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PLoS Negl Trop Dis. 2019 Feb 4;13(2):e0007052. doi: 10.1371/journal.pntd.0007052. eCollection 2019 Feb.

Genomic instability at the locus of sterol C24-methyltransferase promotes amphotericin B resistance in Leishmania parasites.

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Wellcome Centre for Molecular Parasitology, Institute of Infection, Immunity & Inflammation, University of Glasgow, Glasgow, United Kingdom.
Department of Microbiology and Molecular Genetics, University of Texas Health Science Center at Houston, Houston, Texas, United States of America.
Glasgow Polyomics, College of Medical, Veterinary & Life Sciences, University of Glasgow, Garscube Estate, Bearsden, Glasgow, United Kingdom.
Division of Biomedical and Life Sciences, Faculty of Health and Medicine, Lancaster University, United Kingdom.
Marine Biomedical & Biotechnology Research Program, Florida Atlantic University Harbor Branch Oceanographic Institute, Fort Pierce, Florida, United States of America.


Amphotericin B is an increasingly important tool in efforts to reduce the global disease burden posed by Leishmania parasites. With few other chemotherapeutic options available for the treatment of leishmaniasis, the potential for emergent resistance to this drug is a considerable threat. Here we characterised four novel amphotericin B-resistant Leishmania mexicana lines. All lines exhibited altered sterol biosynthesis, and hypersensitivity to pentamidine. Whole genome sequencing demonstrated resistance-associated mutation of the sterol biosynthesis gene sterol C5-desaturase in one line. However, in three out of four lines, RNA-seq revealed loss of expression of sterol C24-methyltransferase (SMT) responsible for drug resistance and altered sterol biosynthesis. Additional loss of the miltefosine transporter was associated with one of those lines. SMT is encoded by two tandem gene copies, which we found to have very different expression levels. In all cases, reduced overall expression was associated with loss of the 3' untranslated region of the dominant gene copy, resulting from structural variations at this locus. Local regions of sequence homology, between the gene copies themselves, and also due to the presence of SIDER1 retrotransposon elements that promote multi-gene amplification, correlate to these structural variations. Moreover, in at least one case loss of SMT expression was not associated with loss of virulence in primary macrophages or in vivo. Whilst such repeat sequence-mediated instability is known in Leishmania genomes, its presence associated with resistance to a major antileishmanial drug, with no evidence of associated fitness costs, is a significant concern.

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Conflict of interest statement

The authors have declared that no competing interests exist.

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