Establishment of a structure-activity relationship of 1H-imidazo[4,5-c]quinoline-based kinase inhibitor NVP-BEZ235 as a lead for African sleeping sickness

Pharmacophore Identification and Structure-Activity Relationship Analysis of a Series of Substituted Azaindoles as Inhibitors of Trypanosoma brucei

Human African trypanosomiasis is among the World Health Organization's designated neglected tropical diseases. Repurposing strategies are often employed in academic drug discovery programs due to financial limitations, and in this instance, we used human kinase inhibitor chemotypes to identify substituted 4-aminoazaindoles, exemplified by 1. Structure-activity and structure-property relationship analysis, informed by cheminformatics, identified 4s as a potent inhibitor of Trypanosoma brucei growth. While 4s appeared to be fast acting and cidal in the in vitro assays, it failed to cure a murine model of infection. Preliminary efforts to identify the potential mechanism of action of the series pointed to arginine kinase, though, as we demonstrate, this does not appear to be the sole target of our compounds. This comprehensive approach to drug discovery, encompassing cheminformatics, structure-potency and structure-property analysis, and pharmacophore identification, highlights our multipronged efforts to identify novel lead compounds for this deadly disease.

An Aldehyde-Driven, Fe(0)-Mediated, One-Pot Reductive Cyclization: Direct Access to 5,6-Dihydro-quinazolino[4,3-b]quinazolin-8-ones and Photophysical Study

A short, proficient, and regioselective synthesis of biheterocyclic 5,6-dihydro-quinazolino[4,3-b]quinazolin-8-ones has been revealed via an Fe(0)-powder-mediated, one-pot reductive cyclization protocol. Mechanistic investigation proved that water acts as a source of hydrogen for the reduction of the nitro group and the reaction rate was accelerated by an aldehyde. The designed transformation works under aerobic conditions, providing a series of bio-inspired molecular scaffolds. In addition, the photophysical study showed blue fluorescence emission with a good fluorescence quantum yield.

Photophysical evaluation on the electronic properties of synthesized biologically significant pyrido fused imidazo[4,5-c]quinolines

A single pot microwave assisted method was employed to synthesize a series of novel pyrido fused imidazo[4,5-c]quinolines. The electronic properties of these derivatives were investigated by following their photophysical behaviour under isolated and solvated conditions via computational and experimental approaches. The solvatochromic effect of these derivatives was investigated in the ground and excited singlet states by following the absorption and fluorescence emission and excitation spectra. Further the effect of general and specific solvent effects were also investigated by plotting Stokes shift against Lippert-Mataga, ET(30) and Kamlet-Taft polarity parameters respectively. The deviation from linearity in ET(30) plot indicates that formation of different species in polar protic solvents. The biological applications of these derivatives as potential drug candidates were evaluated by in silico computational methods followed by pharmacokinetic properties predictions. The ability of these derivatives to inhibit human casein kinase 2 (CK2) was evaluated. The structure activity relationships were correlated by evaluating the electronic properties through experimental photophysical investigations including solvatochromic effect and computational electronic structure calculations. Of the various derivatives, p-nitro phenyl substituted pyrido fused imidazo[4,5-c]quinoline exhibited good inhibitory activity against CK2 enzyme and hence could serve as a promising drug candidate.

The crystal structure of 3,5-bis(propan-2-yl)-1H-pyrazol-4-amine, C9H17N3

C9H17N3, monoclinic, P21/c (no. 14), a = 9.5601(3) Å, b = 9.5210(3) Å, c = 10.7651(3) Å, β = 94.564(3)°, V = 976.75(5) Å3, Z = 4, Rgt (F) = 0.0432, wRref (F 2) = 0.1223, T = 178(2) K.

Quinoline-Based Molecules Targeting c-Met, EGF, and VEGF Receptors and the Proteins Involved in Related Carcinogenic Pathways

The quinoline ring system has long been known as a versatile nucleus in the design and synthesis of biologically active compounds. Currently, more than one hundred quinoline compounds have been approved in therapy as antimicrobial, local anaesthetic, antipsychotic, and anticancer drugs. In drug discovery, indeed, over the last few years, an increase in the publication of papers and patents about quinoline derivatives possessing antiproliferative properties has been observed. This trend can be justified by the versatility and accessibility of the quinoline scaffold, from which new derivatives can be easily designed and synthesized. Within the numerous quinoline small molecules developed as antiproliferative drugs, this review is focused on compounds effective on c-Met, VEGF (vascular endothelial growth factor), and EGF (epidermal growth factor) receptors, pivotal targets for the activation of important carcinogenic pathways (Ras/Raf/MEK and PI3K/AkT/mTOR). These signalling cascades are closely connected and regulate the survival processes in the cell, such as proliferation, apoptosis, differentiation, and angiogenesis. The antiproliferative biological data of remarkable quinoline compounds have been analysed, confirming the pivotal importance of this ring system in the efficacy of several approved drugs. Furthermore, in view of an SAR (structure-activity relationship) study, the most recurrent ligand–protein interactions of the reviewed molecules are summarized.

Structure-property studies of an imidazoquinoline chemotype with antitrypanosomal activity

Human African trypanosomiasis is a neglected tropical disease (NTD) that is fatal if left untreated. Although approximately 13 million people live in moderate- to high-risk areas for infection, current treatments are plagued by problems with safety, efficacy, and emerging resistance. In an effort to fill the drug development pipeline for HAT, we have expanded previous work exploring the chemotype represented by the compound NEU-1090, with a particular focus on improvement of absorption, distribution, metabolism and elimination (ADME) properties. These efforts resulted in several compounds with substantially improved aqueous solubility, although these modifications typically resulted in a loss of trypanosomal activity. We herein report the results of our investigation into the antiparasitic activity, toxicity, and ADME properties of this class of compounds in the interest of informing the NTD drug discovery community and avoiding duplication of effort.

In Vitro and in Vivo Activity of mTOR Kinase and PI3K Inhibitors Against Leishmania donovani and Trypanosoma brucei

Kinetoplastid parasites, including Leishmania and Trypanosoma spp., are life threatening pathogens with a worldwide distribution. Next-generation therapeutics for treatment are needed as current treatments have limitations, such as toxicity and drug resistance. In this study, we examined the activities of established mammalian target of rapamycin (mTOR)/phosphoinositide 3-kinase (PI3K) inhibitors against these tropical diseases. High-throughput screening of a library of 1742 bioactive compounds against intracellular L. donovani was performed, and seven mTOR/PI3K inhibitors were identified. Dose-dilution assays revealed that these inhibitors had half maximal effective concentration (EC₅₀₎ values ranging from 0.14 to 13.44 μM for L. donovani amastigotes and from 0.00005 to 8.16 μM for T. brucei. The results of a visceral leishmaniasis mouse model indicated that treatment with Torin2, dactolisib, or NVP-BGT226 resulted in reductions of 35%, 53%, and 54%, respectively, in the numbers of liver parasites. In an acute T. brucei mouse model using NVP-BGT226 parasite numbers were reduced to under the limits of detection by five consecutive days of treatment. Multiple sequence and structural alignment results indicated high similarities between mTOR and kinetoplastid TORs; the inhibitors are predicted to bind in a similar manner. Taken together, these results indicated that the TOR pathways of parasites have potential for the discovery of novel targets and new potent inhibitors.

Evaluation of a class of isatinoids identified from a high-throughput screen of human kinase inhibitors as anti-Sleeping Sickness agents

New treatments are needed for neglected tropical diseases (NTDs) such as Human African trypanosomiasis (HAT), Chagas disease, and schistosomiasis. Through a whole organism high-throughput screening campaign, we previously identified 797 human kinase inhibitors that grouped into 59 structural clusters and showed activity against T. brucei, the causative agent of HAT. We herein report the results of further investigation of one of these clusters consisting of substituted isatin derivatives, focusing on establishing structure-activity and -property relationship scope. We also describe their in vitro absorption, distribution, metabolism, and excretion (ADME) properties. For one isatin, NEU-4391, which offered the best activity-property profile, pharmacokinetic parameters were measured in mice.

Human African trypanosomiasis (HAT) is a parasitic disease prevalent in sub-Saharan Africa. Current treatments cause severe toxicity, are difficult to administer, and are susceptible to resistance. In order to quickly discover new leads for HAT drug discovery, we screened human kinase inhibitors against Trypanosoma brucei, the parasite that causes HAT, and discovered several hundred compounds that demonstrated antiparasitic activity. In this paper, we present the results of medicinal chemistry follow-up work on a group of compounds known as isatins.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Host-Directed Drug Therapies for Neglected Tropical Diseases Caused by Protozoan Parasites

The neglected tropical diseases (NTDs) caused by protozoan parasites are responsible for significant morbidity and mortality worldwide. Current treatments using anti-parasitic drugs are toxic and prolonged with poor patient compliance. In addition, emergence of drug-resistant parasites is increasing worldwide. Hence, there is a need for safer and better therapeutics for these infections. Host-directed therapy using drugs that target host pathways required for pathogen survival or its clearance is a promising approach for treating infections. This review will give a summary of the current status and advances of host-targeted therapies for treating NTDs caused by protozoa.

The Importance of Collaboration between Industry, Academics, and Nonprofits in Tropical Disease Drug Discovery

Collaborations between academic, industrial, and nonprofit companies can provide sufficient impetus to propel projects that have little economic return; such projects are prevalent in tropical disease drug discovery. In these collaborations, each partner contributes a unique set of skills and technical expertise which is advantageous to the project as a whole. Highly product-focused processes and specialized expertise sets dominate industry groups. When coupled with the strategic guidance from public-private partnerships and the academic tendency to work on high-risk projects with low financial rewards, a powerful combination results. There are numerous examples throughout the literature about these collaborative efforts to combat a variety of tropical diseases (including leishmaniasis, Chagas disease, African sleeping sickness, and malaria), from all stages of the drug discovery process to the advancement of new drugs into the clinic. However, there is still uncertainty from many academic institutions as to how to establish and engage in these research consortiums. This Viewpoint highlights opportunities, benefits, and suggestions for productive collaborations in this disease space.

Acid-Promoted Cascade Reaction of N-(4-Chloroquinolin-3-yl)carbamates with Amines: One-Pot Assembly of Imidazo[4,5-c]quinolin-2-one

An acid-promoted cascade reaction of 4-chloroquinolin-3-yl carbamates with amines is described. This method achieves the formation of two new C-N bonds through an intermolecular amination/intramolecular cyclization reaction sequence. In combination with subsequent Suzuki coupling, this three-component telescopic procedure provides rapid access to various bioactive imidazo[4,5-c]quinolin-2-one derivatives.

Carbonyl Iron Powder: A Reagent for Nitro Group Reductions under Aqueous Micellar Catalysis Conditions

An especially mild, safe, efficient, and environmentally responsible reduction of aromatic and heteroaromatic nitro-group-containing educts is reported that utilizes very inexpensive carbonyl iron powder (CIP), a highly active commercial grade of iron powder. These reductions are conducted in the presence of nanomicelles composed of TPGS-750-M in water, a recyclable aqueous micellar reaction medium. This new technology also shows broad scope and scalability and presents opportunities for multistep one-pot sequences involving this reducing agent.

Optimization of physicochemical properties for 4-anilinoquinazoline inhibitors of trypanosome proliferation

Human African trypanosomiasis (HAT) is a deadly disease in need of new chemotherapeutics that can cross into the central nervous system. We previously reported the discovery of 2 (NEU-617), a small molecule with activity against T. brucei bloodstream proliferation. Further optimization of 2 to improve the physicochemical properties (LogP, LLE, [1], and MPO score) [2] have led us to twelve sub-micromolar compounds, most importantly the headgroup variants 9i and 9j, and the linker variant 18. Although these 3 compounds had reduced potency compared to 2, they all had improved LogP, LLE and MPO scores. Cross-screening these analogs against other protozoan parasites uncovered 9o with potent activity towards T. brucei, T. cruzi and L. major, while four others compounds (17, 18, 21, 26) showed activity towards P. falciparum D6. This reinforces the effectiveness of lead repurposing for the discovery of new protozoan disease therapeutics.

Novel lead compounds in pre-clinical development against African sleeping sickness

Human African trypanosomiasis (HAT), also known as African sleeping sickness, is caused by parasitic protozoa of the genus Trypanosoma. As the disease progresses, the parasites cross the blood brain barrier and are lethal for the patients if the disease is left untreated. Current therapies suffer from several drawbacks due to e.g. toxicity of the respective compounds or resistance to approved antitrypanosomal drugs. In this review, the different strategies of drug development against HAT are considered, namely the target-based approach, the phenotypic high throughput screening and the drug repurposing strategy. The most promising compounds emerging from these approaches entering an in vivo evaluation are mentioned herein. Of note, it may turn out to be difficult to confirm in vitro activity in an animal model of infection; however, possible reasons for the missing efficacy in unsuccessful in vivo studies are discussed.

In vitro evaluation of imidazo[4,5-c]quinolin-2-ones as gametocytocidal antimalarial agents

Novel imidazo[4,5-c]quinolin-2-ones were synthesized and evaluated in asexual blood stage and late stage gametocyte assays of Plasmodium falciparum, a major causative agent of malaria. The design of these compounds is based on a recently identified lead compound from a high throughput screen. A concise synthesis was developed that allowed for generation of analogues with substitution around both the quinoline and imidazolidinone rings. Through structure-activity relationship studies, a number of potent compounds were identified that possessed excellent antimalarial activity against both the asexual and sexual stages with minimal cytotoxicity in mammalian cells. This is the first Letter describing SAR and gametocytocidal activity of imidazo[4,5-c]quinolin-2-ones, a new lead series for malaria treatment and prevention.

Repurposing strategies for tropical disease drug discovery

Neglected tropical diseases (NTDs) and other diseases of the developing world, such as malaria, attract research investments that are disproportionately low compared to their impact on human health worldwide. Therefore, pragmatic methods for launching new drug discovery programs have emerged that repurpose existing chemical matter as new drugs or new starting points for optimization. In this Digest we describe applications of different repurposing approaches for NTDs, and provide a means by which these approaches may be differentiated from each other. These include drug repurposing, target repurposing, target class repurposing, and lead repurposing.

Identification of "Preferred" Human Kinase Inhibitors for Sleeping Sickness Lead Discovery. Are Some Kinases Better than Others for Inhibitor Repurposing?

A kinase-targeting cell-based high-throughput screen (HTS) against Trypanosoma brucei was recently reported, and this screening set included the Published Kinase Inhibitor Set (PKIS). From the PKIS was identified 53 compounds with pEC₅₀ ≥ 6. Utilizing the published data available for the PKIS, a statistical analysis of these active antiparasitic compounds was performed, allowing identification of a set of human kinases having inhibitors that show a high likelihood for blocking T. brucei cellular proliferation in vitro. This observation was confirmed by testing other established inhibitors of these human kinases and by mining past screening campaigns at GlaxoSmithKline. Overall, although the parasite targets of action are not known, inhibitors of this set of human kinases displayed an enhanced hit rate relative to a random kinase-targeting HTS campaign, suggesting that repurposing efforts should focus primarily on inhibitors of these specific human kinases. We therefore term this statistical analysis-driven approach “preferred lead repurposing”.

Synthesis and anti-cancer activity of 1,4-disubstituted imidazo[4,5-c]quinolines

Synthesis of 4-substituted imidazo[4,5-c]quinolines using a Yb(OTf)₃ catalyzed modified Pictet–Spengler reaction as the key final step.

Protozoan Parasite Growth Inhibitors Discovered by Cross-Screening Yield Potent Scaffolds for Lead Discovery

Tropical protozoal infections are a significant cause of morbidity and mortality worldwide; four in particular (human African trypanosomiasis (HAT), Chagas disease, cutaneous leishmaniasis, and malaria) have an estimated combined burden of over 87 million disability-adjusted life years. New drugs are needed for each of these diseases. Building on the previous identification of NEU-617 (1) as a potent and nontoxic inhibitor of proliferation for the HAT pathogen (Trypanosoma brucei), we have now tested this class of analogs against other protozoal species: T. cruzi (Chagas disease), Leishmania major (cutaneous leishmaniasis), and Plasmodium falciparum (malaria). Based on hits identified in this screening campaign, we describe the preparation of several replacements for the quinazoline scaffold and report these inhibitors’ biological activities against these parasites. In doing this, we have identified several potent proliferation inhibitors for each pathogen, such as 4-((3-chloro-4-((3-fluorobenzyl)oxy)phenyl)amino)-6-(4-((4-methyl-1,4-diazepan-1-yl)sulfonyl)phenyl)quinoline-3-carbonitrile (NEU-924, 83) for T. cruzi and N-(3-chloro-4-((3-fluorobenzyl)oxy)phenyl)-7-(4-((4-methyl-1,4-diazepan-1-yl)sulfonyl)phenyl)cinnolin-4-amine (NEU-1017, 68) for L. major and P. falciparum.

EVALUATION OF AROMATIC 6-SUBSTITUTED THIENOPYRIMIDINES AS SCAFFOLDS AGAINST PARASITES THAT CAUSE TRYPANOSOMIASIS, LEISHMANIASIS, AND MALARIA

Target repurposing is a proven method for finding new lead compounds that target Trypanosoma brucei, the causative agent of human African trypanosomiasis. Due to the recent discovery of a lapatinib-derived analog 2 with excellent potency against T. brucei (EC₅₀ = 42 nM) and selectivity over human host cells, we have explored other classes of human tyrosine kinase inhibitor scaffolds in order to expand the range of chemotypes for pursuit. Following library expansion, we found compound 11e to have an EC₅₀ of 84 nM against T. brucei cells while maintaining selectivity over human hepatocytes. In addition, the library was tested against causative agents of Chagas' disease, leishmaniasis, and malaria. Two analogs with sub-micromolar potencies for T. cruzi (4j) and Plasmodium falciparum (11j) were discovered, along with an analog with considerable potency against Leishmania major amastigotes (4e). Besides identifying new and potent protozoan growth inhibitors, these data highlight the value of concurrent screening of a chemical library against different protozoan parasites.

Identification and characterization of hundreds of potent and selective inhibitors of Trypanosoma brucei growth from a kinase-targeted library screening campaign

In the interest of identification of new kinase-targeting chemotypes for target and pathway analysis and drug discovery in Trypanosomal brucei, a high-throughput screen of 42,444 focused inhibitors from the GlaxoSmithKline screening collection was performed against parasite cell cultures and counter-screened against human hepatocarcinoma (HepG2) cells. In this way, we have identified 797 sub-micromolar inhibitors of T. brucei growth that are at least 100-fold selective over HepG2 cells. Importantly, 242 of these hit compounds acted rapidly in inhibiting cellular growth, 137 showed rapid cidality. A variety of in silico and in vitro physicochemical and drug metabolism properties were assessed, and human kinase selectivity data were obtained, and, based on these data, we prioritized three compounds for pharmacokinetic assessment and demonstrated parasitological cure of a murine bloodstream infection of T. brucei rhodesiense with one of these compounds (NEU-1053). This work represents a successful implementation of a unique industrial-academic collaboration model aimed at identification of high quality inhibitors that will provide the parasitology community with chemical matter that can be utilized to develop kinase-targeting tool compounds. Furthermore these results are expected to provide rich starting points for discovery of kinase-targeting tool compounds for T. brucei, and new HAT therapeutics discovery programs.

Human African trypanosomiasis, or sleeping sickness, affects 10,000 patients annually, yet current drugs for this disease are poor, with high toxicity and inconvenient dosing requirements. Trypanosoma brucei, the parasite that causes sleeping sickness, is sensitive to a class of compounds called kinase inhibitors, and our project was aimed at identifying kinase-targeting compounds that rapidly and irreversibly inhibit parasite growth. This was accomplished by high-throughput screening of over 42,000 compounds, which resulted in identification of 797 potent inhibitors of parasite growth that are non-toxic to human cells. These inhibitors were studied for the speed of their effects and reversibility of growth inhibition, and were grouped on the basis of chemical structure similarity. One compound was shown to cure mice from a bloodstream of infection of T. brucei. These compounds can now be utilized by the research community as starting points for new drug discovery, and also as tool compounds for understanding the function of kinases in T. brucei.