our objective was to identify a more potent curcumin derivative with specific activity against Mycobacterium tuberculosis.

MATERIALS & METHODS

A total of 21 curcumin derivatives were synthesized and detailed bio-evaluation was carried out including determination of static/cidality, synergy with front-line antituberculosis drugs and determination of efficacy in the murine model of M. tuberculosis infection.

RESULTS

We identified CPMD-6d dihydrochloride exhibiting concentration-dependent bactericidal activity against M. tuberculosis (MIC 2 μg/ml), even against drug-resistant strains. In addition, it synergizes with front-line antituberculosis drugs as well as significantly reduces bacterial load in mice lungs and spleen at 25 mg/kg as compared with ethambutol at 100 mg/kg.

CONCLUSION

Taken together, CPMD-6d dihydrochloride exhibits all properties to be positioned as a novel molecule of interest for treatment of tuberculosis. Graphical abstract: [Formula: see text].

Design, Synthesis, and Characterization of N-Oxide-Containing Heterocycles with in Vivo Sterilizing Antitubercular Activity

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is the infectious disease responsible for the highest number of deaths worldwide. Herein, 22 new N-oxide-containing compounds were synthesized followed by in vitro and in vivo evaluation of their antitubercular potential against Mtb. Compound 8 was found to be the most promising compound, with MIC₉₀ values of 1.10 and 6.62 μM against active and nonreplicating Mtb, respectively. Additionally, we carried out in vivo experiments to confirm the safety and efficacy of compound 8; the compound was found to be orally bioavailable and highly effective, leading to a reduction of Mtb to undetectable levels in a mouse model of infection. Microarray-based initial studies on the mechanism of action suggest that compound 8 blocks translation. Altogether, these results indicate that benzofuroxan derivative 8 is a promising lead compound for the development of a novel chemical class of antitubercular drugs.

Anti-mycobacterium tuberculosis activity of polyherbal medicines used for the treatment of tuberculosis in Eastern Cape, South Africa

BACKGROUND

The emergence of drug-resistant strains of Mycobacterium tuberculosis has become a global public health problem. Polyherbal medicines offer great hope for developing alternative drugs for the treatment of tuberculosis.

OBJECTIVE

To evaluate the anti-tubercular activity of polyherbal medicines used for the treatment of tuberculosis.

METHODS

The remedies were screened against Mycobacterium tuberculosis H37Rv using Middlebrook 7H9 media and MGIT BACTEC 960 system. They were liquid preparations from King Williams Town site A (KWTa), King Williams Town site B (KWTb), King Williams Town site C (KWTc), Hogsback first site (HBfs), Hogsback second site (HBss), Hogsback third site (HBts), East London (EL), Alice (AL) and Fort Beaufort (FB).

RESULTS

The susceptibility testing revealed that all the remedies contain anti-tubercular activity with KWTa, KWTb, KWTc, HBfs, HBts, AL and FB exhibiting more activity at a concentration below 25 µl/ml. Furthermore, MIC values exhibited inhibitory activity with the most active remedies from KWTa, HBfs and HBts at 1.562 µg/ml. However, isoniazid showed more inhibitory activity against M. tuberculosis at 0.05 µg/ml when compare to the polyherbal remedies.

CONCLUSION

This study has indicated that these remedies could be potential sources of new anti-mycobacterial agents against M. tuberculosis. However, the activity of these preparations and their active principles still require in vivo study in order to assess their future as new anti-tuberculosis agents.

Nanoparticle-Formulated Curcumin Prevents Posttherapeutic Disease Reactivation and Reinfection with Mycobacterium tuberculosis following Isoniazid Therapy

Curcumin, the bioactive component of turmeric also known as “Indian Yellow Gold,” exhibits therapeutic efficacy against several chronic inflammatory and infectious diseases. Even though considered as a wonder drug pertaining to a myriad of reported benefits, the translational potential of curcumin is limited by its low systemic bioavailability due to its poor intestinal absorption, rapid metabolism, and rapid systemic elimination. Therefore, the translational potential of this compound is specifically challenged by bioavailability issues, and several laboratories are making efforts to improve its bioavailability. We developed a simple one-step process to generate curcumin nanoparticles of ~200 nm in size, which yielded a fivefold enhanced bioavailability in mice over regular curcumin. Curcumin nanoparticles drastically reduced hepatotoxicity induced by antitubercular antibiotics during treatment in mice. Most interestingly, co-treatment of nanoparticle-formulated curcumin along with antitubercular antibiotics dramatically reduced the risk for disease reactivation and reinfection, which is the major shortfall of current antibiotic treatment adopted by Directly Observed Treatment Short-course. Furthermore, nanoparticle-formulated curcumin significantly reduced the time needed for antibiotic therapy to obtain sterile immunity, thereby reducing the possibility of generating drug-resistant variants of the organisms. Therefore, adjunct therapy of nano-formulated curcumin with enhanced bioavailability may be beneficial to treatment of tuberculosis and possibly other diseases.

Biological activities of curcuminoids, other biomolecules from turmeric and their derivatives - A review

In recent years, several drugs have been developed deriving from traditional products and current drug research is actively investigating the possible therapeutic roles of many Ayruvedic and Traditional Indian medicinal therapies. Among those being investigated is Turmeric. Its most important active ingredient is curcuminoids. Curcuminoids are phenolic compounds commonly used as a spice, pigment and additive also utilized as a therapeutic agent used in several foods. Comprehensive research over the last century has revealed several important functions of curcuminoids. Various preclinical cell culture and animals studies suggest that curcuminoids have extensive biological activity as an antioxidant, neuroprotective, antitumor, anti-inflammatory, anti-acidogenic, radioprotective and arthritis. Different clinical trials also suggest a potential therapeutic role for curcuminoids in numerous chronic diseases such as colon cancer, lung cancer, breast cancer, inflammatory bowel diseases. The aim of this review is to summarize the chemistry, analog, metal complex, formulations of curcuminoids and their biological activities.

Synthesis and biological activity of furoxan derivatives against Mycobacterium tuberculosis

Tuberculosis (TB) remains a serious health problem responsible to cause millions of deaths annually. The scenario becomes alarming when it is evaluated that the number of new drugs does not increase proportionally to the emergence of resistance to the current therapy. Furoxan derivatives, known as nitric oxide (NO) donors, have been described to exhibit antitubercular activity. Herein, a novel series of hybrid furoxan derivatives (1,2,5-oxadiazole 2-N-oxide) (compounds 4a-c, 8a-c and 14a-c) were designed, synthesized and evaluated in vitro against Mycobacterium tuberculosis (MTB) H37Rv (ATCC 27294) and a clinical isolate MDR-TB strain. The furoxan derivatives have exhibited MIC90 values ranging from 1.03 to 62 μM (H37Rv) and 7.0-50.0 μM (MDR-TB). For the most active compounds (8c, 14a, 14b and 14c) the selectivity index ranged from 3.78 to 52.74 (MRC-5 cells) and 1.25-34.78 (J774A.1 cells). In addition, it was characterized for those compounds logPo/w values between 2.1 and 2.9. All compounds were able to release NO at levels ranging from 0.16 to 44.23%. Among the series, the phenylsulfonyl furoxan derivatives (compounds 14a-c) were the best NO-donor with the lowest MIC90 values. The most active compound (14c) was also stable at different pHs (5.0 and 7.4). In conclusion, furoxan derivatives were identified as new promising compounds useful to treat tuberculosis.

2,2'-Fluorine mono-carbonyl curcumin induce reactive oxygen species-Mediated apoptosis in Human lung cancer NCI-H460 cells

In this paper, we synthesized three fluorine-substituted mono-carbonyl curcumin analogs and evaluated their cytotoxicity against several cancer cells by the MTT assay. The results exhibited that all the three compounds were more active than the leading curcumin. Especially, 2,2'-F mono-carbonyl curcumin, 1a, surfaced as an important lead compound displaying almost 4-fold cytotoxicity relative to curcumin. More importantly, 1a was more stable in (RPMI)-1640 medium and more massive uptake than curcumin, which may be relationship to their cytotoxicity, apoptotic acitivity and reactive oxygen species generation. And then, the generation of reactive oxygen species can disrupt the intracellular redox balance, induce lipid peroxidation, cause the collapse of the mitochondrial membrane potential and ultimately lead to apoptosis. The results not only suggest that 2,2'-F mono-carbonyl curcumin (1a) may cause cancer cells apoptosis through reactive oxygen species-Mediated pathway, but also gives us an important information for design of mono-carbonyl curcumin analog.

Discovery of in vitro antitubercular agents through in silico ligand-based approaches

The development of new anti-tubercular agents represents a constant challenge mostly due to the insurgency of resistance to the currently available drugs. In this study, a set of 60 molecules were selected by screening the Asinex and the ZINC collections and an in house library by means of in silico ligand-based approaches. Biological assays in Mycobacterium tuberculosis H37Ra ATCC 25177 strain highlighted (±)-1-(4-chlorophenyl)-2-(1H-imidazol-1-yl)ethyl-4-(3,4-dichlorophenyl)piperazine-1-carboxylate (5i) and 3-(4-chlorophenyl)-5-(2,4-dimethylpyrimidin-5-yl)-2-methylpyrazolo[1.5-a]pyrimidin-7(4H)-one (42) as the most potent compounds, having a Minimum Inhibitory Concentration (MIC) of 4 and 2 μg/mL respectively. These molecules represent a good starting point for further optimization of effective anti-TB agents.

Triazole tethered C5-curcuminoid-coumarin based molecular hybrids as novel antitubulin agents: Design, synthesis, biological investigation and docking studies

Keeping in view the confines allied with presently accessible antitumor agents and success of C5-curcuminoid based bifunctional hybrids as novel antitubulin agnets, molecular hybrids of C5-curcuminoid and coumarin tethered by triazole ring have been synthesized and investigated for in-vitro cytotoxicity against THP-1, COLO-205, HCT-116 and PC-3 human tumor cell lines. The results revealed that the compounds A-2 to A-9, B-2, B-3, B-7 showed significant cytotoxic potential against THP-1, COLO-205 and HCT-116 cell lines, while the PC-3 cell line among these was found to be almost resistant. Structure activity relationship revealed that the nature of Ring X and the length of carbon-bridge (n) connecting triazole ring with coumarin moiety considerably influence the activity. Methoxy substituted phenyl ring as Ring X and two carbon-bridges were found to be the ideal structural features. The most potent compounds (A-2, A-3 and A-7) were further tested for tubulin polymerization inhibition. Compound A-2 was found to significantly inhibit the tubulin polymerization (IC50 = 0.82 μM in THP-1 tumor cells). The significant cytotoxicity and tubulin polymerization inhibition by A-2 was further rationalized by docking studies where it was docked at the curcumin binding site of tubulin.