Tafenoquine and its potential in the treatment and relapse prevention of Plasmodium vivax malaria: the evidence to date

Pharmacokinetic Models of Tafenoquine: Insights for Optimal Malaria Treatment Strategies

Tafenoquine (TQ) is a new 8-aminoquinoline antimalarial drug developed by the US Army for Plasmodium vivax malaria treatment. Modeling and simulation are essential tools for drug development and improving rationality in pharmacotherapy, and different modeling approaches are used. This study aims to summarize and explore the pharmacokinetic (PK) models available for tafenoquine in the literature. An integrative methodology was used to collect and review published data. Fifteen articles were identified using three modeling approaches: non-compartmental analysis (NCA), population pharmacokinetic analysis (popPK), and pharmacokinetic/pharmacodynamic analysis (PK/PD). An NCA was mainly used to describe the PK profile of TQ and to compare its PK profile alone to those obtained in association with other drugs. PopPK was used to assess TQ population PK parameters, covariates' impact, and dose selection. PK/PD helped understand the relationship between TQ concentrations, some adverse events common for 8-aminoquilones, and the efficacy assessment for Plasmodium falciparum. In summary, pharmacokinetic models were widely used during TQ development. However, there is still a need for different modeling approaches to support further therapeutic questions, such as treatment for special populations and potential drug-drug interactions.

Liver-targeted polymeric prodrugs delivered subcutaneously improve tafenoquine therapeutic window for malaria radical cure

Approximately 3.3 billion people live with the threat of Plasmodium vivax malaria. Infection can result in liver-localized hypnozoites, which when reactivated cause relapsing malaria. This work demonstrates that an enzyme-cleavable polymeric prodrug of tafenoquine addresses key requirements for a mass administration, eradication campaign: excellent subcutaneous bioavailability, complete parasite control after a single dose, improved therapeutic window compared to the parent oral drug, and low cost of goods sold (COGS) at less than $1.50 per dose. Liver targeting and subcutaneous dosing resulted in improved liver:plasma exposure profiles, with increased efficacy and reduced glucose 6-phosphate dehydrogenase-dependent hemotoxicity in validated preclinical models. A COGS and manufacturability analysis demonstrated global scalability, affordability, and the ability to redesign this fully synthetic polymeric prodrug specifically to increase global equity and access. Together, this polymer prodrug platform is a candidate for evaluation in human patients and shows potential for P. vivax eradication campaigns.

Omega-3 and omega-6 polyunsaturated fatty acids and their potential therapeutic role in protozoan infections

Protozoa exert a serious global threat of growing concern to human, and animal, and there is a need for the advancement of novel therapeutic strategies to effectively treat or mitigate the impact of associated diseases. Omega polyunsaturated fatty acids (ω-PUFAs), including Omega-3 (ω-3) and omega-6 (ω-6), are constituents derived from various natural sources, have gained significant attention for their therapeutic role in parasitic infections and a variety of essential structural and regulatory functions in animals and humans. Both ω-3 and ω-6 decrease the growth and survival rate of parasites through metabolized anti-inflammatory mediators, such as lipoxins, resolvins, and protectins, and have both in vivo and in vitro protective effects against various protozoan infections. The ω-PUFAs have been shown to modulate the host immune response by a commonly known mechanism such as (inhibition of arachidonic acid (AA) metabolic process, production of anti-inflammatory mediators, modification of intracellular lipids, and activation of the nuclear receptor), and promotion of a shift towards a more effective immune defense against parasitic invaders by regulation the inflammation like prostaglandins, leukotrienes, thromboxane, are involved in controlling the inflammatory reaction. The immune modulation may involve reducing inflammation, enhancing phagocytosis, and suppressing parasitic virulence factors. The unique properties of ω-PUFAs could prevent protozoan infections, representing an important area of study. This review explores the clinical impact of ω-PUFAs against some protozoan infections, elucidating possible mechanisms of action and supportive therapy for preventing various parasitic infections in humans and animals, such as toxoplasmosis, malaria, coccidiosis, and chagas disease. ω-PUFAs show promise as a therapeutic approach for parasitic infections due to their direct anti-parasitic effects and their ability to modulate the host immune response. Additionally, we discuss current treatment options and suggest perspectives for future studies. This could potentially provide an alternative or supplementary treatment option for these complex global health problems.

An increase in urinary primaquine and a reduction in urinary primaquine-5,6-orthoquinone in the Thai population with CYP2D6 reduced enzyme function

Objectives

Primaquine is metabolized by the cytochrome P450-2D6 enzyme (CYP2D6) to an active primaquine-5,6-orthoquinone (POQ). No relationships of CYP2D6 polymorphisms with the pharmacokinetics of primaquine and POQ were reported in the Thai population.

Methods

We evaluated the genetic distribution of CYP2D6 in 345 Thai army populations together with the pharmacokinetic profiles of primaquine and POQ in plasma and urine (n = 44, descriptive data are presented in median (range)). All dose-related pharmacokinetic parameters were normalized by primaquine dose per body weight before statistical analysis.

Results

CYP2D6*10 was the allele observed with the highest frequency (56.62%) corresponding to CYP2D6*10/*10 (32.94%) and CYP2D6*1/*10 (27.94%) genotypes. CYP2D6 intermediate metabolizers (CYP2D6 IM) were found in 44.41% of the cohort and had an increase in the cumulative amount of primaquine excreted (CAE) in urine compared to normal metabolizers of CYP2D6 (CYP2D6 NM); (CYP2D6 IM vs. CYP2D6 NM: 2444 (1697-3564) vs. 1757 (1092-2185) μg/mg/kg, p = 0.039), a reduction in urine CAE of POQ (CYP2D6 IM vs CYP2D6 NM: 115 (46-297) vs. 318 (92-498) μg/mg/kg, p = 0.047) and a reduction in the POQ/primaquine CAE ratio in urine (CYP2D6 IM vs. CYP2D6 NM: 0.06 (0.01-0.11) vs. 0.16 (0.06-0.26), p = 0.009). No significant differences were found in the pharmacokinetic profiles of plasma primaquine and POQ.

Conclusions

The CYP2D6 polymorphisms influenced the changes in primaquine and POQ that were noticeable in the urine, supporting the role of the CYP2D6 gene testing before drug administration.

Recent developments in antimalarial drug discovery

Although malaria remains a big burden to many countries that it threatens their socio-economic stability, particularly in the countries where malaria is endemic, there have been great efforts to eradicate this disease with both successes and failures. For example, there has been a great improvement in malaria prevention and treatment methods with a net reduction in infection and mortality rates. However, the disease remains a global threat in terms of the number of people affected because it is one of the infectious diseases that has the highest prevalence rate, especially in Africa where the deadly Plasmodium falciparum is still widely spread. Methods to fight malaria are being diversified, including the use of mosquito nets, the target candidate profiles (TCPs) and target product profiles (TPPs) of medicine for malarial venture (MMV) strategy, the search for newer and potent drugs that could reverse chloroquine resistance, and the use of adjuvants such as rosiglitazone and sevuparin. Although these adjuvants have no antiplasmodial activity, they can help to alleviate the effects which result from plasmodium invasion such as cytoadherence. The list of new antimalarial drugs under development is long, including the out of ordinary new drugs MMV048, CDRI-97/78 and INE963 from South Africa, India and Novartis, respectively.

Malaria therapeutics: are we close enough?

Malaria is a vector-borne parasitic disease caused by the apicomplexan protozoan parasite Plasmodium. Malaria is a significant health problem and the leading cause of socioeconomic losses in developing countries. WHO approved several antimalarials in the last 2 decades, but the growing resistance against the available drugs has worsened the scenario. Drug resistance and diversity among Plasmodium strains hinder the path of eradicating malaria leading to the use of new technologies and strategies to develop effective vaccines and drugs. A timely and accurate diagnosis is crucial for any disease, including malaria. The available diagnostic methods for malaria include microscopy, RDT, PCR, and non-invasive diagnosis. Recently, there have been several developments in detecting malaria, with improvements leading to achieving an accurate, quick, cost-effective, and non-invasive diagnostic tool for malaria. Several vaccine candidates with new methods and antigens are under investigation and moving forward to be considered for clinical trials. This article concisely reviews basic malaria biology, the parasite's life cycle, approved drugs, vaccine candidates, and available diagnostic approaches. It emphasizes new avenues of therapeutics for malaria.

Are we ready to combat the ecotoxicity of COVID-19 pharmaceuticals? An in silico aquatic risk assessment

To fight COVID-19 with uncountable medications and bioproducts throughout the world has taken us to another challenge of ecotoxicity. The indiscriminate usage followed by improper disposal of unused antibacterials, antivirals, antimalarials, immunomodulators, angiotensin II receptor blockers, corticosteroids, anthelmintics, anticoagulants etc. can lead us to an unimaginable ecotoxicity in the long run. A series of studies already identified active pharmaceutical ingredients (APIs) of the mentioned therapeutic classes and their metabolites in aquatic bodies as well as in wastewater treatment plants. Therefore, an initial ecotoxicity assessment of the majorly used pharmaceuticals is utmost requirement of the present time. The present in silico risk assessment study is focused on the aquatic toxicity prediction of 81 pharmaceuticals where 77 are most-used pharmaceuticals for COVID-19 throughout the world based on the literature along with one drug nirmatrelvir [PF-07321332] approved for emergency use by US-FDA and three other molecules under clinical trial. The ecotoxicity of the studied compounds were predicted based on the three aquatic species fish, algae and crustaceans employing the highest quality QSAR models available from the literature as well as using ECOSAR and QSAR Toolbox. To compare the toxicity thresholds, we have also used 4 control pharmaceuticals based on the worldwide occurrence from river, lake, STP, WWTPs, influent and effluent followed by high reported aquatic toxicity over the years as per the literature. Based on the statistical comparison, we have proposed top 3 pharmaceuticals used for the COVID-19 most toxic to the aquatic environment. The study will provide confident predictions of aquatic ecotoxicity data related to abundant use of COVID-19 drugs. The major aim of the study is to fill up the aquatic ecotoxicity data gap of major medications used for COVID-19.

Eficacia de la tafenoquina en la profilaxis y tratamiento de la malaria por Plasmodium vivax, revisión sistemática y metaanálisis

Introducción.

La tafenoquina fue aprobada en el 2018 por la Food and Drug Administration de Estados Unidos y, en el 2019, por la Therapeutic Goods Administration en Australia. Su administración en dosis única y su mecanismo de acción en las fases aguda y latente han sido objeto de estudio para cambiar el esquema de tratamiento de la malaria por Plasmodium vivax.

Objetivo.

Evaluar la evidencia científica disponible sobre la eficacia de la tafenoquina en la profilaxis y el tratamiento de la malaria por P. vivax, entre el 2009 y el 2019.

Materiales y métodos.

Se establecieron los descriptores MeSH y DeCS. Se utilizó la sintaxis ((Malaria Vivax) AND (tafenoquine) AND (prophylaxis)) OR [(Malaria Vivax) AND (tafenoquine) AND (relapse)] en las siguientes bases de datos: Pubmed, The Cochrane Central Register of Controlled Clinical Trials (CENTRAL), ISIS Web of Science, Lilacs y Scopus. Los resultados obtenidos se sometieron a análisis crítico (matriz CASPE). El análisis cuantitativo se realizó utilizando la diferencia de riesgos en análisis de supervivencia (Kaplan-Meier) en los tres artículos finales.

Resultados.

Se sometieron tres estudios a metaanálisis (Llanos-Cuentas, 2014; Llanos- Cuentas, 2019, y Lacerda, 2019) para evaluar la eficacia del tratamiento con tafenoquina en comparación con primaquina. Se obtuvo una diferencia de riesgo global de 0,04 (IC95% 0-0,08; p=0,07). La tafenoquina no mostró inferioridad en la eficacia del tratamiento frente al esquema de primaquina.

Conclusión.

La tafenoquina es una alternativa que mejora el cumplimiento del tratamiento, lo que podría acercar a Colombia a las metas de la Estrategia Técnica Mundial contra la Malaria, 2016-2030.

Higher-Dose Primaquine to Prevent Relapse of Plasmodium vivax Malaria

BACKGROUND

In most of the Americas, the recommended treatment to prevent relapse of Plasmodium vivax malaria is primaquine at a total dose of 3.5 mg per kilogram of body weight, despite evidence of only moderate efficacy.

METHODS

In this trial conducted in Brazil, we evaluated three primaquine regimens to prevent relapse of P. vivax malaria in children at least 5 years of age and in adults with microscopy-confirmed P. vivax monoinfection. All the patients received directly observed chloroquine for 3 days (total dose, 25 mg per kilogram). Group 1 received a total primaquine dose of 3.5 mg per kilogram (0.5 mg per kilogram per day) over 7 days with unobserved administration; group 2 received the same regimen as group 1 but with observed administration; and group 3 received a total primaquine dose of 7.0 mg per kilogram over 14 days (also 0.5 mg per kilogram per day) with observed administration. We monitored the patients for 168 days.

RESULTS

We enrolled 63 patients in group 1, 96 in group 2, and 95 in group 3. The median age of the patients was 22.4 years (range, 5.4 to 79.8). By day 28, three P. vivax recurrences were observed: 2 in group 1 and 1 in group 2. By day 168, a total of 70 recurrences had occurred: 24 in group 1, 34 in group 2, and 12 in group 3. No serious adverse events were noted. On day 168, the percentage of patients without recurrence was 58% (95% confidence interval [CI], 44 to 70) in group 1, 59% (95% CI, 47 to 69) in group 2, and 86% (95% CI, 76 to 92) in group 3. Survival analysis showed a difference in the day 168 recurrence-free percentage of 27 percentage points (97.5% CI, 10 to 44; P<0.001) between group 1 and group 3 and a difference of 27 percentage points (97.5% CI, 12 to 42; P<0.001) between group 2 and group 3.

CONCLUSIONS

The administration of primaquine at a total dose of 7.0 mg per kilogram had higher efficacy in preventing relapse of P. vivax malaria than a total dose of 3.5 mg per kilogram through day 168. (Supported by the U.S. Agency for International Development; ClinicalTrials.gov number, NCT03610399.).

Tafenoquine and its derivatives as inhibitors for the severe acute respiratory syndrome coronavirus 2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has severely affected human lives around the world as well as the global economy. Therefore, effective treatments against COVID-19 are urgently needed. Here, we screened a library containing Food and Drug Administration (FDA)-approved compounds to identify drugs that could target the SARS-CoV-2 main protease (M^pro), which is indispensable for viral protein maturation and regard as an important therapeutic target. We identified antimalarial drug tafenoquine (TFQ), which is approved for radical cure of Plasmodium vivax and malaria prophylaxis, as a top candidate to inhibit M^pro protease activity. The crystal structure of SARS-CoV-2 M^pro in complex with TFQ revealed that TFQ noncovalently bound to and reshaped the substrate-binding pocket of M^pro by altering the loop region (residues 139–144) near the catalytic Cys145, which could block the catalysis of its peptide substrates. We also found that TFQ inhibited human transmembrane protease serine 2 (TMPRSS2). Furthermore, one TFQ derivative, compound 7, showed a better therapeutic index than TFQ on TMPRSS2 and may therefore inhibit the infectibility of SARS-CoV-2, including that of several mutant variants. These results suggest new potential strategies to block infection of SARS-CoV-2 and rising variants.

Multi-omics approaches to improve malaria therapy

Malaria contributes to the most widespread infectious diseases worldwide. Even though current drugs are commercially available, the ever-increasing drug resistance problem by malaria parasites poses new challenges in malaria therapy. Hence, searching for efficient therapeutic strategies is of high priority in malaria control. In recent years, multi-omics technologies have been extensively applied to provide a more holistic view of functional principles and dynamics of biological mechanisms. We briefly review multi-omics technologies and focus on recent malaria progress conducted with the help of various omics methods. Then, we present up-to-date advances for multi-omics approaches in malaria. Next, we describe resistance phenomena to established antimalarial drugs and underlying mechanisms. Finally, we provide insight into novel multi-omics approaches, new drugs and vaccine developments and analyze current gaps in multi-omics research. Although multi-omics approaches have been successfully used in malaria studies, they are still limited. Many gaps need to be filled to bridge the gap between basic research and treatment of malaria patients. Multi-omics approaches will foster a better understanding of the molecular mechanisms of Plasmodium that are essential for the development of novel drugs and vaccines to fight this disastrous disease.

Malaria and tuberculosis as diseases of neglected populations: state of the art in chemotherapy and advances in the search for new drugs

Malaria and tuberculosis are no longer considered to be neglected diseases by the World Health Organization. However, both are huge challenges and public health problems in the world, which affect poor people, today referred to as neglected populations. In addition, malaria and tuberculosis present the same difficulties regarding the treatment, such as toxicity and the microbial resistance. The increase of Plasmodium resistance to the available drugs along with the insurgence of multidrug- and particularly tuberculosis drug-resistant strains are enough to justify efforts towards the development of novel medicines for both diseases. This literature review provides an overview of the state of the art of antimalarial and antituberculosis chemotherapies, emphasising novel drugs introduced in the pharmaceutical market and the advances in research of new candidates for these diseases, and including some aspects of their mechanism/sites of action.

Screening Marine Natural Products for New Drug Leads against Trypanosomatids and Malaria

Neglected Tropical Diseases (NTD) represent a serious threat to humans, especially for those living in poor or developing countries. Almost one-sixth of the world population is at risk of suffering from these diseases and many thousands die because of NTDs, to which we should add the sanitary, labor and social issues that hinder the economic development of these countries. Protozoan-borne diseases are responsible for more than one million deaths every year. Visceral leishmaniasis, Chagas disease or sleeping sickness are among the most lethal NTDs. Despite not being considered an NTD by the World Health Organization (WHO), malaria must be added to this sinister group. Malaria, caused by the apicomplexan parasite Plasmodium falciparum, is responsible for thousands of deaths each year. The treatment of this disease has been losing effectiveness year after year. Many of the medicines currently in use are obsolete due to their gradual loss of efficacy, their intrinsic toxicity and the emergence of drug resistance or a lack of adherence to treatment. Therefore, there is an urgent and global need for new drugs. Despite this, the scant interest shown by most of the stakeholders involved in the pharmaceutical industry makes our present therapeutic arsenal scarce, and until recently, the search for new drugs has not been seriously addressed. The sources of new drugs for these and other pathologies include natural products, synthetic molecules or repurposing drugs. The most frequent sources of natural products are microorganisms, e.g., bacteria, fungi, yeasts, algae and plants, which are able to synthesize many drugs that are currently in use (e.g. antimicrobials, antitumor, immunosuppressants, etc.). The marine environment is another well-established source of bioactive natural products, with recent applications against parasites, bacteria and other pathogens which affect humans and animals. Drug discovery techniques have rapidly advanced since the beginning of the millennium. The combination of novel techniques that include the genetic modification of pathogens, bioimaging and robotics has given rise to the standardization of High-Performance Screening platforms in the discovery of drugs. These advancements have accelerated the discovery of new chemical entities with antiparasitic effects. This review presents critical updates regarding the use of High-Throughput Screening (HTS) in the discovery of drugs for NTDs transmitted by protozoa, including malaria, and its application in the discovery of new drugs of marine origin.

Tafenoquine: A Step toward Malaria Elimination

There is a pressing need for compounds with broad-spectrum activity against malaria parasites at various life cycle stages to achieve malaria elimination. However, this goal cannot be accomplished without targeting the tenacious dormant liver-stage hypnozoite that causes multiple relapses after the first episode of illness. In the search for the magic bullet to radically cure Plasmodium vivax malaria, tafenoquine outperformed other candidate drugs and was approved by the U.S. Food and Drug Administration in 2018. Tafenoquine is an 8-aminoquinoline that inhibits multiple life stages of various Plasmodium species. Additionally, its much longer half-life allows for single-dose treatment, which will improve the compliance rate. Despite its approval and the long-time use of other 8-aminoquinolines, the mechanisms behind tafenoquine's activity and adverse effects are still largely unknown. In this Perspective, we discuss the plausible underlying mechanisms of tafenoquine's antiparasitic activity and highlight its role as a cellular stressor. We also discuss potential drug combinations and the development of next-generation 8-aminoquinolines to further improve the therapeutic index of tafenoquine for malaria treatment and prevention.

Could the Drug Tafenoquine Revolutionize Treatment of Babesia microti Infection?

BACKGROUND

Tafenoquine (TQ) was recently approved by the US Food and Drug Administration for prophylaxis of malaria and, in addition, for eradication of the hepatic phase of the relevant Plasmodium species. In this study, we evaluated the efficacy of TQ for treatment of Babesia microti infection in mice with severe combined immunodeficiency (SCID).

METHODS

SCID mice were infected with 1.1-1.5 × 108 B. microti-infected red blood cells by intraperitoneal injection. On day 3 or 4 postinfection, when parasitemia levels typically exceeded 10%, mice were treated with TQ vs vehicle alone, both administered by oral gavage.

RESULTS

A single dose of TQ completely eliminated detectable parasites, with a >90% reduction in the level of parasitemia within just 4 days. Before elimination, a conspicuous phenotypic change in the parasite was observed. Although parasitologic cure was not achieved, there was no evidence for the development of drug resistance.

CONCLUSIONS

This study suggests that TQ may be a highly useful drug to treat B. microti infection in patients. If further animal studies establish that a marked reduction in B. microti parasitemia can be reliably achieved with peak blood levels of TQ known to be well tolerated in humans, a clinical trial in patients should be considered.

Newly Developed Prodrugs and Prodrugs in Development; an Insight of the Recent Years

BACKGROUND

The design and development of prodrugs is the most common and effective strategy to overcome pharmacokinetic and pharmacodynamic drawbacks of active drugs. A respected number of prodrugs have been reached the drugs market throughout history and the recent years have witnessed a significant increase in the use of prodrugs as a replacement of their parent drugs for an efficient treatment of various ailment.

METHODS

A Scan conducted to find recent approved prodrugs and prodrugs in development.

RESULTS

Selected prodrugs were reported and categorized in accordance to their target systems.

CONCLUSIONS

the prodrug approach has shown many successes and still remains a viable and effective approach to deliver new active agents. This conclusion is supported by the recent approved prodrugs and the scan of clinical trials conducted between 2013-2018.

Performance of the Access Bio/CareStart rapid diagnostic test for the detection of glucose-6-phosphate dehydrogenase deficiency: A systematic review and meta-analysis

BACKGROUND

To reduce the risk of drug-induced haemolysis, all patients should be tested for glucose-6-phosphate dehydrogenase (G6PD) deficiency (G6PDd) prior to prescribing primaquine (PQ)-based radical cure for the treatment of vivax malaria. This systematic review and individual patient meta-analysis assessed the utility of a qualitative lateral flow assay from Access Bio/CareStart (Somerset, NJ) (CareStart Screening test for G6PD deficiency) for the diagnosis of G6PDd compared to the gold standard spectrophotometry (International Prospective Register of Systematic Reviews [PROSPERO]: CRD42019110994).

METHODS AND FINDINGS

Articles published on PubMed between 1 January 2011 and 27 September 2019 were screened. Articles reporting performance of the standard CSG from venous or capillary blood samples collected prospectively and considering spectrophotometry as gold standard (using kits from Trinity Biotech PLC, Wicklow, Ireland) were included. Authors of articles fulfilling the inclusion criteria were contacted to contribute anonymized individual data. Minimal data requested were sex of the participant, CSG result, spectrophotometry result in U/gHb, and haemoglobin (Hb) reading. The adjusted male median (AMM) was calculated per site and defined as 100% G6PD activity. G6PDd was defined as an enzyme activity of less than 30%. Pooled estimates for sensitivity and specificity, unconditional negative predictive value (NPV), positive likelihood ratio (LR+), and negative likelihood ratio (LR-) were calculated comparing CSG results to spectrophotometry using a random-effects bivariate model. Of 11 eligible published articles, individual data were available from 8 studies, 6 from Southeast Asia, 1 from Africa, and 1 from the Americas. A total of 5,815 individual participant data (IPD) were available, of which 5,777 results (99.3%) were considered for analysis, including data from 3,095 (53.6%) females. Overall, the CSG had a pooled sensitivity of 0.96 (95% CI 0.90-0.99) and a specificity of 0.95 (95% CI 0.92-0.96). When the prevalence of G6PDd was varied from 5% to 30%, the unconditional NPV was 0.99 (95% CI 0.94-1.00), with an LR+ and an LR- of 18.23 (95% CI 13.04-25.48) and 0.05 (95% CI 0.02-0.12), respectively. Performance was significantly better in males compared to females (p = 0.027) but did not differ significantly between samples collected from capillary or venous blood (p = 0.547). Limitations of the study include the lack of wide geographical representation of the included data and that the CSG results were generated under research conditions, and therefore may not reflect performance in routine settings.

CONCLUSIONS

The CSG performed well at the 30% threshold. Its high NPV suggests that the test is suitable to guide PQ treatment, and the high LR+ and low LR- render the test suitable to confirm and exclude G6PDd. Further operational studies are needed to confirm the utility of the test in remote endemic settings.

The past, present and future of anti-malarial medicines

Great progress has been made in recent years to reduce the high level of suffering caused by malaria worldwide. Notably, the use of insecticide-treated mosquito nets for malaria prevention and the use of artemisinin-based combination therapy (ACT) for malaria treatment have made a significant impact. Nevertheless, the development of resistance to the past and present anti-malarial drugs highlights the need for continued research to stay one step ahead. New drugs are needed, particularly those with new mechanisms of action. Here the range of anti-malarial medicines developed over the years are reviewed, beginning with the discovery of quinine in the early 1800s, through to modern day ACT and the recently-approved tafenoquine. A number of new potential anti-malarial drugs currently in development are outlined, along with a description of the hit to lead campaign from which it originated. Finally, promising novel mechanisms of action for these and future anti-malarial medicines are outlined.

Area of exposure and treatment challenges of malaria in Eritrean migrants: a GeoSentinel analysis

Background

Recent reports highlight malaria as a frequent diagnosis in migrants who originate from Eritrea. A descriptive analysis of GeoSentinel cases of malaria in Eritrean migrants was done together with a literature review to elucidate key attributes of malaria in this group with a focus on possible areas of acquisition of malaria and treatment challenges.

Results

A total of 146 cases were identified from the GeoSentinel database from 1999 through September 2017, with a marked increase in 2014 and 2015. All patients originated from Eritrea and the main reporting GeoSentinel sites were in Norway, Switzerland, Sweden, Israel and Germany. The majority of patients (young adult males) were diagnosed with malaria following arrival in the host country. All patients had a possible exposure in Eritrea, but may have been exposed in documented transit countries including Ethiopia, Sudan and possibly Libya in detention centres. Most infections were due to Plasmodium vivax (84.2%), followed by Plasmodium falciparum (8.2%). Two patients were pregnant, and both had P. vivax malaria. Some 31% of the migrants reported having had malaria while in transit. The median time to onset of malaria symptoms post arrival in the host country was 39 days. Some 66% of patients were hospitalized and nine patients had severe malaria (according to WHO criteria), including five due to P. vivax.

Conclusions

The 146 cases of mainly late onset, sometimes severe, P. vivax malaria in Eritrean migrants described in this multi-site, global analysis reflect the findings of single-centre analyses identified in the literature search. Host countries receiving asylum-seekers from Eritrea need to be prepared for large surges in vivax and, to a lesser extent, falciparum malaria, and need to be aware and prepared for glucose-6-phosphate dehydrogenase deficiency testing and primaquine treatment, which is difficult to procure and mainly unlicensed in Europe. There is an urgent need to explore the molecular epidemiology of P. vivax in Eritrean asylum-seekers, to investigate the area of acquisition of P. vivax along common transit routes and to determine whether there has been re-introduction of malaria in areas, such as Libya, where malaria is considered eliminated, but where capable vectors and Plasmodium co-circulate.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2586-9) contains supplementary material, which is available to authorized users.

Field evaluation of quantitative point of care diagnostics to measure glucose-6-phosphate dehydrogenase activity

BACKGROUND

Glucose-6-Phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy worldwide, no reliable bedside diagnostic tests to quantify G6PD activity exist. This study evaluated two novel quantitative G6PD diagnostics.

METHODS

Participants with known G6PD activity were enrolled in Bangladesh. G6PD activity was measured by spectrophotometry, Biosensor (BS; AccessBio/CareStart, USA) and STANDARD G6PD (SG; SDBiosensor, ROK). G6PD activity was measured repeatedly in a subset of samples stored at room temperature and 4°C.

RESULTS

158 participants were enrolled, 152 samples tested by BS, 108 samples by SG and 102 samples were tested by all three methods. In comparison to spectrophotometry BS had sensitivity and specificity of 72% (95%CI: 53-86) and 100% (95%CI: 97-100) at 30% cut off respectively, while SG had a sensitivity of 100% (95%CI: 88-100) and specificity of 97% (95%CI: 91-99) at the same cut off. The sensitivity and specificity at 70% cut off activity were 71% (95%CI: 59-82) and 98% (95%CI, 92-100) respectively for BS and 89% (95%CI: 77-96) and 93% (95%CI: 83-98) respectively for SG. When an optimal cut-off was applied the sensitivity of the BS at 70 cut off rose to 91% [95%CI: 80-96] and specificity to 82% [95%CI: 83-89]; a diagnostic accuracy comparable to that of the SG (p = 0.879). G6PD activity dropped significantly (-0.31U/gHb, 95%CI: -0.61 to -0.01, p = 0.022) within 24 hours in samples stored at room temperature, but did not fall below 90% of baseline activity until day 13 (-0.87U/gHb, 95%CI: (-1.11 to -0.62), p<0.001).

CONCLUSION

BS and SG are the first quantitative diagnostics to measure G6PD activity reliably at the bedside and represent suitable alternatives to spectrophotometry in resource poor settings. If samples are stored at 4°C, G6PD activity can be measured reliably for at least 7 days after sample collection.

Comparison of glucose-6 phosphate dehydrogenase status by fluorescent spot test and rapid diagnostic test in Lao PDR and Cambodia

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy worldwide. Primaquine is the only licensed drug that effectively removes Plasmodium vivax hypnozoites from the human host and prevents relapse. While well tolerated by most recipients, primaquine can cause haemolysis in G6PD deficient individuals and is, therefore, underused. Rapid diagnostic tests (RDTs) could permit ascertainment of G6PD status outside of laboratory settings and hence safe treatment in remote areas. The performance of the fluorescent spot test (Trinity, Ireland; FST) and a G6PD RDT (Carestart, USA) against spectrophotometry were assessed.

METHODS

Participants were enrolled during cross-sectional surveys in Laos and by purposive sampling in Cambodia. FST and RDT were performed during village surveys and 3 mL of venous blood was collected for subsequent G6PD measurement by spectrophotometry.

RESULTS

A total of 757 participants were enrolled in Laos and 505 in Cambodia. FST and RDT performed best at 30% cut-off activity and performed significantly better in Laos than in Cambodia. When defining intermediate results as G6PD deficient, the FST had a sensitivity of 100% (95%CI 90-100) and specificity of 90% (95%CI 87.7-92.2) in Laos and sensitivity of 98% (94.1-99.6) and specificity of 71% (95%CI 66-76) in Cambodia (p < 0.001). The RDT had sensitivity and specificity of 100% (95%CI 90-100) and 99% (95%CI 97-99) in Laos and sensitivity and specificity of 91% (86-96) and 93% (90-95) in Cambodia (p < 0.001). The RDT performed significantly better (all p < 0.05) than the FST when intermediate FST results were defined as G6PD deficient.

CONCLUSION

The interpretation of RDT results requires some training but is a good alternative to the FST. Trial registration clinicaltrials.gov; NCT01872702; 06/27/2013; https://clinicaltrials.gov/ct2/show/NCT01872702.

Application of the Stable Isotope Label Approach in Clinical Development-Supporting Dissolution Specifications for a Commercial Tablet Product with Tafenoquine, a Long Half-life Compound

Bioavailability/bioequivalence studies supporting clinical drug development or commercial supply of drug formulations are often time, cost, and resource intensive. The drug's pharmacokinetic (PK) variability, systemic half-life, and safety issues may pose additional challenges. The stable isotope label (SIL) approach provides a useful tool to significantly reduce the study size in clinical PK studies. Tafenoquine (TQ) is an 8-aminoquinoline under development for preventing Plasmodium vivax malaria relapse. This SIL study assessed the impact of differences in the in vitro dissolution profiles on in vivo exposure of TQ tablets. Fourteen healthy volunteers received a single dose of 300 mg TQ Intermediate Aged or 300 mg TQ Control formulations in this single-center, two-arm, randomized, open-label, parallel-group study. Endpoints included the geometric means ratio of the area under the concentration-time curve (AUC_(0-t) and AUC_(0-∞); primary endpoint) and maximum plasma concentration (C_max) for Intermediate Aged versus Control TQ; correlation of PK parameters for venous versus peripheral (via microsample) blood samples; and safety and tolerability endpoints. Geometric mean ratios for PK parameters (AUC and C_max) and their 90% confidence intervals fell well within standard bioequivalence limits (0.80-1.25). Only one mild adverse event (skin abrasion) was reported. In summary, this SIL methodology-based study demonstrates that the observed differences in the in vitro dissolution profiles between the Control and Intermediate Aged TQ tablets have no clinically relevant effect on systemic TQ exposure. The SIL approach was successfully implemented to enable the setting of a clinically relevant dissolution specification.

CLINICAL TRIAL

This study (GSK study number 201780) is registered at clinicaltrials.gov with identifier NCT02751294.

The antimalarial pipeline

Over the past decade, new high-throughput phenotypic assays with malaria parasites have been developed, and these were used to screen millions of compounds. This effort, as well as improving older chemical scaffolds and optimising compounds against both known and new drug targets has resulted in the discovery of exciting new pipeline drug candidates that are now being evaluated in a number of clinical trials. In addition, the pitfalls and opportunities from this experience has led to a better definition of the optimal target compound and product profiles for new antimalarials, including medicines that treat uncomplicated or severe malaria, provide chemoprevention, or stop disease transmission, covering all stages of the parasite. An important decision element is how to combine these new molecules with existing ones in today's dynamic resistance landscape.

Differential activity of methylene blue against erythrocytic and hepatic stages of Plasmodium

BACKGROUND

In the context of malaria elimination/eradication, drugs that are effective against the different developmental stages of the parasite are highly desirable. The oldest synthetic anti-malarial drug, the thiazine dye methylene blue (MB), is known for its activity against Plasmodium blood stages, including gametocytes. The aim of the present study was to investigate a possible effect of MB against malaria parasite liver stages.

METHODS

MB activity was investigated using both in vitro and in vivo models. In vitro assays consisted of testing MB activity on Plasmodium falciparum, Plasmodium cynomolgi and Plasmodium yoelii parasites in human, simian or murine primary hepatocytes, respectively. MB in vivo activity was evaluated using intravital imaging in BALB/c mice infected with a transgenic bioluminescent P. yoelii parasite line. The transmission-blocking activity of MB was also addressed using mosquitoes fed on MB-treated mice.

RESULTS

MB shows no activity on Plasmodium liver stages, including hypnozoites, in vitro in primary hepatocytes. In BALB/c mice, MB has moderate effect on P. yoelii hepatic development but is highly effective against blood stage growth. MB is active against gametocytes and abrogates parasite transmission from mice to mosquitoes.

CONCLUSION

While confirming activity of MB against both sexual and asexual blood stages, the results indicate that MB has only little activity on the development of the hepatic stages of malaria parasites.

Malaria 2017: Update on the Clinical Literature and Management

PURPOSE OF REVIEW

Malaria is a prevalent disease in travelers to and residents of malaria-endemic regions. Health care workers in both endemic and non-endemic settings should be familiar with the latest evidence for the diagnosis, management and prevention of malaria. This article will discuss the recent malaria epidemiologic and medical literature to review the progress, challenges, and optimal management of malaria.

RECENT FINDINGS

There has been a marked decrease in malaria-related global morbidity and mortality secondary to malaria control programs over the last few decades. This exciting progress is tempered by continued levels of high transmission in some regions, the emergence of artemisinin-resistant Plasmodium falciparum malaria in Southeast Asia, and the lack of a highly protective malaria vaccine. In the United States (US), the number of travelers returning with malaria infection has increased over the past few decades. Thus, US health care workers need to maintain expertise in the diagnosis and treatment of this infection. The best practices for treatment and prevention of malaria need to be continually updated based on emerging data. Here, we present an update on the recent literature on malaria epidemiology, drug resistance, severe disease, and prevention strategies.

Primaquine-thiazolidinones block malaria transmission and development of the liver exoerythrocytic forms

Background

Primaquine is an anti-malarial used to prevent Plasmodium vivax relapses and malaria transmission. However, PQ metabolites cause haemolysis in patients deficient in the enzyme glucose-6-phosphate dehydrogenase (G6PD). Fifteen PQ-thiazolidinone derivatives, synthesized through one-post reactions from primaquine, arenealdehydes and mercaptoacetic acid, were evaluated in parallel in several biological assays, including ability to block malaria transmission to mosquitoes.

Results

All primaquine derivatives (PQ-TZs) exhibited lower cell toxicity than primaquine; none caused haemolysis to normal or G6PD-deficient human erythrocytes in vitro. Sera from mice pretreated with the test compounds thus assumed to have drug metabolites, caused no in vitro haemolysis of human erythrocytes, whereas sera from mice pretreated with primaquine did cause haemolysis. The ability of the PQ-TZs to block malaria transmission was evaluated based on the oocyst production and percentage of mosquitoes infected after a blood meal in drug pre-treated animals with experimental malaria caused by either Plasmodium gallinaceum or Plasmodium berghei; four and five PQ-TZs significantly inhibited sporogony in avian and in rodent malaria, respectively. Selected PQ-TZs were tested for their inhibitory activity on P. berghei liver stage development, in mice and in vitro, one compound (4m) caused a 3-day delay in the malaria pre-patent period.

Conclusions

The compound 4m was the most promising, blocking malaria transmissions and reducing the number of exoerythrocytic forms of P. berghei (EEFs) in hepatoma cells in vitro and in mice in vivo. The same compound also caused a 3-day delay in the malaria pre-patent period.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1755-6) contains supplementary material, which is available to authorized users.

Malaria Parasites Distribute Subversive Messages across Enemy Lines

During its life cycle, the malaria parasite must cope with a set of diverse environments and institute strategies to alter its host's responses. A recent study remarkably demonstrates how these parasites exploit red blood cell products, loading them into 'armed' secreted vesicles sent to manipulate their host's 'endothelium battlefront', thereby promoting malaria infection.