A major cause of the paucity of new starting points for drug discovery is the lack of interaction between academia and industry. Much of the global resource in biology is present in universities, whereas the focus of medicinal chemistry is still largely within industry. Open source drug discovery, with sharing of information, is clearly a first step towards overcoming this gap. But the interface could especially be bridged through a scale-up of open sharing of physical compounds, which would accelerate the finding of new starting points for drug discovery. The Medicines for Malaria Venture Malaria Box is a collection of over 400 compounds representing families of structures identified in phenotypic screens of pharmaceutical and academic libraries against the Plasmodium falciparum malaria parasite. The set has now been distributed to almost 200 research groups globally in the last two years, with the only stipulation that information from the screens is deposited in the public domain. This paper reports for the first time on 236 screens that have been carried out against the Malaria Box and compares these results with 55 assays that were previously published, in a format that allows a meta-analysis of the combined dataset. The combined biochemical and cellular assays presented here suggest mechanisms of action for 135 (34%) of the compounds active in killing multiple life-cycle stages of the malaria parasite, including asexual blood, liver, gametocyte, gametes and insect ookinete stages. In addition, many compounds demonstrated activity against other pathogens, showing hits in assays with 16 protozoa, 7 helminths, 9 bacterial and mycobacterial species, the dengue fever mosquito vector, and the NCI60 human cancer cell line panel of 60 human tumor cell lines. Toxicological, pharmacokinetic and metabolic properties were collected on all the compounds, assisting in the selection of the most promising candidates for murine proof-of-concept experiments and medicinal chemistry programs. The data for all of these assays are presented and analyzed to show how outstanding leads for many indications can be selected. These results reveal the immense potential for translating the dispersed expertise in biological assays involving human pathogens into drug discovery starting points, by providing open access to new families of molecules, and emphasize how a small additional investment made to help acquire and distribute compounds, and sharing the data, can catalyze drug discovery for dozens of different indications. Another lesson is that when multiple screens from different groups are run on the same library, results can be integrated quickly to select the most valuable starting points for subsequent medicinal chemistry efforts.

The design of new antimalarial combinations to treat Plasmodium falciparum infections requires drugs that, in addition to resolving disease symptoms caused by asexual blood stage parasites, can also interrupt transmission to the mosquito vector. Gametocytes, which are essential for transmission, develop as sexual blood stage parasites in the human host over 8 to 12 days and are the most accessible developmental stage for transmission-blocking drugs. Considerable effort is currently being devoted to identifying compounds active against mature gametocytes. However, investigations on the drug sensitivity of developing gametocytes, as well as screening methods for identifying inhibitors of early gametocytogenesis, remain scarce. We have developed a luciferase-based high-throughput screening (HTS) assay using tightly synchronous stage I to III gametocytes from a recombinant P. falciparum line expressing green fluorescent protein (GFP)-luciferase. The assay has been used to evaluate the earlystage gametocytocidal activity of the MMV Malaria Box, a collection of 400 compounds with known antimalarial (asexual blood stage) activity. Screening this collection against early-stage (I to III) gametocytes yielded 64 gametocytocidal compounds with 50% inhibitory concentrations (IC 50 s) below 2.5 M. This assay is reproducible and suitable for the screening of large compound libraries, with an average percent coefficient of variance (%CV) of <5%, an average signal-to-noise ratio (S:N) of >30, and a Z= of ϳ0.8. Our findings highlight the need for screening efforts directed specifically against early gametocytogenesis and indicate the importance of experimental verification of early-stage gametocytocidal activity in the development of new antimalarial candidates for combination therapy. P lasmodium falciparum malaria remains a primary global cause of death and disability from infectious disease, particularly in infants and pregnant women (1). Malaria treatment currently relies on artemisinin-based combination therapy (ACT); however, emerging resistance to artemisinins in the field (2, 3) underscores the need to progress new antimalarial candidates through the drug development pipeline. Recent in vitro high-throughput screening (HTS) campaigns against P. falciparum asexual blood stages, the forms responsible for the clinical manifestations of the disease, have identified a wealth of active chemical classes, representing a promising starting point for the discovery of new therapeutic agents (4-7). The current malaria elimination strategy has also highlighted the need for all new antimalarial combination therapies to include components capable of interrupting the transmission of sexual-stage gametocytes to Anopheles mosquitoes (8, 9). Methods to enable prioritization of inhibitors of the asexual parasite stages based on their additional transmission-blocking activity are therefore urgently required.P. falciparum gametocytes develop through five morphologically distinct stages in the human blood over 8 to 12 days (10) and thereafter ...

There is an urgent clinical need for antimalarial compounds that target malaria caused by both Plasmodium falciparum and Plasmodium vivax. The M1 and M17 metalloexopeptidases play key roles in Plasmodium hemoglobin digestion and are validated drug targets. We used a multitarget strategy to rationally design inhibitors capable of potent inhibition of the M1 and M17 aminopeptidases from both P. falciparum (Pf-M1 and Pf-M17) and P. vivax (Pv-M1 and Pv-M17). The novel chemical series contains a hydroxamic acid zinc binding group to coordinate catalytic zinc ion/s, and a variety of hydrophobic groups to probe the S1′ pockets of the four target enzymes. Structural characterization by cocrystallization showed that selected compounds utilize new and unexpected binding modes; most notably, compounds substituted with bulky hydrophobic substituents displace the Pf-M17 catalytic zinc ion. Excitingly, key compounds of the series potently inhibit all four molecular targets and show antimalarial activity comparable to current clinical candidates.

The discovery of new antimalarial drugs able to target both the asexual and gametocyte stages of Plasmodium falciparum is critical to the success of the malaria eradication campaign. We have developed and validated a robust, rapid, and cost-effective highthroughput reporter gene assay to identify compounds active against late-stage (stage IV and V) gametocytes. The assay, which is suitable for testing compound activity at incubation times up to 72 h, demonstrates excellent quality and reproducibility, with average Z= values of 0.85 ؎ 0.01. We used the assay to screen more than 10,000 compounds from three chemically diverse libraries. The screening outcomes highlighted the opportunity to use collections of compounds with known activity against the asexual stages of the parasites as a starting point for gametocytocidal activity detection in order to maximize the chances of identifying gametocytocidal compounds. This assay extends the capabilities of our previously reported luciferase assay, which tested compounds against early-stage gametocytes, and opens possibilities to profile the activities of gametocytocidal compounds over the entire course of gametocytogenesis.T he complex life cycle of the Plasmodium falciparum parasite, responsible for malaria, involves a human host, in which the intraerythrocytic asexual stages of the parasite cause the disease manifestations, and an anopheline mosquito vector, in which the parasite transmission stages genetically recombine and develop to successfully infect new human hosts. Parasite transmission to both the mosquito vector and the next human host rely on the sexual stage gametocytes. In P. falciparum, gametocytes emerge in low numbers from the asexual population and mature over a 10-to 12-day period, progressing through five morphologically distinct stages (I to V) (1). Mature stage V gametocytes can remain infective to the mosquito for an extended time, even if the asexual parasite population has been decreased by therapeutic drugs (2).The last 15 years have witnessed an unprecedented effort in the fight against malaria, with the deployment of large-scale interventions, including the distribution of artemisinin-based combination therapies (ACTs); targeted chemoprophylaxis of patient populations at particular risk, notably pregnant women and children under the age of 5 years; and vector control measures, including insecticide-treated bed nets. As a result, a 48% decrease in global malaria mortality rates was achieved between 2000 and 2015, and 16 countries have successfully eliminated malaria since 2010 (3). Although these impressive achievements have required a substantial economic outlay, it has become increasingly clear that an aggressive strategy aimed at malaria eradication is the only sustainable, albeit ambitious, goal in the long term (4). Achieving this ultimate goal is challenging, as malaria claims nearly 440,000 lives annually, and nearly half of the world's population is at risk of contracting the disease (3). The emergence of parasites resistant to current ...

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