Abstract:
Malaria is a significant disease in Africa, certain countries in Asia, and Central and South America. In 2022, malaria infected approximately 233 million people and caused 608,000 death. During its intraerythrocytic stage (which is responsible for the clinical symptoms), Plasmodium requires various vitamins as cofactors for biochemical processes. While nutrients such as amino acids and glucose are obtained from the host plasma or erythrocyte, thiamine  (vitamin B₁) can either be synthesized by the parasite itself or acquired from the host. Thiamine needs to be converted into thiamine pyrophosphate (TPP) by the enzyme thiamine pyrophosphokinase (TPK) before functioning as a cofactor of several enzymes. In my study, I investigated thiamine metabolism in Plasmodium as a potential target for antimalarial drugs. Previously, oxythiamine, an antiplasmodial thiamine analogue, has been shown to kill P. falciparum by being converted into the antimetabolite oxythiamine pyrophosphate (OxPP) by TPK. To expand on this finding, I tested the antiplasmodial activity of various thiamine analogues that were synthesized or commercially available, aiming to find a thiamine analogue with improved properties compared to oxythiamine. To investigate the mechanism of action of oxythiamine in more detail, I conducted in vitro evolution to generate parasites that are resistant to oxythiamine. Through this, I identified a mutation in TPK likely responsible for the parasite's resistance to oxythiamine consistent with TPK playing a crucial role in the antiplasmodial activity of oxythiamine. Furthermore, I knocked out TPK in a murine malaria parasite and studied its effect on the parasite’s entire life cycle. I found that TPK is essential for the formation of sporozoites – the stage of the parasite that infects the liver. My overall findings support the idea that thiamine conversion by Plasmodium should be explored for targeted, multi-stage drug development.