In Vitro Antimalarial Activity of Trichothecenes against Liver and Blood Stages of Plasmodium Species.

Trichothecenes (TCNs) are a large group of tricyclic sesquiterpenoid mycotoxins that have intriguing structural features and remarkable biological activities. Herein, we focused on three TCNs (anguidine, verrucarin A, and verrucarol) and their ability to target both the blood and liver stages of Plasmodium species, the parasite responsible for malaria. Anguidine and verrucarin A were found to be highly effective against the blood and liver stages of malaria, while verrucarol had no effect at the highest concentration tested. However, these compounds were also found to be cytotoxic and, thus, not selective, making them unsuitable for drug development. Nonetheless, they could be useful as chemical probes for protein synthesis inhibitors due to their direct impact on parasite synthesis processes.

Structure-activity and structure-property relationship studies of spirocyclic chromanes with antimalarial activity.

Malaria is a prevalent and lethal disease. The fast emergence and spread of resistance to current therapies is a major concern and the development of a novel line of therapy that could overcome, the problem of drug resistance, is imperative. Screening of a set of compounds with drug/natural product-based sub-structural motifs led to the identification of spirocyclic chroman-4-one 1 with promising antimalarial activity against the chloroquine-resistant Dd2 and chloroquine-sensitive 3D7 strains of the parasite. Extensive structure-activity and structure-property relationship studies were conducted to identify the essential features necessary for its activity and properties.

Indoloquinoline Alkaloids as Antimalarials: Advances, Challenges, and Opportunities.

Malaria infections affect almost half of the world's population, with over 200 million cases reported annually. Cryptolepis sanguinolenta, a plant native to West Africa, has long been used across various regions of Africa for malaria treatment. Chemical analysis has revealed that the plant is abundant in indoloquinolines, which have been shown to possess antimalarial properties. Cryptolepine, neocryptolepine, and isocryptolepine are well-studied indoloquinoline alkaloids known for their potent antimalarial activity. However, their structural rigidity and associated cellular toxicity are major drawbacks for preclinical development. This review focuses on the potential of indoloquinoline alkaloids (cryptolepine, neocryptolepine, and isocryptolepine) as scaffolds in drug discovery. The article delves into their antimalarial effects in vitro and in vivo, as well as their proposed mechanisms of action and structure-activity relationship studies. Several studies aim to improve these leads by reducing cytotoxicity while preserving or enhancing antimalarial activity and gaining insights into their mechanisms of action. These investigations highlight the potential of indoloquinolines as a scaffold for developing new antimalarial drugs.

Optimization of diastereomeric dihydropyridines as antimalarials.

The increase in research funding for the development of antimalarials since 2000 has led to a surge of new chemotypes with potent antimalarial activity. High-throughput screens have delivered several thousand new active compounds in several hundred series, including the 4,7-diphenyl-1,4,5,6,7,8-hexahydroquinolines, hereafter termed dihydropyridines (DHPs). We optimized the DHPs for antimalarial activity. Structure-activity relationship studies focusing on the 2-, 3-, 4-, 6-, and 7-positions of the DHP core led to the identification of compounds potent (EC50 < 10 nM) against all strains of P. falciparum tested, including the drug-resistant parasite strains K1, W2, and TM90-C2B. Evaluation of efficacy of several compounds in vivo identified two compounds that reduced parasitemia by >75 % in mice 6 days post-exposure following a single 50 mg/kg oral dose. Resistance acquisition experiments with a selected dihydropyridine led to the identification of a single mutation conveying resistance in the gene encoding for Plasmodium falciparum multi-drug resistance protein 1 (PfMDR1). The same dihydropyridine possessed transmission blocking activity. The DHPs have the potential for the development of novel antimalarial drug candidates.

Shotgun Kinetic Target-Guided Synthesis Approach Enables the Discovery of Small-Molecule Inhibitors against Pathogenic Free-Living Amoeba Glucokinases.

Pathogenic free-living amoebae (pFLA) can cause life-threatening central nervous system (CNS) infections and warrant the investigation of new chemical agents to combat the rise of infection from these pathogens. Naegleria fowleri glucokinase (NfGlck), a key metabolic enzyme involved in generating glucose-6-phosphate, was previously identified as a potential target due to its limited sequence similarity with human Glck (HsGlck). Herein, we used our previously demonstrated multifragment kinetic target-guided synthesis (KTGS) screening strategy to identify inhibitors against pFLA glucokinases. Unlike the majority of previous KTGS reports, our current study implements a "shotgun" approach, where fragments were not biased by predetermined binding potentials. The study resulted in the identification of 12 inhibitors against 3 pFLA glucokinase enzymes─NfGlck, Balamuthia mandrillaris Glck (BmGlck), and Acanthamoeba castellanii Glck (AcGlck). This work demonstrates the utility of KTGS to identify small-molecule binders for biological targets where resolved X-ray crystal structures are not readily accessible.

Synthesis of Mono- and Bisperoxide-Bridged Artemisinin Dimers to Elucidate the Contribution of Dimerization to Antimalarial Activity.

During the past decade, artemisinin as an antimalarial has been in the spotlight, in part due to the Nobel Prize in Physiology or Medicine awarded to Tu Youyou. While many studies have been completed detailing the significant increase in activity resulting from the dimerization of natural product artemisinin, activity increases unaccounted for by the peroxide bridge have yet to be researched. Here we outline the synthesis and testing for antimalarial activity of artemisinin dimers in which the peroxide bridge in one-half of the dimer is reduced, resulting in a dimer with one active and one deactivated artemisinin moiety.

Aminoalkoxycarbonyloxymethyl Ether Prodrugs with a pH-Triggered Release Mechanism: A Case Study Improving the Solubility, Bioavailability, and Efficacy of Antimalarial 4(1H)-Quinolones with Single Dose Cures.

Preclinical and clinical development of numerous small molecules is prevented by their poor aqueous solubility, limited absorption, and oral bioavailability. Herein, we disclose a general prodrug approach that converts promising lead compounds into aminoalkoxycarbonyloxymethyl (amino AOCOM) ether-substituted analogues that display significantly improved aqueous solubility and enhanced oral bioavailability, restoring key requirements typical for drug candidate profiles. The prodrug is completely independent of biotransformations and animal-independent because it becomes an active compound via a pH-triggered intramolecular cyclization-elimination reaction. As a proof-of-concept, the utility of this novel amino AOCOM ether prodrug approach was demonstrated on an antimalarial compound series representing a variety of antimalarial 4(1H)-quinolones, which entered and failed preclinical development over the last decade. With the amino AOCOM ether prodrug moiety, the 3-aryl-4(1H)-quinolone preclinical candidate was shown to provide single-dose cures in a rodent malaria model at an oral dose of 3 mg/kg, without the use of an advanced formulation technique.