1,2,4,5-Tetraoxane derivatives/hybrids as potent antimalarial endoperoxides: Chronological advancements, structure-activity relationship (SAR) studies and future perspectives

Malaria is a life-threatening disease that affects tropical and subtropical regions worldwide. Various drugs were used to treat malaria, including artemisinin and derivatives, antibiotics (tetracycline, doxycycline), quinolines (chloroquine, amodiaquine), and folate antagonists (sulfadoxine and pyrimethamine). Since the malarial parasites developed drug resistance, there is a need to develop new chemical entities with high efficacy and low toxicity. In this context, 1,2,4,5-tetraoxanes emerged as an essential scaffold and have shown promising antimalarial activity. To improve activity and overcome resistance to various antimalarial drugs; 1,2,4,5-tetraoxanes were fused with various aryl/heteroaryl/alicyclic/spiro moieties (steroid-based 1,2,4,5-tetraoxanes, triazine-based 1,2,4,5-tetraoxanes, aminoquinoline-based 1,2,4,5-tetraoxanes, dispiro-based 1,2,4,5-tetraoxanes, piperidine-based 1,2,4,5-tetraoxanes and diaryl-based 1,2,4,5-tetraoxanes). The present review aims to focus on covering the relevant literature published during the past 30 years (1992-2022). We summarize the most significant in vitro, in vivo results and structure-activity relationship studies of 1,2,4,5-tetraoxane-based hybrids as antimalarial agents. The structural evolution of different hybrids can provide the framework for the future development of 1,2,4,5-tetraoxane-based hybrids to treat malaria.

Anti-Proliferative Properties of the Novel Hybrid Drug Met-ITC, Composed of the Native Drug Metformin with the Addition of an Isothiocyanate H2S Donor Moiety, in Different Cancer Cell Lines

Metformin (Met) is the first-line therapy in type 2 diabetes mellitus but, in last few years, it has also been evaluated as anti-cancer agent. Several pathways, such as AMPK or PI3K/Akt/mTOR, are likely to be involved in the anti-cancer Met activity. In addition, hydrogen sulfide (H2S) and H2S donors have been described as anti-cancer agents affecting cell-cycle and inducing apoptosis. Among H2S donors, isothiocyanates are endowed with a further anti-cancer mechanism: the inhibition of the histone deacetylase enzymes. On this basis, a hybrid molecule (Met-ITC) obtained through the addition of an isothiocyanate moiety to the Met molecule was designed and its ability to release Met has been demonstrated. Met-ITC exhibited more efficacy and potency than Met in inhibiting cancer cells (AsPC-1, MIA PaCa-2, MCF-7) viability and it was less effective on non-tumorigenic cells (MCF 10-A). The ability of Met-ITC to release H2S has been recorded both in cell-free and in cancer cells assays. Finally, its ability to affect the cell cycle and to induce both early and late apoptosis has been demonstrated on the most sensitive cell line (MCF-7). These results confirmed that Met-ITC is a new hybrid molecule endowed with potential anti-cancer properties derived both from Met and H2S.

Targeting carbonic anhydrases for the management of hypoxic metastatic tumors

INTRODUCTION

Several isoforms of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) are connected with tumorigenesis. Hypoxic tumors overexpress CA IX and XII as a consequence of HIF activation cascade, being involved in pH regulation, metabolism, and metastases formation. Other isoforms (CA I, II, III, IV) were also reported to be present in some tumors.

AREAS COVERED

Some CA isoforms are biomarkers for disease progression or response to therapy. Inhibitors, antibodies, and other procedures for targeting these enzymes for the treatment of tumors/metastases are discussed. Sulfonamides and coumarins represent the most investigated classes of inhibitors, but carboxylates, selenium, and tellurium-containing inhibitors were also investigated. Hybrid drugs of CA inhibitors with other antitumor agents for multitargeted therapy were reported.

EXPERT OPINION

Targeting CAs present in solid or hematological tumors with selective, targeted inhibitors is a validated approach, which has been consolidated in the last years. A host of new preclinical data and several clinical trials of antibodies and small-molecule inhibitors are ongoing, which connected with the large number of new chemotypes/procedures discovered to be effective, may lead to a breakthrough in this therapeutic area. The scientific/patent literature has been searched for on PubMed, ScienceDirect, Espacenet, and PatentGuru, from 2018 to 2023.

Hydrogen sulfide: Recent development of its dual donors and hybrid drugs

Hydrogen sulfide (H2 S) is an important gaseous signalling molecule known to be critically involved in regulating cellular redox homeostasis. As the beneficial and therapeutic effects of H2 S in pathophysiology, such as in cardiovascular and neurodegenerative diseases, have emerged, so too has the drive for the development of H2 S-releasing compounds (aka donors) and their therapeutic applications. Most reported donor compounds singularly release H2 S through biocompatible triggers. An emerging area in the field is the development of compounds that can co-deliver H2 S with other drugs or biologically relevant species, such as reactive oxygen and nitrogen species (ROS and RNS, respectively). These H2 S-based dual donors and hybrid drugs are expected to offset negative side effects from individual treatments or achieve synergistic effects rendering them more clinically effective. Additionally, considering that molecules exist and interact physiologically, dual donors may more accurately mimic biological systems as compared to single donors and allow for the elucidation of fundamental chemistry and biology. This review focuses on the recent advances in the development of H2 S-based dual donors and hybrid drugs along with their design principles and synergistic effects.

Synthesis and biological evaluation of new antiseizure compounds derived from valproic acid

Background: New hybrid compounds were synthesized by linking the valproic acid (VPA) structure with other anticonvulsant/anti-inflammatory scaffolds. Materials & methods: The chemistry involved the incorporation of the linker oxymethyl ester into VPA, followed by reaction with the second scaffold. The antiseizure effects were investigated by the maximal electroshock seizure test, and the most active compound was additionally evaluated in the 6 Hz test and pentylenetetrazol test in mice. Results: The compounds showed protection against seizures. The hybrid structure with the butylparaben scaffold exhibited an ED₅₀ of 8.265 mg/kg (0.0236 mmol/Kg) in the maximal electroshock seizure test and 50.00 mg/kg (0.147 mmol/kg) in the 6 Hz test. Conclusion: The antiseizure activity of the synthesized compounds highlighted the potential of hybrid structures to treat multifactorial diseases such as epilepsy.

Multitargeting approaches involving carbonic anhydrase inhibitors: hybrid drugs against a variety of disorders

Carbonic anhydrases (CAs, EC 4.2.1.1) are enzymes involved in a multitude of diseases, and their inhibitors are in clinical use as drugs for the management of glaucoma, epilepsy, obesity, and tumours. In the last decade, multitargeting approaches have been proposed by hybridisation of CA inhibitors (CAIs) of sulphonamide, coumarin, and sulphocoumarin types with NO donors, CO donors, prostaglandin analogs, β-adrenergic blockers, non-steroidal anti-inflammatory drugs, and a variety of anticancer agents (cytotoxic drugs, kinase/telomerase inhibitors, P-gp and thioredoxin inhibitors). Many of the obtained hybrids showed enhanced efficacy compared to the parent drugs, making multitargeting an effective and innovative approach for various pharmacological applications.

Advances in the discovery of novel agents for the treatment of glaucoma

INTRODUCTION

Glaucoma, a neuropathy characterized by increased intraocular pressure (IOP), is the major cause of blindness worldwide and its treatment aims at reducing IOP.

AREAS COVERED

The authors review the design of the main classes of anti-glaucoma agents. Drugs which interfere with the aqueous humor secretion (adrenergic agonists/antagonists, carbonic anhydrase inhibitors) and with its outflow, by means of both conventional and non-conventional pathways (prostaglandin (PG) analogs, rho kinase inhibitors, nitric oxide (NO) donors) as well as new agents (adenosine receptors modulators, melatonin - fatty acid amide hydrolase hybrids, tyrosine kinase activators, natriuretic peptide analogs) are considered.

EXPERT OPINION

The anti-glaucoma drug field has undergone several developments in recent years with the approval of at least three new drugs belonging to novel pharmacological classes, the rho kinase inhibitors ripasudil and netarsudil, and the PG-NO donor hybrid latanoprostene bunod. Eye drops with combinations of two different drugs are also available, allowing for effective IOP control, with once daily administration for some of them, which assures a better patient compliance and ease of administration. Overall, after more than a decade without new anti-glaucoma drugs, the last year afforded interesting new pharmacological opportunities for the management of this disease.

Anti-COVID drugs: repurposing existing drugs or search for new complex entities, strategies and perspectives

At the end of 2019, a novel virus causing severe acute respiratory syndrome to spread globally. There are currently no effective drugs targeting SARS-CoV-2. In this study, based on the analysis of numerous references and selected methods of computational chemistry, the strategy of integrative structural modification of small molecules with antiviral activity into potential active complex molecules has been presented. Proposed molecules have been designed based on the structure of triterpene oleanolic acid and complemented by structures characteristic of selected anti-COVID therapy assisted drugs. Their pharmaceutical molecular parameters and the preliminary bioactivity were calculated and predicted. The results of the above analyses show that among the designed complex substances there are potential antiviral agents directed mainly on SARS-CoV-2.

Discovery of Sustainable Drugs for Neglected Tropical Diseases: Cashew Nut Shell Liquid (CNSL)-Based Hybrids Target Mitochondrial Function and ATP Production in Trypanosoma brucei

In the search for effective and sustainable drugs for human African trypanosomiasis (HAT), we developed hybrid compounds by merging the structural features of quinone 4 (2‐phenoxynaphthalene‐1,4‐dione) with those of phenolic constituents from cashew nut shell liquid (CNSL). CNSL is a waste product from cashew nut processing factories, with great potential as a source of drug precursors. The synthesized compounds were tested against Trypanosoma brucei brucei, including three multidrug‐resistant strains, T. congolense, and a human cell line. The most potent activity was found against T. b. brucei, the causative agent of HAT. Shorter‐chain derivatives 20 (2‐(3‐(8‐hydroxyoctyl)phenoxy)‐5‐methoxynaphthalene‐1,4‐dione) and 22 (5‐hydroxy‐2‐(3‐(8‐hydroxyoctyl)phenoxy)naphthalene‐1,4‐dione) were more active than 4, displaying rapid micromolar trypanocidal activity, and no human cytotoxicity. Preliminary studies probing their mode of action on trypanosomes showed ATP depletion, followed by mitochondrial membrane depolarization and mitochondrion ultrastructural damage. This was accompanied by reactive oxygen species production. We envisage that such compounds, obtained from a renewable and inexpensive material, might be promising bio‐based sustainable hits for anti‐trypanosomatid drug discovery.

Conception, synthesis, and characterization of a rofecoxib-combretastatin hybrid drug with potent cyclooxygenase-2 (COX-2) inhibiting and microtubule disrupting activities in colon cancer cell culture and xenograft models

Tumor heterogeneity and drug resistance pose severe limitations to chemotherapy of colorectal cancers (CRCs) necessitating innovative approaches to trigger multiple cytocidal events for increased efficacy. Here, we developed a hybrid drug called KSS19 by combining the COX-2 selective NSAID rofecoxib with the cis-stilbene found in combretastatin A4 (CA4), a problematic, but potent antimicrotubule and anti-angiogenesis agent. The structural design of KSS19 completely prevented the isomerization of CA4 its biologically inactive trans-form. Molecular modeling showed that KSS19 bound avidly to the COX-2 active site and colchicine -binding site of tubulin, with similar docking scores of rofecoxib and CA4 respectively. KSS-19 showed potent anti-proliferative activity against a panel of colon cancer cell lines; HT29 cells, which are resistant to CA4 were 100 times more sensitive to KSS19. The hybrid drug potently inhibited the tubulin polymerization in vitro and in cells inducing a G2/M arrest and aberrant mitotic spindles. Both the basal and LPS-activated levels of COX-2 in colon cancer cells were highly suppressed by the KSS-19. The cancer cell migration/invasion was inhibited and accompanied by increased E-cadherin levels and activated NF-kB/Snail pathways in KSS19-treated cells. The drug also curtailed the formation of endothelial tubes in three-dimensional cultures of the HUVE cells at 250 nM, indicating strong anti-angiogenic properties. In subcutaneous HT29 colon cancer xenografts, KSS19, as a single agent (25 mg/kg/day) significantly inhibited the tumor growth and downregulated the intratumoral COX-2, Ki-67, the angiogenesis marker CD31, however, the cleaved caspase-3 was elevated. Collectively, KSS19 represents a rational hybrid drug with clinical relevance to CRC.

Dual abrogation of MNK and mTOR: a novel therapeutic approach for the treatment of aggressive cancers

Targeting the translational machinery has emerged as a promising therapeutic option for cancer treatment. Cancer cells require elevated protein synthesis and exhibit augmented activity to meet the increased metabolic demand. Eukaryotic translation initiation factor 4E is necessary for mRNA translation, its availability and phosphorylation are regulated by the PI3K/AKT/mTOR and MNK1/2 pathways. The phosphorylated form of eIF4E drives the expression of oncogenic proteins including those involved in metastasis. In this article, we will review the role of eIF4E in cancer, its regulation and discuss the benefit of dual inhibition of upstream pathways. The discernible interplay between the MNK and mTOR signaling pathways provides a novel therapeutic opportunity to target aggressive migratory cancers through the development of hybrid molecules.

Recent progress in repositioning Alzheimer's disease drugs based on a multitarget strategy

Alzheimer's disease (AD) is a serious progressive neurological disorder, characterized by impaired cognition and profound irreversible memory loss. The multifactorial nature of AD and the absence of a cure so far have stimulated medicinal chemists worldwide to follow multitarget drug-design strategies based on repositioning approved drugs. This review describes a summary of recently published works focused on tailoring new derivatives of US FDA-approved acetylcholinesterase inhibitors, in addition to huperzine (a drug approved in China), either by hybridization with other pharmacophore elements (to hit more AD targets), or by combination of two FDA-approved drugs. Besides the capacity for improving the cholinergic activity, these polyfunctional derivatives are also able to tackle other important neuroprotective properties, such as anti-β-amyloid aggregation, scavenging of radical oxygen species, modulation of redox-active metals or inhibition of monoamine oxidase, thereby resulting in potentially novel and more effective therapeutics for the treatment of AD.

Arylthioamides as H2S Donors: l-Cysteine-Activated Releasing Properties and Vascular Effects in Vitro and in Vivo

A small library of arylthioamides 1-12 was easily synthesized, and their H2S-releasing properties were evaluated both in the absence or in the presence of an organic thiol such as l-cysteine. A number of arylthioamides (1-3 and 7) showed a slow and l-cysteine-dependent H2S-releasing mechanism, similar to that exhibited by the reference slow H2S-releasing agents, such as diallyl disulfide (DADS) and the phosphinodithioate derivative GYY 4137. Compound 1 strongly abolished the noradrenaline-induced vasoconstriction in isolated rat aortic rings and hyperpolarized the membranes of human vascular smooth muscle cells in a concentration-dependent fashion. Finally, a significant reduction of the systolic blood pressure of anesthetized normotensive rats was observed after its oral administration. Altogether these results highlighted the potential of arylthioamides 1-3 and 7 as H2S-donors for basic studies, and for the rational design/development of promising pharmacotherapeutic agents to treat cardiovascular diseases.

Highly selective inhibition of butyrylcholinesterase by a novel melatonin-tacrine heterodimers

Novel inhibitors of cholinesterases, especially butyrylcholinesterase (BuChE), were obtained by coupling melatonin-tacrine heterodimers via the carbamate bond. Compounds 14a-i possessed potent cholinesterase inhibitory activity (with IC50 values as low as 1.18 nM for acetylcholinesterase (AChE) and 0.24 nM for butyrylcholinesterase (BuChE)). These heterodimers exhibit selectivity toward BuChE, being from 4- to 256-fold more active toward BuChE than AChE, but still acting as better AChE inhibitors than tacrine 4.

Chemical-biological characterization of a cruzain inhibitor reveals a second target and a mammalian off-target

Inhibition of the Trypanosoma cruzi cysteine protease cruzain has been proposed as a therapeutic approach for the treatment of Chagas’ disease. Among the best-studied cruzain inhibitors to date is the vinylsulfone K777 (1), which has proven effective in animal models of Chagas’ disease. Recent structure–activity studies aimed at addressing potential liabilities of 1 have now produced analogues such as N-[(2S)-1-[[(E,3S)-1-(benzenesulfonyl)-5-phenylpent-1-en-3-yl]amino]-3-(4-methylphenyl)-1-oxopropan-2-yl]pyridine-4-carboxamide (4), which is trypanocidal at ten-fold lower concentrations than for 1. We now find that the trypanocidal activity of 4 derives primarily from the inhibition of T. cruzi 14-α-demethylase (TcCYP51), a cytochrome P450 enzyme involved in the biosynthesis of ergosterol in the parasite. Compound 4 also inhibits mammalian CYP isoforms but is trypanocidal at concentrations below those required to significantly inhibit mammalian CYPs in vitro. A chemical-proteomics approach employing an activity-based probe derived from 1 was used to identify mammalian cathepsin B as a potentially important off-target of 1 and 4. Computational docking studies and the evaluation of truncated analogues of 4 reveal structural determinants for TcCYP51 binding, information that will be useful in further optimization of this new class of inhibitors.