Multidrug resistance is a significant drawback in malaria treatment, and mutations in the active sites of the many critical antimalarial drug targets have remained challenging. Therefore, this has necessitated the global search for new drugs with new mechanisms of action. Plasmodium falciparum lactate dehydrogenase (pfLHD), a glycolytic enzyme, has emerged as a potential target for developing new drugs due to the parasite reliance on glycolysis for energy. Strong substrate‐binding is required in pfLDH enzymatic catalysis; however, there is a lack of information on small molecules’ inhibitory mechanism bound to the substrate‐binding pocket. Therefore, this study investigated a potential allosteric inhibition of pfLDH by targeting the substrate‐binding site. The structural and functional behaviour of madecassic acid (MA), the most promising among the six triterpenes bound to pfLDH, were unravelled using molecular dynamic simulations at 300 ns to gain insights into its mechanism of binding and inhibition and chloroquine as a standard drug. The docking studies identified that the substrate site has the preferred position for the compounds even in the absence of a co‐factor. The bound ligands showed comparably higher binding affinity at the substrate site than at the co‐factor site. Mechanistically, a characteristic loop implicated in the enzyme catalytic activity was identified at the substrate site. This loop accommodates key interacting residues (LYS174, MET175, LEU177 and LYS179) pivotal in the MA binding and inhibitory action. The MA‐bound pfLHD average RMSD (1.60 Å) relative to chloroquine‐bound pfLHD RMSD (2.00 Å) showed higher stability for the substrate pocket, explaining the higher binding affinity (−33.40 kcal/mol) observed in the energy calculations, indicating that MA exhibited profound inhibitory activity. The significant pfLDH loop conformational changes and the allostery substrate‐binding landscape suggested inhibiting the enzyme function, which provides an avenue for designing antimalarial compounds in the future studies of pfLDH protein as a target.

Bioactivity-guided phytochemical fractionation of the methanol extract of Olax subscorpioidea root has led to the isolation of six triterpenes. Three of these compounds are previously undescribed triterpenoid saponins: oleanolic acid 3-O-[α-L-rhamnopyranosyl-(1→3)-β-D-glucopyranosyl-(1 → 2)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (2), oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 3)-β-D-glucopyranoside] (3), and oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-6-O-methyl-β-D-glucuronopyranoside] ester (5). Other reported known compounds include two triterpene glycosides: oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (1) and oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-glucuronopyranoside] (4); and a triterpene acid, oleanolic acid (6). The structures of these compounds were elucidated by spectroscopic means. The isolated compounds were tested against human cervical cancer (HeLa), colorectal cancer (Caco-2) and breast cancer (MCF-7) cell lines using the in vitro 3-[4,5-dimethylthiazole-2-yl] 3,5-diphenyltetrazolium bromide (MTT) assay, with vincristine as positive control. The cytotoxicity assay showed that compounds 3 and 5 exhibited significant inhibitory effects on the HeLa cell line, with IC₅₀ values of 7.42 ± 0.34 μM and 10.27 ± 1.26 μM; and moderate effects on MCF-7 (IC₅₀ values, 36.67 ± 1.23 μM and 43.83 ± 0.65 μM) and Caco-2 (IC₅₀ values, 35.83 ± 0.55 μM and 39.03 ± 4.38 μM, respectively) cell lines. They were also more selectively cytotoxic than vincristine against the cancer cell lines, when compared with cytotoxicity against the normal lung cell line MRC5.

Cancer is a leading cause of global death. Medicinal plants have gained increasing attention in cancer drug discovery. In this study, the stem bark extract of Olax subscorpioidea, which is used in ethnomedicine to treat cancer, was subjected to phytochemical investigation leading to the isolation of oleanolic acid (OA). The structure was elucidated by 1-dimensional and 2-dimensional nuclear magnetic resonance spectroscopic (NMR) data, and by comparing its data with previously reported data. Molecular docking was used to investigate the interactions of OA with nine selected cancer-related protein targets. OA docked well with human 17β-hydroxysteroid dehydrogenase type-1 (17βHSD1), caspase-3, and epidermal growth factor receptor tyrosine kinase (binding affinities: -9.8, -9.3, and -9.1 kcal/mol, respectively). OA is a triterpenoid compound with structural similarity to steroids. This similarity with the substrates of 17βHSD1 gives the inhibitor candidate an excellent opportunity to bind to 17βHSD1. The structural and functional dynamics of OA-17βHSD1 were investigated by molecular dynamics simulations at 240 ns. Molecular mechanics/Poisson-Boltzmann surface area (MMPBSA) studies showed that OA had a binding free energy that is comparable with that of vincristine (-52.76, and -63.56 kcal/mol, respectively). The average C-α root mean square of deviation (RMSD) value of OA (1.69 Å) compared with the unbound protein (2.01 Å) indicated its high stability at the protein's active site. The binding energy and stability at the active site of 17βHSD1 recorded in this study indicate that OA exhibited profound inhibitory potential. OA could be a good scaffold for developing new anti-breast cancer drugs.

Malaria remains a major public health concern which affects millions of people, particularly in Sub-Saharan Africa. The need for the development of alternate treatment means has become critical because of the emergence of resistance to nearly all antimalarial drugs (Kim and Schneider, 2013). Trema orientalis (L.) Blume (Ulmaceae) is used locally for the treatment of malaria. This study was designed to determine the anti-plasmodial activity of the acetone extract of T. orientalis and carry out a bio-guided separation of the extract. Acetone extract of T. orientalis leaves was investigated for its antimalarial activity in a mouse model of Plasmodium berghei using the 4 day suppressive test. Bioguided investigation was carried out by using column chromatographic fractions for in-vivo antiplasmodial screening. Preliminary spectroscopic profile of the most active fraction was obtained. Treatment with graded doses (100 to 800 mg/Kg) of acetone extract of T. orientalis resulted in significant chemosuppression of parasite growth that ranged from 44.0 to 83.8%. The most active fraction which was identified as M6 showed significant schizontocidal activity (P < 0.001). 1H NMR and Infrared spectra data indicated that the most active fraction contained flavonoids. This study justified the folkloric use of T. orientalis. Compounds from this plant could be a potential source of antimalarial agents. Key words: Antimalarial, PCV, Plasmodium berghei, anaemia, Trema orientalis.

Combretum genus (Combretaceae) is used locally in the treatment of various diseases including malaria. Current study aimed to investigate the antiplasmodial activities of methanol extract of C. zenkeri in Plasmodium falciparum chloroquine sensitive (D10) and resistant (W2) strains and identify the bioactive principles. Repeated chromatographic separation was carried out on the chloroform fraction to afford the isolation of bioactive compounds which was characterized by application of spectroscopic techniques (ESI-MS, HR-ESIMS, 1D and 2D NMR). Antiplasmodial activities of chloroform fraction (D10; IC 50 = 12.57±1.57 μg/mL and W2; IC 50 = 12.14±0.95 μg/mL) showed more activity than the n-butanol fraction (D10; IC 50 = 61.98±3.25 μg/mL and W2; IC 50 = 61.26±8.64 μg/mL). Phytochemical investigation of the extract afforded isolation of two triterpenes with antimalarial activities. This paper identified for the first time the antimalarial principles in C. zenkeri as ursolic and oleanolic acids; which justified the local use of the plant in the treatment of malaria.