Chemotherapy of Leishmaniasis: Past, Present and Future
Leishmaniasis is a parasitic disease caused by hemoflagellate, Leishmania spp. The parasite is transmitted by the bite of an infected female phlebotomine sandfly. The disease is prevalent throughout the world and in at least 88 countries. Nearly 25 compounds are reported to have anti-leishmanial effects but not all are in use. The pentavalent antimony compounds have remained mainstay for nearly 75 years. Pentavalent antimony is a prodrug that is reduced by glutathione to active trivalent species catalyzed by thiol-dependent-reductase. However, emergence of resistance led to the use of other compounds -amphotericin B, pentamidine, paromomycin, allopurinol etc. Amphotericin B, an antifungal macrolide polyene is characterized by the hydrophilic polyhydroxyl and hydrophobic polyene faces on it long axis. Presently, it is the only drug with highest cure rate. It acts on membrane sterols resulting in parasite cell lysis. Its lipid formulations have been developed to minimize side effects. Other anti-fungals like ketoconazole, fluconazole and terbinafine are found less effective. Recently, anticancer alkylphosphocholines have been found most effective oral compounds. These act as membrane synthetic ether-lipid analogues, and consist of alkyl chains in the lipid portions. Most promising of these are miltefosine (hexadecylphosphocholine), edelfosine (ET-18-OCH3) and ilmofosine (BM 41.440). However, the recent focus has been on identifying newer therapeutic targets in the parasite such as DNA topoisomerases. The present review describes the current understanding of different drugs against leishmaniasis, their chemistry, mode of action and the mechanism of resistance in the parasite. Future perspectives in the area of new anti-leishmanial drug targets are also enumerated. However, due to the vastness of the topic main emphasis is given on visceral leishmaniasis.
Keywords: Leishmaniasis, Kala-azar, Antileishmanial drugs, Chemotherapy, Drug resistance, Antimonials, Miltefosine and Natural Products
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