Neglected Tropical Diseases (NTD), which include helminthiasis and leishmaniasis, are a group of thirteen parasitic and bacterial infections that affect over 1.4 billion people. Although these are devastating diseases of global concern, their neglected status relative to other health concerns has resulted in a limited arsenal of therapeutic compounds for their treatment. The trypanosomatid parasites L. major and L. amazonensis are causative agents of human cutaneous leishmaniasis in the Old World and New World, respectively. Combined, these two species are responsible for an estimated 2 million new infections annually with ~350 million people living in areas of active parasite transmission. In many regions of the world, treatment of leishmaniasis still relies on toxic drugs such as pentavalent antimony, which requires high doses and lengthy courses of treatment, and alternative drugs are still costly and not widely available in endemic areas. This situation, combined with the recent increase in Leishmania infections in urban areas, highlights the urgent need for identification of essential pathways in these organisms that can be targeted by new drugs with lower toxicity. This proposal details a highly innovative and interdisciplinary route to antagonize pathways for the transport of an essential nutrient for parasite survival - heme - which most parasites need to ingest from their environment. This therapeutic strategy was deliberately chosen based on the following key observations: (a) heme is utilized in multiple, critical processes; (b) heme is required in all stages of development; (c) Leishmania cannot live without heme and actively ingest it; and (d) both humans and their parasites require heme, but the mechanisms used to fulfill this requirement are different. Thus drugs that target heme transport pathways unique to the parasite and not shared by its mammalian host offers great therapeutic potential. The studies described in this application will validate heme transporters as novel targets for treating Leishmania infections and provide novel chemical matter as drug leads. LHR1 is a heme transporter that is essential for Leishmania survival. Loss of a single LHR1 allele (LHR1+/-) causes severe growth defects while LHR1 null mutants (LHR1-/-) are not viable suggesting that a 50% reduction in LHR1 function is sufficient to significantly impair growth. In this Phase I STTR application, we will (a) structurally refine and synthesize novel small molecule antagonists of LHR1 heme transporter from Leishmania, evaluate the efficacy of these novel compounds in dose-response growth of axenic amastigotes, assess the specificity of antagonism, and measure heme transport inhibition; and (b) determine the physiological consequences of pharmacologic targeting of LHR1 in intracellular amastigotes of L. amazonensis, which causes cutaneous leishmaniasis, and expand our in vivo efficacy studies of specific lead compounds against intracellular amastigotes of L. donovani, the causative agent of the more fatal visceral Leishmaniasis, in primary macrophages. More broadly, the success of this Phase I project will lay the groundwork for future Phase II studies in animals and for the treatment of other NTD.
As most parasitic nematodes / helminths and single-celled parasites such as Trypanosomes and Leishmania do not have an intact heme synthesis pathway and instead rely on environmental heme for sustenance, drugs that target heme transport pathways unique to the parasite and not shared by its mammalian host offers great therapeutic potential and could be the parasites' Achilles heel. Results from our proposed studies could be directly applied to the treatment of infections caused by a diverse group of parasites, including intestinal nematodes, lymphatic and cutaneous filarial nematodes, and the kinetoplastids.
| Soares, Miguel P; Hamza, Iqbal (2016) Macrophages and Iron Metabolism. Immunity 44:492-504 |
