Novel Transmission-Blocking Antimalarials Identified by High-Throughput Screening of Plasmodium berghei Ookluc.

Safe and effective malaria transmission-blocking chemotherapeutics would allow a community-level approach to malaria control and eradication efforts by targeting the mosquito sexual stage of the parasite life cycle. However, only a single drug, primaquine, is currently approved for use in reducing transmission, and drug toxicity limits its widespread implementation. To address this limitation in antimalarial chemotherapeutics, we used a recently developed transgenic Plasmodium berghei line, Ookluc, to perform a series of high-throughput in vitro screens for compounds that inhibit parasite fertilization, the initial step of parasite development within the mosquito. Screens of antimalarial compounds, approved drug collections, and drug-like molecule libraries identified 185 compounds that inhibit parasite maturation to the zygote form. Seven compounds were further characterized to block gametocyte activation or to be cytotoxic to formed zygotes. These were further validated in mosquito membrane-feeding assays using Plasmodium falciparum and P. vivax. This work demonstrates that high-throughput screens using the Ookluc line can identify compounds that are active against the two most relevant human Plasmodium species and provides a list of compounds that can be explored for the development of new antimalarials to block transmission.

Screening the Pathogen Box for Molecules Active against Plasmodium Sexual Stages Using a New Nanoluciferase-Based Transgenic Line of P. berghei Identifies Transmission-Blocking Compounds.

Malaria remains an important parasitic disease with a large morbidity and mortality burden. Plasmodium transmission-blocking (TB) compounds are essential for achieving malaria elimination efforts. Recent efforts to develop high-throughput screening (HTS) methods to identify compounds that inhibit or kill gametocytes, the Plasmodium sexual stage infectious to mosquitoes, have yielded insight into new TB compounds. However, the activities of these compounds against gametes, formed in the first minutes of mosquito infection, are typically not assessed, unless screened in a standard membrane feeding assay, a labor-intensive assay. We demonstrate here the generation of a Plasmodium model for drug screens against gametes and fertilization. The new P. berghei line, named Ookluc, was genetically and pharmacologically validated and scalable for HTS. Screening the Pathogen Box from the Medicines for Malaria Venture using the new model identified promising TB compounds. The use of Ookluc in different libraries of compounds may aid in the identification of transmission-blocking drugs not assessed in screens against asexual stages or gametocytes.

Actinoramide A Identified as a Potent Antimalarial from Titration-Based Screening of Marine Natural Product Extracts.

Methods to identify the bioactive diversity within natural product extracts (NPEs) continue to evolve. NPEs constitute complex mixtures of chemical substances varying in structure, composition, and abundance. NPEs can therefore be challenging to evaluate efficiently with high-throughput screening approaches designed to test pure substances. Here we facilitate the rapid identification and prioritization of antimalarial NPEs using a pharmacologically driven, quantitative high-throughput-screening (qHTS) paradigm. In qHTS each NPE is tested across a concentration range from which sigmoidal response, efficacy, and apparent EC50s can be used to rank order NPEs for subsequent organism reculture, extraction, and fractionation. Using an NPE library derived from diverse marine microorganisms we observed potent antimalarial activity from two Streptomyces sp. extracts identified from thousands tested using qHTS. Seven compounds were isolated from two phylogenetically related Streptomyces species: Streptomyces ballenaensis collected from Costa Rica and Streptomyces bangulaensis collected from Papua New Guinea. Among them we identified actinoramides A and B, belonging to the unusually elaborated nonproteinogenic amino-acid-containing tetrapeptide series of natural products. In addition, we characterized a series of new compounds, including an artifact, 25-epi-actinoramide A, and actinoramides D, E, and F, which are closely related biosynthetic congeners of the previously reported metabolites.

Can diabetes mellitus be prevented? - abstract

Many secondary and tertiary interventions have proven effective in preventing the complications of diabetes mellitus. Of note, The Diabetes Control and Complications Trial has established that intensive treatment of diabetes mellitus with the goal of normo-glycaemia delays the development and slows the progression of renal failure. Screening and photocoagulation for macular oedema and proliferative retinopathy are highly effacious at reducing the progression of these complications to blindness. It is estimated that more than half of the non-traumatic amputations in diabetics can be prevented by appropriate education, footcare and early intervention for trauma, ulcer and infection. Patients and purveyors of care to patients with diabetes mellitus should institute these interventions in their patients to reduce the long-term effects of hyperglycaemia. At present, however, there are no interventions which have been proven to prevent development (primary prevention) of diabetes mellitus. Several large scale trials (Diabetes Prevention Trial - Type 1 Diabetes (DPT-1), European Nicotinamide Diabetes Intervention Trial (ENDIT), European Insulin Trial (EUROINS) are underway to try and prevent IDDM by administration of nicotinamide or insulin to individuals with increased risk of developing diabetes mellitus. Large scale studies of primary prevention studies of NIDDM are planned or are underway. Primary prevention of diabetes mellitus is intuitively attractive. Chronic disease models indicate that the delaying of the onset of diabetes mellitus enhances the effect of intensive treatment on reducing complications, and that the combined approach is more effective than either alone. It is appropriate to allocate research resources to large-scale clinical trials of diabetes primary prevention at this time. Trials of immunomodulation of the natural history of IDDM is supported by work in animals and pilot studies in man. Epidemiological studies suggest that lifestyle interventions such as diet and exercise may prevent development of NIDDM in susceptible individuals, and drugs that affect insulin secretion and/or action are also potential candidates for primary prevention of NIDDM (AU)