Antimalarial drug candidates in phase I and II drug development: a scoping review

The emergence and spread of parasite resistance to currently available antimalarials has highlighted the importance of developing novel antimalarials. This scoping review provides an overview of antimalarial drug candidates undergoing phase I and II studies between 1 January 2016 and 28 April 2021. PubMed, Web of Science, Embase, clinical trial registries and reference lists were searched for relevant studies. Information regarding antimalarial compound details, clinical trial characteristics, study population, drug pharmacokinetics and pharmacodynamics (PK-PD) were extracted. A total of 50 studies were included of which 24 had published their results and 26 were unpublished. New antimalarial compounds were evaluated as monotherapy (28 studies, 14 drug candidates) and combination therapy (9 studies, 10 candidates). Fourteen active compounds were identified in the current antimalarial drug development pipeline together with 11 compounds that are inactive; six due to insufficient efficacy. PK-PD data were available from 24 studies published as open-access articles. Four unpublished studies have made their results publicly available on clinical trial registries. The terminal elimination half-life of new antimalarial compounds ranged from 14.7 to 483 hours. The log 10 parasite reduction ratio over 48 hours and parasite clearance half-life for P. falciparum following a single dose monotherapy were 1.55–4.1 and 3.4–9.4 hours, respectively. The antimalarial drug development landscape has seen a number of novel compounds, with promising PK-PD properties, evaluated in phase I and II studies over the past 5 years. Timely public disclosure of PK-PD data is crucial for informative decision-making and drug development strategy.

COVID-19 Pandemic and the Debatable Use of Hydroxychloroquine

Healthcare professionals and scientists were not able to provide a good answer to the COVID-19 pandemic that shook the whole world. Hydroxychloroquine is an antimalarial drug with a good safety profile. It can be used in pediatric subjects as well as pregnant and breastfeeding women. Hydroxychloroquine is a widely used, essential drug in dermatology. It has got anti-inflammatory, antibacterial, antiviral and immunomodulatory properties. It was globally prescribed to prevent and treat COVID-19 caused by SARS-CoV-2 virus. The use of this drug in treating COVID-19 is debatable and for sure is not indicated in the labelling documents provided by the companies that manufacture this drug. The unnecessary use of this drug also led to short supply. We hereby review its properties, mechanism, safety profile and the issue COVID pandemic has caused to the supply of this drug.

Artemether–lumefantrine and dihydroartemisinin–piperaquine treatment outcomes among children infected with uncomplicated Plasmodium falciparum malaria in Mwanza, Tanzania

Background Artemisinin based combination therapies (ACTs) have been a cornerstone in the treatment of malaria in the world. A rapid decline in dihydroartemisinin piperaquine (DHP) and artemether lumefantrine (ALU) efficacies has been reported in some parts of South East Asia, the historical epicenter for the antimalarial drug resistance. Prolonged drug use is associated with selection of resistant parasites due to exposure to inadequate drug levels hence effects on treatment outcomes in malaria. ALU and DHP are used as first line and alternative first line, respectively, in Tanzania. This study was carried in Igombe, Tanzania to assess the efficacies of ALU and DHP in routine treatment of uncomplicated malaria among children. Methods This was a prospective study involving children up to 10 years and followed up for 28 and 35 days as per the WHO protocol, 2015 for monitoring antimalarial drug efficacy. The primary end points were crude and adjusted Adequate Clinical and Parasitological Response (ACPR), parasite clearance rate and reported adverse events. Results A total of 205 children with uncomplicated malaria were enrolled. One hundred and sixteen participants were treated with ALU, while 89 participants were treated with DHP. Two participants in the ALU group were lost within the 24 h of follow-up. The PCR unadjusted ACPR was108 (94.7%) for ALU and 88 (98.9%) for DHP, while the PCR adjusted ACPR was 109(95.6%) and 88(98.9%) for ALU and DHP, respectively, at 28 day follow-up. No treatment failure was observed in both groups. Cumulative risk of recurrent parasitemia was similar in both groups (p = 0.32). Age and parasite density were strong predictors for persistent day 1 parasitemia (p = 0.034 and 0.026, respectively). Nausea and vomiting, abdominal pain and headache were the most clinical adverse events reported in both groups of patients. Conclusion The present study shows that ALU and DHP are still efficacious after more than a decade of use with PCR corrected efficacies greater than 95% implying a failure rate less than 5% which is below the WHO minimum threshold requirement for recommendation of a change in the treatment policy. Both drugs were well tolerated with no major adverse events reported.

Expanding the scope of prenylated 1,2,3-triazoles as new antiparasitic drug candidates

We have previously shown that prenyl and aliphatic triazoles are interesting motifs to prepare new chemical entities for antiparasitic and antituberculosis drug development. In this opportunity a new series of prenyl-1,2,3-triazoles were prepared from isoprenyl azides and different alkynes looking for new antimalarial drug candidates. The compounds were prepared by copper(I) catalyzed dipolar cycloaddition of the isoprenyl azide equilibrium mixture providing exclusively 1,4-disubstituted 1,2,3-triazols in a regiospecific fashion. The complete collection of 64 compounds was tested on chloroquine -sensitive, Sierra Leone (D6), and the chloroquine-resistant, Indochina (W2), strains of Plasmodium falciparum and those compounds which were not previously reported were also tested against Leishmania donovani , the causative agent for visceral leishmaniasis. Thirteen analogs displayed antimalarial activity with IC50 below 10 uM, while the antileishmanial activity was less potent than the previously reported analogs. The cytotoxicity assay against Vero cells revealed that none of the compounds was cytotoxic up to concentrations of 4.75 ug/mL. Compounds 1o and 1r were identified as the most promising antimalarial drug leads with IC50 below 3.0 uM for both CQ-sensitive and resistant P. falciparum strains. Finally, a chemoinformatic in silico analysis was performed to evaluate physicochemical parameters, cytotoxicity risk and drug score. The validation of a bifunctional farnesyl/geranylgeranyl diphosphate synthase PfFPPS/GGPPS as the potential target of the antimalarial activity of selected analogs should be further investigated.

Our Exciting Journey to ACT-451840

We describe our work resulting in the selection of ACT-451840 ( 38 ) as a novel antimalarial drug with a novel mode of action. The compound was broadly characterized in vitro as well as in vivo in rat PK experiments as well as two different mouse malaria models. In the P. berghei infected mouse model cure could be achieved at oral doses of 300 mg/kg over 3 consecutive days. ACT-451840 was clinically investigated up to an experimental human malaria infection model, where therapeutic effects could be shown.

Targeting the Plasmodium falciparum Proteome and Organelles for Potential Antimalarial Drug Candidates

There is an overarching need to find alternative treatment options for malaria and this quest is more pressing in current times due to the morbidity and mortality data arising from most endemic countries and partially owing to the fact that the SARS-Cov-2 pandemic has diverted much public health attention. Additionally, the therapeutic options available for malaria has been severely threatened with the emergence of resistance to almost all existing drugs by the human malaria parasite. The Artemisinin Combination Therapies (ACTs) which hitherto have been the mainstay for malaria have encountered resistance in South East Asia, a notorious ground zero for the emergence of antimalarial drug resistance. This review analyses few key druggable targets of the parasite and the potential to leverage strategic inhibitors to mitigate the scourge of malaria by providing a concise assessment of the essential proteins of the malaria parasite that could serve as targets. Furthermore, this work provides a summary of the advances made in malaria parasite biology and the potential to leverage such findings for antimalarial drug production.

Deletion of Plasmodium falciparum ubc13 increases parasite sensitivity to the mutagen, methyl methanesulfonate and dihydroartemisinin

The inducible Di-Cre system was used to delete the putative ubiquitin-conjugating enzyme 13 gene (ubc13) of Plasmodium falciparum to study its role in ubiquitylation and the functional consequence during the parasite asexual blood stage. Deletion resulted in a significant reduction of parasite growth in vitro, reduced ubiquitylation of the Lys63 residue of ubiquitin attached to protein substrates, and an increased sensitivity of the parasite to both the mutagen, methyl methanesulfonate and the antimalarial drug dihydroartemisinin (DHA), but not chloroquine. The parasite was also sensitive to the UBC13 inhibitor NSC697923. The data suggest that this gene does code for an ubiquitin conjugating enzyme responsible for K63 ubiquitylation, which is important in DNA repair pathways as was previously demonstrated in other organisms. The increased parasite sensitivity to DHA in the absence of ubc13 function indicates that DHA may act primarily through this pathway and that inhibitors of UBC13 may both enhance the efficacy of this antimalarial drug and directly inhibit parasite growth.