New Insights into Antimalarial Chemopreventive Activity of Antifolates

Abstract

Antifolates targeting dihydrofolate reductase (DHFR) are antimalarial compounds that have long been used for malaria treatment and chemoprevention (inhibition of infection from mosquitoes to humans). Despite their extensive applications, the thorough understanding of antifolate activity against hepatic malaria parasites, especially resistant parasites, have yet to be achieved. Using a transgenic P. berghei harboring quadruple mutant dhfr from P. falciparum (Pb::Pfdhfr -4M ) , we demonstrate that quadruple mutations on Pfdhfr confer complete chemoprevention resistance to pyrimethamine, the previous generation of antifolate, but not to a new class of antifolate designed to overcome the resistance such as P218. Detailed investigation to pin-point stage-specific chemoprevention further demonstrated that it is unnecessary for the drug to be present throughout hepatic development. The drug is most potent against the developmental stages from early hepatic trophozoite to late hepatic trophozoite, but is not effective at inhibiting sporozoite and early hepatic stage development from sporozoite to early trophozoite. Our data shows that P218 also inhibited the late hepatic stage development, from trophozoite to mature schizonts to a lesser extent. With a single dose of 15 mg/kg, P218 prevented infection from up to 25,000 pyrimethamine-resistant sporozoites, a number equal to thousands of infectious mosquito bites. Additionally, the hepatic stage of malaria parasite is much more susceptible to antifolates than the asexual blood stage. This study provides important insights into the activity of antifolates, as a chemopreventive therapeutic which could lead to a more efficient and cost effective treatment regime.

Streamlined and Robust Stage-Specific Profiling of Gametocytocidal Compounds Against Plasmodium falciparum

“…Pyronaridine displays submicromolar activity against mature gametocytes (IC 50 = 938 nM), in contrast to earlier reports ( Duffy and Avery, 2013 ; Plouffe et al., 2016 ). The sulfonamides and antifolates (e.g., P218) have no activity against any stage of gametocytes, although antifolates are potently active against ABS ( Duffy and Avery, 2013 ; Pethrak et al., 2022 ). The antibiotic, thiostrepton, retains activity against all stages, possibly through targeting general processes such as protein degradation.…”

In Vitro Efficacy of Next Generation Dihydrotriazines and Biguanides Against Babesiosis and Malaria Parasites

“…A major challenge to the efficacy of antifolate-based drug therapy arose with the emergence of antifolate-resistant isolates [29,30]. Parasite lines with point mutations in the DHFR-TS enzyme showed reduced susceptibility to treatment with a combination of sulfonamide and pyrimethamine [31][32][33]. The prevalent mutations in PfDHFR-TS associated with resistance to pyrimethamine include N51I, C59R, S108N, and I164L.…”

Exploration and Biological Evaluation of 1,3-Diamino-7H-pyrrol[3,2-f]quinazoline Derivatives as Dihydrofolate Reductase Inhibitors

“…If the catalytic reduction activity of DHFR is selectively inhibited, the reduction of DHF to THF can be directly blocked, affecting DNA synthesis and ultimately leading to cellular (bacterial) death. 2 DHFR inhibitors have proven utility in combating various diseases, including cancer, 3 malaria, 4 and other protozoan infections. Moreover, they exhibit effectiveness in fighting against fungal, 5 bacterial, 6 and mycobacterial infections 7 (Figure 1).…”