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David B A Hutchinson - One of the best experts on this subject based on the ideXlab platform.
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Atovaquone proguanil compared with chloroquine and chloroquine sulfadoxine pyrimethamine for treatment of acute plasmodium falciparum malaria in the philippines
The Journal of Infectious Diseases, 1999Co-Authors: Dorina G Bustos, Craig J Canfield, Editha Canetemiguel, David B A HutchinsonAbstract:This randomized, open-label clinical trial compared a fixed-dose combination of Atovaquone and proguanil (n = 55) with chloroquine (n = 23) or a combination of chloroquine, sulfadoxine, and pyrimethamine (n = 32) for treatment of acute falciparum malaria in the Philippines. Patients were hospitalized for 28 days to ensure medication compliance and prevent reinfection. Atovaquone-proguanil produced a significantly higher cure rate (100%) compared with that for chloroquine (30.4%; P<.0001) or chloroquine-sulfadoxine-pyrimethamine (87.5%; P<.05). Treatments did not differ significantly with respect to parasite clearance time (mean: 46.7 h for Atovaquone-proguanil, 60.0 h for chloroquine, and 42.8 h for chloroquine-sulfadoxine-pyrimethamine) or fever clearance time (mean, 38.8, 46.8, and 34.5 h, respectively). Adverse events were typical of malaria symptoms; the most frequently reported events were vomiting (18% for Atovaquone-proguanil, 17% for chloroquine, and 9% for chloroquine-sulfadoxine-pyrimethamine), abdominal pain (15%, 17%, and 3%, respectively), anorexia (11%, 13%, and 0%, respectively), and headache (6%, 17%, and 3%, respectively). Atovaquone-proguanil was well tolerated and more effective than chloroquine or chloroquine-sulfadoxine-pyrimethamine for treatment of multidrug-resistant falciparum malaria in the Philippines.
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malarone Atovaquone and proguanil hydrochloride a review of its clinical development for treatment of malaria malarone clinical trials study group
American Journal of Tropical Medicine and Hygiene, 1999Co-Authors: Sornchai Looareesuwan, J D Chulay, Craig J Canfield, David B A HutchinsonAbstract:The continuing spread of drug-resistant malaria emphasizes the need for new antimalarial drugs. Ato- vaquone is a broad-spectrum antiprotozoal drug with a novel mechanism of action, via inhibition of parasite mito- chondrial electron transport, and a favorable safety profile. Early studies with Atovaquone alone for treatment of malaria demonstrated good initial control of parasitemia but an unacceptable rate of recrudescent parasitemia. Parasites isolated during recrudescence after treatment with Atovaquone alone were resistant to Atovaquone in vitro. The com- bination of Atovaquone and proguanil is synergistic in vitro, and clinical studies demonstrated enhanced efficacy of the combination compared to either drug alone for treatment of malaria. Malarone y, a fixed-dose combination of 250 mg of Atovaquone and 100 mg of proguanil hydrochloride, is available in many countries for treatment of acute, uncomplicated malaria caused by Plasmodium falciparum.At the recommended dose (in adults, four tablets once a day for three days), the overall cure rate was . 98% in more than 500 patients with falciparum malaria. In four randomized, controlled clinical trials, treatment with Atovaquone and proguanil hydrochloride was significantly more effective than mefloquine (Thailand), amodiaquine (Gabon), chloroquine (Peru and the Philippines) or chloroquine plus pyrimethamine/sulfadoxine (Philippines). In clinical trials where the comparator drug was highly effective, treat- ment with Atovaquone and proguanil hydrochloride was equally effective. Parasites isolated during recrudescence after treatment with the combination of Atovaquone and proguanil were not resistant to Atovaquone in vitro. The most commonly reported adverse events in clinical trials (abdominal pain, anorexia, nausea, vomiting, diarrhea and cough- ing) occurred with similar frequency in patients treated with a comparator drug. Malarone is a safe and effective new agent for treatment of malaria.
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efficacy and safety of Atovaquone proguanil compared with mefloquine for treatment of acute plasmodium falciparum malaria in thailand
American Journal of Tropical Medicine and Hygiene, 1999Co-Authors: S Looareesuwan, Craig J Canfield, Polrat Wilairatana, K Chalermarut, Y Rattanapong, David B A HutchinsonAbstract:The increasing frequency of therapeutic failures in falciparum malaria underscores the need for novel, rapidly effective antimalarial drugs or drug combinations. Atovaquone and proguanil are blood schizonticides that demonstrate synergistic activity against multi-drug-resistant Plasmodium falciparum in vitro. In an open-label, randomized, controlled clinical trial conducted in Thailand, adult patients with acute P. falciparum malaria were randomly assigned to treatment with Atovaquone and proguanil/hydrochloride (1,000 mg and 400 mg, respectively, administered orally at 24-hr intervals for three doses) or mefloquine (750 mg administered orally, followed 6 hr later by an additional 500-mg dose). Efficacy was assessed by cure rate (the percentage of patients in whom parasitemia was eliminated and did not recur during 28 days of follow-up), parasite clearance time (PCT), and fever clearance time (FCT). Safety was assessed by sequential clinical and laboratory assessments for 28 days. Atovaquone/proguanil was significantly more effective than mefloquine (cure rate 100% [79 of 79] vs. 86% [68 of 79]; P < 0.002). The Atovaquone/proguanil and mefloquine treatments did not differ with respect to PCT (mean = 65 hr versus 74 hr) or FCT (mean = 59 hr versus 51 hr). Adverse events were generally typical of malaria symptoms and each occurred in < 10% of the patients in either group, with the exception of increased vomiting found in the Atovaquone/proguanil group. Transient elevations of liver enzyme levels occurred more frequently in patients treated with Atovaquone/proguanil than with mefloquine, but the differences were not significant and values returned to normal by day 28 in most patients. The combination of Atovaquone and proguanil was well tolerated and more effective than mefloquine in the treatment of acute uncomplicated multidrug-resistant falciparum malaria in Thailand.
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clinical studies of Atovaquone alone or in combination with other antimalarial drugs for treatment of acute uncomplicated malaria in thailand
American Journal of Tropical Medicine and Hygiene, 1996Co-Authors: Sornchai Looareesuwan, Dennis E. Kyle, David B A Hutchinson, C Viravan, Kyle H Webster, Craig J CanfieldAbstract:Abstract The therapy of Plasmodium falciparum malaria continues to be a problem in many parts of Southeast Asia because of multidrug resistance to nearly all existing antimalarial drugs. Atovaquone is a novel hydroxynaphthoquinone with broad spectrum anti-protozoal activity. We recently evaluated the antimalarial activity of Atovaquone in a series of dose-ranging studies in 317 patients with malaria at the Bangkok Hospital for Tropical Diseases. Originally, the drug was administered alone. Using Atovaquone alone resulted in satisfactory, initial clinical responses in all patients; the mean parasite and fever clearance times were 62 and 53 hr, respectively. However, irrespective of the duration of therapy, overall cure rates were approximately 67%. In vitro sensitivity studies on parasites taken from patients prior to treatment and at the time of recrudescence showed a marked decrease in susceptibility to Atovaquone in the recrudescent parasites. To improve cure rates, Atovaquone was administered in combination with other drugs with antimalarial activity. Proguanil and tetracycline were chosen due to laboratory evidence of potentiation; doxycycline was selected because it has a longer half-life than tetracycline. Although pyrimethamine did not show laboratory evidence of potentiation with Atovaquone, it was chosen as an alternative inhibitor of dihydrofolic acid reductase with a longer half-life than proguanil. The clinical studies with these drug combinations confirmed the laboratory results with marked improvement in cure rates for proguanil, tetracycline, and doxycycline; pyrimethamine showed only minimal improvement. Proguanil was subsequently selected as the preferred drug partner because of its long record of safety and the ability to use the drug in pregnant women and children. Of the 104 patients with falciparum malaria treated with Atovaquone plus proguanil for 3–7 days, 101 were cured and had virtually no adverse side effects. The combination of Atovaquone and proguanil also was effective in eliminating erythrocytic forms of P. vivax, but parasitemia recurred in most patients.
Neil S Roskell - One of the best experts on this subject based on the ideXlab platform.
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Atovaquone proguanil versus chloroquine proguanil for malaria prophylaxis in nonimmune pediatric travelers results of an international randomized open label study
Clinical Infectious Diseases, 2004Co-Authors: D Camus, Felix Djossou, Herbert Schilthuis, Birthe Hogh, Emmanuel Dutoit, Denis Malvy, Neil S Roskell, Corinne Hedgley, Erika H De Boever, Gerri B MillerAbstract:7 Collegeville, Pennsylvania, and 8 Research Triangle Park, North Carolina Atovaquone-proguanil has been shown to be effective and well tolerated for malaria prophylaxis in residents of countries of endemicity and in nonimmune adult travelers, but data about traveling children are limited. In a randomized, open-label, multicenter prophylaxis trial, 221 nonimmune pediatric travelers (age, 2-17 years) received either Atovaquone-proguanil or chloroquine-proguanil. Safety and clinical outcome were eval- uated 7, 28, and 60 days after travel. By posttravel day 7, a total of 39 (35%) of 110 Atovaquone-proguanil and 41 (37%) of 111 chloroquine-proguanil recipients reported 1 adverse event. The data indicate that, over the course of treatment, fewer Atovaquone-proguanil recipients had treatment-related adverse events (8% vs. 14%), including gastrointestinal complaints (5% vs. 10%). Two subjects discontinued prophylaxis because of drug-related adverse events; both had received chloroquine-proguanil. Observed compliance with prophylaxis was similar before and during travel, but it was higher for Atovaquone-proguanil in the posttravel period. No study participant developed malaria. Atovaquone-proguanil was well tolerated and is an important addition to the limited arsenal of prophylactic agents available to children.
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Atovaquone proguanil versus chloroquine proguanil for malaria prophylaxis in non immune travellers a randomised double blind study
The Lancet, 2000Co-Authors: Birthe Hogh, David Overbosch, Kevin C Kain, D Camus, Paul Clarke, Hans Dieter Nothdurft, Matthias Gunther, Izak Joubert, Dea Shaw, Neil S RoskellAbstract:Summary Background Chloroquine plus proguanil is widely used for malaria chemoprophylaxis despite low effectiveness in areas where multidrug-resistant malaria occurs. Studies have shown that Atovaquone and proguanil hydrochloride is safe and effective for prevention of falciparum malaria in lifelong residents of malaria-endemic countries, but little is known about non-immune travellers. Methods In a double-blind equivalence trial, 1083 participants travelling to a malaria-endemic area were randomly assigned to two treatment groups: Atovaquone-proguanil plus placebos for chloroquine and proguanil, or chloroquine, proguanil, and placebo for Atovaquone-proguanil. Follow-up was by telephone 7 and 60 days after travel and at a clinic at 28 days. Serum samples were tested for antibodies to a malaria circumsporozoite protein. Blood and serum samples of participants with a potential malaria diagnosis were tested in a reference laboratory. Findings 7 days after travel, at least one adverse event was reported by 311 (61%) of 511 participants who received Atovaquone-proguanil and 329 (64%) of 511 who received chloroquine-proguanil. People receiving Atovaquone-proguanil had a lower frequency of treatment-related gastrointestinal adverse events (59 [12%] vs 100 [20%], p=0·001), and of treatment-related adverse events of moderate or severe intensity (37 [7%] vs 56 [11%], p=0·05). There were fewer treatment-related adverse events that caused prophylaxis to be discontinued in the Atovaquone-proguanil group than in the chloroquine-proguanil group (one [0·2%] vs ten [2%], p=0·015). Interpretation Overall the two preparations were similarly tolerated. However, significantly fewer adverse gastro-intestinal events were observed in the Atovaquone-proguanil group in than in the chloroquine-proguanil group.
P G Kremsner - One of the best experts on this subject based on the ideXlab platform.
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Atovaquone and proguanil hydrochloride for treatment of malaria.
Journal of travel medicine, 1999Co-Authors: P G Kremsner, S Looareesuwan, J D ChulayAbstract:Safe and effective new drugs are needed for treatment of malaria. Atovaquone and proguanil hydrochloride is a new antimalarial combination that has recently become available in many countries. Data from clinical trials evaluating Atovaquone/proguanil for treatment of malaria were reviewed. In 10 open-label clinical trials, treatment of uncomplicated falciparum malaria with 1000 mg Atovaquone and 400 mg proguanil hydrochloride (or the equivalent based on body weight in patients < or = 40 kg) once daily for 3 days achieved cure in 514 of 521 (99%) evaluable patients. Treatment-limiting adverse events occurred in < 1% of patients (vomiting in four, anaphylaxis in one). Atovaquone/proguanil has been used to provide radical cure of asymptomatic Plasmodium falciparum infections prior to initiation of placebo-controlled trials of malaria prophylaxis. Recurrent parasitemia occurred within 28 days in 0 of 99 subjects who subsequently received prophylaxis with Atovaquone/proguanil and 1 of 81 subjects who subsequently received placebo. Atovaquone/proguanil is also effective for treatment of malaria caused by the other three Plasmodium species that cause malaria in humans. For treatment of vivax malaria, therapy with primaquine in addition to Atovaquone/proguanil is needed to prevent relapse from latent hepatic hypnozoites. Atovaquone and proguanil hydrochloride is a safe and effective combination for treatment of malaria.
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Atovaquone and proguanil hydrochloride for prophylaxis of malaria
Journal of Travel Medicine, 1999Co-Authors: G D Shanks, P G Kremsner, T Y Sukwa, J D Van Der Berg, T A Shapiro, T R Scott, J D ChulayAbstract:BACKGROUND: The spread of drug-resistant malaria and appreciation of side effects associated with existing antimalarial drugs emphasize the need for new drugs to prevent malaria. The combination of Atovaquone and proguanil hydrochloride was previously shown to be safe and highly effective for treatment of malaria, including multi-drug-resistant Plasmodium falciparum. METHODS: We reviewed results of clinical trials that evaluated either a fixed-dose combination of Atovaquone and proguanil hydrochloride for malaria prophylaxis or Atovaquone alone for causal prophylactic activity against P. falciparum. RESULTS: In three placebo-controlled trials, 331 subjects received 250 mg Atovaquone and 100 mg proguanil hydrochloride (or an equivalent dose based on body weight in children) once daily for 10 to 12 weeks. The overall efficacy for preventing parasitemia was 98%. Among 175 nonimmune volunteers taking the same dose of Atovaquone/proguanil once daily for 10 weeks while temporarily residing in a malaria-endemic area, malaria developed in one patient who was noncompliant with therapy. Results of volunteer challenge studies indicate that both Atovaquone and proguanil have causal prophylactic activity directed against the liver stages of P. falciparum. Adverse events occurred with similar or lower frequencies in subjects treated with Atovaquone/proguanil compared to placebo. Less than 1% of patients discontinued from these studies due to a treatment-related adverse event. CONCLUSION: A fixed-dose combination of Atovaquone and proguanil hydrocloride is a promising new alternative for malaria prophylaxis.
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randomised placebo controlled study of Atovaquone plus proguanil for malaria prophylaxis in children
The Lancet, 1998Co-Authors: P G Kremsner, Bertrand Lell, Doris Luckner, Maryse Ndjave, Trevor ScottAbstract:Summary Background The combination of Atovaquone and proguanil is highly effective and safe for the treatment of Plasmodium falciparum malaria. We aimed in this randomised, double-blind, placebo-controlled study to assess the efficacy and safety of this combination for malaria prophylaxis. Methods 320 children who lived in a hyperendemic area for P falciparum malaria were stratified by weight and randomly assigned Atovaquone plus proguanil or placebo once daily for 12 weeks. All children received initial curative treatment with Atovaquone and proguanil before the start of chemosuppression. We recorded adverse events daily and collected thick blood smears once a week. The primary endpoint was a positive blood smear. Findings 25 of 140 children in the placebo group and none of the 125 children in the Atovaquone plus proguanil group had positive smears during chemosuppression (p Interpretation The combination of Atovaquone plus proguanil is a highly effective and well-tolerated chemosuppressive antimalarial in children. This drug combination could replace current regimens.
Kevin C Kain - One of the best experts on this subject based on the ideXlab platform.
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Atovaquone proguanil report from the cdc expert meeting on malaria chemoprophylaxis ii
American Journal of Tropical Medicine and Hygiene, 2007Co-Authors: Andrea K Boggild, Monica E Parise, Linda S Lewis, Kevin C KainAbstract:The fixed dose combination of Atovaquone and proguanil hydrochloride, marketed under the trade name Malarone™, is the most recently approved agent in North America for the prevention and treatment of chloroquine- and multi-drug resistant Plasmodium falciparum malaria. In both adult and pediatric populations, Atovaquone-proguanil demonstrates consistently high protective efficacy against P. falciparum, and in treatment trials, cure rates exceed 93%. Only a handful of genetically confirmed treatment failures have been reported to date. Atovaquone-proguanil has an excellent safety profile during both prophylaxis and treatment courses, with severe adverse events rarely reported. This topical review will examine the evidence behind the current indications for use of Atovaquone-proguanil, and will summarize the current body of literature surrounding safety and tolerability.
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Atovaquone proguanil versus mefloquine for malaria prophylaxis in nonimmune travelers results from a randomized double blind study
Clinical Infectious Diseases, 2001Co-Authors: David Overbosch, Kevin C Kain, Herbert Schilthuis, Hans Dieter Nothdurft, Ulrich Bienzle, Ron H Behrens, Paul D Clarke, Stephen Toovey, J Knobloch, Dea ShawAbstract:Concerns about the tolerability of mefloquine highlight the need for new drugs to prevent malaria. Atovaquone-proguanil (Malarone; GlaxoSmithKline) was safe and effective for prevention of falciparum malaria in lifelong residents of malaria-endemic countries, but experience in nonimmune people is limited. In a randomized, double-blind study, nonimmune travelers received malaria prophylaxis with Atovaquone-proguanil (493 subjects) or mefloquine (483 subjects). Information about adverse events (AEs) and potential episodes of malaria was obtained 7, 28, and 60 days after travel. AEs were reported by an equivalent proportion of subjects who had received Atovaquone-proguanil or mefloquine (71.4% versus 67.3%; difference, 4.1%; 95% confidence interval, -1.71 to 9.9). Subjects who received Atovaquone-proguanil had fewer treatment-related neuropsychiatric AEs (14% versus 29%; P = .001), fewer AEs of moderate or severe intensity (10% versus 19%; P = .001), and fewer AEs that caused prophylaxis to be discontinued (1.2% versus 5.0%; P = .001), compared with subjects who received melfoquine. No confirmed diagnoses of malaria occurred in either group. Atovaquone-proguanil was better tolerated than was mefloquine, and it was similarly effective for malaria prophylaxis in nonimmune travelers.
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causal prophylactic efficacy of Atovaquone proguanil malaronetm in a human challenge model
Transactions of The Royal Society of Tropical Medicine and Hygiene, 2001Co-Authors: Jonathan D Berman, J D Chulay, Robin K Nielsen, Megan Dowler, Kevin C Kain, Kent E Kester, Jackie Williams, A C Whelen, Moshe J ShmuklarskyAbstract:Abstract Plasmodia infect the liver for about 7 days before subsequently infecting the blood. Present prophylaxis against Plasmodium falciparum malaria employs agents that primarily kill blood stages and must be continued for 28 days after the last exposure. Atovaquone-proguanil (MalaroneTM) is a new antimalarial agent that is licensed in 35 countries as treatment against blood-stage infection, but its components (Atovaquone and proguanil) have separately been shown to be active also against liver stages. To determine whether Atovaquone-proguanil is sufficiently active against liver stages to be discontinued 7 days after exposure, we challenged 16 volunteers with P. falciparum via infected mosquitoes. Twelve volunteers received Atovaquone-proguanil (1 tablet daily) on the day prior to challenge, on the day of challenge, and for the next 6 days; 4 volunteers received matching placebo. All placebo volunteers demonstrated parasitaemia and malarial symptoms beginning on days 11–12 after challenge. No Atovaquone-proguanil volunteer acquired malaria. Atovaquone-proguanil is the first licensed antimalarial agent that kills P. falciparum in the liver and that may be discontinued 7 days after the last exposure.
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Atovaquone proguanil versus chloroquine proguanil for malaria prophylaxis in non immune travellers a randomised double blind study
The Lancet, 2000Co-Authors: Birthe Hogh, David Overbosch, Kevin C Kain, D Camus, Paul Clarke, Hans Dieter Nothdurft, Matthias Gunther, Izak Joubert, Dea Shaw, Neil S RoskellAbstract:Summary Background Chloroquine plus proguanil is widely used for malaria chemoprophylaxis despite low effectiveness in areas where multidrug-resistant malaria occurs. Studies have shown that Atovaquone and proguanil hydrochloride is safe and effective for prevention of falciparum malaria in lifelong residents of malaria-endemic countries, but little is known about non-immune travellers. Methods In a double-blind equivalence trial, 1083 participants travelling to a malaria-endemic area were randomly assigned to two treatment groups: Atovaquone-proguanil plus placebos for chloroquine and proguanil, or chloroquine, proguanil, and placebo for Atovaquone-proguanil. Follow-up was by telephone 7 and 60 days after travel and at a clinic at 28 days. Serum samples were tested for antibodies to a malaria circumsporozoite protein. Blood and serum samples of participants with a potential malaria diagnosis were tested in a reference laboratory. Findings 7 days after travel, at least one adverse event was reported by 311 (61%) of 511 participants who received Atovaquone-proguanil and 329 (64%) of 511 who received chloroquine-proguanil. People receiving Atovaquone-proguanil had a lower frequency of treatment-related gastrointestinal adverse events (59 [12%] vs 100 [20%], p=0·001), and of treatment-related adverse events of moderate or severe intensity (37 [7%] vs 56 [11%], p=0·05). There were fewer treatment-related adverse events that caused prophylaxis to be discontinued in the Atovaquone-proguanil group than in the chloroquine-proguanil group (one [0·2%] vs ten [2%], p=0·015). Interpretation Overall the two preparations were similarly tolerated. However, significantly fewer adverse gastro-intestinal events were observed in the Atovaquone-proguanil group in than in the chloroquine-proguanil group.
Bernard L. Trumpower - One of the best experts on this subject based on the ideXlab platform.
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The interaction of Atovaquone with the P. carinii cytochrome bc1 complex.
Journal of Eukaryotic Microbiology, 2020Co-Authors: Steven R. Meshnick, Powel Kazanjian, Edward A. Berry, Jürgen H. Nett, Bernard L. TrumpowerAbstract:Author(s): Trumpower, B. | Abstract: Atovaquone is an important second-line therapeutic and prophylactic agent for Pneumocystis carinii pneumonia although it was originally developed as an antimalarial [11]. For malaria, Atovaquone is now only used in combination with proguanil, another antimalarial. This combination (Malaronel) is used because Atovaquone monotherapy leads to resistance [9]. Atovaquone is structurally similar to ubiquinone (CoQ). UHDBT and stigmatellin are other CoQ analogs that have been well studied in experimental systems. Both UHDBT and stigmatellin are known to inhibit electron transport by binding to the Q0 site of the cytochrome bc1 complex. Atovaquone probably acts at the same site, since it has also been shown to inhibit electron transport in both malaria and P. carinii [4, 6]. This mechanism could also explain the rapid emergence of resistance to monotherapy; mutations could arise easily in cytochrome b, since it is encoded in the mitochondrial genome where the spontaneous mutation rate is 10x higher than in nucleus [1].
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Molecular basis of Toxoplasma gondii Atovaquone resistance modeled in Saccharomyces cerevisiae.
Molecular and Biochemical Parasitology, 2005Co-Authors: Jacques J. Kessl, Kevin H. Ha, Anne K. Merritt, Steven R. Meshnick, Bernard L. TrumpowerAbstract:0 d ondii is a widespread disease affecting primarily immunocomromised and pregnant individuals [1]. Atovaquone is a recently ntroduced anti-malarial compound with broad spectrum activty against various apicomplexan parasites [2–5] including T. ondii [6]. Approved by the FDA in 1995, this drug is a potent nd specific inhibitor of the cytochrome bc1 complex [7], an ssential respiratory enzyme present in the inner mitochondrial embrane. Two recent studies on treatment of malaria during regnancy show that Atovaquone is a remarkably well tolerated olecule, safe for both the mother and the fetus [8,9]. Unforunately, there is strong evidence that the targeted parasites are ble to spontaneously develop drug resistance by mutation of mino acid residues located in or near the Atovaquone-binding ite on cytochrome b. Because the yeast bc1 complex is also trongly inhibited by Atovaquone, we have previously develped Saccharomyces cerevisiae as a model to study cytochrome mutations conferring Atovaquone resistance in Pneumocystis 10,11] and Plasmodium species [12]. In the present study, we ave successfully transferred two mutations associated with atoaquone resistance in T. gondii [13] into the yeast cytochrome to the one recently found in the crystal structure of the yeast bc1 complex with a hydroxy-benzoxythiazol bound at center P [14]. The hydroxyl group of the hydroxy-naphthoquinone binds via a hydrogen bond to the nitrogen of His-181 of the Rieske iron–sulfur protein. On the opposite side of the ring system the carbonyl group at position 4 of the quinone ring of Atovaquone forms a water-mediated hydrogen bond with Glu-272 of cytochrome b. The bulk of the molecular interactions between Atovaquone and cytochrome b are essentially hydrophobic with a network of aromatic and aliphatic side chains surrounding the inhibitor. There is a high score of cytochrome b sequence identity (about 70%) within the Atovaquone binding pocket between S. cerevisiae and T. gondii (Fig. 1A). We have thus chosen the yeast to study how mutations can affect the drug efficacy. Both Atovaquone-resistant mutations in the cytochrome b sequence previously identified in T. gondii were localized within this binding site [13]. These two mutations (M129L and I254L in T. gondii numbering, equivalent to M139L and I269L in the yeast numbering system) associated with resistance in T. gondii gene. This has allowed us to biochemically confirm the linkge of Atovaquone resistance to the cytochrome b mutations and o predict at the molecular level the mechanism by which T. ondiimay counter the efficacy of this potential anti-toxoplasma rug. were transferred into the S. cerevisiae cytochrome b gene by the biolistic method [11]. Growth of the two mutated strains was monitored in a nonfermentable medium in order to study the impact of the mutations on the yeast cells’ respiration. The growth curves revealed t s n o v m The molecular target of Atovaquone is now known to be he ubiquinol oxidation pocket at center P of the cytochrome
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molecular basis for Atovaquone resistance in pneumocystis jirovecii modeled in the cytochrome bc 1 complex of saccharomyces cerevisiae
Journal of Biological Chemistry, 2004Co-Authors: Jacques J. Kessl, Steven R. Meshnick, Philip Hill, Benjamin B Lange, Brigitte Meunier, Bernard L. TrumpowerAbstract:Abstract Atovaquone is a substituted hydroxynaphthoquinone that is widely used to prevent and clear Plasmodium falciparum malaria and Pneumocystis jirovecii pneumonia. Atovaquone inhibits respiration in target organisms by specifically binding to the ubiquinol oxidation site at center P of the cytochrome bc1 complex. The failure of Atovaquone treatment and mortality of patients with malaria and P. jirovecii pneumonia has been linked to the appearance of mutations in the cytochrome b gene. To better understand the molecular basis of Atovaquone resistance, we have introduced seven of the mutations from Atovaquone-resistant P. jirovecii into the cytochrome b gene of Saccharomyces cerevisiae and thus obtained cytochrome bc1 complexes resistant to inhibition by Atovaquone. In these enzymes, the IC50 for Atovaquone increases from 25 nm for the enzyme from wild-type yeast to >500 nm for some of the mutated enzymes. Modeling of the changes in cytochrome b structure and Atovaquone binding with the mutated bc1 complexes provides the first quantitative explanation for the molecular basis of Atovaquone resistance.
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molecular basis for Atovaquone binding to the cytochrome bc1 complex
Journal of Biological Chemistry, 2003Co-Authors: Jacques J. Kessl, Steven R. Meshnick, Philip Hill, Benjamin B Lange, Brigitte Meunier, Carola Hunte, Torsten Merbitzzahradnik, Klaus Zwicker, Hildur Palsdottir, Bernard L. TrumpowerAbstract:Atovaquone is a substituted 2-hydroxynaphthoquinone that is used therapeutically to treat Plasmodium falciparum malaria, Pneumocystis carinii pneumonia, and Toxoplasma gondii toxoplasmosis. It is thought to act on these organisms by inhibiting the cytochrome bc1 complex. We have examined the interaction of Atovaquone with the bc1 complex isolated from Saccharomyces cerevisiae, a surrogate, nonpathogenic fungus. Atovaquone inhibits the bc1 complex competitively with apparent Ki 9n M, raises the midpoint potential of the Rieske iron-sulfur protein from 285 to 385 mV, and shifts the g values in the EPR spectrum of the Rieske center. These results indicate that Atovaquone binds to the ubiquinol oxidation pocket of the bc1 complex, where it interacts with the Rieske iron-sulfur protein. A computed energy-minimized structure for Atovaquone liganded to the yeast bc1 complex suggests that a phenylalanine at position 275 of cytochrome b in the bovine bc1 complex, as opposed to leucine at the equivalent position in the yeast enzyme, is responsible for the decreased sensitivity of the bovine bc1 complex (Ki 80 nM) to Atovaquone. When a L275F mutation was introduced into the yeast cytochrome b, the sensitivity of the yeast enzyme to Atovaquone decreased (Ki 100 nM) with no loss in activity, confirming that the L275F exchange contributes to the differential sensitivity of these two species to Atovaquone. These results provide the first molecular description of how Atovaquone binds to the bc1 complex and explain the differential inhibition of the fungal versus mammalian enzymes.