Growth Rate of Plasmodium falciparum: Analysis of Parasite Growth Data From Malaria Volunteer Infection Studies

Background

Growth rate of malaria parasites in the blood of infected subjects is an important measure of efficacy of drugs and vaccines.

Methods

We used log-linear and sine-wave models to estimate the parasite growth rate of the 3D7 strain of Plasmodium falciparum using data from 177 subjects from 14 induced blood stage malaria (IBSM) studies conducted at QIMR Berghofer. We estimated parasite multiplication rate per 48 hour (PMR₄₈), PMR per life-cycle (PMR_LC), and parasite life-cycle duration. We compared these parameters to those from studies conducted elsewhere with infections induced by IBSM (n=66), sporozoites via mosquito bite (n=336) or injection (n=51).

Results

The parasite growth rate of 3D7 in QIMR Berghofer studies was 0.75/day (95% CI: 0.73–0.77/day), PMR₄₈ was 31.9 (95% CI: 28.7–35.4), PMR_LC was 16.4 (95% CI: 15.1–17.8) and parasite life-cycle was 38.8 hour (95% CI: 38.3–39.2 hour). These parameters were similar to estimates from IBSM studies elsewhere (0.71/day, 95% CI: 0.67–0.75/day; PMR₄₈ 26.6, 95% CI: 22.2–31.8), but significantly higher (P < 0.001) than in sporozoite studies (0.47/day, 95% CI: 0.43–0.50/day; PMR₄₈ 8.6, 95% CI: 7.3–10.1).

Conclusions

Parasite growth rates were similar across different IBSM studies and higher than infections induced by sporozoite.

Discovery of 3-Cinnamamido-N-Substituted Benzamides as Potential Antimalarial Agents

BACKGROUND

Malaria is one of the most devastating parasitic diseases, yet the discovery of antimalarial agents remains profoundly challenging. Very few new antimalarials have been developed in the past 50 years, while the emergence of drug-resistance continues to appear.

OBJECTIVE

This study focuses on the discovery, design, synthesis, and antimalarial evaluation of 3- cinnamamido-N-substituted benzamides.

METHOD

In this study, a screening of our compound library was carried out against the multidrugsensitive Plasmodium falciparum 3D7 strain. Derivatives of the hit were designed, synthesized and tested against P. falciparum 3D7 and the in vivo antimalarial activity of the most active compounds was evaluated using the method of Peters’ 4-day suppressive test.

RESULTS

The retrieved hit compound 1 containing a 3-cinnamamido-N-substituted benzamide skeleton showed moderate antimalarial activity (IC50 = 1.20 μM) for the first time. A series of derivatives were then synthesized through a simple four-step workflow, and half of them exhibited slightly better antimalarial effect than the precursor 1 during the subsequent in vitro assays. Additionally, compounds 11, 23, 30 and 31 displayed potent activity with IC50 values of approximately 0.1 μM, and weak cytotoxicity against mammalian cells. However, in vivo antimalarial activity is not effective, which might be ascribed to the poor solubility of these compounds.

CONCLUSION

In this study, the phenotypic screen of our compound library resulted in the first report of a 3-cinnamamide framework with antimalarial activity and 40 derivatives were then designed and synthesized. Subsequent structure-activity studies showed that compounds 11, 23, 30 and 31 exhibited the most potent and selective activity against the P. falciparum 3D7 strain with IC50 values around 0.1 μM. Our work herein sets another example of phenotypic screen-based drug discovery, leading to potentially promising candidates of novel antimalarial agents once given further optimization.

Enhanced uptake, high selective and microtubule disrupting activity of carbohydrate fused pyrano-pyranones derived from natural coumarins attributes to its anti-malarial potential

Background

Malaria is one of the deadliest infectious diseases caused by protozoan parasite of Plasmodium spp. Increasing resistance to anti-malarials has become global threat in control of the disease and demands for novel anti-malarial interventions. Naturally-occurring coumarins, which belong to a class of benzo-α-pyrones, found in higher plants and some essential oils, exhibit therapeutic potential against various diseases. However, their limited uptake and non-specificity has restricted their wide spread use as potential drug candidates.

Methods

Two series of carbohydrate fused pyrano[3,2-c]pyranone carbohybrids which were synthesized by combination of 2-C-formyl galactal and 2-C-formyl glucal, with various freshly prepared 4-hydroxycoumarins were screened against Plasmodium falciparum. The anti-malarial activity of these carbohybrids was determined by growth inhibition assay on P. falciparum 3D7 strain using SYBR green based fluorescence assay. Haemolytic activity of carbohybrid 12, which showed maximal anti-malarial activity, was determined by haemocompatibility assay. The uptake of the carbohybrid 12 by parasitized erythrocytes was determined using confocal microscopy. Growth progression assays were performed to determine the stage specific effect of carbohybrid 12 treatment on Pf3D7. In silico studies were conducted to explore the mechanism of action of carbohybrid 12 on parasite microtubule dynamics. These findings were further validated by immunofluorescence assay and drug combination assay.

Results

2-C-formyl galactal fused pyrano[3,2-c]pyranone carbohybrid 12 exhibited maximum growth inhibitory potential against Plasmodium with IC₅₀ value of 5.861 µM and no toxicity on HepG2 cells as well as no haemolysis of erythrocytes. An enhanced uptake of this carbohybrid compound was observed by parasitized erythrocytes as compared to uninfected erythrocytes. Further study revealed that carbohybrid 12 arrests the growth of parasite at trophozoite and schizonts stage during course of progression through asexual blood stages. Mechanistically, it was shown that the carbohybrid 12 binds to α,β-heterodimer of tubulin and affects microtubule dynamics.

Conclusion

These findings show carbohydrate group fusion to 4-hydroxycoumarin precursor resulted in pyrano-pyranones derivatives with better solubility, enhanced uptake and improved selectivity. This data confirms that, carbohydrate fused pyrano[3,2-c]pyranones carbohybrids are effective candidates for anti-malarial interventions against P. falciparum.

hygroscopicus on Plasmodium falciparum 3D7 in Vitro

BACKGROUND

Malaria eradication has been complicated by the repeated emergence of antimalarial drug resistances. We aimed to determine whether a metabolite extract of Streptomyces hygrocopicus subsp. hygroscopicus could decrease the viability of Plasmodium falciparum 3D7 in vitro.

METHODS

S. hygroscopicus subsp. hygroscopicus isolates were inoculated and fermented on the ISP4 medium. The fermented S. hygroscopicus was mixed with ethylacetate 1:5 (v/v), and the solvent phase was evaporated. Several concentrations of isolated extract was added to the P. falciparum 3D7 culture containing trophozoite and schizont stages in 24 wells plates when the degree of parasite-infected erythrocytes reached 5%, then incubated for 8 hours. DNA parasite density was measured using flow cytometry, parasite degree and morphology were observed under microscopic by Giemsa-stained smears.

RESULTS

The metabolite extract affected the morphology of almost all of parasite asexual stages. Schizonts and trophozoites failed to grow and appeared damaged with pycnotic cores and loss of cytoplasmic content. At 8 hours there was a significant decrease in DNA parasite density in culture exposed to 2.6 mg/ml and 13 mg/ml (P = 0.002; P = 0.024) of the extract. The degree of parasite-infected erythrocytes was decreased from the beginning of exposure (0.02 mg/ml of the extract). There was a significant inverse correlation between the concentration of extract and the degree of parasite-infected erythrocytes as well as the density of DNA parasite (r = -0.772, P = 0.000; r =-0.753; P =0.000).

CONCLUSION

Metabolite extract of S. hygroscopicus subsp. hygroscopicus causes morphological damage, decreases the degree of parasite-infected erythrocytes and the DNA density of P. falciparum 3D7 in vitro.

Molecular-docking study of malaria drug target enzyme transketolase in Plasmodium falciparum 3D7 portends the novel approach to its treatment

BACKGROUND

Malaria has been a major life threatening mosquito borne disease from long since. Unavailability of any effective vaccine and recent emergence of multi drug resistant strains of malaria pathogen Plasmodium falciparum continues to cause persistent deaths in the tropical and sub-tropical region. As a result, demands for new targets for more effective anti-malarial drugs are escalating. Transketolase is an enzyme of the pentose phosphate pathway; a novel pathway which is involved in energy generation and nucleic acid synthesis. Moreover, significant difference in homology between Plasmodium falciparum transketolase (Pftk) and human (Homo sapiens) transketolase makes it a suitable candidate for drug therapy. Our present study is aimed to predict the 3D structure of Plasmodium falciparum transketolase and design an inhibitor against it.

RESULTS

The primary and secondary structural features of the protein is calculated by ProtParam and SOPMA respectively which revealed the protein is composed of 43.3 % alpha helix and 33.04 % random coils along with 15.62 % extended strands, 8.04 % beta turns. The three dimensional structure of the transketolase is constructed using homology modeling tool MODELLAR utilizing several available transketolase structures as templates. The structure is then subjected to deep optimization and validated by structure validation tools PROCHECK, VERIFY 3D, ERRAT, QMEAN. The predicted model scored 0.74 for global model reliability in PROCHECK analysis, which ensures the quality of the model. According to VERIFY 3D the predicted model scored 0.77 which determines good environmental profile along with ERRAT score of 78.313 which is below 95 % rejection limit. Protein-protein and residue-residue interaction networks are generated by STRING and RING server respectively. CASTp server was used to analyze active sites and His 109, Asn 108 and His 515 are found to be more positive site to dock the substrate, in addition molecular docking simulation with Autodock vina determined the estimated free energy of molecular binding was of -6.6 kcal/mol for most favorable binding of 6'-Methyl-Thiamin Diphosphate.

CONCLUSION

This predicted structure of Pftk will serve first hand in the future development of effective Pftk inhibitors with potential anti-malarial activity. However, this is a preliminary study of designing an inhibitor against Plasmodium falciparum 3D7; the results await justification by in vitro and in vivo experimentations.

A Bioinformatics Approach for Homology Modeling and Binding Site Identification of Triosephosphate Isomerase from Plasmodium falciparum 3D7

Malaria is a major public health concern, and malarial parasites have developed resistance against the commonly available drugs. So now a days it is a major concern to find out a new target for drug therapy. Plasmodium falciparum 3D7, one of the strains of plasmodium species also lacks in a functional tricarboxylic acid cycle and solely dependent on glycolysis for its energy supply like other plasmodium species. Although enzymes of malarial parasite have been considered as potential antimalarial drug targets, a little is known about their structural biology. The tertiary structure of triose phosphate isomerase of P. falciparum 3D7 was determined by means of homology modeling through multiple alignment followed by intensive optimization and validation. The modeling was done by Swiss-Model Workspace. The obtained model was verified with the structure validation programs such as, PROCHECK, Verify3D, and QMEAN for reliability. The verify3D value of 0.69 indicates that the environment profile of the model is good. A self-optimized prediction method with alignment or SOPMA is employed for calculation of the secondary structural features of triose phosphate isomerase. The secondary structure indicates that the predicted 3D structure of triosephosphate isomerase of P. falciparum 3D7 contains 48.37% α-helix, 29.27% random coil, and 16.67% extended strand. Active site determination through CASTp suggests that this protein can be utilized as a potential drug target. However, these will further be tested by wet lab studies for a targeted vaccine design against P. falciparum 3D7.