Potentiation of rifampin activity in a mouse model of tuberculosis by activation of host transcription factor EB.

Efforts at host-directed therapy of tuberculosis have produced little control of the disease in experimental animals to date. This is not surprising, given that few specific host targets have been validated, and reciprocally, many of the compounds tested potentially impact multiple targets with both beneficial and detrimental consequences. This puts a premium on identifying appropriate molecular targets and subjecting them to more selective modulation. We discovered an aminopyrimidine small molecule, 2062, that had no direct antimycobacterial activity, but synergized with rifampin to reduce bacterial burden in Mtb infected macrophages and mice and also dampened lung immunopathology. We used 2062 and its inactive congeners as tool compounds to identify host targets. By biochemical, pharmacologic, transcriptomic and genetic approaches, we found that 2062's beneficial effects on Mtb control and clearance in macrophages and in mice are associated with activation of transcription factor EB via an organellar stress response. 2062-dependent TFEB activation led to improved autophagy, lysosomal acidification and lysosomal degradation, promoting bacterial clearance in macrophages. Deletion of TFEB resulted in the loss of IFNγ-dependent control of Mtb replication in macrophages. 2062 also targeted multiple kinases, such as PIKfyve, VPS34, JAKs and Tyk2, whose inhibition likely limited 2062's efficacy in vivo. These findings support a search for selective activators of TFEB for HDT of TB.

Evaluation of Alitretinoin for the Treatment of Mycosis Fungoides and Sézary Syndrome.

BACKGROUND: Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common subtypes of cutaneous T-cell lymphoma (CTCL). There is currently no cure for CTCL, and treatment is aimed at limiting disease progression. This study evaluated the efficacy and tolerability of alitretinoin in CTCL management. METHODS: A retrospective, multicenter study was conducted on CTCL patients treated with alitretinoin as a primary agent or in combination with standard therapies. RESULTS: Forty-eight patients with MF (n = 40) and SS (n = 8) with a median age of 59.7 years (±14.3) were eligible for study inclusion. Treatment response data were evaluated in 40 patients and safety in 42 patients. 40.0% of the patients had early-stage, 43.8% had advanced-stage CTCL, and in 16.7% of patients there was insufficient information for staging. 40.0% (16/40) of the patients achieved a complete or partial response, whereas 47.5% (19/40) achieved stable disease, 12.5% (5/40) had progressive disease, and there were no cases of disease relapses in responders. Both early and advanced stages of CTCL were responsive to alitretinoin as a primary or combined modality. Alitretinoin was well tolerated, and 64.3% (27/42) of patients did not report any side effects. The most commonly observed side effect was hypertriglyceridemia. CONCLUSIONS: This retrospective analysis supports the efficacy and safety of alitretinoin in clearing skin disease and preventing disease progression in CTCL as a monotherapy or in combination with standard therapies.

Investigating Sulfoxide-to-Sulfone Conversion as a Prodrug Strategy for a Phosphatidylinositol 4-Kinase Inhibitor in a Humanized Mouse Model of Malaria.

The in vivo antimalarial efficacies of two phosphatidylinositol 4-kinase (PI4K) inhibitors, a 3,5-diaryl-2-aminopyrazine sulfoxide and its corresponding sulfone metabolite, were evaluated in the NOD-scid IL2Rγnull (NSG) murine malaria disease model of Plasmodium falciparum infection. We hypothesized that the sulfoxide would serve as a more soluble prodrug for the sulfone, which would lead to improved drug exposure with oral dosing. Both compounds had similar efficacy (90% effective dose [ED90], 0.1 mg kg-1 of body weight) across a quadruple-dose regimen. Pharmacokinetic profiling revealed rapid sulfoxide clearance via conversion to sulfone, with sulfone identified as the major active metabolite. When the sulfoxide was dosed, the exposure of the sulfone achieved was as much as 2.9-fold higher than when the sulfone was directly dosed, thereby demonstrating that the sulfoxide served as an effective prodrug for the treatment of malaria.

UCT943, a Next-Generation Plasmodium falciparum PI4K Inhibitor Preclinical Candidate for the Treatment of Malaria.

The 2-aminopyridine MMV048 was the first drug candidate inhibiting Plasmodium phosphatidylinositol 4-kinase (PI4K), a novel drug target for malaria, to enter clinical development. In an effort to identify the next generation of PI4K inhibitors, the series was optimized to improve properties such as solubility and antiplasmodial potency across the parasite life cycle, leading to the 2-aminopyrazine UCT943. The compound displayed higher asexual blood stage, transmission-blocking, and liver stage activities than MMV048 and was more potent against resistant Plasmodium falciparum and Plasmodium vivax clinical isolates. Excellent in vitro antiplasmodial activity translated into high efficacy in Plasmodium berghei and humanized P. falciparum NOD-scid IL-2Rγ null mouse models. The high passive permeability and high aqueous solubility of UCT943, combined with low to moderate in vivo intrinsic clearance, resulted in sustained exposure and high bioavailability in preclinical species. In addition, the predicted human dose for a curative single administration using monkey and dog pharmacokinetics was low, ranging from 50 to 80 mg. As a next-generation Plasmodium PI4K inhibitor, UCT943, based on the combined preclinical data, has the potential to form part of a single-exposure radical cure and prophylaxis (SERCaP) to treat, prevent, and block the transmission of malaria.

Potent Plasmodium falciparum gametocytocidal compounds identified by exploring the kinase inhibitor chemical space for dual active antimalarials.

Objectives: Novel chemical tools to eliminate malaria should ideally target both the asexual parasites and transmissible gametocytes. Several imidazopyridazines (IMPs) and 2-aminopyridines (2-APs) have been described as potent antimalarial candidates targeting lipid kinases. However, these have not been extensively explored for stage-specific inhibition of gametocytes in Plasmodium falciparum parasites. Here we provide an in-depth evaluation of the gametocytocidal activity of compounds from these chemotypes and identify novel starting points for dual-acting antimalarials. Methods: We evaluated compounds against P. falciparum gametocytes using several assay platforms for cross-validation and stringently identified hits that were further profiled for stage specificity, speed of action and ex vivo efficacy. Physicochemical feature extraction and chemogenomic fingerprinting were applied to explore the kinase inhibition susceptibility profile. Results: We identified 34 compounds with submicromolar activity against late stage gametocytes, validated across several assay platforms. Of these, 12 were potent at <100 nM (8 were IMPs and 4 were 2-APs) and were also active against early stage gametocytes and asexual parasites, with >1000-fold selectivity towards the parasite over mammalian cells. Front-runner compounds targeted mature gametocytes within 48 h and blocked transmission to mosquitoes. The resultant chemogenomic fingerprint of parasites treated with the lead compounds revealed the importance of targeting kinases in asexual parasites and gametocytes. Conclusions: This study encompasses an in-depth evaluation of the kinase inhibitor space for gametocytocidal activity. Potent lead compounds have enticing dual activities and highlight the importance of targeting the kinase superfamily in malaria elimination strategies.

Synthesis and biological evaluation of aryl-oxadiazoles as inhibitors of Mycobacterium tuberculosis.

Despite increased research efforts to find new treatments for tuberculosis in recent decades, compounds with novel mechanisms of action are still required. We previously identified a series of novel aryl-oxadiazoles with anti-tubercular activity specific for bacteria using butyrate as a carbon source. We explored the structure activity relationship of this series. Structural modifications were performed in all domains to improve potency and physico-chemical properties. A number of compounds displayed sub-micromolar activity against M. tuberculosis utilizing butyrate, but not glucose as the carbon source. Compounds showed no or low cytotoxicity against eukaryotic cells. Three compounds were profiled in mouse pharmacokinetic studies. Plasma clearance was low to moderate but oral exposure suggested solubility-limited drug absorption in addition to first pass metabolism. The presence of a basic nitrogen in the linker slightly increased solubility, and salt formation optimized aqueous solubility. Our findings suggest that the 1,3,4-oxadiazoles are useful tools and warrant further investigation.

Aminopyrazolo[1,5-a]pyrimidines as potential inhibitors of Mycobacterium tuberculosis: Structure activity relationships and ADME characterization.

Whole-cell high-throughput screening of a diverse SoftFocus library against Mycobacterium tuberculosis (Mtb) generated a novel aminopyrazolo[1,5-a]pyrimidine hit series. The synthesis and structure activity relationship studies identified compounds with potent antimycobacterial activity. The SAR of over 140 compounds shows that the 2-pyridylmethylamine moiety at the C-7 position of the pyrazolopyrimidine scaffold was important for Mtb activity, whereas the C-3 position offered a higher degree of flexibility. The series was also profiled for in vitro cytotoxicity and microsomal metabolic stability as well as physicochemical properties. Consequently liabilities to be addressed in a future lead optimization campaign have been identified.

Fast in vitro methods to determine the speed of action and the stage-specificity of anti-malarials in Plasmodium falciparum.

BACKGROUND: Recent whole cell in vitro screening campaigns identified thousands of compounds that are active against asexual blood stages of Plasmodium falciparum at submicromolar concentrations. These hits have been made available to the public, providing many novel chemical starting points for anti-malarial drug discovery programmes. Knowing which of these hits are fast-acting compounds is of great interest. Firstly, a fast action will ensure rapid relief of symptoms for the patient. Secondly, by rapidly reducing the parasitaemia, this could minimize the occurrence of mutations leading to new drug resistance mechanisms.An in vitro assay that provides information about the speed of action of test compounds has been developed by researchers at GlaxoSmithKline (GSK) in Spain. This assay also provides an in vitro measure for the ratio between parasitaemia at the onset of drug treatment and after one intra-erythrocytic cycle (parasite reduction ratio, PRR). Both parameters are needed to determine in vitro killing rates of anti-malarial compounds. A drawback of the killing rate assay is that it takes a month to obtain first results. METHODS: The approach described in the present study is focused only on the speed of action of anti-malarials. This has the advantage that initial results can be achieved within 4-7 working days, which helps to distinguish between fast and slow-acting compounds relatively quickly. It is expected that this new assay can be used as a filter in the early drug discovery phase, which will reduce the number of compounds progressing to secondary, more time-consuming assays like the killing rate assay. RESULTS: The speed of action of a selection of seven anti-malarial compounds was measured with two independent experimental procedures using modifications of the standard [3H]hypoxanthine incorporation assay. Depending on the outcome of both assays, the tested compounds were classified as either fast or non-fast-acting. CONCLUSION: The results obtained for the anti-malarials chloroquine, artesunate, atovaquone, and pyrimethamine are consistent with previous observations, suggesting the methodology is a valid way to rapidly identify fast-acting anti-malarial compounds. Another advantage of the approach is its ability to discriminate between static or cidal compound effects.

The synthesis and preclinical evaluation in rhesus monkey of [¹8F]MK-6577 and [¹¹C]CMPyPB glycine transporter 1 positron emission tomography radiotracers.

Two positron emission tomography radiotracers for the glycine transporter 1 (GlyT1) are reported here. Each radiotracer is a propylsulfonamide-containing benzamide and was labeled with either carbon-11 or fluorine-18. [¹¹C]CMPyPB was synthesized by the alkylation of a 3-hydroxypyridine precursor using [¹¹C]MeI, and [¹8F]MK-6577 was synthesized by a nucleophilic aromatic substitution reaction using a 2-chloropyridine precursor. Each tracer shows good uptake into rhesus monkey brain with the expected distribution of highest uptake in the pons, thalamus, and cerebellum and lower uptake in the striatum and gray matter of the frontal cortex. In vivo blockade and chase studies of [¹8F]MK-6577 showed a large specific signal and reversible binding. In vitro autoradiographic studies with [¹8F]MK-6577 showed a large specific signal in both rhesus monkey and human brain slices and a distribution consistent with the in vivo results and those reported in the literature. In vivo metabolism studies in rhesus monkeys demonstrated that only more-polar metabolites are formed for each tracer. Of these two tracers, [¹8F]MK-6577 was more extensively characterized and is a promising clinical positron emission tomography tracer for imaging GlyT1 and for measuring GlyT1 occupancy of therapeutic compounds.

Benzotriazinone and benzopyrimidinone derivatives as potent positive allosteric AMPA receptor modulators.

AMPA receptors (AMPARs) have been demonstrated to be an important therapeutic CNS target. A series of substituted benzotriazinone and benzopyrimidinone derivatives were prepared with the aim to improve in vivo activity over the previously reported bis-benzoxazinone based AMPAKINE series from our laboratory. These compounds were shown to be potent, positive allosteric AMPAR modulators that have better in vivo activity and improved metabolic stability over the analogous benzoxazinone derivatives.

Benzobistriazinones and related heterocyclic ring systems as potent, orally bioavailable positive allosteric AMPA receptor modulators.

AMPA receptors (AMPARs) are an important therapeutic target in the CNS. A series of substituted benzobistriazinone, benzobispyrimidinone and related derivatives have been prepared with high potency and selectivity for the allosteric binding site of AMPARs. Further improvements have been made to previously reported series of positive AMPAR modulators and these compounds exhibit excellent in vivo activity and improved in vivo metabolic stability with up to 100% oral bioavailability in rat.

Benzoheterocyclic Oxime Carbamates Active against Mycobacterium tuberculosis: Synthesis, Structure-Activity Relationship, Metabolism, and Biology Triaging.

Screening of a library of small polar molecules against Mycobacterium tuberculosis (Mtb) led to the identification of a potent benzoheterocyclic oxime carbamate hit series. This series was subjected to medicinal chemistry progression underpinned by structure-activity relationship studies toward identifying a compound for proof-of-concept studies and defining a lead optimization strategy. Carbamate and free oxime frontrunner compounds with good stability in liver microsomes and no hERG channel inhibition liability were identified and evaluated in vivo for pharmacokinetic properties. Mtb-mediated permeation and metabolism studies revealed that the carbamates were acting as prodrugs. Toward mechanism of action elucidation, selected compounds were tested in biology triage assays to assess their activity against known promiscuous targets. Taken together, these data suggest a novel yet unknown mode of action for these antitubercular hits.

Identification and Profiling of a Novel Diazaspiro[3.4]octane Chemical Series Active against Multiple Stages of the Human Malaria Parasite Plasmodium falciparum and Optimization Efforts.

A novel diazaspiro[3.4]octane series was identified from a Plasmodium falciparum whole-cell high-throughput screening campaign. Hits displayed activity against multiple stages of the parasite lifecycle, which together with a novel sp3-rich scaffold provided an attractive starting point for a hit-to-lead medicinal chemistry optimization and biological profiling program. Structure-activity-relationship studies led to the identification of compounds that showed low nanomolar asexual blood-stage activity (<50 nM) together with strong gametocyte sterilizing properties that translated to transmission-blocking activity in the standard membrane feeding assay. Mechanistic studies through resistance selection with one of the analogues followed by whole-genome sequencing implicated the P. falciparum cyclic amine resistance locus in the mode of resistance.

Lerisetron Analogues with Antimalarial Properties: Synthesis, Structure-Activity Relationship Studies, and Biological Assessment.

A phenotypic whole cell high-throughput screen against the asexual blood and liver stages of the malaria parasite identified a benzimidazole chemical series. Among the hits were the antiemetic benzimidazole drug Lerisetron 1 (IC50 NF54 = 0.81 µM) and its methyl-substituted analogue 2 (IC50 NF54 = 0.098 µM). A medicinal chemistry hit to lead effort led to the identification of chloro-substituted analogue 3 with high potency against the drug-sensitive NF54 (IC50 NF54 = 0.062 µM) and multidrug-resistant K1 (IC50 K1 = 0.054 µM) strains of the human malaria parasite Plasmodium falciparum. Compounds 2 and 3 gratifyingly showed in vivo efficacy in both Plasmodium berghei and P. falciparum mouse models of malaria. Cardiotoxicity risk as expressed in strong inhibition of the human ether-a-go-go-related gene (hERG) potassium channel was identified as a major liability to address. This led to the synthesis and biological assessment of around 60 analogues from which several compounds with improved antiplasmodial potency, relative to the lead compound 3, were identified.

Identification of 2,4-Disubstituted Imidazopyridines as Hemozoin Formation Inhibitors with Fast-Killing Kinetics and In Vivo Efficacy in the Plasmodium falciparum NSG Mouse Model.

A series of 2,4-disubstituted imidazopyridines, originating from a SoftFocus Kinase library, was identified from a high throughput phenotypic screen against the human malaria parasite Plasmodium falciparum. Hit compounds showed moderate asexual blood stage activity. During lead optimization, several issues were flagged such as cross-resistance against the multidrug-resistant K1 strain, in vitro cytotoxicity, and cardiotoxicity and were addressed through structure-activity and structure-property relationship studies. Pharmacokinetic properties were assessed in mice for compounds showing desirable in vitro activity, a selectivity window over cytotoxicity, and microsomal metabolic stability. Frontrunner compound 37 showed good exposure in mice combined with good in vitro activity against the malaria parasite, which translated into in vivo efficacy in the P. falciparum NOD-scid IL-2Rγnull (NSG) mouse model. Preliminary mechanistic studies suggest inhibition of hemozoin formation as a contributing mode of action.

Optimisation of a series of potent, selective and orally bioavailable GlyT1 inhibitors.

A series of heterocyclic sulfonamides have been developed which are potent and selective inhibitors of hGlyT1. SAR studies to optimise the in vitro and in vivo properties are described. Optimisation of the central scaffold resulted in cyclohexane sulfones 28 and 29, which have good PK properties and show promise for further development.

Antimalarial Lead-Optimization Studies on a 2,6-Imidazopyridine Series within a Constrained Chemical Space To Circumvent Atypical Dose-Response Curves against Multidrug Resistant Parasite Strains.

A lead-optimization program around a 2,6-imidazopyridine scaffold was initiated based on the two early lead compounds, 1 and 2, that were shown to be efficacious in an in vivo humanized Plasmodium falciparum NODscidIL2Rγnull mouse malaria infection model. The observation of atypical dose-response curves when some compounds were tested against multidrug resistant malaria parasite strains guided the optimization process to define a chemical space that led to typical sigmoidal dose-response and complete kill of multidrug resistant parasites. After a structure and property analysis identified such a chemical space, compounds were prepared that displayed suitable activity, ADME, and safety profiles with respect to cytotoxicity and hERG inhibition.

Identification, Characterization, and Optimization of 2,8-Disubstituted-1,5-naphthyridines as Novel Plasmodium falciparum Phosphatidylinositol-4-kinase Inhibitors with in Vivo Efficacy in a Humanized Mouse Model of Malaria.

A novel 2,8-disubstituted-1,5-naphthyridine hit compound stemming from the open access Medicines for Malaria Venture Pathogen Box formed a basis for a hit-to-lead medicinal chemistry program. Structure-activity relationship investigations resulted in compounds with potent antiplasmodial activity against both chloroquine sensitive (NF54) and multidrug resistant (K1) strains of the human malaria parasite Plasmodium falciparum. In the humanized P. falciparum mouse efficacy model, one of the frontrunner compounds showed in vivo efficacy at an oral dose of 4 × 50 mg·kg-1. In vitro mode-of-action studies revealed Plasmodium falciparum phosphatidylinositol-4-kinase as the target.

Identification of Fast-Acting 2,6-Disubstituted Imidazopyridines That Are Efficacious in the in Vivo Humanized Plasmodium falciparum NODscidIL2Rγ null Mouse Model of Malaria.

Optimization of a chemical series originating from whole-cell phenotypic screening against the human malaria parasite, Plasmodium falciparum, led to the identification of two promising 2,6-disubstituted imidazopyridine compounds, 43 and 74. These compounds exhibited potent activity against asexual blood stage parasites that, together with their in vitro absorption, distribution, metabolism, and excretion (ADME) properties, translated to in vivo efficacy with clearance of parasites in the PfSCID mouse model for malaria within 48 h of treatment.