L eishmaniasis is one of the 17 neglected tropical diseases (NTDs) assigned by the World Health Organization (WHO). NTDs affect 1 billion people worldwide (1). The primary occurrences are in low-income countries in sub-Saharan Africa, Asia, and Latin America, but the Mediterranean countries of Europe are also concerned (2). Among the NTDs is the group of "most neglected diseases," affecting the poorest, mainly rural areas, including leishmaniases, sleeping sickness (African trypanosomiasis), and Chagas' disease (3). These three NTDs have the highest rates of death. However, the NTD drug discovery pipeline is almost empty, thus leading to a lack of efficient and safe drugs (2, 4). Because of climate warming and tourism, the occurrence of leishmaniasis is also reported in states around the Mediterranean Sea (1).Leishmaniasis is caused by more than 20 species of protozoan parasites belonging to the genus Leishmania. The parasite life cycle is characterized by two morphological stages: extracellular flagellated promastigotes, occurring in the insect vector, and intracellular aflagellated amastigotes, occurring in the mammalian host. The promastigotes are transmitted by an insect bite into the skin of the host, where they are internalized by macrophages, dendritic cells, neutrophils, and fibroblasts and differentiate into amastigotes residing and replicating in parasitophorous vacuoles of these phagocytes. The parasites disseminate through the lymphatic and vascular systems. During the blood meal of an (uninfected) sand fly, amastigotes are transmitted back from the infected mammalian host to the insect vector and differentiate again into promastigotes (5, 6).The clinical outcome of leishmaniasis depends on the complex interactions between the virulence characteristics of the infecting species and the type of immune response of the host. There are three clinical forms: cutaneous, mucocutaneous, and visceral leishmaniases (6).Concerning the treatment of leishmaniasis, it is obvious that new drugs must circumvent the limitations of currently established chemotherapies, i.e., toxicity, long courses of treatment, the frequent need for parenteral administration, high costs in countries where the disease is endemic, and the emergence of resistance. Therefore, it is important not only to test and apply combinations of existing drugs to avoid resistance but also to develop new potential leishmanicidal compounds with alternative mechanisms, as well as vaccination strategies (7,8).Cysteine proteases (CPs) of parasites such as Plasmodium, Trypanosoma, and worms are druggable targets for developing a new promising strategy for chemotherapy based on protease inhi-