Ebola virus (EBOV) causes a severe and often fatal hemorrhagic fever in humans for which effective postexposure countermeasures are lacking. Herein, we describe the evaluation of an S-adenosylhomocysteine hydrolase inhibitor, MSD-914, using mouse and nonhuman primate (NHP) models of lethal EBOV. Mice were completely protected from severe disease and death at doses as low as 0.31 mg/kg/day administered orally. From the pharmacological data and a toxicokinetic study, a predicted protective dose was selected for rhesus macaques (RMs). Surprisingly, orally administered MSD-914 was unable to protect RMs at doses as high as 0.8 mg/kg/day despite providing similar exposure of the drug to the efficacious dose observed in the mouse model.

NaV1.8 is a key mediator of peripheral nociceptive signaling and an attractive nonopioid target for pain therapeutics. We report the discovery of MK 5661, a potent, selective, and orally bioavailable NaV1.8 inhibitor amenable to once-daily dosing. Optimization of an initial lead, guided by reduction of PXR activation, and dose optimization focusing on half-life and volume ligand efficiency are described. MK-5661 demonstrates a favorable pharmacokinetic profile in preclinical species, as well as efficacy in preclinical models for pain.

Linezolid, an oxazolidinone, is a cornerstone of treatment regimens for highly drug-resistant tuberculosis but cannot be used in drug-susceptible disease because of toxicity. This toxicity results from inhibition of mammalian mitochondrial protein synthesis. Here we show the development of a new oxazolidinone, MK-7762, with antitubercular activity that is better than linezolid and limited mitochondrial protein synthesis inhibition. The cryogenic electron microscopy structure of the stalled mycobacterial ribosome with MK-7762 revealed the basis for this selectivity. BALB/c mouse models of disease showed MK-7762 reduced lung bacterial burden by a 3-log-fold decrease in an acute model (N = 18) and a 2-log-fold decrease in chronically infected animals (N = 18). MK-7762 showed lesion penetration similar to linezolid in C3HeB/FeJ mice. MK-7762 had pharmacokinetic properties predicting low once-daily doses in humans and a favorable 14-day preclinical safety profile in Wistar Han rats (N = 30) and Beagle dogs (N = 6). Four-month safety studies in both rats (N = 20) and dogs (N = 24) showed no changes in hematology parameters at exposures well above the 100-mg predicted human dose. These data will enable MK-7762 to be explored as a component of new tuberculosis treatment combinations for all forms of the disease.

Background The global burden of malaria remains substantial, and increasing parasite resistance to current antimalarials necessitates the development of drugs with unique mechanisms of action. This study aimed to develop and characterise a new antimalarial compound targeting Plasmodium aspartic proteases. Methods We conducted high-throughput screening, medicinal chemistry optimisation, and extensive in vitro and in vivo testing to develop and evaluate MK-7602, a dual inhibitor of plasmepsins IX and X. Findings MK-7602, a clinical candidate, acts as a dual sub-nanomolar inhibitor of plasmepsins IX and X in multiple Plasmodium species. It exhibits favourable pharmacokinetic properties and a promising safety profile. MK-7602 demonstrates activity against liver and blood life-cycle stages of the parasite and blocks transmission to mosquitoes. Importantly, it shows a high barrier to resistance development and lacks cross-resistance with Plasmodium falciparum strains resistant to other antimalarials. MK-7602 effectively inhibits both wild-type parasites and those with increased plasmepsin expression, highlighting its potential to overcome existing resistance mechanisms. Interpretation MK-7602 represents a new class of antimalarial for treating uncomplicated malaria with a new mechanism of action and the potential to address drug-resistant malaria. Clinical evaluation of MK-7602's activity against P. falciparum is ongoing. Funding This work was funded by The Wellcome Trust (109662/Z/15/Z, 202749/Z/16/Z, 219658/Z/19/Z), NHMRC (GNT1176955, GNT637406, GNT1173049), the Human Frontiers Science Program (LT0001/2022-L, JMD), Drakensberg Trust, the Victorian State Government Operational Infrastructure Support grant, and the Australian Government NHMRC IRIISS. JPo was supported by the NIH/NIAID (R01AI173171, R01AI175134 and R61AI187100) and the Pasteur International Unit PvESMEE.

ABSTRACTAlthough smallpox has been eradicated, other orthopoxviruses continue to be a public health concern as exemplified by the ongoing Mpox (formerly monkeypox) global outbreak. While medical countermeasures (MCMs) previously approved by the Food and Drug Administration for the treatment of smallpox have been adopted for Mpox, previously described vulnerabilities coupled with the questionable benefit of at least one of the therapeutics during the 2022 Mpox outbreak reinforce the need for identifying and developing other MCMs against orthopoxviruses. Here, we screened a panel of Merck proprietary small molecules and identified a novel nucleoside inhibitor with potent broad-spectrum antiviral activity against multiple orthopoxviruses. Efficacy testing of a 7-day dosing regimen of the orally administered nucleoside in a murine model of severe orthopoxvirus infection yielded a dose-dependent increase in survival. Treated animals had greatly reduced lesions in the lung and nasal cavity, particularly in the 10 µg/mL dosing group. Viral levels were also markedly lower in the UMM-766-treated animals. This work demonstrates that this nucleoside analog has anti-orthopoxvirus efficacy and can protect against severe disease in a murine orthopox model.IMPORTANCEThe recent monkeypox virus pandemic demonstrates that members of the orthopoxvirus, which also includes variola virus, which causes smallpox, remain a public health issue. While currently FDA-approved treatment options exist, risks that resistant strains of orthopoxviruses may arise are a great concern. Thus, continued exploration of anti-poxvirus treatments is warranted. Here, we developed a template for a high-throughput screening assay to identify anti-poxvirus small-molecule drugs. By screening available drug libraries, we identified a compound that inhibited orthopoxvirus replication in cell culture. We then showed that this drug can protect animals against severe disease. Our findings here support the use of existing drug libraries to identify orthopoxvirus-targeting drugs that may serve as human-safe products to thwart future outbreaks.

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) continues to be a global threat due to its ability to evolve and generate new subvariants, leading to new waves of infection. Additionally, other coronaviruses like Middle East respiratory syndrome coronavirus (MERS-CoV, formerly known as hCoV-EMC), which first emerged in 2012, persist and continue to present a threat of severe illness to humans. The continued identification of novel coronaviruses, coupled with the potential for genetic recombination between different strains, raises the possibility of new coronavirus clades of global concern emerging. As a result, there is a pressing need for pan-CoV therapeutic drugs and vaccines. After the extensive optimization of an HCV protease inhibitor screening hit, a novel 3CLPro inhibitor (MK-7845) was discovered and subsequently profiled. MK-7845 exhibited nanomolar in vitro potency with broad spectrum activity against a panel of clinical SARS-CoV-2 subvariants and MERS-CoV. Furthermore, when administered orally, MK-7845 demonstrated a notable reduction in viral burdens by >6 log orders in the lungs of transgenic mice infected with SARS-CoV-2 (K18-hACE2 mice) and MERS-CoV (K18-hDDP4 mice).

As SARS-CoV-2 continues to circulate, antiviral treatments are needed to complement vaccines. The virus's main protease, 3CLPro, is an attractive drug target in part because it recognizes a unique cleavage site, which features a glutamine residue at the P1 position and is not utilized by human proteases. Herein, we report the invention of MK-7845, a novel reversible covalent 3CLPro inhibitor. While most covalent inhibitors of SARS-CoV-2 3CLPro reported to date contain an amide as a Gln mimic at P1, MK-7845 bears a difluorobutyl substituent at this position. SAR analysis and X-ray crystallographic studies indicate that this group interacts with His163, the same residue that forms a hydrogen bond with the amide substituents typically found at P1. In addition to promising in vivo efficacy and an acceptable projected human dose with unboosted pharmacokinetics, MK-7845 exhibits favorable properties for both solubility and absorption that may be attributable to the unusual difluorobutyl substituent.

Amorphous solid dispersions feature prominently in the approach to mitigate low bioavailability of poorly water-soluble small molecules, particularly in the early development space focusing on toxicity evaluations and clinical studies in normal healthy volunteers, where high exposures are needed to establish safety margins. Spray drying has been the go-to processing route for a number of reasons, including ubiquitous availability of equipment, the ability to accommodate small scale deliveries, and established processes for delivering single phase amorphous material. Active pharmaceutical ingredients (APIs) with low glass transition temperatures (Tg) can pose challenges to this approach. This study addresses multiple routes towards overcoming issues encountered with a low Tg (∼ 12 °C) API during manufacture of a spray dry intermediate (SDI). Even once formulated as an amorphous solid dispersion (ASD) with HPMCAS-LG, the Tg of the ASD was sufficiently low to require the use of non-ideal solvents, posing safety concerns and ultimately resulting in low yields with frequent process interruptions to resolve product build-up. To resolve challenges with spray drying the HPMCAS-L SDI, higher Tg polymers were assessed during spray drying, and an alternative antisolvent precipitation-based process was evaluated to generate co-precipitated amorphous dispersions (cPAD) with either HPMCAS-L or the additional higher Tg polymers. Both approaches were found to be viable alternatives to achieve single phase ASDs while demonstrating comparable in vitro and in vivo bioperformance compared to the SDI. The results of this effort offer valuable considerations for future early-stage activities for ASDs with low Tg APIs.

Tricyclic pyrrolopyrimidines (TPPs) are a new class of antibacterials inhibiting the ATPase of DNA gyrase. TPP8, a representative of this class, is active against Mycobacterium abscessus in vitro. Spontaneous TPP8 resistance mutations mapped to the ATPase domain of M. abscessus DNA gyrase, and the compound inhibited DNA supercoiling activity of recombinant M. abscessus enzyme. Further profiling of TPP8 in macrophage and mouse infection studies demonstrated proof-of-concept activity against M. abscessus ex vivo and in vivo.

Drug resistance to first-line antimalarials-including artemisinin-is increasing, resulting in a critical need for the discovery of new agents with novel mechanisms of action. In collaboration with the Walter and Eliza Hall Institute and with funding from the Wellcome Trust, a phenotypic screen of Merck's aspartyl protease inhibitor library identified a series of plasmepsin X (PMX) hits that were more potent than chloroquine. Inspired by a PMX homology model, efforts to optimize the potency resulted in the discovery of leads that, in addition to potently inhibiting PMX, also inhibit another essential aspartic protease, plasmepsin IX (PMIX). Further potency and pharmacokinetic profile optimization efforts culminated in the discovery of WM382, a very potent dual PMIX/X inhibitor with robust in vivo efficacy at multiple stages of the malaria parasite life cycle and an excellent resistance profile.

Amorphous solid dispersions (ASD) have become a well-established strategy to improve exposure for compounds with insufficient aqueous solubility. Of methods to generate ASDs, spray drying is a leading route due to its relative simplicity, availability of equipment, and commercial scale capacity. However, the broader industry adoption of spray drying has revealed potential limitations, including the inability to process compounds with low solubility in volatile solvents, inconsistent molecular uniformity of spray dried amorphous dispersions, variable physical properties across batches and scales, and challenges containing potent compounds. In contrast, generating ASDs via co-precipitation to yield co-precipitated amorphous dispersions (cPAD) offers solutions to many of those challenges and has been shown to achieve ASDs comparable to those manufactured via spray drying. This manuscript applies co-precipitation for early safety studies, developing a streamlined process to achieve material suitable for dosing as a suspension in conventional toxicity studies. Development targets involved achieving a rapid, safely contained process for generating ASDs with high recovery yields. Furthermore, a hierarchical particle approach was used to generate composite particles where the cPAD material is incorporated in a matrix of water-soluble excipients to allow for rapid re-dispersibility in the safety study vehicle to achieve a uniform suspension for consistent dosing. Adopting such an approach yielded a co-precipitated amorphous dispersion with comparable stability, thermal properties, and in vivo pharmacokinetics to spray dried amorphous materials of the same composition.

A diverse set of drug and polymer combinations have been effectively evaluated utilizing a newly developed method called acoustic fusion to form amorphous solid dispersions (ASD) on the mg-scale, indicating that this approach is a general procedure that can be applied for ASD drug formulations. We have demonstrated the effectiveness of this acoustic fusion process by generating amorphous solid dispersions of various BCS class 2 and 4 drug candidates, including torcetrapib, itraconazole, and lopinavir, with a variety of polymer systems, including HPMCAS (L, M, and H), copovidone, Soluplus®, PEG1500, Vitamin-E TPGS, Kolliphor EL, and Eudragit, etc. Formulations of these ASD drug products demonstrated significantly elevated solubility of the drug substance compared to the solubility of the crystalline form of the drug. Acoustic fusion products using the model drug torcetrapib in either HPMCAS-LF, copovidone + Vitamin-E TPGS, or Soluplus®, exhibited enhanced supersaturation solubility in aqueous buffer in vitro compared to the drug in crystalline form, indicating that the acoustic fusion process resulted in an amorphous solid dispersion state similar to those formed in spray drying (SD) or hot melt extrusion (HME) processes. In vivo dosing of formulations of the acoustic fusion products in a rat pharmacokinetic study at a dose level of 10 mg/kg resulted in an improvement in exposures of approximately 8-fold by AUC(0-24) in comparison to a conventional suspension formulation of the drug material in crystalline form, thus validating the efficiency of this novel acoustic fusion approach for elevating the bioperformance in preclinical studies.

Artemisin combination therapy (ACT) is the main treatment option for malaria, which is caused by the intracellular parasite Plasmodium. However, increased resistance to ACT highlights the importance of finding new drugs. Recently, the aspartic proteases Plasmepsin IX and X (PMIX and PMX) were identified as promising drug targets. In this study, we describe dual inhibitors of PMIX and PMX, including WM382, that block multiple stages of the Plasmodium life cycle. We demonstrate that PMX is a master modulator of merozoite invasion and direct maturation of proteins required for invasion, parasite development, and egress. Oral administration of WM382 cured mice of P. berghei and prevented blood infection from the liver. In addition, WM382 was efficacious against P. falciparum asexual infection in humanized mice and prevented transmission to mosquitoes. Selection of resistant P. falciparum in vitro was not achievable. Together, these show that dual PMIX and PMX inhibitors are promising candidates for malaria treatment and prevention.

Nasal congestion is one of the most troublesome symptoms of many upper airways diseases. We characterized the effect of selective α2c-adrenergic agonists in animal models of nasal congestion. In porcine mucosa tissue, compound A and compound B contracted nasal veins with only modest effects on arteries. In in vivo experiments, we examined the nasal decongestant dose-response characteristics, pharmacokinetic/pharmacodynamic relationship, duration of action, potential development of tolerance, and topical efficacy of α2c-adrenergic agonists. Acoustic rhinometry was used to determine nasal cavity dimensions following intranasal compound 48/80 (1%, 75 µl). In feline experiments, compound 48/80 decreased nasal cavity volume and minimum cross-sectional areas by 77% and 40%, respectively. Oral administration of compound A (0.1–3.0 mg/kg), compound B (0.3–5.0 mg/kg), and d-pseudoephedrine (0.3 and 1.0 mg/kg) produced dose-dependent decongestion. Unlike d-pseudoephedrine, compounds A and B did not alter systolic blood pressure. The plasma exposure of compound A to produce a robust decongestion (EC80) was 500 nM, which related well to the duration of action of approximately 4.0 hours. No tolerance to the decongestant effect of compound A (1.0 mg/kg p.o.) was observed. To study the topical efficacies of compounds A and B, the drugs were given topically 30 minutes after compound 48/80 (a therapeutic paradigm) where both agents reversed nasal congestion. Finally, nasal-decongestive activity was confirmed in the dog. We demonstrate that α2c-adrenergic agonists behave as nasal decongestants without cardiovascular actions in animal models of upper airway congestion.