X-ray Crystal Structure of Human Heme Oxygenase-1 with (2R,4S)-2-[2-(4-Chlorophenyl)ethyl]-2-[(1H-imidazol-1-yl)methyl]-4[((5-trifluoromethylpyridin-2-yl)thio)methyl]-1,3-dioxolane: A Novel, Inducible Binding Mode

Evaluation of the anticancer effects exerted by 5-fluorouracil and heme oxygenase-1 inhibitor hybrids in HTC116 colorectal cancer cells

Colon cancer remains a clinical challenge in industrialised countries. Its treatment with 5-Flurouracil (5-FU) develops many side effects and resistance. Thus, several strategies have been undertaken so far, including the use of drug cocktails and polypharmacology. Heme oxygenase-1 (HO-1) is an emerging molecular target in the treatment of various cancers. We recently demonstrated that a combination of HO-1 inhibitors with 5-FU and the corresponding hybrids SI1/17, SI1/20, and SI1/22, possessed anticancer activity against prostate and lung cancer cells. In this work, we evaluated these hybrids in a model of colon cancer and found that SI1/22 and the respective combo have greater potency than 5-FU. Particularly, compounds inhibit HO-1 activity in cell lysates, increase ROS and the expression of HO-1, SOD, and Nrf2. Moreover, we observed a decrease of pro-caspase and an increase in cleaved PARP-1 and p62, suggesting apoptotic and autophagic cell death and potential application of these drugs as anticancer agents.

Icariin prevents methylmercury-induced experimental neurotoxicity: Evidence from cerebrospinal fluid, blood plasma, brain samples, and in-silico investigations

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that causes significant neurodegeneration. Methylmercury (MeHg+) is a neurotoxin that induces axonal neurodegeneration and motor nerve degeneration by destroying oligodendrocytes, degenerating white matter, inducing apoptosis, excitotoxicity, and reducing myelin basic protein (MBP). This study examines the inhibition of SIRT-1 (silence information regulator 1), Nrf-2 (nuclear factor E2-related factor 2), HO-1 (heme oxygenase 1), and TDP-43 (TAR-DNA-binding protein 43) accumulation in the context of ALS, as well as the modulation of these proteins by icariin (15 and 30 mg/kg, orally), a glycoside flavonoid with neuroprotective properties. Neuroprotective icariin activates SIRT-1, Nrf-2, and HO-1, mitigating inflammation and neuronal injury in neurodegenerative disorders. In-vivo and in-silico testing of experimental ALS models confirmed icariin efficacy in modulating these cellular targets. The addition of sirtinol 10 mg/kg, an inhibitor of SIRT-1, helps determine the effectiveness of icariin. In this study, we also examined neurobehavioral, neurochemical, histopathological, and LFB (Luxol fast blue) markers in various biological samples, including Cerebrospinal fluid (CSF), blood plasma, and brain homogenates (Cerebral Cortex, Hippocampus, Striatum, mid-brain, and Cerebellum). These results demonstrate that the administration of icariin ameliorates experimental ALS and that the mechanism underlying these benefits is likely related to regulating the SIRT-1, Nrf-2, and HO-1 signaling pathways.

Canagliflozin ameliorates ulcerative colitis via regulation of TLR4/MAPK/NF-κB and Nrf2/PPAR-γ/SIRT1 signaling pathways

Ulcerative colitis (UC) is one of the most common subtypes of inflammatory bowel disease (IBD) that affects the colon and is characterized by severe intestinal inflammation. Canagliflozin is a widely used antihyperglycemic agent, a sodium-glucose cotransporter-2 (SGLT2) inhibitor that enhances urinary glucose excretion. This study aims to provide insights into the potential benefits of canagliflozin as a treatment for UC by addressing possible cellular signals. Acetic acid (AA; 4% v/v) was administered intrarectally to induce colitis. Canagliflozin is given orally at a dose of 10 mg/kg/day. Canagliflozin attenuates inflammation in AA-induced colitis, evidenced by significant and dose-dependently downregulation of p38 MAPK, NF-κB-p65, IKK, IRF3, and NADPH-oxidase as well as colonic levels of IL-6 and IL-1β and MPO enzymatic activity. Canagliflozin mitigates colonic oxidative stress by decreasing MDA content and restoring SOD enzymatic activities and GSH levels mediated by co-activating of Nrf2, PPARγ, and SIRT1 pathways. Moreover, an in-silico study confirmed that canagliflozin was specific to all target proteins in this study. Canagliflozin's binding affinity with its target proteins indicates and confirms its effectiveness in regulating these pathways. Also, network pharmacology analysis supported that canagliflozin potently attenuates UC via a multi-target and multi-pathway approach.

Ameliorate impacts of scopoletin against vancomycin-induced intoxication in rat model through modulation of Keap1-Nrf2/HO-1 and IκBα-P65 NF-κB/P38 MAPK signaling pathways: Molecular study, molecular docking evidence and network pharmacology analysis

Nephrotoxicity is an indication for the damage of kidney-specific detoxification and excretion mechanisms by exogenous or endogenous toxicants. Exposure to vancomycin predominantly results in renal damage and losing the control of body homeostasis. Vancomycin-treated rats (200 mg/kg/once daily, for seven consecutive days, i.p.) revealed significant increase in serum pivotal kidney function, oxidative stress, and inflammatory biomarkers. Histologically, vancomycin showed diffuse acute tubular necrosis, denudation of epithelium and infiltration of inflammatory cells in the lining tubular epithelium in cortical portion. In the existing study, the conservative consequences of scopoletin against vancomycin nephrotoxicity was investigated centering on its capacity to alleviate oxidative strain and inflammation through streamlining nuclear factor (erythroid-derived-2) like 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling and prohibiting the nuclear factor kappa B (NF-κB)/mitogen-activated protein kinase (p38 MAPK) pathway. With respect to vancomycin group, scopoletin pretreatment (50 mg/kg/once daily, i.p.) efficiently reduced kidney function, oxidative stress biomarkers and inflammatory mediators. Moreover, histological and immunohistochemical examination of scopoletin-treated group showed remarkable improvement in histological structure and reduced vancomycin-induced renal expression of iNOS, NF-κB and p38 MAPK. In addition, scopoletin downregulated (Kelch Like ECH Associated Protein1) Keap1, P38MAPK and NF-κB expression levels while upregulated renal expression levels of regulatory protein (IκBα), Nrf2 and HO-1. Furthermore, molecular docking and network approach were constructed to study the prospect interaction between scopoletin and the targeted proteins that streamline oxidative stress and inflammatory pathways. The present investigations elucidated that scopoletin co-treatment with vancomycin may be a rational curative protocol for mitigation of vancomycin-induced renal intoxication.

Discovery of Novel Acetamide-Based Heme Oxygenase-1 Inhibitors with Potent In Vitro Antiproliferative Activity

Heme oxygenase-1 (HO-1) promotes heme catabolism exercising cytoprotective roles in normal and cancer cells. Herein, we report the design, synthesis, molecular modeling, and biological evaluation of novel HO-1 inhibitors. Specifically, an amide linker in the central spacer and an imidazole were fixed, and the hydrophobic moiety required by the pharmacophore was largely modified. In many tumors, overexpression of HO-1 correlates with poor prognosis and chemoresistance, suggesting the inhibition of HO-1 as a possible antitumor strategy. Accordingly, compounds 7i and 7l-p emerged for their potency against HO-1 and were investigated for their anticancer activity against prostate (DU145), lung (A549), and glioblastoma (U87MG, A172) cancer cells. The selected compounds showed the best activity toward U87MG cells. Compound 7l was further investigated for its in-cell enzymatic HO-1 activity, expression levels, and effects on cell invasion and vascular endothelial growth factor (VEGF) extracellular release. The obtained data suggest that 7l can reduce cell invasivity acting through modulation of HO-1 expression.

LC-MS characterized methanolic extract of zanthoxylum armatum possess anti-breast cancer activity through Nrf2-Keap1 pathway: An in-silico, in-vitro and in-vivo evaluation

ETHNOPHARMACOLOGICAL RELEVANCE

Zanthoxylum armatum DC (Rutaceae) containing flavonoids, alkaloids, coumarins, lignans, amides and terpenoid is well-known for its curative properties against various ailments including cancer. In the current research, phytochemicals present in the methanolic extract of Zanthoxylum armatum bark (MeZb) were characterized by LC-MS/MS analysis and chemotherapeutic potential of this extract was determined on DMBA-induced female Sprague Dawley rats.

MATERIALS AND METHODS

A simple and fast high-performance liquid chromatography-mass spectroscopy (LC-MS/MS) of MeZb was established followed by in-vitro antioxidant assays. This was followed by in-silico docking analysis as well as cytotoxicity assessment. Successively in-vivo study of MeZb was performed in DMBA-induced Sprague Dawley rats possessing breast cancer along with detailed molecular biology studies involving immunofluorescence, RT-qPCR and Western blot analysis.

RESULTS

LC-MS/MS investigation revealed the presence of compounds belonging to flavonoid, alkaloid and glycoside groups. MeZb revealed potential antioxidant activity in in-vitro antioxidant assays and strong binding energy of identified compounds was seen from the in-silico study with both HO1 and Keap1 receptor. Furthermore, the antioxidant action of MeZb was proven from the in-vivo analysis of antioxidant marker enzymes (lipid peroxidation, enzymic and non-enzymic antioxidants). This study also revealed upregulation of protective Nrf-2 following downregulation of Keap1 after MeZb treatment with respect to untreated cancerous rats.

CONCLUSION

These results exhibited anti-breast-cancer potential of MeZb through Nrf2-Keap1 pathway which may be due to the flavonoids, alkaloids and glycosides present in it.

East to West not North-West: Structure-Based Mechanistic Resolution of 8-Hydroxyl Replacement and Resulting Effects on the Activities of Imidazole-Based Heme Oxygenase-1 Inhibitors

Upregulation of Heme Oxygenase-1 (HO-1) has been widely implicated in cancer growth and chemoresistance. This explains the numerous drug discovery efforts aimed at mitigating its pro-carcinogenic roles till date. In a recent study, two selective azole-based HO-1 inhibitors (Cpd1 and Cpd2) were synthesized, which exhibited differential inhibitory potencies of ~200μm. Interestingly, variations in the affinities of these compounds were determined by their positioning across specific regions of the HO-1 binding domain, pin-pointing a pharmacological interrelationship that remains unresolved. Therefore, in this study, using molecular dynamics simulations and binding free energy calculations, we investigate how dynamical orientations of these compounds influence their binding affinities at the active HO-1 domain. Findings revealed favorable binding for the bromobenzene and imidazole substituents of Cpd1 at the western and eastern regions of the HO-1 active domain. The constituent hydroxyl group was coordinated by residues Asp140 and Arg136 over the simulation period. On the contrary, stable binding of the bromobenzene and imidazole substituents were negated by the optimal orientations of the benzyl substituent, which extended into the northeastern region. These were supported by the displacement of Asp140 and Arg136, crucial for hydrogen bond formation in Cpd1. Also, we observed that Cpd2 exhibited high deviations indicative of an unstable binding relative to Cpd1. This further supports the presumption that Cpd2 was systematically oriented away from the active HO-1 region, a phenomenon that was due to the optimal motions of the benzyl group at the northeastern regions. The highlight of our findings is that the benzyl substituent in Cpd2 elicited negative effects on HO-1, vis a vis, instability, displacement of crucial residues, and low binding energy when compared to Cpd1. Findings pave the way for future drug discovery efforts related to HO-1 inhibition in cancer therapy.

Recent Advances in the Understanding of the Reaction Chemistries of the Heme Catabolizing Enzymes HO and BVR Based on High Resolution Protein Structures

In mammals, catabolism of the heme group is indispensable for life. Heme is first cleaved by the enzyme Heme Oxygenase (HO) to the linear tetrapyrrole Biliverdin IXα (BV), and BV is then converted into bilirubin by Biliverdin Reductase (BVR). HO utilizes three Oxygen molecules (O2) and seven electrons supplied by NADPH-cytochrome P450 oxidoreductase (CPR) to open the heme ring and BVR reduces BV through the use of NAD(P)H. Structural studies of HOs, including substrate-bound, reaction intermediate-bound, and several specific inhibitor-bound forms, reveal details explaining substrate binding to HO and mechanisms underlying-specific HO reaction progression. Cryo-trapped structures and a time-resolved spectroscopic study examining photolysis of the bond between the distal ligand and heme iron demonstrate how CO, produced during the HO reaction, dissociates from the reaction site with a corresponding conformational change in HO. The complex structure containing HO and CPR provides details of how electrons are transferred to the heme-HO complex. Although the tertiary structure of BVR and its complex with NAD+ was determined more than 10 years ago, the catalytic residues and the reaction mechanism of BVR remain unknown. A recent crystallographic study examining cyanobacterial BVR in complex with NADP+ and substrate BV provided some clarification regarding these issues. Two BV molecules are bound to BVR in a stacked manner, and one BV may assist in the reductive catalysis of the other BV. In this review, recent advances illustrated by biochemical, spectroscopic, and crystallographic studies detailing the chemistry underlying the molecular mechanism of HO and BVR reactions are presented.

Progress in the development of selective heme oxygenase-1 inhibitors and their potential therapeutic application

Heme oxygenases (HOs) are a family of enzymes involved in the selective catabolism of free circulating heme. While HO-2 is constitutively expressed, HO-1 is strongly overexpressed under stressful stimuli (e.g., oxidative stress). Under these conditions, HO-1 exerts its strong cytoprotective activities and plays a crucial role in stimulating cell survival by removing the pro-oxidant heme and by producing carbon monoxide and biliverdin (promptly reduced to bilirubin). Unfortunately, the broad spectrum of HO-1 cytoprotective effects has been well experimentally documented both in normal and tumor cells, where the enzyme can be overexpressed, making it an exciting target in the management of some type of tumors. Development of non-competitive HO-1 inhibitors dates back in 2002 with the discovery of Azalanstat. Since then, many efforts have been devoted to the identification of selective HO-1 and HO-2 inhibitors and to unravel the molecular determinants responsible for selectivity. Molecular modeling studies supported the identification of chemical features involved in the recognition and inhibition of these enzymes. Herein, medicinal chemistry aspects and in silico studies related to the development of HO inhibitors will be discussed. The purpose of this review is to highlight recent advances in the development of new selective HO-1 and HO-2 inhibitors and covers the last six years (2013-2018).

Potholing of the hydrophobic heme oxygenase-1 western region for the search of potent and selective imidazole-based inhibitors

Here we report the design, synthesis, and molecular modeling of new potent and selective imidazole-based HO-1 inhibitors in which the imidazole nucleus and the hydrophobic groups are linked by a phenylethanolic spacer. Most of the tested compounds showed a good inhibitor activity with IC₅₀ values in the low micromolar range, with two of them (1b and 1j) exhibiting also high selectivity toward HO-2. These results were obtained by the idea of potholing the entire volume of the principal hydrophobic western region with an appropriate ligand volume. Molecular modeling studies showed that these molecules bind to the HO-1 in the consolidated fashion where the imidazolyl moiety coordinates the heme iron while the aromatic groups are stabilized by hydrophobic interaction in the western region of the binding pocket. Finally, the synthesized compounds were analyzed for in silico ADME-Tox properties to establish oral drug-like behavior and showed satisfactory results.

How does binding of imidazole-based inhibitors to heme oxygenase-1 influence their conformation? Insights combining crystal structures and molecular modelling

Heme oxygenase-1 (HO-1) inhibition is associated with antitumor activity. Imidazole-based analogues show effective and selective inhibitory potency of HO-1. In this work, five single-crystal structures of four imidazole-based compounds are presented, with an in-depth structural analysis. In order to study the influence of the conformation of the ligands on binding to protein, conformational data from crystallography are compared with quantum mechanics analysis and molecular docking studies. Molecular docking of imidazole-based analogues in the active site of HO-1 is in good agreement with the experimental structures. Inhibitors interact with the heme cofactor and a hydrophobic pocket (Met34, Phe37, Val50, Leu147 and Phe214) in the HO-1 binding site. An alternate binding mode can be hypothesized for some inhibitors in the series.

Novel lead structures and activation mechanisms for CO-releasing molecules (CORMs)

Carbon monoxide (CO) is an endogenous small signalling molecule in the human body, produced by the action of haem oxygenase on haem. Since it is very difficult to apply safely as a gas, solid storage and delivery forms for CO are now explored. Most of these CO-releasing molecules (CORMs) are based on the inactivation of the CO by coordinating it to a transition metal centre in a prodrug approach. After a brief look at the potential cellular target structures of CO, an overview of the design principles and activation mechanisms for CO release from a metal coordination sphere is given. Endogenous and exogenous triggers discussed include ligand exchange reactions with medium, enzymatically-induced CO release and photoactivated liberation of CO. Furthermore, the attachment of CORMs to hard and soft nanomaterials to confer additional target specificity to such systems is critically assessed. A survey of analytical methods for the study of the stoichiometry and kinetics of CO release, as well as the tracking of CO in living systems by using fluorescent probes, concludes this review. CORMs are very valuable tools for studying CO bioactivity and might lead to new drug candidates; however, in the design of future generations of CORMs, particular attention has to be paid to their drug-likeness and the tuning of the peripheral 'drug sphere' for specific biomedical applications. Further progress in this field will thus critically depend on a close interaction between synthetic chemists and researchers exploring the physiological effects and therapeutic applications of CO.

Structural insights into human heme oxygenase-1 inhibition by potent and selective azole-based compounds

The development of heme oxygenase (HO) inhibitors, especially those that are isozyme-selective, promises powerful pharmacological tools to elucidate the regulatory characteristics of the HO system. It is already known that HO has cytoprotective properties and may play a role in several disease states, making it an enticing therapeutic target. Traditionally, the metalloporphyrins have been used as competitive HO inhibitors owing to their structural similarity with the substrate, heme. However, given heme's important role in several other proteins (e.g. cytochromes P450, nitric oxide synthase), non-selectivity is an unfortunate side-effect. Reports that azalanstat and other non-porphyrin molecules inhibited HO led to a multi-faceted effort to develop novel compounds as potent, selective inhibitors of HO. This resulted in the creation of non-competitive inhibitors with selectivity for HO, including a subset with isozyme selectivity for HO-1. Using X-ray crystallography, the structures of several complexes of HO-1 with novel inhibitors have been elucidated, which provided insightful information regarding the salient features required for inhibitor binding. This included the structural basis for non-competitive inhibition, flexibility and adaptability of the inhibitor binding pocket, and multiple, potential interaction subsites, all of which can be exploited in future drug-design strategies.

A novel, "double-clamp" binding mode for human heme oxygenase-1 inhibition

The development of heme oxygenase (HO) inhibitors is critical in dissecting and understanding the HO system and for potential therapeutic applications. We have established a program to design and optimize HO inhibitors using structure-activity relationships in conjunction with X-ray crystallographic analyses. One of our previous complex crystal structures revealed a putative secondary hydrophobic binding pocket which could be exploited for a new design strategy by introducing a functional group that would fit into this potential site. To test this hypothesis and gain further insights into the structural basis of inhibitor binding, we have synthesized and characterized 1-(1H-imidazol-1-yl)-4,4-diphenyl-2-butanone (QC-308). Using a carbon monoxide (CO) formation assay on rat spleen microsomes, the compound was found to be ∼15 times more potent (IC₅₀ = 0.27±0.07 µM) than its monophenyl analogue, which is already a potent compound in its own right (QC-65; IC₅₀ = 4.0±1.8 µM). The crystal structure of hHO-1 with QC-308 revealed that the second phenyl group in the western region of the compound is indeed accommodated by a definitive secondary proximal hydrophobic pocket. Thus, the two phenyl moieties are each stabilized by distinct hydrophobic pockets. This “double-clamp” binding offers additional inhibitor stabilization and provides a new route for improvement of human heme oxygenase inhibitors.

Recombinant truncated and microsomal heme oxygenase-1 and -2: differential sensitivity to inhibitors

Recombinant truncated forms of heme oxygenase-1 and -2 (HO-1 and HO-2) were compared with their crude microsomal counterparts from brain and spleen tissue of adult male rats with respect to their inhibition by azole-based, nonporphyrin HO inhibitors. The drugs tested were an imidazole-alcohol, an imidazole-dioxolane, and a triazole-ketone. Both the recombinant and crude forms of HO-2 were similarly inhibited by the 3 drugs. The crude microsomal spleen form of HO-1 was more susceptible to inhibition than was the truncated recombinant form. This difference is attributed to the extra amino acids in the full-length enzyme. These observations may be relevant in the design of drugs as inhibitors of HO and other membrane proteins.