Screening of an open-source compound library against the livestock parasite Trypanosoma evansi

Ansah, Michael Leroy Kwame

Abstract

Surra is a neglected tropical veterinary disease that causes a large socioeconomic burden in sub-Saharan Africa, South America, the middle east, Asia, and parts of Southern Europe. Although symptoms can be mild in wild animal species, disease in domesticated species is often acute in nature and can lead to death if left untreated. The causative agent of this disease is Trypanosoma evansi (T. evansi). T. evansi is mainly transmitted mechanically by tabanids (horse-flies) and Stomoxys (stable-flies). Current therapeutic treatments for Surra are toxic and fail to treat the disease once the parasite has infiltrated the central nervous system (CNS), particularly, in camels and canines. Previous frontline treatments, suramin and isometamidine chloride, are no longer used in veterinary practice in a number of countries due to widespread resistance. Therefore, it is essential to identify novel or repurposed drugs and compounds that could be used to treat Surra in the future.

This thesis investigates the activity of fertility drug clomiphene citrate against T. evansi. The PrestoBlue assay determined that the EC50 of clomiphene citrate against T. evansi was 252 nM. Although this value is higher than typical EC50 values for current Surra treatments, clomiphene citrate is already a licensed drug for humans and has the potential to be repurposed. This thesis also investigates the GSK anti-kinetoplastid chemical box against T. evansi using a high throughput screening approach. A primary screen at a concentration of 1 μM using the PrestoBlue (AlamarBlue) assay yielded 103 ‘hit’ compounds that were active against T. evansi (demonstrated <10% cell viability after incubation for 48 hours). A secondary screen at 100 nM then yielded 13 ‘hit’ compounds. The EC50 values of 9 of these final ‘hit’ compounds were determined, with 8/9 compounds demonstrating an EC50 <100 nM. The best performing compounds were TCMDC-143326, TCMDC-143341 and TCMDC-143643 with EC50 values against T. evansi of 10.6 nM, 20.4 nM and 12.0 nM respectively. These EC50 values are similar to current treatments for Surra such as diminazene aceturate (8.8 nM).

In summary, clomiphene citrate, as well as several compounds from the GSK antikinetoplastid box, demonstrate activity against T. evansi with similar in vitro effectiveness to current frontline treatments. Further work is required to establish mode of action and cytotoxicity towards specific domestic animal cells.

Citation

Ansah, M. L. K. (2024). Screening of an open-source compound library against the livestock parasite Trypanosoma evansi. (Thesis). Keele University. Retrieved from https://keele-repository.worktribe.com/output/853242

• Thesis Type: Thesis
• Deposit Date: Jun 21, 2024
• Publicly Available Date: Jun 21, 2024
• Public URL: https://keele-repository.worktribe.com/output/853242
• Award Date: 2024-06