A Reprofiled Drug, Auranofin, Is Effective against Metronidazole-Resistant Giardia lamblia

Abstract

Giardiasis is one of the most common causes of diarrheal disease worldwide. Treatment is primarily with 5-nitro antimicrobials, particularly metronidazole. Resistance to metronidazole has been described, and treatment failures can occur in up to 20% of cases, making development of alternative antigiardials an important goal. To this end, we have screened a chemical library of 746 approved human drugs and 164 additional bioactive compounds for activity against Giardia lamblia. We identified 56 compounds that caused significant inhibition of G. lamblia growth and attachment. Of these, 15 were previously reported to have antigiardial activity, 20 were bioactive but not approved for human use, and 21 were drugs approved for human use for other indications. One notable compound of the last group was the antirheumatic drug auranofin. Further testing revealed that auranofin was active in the low (4 to 6)-micromolar range against a range of divergent G. lamblia isolates representing both humanpathogenic assemblages A and B. Most importantly, auranofin was active against multiple metronidazole-resistant strains. Mechanistically, auranofin blocked the activity of giardial thioredoxin oxidoreductase, a critical enzyme involved in maintaining normal protein function and combating oxidative damage, suggesting that this inhibition contributes to the antigiardial activity. Furthermore, auranofin was efficacious in vivo, as it eradicated infection with different G. lamblia isolates in different rodent models. These results indicate that the approved human drug auranofin could be developed as a novel agent in the armamentarium of antigiardial drugs, particularly against metronidazole-resistant strains. Giardiasis is one of the most common human parasitic infections of the intestinal tract worldwide, affecting hundreds of millions of people, mostly in developing countries. It has been included in the Neglected Diseases Initiative of the WHO (1). Giardia exists in two forms, the infectious cyst and the diseasecausing trophozoite that colonizes the small intestinal lumen. Cysts are spread through drinking water, food, and person-toperson contact. The clinical symptoms of giardiasis include diarrhea, abdominal pain, malabsorption, and weight loss. A recent cohort study following a major giardiasis outbreak in Norway showed that infection with Giardia lamblia was associated with a high prevalence of irritable bowel syndrome and chronic fatigue 3 years after acute illness (2), highlighting the major health impact of giardiasis even in areas where it is not endemic. Treatment of giardiasis relies on antimicrobial drug therapy, most commonly with 5-nitroheterocyclic drugs, particularly metronidazole and, more recently, nitazoxanide (3). However, cross-resistance among 5-nitro antimicrobials exists, and treatment failures occur in up to 20% of cases (4-6). Alternative antimicrobials exist, but these are generally less effective than 5-nitro drugs (3, 7).One important strategy in the development of new antimicrobials is the screening of e...

Giardia lamblia: missing evidence for a canonical thioredoxin system

“…Thus, at present our understanding of the thioredoxin system in G. lamblia remains incomplete as there is no evidence for any protein that shuttles electrons from TrxR to peroxiredoxin or any other protein. It was clearly demonstrated that G. lamblia TrxR exerts disulphide reductase activity (Tejman-Yarden et al 2013;Leitsch et al 2016) but whether it functions as a true TrxR remains unclear. Interestingly, the impact of TrxR activity seems to be rather limited because strong overexpression of the enzyme had only little ATP-dependent RNA helicase p47, putative GL50803_16376…”

“…In light of its important function as the reducing enzyme of thioredoxin, TrxR has been repeatedly suggested to have considerable potential as a drug target for antigiardial chemotherapy (Tejman-Yarden et al 2013;Watkins and Eckmann, 2016). Comparably little, however, is known about the components of the thioredoxin-mediated redox system in G. lamblia.…”

2-Amino-4-arylthiazole Derivatives as Anti-giardial Agents: Synthesis, Biological Evaluation and QSAR Studies

“…Moreover, previous studies have also demonstrated mutagenic, teratogenic, and other cytotoxic effects [7,8]. In addition Giardia strains have been developing resistance to MTZ in vivo and manifesting cross-resistance to other nitroimidazole analogues, which results in treatment failures in up to 20% of cases [8][9][10]. Early in the last decade, US Food and Drug Administration has approved the use of nitazoxanide (NIT) for treatment giardiasis.…”

Evidence that the antiproliferative effects of auranofin in Saccharomyces cerevisiae arise from inhibition of mitochondrial respiration

“…In fact, inhibition of a few inflammatory pathways and of various thiol redox enzymes makes AF, an optimal candidate for cancer therapy and for treatment of various parasitic and microbial infections in the frame of a more general "drug repositioning strategy". For instance, relevant therapeutic actions were reported for AF toward Schistosoma japonicum (Song et al, 2012), Giardia lamblia (Tejman-Yarden et al, 2013) and Entamoeba histolytica (Debnath et al, 2012). In addition, four clinical trials were started against various cancer types and are still ongoing.…”