Rottlerin inhibits chlamydial intracellular growth and blocks chlamydial acquisition of sphingolipids from host cells

The Chlamydia pneumoniae inclusion membrane protein Cpn0308 interacts with host protein ACBD3

Chlamydia pneumoniae is an obligate intracellular bacterium of eukaryotic cells characterized by a unique biphasic life cycle; its biosynthesis and replication must occur within a cytoplasmic vacuole or inclusion. Certain inclusion membrane proteins have been demonstrated to mediate the interactions between intra-inclusion chlamydial organisms and the host cell. It has been demonstrated previously that the C. pneumoniae-encoded Cpn0308 localizes to the inclusion membrane; however, its function remains unknown. In the current study, a yeast two-hybrid assay was conducted to screen Cpn0308 as a bait against a HeLa cell cDNA library, revealing its binding to the host protein acyl-coenzyme A binding domain-containing 3 (ACBD3). The interaction between Cpn0308 and ACBD3 was confirmed through co-immunoprecipitation and GST (Glutathione S-transferase) pull-down assays. The two proteins were also co-localized in HeLa cells co-expressing Cpn0308 and ACBD3, as well as in C. pneumoniae-infected cells, as observed under confocal fluorescence microscopy. Given that ACBD3 plays a crucial role in maintaining host cell lipid homeostasis and its Golgi dynamic domain is responsible for interacting with Cpn0308, we hypothesize that the Cpn0308-ACBD3 interaction may facilitate C. pneumoniae's acquisition of host lipids, thereby benefiting chlamydial survival. This study lays a foundation for further elucidating the mechanisms of Cpn0308-mediated C. pneumoniae pathogenesis.IMPORTANCEThe biosynthesis and replication of Chlamydia pneumoniae (Cpn) must occur within the cytoplasmic vacuoles or inclusions of host cells. Inclusion bodies play a crucial role in mediating the interactions between Cpn and host cells. Cpn0308 is localized to the inclusion membrane; however, its function is unknown. In this study, Cpn0308 was found to bind to host protein acyl-coenzyme A binding domain-containing 3 (ACBD3) through some standard approaches. Co-localization of the two proteins was observed in both original HeLa cells and Cpn-infected HeLa cells. ACBD3 plays a significant role in maintaining lipid homeostasis in host cells; we speculate that the Cpn0308-ACBD3 interaction may facilitate the acquisition of host lipids by C. pneumoniae, thereby enhancing chlamydial survival.

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.

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.

Unraveling the Aquaporin-3 Inhibitory Effect of Rottlerin by Experimental and Computational Approaches

The natural polyphenolic compound Rottlerin (RoT) showed anticancer properties in a variety of human cancers through the inhibition of several target molecules implicated in tumorigenesis, revealing its potential as an anticancer agent. Aquaporins (AQPs) are found overexpressed in different types of cancers and have recently emerged as promising pharmacological targets. Increasing evidence suggests that the water/glycerol channel aquaporin-3 (AQP3) plays a key role in cancer and metastasis. Here, we report the ability of RoT to inhibit human AQP3 activity with an IC₅₀ in the micromolar range (22.8 ± 5.82 µM for water and 6.7 ± 2.97 µM for glycerol permeability inhibition). Moreover, we have used molecular docking and molecular dynamics simulations to understand the structural determinants of RoT that explain its ability to inhibit AQP3. Our results show that RoT blocks AQP3-glycerol permeation by establishing strong and stable interactions at the extracellular region of AQP3 pores interacting with residues essential for glycerol permeation. Altogether, our multidisciplinary approach unveiled RoT as an anticancer drug against tumors where AQP3 is highly expressed providing new information to aquaporin research that may boost future drug design.

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.

Drug-Screening Strategies for Inhibition of Virus-Induced Neuronal Cell Death

A number of viruses, including Herpes Simplex Virus (HSV), West Nile Virus (WNV), La Crosse Virus (LACV), Zika virus (ZIKV) and Tick-borne encephalitis virus (TBEV), have the ability to gain access to the central nervous system (CNS) and cause severe neurological disease or death. Although encephalitis cases caused by these viruses are generally rare, there are relatively few treatment options available for patients with viral encephalitis other than palliative care. Many of these viruses directly infect neurons and can cause neuronal death. Thus, there is the need for the identification of useful therapeutic compounds that can inhibit virus replication in neurons or inhibit virus-induced neuronal cell death. In this paper, we describe the methodology to test compounds for their ability to inhibit virus-induced neuronal cell death. These protocols include the isolation and culturing of primary neurons; the culturing of neuroblastoma and neuronal stem cell lines; infection of these cells with viruses; treatment of these cells with selected drugs; measuring virus-induced cell death using MTT or XTT reagents; analysis of virus production from these cells; as well as the basic understanding in mode of action. We further show direct evidence of the effectiveness of these protocols by utilizing them to test the effectiveness of the polyphenol drug, Rottlerin, at inhibiting Zika virus infection and death of neuronal cell lines.

Hijacking and Use of Host Kinases by Chlamydiae

Chlamydia species are causative agents of sexually transmitted infections, blinding trachoma, and animal infections with zoonotic potential. Being an obligate intracellular pathogen, Chlamydia relies on the host cell for its survival and development, subverting various host cell processes throughout the infection cycle. A key subset of host proteins utilized by Chlamydia include an assortment of host kinase signaling networks which are vital for many chlamydial processes including entry, nutrient acquisition, and suppression of host cell apoptosis. In this review, we summarize the recent advancements in our understanding of host kinase subversion by Chlamydia.

Multiple mechanisms of Rottlerin toxicity in A375 melanoma cells

Rottlerin is a cytostatic and cytotoxic drug in a variety of cancer cells. Our previous experience demonstrated that depending upon the genetic/biochemical background of cancer cells, rottlerin is able to induce both apoptotic and autophagic cell death, or dramatically disturb protein homeostasis leading to lethal cellular atrophy. In the current study, we investigated the cytotoxic effects and mechanisms of rottlerin against human amelanotic A375 melanoma cells. In this cell line, rottlerin exhibits its main and newest cytotoxic properties, that is, growth arrest, apoptosis induction, and translation shutoff. In fact, the drug, time-, and dose-dependently, markedly inhibited cell proliferation through cyclin D1 downregulation and induced apoptotic cell death as early as after 18 h treatment. Mechanistically, rottlerin triggered apoptosis by both intrinsic and extrinsic pathways. Both pathways are likely activated by the downregulation of the antiapoptotic B-cell lymphoma 2 (Bcl-2) protein, which simultaneously affects mitochondrial and endoplasmic reticulum (ER) membranes stability. Concomitantly to extrinsic apoptosis induction, the rottlerin-activated ER stress/eukaryotic initiation factor 2 (eIF2) α axis blocked the translational apparatus. The altered proteostasis precluded the complete cells' rescue from death in the presence of apoptosis inhibitors.

Sphingolipid Metabolism and Transport in Chlamydia trachomatis and Chlamydia psittaci Infections

Chlamydia species infect a large range of vertebral hosts and have become of major economic and public health concern over the last decades. They are obligate intracellular bacteria that undergo a unique cycle of development characterized by the presence of two distinct bacterial forms. After infection of the host cell, Chlamydia are found inside a membrane-bound compartment, the inclusion. The surrounding membrane of the inclusion contributes to the host-Chlamydia interface and specific pathogen-derived Inc proteins shape this interface allowing interactions with distinct cellular proteins. In contrast to many other bacteria, Chlamydia species acquire sphingomyelin from the host cell. In recent years a clearer picture of how Chlamydia trachomatis acquires this lipid emerged showing that the bacteria interact with vesicular and non-vesicular transport pathways that involve the recruitment of specific RAB proteins and the lipid-transfer protein CERT. These interactions contribute to the development of a new sphingomyelin-producing compartment inside the host cell. Interestingly, recruitment of CERT is conserved among different Chlamydia species including Chlamydia psittaci. Here we discuss our current understanding on the molecular mechanisms used by C. trachomatis and C. psittaci to establish these interactions and to create a novel sphingomyelin-producing compartment inside the host cell important for the infection.

The Mosaic of Rottlerin: The Sequel

Rottlerin (1) is a potent protein kinase C δ inhibitor that possesses a wide range of biological activities. However, the potential of this molecule to be developed as a drug has been restricted by its limited availability. We report herein a gram scale quantity synthesis of rottlerin in a five-step synthetic route that can be completed within 2 days. The methodology was extended by the reaction of the key aminochromene intermediate (15) with various electron-rich arenes, forming novel unsymmetrical methylene-bridged compounds. The X-ray crystal structure revealed the boomerang shape of this kind of molecule for the first time. The direct transformation of rottlerin (1) into the natural product, isorottlerin (35), was observed for the first time, and we named this transformation the "isorottlerin change". In addition, the antibacterial activities of rottlerin (1) and new rottlerin analogues 32-34 were examined against Staphylococcus aureus. The compounds showed MIC values as low as 2.0 μM, which were comparable to the clinically used antibiotic gentamicin.

Non-conventional rottlerin anticancer properties

In the past few years, we focused the interest on rottlerin, an old/new natural substance that, over the time, has revealed a number of cellular and molecular targets, all potentially implicated in the fight against cancer. Past and recent literature well demonstrated that rottlerin is an inhibitor of enzymes, transcription factors and signaling molecules that control cancer cell life and death. Although the rottlerin anticancer activity has been mainly ascribed to apoptosis and/or autophagy induction, recent findings unveiled the existence of additional mechanisms of toxicity. The major novelties highlighted in this mini review are the ability to bind and inhibit key molecules, such as ERK and mTOR, directly, thus independently of upstream signaling cascades, and to cause a profound dysregulation of cap-dependent protein translation through the mTORC1/4EBP1/eIF4E axis and by inhibition of eIF2, an initiation factor of translation that is negatively regulated by endoplasmic reticulum (ER) stress. These last mechanisms, proved to be lethal in cancer cell lines derived from breast and skin, strongly enforce the potential of rottlerin as a promising natural lead compound for the development of novel therapeutic approaches.

Rottlerin-mediated inhibition of Toxoplasma gondii growth in BeWo trophoblast-like cells

Autophagy is a crucial and physiological process for cell survival from yeast to mammals, including protozoan parasites. Toxoplasma gondii, an intracellular parasite, typically exploits autophagic machinery of host cell; however host cell upregulates autophagy to combat the infection. Herein we tested the efficacy of Rottlerin, a natural polyphenol with autophagic promoting properties, against Toxoplasma infection on the chorioncarcinoma-derived cell line BeWo. We found that Rottlerin, at sub-toxic doses, induced morphological and biochemical alterations associated with autophagy and decreased Toxoplasma growth in infected cells. Although autophagy was synergically promoted by Toxoplasma infection in combination with Rottlerin treatment, the use of the autophagy inhibitor chloroquine revealed that Rottlerin anti-parasitic effect was largely autophagy-independent and likely mediated by the converging inhibitory effect of Rottlerin and Toxoplasma in host protein translation, mediated by mTOR inhibition and eIF2α phosphorylation. Both events, which on one hand could explain the additive effect on autophagy induction, on the other hand led to inhibition of protein synthesis, thereby depriving Toxoplasma of metabolically essential components for multiplication. We suggest that modulation of the competition between pathogen requirement and host cell defense might be an attractive, novel therapeutic approach against Toxoplasma infection and encourage the development of Rottlerin-based new therapeutic formulations.

Lipid acquisition by intracellular Chlamydiae

Chlamydia species are obligate intracellular pathogens that are important causes of human genital tract, ocular and respiratory infections. The bacteria replicate within a specialized membrane-bound compartment termed the inclusion and require host-derived lipids for intracellular growth and development. Emerging evidence indicates that Chlamydia has evolved clever strategies to fulfil its lipid needs by interacting with multiple host cell compartments and redirecting trafficking pathways to its intracellular niche. In this review, we highlight recent findings that have significantly expanded our understanding of how Chlamydia exploit lipid trafficking pathways to ensure the survival of this important human pathogen.

Role for the SRC family kinase Fyn in sphingolipid acquisition by chlamydiae

The bacterial obligate intracellular pathogen Chlamydia trachomatis replicates within a membrane-bound vacuole termed the inclusion. From within this protective environment, chlamydiae usurp numerous functions of the host cell to promote chlamydial survival and replication. Here we utilized a small interfering RNA (siRNA)-based screening protocol designed to identify host proteins involved in the trafficking of sphingomyelin to the chlamydial inclusion. Twenty-six host proteins whose deficiency significantly decreased sphingomyelin trafficking to the inclusion and 16 proteins whose deficiency significantly increased sphingomyelin trafficking to the inclusion were identified. The reduced sphingomyelin trafficking caused by downregulation of the Src family tyrosine kinase Fyn was confirmed in more-detailed analyses. Fyn silencing did not alter sphingomyelin synthesis or trafficking in the absence of chlamydial infection but reduced the amount of sphingomyelin trafficked to the inclusion in infected cells, as determined by two independent quantitative assays. Additionally, inhibition of Src family kinases resulted in increased cellular retention of sphingomyelin and significantly decreased incorporation into elementary bodies of both C. trachomatis and Chlamydophila caviae.

Rottlerin exhibits antiangiogenic effects in vitro

Rottlerin, a natural product purified from Mallotus philippinensis, has a number of target molecules and biological effects. We recently found that Rottlerin caused growth arrest in MCF-7 breast cancer cells and human immortalized keratinocytes, through inhibition of NFκB and downregulation of cyclin D-1. To evaluate whether this effect could be generalized to primary cells, human microvascular endothelial cells were treated with Rottlerin. In this study, we demonstrated that Rottlerin prevents basal and TNFα-stimulated NFκB nuclear migration and DNA binding also in human microvascular endothelial cell, where NFκB inhibition was accompanied by the downregulation of NFκB target gene products, such as cyclin D-1 and endothelin-1, which are essential molecules for endothelial cell proliferation and survival. Rottlerin, indeed, inhibited human microvascular endothelial cells proliferation and tube formation on Matrigel. Rottlerin also increases cytoplasmic free calcium and nitric oxide levels and downregulates endothelin converting enzyme-1 expression, thus contributing to the drop in endothelin-1 and growth arrest. These results suggest that Rottlerin may prove useful in the development of therapeutic agents against angiogenesis.

Anti-tuberculosis Compounds from Mallotus philippinensis

Bioassay-directed fractionation of the organic extract of Mallotus philippinensis gave five compounds (1-5), the most active of which against Mycobacterium tuberculosis was a new compound, 8-cinnamoyl-5,7-dihydroxy-2,2-dimethyl-6-geranylchromene (1) for which the name mallotophilippen F is suggested. Compound (2), 8-cinnamoyl-2,2-dimethyl-7-hydroxy-5-methoxychromene, was isolated from a natural source for the first time, while the remaining three compounds, rottlerin (3), isoallorottlerin=isorottlerin (4) and the so-called “red compound,” 8-cinnamoyl-5,7-dihydroxy-2,2,6-trimethylchromene (5), had been isolated previously from this plant. All compounds were identified by analysis of their spectra including 2D-NMR, which was used to correct the literature NMR spectral assignments of compounds 2-4. The C-13 NMR of 5 is reported for the first time.

A novel inhibitor of Chlamydophila pneumoniae protein kinase D (PknD) inhibits phosphorylation of CdsD and suppresses bacterial replication

Background

We have shown previously that Chlamydophila pneumoniae contains a dual-specific Ser/Thr protein kinase that phosphorylates CdsD, a structural component of the type III secretion apparatus. To further study the role of PknD in growth and development we sought to identify a PknD inhibitor to determine whether PknD activity is required for replication.

Results

Using an in vitro kinase assay we screened 80 known eukaryotic protein kinase inhibitors for activity against PknD and identified a 3'-pyridyl oxindole compound that inhibited PknD autophosphorylation and phosphorylation of CdsD. The PknD inhibitor significantly retarded the growth rate of C. pneumoniae as evidenced by the presence of very small inclusions with a reduced number of bacteria as seen by electron microscopy. These inclusions contained the normal replicative forms including elementary bodies (EB), intermediate bodies (IB) and reticulate bodies (RB), but lacked persistent bodies (PB), indicating that induction of persistence was not the cause of reduced chlamydial growth. Blind passage of C. pneumoniae grown in the presence of this PknD inhibitor for 72 or 84 hr failed to produce inclusions, suggesting this compound blocks an essential step in the production of infectious chlamydial EB. The compound was not toxic to HeLa cells, did not block activation of the MEK/ERK pathway required for chlamydial invasion and did not block intracellular replication of either Chlamydia trachomatis serovar D or Salmonella enterica sv. Typhimurium suggesting that the inhibitory effect of the compound is specific for C. pneumoniae.

Conclusion

We have identified a 3'-pyridyl oxindole compound that inhibits the in vitro kinase activity of C. pneumoniae PknD and inhibits the growth and production of infectious C. pneumoniae progeny in HeLa cells. Together, these results suggest that PknD may play a key role in the developmental cycle of C. pneumoniae.

Killing me softly: chlamydial use of proteolysis for evading host defenses

Chlamydial infections in humans cause severe health problems, including blinding trachoma and sexually transmitted diseases. Although the involved pathogenic mechanisms remain unclear, the ability to replicate and maintain long-term residence in the infected cells seems to significantly contribute to chlamydial pathogenicity. These obligate intracellular parasites maintain a delicate balance between exploiting and protecting their host: they occupy intracellular space and acquire nutrients from the infected cells, but at the same time they have to maintain the integrity of the host cells for the completion of their intracellular growth. For this purpose, chlamydiae hijack certain signaling pathways that prevent the host cells from undergoing apoptosis induced by intracellular stress and protect the infected cells from recognition and attack by host defenses. Interestingly, one of the strategies that chlamydiae use for these purposes is the induction of limited proteolysis of host proteins, which is the main focus of this article.