ABSTRACT
Cholesterol is essential for the growth and development of Plasmodium falciparum during its asexual blood stages. However, neither the parasite nor host red blood cells can synthesise cholesterol de novo and must acquire it from the host, making the pathway an attractive target. However, its source and mechanism of uptake remain poorly understood.

During my PhD, I investigated the sources of cholesterol for P. falciparum-infected RBCs and the mechanisms involved. Using a fluorescent cholesterol analogue, I showed that cholesterol uptake is dependent on parasite life stage and time. I then explored the potential involvement of different transporters/pathways and found a likely role for the P. falciparum Niemann-Pick type C1-related (PfNCR1) transporter in the uptake process. Additionally, I found that naïve uninfected RBCs also serve as a source of cholesterol for the infected RBCs.

Building on this, I next exploited the cholesterol uptake pathway for drug delivery to infected RBCs. Previous work from our lab showed that cholesterol mimics (DHEA) conjugated to antimalarial drugs improve efficacy against P. falciparum. I performed structure-activity relationship analysis by keeping the drug (primaquine) constant while modifying the cholesterol using closely related steroids. By conjugating different sterol mimics to primaquine, I demonstrated enhanced efficacy against P. falciparum without cytotoxicity to human cells. Chemical inhibition of PfNCR1 and other related pathways did not reduce conjugate efficacy, suggesting the conjugates could use an alternative route of entry.

Together, my PhD work defines the sources and mechanisms of cholesterol uptake in P. falciparum-infected RBCs and demonstrates how this pathway can be exploited to improve antimalarial drug delivery and therapeutic index.