Boromycin has Rapid-Onset Antibiotic Activity Against Asexual and Sexual Blood Stages of Plasmodium falciparum

Boromycin is a boron-containing macrolide antibiotic produced by Streptomyces antibioticus with potent activity against certain viruses, Gram-positive bacteria and protozoan parasites. Most antimalarial antibiotics affect plasmodial organelles of prokaryotic origin and have a relatively slow onset of action. They are used for malaria prophylaxis and for the treatment of malaria when combined to a fast-acting drug. Despite the success of artemisinin combination therapies, the current gold standard treatment, new alternatives are constantly needed due to the ability of malaria parasites to become resistant to almost all drugs that are in heavy clinical use. In vitro antiplasmodial activity screens of tetracyclines (omadacycline, sarecycline, methacycline, demeclocycline, lymecycline, meclocycline), macrolides (oleandomycin, boromycin, josamycin, troleandomycin), and control drugs (chloroquine, clindamycin, doxycycline, minocycline, eravacycline) revealed boromycin as highly potent against Plasmodium falciparum and the zoonotic Plasmodium knowlesi. In contrast to tetracyclines, boromycin rapidly killed asexual stages of both Plasmodium species already at low concentrations (~ 1 nM) including multidrug resistant P. falciparum strains (Dd2, K1, 7G8). In addition, boromycin was active against P. falciparum stage V gametocytes at a low nanomolar range (IC50: 8.5 ± 3.6 nM). Assessment of the mode of action excluded the apicoplast as the main target. Although there was an ionophoric activity on potassium channels, the effect was too low to explain the drug´s antiplasmodial activity. Boromycin is a promising antimalarial candidate with activity against multiple life cycle stages of the parasite.

In vivo antiplasmodial properties of fractions and flavonoids of Pseudarthria hooheri Wight & Arn. (Fabaceae)

Malaria is regarded as one of the most lethal diseases. Resistance to artemisinin and its derivatives jeopardises effective malaria treatment. Finding novel antimalarial chemicals is critical given the existing treatment situation. This work aimed to examine the antiplasmodial capabilities of <i>Pseudarthria hookeri</i> fractions and flavonoids in vivo. The fractions and compounds antiplasmodial activity were evaluated on male Swiss albino mice infected with <i>Plasmodium berghei</i>, and on healthy female Swiss albino mice, the crude extract's acute toxicity was assessed. The EtOAc fraction had significant antiplasmodial activity (32.53 percent suppression at 500 mg/kg BW) and considerably prolonged the survival period of infected mice (9.8 days) compared to control mice (7.8 days). Parasitaemia was dramatically reduced (85.01, 59.41, and 70.39 percent), and the mean survival time extended (11.33, 10.00, and 9.33 days) with 15, 20 and 35 mg/kg of quercetin (<b>1</b>), 7-O-benzyl-6-prenylpinocembrin (<b>6</b>) and 6,8-diprenyleriodictyol (<b>11</b>) (isolates of the EtOAc fraction), respectively. BW loss and PCV reduction were also averted. Moreover, at 2500 mg/kg, the crude extract of <i>P. hookeri</i> showed no acute toxicity in mice. LC-MS analysis of the EtOAc fraction enabled the identification of nine flavonoids, with <b>8</b> and <b>11</b> being the main components. The present investigation confirmed <i>P. hookeri</i>'s antiplasmodial action, substantiating its ethnomedicinal application for malaria treatment.

Synthesis and antiplasmodial activity of regioisomers and epimers of second-generation dual acting ivermectin hybrids

With its strong effect on vector-borne diseases, and insecticidal effect on mosquito vectors of malaria, inhibition of sporogonic and blood-stage development of Plasmodium falciparum, as well as in vitro and in vivo impairment of the P. berghei development inside hepatocytes, ivermectin (IVM) continues to represent an antimalarial therapeutic worthy of investigation. The in vitro activity of the first-generation IVM hybrids synthesized by appending the IVM macrolide with heterocyclic and organometallic antimalarial pharmacophores, against the blood-stage and liver-stage infections by Plasmodium parasites prompted us to design second-generation molecular hybrids of IVM. Here, a structural modification of IVM to produce novel molecular hybrids by using sub-structures of 4- and 8-aminoquinolines, the time-tested antiplasmodial agents used for treating the blood and hepatic stage of Plasmodium infections, respectively, is presented. Successful isolation of regioisomers and epimers has been demonstrated, and the evaluation of their in vitro antiplasmodial activity against both the blood stages of P. falciparum and the hepatic stages of P. berghei have been undertaken. These compounds displayed structure-dependent antiplasmodial activity, in the nM range, which was more potent than that of IVM, its aglycon or primaquine, highlighting the superiority of this hybridization strategy in designing new antiplasmodial agents.

Mineral Fertilization Influences the Growth, Cryptolepine Yield, and Bioefficacy of Cryptolepis sanguinolenta (Lindl.) Schlt.

Cryptolepis sanguinolenta (Lindl.) Schlt., the main source of cryptolepine alkaloid, is intensively exploited in the wild to treat malaria and Lyme disease. In this study, the influence of four inorganic fertilizers (supplying N, P, K, or NPK) and four growth periods (3, 6, 9, and 12 months after transplanting) on the herb’s root biomass, cryptolepine content and yield, and biological activities were investigated in a pot and field trial. The results showed the application of N (in the form of Urea or NPK) increased root biomass yield, cryptolepine content, and cryptolepine yield compared to unfertilized plants. The 9-month-old plants recorded the maximum cryptolepine content (2.26 mg/100 mg dry root) and cryptolepine yield (304.08 mg/plant), indicating the perfect time to harvest the herb. Plant age at harvest had a more significant influence (50.6–55.7%) on cryptolepine production than fertilizer application (29.2–33.3%). Cryptolepine extracts from 9- to 12-month-old plants had the highest antiplasmodial activity (IC50 = 2.56–4.65 µg/mL) and drug selectivity index (2.15–3.91) against Plasmodium falciparum Dd2. These extracts were also cytotoxic to Jurkat leukaemia cell lines (CC50 < 62.56 µg/mL), indicating the possible use of cryptolepine for cancer management. Growing the herb in the field increased cryptolepine yield 2.5 times compared to growth in a pot, but this did not influence the antiplasmodial activity of the extract. Commercial cultivation of C. sanguinolenta for 9 months combined with N application could be a promising solution to the sustainable use of this threatened medicinal species.

Synthesis, Molecular Docking and Antiplasmodial Activities of New Tetrahydro-β-Carbolines

Malaria is still one of the most dangerous infectious diseases and the emergence of drug resistant parasites only worsens the situation. A series of new tetrahydro-β-carbolines were designed, synthesized by the Pictet–Spengler reaction, and characterized. Further, the compounds were screened for their in vitro antiplasmodial activity against chloroquine-sensitive (D10) and chloroquine-resistant (W2) strains of Plasmodium falciparum. Moreover, molecular modeling studies were performed to assess the potential action of the designed molecules and toxicity assays were conducted on the human microvascular endothelial (HMEC-1) cell line and human red blood cells. Our studies identified N-(3,3-dimethylbutyl)-1-octyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b] indole-3-carboxamide (7) (a mixture of diastereomers) as the most promising compound endowed with the highest antiplasmodial activity, highest selectivity, and lack of cytotoxicity. In silico simulations carried out for (1S,3R)-7 provided useful insights into its possible interactions with enzymes essential for parasite metabolism. Further studies are underway to develop the optimal nanosized lipid-based delivery system for this compound and to determine its precise mechanism of action.

Repurposing Dihydroartemisinin-Piperaquine-Doxycycline as an Antimalarial Drug: A Study in Plasmodium berghei-Infected Mice

Artemisinin-based combination (ACT) therapy is the mainstay for malaria treatment. However, Plasmodium parasite with decreased susceptibility to ACT has emerged. Hence, it is imperative to discover new drugs or explore new drug combinations that can decrease Plasmodium parasite resistance. This study assessed the antiplasmodial activity of dihydroartemisinin-piperaquine- doxycycline (D-P-DX) on mice infected with Plasmodium berghei. Swiss albino mice (25-30g) of both sexes inoculated with 1x107 Plasmodium berghei intraperitoneally were used. The mice were randomly grouped and orally treated with DX (2.2 mg/kg), D-P (1.71/13.7 mg/kg) and D-P-DX daily in curative, suppressive and prophylactic studies. The negative and the positive controls were treated daily with normal saline (0.2mL) and chloroquine (CQ) (10mg/kg), respectively. After treatment, blood samples were assessed for percentage parasitemia, hematological and lipid parameters. Also, the mice were observed for mean survival time. D-P, DX, and D-P-DX produced significant decreases in percentage parasitemia at p<0.05, p<0.01 and p<0.001, respectively when compared to negative control. In the curative study, D-P, DX, and D-P-DX produced 64.9%, 71.1%, and 93.6% parasitemia inhibitions when compared to 70.0% inhibition produced by CQ. Plasmodium berghei -induced alterations in packed cell volume, white blood cells, red blood cells, hemoglobin, high-density lipoprotein cholesterol, total cholesterol, low-density lipoprotein cholesterol, and triglyceride levels were significantly restored by DX (p<0.05) and D-P (p<0.01) and D-P-DX (p<0.001) when compared to the negative control. D-P-DX showed significant antiplasmodial activity against Plasmodium berghei- infected mice. It may be clinically useful for the treatment of malaria.

Glideosomal GAP50 binders that inhibit invasion and restrict malaria parasite in vitro and in vivo

Malaria continues to be a killer disease even in the modern world. Vaccines and drugs have a lot to learn from the malaria parasite before they can be successful. Here, using a filter for glideosomal anchor protein PfGAP50, we have explored a plethora of small molecules to shortlist eight GAP50 binders with promising antiplasmodial activity (IC50 < 3 µM) that are also highly selective. Of these, Hayatinin, Bedaquiline, MMV688271, Curine, and Brilacidin with PfINDO IC50 ≤ 1 µM were found to stall merozoites invasion by inhibiting IMC formation besides increasing ROS levels in trophozoites. Bedaquiline loaded healthy RBCs showed prophylactic ability to prevent intraerythrocytic development of malaria parasite. Synergistic activities with ΣFIC values as low as 0.22 (Curine and Artemisinin) or 0.37 (Bedaquiline and Artemisinin) augur well for the development of drug combinations to combat malaria effectively. Interestingly, orally delivered Bedaquiline (50 mg/Kg b. wt.) showed substantial suppression of parasitemia in the mouse model of malaria.

Discovery of Novel Cyclic Ethers with Synergistic Antiplasmodial Activity in Combination with Valinomycin

With drug resistance threatening our first line antimalarial treatments, novel chemotherapeutics need to be developed. Ionophores have garnered interest as novel antimalarials due to their theorized ability to target unique systems found in the Plasmodium-infected erythrocyte. In this study, during the bioassay-guided fractionation of the crude extract of Streptomyces strain PR3, a group of cyclodepsipeptides, including valinomycin, and a novel class of cyclic ethers were identified and elucidated. Further study revealed that the ethers were cyclic polypropylene glycol (cPPG) oligomers that had leached into the bacterial culture from an extraction resin. Molecular dynamics analysis suggests that these ethers are able to bind cations such as K+, NH4+ and Na+. Combination studies using the fixed ratio isobologram method revealed that the cPPGs synergistically improved the antiplasmodial activity of valinomycin and reduced its cytotoxicity in vitro. The IC50 of valinomycin against P. falciparum NF54 improved by 4–5-fold when valinomycin was combined with the cPPGs. Precisely, it was improved from 3.75 ± 0.77 ng/mL to 0.90 ± 0.2 ng/mL and 0.75 ± 0.08 ng/mL when dosed in the fixed ratios of 3:2 and 2:3 of valinomycin to cPPGs, respectively. Each fixed ratio combination displayed cytotoxicity (IC50) against the Chinese Hamster Ovary cell line of 57–65 µg/mL, which was lower than that of valinomycin (12.4 µg/mL). These results indicate that combinations with these novel ethers may be useful in repurposing valinomycin into a suitable and effective antimalarial.