Effects of atovaquone and diospyrin-based drugs on the cellular ATP of Pneumocystis carinii f. sp. carinii.

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Cushion MT, Collins M, Hazra B, Kaneshiro ES

Effects of atovaquone and diospyrin-based drugs on the cellular ATP of Pneumocystis carinii f. sp. carinii.

Antimicrob Agents Chemother. 2000 Mar;44(3):713-9.

PubMed ID

10681344 [ View in PubMed

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Abstract

Atovaquone (also called Mepron, or 566C80) is a napthoquinone used for the treatment of infections caused by pathogens such as Plasmodium spp. and Pneumocystis carinii. The mechanism of action against the malarial parasite is the inhibition of dihydroorotate dehydrogenase (DHOD), a consequence of blocking electron transport by the drug. As an analog of ubiquinone (coenzyme Q [CoQ]), atovaquone irreversibly binds to the mitochondrial cytochrome bc(1) complex; thus, electrons are not able to pass from dehydrogenase enzymes via CoQ to cytochrome c. Since DHOD is a critical enzyme in pyrimidine biosynthesis, and because the parasite cannot scavenge host pyrimidines, the drug is lethal to the organism. Oxygen consumption in P. carinii is inhibited by the drug; thus, electron transport has also been identified as the drug target in P. carinii. However, unlike Plasmodium DHOD, P. carinii DHOD is inhibited only at high atovaquone concentrations, suggesting that the organism may salvage host pyrimidines and that atovaquone exerts its primary effects on ATP biosynthesis. In the present study, the effect of atovaquone on ATP levels in P. carinii was measured directly from 1 to 6 h and then after 24, 48, and 72 h of exposure. The average 50% inhibitory concentration after 24 to 72 h of exposure was 1.5 microgram/ml (4.2 microM). The kinetics of ATP depletion were in contrast to those of another family of naphthoquinone compounds, diospyrin and two of its derivatives. Whereas atovaquone reduced ATP levels within 1 h of exposure, the diospyrins required at least 48 h. After 72 h, the diospyrins were able to decrease ATP levels of P. carinii at nanomolar concentrations. These data indicate that although naphthoquinones inhibit the electron transport chain, the molecular targets in a given organism are likely to be distinct among members of this class of compounds.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Atovaquone	Cytochrome b	Protein	Plasmodium falciparum	Yes	Inhibitor	Details
Atovaquone	Dihydroorotate dehydrogenase (quinone), mitochondrial	Protein	Plasmodium falciparum (isolate 3D7)	Yes	Inhibitor	Details