ß-Carboline-3-carboxamide Antimalarials: Structure-Activity Relationship, ADME-Tox Studies, and Resistance Profiling.

The development of parasite resistance to both artemisinin derivatives and their partner drugs jeopardizes the effectiveness of the artemisinin combination therapy. Thus, the discovery of new antimalarial drugs, with new mechanisms of action, is urgently needed. We recently disclosed that ß-carboline 1a was orally efficacious in Plasmodium berghei-infected mice and that it showed low cross-resistance between susceptible Plasmodium falciparum and four different drug-resistant strains. In this report, we describe the synthesis and in vitro antimalarial evaluation of 91 new derivatives of 1a. The asexual blood stage growth inhibition data show a clear preference for a 3,4-dihalogenated, 3,5-dihalogenated, 3,4,5-trichloro-, or 4-trifluoromethyphenyl ring at the C1-position. The most potent compound, 3,4,5-trichlorophenyl-substituted 42a, is twice as potent as 1a. Six potent analogues were assessed for their drug-like properties, and four of these were subjected to in vitro barcoded cross-resistance profiling. Compounds 1a, 1m, 42a, and 42m showed no cross-resistance to 32 resistance mutations on the Dd2 genetic background and 10 resistance mutations on the 3D7 genetic background. These data suggest that compounds in this scaffold possess a novel mechanism of antimalarial action.

Exploration and characterization of the antimalarial activity of cyclopropyl carboxamides that target the mitochondrial protein, cytochrome b.

Drug resistance against antimalarials is rendering them increasingly ineffective and so there is a need for the development of new antimalarials. To discover new antimalarial chemotypes a phenotypic screen of the Janssen Jumpstarter library against the P. falciparum asexual stage was undertaken, uncovering the cyclopropyl carboxamide structural hit class. Structure-activity analysis revealed that each structural moiety was largely resistant to change, although small changes led to the frontrunner compound, WJM280, which has potent asexual stage activity (EC50 40 nM) and no human cell cytotoxicity. Forward genetics uncovered that cyclopropyl carboxamide resistant parasites have mutations and an amplification in the cytochrome b gene. Cytochrome b was then verified as the target with profiling against cytochrome b drug-resistant parasites and a mitochondrial oxygen consumption assay. Accordingly, the cyclopropyl carboxamide class was shown to have slow-acting asexual stage activity and activity against male gametes and exoerythrocytic forms. Enhancing metabolic stability to attain efficacy in malaria mouse models remains a challenge in the future development of this antimalarial chemotype.

Lactam Truncation Yields a Dihydroquinazolinone Scaffold with Potent Antimalarial Activity that Targets PfATP4.

The emergence of resistance against current antimalarial treatments has necessitated the need for the development of novel antimalarial chemotypes. Toward this goal, we recently optimised the antimalarial activity of the dihydroquinazolinone scaffold and showed it targeted PfATP4. Here, we deconstruct the lactam moiety of the tricyclic dihydroquinazolinone scaffold and investigate the structure-activity relationship of the truncated scaffold. It was shown that SAR between scaffolds was largely transferrable and generated analogues with potent asexual stage activity. Evaluation of the truncated analogues against PfATP4 mutant drug resistant parasite strains and in assays measuring PfATP4-associated ATPase activity demonstrated retention of PfATP4 as the molecular target. Analogues exhibited activity against both male and female gametes and multidrug resistant parasites. Limited efficacy of analogues in a P. berghei asexual stage mouse model was attributed to their moderate metabolic stability and low aqueous stability. Further development is required to address these attributes toward the potential use of the dihydroquinazolinone class in a curative and transmission blocking combination antimalarial therapy.

Property and Activity Refinement of Dihydroquinazolinone-3-carboxamides as Orally Efficacious Antimalarials that Target PfATP4.

To contribute to the global effort to develop new antimalarial therapies, we previously disclosed initial findings on the optimization of the dihydroquinazolinone-3-carboxamide class that targets PfATP4. Here we report on refining the aqueous solubility and metabolic stability to improve the pharmacokinetic profile and consequently in vivo efficacy. We show that the incorporation of heterocycle systems in the 8-position of the scaffold was found to provide the greatest attainable balance between parasite activity, aqueous solubility, and metabolic stability. Optimized analogs, including the frontrunner compound S-WJM992, were shown to inhibit PfATP4-associated Na+-ATPase activity, gave rise to a metabolic signature consistent with PfATP4 inhibition, and displayed altered activities against parasites with mutations in PfATP4. Finally, S-WJM992 showed appreciable efficacy in a malaria mouse model and blocked gamete development preventing transmission to mosquitoes. Importantly, further optimization of the dihydroquinazolinone class is required to deliver a candidate with improved pharmacokinetic and risk of resistance profiles.

The Role of the Flexor Hallucis Longus in the Treatment of the Painful Hallux Metatarsophalangeal Joint.

BACKGROUND: Pain in the hallux metatarsophalangeal joint (MTPJ) is very common, yet the underlying etiology remains unknown. Previous clinical research and biomechanical research has implicated stenosing flexor hallucis longus (FHL) tendonitis as a possible cause. The hypothesis of this study was that treatment solely focusing on alleviating restricted FHL excursion would be beneficial in patients with hallux MTPJ pain. METHODS: This is a retrospective study of those treated in the Foot & Ankle Division between January 2009, and December 2018, who were diagnosed with FHL tendonitis with associated pain in the hallux MTPJ. Demographics, comorbidities, examination findings, imaging results, pain scores, treatment instituted, and outcome was obtained from the electronic medical record. The primary outcome was the improvement in the pain score (visual analog scale [VAS]). The surgical patients were included if their procedure was solely related to the FHL (posteromedial ankle release ± os trigonum resection). The decision to have surgery was analyzed by univariate and multivariable statistics using demographics, comorbidities, and clinical findings as potential factors (P < .05). RESULTS: In 75% (59 of 79 feet), nonoperative treatment of FHL stenosis resulted in a decrease in pain scores that the patients felt was satisfactory. The operative group that had an FHL release showed decreased pain in 90% (18 of 20 feet). Multivariable analysis identified the need for immobilization (OR 9.8, 95% CI 1.8-55.2, P = .009), participating in athletics (OR 8.7, 95% CI 1.8-42.2, P = .007), and higher initial VAS (OR 1.7, 95% CI 1.3-2.3, P < .001) as being associated with the decision for surgery. CONCLUSION: Previous biomechanical studies have suggested that stenosing FHL synovitis can cause increased intraarticular loading in the hallux MTPJ. The current clinical study supports this hypothesis, demonstrating that treatment focused on relieving restricted FHL excursion can ameliorate pain in the hallux MTPJ in select cases.

Optimization of pyrazolopyridine 4-carboxamides with potent antimalarial activity for which resistance is associated with the P. falciparum transporter ABCI3.

Emerging resistance to current antimalarials is reducing their effectiveness and therefore there is a need to develop new antimalarial therapies. Toward this goal, high throughput screens against the P. falciparum asexual parasite identified the pyrazolopyridine 4-carboxamide scaffold. Structure-activity relationship analysis of this chemotype defined that the N1-tert-butyl group and aliphatic foliage in the 3- and 6-positions were necessary for activity, while the inclusion of a 7'-aza-benzomorpholine on the 4-carboxamide motif resulted in potent anti-parasitic activity and increased aqueous solubility. A previous report that resistance to the pyrazolopyridine class is associated with the ABCI3 transporter was confirmed, with pyrazolopyridine 4-carboxamides showing an increase in potency against parasites when the ABCI3 transporter was knocked down. The low metabolic stability intrinsic to the pyrazolopyridine scaffold and the slow rate by which the compounds kill asexual parasites resulted in poor performance in a P. berghei asexual blood stage mouse model. Lowering the risk of resistance and mitigating the metabolic stability and cytochrome P450 inhibition will be challenges in the future development of the pyrazolopyrimidine antimalarial class.

Activity refinement of aryl amino acetamides that target the P. falciparum STAR-related lipid transfer 1 protein.

Malaria is a devastating disease that causes significant morbidity worldwide. The development of new antimalarial chemotypes is urgently needed because of the emergence of resistance to frontline therapies. Independent phenotypic screening campaigns against the Plasmodium asexual parasite, including our own, identified the aryl amino acetamide hit scaffold. In a prior study, we identified the STAR-related lipid transfer protein (PfSTART1) as the molecular target of this antimalarial chemotype. In this study, we combined structural elements from the different aryl acetamide hit subtypes and explored the structure-activity relationship. It was shown that the inclusion of an endocyclic nitrogen, to generate the tool compound WJM-715, improved aqueous solubility and modestly improved metabolic stability in rat hepatocytes. Metabolic stability in human liver microsomes remains a challenge for future development of the aryl acetamide class, which was underscored by modest systemic exposure and a short half-life in mice. The optimized aryl acetamide analogs were cross resistant to parasites with mutations in PfSTART1, but not to other drug-resistant mutations, and showed potent binding to recombinant PfSTART1 by biophysical analysis, further supporting PfSTART1 as the likely molecular target. The optimized aryl acetamide analogue, WJM-715 will be a useful tool for further investigating the druggability of PfSTART1 across the lifecycle of the malaria parasite.

7-N-Substituted-3-oxadiazole Quinolones with Potent Antimalarial Activity Target the Cytochrome bc1 Complex.

The development of new antimalarials is required because of the threat of resistance to current antimalarial therapies. To discover new antimalarial chemotypes, we screened the Janssen Jumpstarter library against the P. falciparum asexual parasite and identified the 7-N-substituted-3-oxadiazole quinolone hit class. We established the structure-activity relationship and optimized the antimalarial potency. The optimized analog WJM228 (17) showed robust metabolic stability in vitro, although the aqueous solubility was limited. Forward genetic resistance studies uncovered that WJM228 targets the Qo site of cytochrome b (cyt b), an important component of the mitochondrial electron transport chain (ETC) that is essential for pyrimidine biosynthesis and an established antimalarial target. Profiling against drug-resistant parasites confirmed that WJM228 confers resistance to the Qo site but not Qi site mutations, and in a biosensor assay, it was shown to impact the ETC via inhibition of cyt b. Consistent with other cyt b targeted antimalarials, WJM228 prevented pre-erythrocytic parasite and male gamete development and reduced asexual parasitemia in a P. berghei mouse model of malaria. Correcting the limited aqueous solubility and the high susceptibility to cyt b Qo site resistant parasites found in the clinic will be major obstacles in the future development of the 3-oxadiazole quinolone antimalarial class.

Optimization of 2,3-Dihydroquinazolinone-3-carboxamides as Antimalarials Targeting PfATP4.

There is an urgent need to populate the antimalarial clinical portfolio with new candidates because of resistance against frontline antimalarials. To discover new antimalarial chemotypes, we performed a high-throughput screen of the Janssen Jumpstarter library against the Plasmodium falciparum asexual blood-stage parasite and identified the 2,3-dihydroquinazolinone-3-carboxamide scaffold. We defined the SAR and found that 8-substitution on the tricyclic ring system and 3-substitution of the exocyclic arene produced analogues with potent activity against asexual parasites equivalent to clinically used antimalarials. Resistance selection and profiling against drug-resistant parasite strains revealed that this antimalarial chemotype targets PfATP4. Dihydroquinazolinone analogues were shown to disrupt parasite Na+ homeostasis and affect parasite pH, exhibited a fast-to-moderate rate of asexual kill, and blocked gametogenesis, consistent with the phenotype of clinically used PfATP4 inhibitors. Finally, we observed that optimized frontrunner analogue WJM-921 demonstrates oral efficacy in a mouse model of malaria.

Phase 3 study evaluating the safety and efficacy of oteseconazole in the treatment of recurrent vulvovaginal candidiasis and acute vulvovaginal candidiasis infections.

BACKGROUND: Recurrent vulvovaginal candidiasis affects nearly 138 million women globally each year. In the United States, fluconazole is considered the standard of care for acute vulvovaginal candidiasis, but until recently there was no US Food and Drug Administration-approved drug for the treatment of recurrent vulvovaginal candidiasis. Oteseconazole is a novel oral selective inhibitor of fungal lanosterol demethylase (sterol 14α-demethylase cytochrome P450, an enzyme required for fungal growth) approved for the treatment of recurrent vulvovaginal candidiasis. OBJECTIVE: This study was conducted to evaluate the efficacy and safety of oral oteseconazole (VT-1161) in the prevention of recurrent culture-verified acute vulvovaginal candidiasis episodes through 50 weeks in participants with recurrent vulvovaginal candidiasis and to compare the efficacy of oteseconazole and fluconazole in the treatment of the presenting acute vulvovaginal candidiasis episode. STUDY DESIGN: Women and postmenarcheal girls aged ≥12 years with a history of recurrent vulvovaginal candidiasis (N=219) were enrolled at 38 US sites. Eligible participants presenting with an active vulvovaginal candidiasis infection entered an induction phase in which they were randomly assigned 2:1 to receive 600 mg oral oteseconazole on day 1 and 450 mg on day 2, with matching placebo capsules, or to 3 sequential 150-mg oral doses (once every 72 hours) of fluconazole, with matching placebo capsules. Following the 2-week induction phase, the 185 participants with resolved acute vulvovaginal candidiasis infection (a clinical signs and symptoms score of <3) entered the maintenance phase and received 150 mg of oteseconazole or placebo weekly for 11 weeks. Participants were observed for an additional 37 weeks. RESULTS: In the induction phase, oteseconazole was noninferior to fluconazole in the proportion of participants in the intent-to-treat population with resolved acute vulvovaginal candidiasis infection at the week 2 (day 14) test-of-cure visit, with 93.2% of participants on oteseconazole vs 95.8% on fluconazole achieving resolution. In the maintenance phase, oteseconazole was superior to placebo in the proportion of participants in the intent-to-treat population with ≥1 culture-verified acute vulvovaginal candidiasis episode through 50 weeks, 5.1% compared with 42.2%, respectively (P<.001). Overall, treatment-emergent adverse event rates were similar in both groups: 54% for participants who received oteseconazole in the induction and maintenance phases vs 64% for participants who received fluconazole in the induction phase and placebo in the maintenance phase. Most treatment-emergent adverse events in each group were mild or moderate, with 3.4% of treatment-emergent adverse events graded as severe or higher in the OTESECONAZOLE/oteseconazole group vs 4.2% in FLUCONAZOLE/placebo group. CONCLUSION: In participants with recurrent vulvovaginal candidiasis, oteseconazole was safe and efficacious in the treatment and prevention of recurrent acute vulvovaginal candidiasis episodes and was noninferior to vulvovaginal candidiasis standard-of-care fluconazole in the treatment of the presenting acute vulvovaginal candidiasis infection.

Reaction hijacking of tyrosine tRNA synthetase as a new whole-of-life-cycle antimalarial strategy.

Aminoacyl transfer RNA (tRNA) synthetases (aaRSs) are attractive drug targets, and we present class I and II aaRSs as previously unrecognized targets for adenosine 5'-monophosphate-mimicking nucleoside sulfamates. The target enzyme catalyzes the formation of an inhibitory amino acid-sulfamate conjugate through a reaction-hijacking mechanism. We identified adenosine 5'-sulfamate as a broad-specificity compound that hijacks a range of aaRSs and ML901 as a specific reagent a specific reagent that hijacks a single aaRS in the malaria parasite Plasmodium falciparum, namely tyrosine RS (PfYRS). ML901 exerts whole-life-cycle-killing activity with low nanomolar potency and single-dose efficacy in a mouse model of malaria. X-ray crystallographic studies of plasmodium and human YRSs reveal differential flexibility of a loop over the catalytic site that underpins differential susceptibility to reaction hijacking by ML901.

Efficacy and Safety of Oteseconazole in Recurrent Vulvovaginal Candidiasis.

BACKGROUND: Management of recurrent vulvovaginal candidiasis (RVVC) is an unmet clinical challenge without approved treatment in the United States. Oteseconazole is a novel oral selective inhibitor of fungal CYP51, designed to treat RVVC without off-target toxicities. VIOLET comprised two global, phase 3, multicenter, randomized, double-blind, placebo-controlled trials (CL-011 and CL-012). The primary objective was to evaluate oteseconazole efficacy through week 48. Key secondary objectives evaluated time to first recurrence, safety, and patient-reported outcomes. METHODS: Women with three or more symptomatic acute vulvovaginal candidiasis (VVC) episodes within the previous 12-month period, including the screening episode (in which the VVC episode cleared with fluconazole induction therapy), were randomly assigned 2:1 at baseline (maintenance phase) to 150 mg of oral oteseconazole daily for 7days and then once weekly for 11 weeks or to matching placebo for 12 weeks. Time-to-first-recurrence data were collected during the maintenance phase. Posttreatment follow-up was 36 weeks. RESULTS: Among 656 women (326 in CL-011 and 330 in CL-012), the averaged percentage of participants with one or more RVVC episodes through week 48 was 6.7% (range, 6.5 to 7.4%) in CL-011 and 3.9% (3.7 to 4.6%) in CL-012 in the oteseconazole groups versus 42.8% (41.3 to 45.0%) and 39.4% (38.0 to 42.6%) in the corresponding placebo groups (P<0.001). Among oteseconazole-treated participants in CL-011 and CL-012 who experienced an RVVC episode (n=22), the mean time to recurrence was 45.7 and 47.2 weeks versus 27.8 and 33.1 weeks for placebo-treated participants (n=84), respectively (hazard ratio [95% confidence interval], 0.11 [0.06 to 0.21] for CL-011 and 0.08 [0.04 to 0.17] for CL-012; P<0.001). Types and frequencies of treatment-emergent adverse events (TEAEs) were similar between groups in both trials, with no drug-related serious TEAEs or adverse effects on pregnancy outcomes, liver function, or QT interval. CONCLUSIONS: Oral oteseconazole was effective in preventing acute VVC recurrence and treating RVVC through week 48 in the CL-011 and CL-012 trials, with mostly mild TEAEs. (Funded by Mycovia Pharmaceuticals, Inc., ClinicalTrials.gov numbers, NCT03562156 for CL-011 and NCT03561701 for CL-012.)

Design of proteasome inhibitors with oral efficacy in vivo against Plasmodium falciparum and selectivity over the human proteasome.

The Plasmodium falciparum proteasome is a potential antimalarial drug target. We have identified a series of amino-amide boronates that are potent and specific inhibitors of the P. falciparum 20S proteasome (Pf20S) ß5 active site and that exhibit fast-acting antimalarial activity. They selectively inhibit the growth of P. falciparum compared with a human cell line and exhibit high potency against field isolates of P. falciparum and Plasmodium vivax They have a low propensity for development of resistance and possess liver stage and transmission-blocking activity. Exemplar compounds, MPI-5 and MPI-13, show potent activity against P. falciparum infections in a SCID mouse model with an oral dosing regimen that is well tolerated. We show that MPI-5 binds more strongly to Pf20S than to human constitutive 20S (Hs20Sc). Comparison of the cryo-electron microscopy (EM) structures of Pf20S and Hs20Sc in complex with MPI-5 and Pf20S in complex with the clinically used anti-cancer agent, bortezomib, reveal differences in binding modes that help to explain the selectivity. Together, this work provides insights into the 20S proteasome in P. falciparum, underpinning the design of potent and selective antimalarial proteasome inhibitors.

Optimisation of 2-(N-phenyl carboxamide) triazolopyrimidine antimalarials with moderate to slow acting erythrocytic stage activity.

Malaria is a devastating parasitic disease caused by parasites from the genus Plasmodium. Therapeutic resistance has been reported against all clinically available antimalarials, threatening our ability to control the disease and therefore there is an ongoing need for the development of novel antimalarials. Towards this goal, we identified the 2-(N-phenyl carboxamide) triazolopyrimidine class from a high throughput screen of the Janssen Jumpstarter library against the asexual stages of the P. falciparum parasite. Here we describe the structure activity relationship of the identified class and the optimisation of asexual stage activity while maintaining selectivity against the human HepG2 cell line. The most potent analogues from this study were shown to exhibit equipotent activity against P. falciparum multidrug resistant strains and P. knowlesi asexual parasites. Asexual stage phenotyping studies determined the triazolopyrimidine class arrests parasites at the trophozoite stage, but it is likely these parasites are still metabolically active until the second asexual cycle, and thus have a moderate to slow onset of action. Non-NADPH dependent degradation of the central carboxamide and low aqueous solubility was observed in in vitro ADME profiling. A significant challenge remains to correct these liabilities for further advancement of the 2-(N-phenyl carboxamide) triazolopyrimidine scaffold as a potential moderate to slow acting partner in a curative or prophylactic antimalarial treatment.

Scaffold-Hopping Strategy on a Series of Proteasome Inhibitors Led to a Preclinical Candidate for the Treatment of Visceral Leishmaniasis.

There is an urgent need for new treatments for visceral leishmaniasis (VL), a parasitic infection which impacts heavily large areas of East Africa, Asia, and South America. We previously reported on the discovery of GSK3494245/DDD01305143 (1) as a preclinical candidate for VL and, herein, we report on the medicinal chemistry program that led to its identification. A hit from a phenotypic screen was optimized to give a compound with in vivo efficacy, which was hampered by poor solubility and genotoxicity. The work on the original scaffold failed to lead to developable compounds, so an extensive scaffold-hopping exercise involving medicinal chemistry design, in silico profiling, and subsequent synthesis was utilized, leading to the preclinical candidate. The compound was shown to act via proteasome inhibition, and we report on the modeling of different scaffolds into a cryo-EM structure and the impact this has on our understanding of the series' structure-activity relationships.

Discovery of Potent and Fast-Acting Antimalarial Bis-1,2,4-triazines.

Novel 3,3'-disubstituted-5,5'-bi(1,2,4-triazine) compounds with potent in vitro activity against Plasmodium falciparum parasites were recently discovered. To improve the pharmacokinetic properties of the triazine derivatives, a new structure-activity relationship (SAR) investigation was initiated with a focus on enhancing the metabolic stability of lead compounds. These efforts led to the identification of second-generation highly potent antimalarial bis-triazines, exemplified by triazine 23, which exhibited significantly improved in vitro metabolic stability (8 and 42 µL/min/mg protein in human and mouse liver microsomes). The disubstituted triazine dimer 23 was also observed to suppress parasitemia in the Peters 4-day test with a mean ED50 value of 1.85 mg/kg/day and exhibited a fast-killing profile, revealing a new class of orally available antimalarial compounds of considerable interest.

A Randomized Phase 2 Study of VT-1161 for the Treatment of Acute Vulvovaginal Candidiasis.

BACKGROUND: Acute vulvovaginal candidiasis (VVC) is common among women, but current azole antifungal treatments are often associated with safety and resistance issues. VT-1161 (oteseconazole) is an oral agent with increased selectivity for fungal CYP51. In this phase 2 clinical study, we evaluated the efficacy and safety of VT-1161 vs fluconazole in participants with moderate to severe acute VVC. METHODS: Participants presenting with an acute episode of VVC (n = 55) were randomized to receive VT-1161 300 mg once daily (q.d.) for 3 days, 600 mg q.d. for 3 days, or 600 mg twice daily (b.i.d.) for 3 days or to receive a single dose of fluconazole 150 mg (FDA-approved dose to treat acute VVC). Participants were followed for 6 months. The primary outcome was the proportion of participants with therapeutic (clinical and mycological) cure at day 28. RESULTS: A larger proportion of participants in the per-protocol population experienced therapeutic cure in the VT-1161 300 mg q.d. (75.0%), VT-1161 600 mg q.d. (85.7%), and VT-1161 600 mg b.i.d. (78.6%) groups vs the fluconazole group (62.5%); differences were not statistically significant. At 3 and 6 months, no participants in the VT-1161 groups vs 28.5% and 46.1% in the fluconazole group, respectively, had evidence of mycological recurrence. No serious adverse events or treatment-emergent adverse events leading to discontinuation were reported. CONCLUSIONS: The majority of participants across all treatment groups achieved therapeutic cure at day 28. VT-1161 was well tolerated at all dose levels through 6 months of follow-up. CLINICAL TRIALS REGISTRATION: NCT01891331.

The proteasome as a target for protozoan parasites.

Introduction: The proteasome is a multi-subunit enzyme complex responsible for the turnover of short-lived, abnormal or damaged proteins in eukaryotic cells. As organisms that undergo rapid growth and cell division, protozoan parasites exist on the knife-edge of proteotoxic catastrophe and thus rely heavily on their protein quality control machinery for survival. Because of this, the proteasome has recently emerged as a desirable drug target.Area covered: This review focuses on efforts to identify protozoan parasite-specific proteasome inhibitors using substrate profiling, library screening, and in vitro evolution of resistance approaches to inform medicinal chemistry. Targeting the parasite's 20S proteasome chymotrypsin-like (ß5) activity and selectively inhibiting protein turnover in parasites compared to human cells are critical properties of potent, selective inhibitors.Expert opinion: Proteasome inhibitors have the potential for rapid action against all stages, all species and all strains of plasmodium and kinetoplastid parasites. Given the high level of conservation of proteasome active sites in eukaryotes, an important challenge is achieving inhibitors that show sufficient selectivity while maintaining properties consistent with drug development.

Preclinical candidate for the treatment of visceral leishmaniasis that acts through proteasome inhibition.

Visceral leishmaniasis (VL), caused by the protozoan parasites Leishmania donovani and Leishmania infantum, is one of the major parasitic diseases worldwide. There is an urgent need for new drugs to treat VL, because current therapies are unfit for purpose in a resource-poor setting. Here, we describe the development of a preclinical drug candidate, GSK3494245/DDD01305143/compound 8, with potential to treat this neglected tropical disease. The compound series was discovered by repurposing hits from a screen against the related parasite Trypanosoma cruzi Subsequent optimization of the chemical series resulted in the development of a potent cidal compound with activity against a range of clinically relevant L. donovani and L. infantum isolates. Compound 8 demonstrates promising pharmacokinetic properties and impressive in vivo efficacy in our mouse model of infection comparable with those of the current oral antileishmanial miltefosine. Detailed mode of action studies confirm that this compound acts principally by inhibition of the chymotrypsin-like activity catalyzed by the ß5 subunit of the L. donovani proteasome. High-resolution cryo-EM structures of apo and compound 8-bound Leishmania tarentolae 20S proteasome reveal a previously undiscovered inhibitor site that lies between the ß4 and ß5 proteasome subunits. This induced pocket exploits ß4 residues that are divergent between humans and kinetoplastid parasites and is consistent with all of our experimental and mutagenesis data. As a result of these comprehensive studies and due to a favorable developability and safety profile, compound 8 is being advanced toward human clinical trials.

Pharmacological Validation of N-Myristoyltransferase as a Drug Target in Leishmania donovani.

Visceral leishmaniasis (VL), caused by the protozoan parasites Leishmania donovani and L. infantum, is responsible for ∼30 000 deaths annually. Available treatments are inadequate, and there is a pressing need for new therapeutics. N-Myristoyltransferase (NMT) remains one of the few genetically validated drug targets in these parasites. Here, we sought to pharmacologically validate this enzyme in Leishmania. A focused set of 1600 pyrazolyl sulfonamide compounds was screened against L. major NMT in a robust high-throughput biochemical assay. Several potent inhibitors were identified with marginal selectivity over the human enzyme. There was little correlation between the enzyme potency of these inhibitors and their cellular activity against L. donovani axenic amastigotes, and this discrepancy could be due to poor cellular uptake due to the basicity of these compounds. Thus, a series of analogues were synthesized with less basic centers. Although most of these compounds continued to suffer from relatively poor antileishmanial activity, our most potent inhibitor of LmNMT (DDD100097, K i of 0.34 nM) showed modest activity against L. donovani intracellular amastigotes (EC50 of 2.4 µM) and maintained a modest therapeutic window over the human enzyme. Two unbiased approaches, namely, screening against our cosmid-based overexpression library and thermal proteome profiling (TPP), confirm that DDD100097 (compound 2) acts on-target within parasites. Oral dosing with compound 2 resulted in a 52% reduction in parasite burden in our mouse model of VL. Thus, NMT is now a pharmacologically validated target in Leishmania. The challenge in finding drug candidates remains to identify alternative strategies to address the drop-off in activity between enzyme inhibition and in vitro activity while maintaining sufficient selectivity over the human enzyme, both issues that continue to plague studies in this area.