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2. The trypanocidal benzoxaborole AN7973 inhibits trypanosome mRNA processing

Author

Begolo, Daniela, Vincent, Isabel M., Giordani, Federica, Pöhner, Ina, Witty, Michael J., Rowan, Timothy G., Bengaly, Zakaria, Gillingwater, Kirsten, Freund, Yvonne, Wade, Rebecca C., Barrett, Michael P., and Clayton, Christine

Subjects
QH301-705.5, Immunologic diseases. Allergy, RC581-607, Biology (General)
Abstract

Kinetoplastid parasites—trypanosomes and leishmanias—infect millions of humans and cause economically devastating diseases of livestock, and the few existing drugs have serious deficiencies. Benzoxaborole-based compounds are very promising potential novel anti-trypanosomal therapies, with candidates already in human and animal clinical trials. We investigated the mechanism of action of several benzoxaboroles, including AN7973, an early candidate for veterinary trypanosomosis. In all kinetoplastids, transcription is polycistronic. Individual mRNA 5'-ends are created by trans splicing of a short leader sequence, with coupled polyadenylation of the preceding mRNA. Treatment of Trypanosoma brucei with AN7973 inhibited trans splicing within 1h, as judged by loss of the Y-structure splicing intermediate, reduced levels of mRNA, and accumulation of peri-nuclear granules. Methylation of the spliced leader precursor RNA was not affected, but more prolonged AN7973 treatment caused an increase in S-adenosyl methionine and methylated lysine. Together, the results indicate that mRNA processing is a primary target of AN7973. Polyadenylation is required for kinetoplastid trans splicing, and the EC50 for AN7973 in T. brucei was increased three-fold by over-expression of the T. brucei cleavage and polyadenylation factor CPSF3, identifying CPSF3 as a potential molecular target. Molecular modeling results suggested that inhibition of CPSF3 by AN7973 is feasible. Our results thus chemically validate mRNA processing as a viable drug target in trypanosomes. Several other benzoxaboroles showed metabolomic and splicing effects that were similar to those of AN7973, identifying splicing inhibition as a common mode of action and suggesting that it might be linked to subsequent changes in methylated metabolites. Granule formation, splicing inhibition and resistance after CPSF3 expression did not, however, always correlate and prolonged selection of trypanosomes in AN7973 resulted in only 1.5-fold resistance. It is therefore possible that the modes of action of oxaboroles that target trypanosome mRNA processing might extend beyond CPSF3 inhibition.

Published
2018

6. Phenotypic and Genotypic Changes in Salmonella entericasubsp. entericaSerotype Typhimurium during Passage in Intestines of Broiler Chickens Fed on Diets That Included Ionophore Anticoccidial Supplements

Author

Scalzo, Salvatore, Corkill, John E., Shanks, David J., Rowan, Timothy G., Delaval, Jose´, Fleetwood, Andrew, Murphy, Martin, and Hart, C. Anthony

Abstract

ABSTRACTThe effect of continuous in-feed administration of anticoccidial agents on antimicrobial sensitivity and the level of bacterial shedding in poultry experimentally infected with Salmonella entericasubsp. entericaserotype Typhimurium definitive type 104 (DT104) were investigated. On day 0, 1,200 1-day-old Salmonella-free broiler chicks were placed into 50 pens, and the pens were randomly allocated to one of five treatments: nonsupplemented (negative control; T1), monensin at 120 mg/kg of diet (T2), salinomycin at 60 mg/kg of diet (T3), semduramicin at 20 mg/kg of diet (T4), or semduramicin at 25 mg/kg of diet (T5). Each bird was inoculated with a well-characterized strain of serotype Typhimurium DT104 on day 10. On day 49, the birds were euthanatized humanely. Bulk fecal samples were collected on days 13, 43, and 48 and were examined for organisms which had acquired resistance. The genetic basis of acquired resistance was determined from representative samples of isolates. Of 784 Salmonella-selective plates supplemented with antimicrobial agents, only 33 showed growth. These isolates came from all treatment regimens, including the nonsupplemented control. A number of phenotypic changes were observed; these included changes in motility, phage type, and agglutination properties. Supplementation of the diet with an anticoccidial drug does not appear to affect antimicrobial resistance or the level of excretion of salmonellae. Most of the changes observed do not seem to be related to the presence of a supplement in feed. Salmonellae appear to be capable of acquiring antimicrobial resistance and phenotypic changes independently of specific antimicrobial selection pressures.

Published
2004
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8. The trypanocidal benzoxaborole AN7973 inhibits trypanosome mRNA processing.

Author

Begolo D, Vincent IM, Giordani F, Pöhner I, Witty MJ, Rowan TG, Bengaly Z, Gillingwater K, Freund Y, Wade RC, Barrett MP, and Clayton C

Subjects
Animals, Benzoxazoles chemistry, Cattle, Drug Resistance genetics, Goats, Humans, Mice, Protozoan Proteins genetics, Protozoan Proteins metabolism, RNA Processing, Post-Transcriptional drug effects, RNA, Messenger genetics, RNA, Messenger metabolism, RNA, Protozoan genetics, Trans-Splicing drug effects, Trypanocidal Agents chemistry, Trypanosoma brucei brucei genetics, Trypanosoma congolense drug effects, Trypanosoma congolense genetics, Trypanosoma congolense metabolism, Trypanosoma vivax drug effects, Trypanosoma vivax genetics, Trypanosoma vivax metabolism, Trypanosomiasis drug therapy, Trypanosomiasis parasitology, Benzoxazoles pharmacology, RNA, Protozoan metabolism, Trypanocidal Agents pharmacology, Trypanosoma brucei brucei drug effects, Trypanosoma brucei brucei metabolism
Abstract

Kinetoplastid parasites-trypanosomes and leishmanias-infect millions of humans and cause economically devastating diseases of livestock, and the few existing drugs have serious deficiencies. Benzoxaborole-based compounds are very promising potential novel anti-trypanosomal therapies, with candidates already in human and animal clinical trials. We investigated the mechanism of action of several benzoxaboroles, including AN7973, an early candidate for veterinary trypanosomosis. In all kinetoplastids, transcription is polycistronic. Individual mRNA 5'-ends are created by trans splicing of a short leader sequence, with coupled polyadenylation of the preceding mRNA. Treatment of Trypanosoma brucei with AN7973 inhibited trans splicing within 1h, as judged by loss of the Y-structure splicing intermediate, reduced levels of mRNA, and accumulation of peri-nuclear granules. Methylation of the spliced leader precursor RNA was not affected, but more prolonged AN7973 treatment caused an increase in S-adenosyl methionine and methylated lysine. Together, the results indicate that mRNA processing is a primary target of AN7973. Polyadenylation is required for kinetoplastid trans splicing, and the EC50 for AN7973 in T. brucei was increased three-fold by over-expression of the T. brucei cleavage and polyadenylation factor CPSF3, identifying CPSF3 as a potential molecular target. Molecular modeling results suggested that inhibition of CPSF3 by AN7973 is feasible. Our results thus chemically validate mRNA processing as a viable drug target in trypanosomes. Several other benzoxaboroles showed metabolomic and splicing effects that were similar to those of AN7973, identifying splicing inhibition as a common mode of action and suggesting that it might be linked to subsequent changes in methylated metabolites. Granule formation, splicing inhibition and resistance after CPSF3 expression did not, however, always correlate and prolonged selection of trypanosomes in AN7973 resulted in only 1.5-fold resistance. It is therefore possible that the modes of action of oxaboroles that target trypanosome mRNA processing might extend beyond CPSF3 inhibition., Competing Interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: Yvonne Freund was employed by Anacor Pharmaceuticals. Benzoxaboroles were supplied by Anacor Pharmaceuticals (YF) which was later taken over by Pfizer. This does not alter our adherence to all the PLOS Pathogens policies on sharing data and materials.

Published
2018
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