Antimalarial Development Research Articles

Cheminformatics techniques in antimalarial drug discovery and development from natural products 2: Molecular scaffold and machine learning approaches

Abstract A large number of natural products, especially those used in ethnomedicine of malaria, have shown varying in-vitro antiplasmodial activities. Cheminformatics involves the organization, integration, curation, standardization, simulation, mining and transformation of pharmacology data (compounds and bioactivity) into knowledge that can drive rational and viable drug development decisions. This chapter will review the application of two cheminformatics techniques (including molecular scaffold analysis and bioactivity predictive modeling via Machine learning) to natural products with in-vitro and in-vivo antiplasmodial activities in order to facilitate their development into antimalarial drug candidates and design of new potential antimalarial compounds.

Phytol suppresses parasitemia and ameliorates anaemia and oxidative brain damage in mice infected with Plasmodium berghei

The quest for the development of a novel antimalarial drug informed the decision to subject phytol to in vivo trials following a demonstration of therapeutic potential against chloroquine sensitive strain of Plasmodium falciparum under in vitro condition. On this basis, the in vivo anti-Plasmodium berghei activity of phytol including the ameliorative effects of the compound on P. berghei-associated anaemia and organ damage were investigated. Mice were infected with chloroquine-sensitive strain of P. berghei and were treated with phytol at a dose of 10 and 20 mg/kg body weight (BW) for four days. The levels of parasitemia, packed cell volume and redox sensitive biomarkers of liver, brain and spleen tissues were determined. Our result revealed that phytol significantly (p < 0.05) suppressed the multiplication of P. berghei in a dose-dependent manner. Additionally, the phytol significantly (p < 0.05) ameliorated the P. berghei-induced anaemia and brain damage. Data from the present study demonstrated that phytol has suppressive effect on P. berghei and could ameliorate some P. berghei-induced pathological changes.

Physicochemical and phytochemical screening of six plants commonly used in the treatment of malaria in Nigeria.

Medicinal plants contain active compounds usually present as complex mixtures though at low concentrations, which accounts for the medicinal properties. Therefore it is important to identify and characterize these compounds. This study aims to quantify and characterize the physicochemical and phytochemical compositions of six plants commonly used in the treatment of malaria using High-Performance Liquid Chromatography (HPLC). These plants which are used individually or in combinations: Enantia chlorantha, Cymbopogon citratus, Curcuma longa, Carica papaya, Alstonia boonei and Mangifera indica, were extracted with hot water and the extracts characterized with HPLC using standard procedures. The results showed that M. indica stem bark had the highest yield with 81.48% and C. papaya had the lowest yield with 53.80%. Physicochemical properties of the extracts of E. chlorantha, C. citratus, C. longa, C. papaya, A. boonei and M. indica respectively are as follows: Melting point 90, 80, 95, 92, 96 and 96; pH 7.43, 8.02, 6.24, 6.81, 6.41, 6.85; moisture content 18.27, 22.77, 9.96, 9.62, 3.85 and 10.00; Total ash 1.45, 3.51, 0.34, 0.57, 9.10,10.21; refractive index 1.34, 1.34, 1.34, 1.34, 1.34, 1.34 and 1.34. Alkaloids, phenols, flavonoids, terpenoids, tannins, coumarin were some of the antimalarial active phytochemicals identified. Alkaloid (Atropine) was highest in C. longa (4382.2mg/g). M. indica (32982.8mg/g) had the highest Rutin Hydrate content. While Quercetin was not detected in C. papaya, it was considerably present in A. boonei (491.1mg/g). All the analyzed six plants contain low phenol (gallic acid). The characterized physicochemical and phytochemical compositions of the examined plants suggests why the plants are effective in the treatment of malaria. The information reported herein describes the physicochemical and phytochemical contents of six commonly used antimalarial plants in Nigeria. It is expected that the information will be useful in understanding the pharmaceutical effects of how the plants work in the body and in the development of efficacious and safe antimalarial drugs.

4-Aminosalicylic Acid-based Hybrid Compounds: Synthesis and In vitro Antiplasmodial Evaluation

Background: Malaria is a deadly and infectious disease responsible for millions of death worldwide, mostly in the African region. The malaria parasite has developed resistance to the currently used antimalarial drugs, and it has urged researchers to develop new strategies to overcome this challenge by designing different classes of antimalarials. Objectives: A class of hybrid compounds containing 4-aminosalicylic acid moiety was prepared via esterification and amidation reactions and characterized using FTIR, NMR and LC-MS. In vitro antiplasmodial evaluation was performed against the asexual NF54 strain of P. falciparum parasites. Methods: In this research, known 4-aminoquinoline derivatives were hybridized with 4- aminosalicylic acid to afford hybrid compounds via esterification and amidation reactions. 4- aminosalicylic acid, a dihydrofolate compound inhibits DNA synthesis in the folate pathway and is a potential pharmacophore for the development of antimalarials. Results: The LC-MS, FTIR, and NMR analysis confirmed the successful synthesis of the compounds. The compounds were obtained in yields in the range of 63-80%. The hybrid compounds displayed significant antimalarial activity when compared to 4-aminosalicylic acid, which exhibited poor antimalarial activity. The IC50 value of the most potent hybrid compound, 9 was 9.54±0.57 nm. Conclusion: 4-aminosalicylic has different functionalities, which can be used for hybridization with a wide range of compounds. It is a potential pharmacophore that can be utilized for the design of potent antimalarial drugs. It was found to be a good potentiating agent when hybridized with 4- aminoquinoline derivatives suggesting that they can be utilized for the synthesis of a new class of antimalarials.

Metabolites from Marine Sponges and Their Potential to Treat Malarial Protozoan Parasites Infection: A Systematic Review.

Malaria is an infectious disease caused by protozoan parasites of the Plasmodium genus through the bite of female Anopheles mosquitoes, affecting 228 million people and causing 415 thousand deaths in 2018. Artemisinin-based combination therapies (ACTs) are the most recommended treatment for malaria; however, the emergence of multidrug resistance has unfortunately limited their effects and challenged the field. In this context, the ocean and its rich biodiversity have emerged as a very promising resource of bioactive compounds and secondary metabolites from different marine organisms. This systematic review of the literature focuses on the advances achieved in the search for new antimalarials from marine sponges, which are ancient organisms that developed defense mechanisms in a hostile environment. The principal inclusion criterion for analysis was articles with compounds with IC50 below 10 µM or 10 µg/mL against P. falciparum culture. The secondary metabolites identified include alkaloids, terpenoids, polyketides endoperoxides and glycosphingolipids. The structural features of active compounds selected in this review may be an interesting scaffold to inspire synthetic development of new antimalarials for selectively targeting parasite cell metabolism.

Mathematical analysis of the impact of transmission-blocking drugs on the population dynamics of malaria

Recently, promising clinical advances have been made in the development of antimalarial drugs that block the parasite transmission and also cures the disease and has prophylactic effects, called transmission-blocking drugs (TBDs). The aim of this paper is to develop and analyze a population level compartmental model of human-mosquito interactions that takes into account an intervention using TBDs. We do this by extending the SEIRS-SEI type model to include a class of humans who are undergoing the treatment with TBDs and a class of those who are protected because of successful treatment. Before we proceed with an analysis of the model’s stability and bifurcation behaviours, we start by ensuring that the model is well-posed in a biologically feasible domain. Mathematical analysis indicates that the model exhibits a forward and backward bifurcation under certain conditions. Results from our analysis shows that the effect of treatment rate on reducing reproduction number depends on other key parameters such as the efficacy of the drug. The projections of the validated model show the benefits of using TBDs in malaria control in preventing new cases and reducing mortality. In particular, we find that treating 35% of the population of Sub-Saharan Africa with a 95% efficacious TBD from 2021 will result in approximately 82% reduction on the number of malaria deaths by 2035.

Erythroid cells and malaria parasites: it's a match!

The current review outlines recent discoveries on the infection of erythroid cells by Plasmodium parasites, focusing on the molecular interactions governing the tropism of parasites for their host cell and the implications of this tropism for parasite biology and erythroid cell maturation. Although most studies about the interactions of Plasmodium parasites and their host cell focused on the deadliest human malaria parasite, Plasmodium falciparum, and the erythrocyte, there is increasing evidence that several Plasmodium species, including P. falciparum, also develop within erythroid precursors. These interactions likely modify the remodeling of the host cell by the parasite and affect the maturation of erythroblast and reticulocytes. A better understanding of the remodeling of immature erythroid cells by Plasmodium parasites will have important implications for the development of antimalarial drugs or vaccines. In addition, deciphering how Plasmodium parasites interfere with erythropoiesis will provide new insights on how these parasites contribute to anemia in malaria patients.

Hybrid Compounds Containing a Ferrocene Scaffold as Potential Antimalarials

AbstractMalaria is an infectious disease, and it remains a serious health problem globally. The drugs developed for its treatment suffer from several shortcomings such as low water solubility, poor bioavailability, drug toxicity, and resistance. Molecular hybridization of different bioactive agents is a promising approach for developing hybrid compounds with improved therapeutic effects. Ferrocene, an organometallic, has been hybridized with several pharmacophores resulting in compounds with potent biological activities. In this research, a modified ferrocene scaffold was hybridized with selected pharmacophores. The synthesized compounds were characterized by Fourier‐Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance Spectroscopy (NMR), and Liquid Chromatography‐Mass Spectroscopy. The hybrid compounds were obtained in good yields (53–76 %). In vitro evaluation against NF54 (drug‐sensitive) strain of Plasmodium falciparum parasites revealed the compounds, 16 and 19 (hybrids containing artesunate scaffold), together with 18 and 21 (hybrids containing oleanolic acid scaffold), as promising antimalarial agents. These compounds displayed IC50 values of 116.73±3.18, 56.33±15.20, 78.22±21.05, and 58.22±15.20 nM, respectively. These findings revealed the potency of ferrocene as a precursor for the development of promising antimalarials.

Development and evaluation of a new Plasmodium falciparum 3D7 blood stage malaria cell bank for use in malaria volunteer infection studies

BackgroundNew anti-malarial therapeutics are required to counter the threat of increasing drug resistance. Malaria volunteer infection studies (VIS), particularly the induced blood stage malaria (IBSM) model, play a key role in accelerating anti-malarial drug development. Supply of the reference 3D7-V2 Plasmodium falciparum malaria cell bank (MCB) is limited. This study aimed to develop a new MCB, and compare the safety and infectivity of this MCB with the existing 3D7-V2 MCB, in a VIS. A second bank (3D7-V1) developed in 1995 was also evaluated.MethodsThe 3D7-V2 MCB was expanded in vitro using a bioreactor to produce a new MCB designated 3D7-MBE-008. This bank and 3D7-V1 were then evaluated using the IBSM model, where healthy participants were intravenously inoculated with blood-stage parasites. Participants were treated with artemether-lumefantrine when parasitaemia or clinical thresholds were reached. Safety, infectivity and parasite growth and clearance were evaluated.ResultsThe in vitro expansion of 3D7-V2 produced 200 vials of the 3D7-MBE-008 MCB, with a parasitaemia of 4.3%. This compares to 0.1% in the existing 3D7-V2 MCB, and < 0.01% in the 3D7-V1 MCB. All four participants (two per MCB) developed detectable P. falciparum infection after inoculation with approximately 2800 parasites. For the 3D7-MBE-008 MCB, the parasite multiplication rate of 48 h (PMR48) using non-linear mixed effects modelling was 34.6 (95% CI 18.5–64.6), similar to the parental 3D7-V2 line; parasitaemia in both participants exceeded 10,000/mL by day 8. Growth of the 3D7-V1 was slower (PMR48 of 11.5 [95% CI 8.5–15.6]), with parasitaemia exceeding 10,000 parasites/mL on days 10 and 8.5. Rapid parasite clearance followed artemether-lumefantrine treatment in all four participants, with clearance half-lives of 4.01 and 4.06 (weighted mean 4.04 [95% CI 3.61–4.57]) hours for 3D7-MBE-008 and 4.11 and 4.52 (weighted mean 4.31 [95% CI 4.16–4.47]) hours for 3D7-V1. A total of 59 adverse events occurred; most were of mild severity with three being severe in the 3D7-MBE-008 study.ConclusionThe safety, growth and clearance profiles of the expanded 3D7-MBE-008 MCB closely resemble that of its parent, indicating its suitability for future studies. Trial Registration: Australian New Zealand Clinical Trials registry numbers: P3487 (3D7-V1): ACTRN12619001085167. P3491 (3D7-MBE-008): ACTRN12619001079134

Biochemical and cellular characterisation of the Plasmodium falciparum M1 alanyl aminopeptidase (PfM1AAP) and M17 leucyl aminopeptidase (PfM17LAP)

The Plasmodium falciparum M1 alanyl aminopeptidase and M17 leucyl aminopeptidase, PfM1AAP and PfM17LAP, are potential targets for novel anti-malarial drug development. Inhibitors of these aminopeptidases have been shown to kill malaria parasites in culture and reduce parasite growth in murine models. The two enzymes may function in the terminal stages of haemoglobin digestion, providing free amino acids for protein synthesis by the rapidly growing intra-erythrocytic parasites. Here we have performed a comparative cellular and biochemical characterisation of the two enzymes. Cell fractionation and immunolocalisation studies reveal that both enzymes are associated with the soluble cytosolic fraction of the parasite, with no evidence that they are present within other compartments, such as the digestive vacuole (DV). Enzyme kinetic studies show that the optimal pH of both enzymes is in the neutral range (pH 7.0–8.0), although PfM1AAP also possesses some activity (< 20%) at the lower pH range of 5.0–5.5. The data supports the proposal that PfM1AAP and PfM17LAP function in the cytoplasm of the parasite, likely in the degradation of haemoglobin-derived peptides generated in the DV and transported to the cytosol.

Antimalarial Activity of Nigella sativa L. Seed Extracts and Selection of Resistance in Plasmodium berghei ANKA in a Mouse Model.

Background Chemotherapy plays a crucial role in malaria control. However, the main obstacle to treatment has been the rise of parasite resistance to most antimalarial drugs. Artemisinin-based combination therapies (ACTs) remain the most effective antimalarial medicines available today. However, malaria parasite tolerance to ACTs is now increasingly prevalent especially in Southeast Asia presenting the danger of the spread of ACTs resistance to other parts of the world. Consequently, this creates the need for alternative effective antimalarials. Therefore, this study sought out to determine antimalarial potential, safety, and resistance development of the extracts in a mouse model. Method Methanolic and ethyl acetate extracts were obtained by solvent extraction. The extracts were assayed for acute toxicity in vivo. Additionally, the two extracts were evaluated for antimalarial activity in vivo against Plasmodium berghei ANKA strain by the 4-day suppressive test at 500, 250, and 125 mg/kg/day. Packed cell volume was evaluated to determine anemia manifestation. Finally, continuous drug pressure experiment at 500 mg/kg and DNA amplification via PCR were conducted. The amplicons underwent through Sanger sequencing. Results There was no toxicity realized in the animals at 2000 mg/kg. Importantly, high parasitemia suppression of 75.52% and 75.30% using a dose of 500 mg/kg of methanolic and ethyl acetate extracts, respectively, was noted. The extracts were able to reverse packed cell volume reduction. Nigella sativa-resistant phenotype was selected as delayed parasite clearance. However, there was no change in the nucleotide sequences of PbMDR1 and PbCRT genes. Conclusion The results provide room for future exploitation of the plant as an antimalarial.

A redox-active crosslinker reveals an essential and inhibitable oxidative folding network in the endoplasmic reticulum of malaria parasites.

Malaria remains a major global health problem, creating a constant need for research to identify druggable weaknesses in P. falciparum biology. As important components of cellular redox biology, members of the Thioredoxin (Trx) superfamily of proteins have received interest as potential drug targets in Apicomplexans. However, the function and essentiality of endoplasmic reticulum (ER)-localized Trx-domain proteins within P. falciparum has not been investigated. We generated conditional mutants of the protein PfJ2-an ER chaperone and member of the Trx superfamily-and show that it is essential for asexual parasite survival. Using a crosslinker specific for redox-active cysteines, we identified PfJ2 substrates as PfPDI8 and PfPDI11, both members of the Trx superfamily as well, which suggests a redox-regulatory role for PfJ2. Knockdown of these PDIs in PfJ2 conditional mutants show that PfPDI11 may not be essential. However, PfPDI8 is required for asexual growth and our data suggest it may work in a complex with PfJ2 and other ER chaperones. Finally, we show that the redox interactions between these Trx-domain proteins in the parasite ER and their substrates are sensitive to small molecule inhibition. Together these data build a model for how Trx-domain proteins in the P. falciparum ER work together to assist protein folding and demonstrate the suitability of ER-localized Trx-domain proteins for antimalarial drug development.

The mechanism of heparin/heparan sulfide in the process of &amp;lt;italic&amp;gt;Plasmodium falciparum&amp;lt;/italic&amp;gt; invasion of red blood cells

Malaria is a parasitic disease caused by plasmodium . Plasmodium is an obligate intracellular parasite that requires two hosts: human and Anopheles . The parasites of humans mainly include Plasmodium falciparum , Plasmodium vivax , Plasmodium Malariae , Plasmodium ovale , and Plasmodium Knosei . Plasmodium falciparum has the strongest pathogenicity, and it is the main pathogen causing the morbidity and death of malaria worldwide. Heparan sulfate is an unbranched polysaccharide widely distributed on the surface of vertebrate cells. It is an important receptor for malaria to invade host red blood cells, and plays a key role in the process of malaria invasion. Plasmodium invasion of host red blood cells is a rapid and complex process. Plasmodium invasion-related proteins play an important role in the process of malaria parasite invasion. They are mainly involved in the processes of adhesion to host red blood cells, formation of mobile junction complexes, and formation and modification of parasitophorous vacuole membrane (PVM). Adhesion is the first step for Plasmodium falciparum to invade host red blood cells. Invasion-related proteins bind to heparan sulfide receptors on the surface of host red blood cells to complete subsequent invasion. Based on domestic and foreign literature, this article summarizes the research on heparin/heparan sulfate in the treatment of Plasmodium falciparum , the binding of Plasmodium falciparum invasion-related proteins and heparin/heparan sulfide, and the mechanism of Plasmodium falciparum invasion-related proteins in the process of merozoites invading host red blood cells. The molecular mechanism of the binding of related proteins to heparin in the process provides a theoretical basis, and also provides a reference for the development and treatment of new antimalarial drugs and vaccines.

Identification of Plasmodium falciparum heat shock 90 inhibitors via molecular docking

A virtual screen was performed to identify anti-malarial compounds targeting Plasmodium falciparum heat shock 90 protein by applying a series of drug-like and commercial availability filters to compounds in the ZINC database, resulting in a virtual library of more than 13 million candidates. The goal of the virtual screen was to identify novel compounds which could serve as a starting point for the development of antimalarials with a mode of action different from anything currently used in the clinic. The screen targeted the ATP binding pocket of the highly conserved Plasmodium heat shock 90 protein, as this protein is critical to the survival of the parasite and has several significant structural differences from the human homolog. The top twelve compounds from the virtual screen were tested in vitro, with all twelve showing no antiproliferative activity against the human fibroblast cell line and three compounds exhibiting single digit or better micromolar antiproliferative activity against the chloroquine-sensitive P. falciparum 3D7 strain.

Acridine-Based Antimalarials-From the Very First Synthetic Antimalarial to Recent Developments.

Malaria is among the deadliest infectious diseases in the world caused by Plasmodium parasites. Due to the high complexity of the parasite’s life cycle, we partly depend on antimalarial drugs to fight this disease. However, the emergence of resistance, mainly by Plasmodium falciparum, has dethroned most of the antimalarials developed to date. Given recent reports of resistance to artemisinin combination therapies, first-line treatment currently recommended by the World Health Organization, in Western Cambodia and across the Greater Mekong sub-region, it seems very likely that artemisinin and its derivatives will follow the same path of other antimalarial drugs. Consequently, novel, safe and efficient antimalarial drugs are urgently needed. One fast and low-cost strategy to accelerate antimalarial development is by recycling classical pharmacophores. Quinacrine, an acridine-based compound and the first clinically tested synthetic antimalarial drug with potent blood schizonticide but serious side effects, has attracted attention due to its broad spectrum of biological activity. In this sense, the present review will focus on efforts made in the last 20 years for the development of more efficient, safer and affordable antimalarial compounds, through recycling the classical quinacrine drug.

Diterpenoids as potential anti-malarial compounds from Andrographis paniculata

BackgroundThe objectives of the current study are to evaluate the traditionally used medicinal plants Andrographis paniculata for in vitro anti-malarial activity against human malarial parasite Plasmodium falciparum and to further characterize the anti-malarial active extract of A. paniculata using spectroscopic and chromatographic methods.ResultsThe chloroform extract of A. paniculata displayed anti-malarial activity with IC50 values 6.36 μg/ml against 3D7 strain and 5.24 μg/ml against K1 strains respectively with no evidence of significant cytotoxicity against mammalian cell line (CC50 > 100 μg/ml). LC-MS analysis of the extract led to the identification of 59 compounds based on their chromatographic and mass spectrometric features (a total of 35 compounds are present in positive ion and 24 compounds in negative ion mode). We have identified 5 flavonoids and 30 compounds as diterpenoids in positive ion mode, while in the negative mode all identified compounds were diterpenoids. Characterization of the most promising class of compound diterpenoids using HPLC-LC-ESI-MS/MS was also undertaken.ConclusionsThe in vitro results undoubtedly validate the traditional use of A. paniculata for the treatment of malaria. The results have led to the identification of diterpenoids from IGNTU_06 extract as potential anti-malarial compounds that need to be further purified and analyzed in anti-malarial drug development programs.Graphical abstract

Multistage and transmission-blocking targeted antimalarials discovered from the open-source MMV Pandemic Response Box

Chemical matter is needed to target the divergent biology associated with the different life cycle stages of Plasmodium. Here, we report the parallel de novo screening of the Medicines for Malaria Venture (MMV) Pandemic Response Box against Plasmodium asexual and liver stage parasites, stage IV/V gametocytes, gametes, oocysts and as endectocides. Unique chemotypes were identified with both multistage activity or stage-specific activity, including structurally diverse gametocyte-targeted compounds with potent transmission-blocking activity, such as the JmjC inhibitor ML324 and the antitubercular clinical candidate SQ109. Mechanistic investigations prove that ML324 prevents histone demethylation, resulting in aberrant gene expression and death in gametocytes. Moreover, the selection of parasites resistant to SQ109 implicates the druggable V-type H+-ATPase for the reduced sensitivity. Our data therefore provides an expansive dataset of compounds that could be redirected for antimalarial development and also point towards proteins that can be targeted in multiple parasite life cycle stages.

Quinolinotriazole antiplasmodials via click chemistry: synthesis and in vitro studies of 7-Chloroquinoline-based compounds

Malaria is nowadays one of the most serious health concerns in a global scale and, although there is an evident increase in research studies in this area, pointed by the vast number of hits and leads, it still appears as a recurrent topic every year due to the drug resistance shown by the parasite exposing the urgent need to develop new antimalarial medications. In this work, 38 molecules were synthesized via copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) or “click” chemistry, following different routes to produce 2 different organic azides, obtained from a 4,7 dicholoquinoline, reacted with 19 different commercially available terminal alkynes. All those new compounds were evaluated for their in vitro activity against the chloroquine resistant malaria parasite Plasmodium falciparum (W2). The cytotoxicity evaluation was accomplished using Hep G2 cells and SI index was calculated for every molecule. Some of the quinoline derivatives have shown high antimalarial activity, with IC50 values in the range of 1.72-8.66 µM, low cytotoxicity, with CC50>1000 µM and selectivity index (SI) in the range of 20-100, with some compounds showing SI>800. Therefore, the quinolinotriazole hybrids could be considered a very important step on the development of new antimalarial drugs.

In vitro anti-plasmodial activity of new synthetic derivatives of 1-(heteroaryl)-2- ((5-nitroheteroaryl)methylene) hydrazine

Objective: To evaluate new compounds synthesized by integrating quinoline, quinazoline, and acridine rings with the active moiety of (5-nitroheteroaryl) methylene hydrazine.Methods: A new series of compounds (1a, 1b, 2a, 2b, 3a, and 3b) were synthesized and evaluated for cytotoxicity against COS-7 cells using the MTT assay. In vitro anti-plasmodial activity of the compounds was measured against CQ-sensitive (3D7) and CQ-resistant (K1) Plasmodium (P.) falciparum strains. β-hematin assay was performed to assess the inhibitory effects of β-hematin formation for new compounds.Results: The synthetic compounds had anti-plasmodial activity against blood-stage of 3D7 [IC50=(0.328-5.483) μM] and K1 [IC50=(0.622-7.746) μM] strains of P. falciparum, with no cytotoxicity against COS-7 cells in effective doses. Compounds 1a, 1b, and 2b were the most effective derivatives against P. falciparum 3D7 and K1 strains. Based on the β-hematin assay, the inhibition of β-hematin formation is the main mechanism of the inhibitory effect of these compounds.Conclusions: The synthetic compounds could inhibit the erythrocytic stages of CQ-sensitive and resistant P. falciparum strains without toxicity towards mammalian cells. Compounds 1b, 2a, and 2b had comparable anti-plasmodial activity against both CQ-sensitive (3D7) and resistant (K1) P. falciparum strains. These compounds may be promising lead structures for the development of new anti-malarial drugs.

Stage-Dependent Topographical and Optical Properties of Plasmodium Falciparum-Infected Red Blood Cells

Addressing the challenge of efficient malaria treatment requires in-depth understanding of the parasite maturation during the intra- erythrocytic cycle. Exploring the structural and functional changes of the parasite through the intra-erythrocytic stages and their impact on red blood cells (RBCs) is a cornerstone of antimalarial drug development. In order to precisely trace such changes, we performed a thorough imaging study of RBCs infected by Plasmo-dium falciparum, by using atomic force microscopy (AFM) and total internal reflection fluorescence microscopy (TIRF), supplemented with bright field microscopy (BFM) for stage assignment. This multifaceted imaging approach allows to reveal structure–function relations via correlations of the parasite maturation with morphological and fluore-scence properties of the host RBCs. We established diagnostic patterns characteristic to the parasite stages based on the topographical profile of infected RBCs, which show close correlation with their TIRF map. Furthermore, we found that hemozoin crystals exhibit a strong optical contrast, possibly due to the quen-ching of fluorescence, which can be used to locate hemozoin crystals within the RBCs and following their growth.