Targeting Plasmodium Falciparum Dihydroorotate Dehydrogenase (PfDHODH) for the Development of New Antimalarials
Malaria remains a global health threat, with drug resistance presenting a persistent challenge. Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH), which catalyzes the fourth rate-limiting step of the de novo pyrimidine synthesis, is a validated drug target, yet no inhibitor has surpassed Phase II clinical trials. Towards this goal, hit compound JT01, a quinazolinone-based molecule identified through an in silico high-throughput screen by our group, exhibited moderate activity against this enzyme (IC50 = 0.91 ± 0.1 μM). Furthermore, the quinazolinone scaffold has not been previously explored for PfDHODH inhibition, thereby providing an opportunity to develop the structure-activity relationship (SAR) for this scaffold. A combined structure-based and ligand-based drug design approach, guided by molecular docking, was used to design JT01 analogues. This strategy yielded two modification sites for structural modification: the linker and the hydrophobic fluoronaphthalene group. Two alternative linkers emerged as promising replacements for the sulfur-carbon bridge, namely a carbon-carbon linker bearing a chiral secondary alcohol and a secondary amine bridge. Given the hydrophobic nature of the binding site, steric restraints imposed by the C276F mutation and poor solubility of large lipophilic groups, smaller aromatic substituents (benzene, p-fluorophenyl and p-trifluoromethylphenyl) were selected to explore alternatives to the bulky fluoronaphthalene group. Additionally, a naphthalene substituent was introduced to probe the effects of fluorine on potency. Consequently, eleven target molecules were selected for synthesis, consisting of five chiral and six achiral molecules. The twenty-one synthesized compounds (including ten pure enantiomers and five racemates) were evaluated for enzyme inhibition by Prof Margaret Phillips’ group (University of Texas Southwestern Medical Center, USA). Four analogues demonstrated activity, including two active racemic mixtures. The most potent compound, 5S (IC50 = 1.8 ± 0.2 μM), maintained the fluoronaphthalene moiety while incorporating the secondary alcohol linker. Furthermore, the presence of the fluorine atom proved crucial for activity, increasing activity by 3.7-fold in one example. While no compound exceeded the potency of JT01, insights were gained into the SAR profile of quinazolinone PfDHODH inhibitors.
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