title: Leishmania is not prone to develop resistance to tamoxifen.
abstract: Tamoxifen, an antineoplastic agent, is active in vitro and in vivo against the parasitic protozoa Leishmania. As part of our efforts to unravel this drug's mechanisms of action against the parasite and understand how resistance could arise, we tried to select tamoxifen-resistant Leishmania amazonensis. Three different strategies to generate tamoxifen resistant mutants were used: stepwise increase in drug concentration applied to promastigote cultures, chemical mutagenesis followed by drug selection and treatment of infected mice followed by selection of amastigotes. For amastigote selection, we employed a method with direct plating of parasites recovered from lesions into semi-solid media. Tamoxifen resistant parasites were not rescued by any of these methods. Miltefosine was used as a control in selection experiments and both stepwise selection and chemical mutagenesis allowed successful isolation of miltefosine resistant mutants. These findings are consistent with a multi-target mode of action to explain tamoxifen's leishmanicidal properties. Considering that drug resistance is a major concern in anti-parasitic chemotherapy, these findings support the proposition of using tamoxifen as a partner in drug combination schemes for the treatment of leishmaniasis.
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 05508-900, SP, Brazil.
authors.forename: Adriano C
authors.initials: AC
authors.lastname: Coelho
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 05508-900, SP, Brazil.
authors.forename: Cristiana T
authors.initials: CT
authors.lastname: Trinconi
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 05508-900, SP, Brazil.
authors.forename: Luisa
authors.initials: L
authors.lastname: Senra
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 05508-900, SP, Brazil.
authors.forename: Jenicer K U
authors.initials: JK
authors.lastname: Yokoyama-Yasunaka
authors.affiliation: Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, 05508-900, SP, Brazil.
authors.forename: Silvia R B
authors.initials: SR
authors.lastname: Uliana
mesh_terms: D000818:Animals; D000981:Antiprotozoal Agents / Q000494:pharmacology / Q000627:therapeutic use; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D005260:Female; D006801:Humans; D007891:Leishmania / Q000187:drug effects*; D007896:Leishmaniasis / Q000188:drug therapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000627:therapeutic use; D020845:Selective Estrogen Receptor Modulators / Q000494:pharmacology / Q000627:therapeutic use; D013629:Tamoxifen / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D000981:Antiprotozoal Agents; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen; D010767:Phosphorylcholine; C039128:miltefosine
keywords: Chemotherapy; Drug resistance; Leishmania amazonensis; MNNG, N-methyl-N-nitroso-N′-nitroguanidine; MT, miltefosine transporter; NBD-PC, 2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl-1-hexadecanoyl-sn-glycero-3-phosphocholine; PBS, phosphate buffered solution; TM, tamoxifen; Tamoxifen