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Pregnane X receptor (PXR) is a nuclear receptor with an essential role in regulating drug metabolism genes. While the mechanism of action for ligand-mediated PXR agonism is ...well-examined, its ligand-mediated inhibition or antagonism is poorly understood. Here we employ microsecond timescale all-atom molecular dynamics (MD) simulations to investigate how our newly identified dual kinase and PXR inhibitor, compound 100, acts as a competitive PXR antagonist and not as a full agonist. We study the PXR ligand binding domain conformational changes associated with compound 100 and compare the results to the full agonist SR12813, in presence and absence of the coactivator. Furthermore, we complement our research by experimentally disclosing the effect of eight key-residue mutations on PXR activation. Finally, simulations of P2X4 inhibitor (BAY-1797) in complex with PXR, which shares an identical structural moiety with compound 100, provide further insights to ligand-induced PXR behaviour. Our MD data suggests ligand-specific influence on conformations of different PXR-LBD regions, including α6 region, αAF-2, α1-α2′, β1′-α3 and β1-β1′ loop. Our results provide important insights on conformational behaviour of PXR and offers guidance how to alleviate PXR agonism or to promote PXR antagonism.
Small-molecule protein kinase inhibitors are used for the treatment of cancer, but off-target effects hinder their clinical use. Especially off-target activation of the pregnane X receptor (PXR) has ...to be considered, as it not only governs drug metabolism and elimination, but also can promote tumor growth and cancer drug resistance. Consequently, PXR antagonism has been proposed for improving cancer drug therapy. Here we aimed to identify small-molecule kinase inhibitors of the Tübingen Kinase Inhibitor Collection (TüKIC) compound library that would act also as PXR antagonists. By a combination of in silico screen and confirmatory cellular reporter gene assays, we identified four novel PXR antagonists and a structurally related agonist with a common phenylaminobenzosuberone scaffold. Further characterization using biochemical ligand binding and cellular protein interaction assays classified the novel compounds as mixed competitive/noncompetitive, passive antagonists, which bind PXR directly and disrupt its interaction with coregulatory proteins. Expression analysis of prototypical PXR target genes ABCB1 and CYP3A4 in LS174T colorectal cancer cells and HepaRG hepatocytes revealed novel antagonists as selective receptor modulators, which showed gene- and tissue-specific effects. These results demonstrate the possibility of dual PXR and protein kinase inhibitors, which might represent added value in cancer therapy.
4-Nonylphenol (4-NP), a para-substituted phenolic compound with a straight or branched carbon chain, is a ubiquitous environmental pollutant and food contaminant. 4-NP, particularly the branched ...form, has been identified as an endocrine disruptor (ED) with potent activities on estrogen receptors. Constitutive Androstane Receptor (CAR) is another crucial nuclear receptor that regulates hepatic lipid, glucose, and steroid metabolism and is involved in the ED mechanism of action. An NP mixture has been described as an extremely potent activator of both human and rodent CAR. However, detailed mechanistic aspects of CAR activation by 4-NP are enigmatic, and it is not known if 4-NP can directly interact with the CAR ligand binding domain (LBD). Here, we examined interactions of individual branched (22NP, 33NP, and 353NP) and linear 4-NPs with CAR variants using molecular dynamics (MD) simulations, cellular experiments with various CAR expression constructs, recombinant CAR LBD in a TR-FRET assay, or a differentiated HepaRG hepatocyte cellular model. Our results demonstrate that branched 4-NPs display more stable poses to activate both wild-type CAR1 and CAR3 variant LBDs in MD simulations. Consistently, branched 4-NPs activated CAR3 and CAR1 LBD more efficiently than linear 4-NP. Furthermore, in HepaRG cells, we observed that all 4-NPs upregulated CYP2B6 mRNA, a relevant hallmark for CAR activation. This is the first study to provide detailed insights into the direct interaction between individual 4-NPs and human CAR-LBD, as well as its dominant variant CAR3. The work could contribute to the safer use of individual 4-NPs in many areas of industry.
The nuclear constitutive androstane receptor (CAR, NR1I3) plays significant roles in many hepatic functions, such as fatty acid oxidation, biotransformation, liver regeneration, as well as clearance ...of steroid hormones, cholesterol, and bilirubin. CAR has been proposed as a hypothetical target receptor for metabolic or liver disease therapy. Currently known prototype high-affinity human CAR agonists such as CITCO (6-(4-chlorophenyl)imidazo2,1-b1,3thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime) have limited selectivity, activating the pregnane X receptor (PXR) receptor, a related receptor of the NR1I subfamily. We have discovered several derivatives of 3-(1H-1,2,3-triazol-4-yl)imidazo1,2-apyridine that directly activate human CAR in nanomolar concentrations. While compound 39 regulates CAR target genes in humanized CAR mice as well as human hepatocytes, it does not activate other nuclear receptors and is nontoxic in cellular and genotoxic assays as well as in rodent toxicity studies. Our findings concerning potent human CAR agonists with in vivo activity reinforce the role of CAR as a possible therapeutic target.
Farnesoid X receptor (FXR) is a nuclear receptor with an essential role in regulating bile acid synthesis and cholesterol homeostasis. FXR activation by agonists is explained by an αAF‐2‐trapping ...mechanism; however, antagonism mechanisms are diverse. We discuss microsecond molecular dynamics (MD) simulations investigating our recently reported FXR antagonists 2a and 2 h. We study the antagonist‐induced conformational changes in the FXR ligand‐binding domain, when compared to the synthetic (GW4064) or steroidal (chenodeoxycholic acid, CDCA) FXR agonists in the FXR monomer or FXR/RXR heterodimer r, and in the presence and absence of the coactivator. Our MD data suggest ligand‐specific influence on conformations of different FXR‐LBD regions, including the α5/α6 region, αAF‐2, and α9‐11. Changes in the heterodimerization interface induced by antagonists seem to be associated with αAF‐2 destabilization, which prevents both co‐activator and co‐repressor recruitment. Our results provide new insights into the conformational behaviour of FXR, suggesting that FXR antagonism/agonism shift requires a deeper assessment than originally proposed by crystal structures.
Molecular dynamics simulations indicate a ligand‐specific influence on conformations of different FXR‐LBD regions, such as αAF‐2 and the heterodimerization interface (α9‐ α11). Changes in the heterodimerization interface seem to be coupled with αAF‐2 destabilization, which prevents recruitment of co‐regulatory elements. These results give insight into the conformational behaviour of FXR, suggesting that FXR antagonism/agonism shift requires a deeper assessment than originally proposed by crystal structures.
Cervical cancer is the fourth most common cancer among women worldwide. Organized cervical screening and vaccination against human papilloma virus (HPV) have been successful interventions for ...prevention of invasive cervical cancer (ICC). Because of cultural and religious considerations, ICC has low incidence in Iran and many other Muslim countries. There is no organized cervical screening in these countries. Therefore, ICC is usually diagnosed in advanced stages with poor prognosis in these countries. We performed a priority setting exercise and suggested priorities for prevention of ICC in this setting.
We invited experts and researchers to a workshop and asked them to list important suggestions for ICC prevention in Iran. After merging similar items and removing the duplicates, we asked the experts to rank the list of suggested items. We used a strategy grid and Go-zone analysis to determine final list of priorities for ICC prevention in Iran.
From 26 final items suggested as priorities for prevention of ICC, the most important priorities were developing national guidelines for cervical screening and quality control protocol for patient follow-up and management of precancerous lesions. In addition, we emphasized considering insurance coverage for cervical screening, public awareness, and research priorities, and establishment of a cervical screening registry.
A comprehensive approach and implementation of organized cervical screening program is necessary for prevention of ICC in Iran and other low incidence Muslim countries. Because of high cost for vaccination and low incidence of cervical cancer, we do not recommend HPV vaccination for the time being in Iran.
This study compared the possible protective effects of silymarin and melatonin against gentamicin (GEN)-induced nephrotoxicity in rats. Rats were allocated to 6 groups: Group I, control group; Groups ...II and III, administered with silymarin or melatonin; Group IV, injected with GEN; and Groups V and VI, administered with silymarin or melatonin, and then injected with GEN. Compared with the rats in the control group, all rats injected with GEN significantly presented elevated levels of serum creatinine and urea that was accompanied by an increase in relative kidney weight, increase in renal reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and reduction in renal glutathione (GSH) level and superoxide dismutase (SOD) activity. Silymarin and melatonin pretreatment significantly lowered the elevated serum urea and creatinine concentration, kidney weight, and renal ROS and MDA levels. In addition, silymarin and melatonin significantly enhanced renal GSH level and SOD activity. This study indicates that silymarin and melatonin can attenuate renal injury in rats treated with GEN possibly by reducing the ROS level.
Background: Muslim cancer patients and healthcare professionals face several challenges about the necessity of fasting and its possible side effects during the holy month of Ramadan. We aimed to ...study the prevalence of fasting among cancer patients during Ramadan and opinions of health care professionals about fasting among cancer patients in Iran. Methods: We conducted a cross-sectional survey during the Ramadan (July-August) in 2013. Participants were 620 cancer patients and, 187 healthcare professionals in several cancer clinics from different provinces of Iran. We used self-administered questionnaires and collected data from patients, and healthcare professionals to collect data. We performed descriptive analysis by using Stata statistical software. Results: Out of 620 patients who participated in this study, 428 (69%) were women. 76 (13%) of patients had fasted for at least a day during Ramadan and, from which 41 (7%) had fasted whole months because of their religious belief. Among patients who had refrained from fasting, the reasons were lack of sufficient physical strength (403, 65%), excessive thirst (141, 23%). 275 (44%) of participants had consulted with their physician about fasting. We found that more than 50% of physicians advised against fasting for patients following surgery, pre-operation, recent hospitalization, and consumption of oral or intravenous chemotherapy. Most of the healthcare professionals (68%) believed that cancer survivors could not fast even if they have no signs or symptoms or side-effects after the treatment. Conclusion: Although most of the cancer patients refrain from fasting, some cancer patients practice fasting and face challenges during the holy month of Ramadan in Iran. Most patients consult about fasting in Ramadan with their doctor who has variable opinions about this issue. Development of guidelines for healthcare professional and cancer patients regarding Ramadan fasting is needed.
Background
Cervical cancer is the fourth most common cancer among women worldwide. Organized cervical screening and vaccination against human papilloma virus (HPV) have been successful interventions ...for prevention of invasive cervical cancer (ICC). Because of cultural and religious considerations, ICC has low incidence in Iran and many other Muslim countries. There is no organized cervical screening in these countries. Therefore, ICC is usually diagnosed in advanced stages with poor prognosis in these countries. We performed a priority setting exercise and suggested priorities for prevention of ICC in this setting.
Methods
We invited experts and researchers to a workshop and asked them to list important suggestions for ICC prevention in Iran. After merging similar items and removing the duplicates, we asked the experts to rank the list of suggested items. We used a strategy grid and Go-zone analysis to determine final list of priorities for ICC prevention in Iran.
Results
From 26 final items suggested as priorities for prevention of ICC, the most important priorities were developing national guidelines for cervical screening and quality control protocol for patient follow-up and management of precancerous lesions. In addition, we emphasized considering insurance coverage for cervical screening, public awareness, and research priorities, and establishment of a cervical screening registry.
Conclusion
A comprehensive approach and implementation of organized cervical screening program is necessary for prevention of ICC in Iran and other low incidence Muslim countries. Because of high cost for vaccination and low incidence of cervical cancer, we do not recommend HPV vaccination for the time being in Iran.
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