Academic literature on the topic 'Antimalarials – Development – Research'

Great progress in the fight against malaria has been made in the last decade. Nevertheless, the development of resistance to almost all commonly used antimalarial drugs poses a major threat to the sustainability of this progress and highlights the need for the discovery of novel potent and inexpensive antimalarials to stay one step ahead. After the finding of ferrocene-containing analog of chloroquine - ferroquine, that can overcome Plasmodium resistance, a ?big-bang? in the metallocene antimalarials research has occurred. This review describes in detail the most recent advances in this important field of medicinal chemistry. Even though it is quite hard to beat ferroquine, it seems that this could be succeeded by suitable modifications in the structure of ferroquine, by the introduction of ? second metal center or through joining metallocenes with two or more proven antimalarial motifs into a single molecule.

SUMMARYThe number of novel antimalarial candidates entering preclinical development has seen an increase over the last several years. Most of these drug candidates were originally identified as hits coming from screening large chemical libraries specifically targeting the asexual blood stages of Plasmodium falciparum. Indeed, a large proportion of the current antimalarial arsenal has mainly targeted the asexual blood stage which is responsible for clinical symptoms of the disease. However, as part of the eradication agenda and to address resistance, any next-generation antimalarial should have additional activity on at least one other parasite life stage, i.e. gametocytocidal and/or tissue schizonticidal activity. We have applied this approach by screening compounds with intrinsic activity on asexual blood stages in assays against sexual and liver stages and identified two new antimalarial chemotypes with activity on multiple parasite life stages. This strategy can be expanded to identify other chemical classes of molecules with similar activity profiles for the next generation antimalarials. The following review summarizes the discovery of the spiroindolones and imidazolopiperazine classes of antimalarials developed by the NGBS consortium (Novartis Institute for Tropical Diseases, Genomic Institute of the Novartis Research Foundation, Biomedical Primate Research Center, and the Swiss Tropical and Public Health Institute) currently in clinical trials.

Malaria in recent years becomes a major health hitch globally due to the surfacing of multidrug-resistant strains of Plasmodium falciparum parasite. In recent times, artemisinin (ART)-based drugs and combination therapies become the drugs of preference for the treatment and prophylaxis of resistant P. falciparum malaria. Endoperoxide compounds natural, semi-synthetic or synthetic signifying a massive number of antimalarial agents which possess a wide structural miscellany with needed antimalarial effectiveness against resistant P. falciparum malaria. The 1,2,4-trioxane ring system deficient the lactone ring which constitutes the most significant endoperoxide structural scaffold which is believed to be the key pharmacophoric moiety and is principally responsible for the pharmacodynamic potential of endoperoxide-based antimalarials. This becomes the main reason for the research related to endoperoxide particularly 1,2,4-trioxane-, 1,2,4-trioxolane- and 1,2,4,5-tetraoxane-based scaffolds gaining the noteworthy interest in recent years for developing antimalarial drugs against resistant malaria. In this paper, a comprehensive endeavour has been made to review the development of different endoperoxide antimalarial agents and structural diversity of endoperoxide molecules derived from 1,2,4-trioxane- based structural scaffolds. Keywords: Endoperoxide; 1,2,4-trioxane; pharmacophores; artemisinin; antimalarial.

Abstract Malaria continues to be one of the leading causes of human mortality in the world, and the therapies available are insufficient for eradication. Severe malaria is caused by the apicomplexan parasite Plasmodium falciparum. Apicomplexan parasites, including the Plasmodium spp., are descendants of photosynthetic algae, and therefore they possess an essential plastid organelle, named the apicoplast. Since humans and animals have no plastids, the apicoplast is an attractive target for drug development. Indeed, after its discovery, the apicoplast was found to host the target pathways of some known antimalarial drugs, which motivated efforts for further research into its biological functions and biogenesis. Initially, many apicoplast inhibitions were found to result in ‘delayed death’, whereby parasite killing is seen only at the end of one invasion-egress cycle. This slow action is not in line with the current standard for antimalarials, which seeded scepticism about the potential of compounds targeting apicoplast functions as good candidates for drug development. Intriguingly, recent evidence of apicoplast inhibitors causing rapid killing could put this organelle back in the spotlight. We provide an overview of drugs known to inhibit apicoplast pathways, alongside recent findings in apicoplast biology that may provide new avenues for drug development.

Plasmodium malariaecauses uncommon benign malaria found in the malaria endemic regions mostly of Sub-Saharan Africa. AsPlasmodium malariaedoes not have a continued liver stage in humans the only way to have reinfection without reexposure is through recrudescence. However, reports of its recrudescence after antimalarials are rare with only a handful of case reports in the literature. Research in this field to date has not been able to establish definitively an emergence of resistance inPlasmodium malariaeto commonly used antimalarials. In the presented case, patient had a recrudescence ofP. malariaeafter full treatment with quinine and clindamycin. This recrudescence was treated with full course of chloroquine with clearance of parasite from blood immediately after treatment and at two months’ follow up. The recrudescence in this case cannot be explained by mechanisms explained in prior articles. We propose that the indolence of some of thePlasmodium malariaetrophozoites in the blood can shield them from the effect of the toxic effects of antimalarials and enable them to produce recrudescence later. However, when recrudescence happens, this should not be considered a case of development of resistance and a course of chloroquine should be considered.

Background:The antimalarials remain to be the main treatment for Systemic Lupus Erythematosus (SLE). Its most important limitation when you want to increase dose or remain using them is the occurrence of retinal toxicity, which appears in a small number of patients. Since the lesions can progress even with drug withdrawal is important to perform a screening for an early diagnosis.Objectives:To describe ocular toxicity in patients with SLE treated with antimalarials that attended the rheumatology office and to identify possible associated risk factors.Methods:We performed a cross-sectional, retrospective study of SLE patients diagnosed of antimalarial drugs associated retinopathy, that were included in the data base of the Rheumatology department in León`s Hospital between 2014-2019. Multiple clinical and therapeutic factors potentially associated with retinal toxicity were analyzed including: age, chronic kidney disease (CKD), liver failure, smoking, hypertension, Diabetes mellitus, presence of previous retinopathy, type of treatment, duration, daily dose and cumulative dose and tamoxifen intake. The diagnosis of retinopathy was performed by the Ophthalmology department. The dose of hydroxychloroquine (HCQ) used was of 400mg/day and chloroquine (CQ) 250mg/day.Results:437 medical records were analyzed, 20 patients diagnosed of antimalarial retinopathy were included (4,57%), 90% of them were women. The age of diagnosis was more than 40 years in 18 patients (90%) and more than 60 years in 10 (50%) with a median of 60 years (IQR: 32,25).The duration of treatment was ≤ 5 years in 10 patients (50%), between 6-10 years in 6 (30%), between 11-15 years in 2(10%) and between 16-20 years in 2 (10%) with a median of exposure of 5,5 years (IQR: 6,5); 15 patients (75%) were in treatment with HCQ, with CQ 2 patients (10%) and with both of them sequentially 3 patients (15%).Of the group of patients treated with HCQ 35 % were above the global accumulated recommended dose (1000 g) and 71% of them were on treatment more than 10 years. In the group treated with CQ none were above the global recommended dose (460g). Of the 3 patients that took both drugs, two were above the recommended dose for HCQ.25% of the patients had CKD and 10% liver failure, 20% of the patients were active smokers and 15% ex-smokers.10% of the sample had previous retinopathy related with other comorbidities (age related retinopathy and diabetes), associating hypertension and diabetes mellitus in the same percentage (15%).Severe retinopathy was found in 1 patient (5%), mild-moderate in 9 patients (45%), retinopathy stages were not specified in 10 patients (50%).Conclusion:In our sample we observed a prevalence of antimalarials retinopathy of 4,57%, similar of what is found in the literature. Half of the patients had retinopathy in a period of treatment ≤ 5 years, being a described risk factor the duration of treatment of more than 6 years. This early manifestation could be related to the presence of other comorbidities like hypertension, diabetes and CKD.Dose readjustment should be considered in patients with a period of treatment of more than 10 years. Age seems to be an associated factor for the development of antimalarials retinopathy and to perform a screening in the first year of treatment is important to rule out basal disease related with more risk to develop ocular toxicity.References:[1]Jorge, A., Ung, C., Young, L.H. et al. Hydroxychloroquine retinopathy — implications of research advances for rheumatology care. Nat Rev Rheumatol 14, 693–703 (2018).[2]Mukwikwi ER, Pineau CA, Vinet E. et al. Retinal Complications in Systemic Lupus Erythematosus Patients Treated with Antimalarial Drugs. J Rheumatol. 2019 Sep 1. jrheum.181102[3]Abdulaziz N, Shah AR, McCune WJ. Hydroxychloroquine: balancing the need to maintain therapeutic levels with ocular safety: an update. Curr Opin Rheumatol. 2018 May;30(3):249-255.Disclosure of Interests:None declared

Background: Malaria remains a life-threatening tropical disease. Due to the development of resistance to the commonly available orthodox antimalarials which of course, poses a great challenge in malaria-controlling-program, alternative and complementary approach becomes imperative thereby making phytotherapy a research focus. Objectives: To investigate the effect of chikadoma plant using its methanol leaf extract against a plasmodium-mediated tropical disease, malaria. Materials and Methods: The culture samples of Plasmodium (P.) falciparum from 20 symptomatic adult outpatients were used in the antimalarial in-vitro test. For cultivation of P. falciparum, the culture medium employed was Roswell Park Memorial Institute (RPMI) 1640. Optical microscopy was used for parasite quantification in the performance of antiplasmodial in-vitro assays. The leaf extract of chikadoma dissolved in dimethylsulphoxide (DMSO) was the treatment, prepared into 7 different levels of concentration (3.125, 6.25, 12.5, 25, 50, 100, and 200 mg/mL) while culture medium with the malarial parasite alone served as negative control. Micromalarial culture preceded by culture synchronized with sorbitol 5%, were divided into “control” and “treated groups”, followed by incubation in CO2 candle jar at 370C for 72 h. The percentage of parasitemia was measured 8 h, showing the activity of the extract on P. falciparum stages of proliferation. Thin blood smear from the erythrocytes layer was made and stained with 10% Giemsa for 30 mins to estimate the parasitemia. The antimalarial activity of the extract was calculated using Probit analysis by counting the 50% growth inhibition (IC50). Results: The growth of P. falciparum was inhibited by the extract on mature schizont stage; and the IC50 of the extract after 40 h incubation was 3.0 mg/mL. Conclusion: The leaf extract of chikadoma significantly has antimalarial effect in-vitro against P. falciparum. Keywords: Chikadoma; Lupinus arboreus; antimalarial activity; tropical disease; Nigeria.

Abstract DNA cytosine modifications are key epigenetic regulators of cellular processes in mammalian cells, with their misregulation leading to varied disease states. In the human malaria parasite Plasmodium falciparum, a unicellular eukaryotic pathogen, little is known about the predominant cytosine modifications, cytosine methylation (5mC) and hydroxymethylation (5hmC). Here, we report the first identification of a hydroxymethylcytosine-like (5hmC-like) modification in P. falciparum asexual blood stages using a suite of biochemical methods. In contrast to mammalian cells, we report 5hmC-like levels in the P. falciparum genome of 0.2–0.4%, which are significantly higher than the methylated cytosine (mC) levels of 0.01–0.05%. Immunoprecipitation of hydroxymethylated DNA followed by next generation sequencing (hmeDIP-seq) revealed that 5hmC-like modifications are enriched in gene bodies with minimal dynamic changes during asexual development. Moreover, levels of the 5hmC-like base in gene bodies positively correlated to transcript levels, with more than 2000 genes stably marked with this modification throughout asexual development. Our work highlights the existence of a new predominant cytosine DNA modification pathway in P. falciparum and opens up exciting avenues for gene regulation research and the development of antimalarials.

ABSTRACTMalaria kills nearly 1 million people each year, and the protozoan parasitePlasmodium falciparumhas become increasingly resistant to current therapies. Isoprenoid synthesis via the methylerythritol phosphate (MEP) pathway represents an attractive target for the development of new antimalarials. The phosphonic acid antibiotic fosmidomycin is a specific inhibitor of isoprenoid synthesis and has been a helpful tool to outline the essential functions of isoprenoid biosynthesis inP. falciparum. Isoprenoids are a large, diverse class of hydrocarbons that function in a variety of essential cellular processes in eukaryotes. InP. falciparum, isoprenoids are used for tRNA isopentenylation and protein prenylation, as well as the synthesis of vitamin E, carotenoids, ubiquinone, and dolichols. Recently, isoprenoid synthesis inP. falciparumhas been shown to be regulated by a sugar phosphatase. We outline what is known about isoprenoid function and the regulation of isoprenoid synthesis inP. falciparum, in order to identify valuable directions for future research.

Malaria remains a public health problem in tropical and subtropical regions. Resistance of Plasmodium falciparum to artemisinins in Southeast Asia is a great concern for disease control and research on discovery and development of new alternative antimalarial drugs is urgently required. In a previous study, the fruit of Piper chaba Hunt. was demonstrated to exhibit promising antimalarial activity against the asexual stage of 3D7 (chloroquine-sensitive) and K1 (chloroquine-resistant) P. falciparum clones. The aim of the present study was to further investigate the antimalarial activity of piperine, the major isolated constituent of Piper chaba Hunt. fruits against both P. falciparum clones. The antimalarial activity was determined using SYBR green-I-based assay and morphological change was observed under the light microscope with Giemsa staining. The median IC50 (concentration that inhibits parasite growth by 50%) values of piperine against 3D7 and K1 P. falciparum were 111.5 and 59 μM, respectively. A marked change in parasite morphology was observed within 48 hours of piperine exposure. Results of real-time PCR showed no effect of piperine on modulating the expression of the three genes associated with antimalarial drug resistance in P. falciparum, i.e., pfcrt, pfmdr1, and pfmrp1. Piperine could be a promising candidate for further development as an antimalarial drug based on its antimalarial potency and low risk of resistance development.

Parasitic diseases remain a health burden affecting more than 500 million people worldwide with malaria having the highest mortality rate. The parasites can be transferred to the human bodies either through the mouth by ingestion of contaminated food and water or through the skin by bug bites or direct contact to environments harbouring them. Epidemiological control seems to be impossible since there is failure to control the insect vectors as well as practice of hygiene. Therefore, this has led to the development of a number of vaccines, chemotherapy and disease control programs. However, parasites have increasingly developed resistance to traditionally used anti-parasitic drugs and due to that fact there is need for alternative medication for parasitic diseases. Heat shock protein 90 (Hsp90) facilitates the folding of proteins in all living cells and their role is more important to parasites because of their environmental changes, from vector to host. Hsp90s play a major role; therefore this justifies the need for a deeper analysis of the parasitic Hsp90s. Recent studies have revealed that, the Plasmodium sp. Hsp90 has an extended linker region which increases the protein’s affinity for ATP and its inhibitors. Therefore we hypothesize that there are also significant features in other parasitic Hsp90s which would lead to Hsp90 being defined as potential drug targets. In the present study an attempt was made to gain more insight into the differences in primary structure of human and parasitic Hsp90s. The sequences were retrieved from the NCBI database and analysis was done in three groups basing on the localization of the Hsp90. The physicochemical properties were calculated and in every group, the protozoan Hsp90s showed significant differences when compared to the human orthologs. Multiple sequence alignments (MSA) showed that endoplasmic reticulum Hsp90s have an extended region in the middle domain indicating their ability to bind to a unique subset of client proteins. Sequence identities between the human and parasites showed that the protozoan Hsp90s are less related to the human Hsp90s as compared to the other parasites. Likewise, motif analysis showed the trypanosomatids and apicomplexan groups have their own unique set of motifs and they were grouped together in the phylogenetic analysis. Phylogenetic analysis also showed that, the protozoan Hsp90s forms their own clades in each group while the helminths did not form in endoplasmic reticulum group. In this study, we concluded that, Hsp90 can be a potential drug target for the protozoan species and more specifically those from the apicomplexan and trypanosomatids groups.

Includes bibliographical references (leaves 132-137).
Malaria ranks among the world's most important tropical parasitic diseases with world prevalence figures between 350 and 550 million clinical cases per annum. [WHO, 2008a] 'Treatment and prevention of malaria places a considerable burden on struggling economies where the disease is rampant. Research in malaria does not stop as the change in response to antimalarial drug treatment requires the development of new drugs and innovation in the use of old drugs. This thesis focused on building a model of the spread of resistance to Sulfadoxine/Pyrimethamine (SP) in a setting where both SP and SP in artemisinin-based combination therapy (ACT) are the first line therapies for malaria. The model itself is suitable to any low transmission setting where antimalarial drug resistance exists but the country of choice in this modeling exercise was Mozambique. The model was calibrated using parameters specific to the malaria situation in Mozambique. This model was intended to be used to aid decision making in countries where antimalarial drug resistance exists to help prevent resistance spreading to such an extent that drugs lose their usefulness in curing malaria. The modeling technique of choice was differential equation modeling; a simulation technique that falls under the System Dynamics banner in the Operations Research armamentarium. It is a technique that allowed the modeling of stocks and flows that represent different stages or groupings in the disease process and the rate of movement between these stages respectively. The base model that was built allowed infected individuals to become infectious, to be treated with SP or ACT and to be sensitive to or fail treatment. Individuals were allowed a period of temporary immunity where they would not be reinfected until the residual SP had been eliminated from their bloodstream. The base model was then further developed to include the pharmacokinetic properties of SP where individuals were allowed to be reinfected with certain strains of infection given the level of residual drug in their bloodstream after their current infection had been cleared. The models used in this thesis were built with idea of expanding on previous models and using available data to improve parameter estimates. The model at its core is similar to the resistance model used in Koella and Antia [2003] where differential equation modeling was used to monitor a population as it became infected with a sensitive or resistant infection and then University of Cape Town recovered. The inclusion in the model of the PK component was derived from Prudhomme-O'Meara et al. [2006] where individuals could be reinfected depending on the residual drug in their bloodstream. Rather than modeling simply sensitive and resistant infections, mutations categories were used as was the case in Watkins et al. [2005] population genetics model. The use of mutation categories allowed one to use parameters specific to these categories rather than the sensitive/resistant stratification and this is particularly relevant in Mozambique where all mutation categories still exhibit some degree of sensitivity to treatment i.e. total resistance has not yet developed for any particular mutation category. The last adaptation of the model was to use gametocyte information directly to determine human infectiousness rather than through using a gametocyte switching rate (constant multiplier used to convert parasite density to gametocyte density) as was done in Pongtavompinyo [2006]. The models developed in this thesis found that the existing vector control and drug policy in Mozambique had the major effect of decreasing total prevalence of malaria by approximately 70% in the 11 year period. The distribution of Res3 (presence of DHFR triple) and Res5 (presence of DHFR triple and DHPS double) infections changed over the 11 year period with Res3 infections initially increasing and then decreasing while Res5 infections started low and increased to overtake Res3 infections. The timing of the change in this composition of infection corresponds with the introduction of ACT and thus it appears that the use of ACT prompted the increased prevalence of quintuple parasites over DHFR triple and sensitive parasites. The total number of failures decreased substantially after the introduction of ACT to 17% of its previous level. The results of the base model corresponded with the observed data from the SEACAT study in terms of the magnitude and the trends of the impact of the change to ACT policy, but underestimated the impact of the vector control strategies compared to rapid effect noted in Sharp et al. [2007]. The Scenario testing of the base model showed that vector control is an effective strategy to reduce prevalence and that it is sensitive to the time at which the control is started as it decreased prevalence very gradually. The Scenario testing of the base model also showed that the introduction of ACT in Mozambique had a greater impact on reducing prevalence and that the start time of the ACT strategy did not decrease the effect on prevalence though earlier start times decreased the total number of resistance cases. The ratio of Res5 to Res3 infections increased faster when ACT was the treatment policy than when SP was the policy. Thus higher values of this ratio are associated with ACT being the treatment strategy in place. Thus differential equation modeling is an effective modeling tool to capture the spread of disease and to test the effects of policy interventions as it allows one to assess these effects on populations and averages out individual-level intricacies to better inform policy decisions.

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New antimalarial drugs are urgently needed to combat emerging multidrug resistant strains of malaria parasites. This Highlight focuses on plant-derived natural products that are of interest as potential leads towards new antimalarial drugs including synthetic analogues of natural compounds, with the exception of artemisinin derivatives, which are not included due to limited space. Since effective antimalarial treatment is often unavailable or unaffordable to many of those who need it, there is increasing interest in the development of locally produced herbal medicines; recent progress in this area will also be reviewed in this Highlight.