title: Selective inhibition of RNA polymerase I transcription as a potential approach to treat African trypanosomiasis.
abstract: Trypanosoma brucei relies on an essential Variant Surface Glycoprotein (VSG) coat for survival in the mammalian bloodstream. High VSG expression within an expression site body (ESB) is mediated by RNA polymerase I (Pol I), which in other eukaryotes exclusively transcribes ribosomal RNA genes (rDNA). As T. brucei is reliant on Pol I for VSG transcription, we investigated Pol I transcription inhibitors for selective anti-trypanosomal activity. The Pol I inhibitors quarfloxin (CX-3543), CX-5461, and BMH-21 are currently under investigation for treating cancer, as rapidly dividing cancer cells are particularly dependent on high levels of Pol I transcription compared with nontransformed cells. In T. brucei all three Pol I inhibitors have IC50 concentrations for cell proliferation in the nanomolar range: quarfloxin (155 nM), CX-5461 (279 nM) or BMH-21 (134 nM) compared with IC50 concentrations in the MCF10A human breast epithelial cell line (4.44 μM, 6.89 μM or 460 nM, respectively). T. brucei was therefore 29-fold more sensitive to quarfloxin, 25-fold more sensitive to CX-5461 and 3.4-fold more sensitive to BMH-21. Cell death in T. brucei was due to rapid inhibition of Pol I transcription, as within 15 minutes treatment with the inhibitors rRNA precursor transcript was reduced 97-98% and VSG precursor transcript 91-94%. Incubation with Pol I transcription inhibitors also resulted in disintegration of the ESB as well as the nucleolus subnuclear structures, within one hour. Rapid ESB loss following the block in Pol I transcription argues that the ESB is a Pol I transcription nucleated structure, similar to the nucleolus. In addition to providing insight into Pol I transcription and ES control, Pol I transcription inhibitors potentially also provide new approaches to treat trypanosomiasis.
authors.affiliation: Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, London, United Kingdom.
authors.forename: Louise E
authors.initials: LE
authors.lastname: Kerry
authors.affiliation: Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, London, United Kingdom.
authors.forename: Elaine E
authors.initials: EE
authors.lastname: Pegg
authors.affiliation: ACRF Department of Cancer Biology and Therapeutics, The John Curtin School of Medical Research, The Australian National University, Canberra, Australia.|Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: Donald P
authors.initials: DP
authors.lastname: Cameron
authors.affiliation: Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, London, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: Budzak
authors.affiliation: ACRF Department of Cancer Biology and Therapeutics, The John Curtin School of Medical Research, The Australian National University, Canberra, Australia.|Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: Gretchen
authors.initials: G
authors.lastname: Poortinga
authors.affiliation: ACRF Department of Cancer Biology and Therapeutics, The John Curtin School of Medical Research, The Australian National University, Canberra, Australia.|Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Hannan
authors.affiliation: ACRF Department of Cancer Biology and Therapeutics, The John Curtin School of Medical Research, The Australian National University, Canberra, Australia.|Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, Melbourne, Australia.
authors.forename: Ross D
authors.initials: RD
authors.lastname: Hannan
authors.affiliation: Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, London, United Kingdom.
authors.forename: Gloria
authors.identifier: 0000-0003-1884-4933
authors.initials: G
authors.lastname: Rudenko
mesh_terms: D004791:Enzyme Inhibitors / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D012318:RNA Polymerase I / Q000037:antagonists & inhibitors*; D014158:Transcription, Genetic / Q000187:drug effects*; D014344:Trypanocidal Agents / Q000494:pharmacology*; D014346:Trypanosoma brucei brucei / Q000187:drug effects* / Q000201:enzymology*; D014353:Trypanosomiasis, African / Q000188:drug therapy*
chemical_list: D004791:Enzyme Inhibitors; D014344:Trypanocidal Agents; D012318:RNA Polymerase I