Interfering with Resistance

Drug efficacy and resistance mechanisms shine a light on how drugs enter cells, which could facilitate the development of new sleeping-sickness treatments. 

Jun 1, 2012
Hannah Waters

TRYPANOSOMA BRUCEI PROTOZOA: The parasite, shown here in purple, causes sleeping sickness, a disease that starts out as fever and inflammation and progresses to neurological symptoms such as confusion and disrupted sleep cycles, eventually leading to coma and death. WIKIMEDIA COMMONS, ALAN R. WALKER


The paper

S. Alsford et al., “High-throughput decoding of antitrypanosomal drug efficacy and resistance,” Nature, 482:232-36, 2012.

The finding

Trypanosoma brucei, the single-cell protozoan that causes the tropical disease sleeping sickness, is becoming increasingly resistant to the few drug treatments available. Using RNA interference (RNAi), David Horn of the London School of Hygiene and Tropical Medicine and colleagues identified 55 genes that contribute to drug susceptibility and resistance.

The interference

Horn used a library of plasmids to create around 750,000 T. brucei clones, each with one of the bug’s 7,500 or so genes knocked down using RNAi. He then treated the pool with five different sleeping sickness drugs, selecting for those clones that gained resistance by losing a gene. Using next-generation sequencing, the team identified 55 susceptibility-related genes in the survivors, marked by the RNAi sequences that had silenced them.

The uptake

Horn and colleagues also gained insights into how these genes, when knocked down, might work. Out of 8 genes whose disabling conferred resistance to the first-line drug suramin, one encoded a previously unidentified cell-surface receptor, ISG75. When ISG75 was knocked down, the drug could not bind to the pathogen’s cell membrane—evidence of how suramin enters and kills cells through endocytosis.

The mechanisms

The paper is important “mainly because we [now] understand better how these drugs work,” said microbiologist Christine Clayton of the University of Heidelberg, which could help researchers design new drugs that bypass the resistance mechanism.