Seeking an optimal dosing regimen for OZ439/DSM265 combination therapy for treating uncomplicated falciparum malaria

Characterizing the pharmacological interaction of the antimalarial combination artefenomel-piperaquine in healthy volunteers with induced blood-stage Plasmodium falciparum to predict efficacy in patients with malaria

BACKGROUND

The combination antimalarial artefenomel-piperaquine failed to achieve target efficacy in a phase 2b study in Africa and Vietnam. We retrospectively evaluated whether characterizing the pharmacological interaction of this antimalarial combination in a volunteer infection study (VIS) would have enabled prediction of the phase 2b study results.

METHODS

Twenty-four healthy adults enrolled over three consecutive cohorts were inoculated with Plasmodium falciparum-infected erythrocytes on day 0. Participants were randomized within each cohort to one of seven dose combination groups and administered a single oral dose of artefenomel-piperaquine on day 8. Participants received definitive antimalarial treatment with artemether-lumefantrine upon parasite regrowth or on day 42 ± 2. The general pharmacodynamic interaction (GPDI) model implemented in the Bliss Independence additivity criterion was developed to characterize the pharmacological interaction between artefenomel and piperaquine. Simulations based on the model were performed to predict the outcomes of the phase 2b combination study.

RESULTS

For a dose of 800 mg artefenomel administered with 640 mg, 960 mg, or 1440 mg piperaquine, the simulated adequate parasitological response at day 28 (APR28), incorporating actual patient pharmacokinetic (PK) data from the phase 2b trial, was 69.4%, 63.9%, and 74.8%, respectively. These results closely matched the observed APR28 in the phase 2b trial of 67.0%, 65.5%, and 75.4%, respectively.

CONCLUSIONS

These results indicate that VIS offer an efficient means for informing antimalarial combination trials conducted in the field, potentially expediting clinical development.

TRIAL REGISTRATION

This study was registered on ClinicalTrials.gov on 11 May 2018 with registration number NCT03542149.

Evaluation of a Bayesian hierarchical pharmacokinetic-pharmacodynamic model for predicting parasitological outcomes in Phase 2 studies of new antimalarial drugs

The rise of multidrug-resistant malaria requires accelerated development of novel antimalarial drugs. Pharmacokinetic-pharmacodynamic (PK-PD) models relate blood antimalarial drug concentrations with the parasite-time profile to inform dosing regimens. We performed a simulation study to assess the utility of a Bayesian hierarchical mechanistic PK-PD model for predicting parasite-time profiles for a Phase 2 study of a new antimalarial drug, cipargamin. We simulated cipargamin concentration- and malaria parasite-profiles based on a Phase 2 study of eight volunteers who received cipargamin 7 days after inoculation with malaria parasites. The cipargamin profiles were generated from a two-compartment PK model and parasite profiles from a previously published biologically informed PD model. One thousand PK-PD data sets of eight patients were simulated, following the sampling intervals of the Phase 2 study. The mechanistic PK-PD model was incorporated in a Bayesian hierarchical framework, and the parameters were estimated. Population PK model parameters describing absorption, distribution, and clearance were estimated with minimal bias (mean relative bias ranged from 1.7% to 8.4%). The PD model was fitted to the parasitaemia profiles in each simulated data set using the estimated PK parameters. Posterior predictive checks demonstrate that our PK-PD model adequately captures the simulated PD profiles. The bias of the estimated population average PD parameters was low-moderate in magnitude. This simulation study demonstrates the viability of our PK-PD model to predict parasitological outcomes in Phase 2 volunteer infection studies. This work will inform the dose-effect relationship of cipargamin, guiding decisions on dosing regimens to be evaluated in Phase 3 trials.

Current Status of Malaria Control and Elimination in Africa: Epidemiology, Diagnosis, Treatment, Progress and Challenges

The African continent carries the greatest malaria burden in the world. Falciparum malaria especially has long been the leading cause of death in Africa. Climate, economic factors, geographical location, human intervention and unstable security are factors influencing malaria transmission. Due to repeated infections and early interventions, the proportion of clinically atypical malaria or asymptomatic plasmodium carriers has increased significantly, which easily lead to misdiagnosis and missed diagnosis. African countries have made certain progress in malaria control and elimination, including rapid diagnosis of malaria, promotion of mosquito nets and insecticides, intermittent prophylactic treatment in high-risk groups, artemisinin based combination therapies, and the development of vaccines. Between 2000 and 2022, there has been a 40% decrease in malaria incidence and a 60% reduction in mortality rate in the WHO African Region. However, many challenges are emerging in the fight against malaria in Africa, such as climate change, poverty, substandard health services and coverage, increased outdoor transmission and the emergence of new vectors, and the growing threat of resistance to antimalarial drugs and insecticides. Joint prevention and treatment, identifying molecular determinants of resistance, new drug development, expanding seasonal malaria chemo-prevention intervention population, and promoting the vaccination of RTS, S/AS01 and R21/Matrix-M may help to solve the dilemma. China's experience in eliminating malaria is conducive to Africa's malaria prevention and control, and China-Africa cooperation needs to be constantly deepened and advanced. Our review aims to help the global public develop a comprehensive understanding of malaria in Africa, thereby contributing to malaria control and elimination.

An overview on the antimalarial activity of 1,2,4-trioxanes, 1,2,4-trioxolanes and 1,2,4,5-tetraoxanes

The demand for novel, fast-acting, and effective antimalarial medications is increasing exponentially. Multidrug resistant forms of malarial parasites, which are rapidly spreading, pose a serious threat to global health. Drug resistance has been addressed using a variety of strategies, such as targeted therapies, the hybrid drug idea, the development of advanced analogues of pre-existing drugs, and the hybrid model of resistant strains control mechanisms. Additionally, the demand for discovering new potent drugs grows due to the prolonged life cycle of conventional therapy brought on by the emergence of resistant strains and ongoing changes in existing therapies. The 1,2,4-trioxane ring system in artemisinin (ART) is the most significant endoperoxide structural scaffold and is thought to be the key pharmacophoric moiety required for the pharmacodynamic potential of endoperoxide-based antimalarials. Several derivatives of artemisinin have also been found as potential treatments for multidrug-resistant strain in this area. Many 1,2,4-trioxanes, 1,2,4-trioxolanes, and 1,2,4,5-tetraoxanes derivatives have been synthesised as a result, and many of these have shown promise antimalarial activity both in vivo and in vitro against Plasmodium parasites. As a consequence, efforts to develop a functionally straight-forward, less expensive, and vastly more effective synthetic pathway to trioxanes continue. This study aims to give a thorough examination of the biological properties and mode of action of endoperoxide compounds derived from 1,2,4-trioxane-based functional scaffolds. The present system of 1,2,4-trioxane, 1,2,4-trioxolane, and 1,2,4,5-tetraoxane compounds and dimers with potentially antimalarial activity will be highlighted in this systematic review (January 1963-December 2022).

Recent approaches in the drug research and development of novel antimalarial drugs with new targets

Malaria is a serious worldwide medical issue that results in substantial annual death and morbidity. The availability of treatment alternatives is limited, and the rise of resistant parasite types has posed a significant challenge to malaria treatment. To prevent a public health disaster, novel antimalarial agents with single-dosage therapies, extensive curative capability, and new mechanisms are urgently needed. There are several approaches to developing antimalarial drugs, ranging from alterations of current drugs to the creation of new compounds with specific targeting abilities. The availability of multiple genomic techniques, as well as recent advancements in parasite biology, provides a varied collection of possible targets for the development of novel treatments. A number of promising pharmacological interference targets have been uncovered in modern times. As a result, our review concentrates on the most current scientific and technical progress in the innovation of new antimalarial medications. The protein kinases, choline transport inhibitors, dihydroorotate dehydrogenase inhibitors, isoprenoid biosynthesis inhibitors, and enzymes involved in the metabolism of lipids and replication of deoxyribonucleic acid, are among the most fascinating antimalarial target proteins presently being investigated. The new cellular targets and drugs which can inhibit malaria and their development techniques are summarised in this study.

On drug discovery against infectious diseases and academic medicinal chemistry contributions

This perspective is an attempt to document the problems that medicinal chemists are facing in drug discovery. It is also trying to identify relevant/possible, research areas in which academics can have an impact and should thus be the subject of grant calls. Accordingly, it describes how hit discovery happens, how compounds to be screened are selected from available chemicals and the possible reasons for the recurrent paucity of useful/exploitable results reported. This is followed by the successful hit to lead stories leading to recent and original antibacterials which are, or about to be, used in human medicine. Then, illustrated considerations and suggestions are made on the possible inputs of academic medicinal chemists. This starts with the observation that discovering a "good" hit in the course of a screening campaign still rely on a lot of luck - which is within the reach of academics -, that the hit to lead process requires a lot of chemistry and that if public-private partnerships can be important throughout these stages, they are absolute requirements for clinical trials. Concerning suggestions to improve the current hit success rate, one academic input in organic chemistry would be to identify new and pertinent chemical space, design synthetic accesses to reach these and prepare the corresponding chemical libraries. Concerning hit to lead programs on a given target, if no new hits are available, previously reported leads along with new structural data can be pertinent starting points to design, prepare and assay original analogues. In conclusion, this text is an actual plea illustrating that, in many countries, academic research in medicinal chemistry should be more funded, especially in the therapeutic area neglected by the industry. At the least, such funds would provide the intensive to secure series of hopefully relevant chemical entities which appears to often lack when considering the results of academic as well as industrial screening campaigns.

Efficient simulation of clinical target response surfaces

Simulation of combination therapies is challenging due to computational complexity. Either a simple model is used to simulate the response for many combinations of concentration to generate a response surface but parameter variability and uncertainty are neglected and the concentrations are constant—the link to the doses to be administered is difficult to make—or a population pharmacokinetic/pharmacodynamic model is used to predict the response to combination therapy in a clinical trial taking into account the time‐varying concentration profile, interindividual variability (IIV), and parameter uncertainty but simulations are limited to only a few selected doses. We devised new algorithms to efficiently search for the combination doses that achieve a predefined efficacy target while taking into account the IIV and parameter uncertainty. The result of this method is a response surface of confidence levels, indicating for all dose combinations the likelihood of reaching the specified efficacy target. We highlight the importance to simulate across a population rather than focus on an individual. Finally, we provide examples of potential applications, such as informing experimental design.

Scoping Review of Antimalarial Drug Candidates in Phase I and II Drug Development

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, and 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, 6 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 h. The log10 parasite reduction ratio over 48 h and parasite clearance half-life for Plasmodium falciparum following a single-dose monotherapy were 1.55 to 4.1 and 3.4 to 9.4 h, 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.