Leishmania parasites are the causative agents of a wide spectrum of human diseases. The clinical mani- festations of leishmaniasis range from self-healing skin lesions to fatality. The World Health Organization has classed leishmaniasis as a category 1 neglected tropical disease. Leishmaniasis represents a major in- ternational health challenge, affecting 12 million people per year and with nearly 310 million people at risk. The first-line chemotherapies used to treat leishmaniasis are intravenous pentavalent antimonials; however, these drugs are highly toxic. As the use of oral treatment options such as paromomycin and mil- tefosine has increased, the incidence of disease relapse has increased and drug resistance to antimonials has developed, emphasizing the importance of identifying new chemotherapies. A novel, target-free fluo- rometric high-throughput screen with an average Z-score of 0.73 + /- 0.13 has been developed to identify small molecules with antileishmanial activity. Screening of 10,0 0 0 small molecules from the ChemBridge DIVER-set TM library cassette #5 yielded 210 compounds that killed 80% of parasites, resulting in a hit rate of 2.1%. One hundred and nine molecular scaffolds were represented within the hit compounds, and one scaffold that exhibited potent antileishmanial activity was 2,4-diaminoquinazoline. Host cell toxicity was determined prior to in-vitro infection of human THP-1 macrophages with Leishmania donovani mCherry expressing promastigotes; successful drug treatment was considered when the half maximal inhibitory concentration was < 10 μM. BALB/c mice were infected with Leishmania major mCherry promastigotes and treated with small molecules that were successful during in-vitro infections. Several small molecules tested were as efficacious at resolving cutaneous leishmaniasis lesions in mice as known antimonial treat- ments.
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