Paul R. Carlier

Due to the emergence of resistance to both artemisinin derivatives, and their partner drugs, new antimalarials are urgently needed. Ideally, new orally active antimalarials would not only engage new targets but also demonstrate a high barrier to resistance selection, and the ability to kill both proliferating rings and growth-arrested rings resulting from artemisinin exposure. In this report we disclose a novel antimalarial chemotype, the imidazo[4,5-c]pyridine-6-carboxamides, and a representative compound 10b that possesses all these qualities. Orally dosed 10b (4 × 60 mg/kg/day or 1 × 160 mg/kg) cures Plasmodium yoelii-infected mice out to 28 days. This compound is unaffected by over 40 distinct target- and efflux-based resistance mutations in the AReBaR resistome screen, suggesting a novel mode of action. Furthermore, at a minimum inoculum of resistance of 10⁹ parasites, 10b proved refractory to resistance selection. Lastly, with a 6 h exposure, 250 nM 10b kills both proliferating rings and dihydroartemisinin-induced dormant parasites.

Henipaviruses such as Nipah (NiV) and Hendra (HeV) are zoonotic pathogens that cause severe and often fatal respiratory illness and encephalitis in both animals and humans. These viruses exhibit high transmissibility and pandemic potential, a situation made worse by the absence of appropriate pharmaceutical countermeasures. To address this deficit, we conducted a hit-to-lead optimization campaign based on hit 1 identified through high-throughput screening against recombinant Cedar virus (rCedV), a nonpathogenic surrogate for NiV and HeV. This effort yielded a focused library of analogs that were initially screened against rCedV, with promising candidates subsequently validated against authentic NiV and HeV. Among these, analog 46 demonstrated superior in vitro metabolic stability and pharmacokinetic properties relative to hit 1 and is now positioned for in vivo efficacy evaluation. Concurrently, the mechanism of action of these first-in-class furopyrimidine-based antiviral agents was probed through time-of-addition assays, escape mutation analysis, and preliminary in silico modeling.

Malaria, caused by Plasmodium falciparum, remains a major global health challenge, with an estimated 263 million new infections and 597,000 deaths annually. Increasing resistance to current antimalarial drugs underscores the urgent need for new therapeutics that target novel pathways in the parasite. We previously reported a novel class of β-carboline antimalarials, exemplified by PRC1584, which demonstrated a favorable oral pharmacokinetic profile, in vivo efficacy in Plasmodium berghei-infected mice, and no cross-resistance with other antimalarials in various P. falciparum strains. In this study, we demonstrate that PRC1584 exhibits a high resistance barrier and retains potent activity against fresh Ugandan P. falciparum isolates. PRC1584, along with its more potent analog PRC1697, demonstrated strong in vitro potency against both actively proliferating ring stages and dihydroartemisinin-induced dormant stages. Additionally, our study demonstrated that PfKelch13-C580Y mutation was associated with an increased susceptibility to PRC1584, whereas PfKelch13-R549T and Pfcoronin-R100 K-E107V mutations were not associated with this effect. These findings underscore the therapeutic potential of this new "irresistible" compound class, support a possible novel mechanism of action, and suggest the future development of novel ACTs active against resistant parasites by targeting DHA dormancy, an essential survival mechanism of P. falciparum.

7-fluoro analog 20c showed greatly improved in vitro metabolic stability relative to 1, with only a 50% reduction in antimalarial potency.

Half the world's population is at risk of developing a malaria infection, which is caused by parasites of the genus Plasmodium. Currently, resistance has been identified to all clinically available antimalarials, highlighting an urgent need to develop novel compounds and better understand common mechanisms of resistance. We previously identified a novel tetrahydro-beta-carboline compound, PRC1590, which potently kills the malaria parasite. To better understand its mechanism of action, we selected for and characterized resistance to PRC1590 in Plasmodium falciparum. Through in vitro selection of resistance to PRC1590, we have identified that a single-nucleotide polymorphism on the parasite's multidrug resistance protein 1 (PfMDR1 G293V) mediates resistance to PRC1590. This mutation results in stereospecific resistance and sensitizes parasites to other antimalarials, such as mefloquine, quinine, and MMV019017. Intraerythrocytic asexual stage specificity assays have revealed that PRC1590 is most potent during the trophozoite stage when the parasite forms a single digestive vacuole (DV) and actively digests hemoglobin. Moreover, fluorescence microscopy revealed that PRC1590 disrupts the function of the DV, indicating a potential molecular target associated with this organelle. Our findings mark a significant step in understanding the mechanism of resistance and the mode of action of this emerging class of antimalarials. In addition, our results suggest a potential link between resistance mediated by PfMDR1 and PRC1590's molecular target. This research underscores the pressing need for future research aimed at investigating the intricate relationship between a compound's chemical scaffold, molecular target, and resistance mutations associated with PfMDR1.

Several arenaviruses, such as the Old World (OW) Lassa virus (LASV) and the New World (NW) Junin virus (JUNV), can cause severe and lethal viral hemorrhagic fevers in humans. Currently, no vaccines or specific antiviral therapies are FDA-approved for treating arenavirus infections. One major challenge for the development of new therapeutic candidates against these highly pathogenic viruses is that they are BSL-3/4 pathogens that need to be handled in high biocontainment laboratories. In this work, a recombinant non-pathogenic New World arenavirus, Pichinde virus (rPICV), was used for the development of a high-throughput screening (HTS) assay in the BSL-2 laboratory for the screening and identification of small molecule inhibitors against arenaviruses. The rPICV is a replication-competent virus expressing the firefly luciferase reporter gene in the infected cells proportionally to the infection rate. rPICV infection was optimized for an automated HTS in 384-well format with robust Z′ scores, high signal-to-background ratios, and low intrinsic variance. Screening an established library allowed for the identification of five top hit compounds, which included ribavirin, a known inhibitor of arenaviral RNA synthesis, showing good potency and selectivity in inhibiting rPICV replication. The antiviral activity of the top hit compounds was further validated against another recombinant arenavirus, the OW lymphocytic choriomeningitis virus (rLCMV) and against laboratory strains of LASV (Josiah) and JUNV (Romero). The use of rPICV in the HTS-based antiviral assay under BSL-2 condition has proven to be safe and suitable for the identification of broad-spectrum small molecule inhibitors against highly pathogenic arenaviruses.