Protein kinase C-δ inhibitor, Rottlerin inhibits growth and survival of mycobacteria exclusively through Shikimate kinase

Determining the Antimycobacterial Action of Rottlerin Against Mycobacterium Species and Toxicity, Antioxidant Properties, and Therapeutic Target Affinity of Rottlerin

Infections by Mycobacterium spp. are responsible for thousands of deaths every year worldwide. Microbial resistance, toxic effects, and adverse consequences of conventional therapies bring forth the need to search for new therapeutic agents. The aim of this study was to determine the antimicrobial action of the molecule Rottlerin against Mycobacterium spp. The broth microdilution assay showed that Rottlerin inhibited the mycobacterial growth at concentrations ≤ 50 µg/mL (≤ 96.81 µM), and the lowest bactericidal concentration was observed against M. tuberculosis (25 µg/mL-48.40 µM). The cytotoxicity of Rottlerin was conducted in a epithelial cell culture and evaluated through 2,3-Bis-(2-Methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) colorimetric assay, revealing an IC50 equivalent to 81.89 ± 4.64 µM. The antioxidant action determined by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrated that Rottlerin reduced at least 50% of free radicals at 109.2 µM. To gain insights into the antimycobacterial activity of Rottlerin, we performed molecular docking simulations with therapeutic targets of M. tuberculosis and observed that Rottlerin binds into the inhibitory site of the anti-infective target diterpene synthase (Rv3378c). Our findings indicate that Rottlerin presents antimicrobial effects with antioxidant action and prominent therapeutic targets, showing its biotechnological potential for the development of new agent against Mycobacterium spp. infection.

Screening novel antiviral compounds to treat Clostridioides difficile infections

Clostridioides difficile is a major cause of nosocomial infections, often associated with individuals who have gut dysbiosis from previous antibiotic therapies. C. difficile infections (CDI) have a high recurrence rate and impose significant financial and mortality burdens on the healthcare system. Therefore, novel anti-C. difficile drugs are urgently needed to treat and reduce the severity and recurrence of infection. In this study, we screened a library of 618 antiviral drugs to identify a potential candidate for repurposing as novel anti-C. difficile therapeutics. Following our preliminary screening, we identified 9 novel compounds that inhibited C. difficile at a concentration of 16 μM or lower. Among these, 4 antiviral compounds demonstrated the most potent anti-C. difficile activity against a panel of 15 C. difficile isolates, with minimum inhibitory concentrations (MICs) comparable to the drug of choice, vancomycin. These include rottlerin (MIC50 = 0.25 μg/mL), α-mangostin (MIC50 = 1 μg/mL), dryocrassin ABBA (MIC50 = 1 μg/mL), and obefazimod (MIC50 = 4 μg/mL). All exhibited minimal to no activity against representative members of the human gut microbiota. Interestingly, α-mangostin, a natural xanthone derived from the mangosteen fruit, exhibited strong bactericidal action, clearing a high inoculum of C. difficile in less than an hour. All other drugs exhibited bacteriostatic activity. Given their characteristics, these compounds show great promise as novel treatments for CDI.

Antibacterial phenolic compounds from the flowering plants of Asia and the Pacific: coming to the light

CONTEXT

The emergence of pan-resistant bacteria requires the development of new antibiotics and antibiotic potentiators.

OBJECTIVE

This review identifies antibacterial phenolic compounds that have been identified in Asian and Pacific Angiosperms from 1945 to 2023 and analyzes their strengths and spectra of activity, distributions, molecular masses, solubilities, modes of action, structures-activities, as well as their synergistic effects with antibiotics, toxicities, and clinical potential.

METHODS

All data in this review was compiled from Google Scholar, PubMed, Science Direct, Web of Science, and library search; other sources were excluded. We used the following combination of keywords: 'Phenolic compound', 'Plants', and 'Antibacterial'. This produced 736 results. Each result was examined and articles that did not contain information relevant to the topic or coming from non-peer-reviewed journals were excluded. Each of the remaining 467 selected articles was read critically for the information that it contained.

RESULTS

Out of ∼350 antibacterial phenolic compounds identified, 44 were very strongly active, mainly targeting the cytoplasmic membrane of Gram-positive bacteria, and with a molecular mass between 200 and 400 g/mol. 2-Methoxy-7-methyljuglone, [6]-gingerol, anacardic acid, baicalin, vitexin, and malabaricone A and B have the potential to be developed as antibacterial leads.

CONCLUSIONS

Angiosperms from Asia and the Pacific provide a rich source of natural products with the potential to be developed as leads for treating bacterial infections.

Rottlerin impairs early and late steps of Toxoplasma gondii infection in human trophoblast cells and villous explants

Congenital toxoplasmosis, caused by the opportunistic protozoan parasite T. gondii, can cause stillbirths, miscarriages and fetal abnormalities, as well as encephalitis and chorioretinitis in newborns. Available treatment options rely on antiparasitic drugs that have been linked to serious side effects, high toxicity and the development of drug-resistant parasites. The search for alternative therapeutics to treat this disease without acute toxicity for the mother and child is essential for the advancement of current therapeutic procedures. The present study aimed to unravel the mode of the anti-T. gondii action of Rottlerin, a natural polyphenol with multiple pharmacological properties described. Herein, we further assessed the antiparasitic activity of Rottlerin against T. gondii infection on the human trophoblastic cells (BeWo cells) and, for the first time, on human villous explants. We found that non-cytotoxic doses of Rottlerin impaired early and late steps of parasite infection with an irreversible manner in BeWo cells. Rottlerin caused parasite cell cycle arrest in G1 phase and compromised the ability of tachyzoites to infect new cells, thus highlighting the possible direct action on parasites. An additional and non-exclusive mechanism of action of Rottlerin involves the modulation of host cell components, by affecting lipid droplet formation, mitochondrial function and upregulation of the IL-6 and MIF levels in BeWo cells. Supporting our findings, Rottlerin also controlled T. gondii proliferation in villous explants with low toxicity and reduced the IL-10 levels, a cytokine associated with parasite susceptibility. Collectively, our results highlighted the potential use of Rottlerin as a promising tool to prevent and/or treat congenital toxoplasmosis.

Mycobacterium tuberculosis and its secreted tyrosine phosphatases

Tuberculosis is one of the most common infectious diseases and has been a major burden for a long time now. Increasing drug resistance in TB is slowing down the process of disease treatment. Mycobacterium tuberculosis, the causative agent of TB is known to have a cascade of virulence factors to fight with host's immune system. The phosphatases (PTPs) of Mtb plays a critical role as these are secretory in nature and help the survival of bacteria in host. Researchers have been trying to synthesize inhibitors against a lot of virulence factors of Mtb but recently the phosphatases have gained a lot of interest due to their secretory nature. This review gives a concise overview of virulence factors of Mtb with emphasis on mPTPs. Here we discuss the current scenario of drug development against mPTPs.

Rottlerin-Liposome Inhibits the Endocytosis of Feline Coronavirus Infection

Rottlerin (R) is a natural extract from Mallotus philippensis with antiviral properties. Feline infectious peritonitis (FIP) is a fatal disease caused by feline coronavirus (FCoV) that is characterized by systemic granulomatous inflammation and high mortality. We investigated the antiviral effect of liposome-loaded R, i.e., rottlerin-liposome (RL), against FCoV. We demonstrated that RL inhibited FCoV replication in a dose-dependent manner, not only in the early endocytosis stage but also in the late stage of replication. RL resolved the low solubility issue of rottlerin and improved its inhibition efficacy at the cellular level. Based on these findings, we suggest that RL is worth further investigation as a potential treatment for FCoV.

Rottlerin plays an antiviral role at early and late steps of Zika virus infection

Infection of Zika virus (ZIKV) may cause microcephaly and other neurological disorders, while no vaccines and drugs are available. Our study revealed that rottlerin confers a broad antiviral activity against several enveloped viruses, including ZIKV, vesicular stomatitis virus, and herpes simplex virus, but not against two naked viruses (enterovirus 71 and encephalomyocarditis virus). Rottlerin does not have a direct virucidal effect on the virions, and its antiviral effect is independent of its regulation on PKCδ or ATP. Both pretreatment and post-treatment of rottlerin effectively reduce the viral replication of ZIKV. The pretreatment of rottlerin disturbs the endocytosis of enveloped viruses, while the post-treatment of rottlerin acts at a late stage through disturbing the maturation of ZIKV. Importantly, administration of rottlerin in neonatal mice significantly decreased the ZIKV replication in vivo, and alleviated the neurological symptoms caused by ZIKV. Our work suggests that rottlerin exerts an antiviral activity at two distinct steps of viral infection, and can be potentially developed as a prophylactic and therapeutic agent.

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Rottlerin confers an antiviral activity against several enveloped viruses including Zika virus.

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Rottlerin interferes with the endocytosis and maturation step of Zika virus.

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Rottlerin inhibits the ZIKV replication in vivo, and alleviates the neurological symptoms caused by Zika virus.

Production and Synthetic Modifications of Shikimic Acid

Shikimic acid is a natural product of industrial importance utilized as a precursor of the antiviral Tamiflu. It is nowadays produced in multihundred ton amounts from the extraction of star anise ( Illicium verum) or by fermentation processes. Apart from the production of Tamiflu, shikimic acid has gathered particular notoriety as its useful carbon backbone and inherent chirality provide extensive use as a versatile chiral precursor in organic synthesis. This review provides an overview of the main synthetic and microbial methods for production of shikimic acid and highlights selected methods for isolation from available plant sources. Furthermore, we have attempted to demonstrate the synthetic utility of shikimic acid by covering the most important synthetic modifications and related applications, namely, synthesis of Tamiflu and derivatives, synthetic manipulations of the main functional groups, and its use as biorenewable material and in total synthesis. Given its rich chemistry and availability, shikimic acid is undoubtedly a promising platform molecule for further exploration. Therefore, in the end, we outline some challenges and promising future directions.

Mycobacterial protein tyrosine kinase, PtkA phosphorylates PtpA at tyrosine residues and the mechanism is stalled by the novel series of inhibitors

Phosphorylation and dephosphorylation are the key mechanisms for mycobacterial physiology and play critical roles in mycobacterial survival and in its pathogenesis. Mycobacteria evade host immune mechanism by inhibiting phagosome - lysosome fusion in which mycobacterial protein tyrosine phosphatase A (PtpA;TP) plays an indispensable role. Tyrosine kinase (PtkA;TK) activated by autophosphorylation; phosphorylates TP, which subsequently leads to increase in its phosphatase activity. The phosphorylated TP is secreted in phagosome of macrophage. In the present study, we have shown that the phosphorylation at two sites of TP; Y¹²⁸ and Y¹²⁹ are critical for TK-mediated phosphatase activity. The disruption of this interaction between TK and TP inhibits activation of later which further leads to the decrease in intracellular survival of mycobacteria. Furthermore, the proof of concept has been established using benzylbenzofurans and benzofuranamides, which inhibit the growth and intracellular survival of mycobacteria, associate with the functional sites of TP and contend with the TK. This binding was further restated by looking at the anchorage of protein-protein and the protein-inhibitor complexes in the homology-based structure models and by surface plasmon resonance analysis.

Protein tyrosine kinase A modulates intracellular survival of mycobacteria through Galectin 3

Mycobacterium tuberculosis (MTB) is a successful pathogen which increases persistence inside the host macrophage by subverting its defence mechanism. Mycobacteria regulate the pathogenesis and intracellular survival by controlling its interaction with host protein(s). Galectin 3 is a member of the β-galactoside binding gene family which is involved in several biological functions. In the present study, we have expressed the mycobacterial protein tyrosine kinase (PtkA) in the cytosol of host macrophages through a eukaryotic promoter vector and found that it down-regulates Galectin 3. Infection by ptkA knocked-out (KO) mycobacterial strain shows increased level of Galectin 3 in the cytosol of macrophages. PtkA regulates Galectin 3 level and stimulates host macrophage through MEK-JNK-cJUN pathway and initiates early apoptosis in H₃₇Ra infected macrophage. The ptkA KO strain showed decreased progression of apoptosis confirming Galectin 3 as anti-apoptotic molecule. The intracellular survival was also found to be impaired in the mice infected with ptkA KO mycobacteria. The hypothesis was also confirmed by looking at the intracellular survival of mycobacteria in Galectin 3 silenced macrophages. The overall findings suggest the significance of Galectin 3 and PtkA interaction in intracellular persistence of mycobacteria.