Malaria is a tropical disease caused by infection of red blood cells by intracellular parasites of the genus Plasmodium, with infection being caused by a bite from an infected mosquito. In humans, malaria can be caused by five Plasmodium species; P. falciparum, P.vivax, P. ovale, P. malariae and P. knowlesi, with species prevalence dependant on geographic location. Global estimates for malaria prevalence report 263 million cases and approximately 600,000 deaths for 2023 (1).
Malaria parasites have a complex lifecycle; therefore, drugs which act against multiple stages are clinically advantageous. Tafenoquine (TQ) is a synthetic long half-life analog of the 8-aminoquinoline primaquine, with activity against blood and liver stage parasites, and was approved for use in 2018 in Australia and USA. The mechanism of action of TQ remains unclear, although it may function to inhibit parasite haematin polymerisation or cause mitochondrial stress (2). The stable TQ metabolite (5,6- orthoquinone tafenoquine, 5,6-OQTQ) is thought to be a marker of TQ activity, analogous to the 5,6-orthoquinone of primaquine. Compounds which enhance production of 5,6-OQTQ are likely to enhance the anti-Plasmodial effect of TQ, and we have therefore undertaken studies to identify such compounds as potential partner drugs for malaria prevention and treatment.
We have identified an FDA-approved anti-fungal agent, clotrimazole which enhances conversion of TQ to 5,6-OQTQ in both macrophage and hepatocyte cell culture models. We quantify the generation of OQTQ by PRM on a Thermo Scientific Q-Exactive plus orbitrap mass spectrometer as per our previous work (3). We have used LFQ-DDA proteomics on a Q-Exactive to investigate the mechanism by which 5,6-OQTQ production is enhanced. Results and implications will be presented.