Post-translational import of protein into the endoplasmic reticulum of a trypanosome: an in vitro system for discovery of anti-trypanosomal chemical entities.

HAT (human African trypanosomiasis), caused by the protozoan parasite Trypanosoma brucei, is an emerging disease for which new drugs are needed. Expression of plasma membrane proteins [e.g. VSG (variant surface glycoprotein)] is crucial for the establishment and maintenance of an infection by T. brucei. Transport of a majority of proteins to the plasma membrane involves their translocation into the ER (endoplasmic reticulum). Thus inhibition of protein import into the ER of T. brucei would be a logical target for discovery of lead compounds against trypanosomes. We have developed a TbRM (T. brucei microsome) system that imports VSG_117 post-translationally. Using this system, MAL3-101, equisetin and CJ-21,058 were discovered to be small molecule inhibitors of VSG_117 translocation into the ER. These agents also killed bloodstream T. brucei in vitro; the concentrations at which 50% of parasites were killed (IC50) were 1.5 microM (MAL3-101), 3.3 microM (equisetin) and 7 microM (CJ-21,058). Thus VSG_117 import into TbRMs is a rapid and novel assay to identify 'new chemical entities' (e.g. MAL3-101, equisetin and CJ-21,058) for anti-trypanosome drug development.