Novel Structural Insight into Inhibitors of Heme Oxygenase-1 (HO-1) by New Imidazole-Based Compounds: Biochemical and In Vitro Anticancer Activity Evaluation

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.

The protective effect of 7-hydroxycoumarin against cisplatin-induced liver injury is mediated via attenuation of oxidative stress and inflammation and upregulation of Nrf2/HO-1 pathway

Cisplatin (CIS) is an effective chemotherapy against different solid cancers. However, the adverse effects, including hepatotoxicity, limit its clinical use. 7-hydroxycoumarin (7-HC) possesses antioxidant and hepatoprotective activities, but its protective effect against CIS hepatotoxicity has not been investigated. This study evaluated the effect of 7-HC on liver injury, oxidative stress (OS), and inflammation provoked by CIS. Rats received 7-HC (25, 50, and 100 mg/kg) orally for 2 weeks followed by intraperitoneal injection of CIS (7 mg/kg) at day 15. CIS increased serum transaminases, alkaline phosphatase (ALP), and bilirubin and provoked tissue injury accompanied by elevated reactive oxygen species (ROS), malondialdehyde (MDA), and nitric oxide (NO). Liver nuclear factor (NF)-κB p65, inducible NO synthase (iNOS), pro-inflammatory cytokines, Bax, and caspase-3 were upregulated, and antioxidant defenses and Bcl-2 were decreased in CIS-treated rats, while 7-HC prevented liver injury and ameliorated OS, inflammatory and apoptosis markers. In addition, 7-HC enhanced nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase (HO)-1 in CIS-administered rats and in silico studies revealed its binding affinity toward HO-1. In conclusion, 7-HC protected against CIS hepatotoxicity by mitigating OS and inflammatory response and modulating Nrf2/HO-1 pathway.

Novel Tyrosine Kinase Inhibitors to Target Chronic Myeloid Leukemia

This paper reports on a novel series of tyrosine kinase inhibitors (TKIs) potentially useful for the treatment of chronic myeloid leukemia (CML). The newly designed and synthesized compounds are structurally related to nilotinib (NIL), a second-generation oral TKI, and to a series of imatinib (IM)-based TKIs, previously reported by our research group, these latter characterized by a hybrid structure between TKIs and heme oxygenase-1 (HO-1) inhibitors. The enzyme HO-1 was selected as an additional target since it is overexpressed in many cases of drug resistance, including CML. The new derivatives 1a–j correctly tackle the chimeric protein BCR-ABL. Therefore, the inhibition of TK was comparable to or higher than NIL and IM for many novel compounds, while most of the new analogs showed only moderate potency against HO-1. Molecular docking studies revealed insights into the binding mode with BCR-ABL and HO-1, providing a structural explanation for the differential activity. Cytotoxicity on K562 CML cells, both NIL-sensitive and -resistant, was evaluated. Notably, some new compounds strongly reduced the viability of K562 sensitive cells.

Senolysis induced by 25-hydroxycholesterol targets CRYAB in multiple cell types

Cellular senescence is a driver of many age-related pathologies. There is an active search for pharmaceuticals termed senolytics that can mitigate or remove senescent cells in vivo by targeting genes that promote the survival of senescent cells. We utilized single-cell RNA sequencing to identify CRYAB as a robust senescence-induced gene and potential target for senolysis. Using chemical inhibitor screening for CRYAB disruption, we identified 25-hydroxycholesterol (25HC), an endogenous metabolite of cholesterol biosynthesis, as a potent senolytic. We then validated 25HC as a senolytic in mouse and human cells in culture and in vivo in mouse skeletal muscle. Thus, 25HC represents a potential class of senolytics, which may be useful in combating diseases or physiologies in which cellular senescence is a key driver.

From Far West to East: Joining the Molecular Architecture of Imidazole-like Ligands in HO-1 Complexes

HO-1 overexpression has been reported in several cases/types of human malignancies. Unfortunately, poor clinical outcomes are reported in most of these cases, and the inhibition of HO-1 is considered a valuable and proven anticancer approach. To identify novel hit compounds suitable as HO-1 inhibitors, we report here a fragment-based approach where ligand joining experiments were used. The two most important parts of the classical structure of the HO-1 inhibitors were used as a starting point, and 1000 novel compounds were generated and then virtually evaluated by structure and ligand-based approaches. The joining experiments led us to a novel series of indole-based compounds. A synthetic pathway for eight selected molecules was designed, and the compounds were synthesized. The biological activity revealed that some molecules reach the micromolar activity, whereas molecule 4d inhibits the HO-1 with an IC₅₀ of 1.03 μM. This study suggested that our joining approach was successful, and a novel hit compound was generated. These results are ongoing for further development.

Growing the molecular architecture of imidazole-like ligands in HO-1 complexes

Up-regulation of HO-1 had been frequently reported in different cases and types of human malignancies. Since poor clinical outcomes are reported in these cases, this enzyme's inhibition is considered a valuable and proven anticancer approach. To identify novel HO-1 inhibitors suitable for drug development, we report a structure-guided fragment-based approach to identify new lead compounds. Different parts of the selected molecules were analyzed, and the different series of novel compounds were virtually evaluated. The growing experiments of the classical HO-1 inhibitors structure led us to different hit-compounds. A synthetic pathway for six selected molecules was designed, and the compounds were synthesized. The biological activity revealed that molecules 10 and 12 inhibit the HO-1 activity with an IC₅₀ of 1.01 and 0.90 μM, respectively. This study suggested that our growing approach was successful, and these results are ongoing for further development.

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.

Mutual Prodrugs of 5-Fluorouracil: From a Classic Chemotherapeutic Agent to Novel Potential Anticancer Drugs

The development of potent antitumor agents with a low toxicological profile against healthy cells is still one of the greatest challenges facing medicinal chemistry. In this context, the “mutual prodrug” approach has emerged as a potential tool to overcome undesirable physicochemical features and mitigate the side effects of approved drugs. Among broad‐spectrum chemotherapeutics available for clinical use today, 5‐fluorouracil (5‐FU) is one of the most representative, also included in the World Health Organization model list of essential medicines. Unfortunately, severe side effects and drug resistance phenomena are still the primary limits and drawbacks in its clinical use. This review describes the progress made over the last ten years in developing 5‐FU‐based mutual prodrugs to improve the therapeutic profile and achieve targeted delivery to cancer tissues.

Novel mutual prodrug of 5-fluorouracil and heme oxygenase-1 inhibitor (5-FU/HO-1 hybrid): design and preliminary in vitro evaluation

In this work, the first mutual prodrug of 5-fluorouracil and heme oxygenase1 inhibitor (5-FU/HO-1 hybrid) has been designed, synthesised, and evaluated for its in vitro chemical and enzymatic hydrolysis stability. Predicted in silico physicochemical properties of the newly synthesised hybrid (3) demonstrated a drug-like profile with suitable Absorption, Distribution, Metabolism, and Excretion (ADME) properties and low toxic liabilities. Preliminary cytotoxicity evaluation towards human prostate (DU145) and lung (A549) cancer cell lines demonstrated that 3 exerted a similar effect on cell viability to that produced by the reference drug 5-FU. Among the two tested cancer cell lines, the A549 cells were more susceptible for 3. Of note, hybrid 3 also had a significantly lower cytotoxic effect on healthy human lung epithelial cells (BEAS-2B) than 5-FU. Altogether our results served as an initial proof-of-concept to develop 5-FU/HO-1 mutual prodrugs as potential novel anticancer agents.

Combination of Heme Oxygenase-1 Inhibition and Sigma Receptor Modulation for Anticancer Activity

Cancer is a multifactorial disease that may be tackled by targeting different signaling pathways. Heme oxygenase-1 (HO-1) and sigma receptors (σRs) are both overexpressed in different human cancers, including prostate and brain, contributing to the cancer spreading. In the present study, we investigated whether HO-1 inhibitors and σR ligands, as well a combination of the two, may influence DU145 human prostate and U87MG human glioblastoma cancer cells proliferation. In addition, we synthesized, characterized, and tested a small series of novel hybrid compounds (HO-1/σRs) 1–4 containing the chemical features needed for HO-1 inhibition and σR modulation. Herein, we report for the first time that targeting simultaneously HO-1 and σR proteins may be a good strategy to achieve increased antiproliferative activity against DU145 and U87MG cells, with respect to the mono administration of the parent compounds. The obtained outcomes provide an initial proof of concept useful to further optimize the structure of HO-1/σRs hybrids to develop novel potential anticancer agents.

Heme Oxygenase-1 Signaling and Redox Homeostasis in Physiopathological Conditions

Heme-oxygenase is the enzyme responsible for degradation of endogenous iron protoporphyirin heme; it catalyzes the reaction’s rate-limiting step, resulting in the release of carbon monoxide (CO), ferrous ions, and biliverdin (BV), which is successively reduced in bilirubin (BR) by biliverdin reductase. Several studies have drawn attention to the controversial role of HO-1, the enzyme inducible isoform, pointing out its implications in cancer and other diseases development, but also underlining the importance of its antioxidant activity. The contribution of HO-1 in redox homeostasis leads to a relevant decrease in cells oxidative damage, which can be reconducted to its cytoprotective effects explicated alongside other endogenous mechanisms involving genes like TIGAR (TP53-induced glycolysis and apoptosis regulator), but also to the therapeutic functions of heme main transformation products, especially carbon monoxide (CO), which has been shown to be effective on GSH levels implementation sustaining body’s antioxidant response to oxidative stress. The aim of this review was to collect most of the knowledge on HO-1 from literature, analyzing different perspectives to try and put forward a hypothesis on revealing yet unknown HO-1-involved pathways that could be useful to promote development of new therapeutical strategies, and lay the foundation for further investigation to fully understand this important antioxidant system.

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.

Synthesis, in vitro and in silico studies of HO-1 inducers and lung antifibrotic agents

Aim: Dimethyl fumarate (DMF) analogs were synthesized to obtain inducers of HO-1 and antifibrotic agents. Methods: HO-1 expression levels were measured on lung fibroblasts (MRC5). NMR and docking studies were performed. Heme oxygenase activity, gene levels and protein expression have been measured for the most active compound 1a. Collagen production by fibroblast after exposure to TGF-β was measured. Results: Compound 1a showed to be a strong HO-1 inducer. Its activity seems to be mediated by activation of nuclear factor erythroid 2 related factor 2 (Nrf2). TGF-β-induced collagen production was significantly decreased on MRC5, pretreated with DMF or 1a. DMF and 1a have a high potential for treatment of lung fibrotic injuries.

Functionalization of Single and Multi-Walled Carbon Nanotubes with Polypropylene Glycol Decorated Pyrrole for the Development of Doxorubicin Nano-Conveyors for Cancer Drug Delivery

A recently reported functionalization of single and multi-walled carbon nanotubes, based on a cycloaddition reaction between carbon nanotubes and a pyrrole derived compound, was exploited for the formation of a doxorubicin (DOX) stacked drug delivery system. The obtained supramolecular nano-conveyors were characterized by wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HR-TEM), and Fourier transform infrared (FT-IR) spectroscopy. The supramolecular interactions were studied by molecular dynamics simulations and by monitoring the emission and the absorption spectra of DOX. Biological studies revealed that two of the synthesized nano-vectors are effectively able to get the drug into the studied cell lines and also to enhance the cell mortality of DOX at a much lower effective dose. This work reports the facile functionalization of carbon nanotubes exploiting the "pyrrole methodology" for the development of novel technological carbon-based drug delivery systems.

Heme Oxygenase-1 in Central Nervous System Malignancies

Central nervous system tumors are the most common pediatric solid tumors and account for 20–25% of all childhood malignancies. Several lines of evidence suggest that brain tumors show altered redox homeostasis that triggers the activation of various survival pathways, leading to disease progression and chemoresistance. Among these pathways, heme oxygenase-1 (HO-1) plays an important role. HO-1 catalyzes the enzymatic degradation of heme with the simultaneous release of carbon monoxide (CO), ferrous iron (Fe²⁺), and biliverdin. The biological effects of HO-1 in tumor cells have been shown to be cell-specific since, in some tumors, its upregulation promotes cell cycle arrest and cellular death, whereas, in other neoplasms, it is associated with tumor survival and progression. This review focuses on the role of HO-1 in central nervous system malignancies and the possibility of exploiting such a target to improve the outcome of well-established therapeutic regimens. Finally, several studies show that HO-1 overexpression is involved in the development and resistance of brain tumors to chemotherapy and radiotherapy, suggesting the use of HO-1 as an innovative therapeutic target to overcome drug resistance. The following keywords were used to search the literature related to this topic: nuclear factor erythroid 2 p45-related factor 2, heme oxygenase, neuroblastoma, medulloblastoma, meningioma, astrocytoma, oligodendroglioma, glioblastoma multiforme, and gliomas.

Iron Metabolism in Cancer Progression

Iron is indispensable for cell metabolism of both normal and cancer cells. In the latter, several disruptions of its metabolism occur at the steps of tumor initiation, progression and metastasis. Noticeably, cancer cells require a large amount of iron, and exhibit a strong dependence on it for their proliferation. Numerous iron metabolism-related proteins and signaling pathways are altered by iron in malignancies, displaying the pivotal role of iron in cancer. Iron homeostasis is regulated at several levels, from absorption by enterocytes to recycling by macrophages and storage in hepatocytes. Mutations in HFE gene alter iron homeostasis leading to hereditary hemochromatosis and to an increased cancer risk because the accumulation of iron induces oxidative DNA damage and free radical activity. Additionally, the iron capability to modulate immune responses is pivotal in cancer progression. Macrophages show an iron release phenotype and potentially deliver iron to cancer cells, resulting in tumor promotion. Overall, alterations in iron metabolism are among the metabolic and immunological hallmarks of cancer, and further studies are required to dissect how perturbations of this element relate to tumor development and progression.

Chromatograpic resolution of phenylethanolic-azole racemic compounds highlighted stereoselective inhibition of heme oxygenase-1 by (R)-enantiomers

Heme oxygenase-1 (HO-1) has been recognized as extensively involved in the development and aggravation of cancer, cell propagation and at in the mechanism of chemoresistance development. Low micromolar HO-1 inhibitors selective towards HO-2 has been recently reported, wherein the azole core and the hydrophobic residues are linked through a phenylethanolic spacer bearing a chiral center. Since less information are known about the stereoselective requirements for HO-1 inhibition, here we report the enantiomeric resolution of 1-(biphenyl-3-yl)-2-(1H-imidazol-1-yl)ethanol (1) and 1-[4-[(4-bromobenzyl)oxy]phenyl]-2-(1H-imidazol-1-yl)ethanol (2), two among the most potent and selective HO-1 inhibitors known thus far when tested as racemates. The absolute configuration was established for 1 by a combination of experimental and in silico derived electronic circular dichroism spectra, while docking approaches were useful in the case of compound 2. Biological evaluation of pure enantiomers highlighted higher HO-1 inhibitory activity of (R)-enantiomers. Docking studies demonstrated the importance of hydrogen bond interaction, more pronounced for the (R)-enantiomers, with a consensus water molecule within the binding pocket. The present study demonstrates that differences in three-dimensional structure amongst compounds 1 and 2 enantiomers affect significantly the selectivity of these HO-1 inhibitors.

New Arylethanolimidazole Derivatives as HO-1 Inhibitors with Cytotoxicity against MCF-7 Breast Cancer Cells

In this paper, a novel series of imidazole-based heme oxygenase-1 (HO-1) inhibitors is reported. These compounds were obtained by modifications of previously described high potent and selective arylethanolimidazoles. In particular, simplification of the central linker and repositioning of the hydrophobic portion were carried out. Results indicate that a hydroxyl group in the central region is crucial for the potency as well as the spatial distribution of the hydrophobic portion. Docking studies revealed a similar interaction of the classical HO-1 inhibitors with the active site of the protein. The most potent and selective compound (5a) was tested for its potential cytotoxic activity against hormone-sensitive and hormone-resistant breast cancer cell lines (MCF-7 and MDA-MB-231).

Non-competitive heme oxygenase-1 activity inhibitor reduces non-small cell lung cancer glutathione content and regulates cell proliferation

Non-small cell lung cancer (NSCLC) remains the leading cause of cancer-related death mainly due to its high metastatic rate. Impairment of redox homeostasis mechanisms has been previously described in NSCLC and is associated with the disease itself as well as with comorbidities such as smoking. The aim of the present in vitro study was to evaluate the effect of selective and non-competitive inhibition of heme oxygenase-1 (HO-1) on cancer redox homeostasis with particular regards to glutathione (GSH) metabolism related enzymes. NSCLC cell line (A549) was treated with the HO-1 activity inhibitor VP13/47 (10 µM) and we further evaluated cell viability, apoptosis, mitochondrial dysfunction and oxidative stress. Our results showed that VP13/47 significantly reduced HO-1 expression and total HO activity thus, resulting in a significant reduction of cell viability, proliferation and increased apoptosis, mitochondrial dysfunction and oxidative stress. Consistently with increased oxidative stress, we also showed that reduced GSH was significantly decreased and such effect was also accompanied by a significant downregulation of the enzymes involved in its biosynthesis. Taken all together our results show that selective HO-1 inhibition significantly impairs NSCLC progression and may represent a possible pharmacological strategy for new chemotherapy agents.

Cannabidiol Protects Dopaminergic Neurons in Mesencephalic Cultures against the Complex I Inhibitor Rotenone Via Modulation of Heme Oxygenase Activity and Bilirubin

Phytocannabinoids protect neurons against stressful conditions, possibly via the heme oxygenase (HO) system. In cultures of primary mesencephalic neurons and neuroblastoma cells, we determined the capability of cannabidiol (CBD) and tetrahydrocannabinol (THC) to counteract effects elicited by complex I-inhibitor rotenone by analyzing neuron viability, morphology, gene expression of IL6, CHOP, XBP1, HO-1 (stress response), and HO-2, and in vitro HO activity. Incubation with rotenone led to a moderate stress response but massive degeneration of dopaminergic neurons (DN) in primary mesencephalic cultures. Both phytocannabinoids inhibited in-vitro HO activity, with CBD being more potent. Inhibition of the enzyme reaction was not restricted to neuronal cells and occurred in a non-competitive manner. Although CBD itself decreased viability of the DNs (from 100% to 78%), in combination with rotenone, it moderately increased survival from 28.6% to 42.4%. When the heme degradation product bilirubin (BR) was added together with CBD, rotenone-mediated degeneration of DN was completely abolished, resulting in approximately the number of DN determined with CBD alone (77.5%). Using N18TG2 neuroblastoma cells, we explored the neuroprotective mechanism underlying the combined action of CBD and BR. CBD triggered the expression of HO-1 and other cell stress markers. Co-treatment with rotenone resulted in the super-induction of HO-1 and an increased in-vitro HO-activity. Co-application of BR completely mitigated the rotenone-induced stress response. Our findings indicate that CBD induces HO-1 and increases the cellular capacity to convert heme when stressful conditions are met. Our data further suggest that CBD via HO may confer full protection against (oxidative) stress when endogenous levels of BR are sufficiently high.

Repurposing of FDA-Approved Drugs for Treating Iatrogenic Botulism: A Paired 3D-QSAR/Docking Approach†

Botulinum neurotoxin (BoNT) is widely used for the treatment of spasticity, focal dystonia, chronic migraine, facial hemispasm, and facial aesthetic treatments. Generally, treatment with botulinum toxin is a safe procedure when conducted by clinicians with expertise, and local side effects are rare and transient. However, occasionally adverse effects can occur due to the spread of the drug to nontargeted muscles and organs, producing dry mouth, fatigue, and flu-like symptoms, up to signs of systemic botulism, which appears to be more frequent in children treated for spasticity than in adults. In silico 3D-QSAR and molecular docking studies were performed to build a structure-based model on selected potent known botulinum neurotoxin type A inhibitors; this was used to screen the US Food and Drug Administration (FDA) database. Thirty molecules were identified as possible light-chain BoNT/A inhibitors. In this study, we applied a well-established ligand- and structure-based methodology for the identification of hit compounds among a database of FDA-approved drugs. The identification of budesonide, protirelin, and ciclesonide followed by other compounds can be considered a starting point for investigations of selected compounds that could bypass much of the time and costs involved in the drug approval process.

Ginseng and heme oxygenase-1: The link between an old herb and a new protective system

Ginseng is an ancient herb, belonging to Asian traditional medicine, that has been considered as a restorative to enhance vitality for centuries. It has been demonstrated that the antioxidant action of ginseng may be mediated through activation of different cellular signaling pathways involving the heme oxygenase (HO) system. Several compounds derived from ginseng have been studied for their potential role in brain, heart and liver protection, and the Nrf2 pathway seems to be the most affected by these natural molecules to exert this effect. Ginseng is also popularly used in cancer patients therapy for the demonstrated capability to defend tissues from chemotherapy-induced damage. Reported results suggest that the effect of ginseng is primarily associated with ROS scavenging, mainly exerted through the activation of Nrf2 pathway, and the consequent induction of HO-1 levels. This review aims to discuss the connection between the antioxidant properties of ginseng and the activation of the HO system, as well as to outline novel therapeutic applications of this medicinal plant to human health.

Role of Heme Oxygenase as a Modulator of Heme-Mediated Pathways

The heme oxygenase (HO) system is essential for heme and iron homeostasis and necessary for adaptation to cell stress. HO degrades heme to biliverdin (BV), carbon monoxide (CO) and ferrous iron. Although mostly beneficial, the HO reaction can also produce deleterious effects, predominantly attributed to excessive product formation. Underrated so far is, however, that HO may exert effects additionally via modulation of the cellular heme levels. Heme, besides being an often-quoted generator of oxidative stress, plays also an important role as a signaling molecule. Heme controls the anti-oxidative defense, circadian rhythms, activity of ion channels, glucose utilization, erythropoiesis, and macrophage function. This broad spectrum of effects depends on its interaction with proteins ranging from transcription factors to enzymes. In degrading heme, HO has the potential to exert effects also via modulation of heme-mediated pathways. In this review, we will discuss the multitude of pathways regulated by heme to enlarge the view on HO and its role in cell physiology. We will further highlight the contribution of HO to pathophysiology, which results from a dysregulated balance between heme and the degradation products formed by HO.

Heme Oxygenase-1 Inhibition Sensitizes Human Prostate Cancer Cells towards Glucose Deprivation and Metformin-Mediated Cell Death

High levels of heme oxygenase (HO)-1 have been frequently reported in different human cancers, playing a major role in drug resistance and regulation of cancer cell redox homeostasis. Metformin (MET), a drug widely used for type 2 diabetes, has recently gained interest for treating several cancers. Recent studies indicated that the anti-proliferative effects of metformin in cancer cells are highly dependent on glucose concentration. The present work was directed to determine whether use of a specific inhibitor of HO-1 activity, alone or in combination with metformin, affected metastatic prostate cancer cell viability under different concentrations of glucose. MTT assay and the xCELLigence system were used to evaluate cell viability and cell proliferation in DU145 human prostate cancer cells. Cell apoptosis and reactive oxygen species were analyzed by flow cytometry. The activity of HO-1 was inhibited using a selective imidazole-based inhibitor; genes associated with antioxidant systems and cell death were evaluated by qRT-PCR. Our study demonstrates that metformin suppressed prostate cancer growth in vitro and increased oxidative stress. Disrupting the antioxidant HO-1 activity, especially under low glucose concentration, could be an attractive approach to potentiate metformin antineoplastic effects and could provide a biochemical basis for developing HO-1-targeting drugs against solid tumors.

Synthesis of Rosmarinic Acid Amides as Antioxidative and Hypoglycemic Agents

Type 2 diabetes mellitus (T2DM) is an important metabolic disorder for which there is an urgent need for new antidiabetic drugs. α-Glucosidase inhibition is an established protocol for T2DM therapy. Because hyperglycemia causes oxidative tissue damage, the development of agents with both α-glucosidase inhibition and antioxidant activity from natural or natural-derived polyphenols such derivatives of rosmarinic acid (RA) represents an attractive therapeutic option. We report a study on amides 1-10 derived from RA and their evaluation for yeast α-glucosidase inhibition and antioxidant activity (DPPH and ORAC tests). All amides showed higher inhibitory activity than that of RA, were by far more potent than the antidiabetic drug acarbose, and proved to be effective antioxidants. A molecular docking study displayed significant binding interactions of RA amides with the active site of α-glucosidase. This in silico optimization study led to the design and synthesis of amides 9 (IC50 = 42.3 μM) and 10 (IC50 = 35.2 μM), showing the most potent α-glucosidase inhibition and good antioxidative properties. A kinetic study showed that 10 acts as a mixed type inhibitor.

Fourfold Filtered Statistical/Computational Approach for the Identification of Imidazole Compounds as HO-1 Inhibitors from Natural Products

Over-regulation of Heme oxygenase 1 (HO-1) has been recently identified in many types of human cancer, and in these cases, poor clinical outcomes are normally reported. Indeed, the inhibition of HO-1 is being considered as an anticancer approach. Imidazole scaffold is normally present in most of the classical HO-1 inhibitors and seems indispensable to the inhibitory activity due to its strong interaction with the Fe(II) of the heme group. In this paper, we searched for new potentially HO-1 inhibitors among three different databases: Marine Natural Products (MNP), ZINC Natural Products (ZNP) and Super Natural II (SN2). 484,527 compounds were retrieved from the databases and filtered through four statistical/computational filters (2D descriptors, 2D-QSAR pharmacophoric model, 3D-QSAR pharmacophoric model, and docking). Different imidazole-based compounds were suggested by our methodology to be potentially active in inhibiting the HO-1, and the results have been rationalized by the bioactivity of the filtered molecules reported in the literature.

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).

Morphing of Ibogaine: A Successful Attempt into the Search for Sigma-2 Receptor Ligands

Ibogaine is a psychoactive indole alkaloid with high affinity for several targets including the σ₂ receptor. Indeed, extensive data support the involvement of the σ₂ receptor in neurological disorders, including Alzheimer’s disease, schizophrenia, alcohol abuse and pain. Due to its serious side effects which prevent ibogaine from potential clinical applications, novel ibogaine derivatives endowed with improved σ₂ receptor affinity may be particularly beneficial. With the purpose to facilitate the investigation of iboga alkaloid derivatives which may serve as templates for the design of selective σ₂ receptor ligands, here we report a deconstruction study on the ibogaine tricyclic moiety and a successive scaffold-hopping of the indole counterpart. A 3D-QSAR model has been applied to predict the σ₂ pK_i values of the new compounds, whereas a molecular docking study conducted upon the σ₂ receptor built by homology modeling was used to further validate the best-scored molecules. We eventually evaluated pinoline, a carboline derivative, for σ₂ receptor affinity through radioligand binding assay and the results confirmed the predicted high µM range of affinity and good selectivity. The obtained results could be helpful in the drug design process of new ibogaine simplified analogs with improved σ₂ receptor binding capabilities.

A Dual Role of Heme Oxygenase-1 in Cancer Cells

Heme oxygenase (HO)-1 is known to metabolize heme into biliverdin/bilirubin, carbon monoxide, and ferrous iron, and it has been suggested to demonstrate cytoprotective effects against various stress-related conditions. HO-1 is commonly regarded as a survival molecule, exerting an important role in cancer progression and its inhibition is considered beneficial in a number of cancers. However, increasing studies have shown a dark side of HO-1, in which HO-1 acts as a critical mediator in ferroptosis induction and plays a causative factor for the progression of several diseases. Ferroptosis is a newly identified iron- and lipid peroxidation-dependent cell death. The critical role of HO-1 in heme metabolism makes it an important candidate to mediate protective or detrimental effects via ferroptosis induction. This review summarizes the current understanding on the regulatory mechanisms of HO-1 in ferroptosis. The amount of cellular iron and reactive oxygen species (ROS) is the determinative momentum for the role of HO-1, in which excessive cellular iron and ROS tend to enforce HO-1 from a protective role to a perpetrator. Despite the dark side that is related to cell death, there is a prospective application of HO-1 to mediate ferroptosis for cancer therapy as a chemotherapeutic strategy against tumors.

A Pseudouridine Isoxazolidinyl Nucleoside Analogue Structural Analysis: A Morphological Approach

An in silico study has been conducted upon (3′RS,5′SR)-5-[2′-benzyl-5′-hydroxymethyl-1′,2′-isoxazolidin-3′-yl]uracil through a molecular dynamics/docking approach that highlights its potential inhibitory activity upon the wild-type pseudouridine 5′-monophosphate glycosidase. The crystal structure of this compound has been solved by means of X-ray single crystal diffraction and the data inferred were used to predict its crystal morphology. These data were compared with optical microscopy images and confirmed the validity of the computed models. This robust approach, already used for several other different compounds, provides a fast and reliable tool to standardize a crystallization method in order to get similar and good quality crystals. As different crystal shapes could be associated with different polymorphic forms, this method could be considered a fast and cheap screening to choose among different and coexistent polymorphic forms. Furthermore, a match with the original crystal structure of pseudouridine 5′-monophosphate is provided.

FABP4 inhibitors 3D-QSAR model and isosteric replacement of BMS309403 datasets

The data have been obtained from FABP4 inhibitor molecules previously published. The 120 compounds were used to build a 3D-QSAR model. The development of the QSAR model has been undertaken with the use of Forge software using the PM3 optimized structure and the experimental IC₅₀ of each compound. The QSAR model was also employed to predict the activity of 3000 new isosteric derivatives of BMS309403. The isosteric replacement was also validated by the synthesis and the biological screening of three new compounds reported in the related research article “3D-QSAR assisted identification of FABP4 inhibitors: An effective scaffold hopping analysis/QSAR evaluation” (Floresta et al., 2019).

iVS analysis to evaluate the impact of scaffold diversity in the binding to cellular targets relevant in cancer

This study reports the application of inverse virtual screening (iVS) methodologies to identify cellular proteins as suitable targets for a library of heterocyclic small-molecules, with potential pharmacological implications. Standard synthetic procedures allow facile generation of these ligands showing a high degree of core scaffold diversity. Specifically, we have computationally investigated the binding efficacy of the new series for target proteins which are involved in cancer pathogenesis. As a result, nine macromolecules demonstrated efficient binding interactions for the molecular dataset, in comparison to the co-crystallised ligand for each target. Moreover, the iVS analysis led us to confirm that 27 analogues have high affinity for one or more examined cellular proteins. The additional evaluation of ADME and drug score for selected hits also highlights their capability as drug candidates, demonstrating valuable leads for further structure optimisation and biological studies.

A Structure- and Ligand-Based Virtual Screening of a Database of "Small" Marine Natural Products for the Identification of "Blue" Sigma-2 Receptor Ligands

Sigma receptors are a fascinating receptor protein class whose ligands are actually under clinical evaluation for the modulation of opioid analgesia and their use as positron emission tomography radiotracers. In particular, peculiar biological and therapeutic functions are associated with the sigma-2 (σ₂) receptor. The σ₂ receptor ligands determine tumor cell death through apoptotic and non-apoptotic pathways, and the overexpression of σ₂ receptors in several tumor cell lines has been well documented, with significantly higher levels in proliferating tumor cells compared to quiescent ones. This acknowledged feature has found practical application in the development of cancer cell tracers and for ligand-targeting therapy. In this context, the development of new ligands that target the σ₂ receptors is beneficial for those diseases in which this protein is involved. In this paper, we conducted a search of new potential σ₂ receptor ligands among a database of 1517 “small” marine natural products constructed by the union of the Seaweed Metabolite and the Chemical Entities of Biological Interest (ChEBI) Databases. The structures were passed through two filters that were constituted by our developed two-dimensional (2D) and three-dimensional Quantitative Structure-Activity Relationship (3D-QSAR) statistical models, and successively docked upon a σ₂ receptor homology model that we built according to the FASTA sequence of the σ₂/TMEM97 (SGMR2_HUMAN) receptor.

Development of new HO-1 inhibitors by a thorough scaffold-hopping analysis

HO-1 inhibition is considered a valuable anticancer approach. In fact, up-regulation of HO-1 had been repeatedly reported in many types of human malignancies, and in these clinical cases, poor outcomes are reported. To identify novel HO-1 inhibitors suitable for drug development, a scaffold-hopping strategy calculation was utilized to design novel derivatives. Different parts of the selected molecule were analyzed and the different series of novel compounds were virtually evaluated. The calculation for the linker moiety of the classical HO-1 inhibitors structure led us to compounds 5 and 6. A synthetic pathway for the two molecules was designed and the compounds were synthesized. The biological activity revealed an HO-1 inhibition of 0.9 and 54 μM for molecules 5 and 6 respectively. This study suggested that our scaffold-hopping approach was successful and these results are ongoing for further development.