Defeating Drug Resistance: A Second Mechanism of Action for Artemisinin and Atovaquone Resistance Transmissibility in P. falciparum

Statement of Problem: Malaria is a serious public health challenge, with 241 million cases and 627,000 deaths occurring in 2020, a 12% rise from the previous year. In addition to a rising death toll, drug resistant parasite spread is also on the rise, particularly artemisinin ring stage resistant parasites. Previously confined to Southeast Asia, artemisinin ring stage resistant parasites have now been detected in Africa. This thesis explores antimalarial drug resistance, specifically characterizing a second mechanism of action of artemisinin and how this second mechanism targets the trophozoite sensitive stages of the parasite. In addition to artemisinin resistance, this thesis also explores parasite resistance to atovaquone, specifically, understanding if resistant parasites can spread through the mosquito vector and into a new mammalian host. Methods: We utilized a pre-formed heme-artemisinin adduct molecule to characterize a second mechanism of action for artemisinin in P. falciparum. An adduct molecule with an inactive endoperoxide bridge was used to study the effect of artemisinin after initial activation in the parasite. Additionally, we created gametocyte competent atovaquone resistant P. falciparum lines and followed parasite progression through An. stephensi to determine the capability of atovaquone resistant parasites to spread. Results: Through exploring a second mechanism of action of artemisinin, we find the heme-artemisinin and heme-artesunate adduct molecules inhibit P. falciparum growth by preventing hemozoin crystal extension. By inhibiting crystal extension, toxic levels of heme accumulate in the parasite, resulting in parasite death. Through exploring atovaquone resistant parasite spread, we find that parasites with specific atovaquone resistance mutations are unable to produce sporozoites visible by microscopy or be transmitted by An. stephensi. Conclusions: Drug resistance continues to pose a significant challenge to malaria control efforts. Fully understanding a drug’s mechanism of action can lead to improved dosing strategies, as is described in this work regarding artemisinin. Additionally, when investigating new uses for an antimalarial drug, the possibility of drug resistant parasite spread should be thoroughly investigated, as is described in our work with atovaquone resistant parasites. Drug resistant parasite spread is a complex challenge, and the work here informs future atovaquone and artemisinin use, and dosing strategies respectively