Population pharmacokinetics of atovaquone in patients with acute malaria caused by Plasmodium falciparum

Identification of FDA Approved Drugs with Antiviral Activity against SARS-CoV-2: A Tale from structure-based drug repurposing to host-cell mechanistic investigation

The continuing heavy toll of the COVID-19 pandemic necessitates development of therapeutic options. We adopted structure-based drug repurposing to screen FDA-approved drugs for inhibitory effects against main protease enzyme (Mpro) substrate-binding pocket of SARS-CoV-2 for non-covalent and covalent binding. Top candidates were screened against infectious SARS-CoV-2 in a cell-based viral replication assay. Promising candidates included atovaquone, mebendazole, ouabain, dronedarone, and entacapone, although atovaquone and mebendazole were the only two candidates with IC50s that fall within their therapeutic plasma concentration. Additionally, we performed Mpro assays on the top hits, which demonstrated inhibition of Mpro by dronedarone (IC50 18 µM), mebendazole (IC50 19 µM) and entacapone (IC50 9 µM). Atovaquone showed only modest Mpro inhibition, and thus we explored other potential mechanisms. Although atovaquone is Dihydroorotate dehydrogenase (DHODH) inhibitor, we did not observe inhibition of DHODH at the respective SARS-CoV-2 IC50. Metabolomic profiling of atovaquone treated cells showed dysregulation of purine metabolism pathway metabolite, showing that ecto-5′-nucleotidase (NT5E) is downregulated by atovaquone at concentrations equivalent to its antiviral IC50. Atovaquone and mebendazole are promising candidates targeting SARS-CoV-2, however atovaquone did not significantly inhibit Mpro at therapeutically meaningful concentrations but may inhibit SARS-CoV-2 viral replication by targeting host purine metabolism.

On the potential for discontinuing atovaquone-proguanil (AP) ad-hoc post-exposure and other abbreviated AP-regimens: Pharmacology, pharmacokinetics and perspectives

According to current guidelines, atovaquone-proguanil (AP) malaria chemoprophylaxis should be taken once daily starting one day before travel and continued for seven days post-exposure. However, drug-sparing regimens, including discontinuing AP after leaving malaria-endemic areas are cost-saving and probably more attractive to travelers, and may thus enhance adherence. AP has causal prophylactic effects, killing malaria parasites during the hepatic stage. If early hepatic stages were already targeted by AP, AP could possibly be discontinued upon return. Pharmacokinetic data and studies on drug-sparing AP regimens suggest this to be the case. Nevertheless, the evidence is weak and considered insufficient to modify current recommendations. Field trials require large numbers of travelers and inherently suffer from the lack of a control group. Safely-designed controlled human malaria infection trials could significantly reduce study participant numbers and safely establish an effective AP abbreviated regimen which we propose as the optimal trial design to test this concept.

OptiMal-PK: an internet-based, user-friendly interface for the mathematical-based design of optimized anti-malarial treatment regimens

Background

The search for highly effective anti-malarial therapies has gathered pace and recent years have seen a number of promising single and combined therapies reach the late stages of development. A key drug development challenge is the need for early assessment of the clinical utility of new drug leads as it is often unclear for developers whether efforts should be focused on efficacy or metabolic stability/exposure or indeed whether the continuation of iterative QSAR (quantitative structure–activity and relationships) cycles of medicinal chemistry and biological testing will translate to improved clinical efficacy. Pharmacokinetic and pharmacodynamic (PK/PD)-based measurements available from in vitro studies can be used for such clinical predictions. However, these predictions often require bespoke mathematical PK/PD modelling expertise and are normally performed after candidate development and, therefore, not during the pre-clinical development phase when such decisions need to be made.

Methods

An internet-based tool has been developed using STELLA^® software. The tool simulates multiple differential equations that describe anti-malarial PK/PD relationships where the user can easily input PK/PD parameters. The tool utilizes a simple stop-light system to indicate the efficacy of each combination of parameters. This tool, called OptiMal-PK, additionally allows for the investigation of the effect of drug combinations with known or custom compounds.

Results

The results of simulations obtained from OptiMal-PK were compared to a previously published and validated mathematical model on which this tool is based. The tool has also been used to simulate the PK/PD relationship for a number of existing anti-malarial drugs in single or combined treatment. Simulations were predictive of the published clinical parasitological clearance activities for these existing therapies.

Conclusions

OptiMal-PK is designed to be implemented by medicinal chemists and pharmacologists during the pre-clinical anti-malarial drug development phase to explore the impact of different PK/PD parameters upon the predicted clinical activity of any new compound. It can help investigators to identify which pharmacological features of a compound are most important to the clinical performance of a new chemical entity and how partner drugs could potentially improve the activity of existing therapies.

Emergence of resistance to atovaquone-proguanil in malaria parasites: insights from computational modeling and clinical case reports

The usefulness of atovaquone-proguanil (AP) as an antimalarial treatment is compromised by the emergence of atovaquone resistance during therapy. However, the origin of the parasite mitochondrial DNA (mtDNA) mutation conferring atovaquone resistance remains elusive. Here, we report a patient-based stochastic model that tracks the intrahost emergence of mutations in the multicopy mtDNA during the first erythrocytic parasite cycles leading to the malaria febrile episode. The effect of mtDNA copy number, mutation rate, mutation cost, and total parasite load on the mutant parasite load per patient was evaluated. Computer simulations showed that almost any infected patient carried, after four to seven erythrocytic cycles, de novo mutant parasites at low frequency, with varied frequencies of parasites carrying varied numbers of mutant mtDNA copies. A large interpatient variability in the size of this mutant reservoir was found; this variability was due to the different parameters tested but also to the relaxed replication and partitioning of mtDNA copies during mitosis. We also report seven clinical cases in which AP-resistant infections were treated by AP. These provided evidence that parasiticidal drug concentrations against AP-resistant parasites were transiently obtained within days after treatment initiation. Altogether, these results suggest that each patient carries new mtDNA mutant parasites that emerge before treatment but are killed by high starting drug concentrations. However, because the size of this mutant reservoir is highly variable from patient to patient, we propose that some patients fail to eliminate all of the mutant parasites, repeatedly producing de novo AP treatment failures.

Modulation of basophils' degranulation and allergy-related enzymes by monomeric and dimeric naphthoquinones

Allergic disorders are characterized by an abnormal immune response towards non-infectious substances, being associated with life quality reduction and potential life-threatening reactions. The increasing prevalence of allergic disorders demands for new and effective anti-allergic treatments. Here we test the anti-allergic potential of monomeric (juglone, menadione, naphthazarin, plumbagin) and dimeric (diospyrin and diosquinone) naphthoquinones. Inhibition of RBL-2H3 rat basophils' degranulation by naphthoquinones was assessed using two complementary stimuli: IgE/antigen and calcium ionophore A23187. Additionally, we tested for the inhibition of leukotrienes production in IgE/antigen-stimulated cells, and studied hyaluronidase and lipoxidase inhibition by naphthoquinones in cell-free assays. Naphthazarin (0.1 µM) decreased degranulation induced by IgE/antigen but not A23187, suggesting a mechanism upstream of the calcium increase, unlike diospyrin (10 µM) that reduced degranulation in A23187-stimulated cells. Naphthoquinones were weak hyaluronidase inhibitors, but all inhibited soybean lipoxidase with the most lipophilic diospyrin, diosquinone and menadione being the most potent, thus suggesting a mechanism of competition with natural lipophilic substrates. Menadione was the only naphthoquinone reducing leukotriene C₄ production, with a maximal effect at 5 µM. This work expands the current knowledge on the biological properties of naphthoquinones, highlighting naphthazarin, diospyrin and menadione as potential lead compounds for structural modification in the process of improving and developing novel anti-allergic drugs.

Atovaquone-proguanil in the treatment of imported uncomplicated Plasmodium falciparum malaria: a prospective observational study of 553 cases

Background

Each year, thousands of cases of uncomplicated malaria are imported into Europe by travellers. Atovaquone-proguanil (AP) has been one of the first-line regimens used in France for uncomplicated malaria for almost ten years. While AP’s efficacy and tolerance were evaluated in several trials, its use in “real life” conditions has never been described. This study aimed to describe outcome and tolerance after AP treatment in a large cohort of travellers returning from endemic areas.

Methods

Between September 2002 and January 2007, uncomplicated malaria treated in nine French travel clinics with AP were followed for 30 days after AP initiation. Clinical and biological data were collected at admission and during the follow-up.

Results

A total of 553 patients were included. Eighty-eight percent of them were born in Africa, and 61.8% were infected in West Africa, whereas 0.5% were infected in Asia. Migrants visiting friends and relatives (VFR) constituted 77.9% of the patients, the remainder (32.1%) were backpackers. Three-hundred and sixty-four patients (66%) fulfilled follow-up at day 7 and 265 (48%) completed the study at day 30. Three patients had treatment failure. One-hundred and seventy-seven adverse drug reactions (ADR) were reported during the follow-up; 115 (77%) of them were digestive ADR. Backpackers were more likely to experiment digestive ADR compared to VFR (OR = 3.8; CI 95% [1.8-8.2]). Twenty patients had to be switched to another regimen due to ADR.

Conclusion

This study seems to be the largest in terms of number of imported uncomplicated malaria cases treated by AP. The high rate of reported digestive ADR is striking and should be taken into account in the follow-up of patients since it could affect their adherence to the treatment. Beside AP, artemisinin combination therapy (ACT) is now recommended as first-line regimen. A comparison of AP and ACT, in terms of efficacy and tolerance, would be useful.

Population-Based Assessments of Clinical Drug-Drug Interactions: Qualitative Indices or Quantitative Measures?

Population-based assessments of drug-drug interactions have become more common since the introduction and acceptance of the population pharmacokinetic approach. Unlike traditional methods, population-based studies provide clinically relevant results that can be applied directly to a target patient population. Furthermore, population-based studies do not demand the traditional requirements of intensive pharmacokinetic sampling, rigorous inpatient stays, or stringent assessment schedules. As such, the population-based approach can effectively be used to confirm known drug-drug interactions and further characterize anticipated interactions. A prospectively designed analysis can also reveal drug-drug interactions that might otherwise have gone undetected with traditional methods. Ultimately, these results could help to alleviate clinicians' concerns about using widely marketed drugs in combination therapies and also reduce patients' risk of experiencing unacceptable side effects. This article intends to provide a balanced overview of the population-based approach and its merits, drawbacks, and potential utility in the assessment of drug-drug interactions during clinical drug development.

Antimalarial pharmacology and therapeutics of atovaquone

Atovaquone is used as a fixed-dose combination with proguanil (Malarone) for treating children and adults with uncomplicated malaria or as chemoprophylaxis for preventing malaria in travellers. Indeed, in the USA, between 2009 and 2011, Malarone prescriptions accounted for 70% of all antimalarial pre-travel prescriptions. In 2013 the patent for Malarone will expire, potentially resulting in a wave of low-cost generics. Furthermore, the malaria scientific community has a number of antimalarial quinolones with a related pharmacophore to atovaquone at various stages of pre-clinical development. With this in mind, it is timely here to review the current knowledge of atovaquone, with the purpose of aiding the decision making of clinicians and drug developers involved in the future use of atovaquone generics or atovaquone derivatives.

Therapy of uncomplicated falciparum malaria in Europe: MALTHER - a prospective observational multicentre study

BACKGROUND

Malaria continues to be amongst the most frequent infectious diseases imported to Europe. Whilst European treatment guidelines are based on data from studies carried out in endemic areas, there is a paucity of original prospective treatment data. The objective was to summarize data on treatments to harmonize and optimize treatment for uncomplicated malaria in Europe.

METHODS

A prospective observational multicentre study was conducted, assessing tolerance and efficacy of treatment regimens for imported uncomplicated falciparum malaria in adults amongst European centres of tropical and travel medicine.

RESULTS

Between December 2003 and 2009, 504 patients were included in 16 centres from five European countries. Eighteen treatment regimens were reported, the top three being atovaquone-proguanil, mefloquine, and artemether-lumefantrine. Treatments significantly differed with respect to the occurrence of treatment changes (p = 0.005) and adverse events (p = 0.001), parasite and fever clearance times (p < 0.001), and hospitalization rates (p = 0.0066) and durations (p = 0.001). Four recrudescences and two progressions to severe disease were observed. Compared to other regimens, quinine alone was associated with more frequent switches to second line treatment, more adverse events and longer inpatient stays. Parasite and fever clearance times were shortest with artemether-mefloquine combination treatment. Vomiting was the most frequent cause of treatment change, occurring in 5.5% of all patients but 9% of the atovaquone-proguanil group.

CONCLUSIONS

This study highlights the heterogeneity of standards of care within Europe. A consensus discussion at European level is desirable to foster a standardized management of imported falciparum malaria.

Early treatment failure during treatment of Plasmodium falciparum malaria with atovaquone-proguanil in the Republic of Ivory Coast

The increased spread of drug-resistant malaria highlights the need for alternative drugs for treatment and chemoprophylaxis. The combination of atovaquone‐proguanil (Malarone®) has shown high efficacy against Plasmodium falciparum with only mild side-effects. Treatment failures have been attributed to suboptimal dosages or to parasite resistance resulting from a point mutation in the cytochrome b gene. In this paper, a case of early treatment failure was reported in a patient treated with atovaquone-proguanil; this failure was not associated with a mutation in the parasite cytochrome b gene, with impaired drug bioavailability, or with re-infection.

Antimalarial drugs - what is in use and what is in the pipeline

Malaria continues to be a potentially fatal threat to almost half of the world's population. In light of this threat, the armory to fight this disease is rather limited. Resistance against the most common and affordable antimalarials is widespread. Only few new drugs are in clinical development, most of them belong to long used classes of antimalarial drugs. This review will concisely cover the drugs which are currently in use, and describe the drug candidates which are in clinical evaluation.

Plasmodium falciparum malaria and atovaquone-proguanil treatment failure

We noticed overrepresentation of atovaquone-proguanil therapeutic failures among Plasmodium falciparum-infected travelers weighing >100 kg. We report here 1 of these cases, which was not due to resistant parasites or impaired drug bioavailability. The follow-up of such patients should be strengthened.

Simplified antimalarial therapeutic monitoring: using the day-7 drug level?

The blood concentration profiles of most antimalarial drugs vary considerably between patients. The interpretation of antimalarial drug trials evaluating efficacy and effectiveness would be improved considerably if the exposure of the infecting parasite population to the antimalarial drug treatment could be measured. Artemisinin combination treatments are now recommended as first-line drugs for the treatment of falciparum malaria. Measurement of the blood, serum or plasma concentration of the slowly eliminated partner antimalarial drug on day 7 of follow-up is simpler and might be a better determinant of therapeutic response than the area under the concentration-time curve. Measurement of the day-7 drug level should be considered as a routine part of antimalarial drug trials.

Clinical atovaquone-proguanil resistance of Plasmodium falciparum associated with cytochrome b codon 268 mutations

Plasmodium falciparum resistance to atovaquone-proguanil has so far been associated with Y268S or Y268N mutations in cytochrome b, although these changes were identified in only seven of the 11 treatment failures. Here, we describe 10 new cases of atovaquone-proguanil treatment failures among which the parasite resistance was confirmed in six cases, either by identifying correct plasma drug concentrations or by observing in vitro atovaquone resistance. Resistance was consistently associated with codon 268 mutations (Y268S or a previously unidentified mutation, Y268C). Notably, mutations were not detected before the treatment but only after the drug exposure.

Atovaquone/proguanil for the prophylaxis and treatment of malaria

Increases in international travel and escalating drug resistance have resulted in a growing number of travelers at risk of contracting malaria. Drug resistance and intolerance to standard agents such as chloroquine, sulfadoxine/pyrimethamine and mefloquine has highlighted the need for new antimalarials. The recently licensed fixed combination of atovaquone and proguanil hydrochloride (Malarone) is a promising new agent to prevent and treat Plasmodium falciparum malaria. Randomized controlled trials have shown that atovaquone/proguanil is well tolerated and efficacious for the prevention and treatment of drug-resistant P. falciparum malaria. Atovaquone/proguanil is active against the liver stage of P. falciparum malaria parasites and when used as a prophylactic agent it can be discontinued shortly after leaving malaria-endemic areas, offering a clear advantage for drug adherence.

The pharmacokinetics and pharmacodynamics of atovaquone and proguanil for the treatment of uncomplicated falciparum malaria in third-trimester pregnant women

OBJECTIVE

To investigate the pharmacokinetics, safety and efficacy of the recommended 3-day treatment regimen of Malarone in third-trimester pregnant women with acute uncomplicated falciparum malaria.

METHODS

Twenty-six pregnant women in their third trimester (gestational age: 24-34 weeks) with acute uncomplicated Plasmodium falciparum malaria who fulfilled the enrollment criteria were recruited from the antenatal clinics of Mae Sot Hospital, Tak Province, Thailand, (n = 8) and the Tropical Diseases Research Centre, Ndola, Zambia (n = 18). Patients were treated with four Malarone tablets (GlaxoSmithKline: each tablet contains 250 mg atovaquone and 100 mg proguanil) once daily for 3 consecutive days. Blood samples were taken for pharmacokinetic investigations of atovaquone, proguanil, and cycloguanil up to 288 h (day 14) after the last dose. Urine samples were collected for the evaluation of proguanil and cycloguanil 0-8, 8-16, 16-24 and 24-48 h after the last dose. Efficacy assessments included the clinical and parasitological evaluation of mothers and newborns. Adverse events were evaluated at each visit to the antenatal clinics.

RESULTS

Malarone appeared to be effective and well tolerated when used for the treatment of falciparum malaria in pregnant women. All patients showed prompt clinical improvement and the disappearance of parasitaemia after treatment. There were no serious adverse effects or unexpected adverse effects and no stillbirths or spontaneous abortions. The plasma concentration-time profiles of atovaquone and proguanil in most cases were best characterised by the two-compartment open model with zero-order input with/without absorption lag time and first-order elimination. There were no significant differences in any of the pharmacokinetic parameters of atovaquone, proguanil or cycloguanil between patients from Thailand and Zambia. For atovaquone, a Cmax of 1.33-8.33 microg/ml was reached at 2.0-9.3 h after the last dose on day 2. V/F, CL/F and t(1/2beta) were 6.9-39.5 l/kg, 83-384 ml/h/kg, and 57.8-130.8 h, respectively. The Cmax and t(max) values for proguanil versus cycloguanil were 383-918 versus 0-129 ng/ml and 3.3-8.6 versus 3-12 h, respectively. V/F, CL/F, and t(1/2beta) values for proguanil were 10.7-34.0 l/kg, 431-1,662 ml/h/kg and 11.2-30.3 h. The CL(R-CG), t(1/2z), (CG), proguanil/cycloguanil metabolic ratios, AUC ratios for proguanil to cycloguanil (AUC(PG/CG)) were 107.2-1,001 ml/h/kg, 5-95 ml/h/kg, 7.8-20.7 h, 5-57, and 4.7-20.2, respectively.

CONCLUSION

The pharmacokinetics of atovaquone and cycloguanil appeared to be influenced by the pregnancy status, resulting in an decrease in the Cmax and AUC of approximately twofold.

Antimalarial combinations

Multidrug resistance has rendered monotherapy for malaria useless in most parts of the world, and has also compromised the usefulness of many of the available combination chemotherapies. New antimalarial regimens are, therefore, urgently needed. We review the various antimalarial combinations that can be used to treat otherwise drug-resistant disease, and discuss what defines an ideal antimalarial combination regimen.

Atovaquone-proguanil for prophylaxis and treatment of malaria

OBJECTIVE

To review the currently available information on atovaquone-proguanil for treatment and prophylaxis of malaria.

DATA SOURCES

A MEDLINE search was conducted from 1966 to February 2003 using key phrases Malarone, atovaquone, proguanil, and malaria. Further articles were identified from a manual search of the references of identified articles.

STUDY SELECTION AND DATA EXTRACTION

English-language studies with animal and human data evaluating preclinical pharmacology, human studies on pharmacokinetics, and clinical trials were evaluated. Relevant data were extracted from identified articles.

DATA SYNTHESIS

Atovaquone-proguanil has been evaluated for treatment of acute, uncomplicated malaria caused by Plasmodium falciparum in 8 clinical trials. In these studies, treatment with atovaquone-proguanil led to a higher (87-100% vs. 72-88%) or equally effective (94-100% vs. 90-100%) cure rate than the comparator antimalarial agents. Atovaquone-proguanil has been evaluated for prophylaxis of malaria in 6 clinical trials. In the 4 placebo-controlled trials for semi-immune residents or nonimmune migrants, the prophylaxis success rates in the atovaquone-proguanil and placebo arms ranged from 98% to 100% and 48% to 82%, respectively. The prophylaxis with success rates were similar among the 2 arms when atovaquone-proguanil was compared with other antimalarial regimens in nonimmune travelers. Atovaquone-proguanil was well tolerated in these clinical trials.

CONCLUSIONS

Atovaquone-proguanil is a safe and effective alternative to current recommended regimens for prophylaxis and treatment of malaria.

Efficacy of atovaquone/proguanil for malaria prophylaxis in children and its effect on the immunogenicity of live oral typhoid and cholera vaccines

A double-blind, placebo-controlled study was conducted to measure the impact of malaria prophylaxis with atovaquone/proguanil (A-P) on the immunogenicity of vaccines against typhoid fever and cholera, Salmonella serotype Typhi Ty21a and Vibrio cholerae CVD103-HgR, respectively. A total of 330 Gabonese schoolchildren were assigned to receive either A-P or placebo for 12 weeks. Vaccination occurred 3 weeks after the start of prophylaxis, and immunogenicity was assessed 4 weeks after vaccination. The protective efficacy of A-P against Plasmodium falciparum malaria was of 97% (95% confidence interval, 79%-100%). The 2 treatment groups did not differ significantly with regard to changes in antibody titers after vaccination (P=.96 for anti-S. Typhi IgG antibodies, P=.07 for anti-S. Typhi IgA antibodies, and P=.64 for vibriocidal antibodies). The A-P combination was highly effective for malaria prophylaxis, without interfering with the in vivo immunogenicity of CVD103-HgR and Ty21a vaccines, and it could therefore be simultaneously administered with these vaccines.

Pharmacokinetic interactions of antimalarial agents

Combination of antimalarial agents has been introduced as a response to widespread drug resistance. The higher number of mutations required to express complete resistance against combinations may retard the further development of resistance. Combination of drugs, especially with the artemisinin drugs, may also offer complete and rapid eradication of the parasite load in symptomatic patients and thus reduce the chance of survival of resistant strains. The advantages of combination therapy should be balanced against the increased chance of drug interactions. During the last decade, much of the pharmacokinetics and metabolic pathways of antimalarial drugs have been elucidated, including the role of the cytochrome P450 (CYP) enzyme complex. Change in protein binding is not a significant cause of interactions between antimalarial agents. CYP3A4 and CYP2C19 are frequently involved in the metabolism of antimalarial agents. Quinidine is a potent inhibitor of CYP2D6, but it appears that this enzyme does not mediate the metabolism of any other antimalarial agent. The new combinations proguanil-atovaquone and chlorproguanil-dapsone do not show significant interactions. CYP2B6 and CYP3A4 are involved in the metabolism of artemisinin and derivatives, but further studies may reveal involvement of more enzymes. Artemisinin may induce CYP2C19. Several artemisinin drugs suffer from auto-induction of the first-pass effect, resulting in a decline of bioavailability after repeated doses. The mechanism of this effect is not yet clear, but induction by other agents cannot be excluded. The combination of artemisinin drugs with mefloquine and the fixed combination artemether-lumefantrine have been studied widely, and no significant drug interactions have been found. The artemisinin drugs will be used at an increasing rate, particularly in combination with other agents. Although clinical studies have so far not shown any significant interactions, drug interactions should be given appropriate attention when other combinations are used.

How can we do pharmacokinetic studies in the tropics?

Information regarding the pharmacokinetic (PK) and pharmacodynamic (PD) properties of a drug provides the basis for optimizing dosing. PK-PD information should be obtained from patients representative of the overall target population, but in many tropical hospitals or health care facilities it may be medically hazardous or logistically difficult for an ill patient or a young child to be sampled repeatedly. Traditional methods used to determine the pharmacokinetic properties of a drug require analysis of a large number of blood samples per subject. However, using modern statistical methods, sparse datasets (i.e. with assay results from only a few, or as little as one blood sample per subject) can now be analysed by a method termed 'the population approach'. Modern assay techniques can often be adapted to small blood volumes allowing finger prick blood samples to be taken. One of the major aims of the population approach is to distinguish and characterize patient and disease contributors to inter-individual variance in drug pharmacokinetics. The purpose of this paper is to explain the basis of the population approach, to highlight its advantages compared to traditional methods of analysis, and to review the application of the population approach to data from field studies of antimalarial drugs. The design of population pharmacokinetic studies is also discussed briefly. The principles discussed in the paper are also applicable to pharmacodynamic data.

Discovery of a potent, highly selective, and orally efficacious small-molecule activator of the insulin receptor

A series of 3,6-diaryl-2,5-dihydroxybenzoquinones were synthesized and evaluated for their abilities to selectively activate human insulin receptor tyrosine kinase (IRTK). 2, 5-Dihydroxy-6-(1-methylindol-3-yl)-3-phenyl-1,4-benzoquinone (2h) was identified as a potent, highly selective, and orally active small-molecule insulin receptor activator. It activated IRTK with an EC(50) of 300 nM and did not induce the activation of closely related receptors (IGFIR, EGFR, and PDGFR) at concentrations up to 30 000 nM. Oral administration of the compound to hyperglycemic db/db mice (0.1-10 mg/kg/day) elicited substantial to nearly complete correction of hyperglycemia in a dose-dependent manner. In ob/ob mice, the compound (10 mg/kg) caused significant reduction in hyperinsulinemia. A structurally related compound 2c, inactive in IRTK assay, failed to affect blood glucose level in db/db mice at equivalent exposure levels. Results from additional studies with compound 2h, aimed at evaluating classical quinone-related phenomena, provided sufficient grounds for optimism to allow more extensive toxicologic evaluation.

Pharmacokinetics and pharmacodynamics of lumefantrine (benflumetol) in acute falciparum malaria

The objective of this study was to conduct a prospective population pharmacokinetic and pharmacodynamic evaluation of lumefantrine during blinded comparisons of artemether-lumefantrine treatment regimens in uncomplicated multidrug-resistant falciparum malaria. Three combination regimens containing an average adult lumefantrine dose of 1,920 mg over 3 days (four doses) (regimen A) or 2,780 mg over 3 or 5 days (six doses) (regimen B or C, respectively) were given to 266 Thai patients. Detailed observations were obtained for 51 hospitalized adults, and sparse data were collected for 215 patients of all ages in a community setting. The population absorption half-life of lumefantrine was 4.5 h. The model-based median (5th and 95th percentiles) peak plasma lumefantrine concentrations were 6.2 (0.25 and 14.8) microgram/ml after regimen A, 9. 0 (1.1 and 19.8) microgram/ml after regimen B, and 8 (1.4 and 17.4) microgram/ml after regimen C. During acute malaria, there was marked variability in the fraction of drug absorbed by patients (coefficient of variation, 150%). The fraction increased considerably and variability fell with clinical recovery, largely because food intake was resumed; taking a normal meal close to drug administration increased oral bioavailability by 108% (90% confidence interval, 64 to 164) (P, 0.0001). The higher-dose regimens (B and C) gave 60 and 100% higher areas under the concentration-time curves (AUC), respectively, and thus longer durations for which plasma lumefantrine concentrations exceeded the putative in vivo MIC of 280 microgram/ml (median for regimen B, 252 h; that for regimen C, 298 h; that for regimen A, 204 h [P, 0.0001]) and higher cure rates. Lumefantrine oral bioavailability is very dependent on food and is consequently poor in acute malaria but improves markedly with recovery. The high cure rates with the two six-dose regimens resulted from increased AUC and increased time at which lumefantrine concentrations were above the in vivo MIC.

Clinical pharmacokinetics and pharmacodynamics and pharmacodynamics of artemether-lumefantrine

The combination of artemether and lumefantrine (benflumetol) is a new and very well tolerated oral antimalarial drug effective even against multidrug-resistant falciparum malaria. The artemether component is absorbed rapidly and biotransformed to dihydroartemisinin, and both are eliminated with terminal half-lives of around 1 hour. These are very active antimalarials which give a rapid reduction in parasite biomass and consequent rapid resolution of symptoms. The lumefantrine component is absorbed variably in malaria, and is eliminated more slowly (half-life of 3 to 6 days). Absorption is very dependent on coadministration with fat, and so improves markedly with recovery from malaria. Thus artemether clears most of the infection, and the lumefantrine concentrations that remain at the end of the 3- to 5-day treatment course are responsible for eliminating the residual 100 to 10 000 parasites. The area under the curve of plasma lumefantrine concentrations versus time, or its correlate the plasma concentration on day 7. has proved an important determinant of therapeutic response. Characterisation of these pharmacokinetic-pharmacodynamic relationships provided the basis for dosage optimisation, an approach that could be applied to other antimalarial drugs.

Combination atovaquone and proguanil hydrochloride vs. halofantrine for treatment of acute Plasmodium falciparum malaria in children

BACKGROUND

Malaria is a major cause of pediatric mortality in sub-Saharan Africa. Worldwide estimates of mortality among children with Plasmodium falciparum malaria range from 1 to 2 million deaths per year. Management of malaria is increasingly difficult because of the global spread of drug-resistant strains of P. falciparum. There is an urgent need for safe and effective new therapies to treat multidrug-resistant malaria.

METHODS

This open label, randomized trial compared atovaquone and proguanil hydrochloride with halofantrine for treatment of acute, uncomplicated P. falciparum malaria in children age 3 to 12 years (84 patients per group). Study drug dosages were adjusted by weight (approximately 20 and 8 mg/kg daily for three doses for atovaquone and proguanil hydrochloride and 8 mg/kg every 6 h for three doses for halofantrine). Patients were monitored by serial clinical and laboratory assessments for 28 days after starting treatment.

RESULTS

Both regimens were effective (cure rate, 93.8% for atovaquone and proguanil hydrochloride and 90.4% for halofantrine) and produced prompt defervescence. Mean parasite clearance times were 50.2 h for halofantrine and 64.9 h for atovaquone and proguanil hydrochloride. More adverse experiences were reported in children treated with halofantrine (119) than with atovaquone and proguanil hydrochloride (73).

CONCLUSIONS

In Kenyan children the combination of atovaquone and proguanil hydrochloride has efficacy comparable with that of halofantrine for treatment of acute uncomplicated multidrug-resistant falciparum malaria and is associated with a lower rate of adverse events.

Population pharmacokinetics and therapeutic response of CGP 56697 (artemether + benflumetol) in malaria patients

AIMS

To investigate the pharmacokinetic and pharmacodynamic properties of artemether and benflumetol in a fixed combination tablet (CGP 56697) and to offer an explanation for the lower than expected cure rate in a Thai clinical trial.

METHODS

Two hundred and sixty patients were enrolled into a randomized, double-blind, parallel group, dose-finding trial. CGP 56697 was given orally, either as: A, 4 x 4 tablets over 48 h; B, 4 x 2 tablets over 48 h or C, 3 x 4 tablets over 24 h. Each tablet contained artemether 20 mg amd benflumetol 120 mg. The pharmacokinetics were determined using a population-based approach combining full profiles (42 patients) and sparse data (218 patients). Parasite clearance time and 28 day cure rate were correlated with the derived pharmacokinetic parameters.

RESULTS

The median absorption half-life of benflumetol was 5.3 h, with a tmax of 10 h and terminal elimination half-life of 4.5 days. For artemether (and its metabolite, dihydroartemisinin), the corresponding values were 1.9 (1.9) h, 1.8 (1.2) h, and 0.84 (0.43) h. The variability in bioavailability of artemether and dihydroartemisinin was large both between doses and between patients, but was less pronounced for benflumetol. Compared with the first dose, benflumetol bioavailability was estimated to increase three-fold by the third and fourth doses. Higher artemether or dihydroartemisinin AUC was found to decrease parasite clearance time. Higher benflumetol AUC was found to significantly increase the chance of cure.

CONCLUSIONS

Using a population-based approach it was confirmed that the pharmacokinetic and pharmacodynamic properties of benflumetol and artemether differ markedly. Benflumetol AUC is associated with cure and the effect of benflumetol when coadministered with artemether is to prevent recrudescence. The mode of action of benflumetol is consistent with its longer elimination half-life. A short course of low-dose artemether, which is rapidly absorbed and has a short elimination half-life, produced effective parasite clearance. The complementary pharmacokinetic and pharmacodynamic properties of benflumetol and artemether was the main rationale for developing a fixed-dose combination. While the 4 x 4 dose regimen is very effective in most endemic areas, the poorer absorption (2.5 fold lower than in China) and the more resistant parasites in Thailand require higher doses of this drug.

Randomised placebo-controlled study of atovaquone plus proguanil for malaria prophylaxis in children

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<0.001). Adverse events during the chemosuppression phase did not differ between the groups.

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.