21Amoebiasis caused by the protozoan parasite Entamoeba histolytica remains a major public health 22 hazard, as being the second cause of death among parasitic infections. Although currently 23 prescribed drugs have shown to be effective in the treatment of amoebiasis, side effects and 24 emergence of parasites resistance prompted the search for novel drug to control this disease. In 25 this regard, the Medicines for Malaria Venture (MMV) Pathogen Box library of selected 26 compounds was screened to identify anti-Entamoeba histolytica agents using the resazurin based 27 fluorescence assay. Overall, the results revealed three novel anti-Entamoeba histolytica scaffolds 28 with low micromolar activity including MMV675968 (IC 50 = 2.10 µM), MMV688179 (IC 50 = 2.38 29 µM) and MMV688844 (IC 50 = 5.63 µM). Structure-Activity-Relationship (SAR) studies led to 30 identification of two analogs ~100 fold more potent and selective than the original hit compound 31 1 (MMV675968): 1k (IC 50 = 0.043 µM) and 1l (IC 50 = 0.055 µM). Predictive analysis using 32 Maestro 11.6 suggested that these hit compounds possess acceptable physicochemical and 33 metabolism properties. These lead compounds are therefore good starting points for lead 34 optimization studies towards identification of drug candidate against amoebiasis. 35 36 37 38 39 40 3 41 Author Summary 42Diarrhoea is a leading cause of death for millions of children worldwide. One of the top 15 causes 43 of severe diarrhoea is Entamoeba histolytica, causing amoebiasis. What makes E. histolytica 44 dangerous is its ability to disseminate easily through a given population via contaminated food and 45 water supplies. Moreover, E. histolytica is quite comfortable in the environment, difficult to kill 46 with chorine and infect people at a very low dose, making it a priority pathogen to eradicate. Many 47 drugs have been developed so far to cure this infection. However, they are not efficient enough to 48 control the disease due to pathogen resistance that is becoming a big issue. In addition to that, 49 almost all the drugs in use are highly toxic to human causing several side effects upon medications. 50 Therefore, new, more efficient and less toxic drugs are urgently needed for the better management 51 of amoebiasis. Since the development of a new drug takes years, repurposing existing drugs has 52 been shown to shortcut the process and boost the discovery rate of new medicines. Using this same 53 approach, we have identified two compounds that potently inhibit E. histolytica and are nontoxic 54 that can enter the drug discovery pipeline for new amoebicidal drug development. Moreover, these 55 new inhibitors could also serve as starting points for the synthesis of a library of amoebicidal 56 compounds. 57 58 59 60 61 4 62 Introduction 63 Diarrhoea that is credited to have caused approximately 8% of all deaths among children under 64 age 5 worldwide in 2016 is considered as a leading executioner of children. Basically, the number 65 of yearly deaths among children is about ...