Exploring Ubiquinone Biosynthesis Inhibition as a Strategy for Improving Atovaquone Efficacy in Malaria

Abstract

Atovaquone (AV) acts on the malaria parasite by competing with ubiquinol (UQH2) for its union to the mitochondrial bc1 complex, preventing the ubiquinone-8,9 (UQ) redox recycling, which is a necessary step in pyrimidine biosynthesis. This study focused on UQ biosynthesis in Plasmodium falciparum and adopted proof-of-concept research to better elucidate the mechanism of action of AV and improve its efficacy. Initially, UQ biosynthesis was evaluated using several radioactive precursors and chromatographic techniques. This methodology was suitable for studying the biosynthesis of both UQ homologs and its redox state. Additionally, the composition of UQ was investigated in parasites cultivated at different oxygen saturations or in the presence AV. AV affected the redox states of both UQ-8 and UQ-9 homologs by increasing the levels of the respective reduced forms. Conversely, low-oxygen environments specifically inhibited UQ-9 biosynthesis and increased the antimalarial efficacy of AV. These findings encouraged us to investigate the biological importance and the potential of UQ biosynthesis as a drug target based on its inhibition by 4-nitrobenzoate (4-NB), a 4-hydroxybenzoate (4-HB) analog. 4-NB effectively inhibits UQ biosynthesis and enhances the effects of AV on parasitic growth and respiration rate. Although 4-NB itself exhibits poor antimalarial activity, its IC50 value increased significantly in the presence of a soluble UQ analog, p-aminobenzoic acid (pABA) or 4-HB. These results indicate the potential of AV combined with 4-NB as a novel therapy for malaria and other diseases caused by AV-sensitive pathogens.

Isoprenoid alcohols utilization by malaria parasites

“…It was also observed that GGOH incorporates better into nonaprenol rather than octaprenol and FOH the opposite. Coincident with this, it was previously reported that [ 3 H] GGPP is better incorporated into ubiquinone-9, while [ 3 H] FPP appeared to be better incorporated into ubiquinone-8 ( Verdaguer et al, 2021 ). These two observations suggest that the distinct polyprenyl synthases possess different levels of specificity and affinity according to the isoprenic chain of the substrate.…”

“…The MEP pathway leads to the formation of isoprenic units, necessary for the formation of several metabolites such as ubiquinones, prenylated proteins, and dolichols ( D'Alexandri et al, 2006 ; Verdaguer et al, 2021 ; Mathews et al, 2019 ; Moura et al, 2001 ). It is also known that P. falciparum produces dolichols of 11–12 and 15-19 isoprenic units which are involved in protein glycosylation as well as protein dolichylation ( D'Alexandri et al, 2006 ; Zimbres et al, 2020 ).…”

“…Reports in the literature indicate that FPP can also be used for the formation of Heme-O ( Simão-Gurge et al, 2019 ). The parasite also should produce longer prenyl pyrophosphates such as octaprenyl and nonaprenyl pyrophosphate (solanesyl pyrophosphate) necessary for the biosynthesis of ubiquinone, cis -polyprenols, and dolichols of 11, 12, and 15-19 isoprene units ( Okada et al, 2022 ; D'Alexandri et al, 2006 ; Zimbres et al, 2020 ; Verdaguer et al, 2021 ; Verdaguer et al, 2019 ). Finally, some authors previously suggested that the parasite can use phytol (POH) to synthesize vitamin E ( Sussmann et al, 2011 ).…”

A unique flavoenzyme operates in ubiquinone biosynthesis in photosynthesis-related eukaryotes

“…The CoQ biosynthetic pathway of apicomplexans provides important drug targets against parasites ( 45 ). CoqF is mechanistically different from Coq7 in mammalian hosts and structurally distinct among flavoenzymes, rendering it an ideal target for the development of drugs for the treatment of malaria, cryptosporidiosis, neosporosis, toxoplasmosis, and other parasitic diseases caused by apicomplexan protists, which remain important health threats to both humans and livestock.…”