Investigating the mechanism of action of a highly potent haloalkoxyacridone against Plasmodium falciparum

Author

Jordan Charlton, Dominican University of CaliforniaFollow

ORCID

0009-0001-1817-4784

Graduation Year

2024

Document Type

Master's Thesis

Degree

Master of Science

Program

Biological Science

Program Director

Meredith Protas, PhD

First Reader

Roland Cooper, PhD

Second Reader

Jane Kelly

Abstract

Malaria is a severe global public health problem, where children and pregnant women are most vulnerable. With drug resistance being reported to artemisinin-based combination therapies (ACT), which are the front-line treatments for uncomplicated malaria, there is a high demand for an affordable, effective, and safe medication. Discovery of chemotype I acridones, a novel antimalarial class, has shown promising results to be a new antimalarial treatment. Chemotype I acridones are proposed to inhibit the Plasmodium falciparum electron transport chain, here we investigate the target and mechanism of action for compound T111, the lead candidate for chemotype I acridones. We used multi-drug resistant P. falciparum strain Dd2 and selected T111 resistance by using continuous incremental drug pressure. Dd2 control parasites exhibited T111 IC₅₀ values of ~ 0.1 nM, while T111-resistant parasites showed IC₅₀ values of ~ 223 nM (~2,200-fold higher). From our T111-resistant populations we derived seven unique haplotypes containing cytochrome b (cyt b) mutations, which demonstrated acquisition of mutations were both ordered and sequential. We reported that most of the mutations were located in the cyt b Q_o site. We found that the selection of the third cyt b mutation was necessary to confer high-level T111 resistance (T111 IC₅₀ value increased from 12 nM to 223 nM). T111-resistant lines with three or more cyt b mutations conferred cross-resistance to myxothiazol, atovaquone, and ELQ400. We identified two T111-resistant lines that harbored a dihydroorotate dehydrogenase mutation in addition to cyt b mutations, which were the only parasite lines to confer cross resistance to DSM265, ELQ300 and T63. We demonstrate that T111-resistant lines did not confer cross resistance to standard antimalarials such as, chloroquine, lumefantrine, piperaquine and dihydroartemisinin. Lastly, we performed ex vivo growth inhibition assays with T111 and analogs against fresh clinical isolates in Uganda and Burkina Faso, which demonstrated that all of the compounds maintained nanomolar activity. Thus, T111 has shown promising results to be a new and effective antimalarial therapeutic.