Synthesis and antileishmanial activity of novel buparvaquone oxime derivatives

A Review of Biologically Active Oxime Ethers

Oxime ethers are a class of compounds containing the >C=N-O-R moiety. The presence of this moiety affects the biological activity of the compounds. In this review, the structures of oxime ethers with specific biological activity have been collected and presented, and bactericidal, fungicidal, antidepressant, anticancer and herbicidal activities, among others, are described. The review includes both those substances that are currently used as drugs (e.g., fluvoxamine, mayzent, ridogrel, oxiconazole), as well as non-drug structures for which various biological activity studies have been conducted. To the best of our knowledge, this is the first review of the biological activity of compounds containing such a moiety. The authors hope that this review will inspire scientists to take a greater interest in this group of compounds, as it constitutes an interesting research area.

Opportunities for Nitric Oxide in Potentiating Cancer Immunotherapy

Despite nearly 30 years of development and recent highlights of nitric oxide (NO) donors and NO delivery systems in anticancer therapy, the limited understanding of exogenous NO's effects on the immune system has prevented their advancement into clinical use. In particular, the effects of exogenously delivered NO differing from that of endogenous NO has obscured how the potential and functions of NO in anticancer therapy may be estimated and exploited despite the accumulating evidence of NO's cancer therapy-potentiating effects on the immune system. After introducing their fundamentals and characteristics, this review discusses the current mechanistic understanding of NO donors and delivery systems in modulating the immunogenicity of cancer cells as well as the differentiation and functions of innate and adaptive immune cells. Lastly, the potential for the complex modulatory effects of NO with the immune system to be leveraged for therapeutic applications is discussed in the context of recent advancements in the implementation of NO delivery systems for anticancer immunotherapy applications. SIGNIFICANCE STATEMENT: Despite a 30-year history and recent highlights of nitric oxide (NO) donors and delivery systems as anticancer therapeutics, their clinical translation has been limited. Increasing evidence of the complex interactions between NO and the immune system has revealed both the potential and hurdles in their clinical translation. This review summarizes the effects of exogenous NO on cancer and immune cells in vitro and elaborates these effects in the context of recent reports exploiting NO delivery systems in vivo in cancer therapy applications.

In Vitro and In Vivo Antifungal Activity of Buparvaquone against Sporothrix brasiliensis

Sporotrichosis has become an important zoonosis in Brazil, and Sporothrix brasiliensis is the primary species transmitted by cats. Improvement of animal treatment will help control and limit the spread and geographic expansion of sporotrichosis. Accordingly, buparvaquone, an antiprotozoal hydroxynaphthoquinone agent marketed as Butalex, was evaluated in vitro and in vivo against feline-borne isolates of S. brasiliensis. Buparvaquone inhibited in vitro fungal growth at concentrations 4-fold lower than itraconazole (the first-choice antifungal used for sporotrichosis) and was 408 times more selective for S. brasiliensis than mammalian cells. Yeasts treated with a subinhibitory concentration of buparvaquone exhibited mitochondrial dysfunction, reactive oxygen species and neutral lipid accumulation, and impaired plasma membranes. Scanning electron microscopy images also revealed buparvaquone altered cell wall integrity and induced cell disruption. In vivo experiments in a Galleria mellonella model revealed that buparvaquone (single dose of 5 mg/kg of body weight) is more effective than itraconazole against infections with S. brasiliensis yeasts. Combined, our results indicate that buparvaquone has a great in vitro and in vivo antifungal activity against S. brasiliensis, revealing the potential application of this drug as an alternative treatment for feline sporotrichosis.

Amidoximes and Oximes: Synthesis, Structure, and Their Key Role as NO Donors

Nitric oxide (NO) is naturally synthesized in the human body and presents many beneficial biological effects; in particular on the cardiovascular system. Recently; many researchers tried to develop external sources to increase the NO level in the body; for example by using amidoximes and oximes which can be oxidized in vivo and release NO. In this review; the classical methods and most recent advances for the synthesis of both amidoximes and oximes are presented first. The isomers of amidoximes and oximes and their stabilities will also be described; (Z)-amidoximes and (Z)-oximes being usually the most energetically favorable isomers. This manuscript details also the biomimetic and biological pathways involved in the oxidation of amidoximes and oximes. The key role played by cytochrome P450 or other dihydronicotinamide-adenine dinucleotide phosphate (NADPH)-dependent reductase pathways is demonstrated. Finally, amidoximes and oximes exhibit important effects on the relaxation of both aortic and tracheal rings alongside with other effects as the decrease of the arterial pressure and of the thrombi formation

Orally Bioavailable and Effective Buparvaquone Lipid-Based Nanomedicines for Visceral Leishmaniasis

Nanoenabled lipid-based drug delivery systems offer a platform to overcome challenges encountered with current failed leads in the treatment of parasitic and infectious diseases. When prepared with FDA or EMA approved excipients, they can be readily translated without the need for further toxicological studies, while they remain affordable and amenable to scale-up. Buparvaquone (BPQ), a hydroxynapthoquinone with in vitro activity in the nanomolar range, failed to clinically translate as a viable treatment for visceral leishmaniasis due to its poor oral bioavailability limited by its poor aqueous solubility (BCS Class II drug). Here we describe a self-nanoemulsifying system (SNEDDS) with high loading and thermal stability up to 6 months in tropical conditions and the ability to enhance the solubilization capacity of BPQ in gastrointestinal media as demonstrated by flow-through cell and dynamic in vitro lipolysis studies. BPQ SNEDDS demonstrated an enhanced oral bioavailability compared to aqueous BPQ dispersions (probe-sonicated), resulting in an increased plasma AUC_0-24 by 55% that is 4-fold higher than any previous reported values for BPQ formulations. BPQ SNEDDS can be adsorbed on low molecular glycol chitosan polymers forming solid dispersions that when compressed into tablets allow the complete dissolution of BPQ in gastrointestinal media. BPQ SNEDDS and BPQ solid SNEDDS demonstrated potent in vitro efficacy in the nanomolar range (<37 nM) and were able to near completely inhibit parasite replication in the spleen while also demonstrating 48 ± 48 and 56 ± 23% inhibition of the parasite replication in the liver, respectively, compared to oral miltefosine after daily administration over 10 days. The proposed platform technology can be used to elicit a range of cost-effective and orally bioavailable noninvasive formulations for a range of antiparasitic and infectious disease drugs that are needed for closing the global health innovation gap.

Targeting Channels and Transporters in Protozoan Parasite Infections

Infectious diseases caused by pathogenic protozoa are among the most significant causes of death in humans. Therapeutic options are scarce and massively challenged by the emergence of resistant parasite strains. Many of the current anti-parasite drugs target soluble enzymes, generate unspecific oxidative stress, or act by an unresolved mechanism within the parasite. In recent years, collections of drug-like compounds derived from large-scale phenotypic screenings, such as the malaria or pathogen box, have been made available to researchers free of charge boosting the identification of novel promising targets. Remarkably, several of the compound hits have been found to inhibit membrane proteins at the periphery of the parasites, i.e., channels and transporters for ions and metabolites. In this review, we will focus on the progress made on targeting channels and transporters at different levels and the potential for use against infections with apicomplexan parasites mainly Plasmodium spp. (malaria) and Toxoplasma gondii (toxoplasmosis), with kinetoplastids Trypanosoma brucei (sleeping sickness), Trypanosoma cruzi (Chagas disease), and Leishmania ssp. (leishmaniasis), and the amoeba Entamoeba histolytica (amoebiasis).

Target ROS to induce apoptosis and cell cycle arrest by 5,7-dimethoxy-1,4-naphthoquinone derivative

The 1,4-naphthoquinone derivatives bearing 5,7-dimethoxyl moiety were designed, synthesized, and tested as the antitumor agents against five human cancer cell lines (A549, Hela, HepG2, NCI-H460 and HL-60). All the compounds are described herein for the first time. The structure-activity relationships indicated that the presence of chlorine atom at the 2-position was crucial for the antiproliferative activity. Further, the electrochemical properties of the representative compounds (7e, 8e and 9e) were evaluated and a definite correlation between the redox potential and the antiproliferative activity. The most potent compound 9e displayed significant anti-leukemic activity with IC₅₀ value of 3.8 μM in HL-60 cells and weak cytotoxicity with IC₅₀ of 40.7 μM in normal cells WI-38. In mechanistic study for 9e, the increased numbers of apoptotic cells and increased cell population at G2/M phase correlated with ROS generation. Together, our results suggested that the derivatives of 2-chlorine-1,4-naphthoquinone might be the promising candidates for the treatment of promyelocytic leukemia.

Prodrug approach: An overview of recent cases

In this review we highlight the most modern trends in the prodrug strategy. In drug research and development, the prodrug concept has found a number of useful applications. Selected examples of this approach are provided in this paper and they are classified according to the aim of their design.

Investigational drugs for visceral leishmaniasis

Introduction: The armamentarium of antileishmanial drugs is small. It is further being threatened by the development of resistance and decreasing sensitivity to the available drugs. The development of newer drugs is sorely needed. Areas covered: The authors have based their review on a literature search performed using PubMed. The article specifically looks at investigational drugs, which have demonstrated, at the very least, in vitro and in vivo activities against the leishmania species that cause visceral leishmaniasis. Specifically, the authors review the nitroimidazole compound fexinidazole, which is one of the few drugs which have reached Phase II trials. The article also discusses the R enantiomer of (S)-PA-824, which has shown good antileishmanial activity. Finally, the article also highlights the many novel delivery systems and oral formulations of amphotericin B, which are both cheap and less toxic and are currently under investigation. Expert opinion: Very few new drugs have reached the clinic for this neglected tropical disease and there is an urgent need for new efficacious therapeutics. The authors believe that support from public-private partnerships would help in enabling the prompt development of drug candidates that could potentially make the clinic.

Synthesis, screening and pharmacokinetic evaluation of potential prodrugs of bupropion. Part one: in vitro development

In general, prodrugs are developed to circumvent deficiencies associated with the absorption, distribution, metabolism, excretion or toxicological (ADMET) profile associated with the active drug. In our study, we select bupropion, a drug with broad pharmacology incorporating dopaminergic, noradrenergic, nicotinic and cytokine modulation properties, but which is rapidly metabolized in vivo. We exploited its carbonyl and secondary amine functionality to facilitate the synthesis of bioprecursor prodrug forms with the sole objective of identifying analogues with enhanced properties over bupropion. A range of analogues were synthesized, ranging from N-methyl, N-benzyl, oximes, enol acetate and ether forms to examples where both functional groups were utilized to form oxadiazine, oxadiazinone, oxazolone and acetylated derivatives. We then developed an in vitro metabolic screen to simulate the human oral delivery route for these analogues. The selection of media in the screens contained a variety of pH, enzymatic and co-factor systems which mimic metabolic in vivo environments that drugs encounter when delivered orally. By coupling our in vitro screening tool to a selective hyphenated technique such as LC-MS, we were able to quickly select potential prodrugs for further in vitro and in vivo development. From the data generated, the N-alkylated bupropion analogues were shown to have the highest potential to act as bioprecursor prodrugs of bupropion.

Structures, targets and recent approaches in anti-leishmanial drug discovery and development

Recent years have seen a significant improvement in available treatment options for leishmaniasis. Two new drugs, miltefosine and paromomycin, have been registered for the treatment of visceral leishmaniasis (VL) in India since 2002. Combination therapy is now explored in clinical trials as a new treatment approach for VL to reduce the length of treatment and potentially prevent selection of resistant parasites. However there is still a need for new drugs due to safety, resistance, stability and cost issues with existing therapies. The search for topical treatments for cutaneous leishmaniasis (CL) is ongoing. This review gives a brief overview of recent developments and approaches in anti-leishmanial drug discovery and development.

Synthesis of marine alkaloid: 8,9-dihydrocoscinamide B and its analogues as Novel class of antileishmanial agents

A series of marine alkaloid 8,9-dihydrocoscinamide B, its analogues and indolylglyoxylamide derivatives have been synthesized and screened for their in vitro antileishmanial activity profile in promastigote and amastigote models. Compounds 7 and 10 have shown 99-100% inhibition against promastigotes and 97-98% inhibition against amastigotes at a concentration of 10 microg/ml.

Prodrugs for the treatment of neglected diseases

Recently, World Health Organization (WHO) and Medicins San Frontieres (MSF) proposed a classification of diseases as global, neglected and extremely neglected. Global diseases, such as cancer, cardiovascular and mental (CNS) diseases represent the targets of the majority of the R&D efforts of pharmaceutical companies. Neglected diseases affect millions of people in the world yet existing drug therapy is limited and often inappropriate. Furthermore, extremely neglected diseases affect people living under miserable conditions who barely have access to the bare necessities for survival. Most of these diseases are excluded from the goals of the R&D programs in the pharmaceutical industry and therefore fall outside the pharmaceutical market. About 14 million people,mainly in developing countries, die each year from infectious diseases. From 1975 to 1999,1393 new drugs were approved yet only 1% were for the treatment of neglected diseases[3]. These numbers have not changed until now, so in those countries there is an urgent need for the design and synthesis of new drugs and in this area the prodrug approach is a very interesting field. It provides, among other effects, activity improvements and toxicity decreases for current and new drugs, improving market availability. It is worth noting that it is essential in drug design to save time and money, and prodrug approaches can be considered of high interest in this respect. The present review covers 20 years of research on the design of prodrugs for the treatment of neglected and extremely neglected diseases such as Chagas' disease (American trypanosomiasis), sleeping sickness (African trypanosomiasis), malaria, sickle cell disease, tuberculosis, leishmaniasis and schistosomiasis.

Development and validation of RP-HPLC-UV method for simultaneous determination of buparvaquone, atenolol, propranolol, quinidine and verapamil: A tool for the standardization of rat in situ intestinal permeability studies

A simple, sensitive and specific reversed phase high performance liquid chromatographic (RP-HPLC) method with UV detection at 251 nm was developed for simultaneous quantitation of buparvaquone (BPQ), atenolol, propranolol, quinidine and verapamil. The method was applicable in rat in situ intestinal permeability study to assess intestinal permeability of BPQ, a promising lead compound for Leishmania donovani infections. The method was validated on a C-4 column with mobile phase comprising ammonium acetate buffer (0.02 M, pH 3.5) and acetonitrile in the ratio of 30:70 (v/v) at a flow rate of 1.0 ml/min. The retention times for atenolol, quinidine, propranolol, verapamil and BPQ were 4.30, 5.96, 6.55, 7.98 and 8.54 min, respectively. The calibration curves were linear (correlation coefficient > or =0.996) in the selected range of each analyte. The method is specific and sensitive with limit of quantitation of 15 microg/ml for atenolol, 0.8 microg/ml for quinidine, 5 microg/ml for propranolol, 10 microg/ml for verapamil and 200 ng/ml for BPQ. The validated method was found to be accurate and precise in the working calibration range. Stability studies were carried out at different storage conditions and all the analytes were found to be stable. This method is simple, reliable and can be routinely used for accurate permeability characterization.

Synthesis of 2,4,6-trisubstituted pyrimidine and triazine heterocycles as antileishmanial agents

A series of 2,4,6 trisubstituted pyrimidines and triazines have been synthesized and screened for its in vitro antileishmanial activity profile in promastigote model. Nine compounds have shown > 94% inhibition against promastigotes at a concentration of 10 microg/mL.

Evaluation of hydroxyimine as cytochrome P450-selective prodrug structure

Hydroxyimine derivatives of ketoprofen (1) and nabumetone (2) were synthesized and evaluated in vitro and in vivo as cytochrome P450-selective intermediate prodrug structures of ketones. 2 released nabumetone in vitro in the presence of isolated rat and human liver microsomes and in different recombinant human CYP isoforms. Bioconversion of 2 to both nabumetone and its active metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA), was further confirmed in rats in vivo. Results indicate that hydroxyimine is a useful intermediate prodrug structure for ketone drugs.

Dihydropyrido[2,3-d]pyrimidines as a new class of antileishmanial agents

A series of dihydropyrido[2,3-d]pyrimidines have been synthesized and screened for its in vitro antileishmanial activity profile in promastigote and amastigote models. Compounds 2a-2l have shown 83-100% inhibition against promastigotes and 79-100% inhibition against amastigotes at a concentration of 50 microg/mL.

Design, synthesis and in vitro evaluation of novel water-soluble prodrugs of buparvaquone

Novel water-soluble phosphate prodrugs (2b-5b) of buparvaquone-oxime (1a) and buparvaquone-O-methyloxime (1b) were synthesized and evaluated in vitro as potential oral prodrugs against leishmaniasis. Buparvaquone-oxime (1a), and most probably also buparvaquone-O-methyloxime (1b), released the parent buparvaquone via a cytochrome P450-catalysed reaction. The prodrugs 2b-5b showed significantly higher aqueous solubilities (>4 mg/ml) than buparvaquone (< or = 0.03 microg/ml) over a pH range of 3.0-7.4. The prodrugs 2b, 3b and 5b rapidly released (t1/2 = 7 min) the corresponding oximes of buparvaquone (1a and 1b), and prodrug 4b at a moderate rate (t1/2 = 22.5 min) in alkaline phosphatase solution in vitro. Prodrug 3b was the most chemically stable in the aqueous solutions over a pH range of 3.0-7.4 (t1/2 > 8 days). Although buparvaquone-oxime (1a) has been shown to undergo a cytochrome P450-catalysed oxidation in liver microsomes to the parent buparvaquone and behave as a novel bioreversible prodrug, its usefulness is limited in oral drug delivery due to its poor aqueous solubility, like buparvaquone itself. Further phosphorylation of an oxime form of buparvaquone significantly increased water solubility, and this novel approach is therefore useful to improve physicochemical properties of drugs containing a ketone functional group.